{"1": {"fulltext": "TD 756\\n.5\\n.C665\\nTt", "height": "4348", "width": "3198", "jp2-path": "constructedwetla00nati_0001.jp2"}, "2": {"fulltext": "", "height": "4283", "width": "3142", "jp2-path": "constructedwetla00nati_0002.jp2"}, "3": {"fulltext": "w\\n\u00e2\u0080\u00a2\u00e2\u0080\u0099bs?\\nr\\\\ o ^%y||fvo$ C aV -/V ^p\u00c2\u00a3|lir o o r\\n*K\u00c2\u00b0ygWs +*0KSr+ 4 \u00c2\u00b03W*\\nn r f*0* JlfjSj gV g^lgjg; a 0 u\\n*va", "height": "4283", "width": "3142", "jp2-path": "constructedwetla00nati_0003.jp2"}, "4": {"fulltext": "", "height": "4283", "width": "3142", "jp2-path": "constructedwetla00nati_0004.jp2"}, "5": {"fulltext": "United States\\nEnvironmental Protection\\nAgency\\nManual\\nOffice of Research and EPA/625/R-99/010\\nDevelopment September 2000\\nCincinnati, Ohio 45268 http://www.epa.gov/ORD/NRMRL\\nConstructed Wetlands\\nTreatment of Municipal\\nWastewaters", "height": "4307", "width": "3198", "jp2-path": "constructedwetla00nati_0005.jp2"}, "6": {"fulltext": "", "height": "4283", "width": "3142", "jp2-path": "constructedwetla00nati_0006.jp2"}, "7": {"fulltext": "EPA/625/R-99/010\\nManual\\nConstructed Wetlands Treatment of\\nMunicipal Wastewaters\\nNational Risk Management Research Laboratory\\nOffice of Research and Development\\nU.S. Environmental Protection Agency\\nCincinnati, Ohio 45268\\nPrinted on Recycled Paper", "height": "4307", "width": "3198", "jp2-path": "constructedwetla00nati_0007.jp2"}, "8": {"fulltext": "Notice\\nThis document has been reviewed in accordance with the U.S. Environmental Protection\\nAgency\u00e2\u0080\u0099s peer and administrative review policies and approved for publication. Mention of trade\\nnames or commercial products does not constitute endorsement or recommendation for use.\\nC\\n1 n I\\nh\\nLC Control Number\\n00\\n329464", "height": "4283", "width": "3142", "jp2-path": "constructedwetla00nati_0008.jp2"}, "9": {"fulltext": "Foreword\\nThe U.S. Environmental Protection Agency is charged by Congress with protecting the\\nNation\u00e2\u0080\u0099s land, air, and water resources. Under a mandate of national environmental laws, the\\nAgency strives to formulate and implement actions leading to a compatible balance between\\nhuman activities and the ability of natural systems to support and nurture life. To meet this\\nmandate, EPA\u00e2\u0080\u0099s research program is providing data and technical support for solving environ\u00c2\u00ac\\nmental prob-lems today and building a science knowledge base necessary to manage our eco\u00c2\u00ac\\nlogical re-sources wisely, understand how pollutants affect our health, and prevent or reduce\\nenvironmen-tal risks in the future.\\nThe National Risk Management Research Laboratory is the Agency\u00e2\u0080\u0099s center for investiga\u00c2\u00ac\\ntion of technicological and management approaches for reducing risks from threats to human\\nhealth and the environment. The focus of the Laboratory\u00e2\u0080\u0099s research program is on methods for\\nthe prevention and control of pollution to air, land, water and subsurface resources; protection\\nof water quality in public water systems; remediation of contaminated sites and ground water;\\nand prevention and control of indoor air pollution. The goal of this research effort is to catalyze\\ndevelopment and implementation of innovative, cost-effective environmental technologies; de\u00c2\u00ac\\nvelop scientific and engineering information needed by EPA to support regulatory and policy\\ndecisions; and provide technical support and information transfer to ensure effective implemen\u00c2\u00ac\\ntation of environmental regulations and strategies.\\nThis publication has been produced as part of the Laboratory\u00e2\u0080\u0099s strategic long-term research\\nplan. It is published and made available by EPA\u00e2\u0080\u0099s Office of Research and Development to assist\\nthe user community and to link researchers with their clients.\\nE. Timothy Oppelt, Director\\nNational Risk Management Research Laboratory", "height": "4307", "width": "3198", "jp2-path": "constructedwetla00nati_0009.jp2"}, "10": {"fulltext": "Abstract\\nThis manual discusses the capabilities of constructed wetlands, a functional design ap\u00c2\u00ac\\nproach, and the management requirements to achieve the designed purpose. The manual also\\nattempts to put the proper perspective on the appropriate use, design and performance of con\u00c2\u00ac\\nstructed wetlands. For some applications, they are an excellent option because they are low in\\ncost and in maintenance requirements, offer good performance, and provide a natural appear\u00c2\u00ac\\nance, if not more beneficial ecological benefits. In other applications, such as large urban areas\\nwith large wastewater flows, they may not be at all appropriate owing to their land requirements.\\nConstructed wetlands are especially well suited for wastewater treatment in small communities\\nwhere inexpensive land is available and skilled operators hard to find and keep.\\nPrimary customers will be engineers who service small communities, state regulators, and\\nplanning professionals. Secondary users will be environmental groups and the academics.\\nIV", "height": "4283", "width": "3142", "jp2-path": "constructedwetla00nati_0010.jp2"}, "11": {"fulltext": "Contents\\nChapter 1 Introduction.1\\n1.1. Scope.1\\n1.2. Terminology.1\\n1.3. Relationship to Previous EPA Documents.2\\n1.4. Wetlands Treatment Database.2\\n1.5. History.4\\n1.6. Common Misperceptions.4\\n1.7. When to Use Constructed Wetlands.5\\n1.8 Use of This Manual.8\\n1.9 References.8\\nChapter 2 Introduction to Constructed Wetlands.10\\n2.1 Understanding Constructed Wetlands.10\\n2.2 Ecology of Constructed Wetlands.12\\n2.3 Botany of Constructed Wetlands.12\\n2.4 Fauna of Constructed Wetlands.16\\n2.5 Ecological Concerns for Constructed Wetland Designers.16\\n2.6 Human Health Concerns.18\\n2.7 Onsite System Applications.19\\n2.8 Related Aquatic Treatment Systems.19\\n2.9 Frequently Asked Questions.20\\n2.10 Glossary.23\\n2.11 References.27\\nChapter 3 Removal Mechanisms and Modeling Performance of Constructed Wetlands.30\\n3.1 Introduction.30\\n3.2 Mechanisms of Suspended Solids Separations and Transformations.30\\n3.3 Mechanisms for Organic Matter Separations and Transformations. 35\\n3.4 Mechanisms of Nitrogen Separations and Transformations.42\\n3.5 Mechanisms of Phosphorus Separations and Transformations.46\\n3.6 Mechanisms of Pathogen Separations and Transformations.48\\n3.7 Mechanisms of Other Contaminant Separations and Transformations.49\\n3.8 Constructed Wetland Modeling.50\\n3.9 References.52\\nChapter 4 Free Water Surface Wetlands.55\\n4.1 Performance Expectations.55\\n4.2 Wetland Hydrology.64\\n4.3 Wetland Hydraulics.65\\n4.4 Wetland System Design and Sizing Rationale.68\\n4.5 Design.69\\n4.6 Design Issues.78\\n4.7 Construction/Civil Engineering Issues.81\\n4.8 Summary of Design Recommendations.83\\n4.9 References.83\\nv", "height": "4307", "width": "3198", "jp2-path": "constructedwetla00nati_0011.jp2"}, "12": {"fulltext": "Contents (cont.)\\nChapter 5 Vegetated Submerged Beds.86\\n5.1 Introduction.86\\n5.2 Theoretical Considerations.86\\n5.3 Hydrology.91\\n5.4 Basis of Design.93\\n5.5 Design Considerations.101\\n5.6 Design Example for a VSB Treating Septic Tank or Primary Effluent.103\\n5.7 On-site Applications.106\\n5.8 Alternative VSB Systems.106\\n5.9 References.107\\nChapter 6 Construction, Start-Up, Operation, and Maintenance.Ill\\n6.1 Introduction.Ill\\n6.2 Construction.Ill\\n6.3 Start-Up.117\\n6.4 Operation and Maintenance.118\\n6.5 Monitoring.119\\n6.6 References.119\\nChapter 7 Capital and Recurring Costs of Constructed Wetlands.120\\n7.1 Introduction.120\\n7.2 Construction Costs.120\\n7.3 Operation and Maintenance Costs.125\\n7.4 References.127\\nChapter 8 Case Studies.128\\n8.1 Free Water Surface (FWS) Constructed Wetlands.128\\n8.2 Vegetated Submerged Bed (VSB) Systems.141\\n8.3 Lessons Learned.152\\nVI", "height": "4283", "width": "3142", "jp2-path": "constructedwetla00nati_0012.jp2"}, "13": {"fulltext": "List of Figures\\n2-1 Constructed wetlands in wastewater treatment train.11\\n2-2 Elements of a free water surface (FWS) constructed wetland.11\\n2-3 Elements of a vegetated submerged bed (VSB) system.11\\n2- 4 Profile of a 3-zone FWS constructed wetland cell.18\\n3- 1 Mechanisms which dominate FWS systems.32\\n3-2 Weekly transect TSS concentration for Areata cell 8 pilot receiving oxidation pond effluent.34\\n3-3 Variation in effluent BOD at the Areata enhancement marsh.36\\n3-4 Carbon transformations in an FWS wetland.37\\n3-5 Dissolved oxygen distribution in emergent and submergent zones of a tertiary FWS.40\\n3-6 Nitrogen transformations in FWS wetlands.43\\n3-7 Phosphorus cycling in an FWS wetland.47\\n3-8 Phosphorus pulsing in pilot cells in Areata.48\\n3-9 Influent versus effluent FC for the TADB systems.49\\n3- 10 Adaptive model building.51\\n4- 1 Effluent BOD vs areal loading.57\\n4-2 Internal release of soluble BOD during treatment.57\\n4-3 Annual detritus BOD load from Scirpus Typha.58\\n4-4 TSS loading vs TSS in effluent.58\\n4-5 Effluent TKN vs TKN loading.59\\n4-6 Effluent TP vs TP areal loading.61\\n4-7 Total phosphorus loading versus effluent concentration for TADB systems.61\\n4-8 Hydraulic retention time vs orthophosphate removal.62\\n4-9 Influent versus effluent FC concentration for TADB systems.63\\n4-10 TSS, BOD and FC removals for Areata Pilot Cell 8.63\\n4-11 Tracer response curve for Sacramento Regional Wastewater Treatment Plant Demonstration\\nWetlands Project Cell 7.67\\n4-12 Transect BOD data for Areata Pilot Cell 8.71\\n4-13 Elements of a free water surface (FWS) constructed wetland.71\\n4- 14 Generic removal of pollutants in a 3-zone FWS system.72\\n5- 1 Seasonal cycle in a VSB.90\\n5-2 Preferential flow in a VSB.93\\n5-3 Lithium chloride tracer studies in a VSB system.94\\n5-4 Effluent TSS vs areal loading rate.95\\n5-5 Effluent TSS vs volumetric loading rate.95\\n5-6 Effluent BOD vs areal loading rate.96\\n5-7 Effluent BOD vs volumetric loading rate.96\\n5-8 Effluent TKN vs areal loading rate.98\\n5-9 Effluent TP vs areal loading rate.99\\n5-10 NADB VSBs treating pond effluent.100\\n5- 11 Proposed Zones in a VSB.102\\n6- 1 Examples of constructed wetland berm construction.112\\n6-2 Examples of constructed wetland inlet designs.114\\nVII", "height": "4307", "width": "3198", "jp2-path": "constructedwetla00nati_0013.jp2"}, "14": {"fulltext": "List of Figures (cont.)\\n6-3 Outlet devices.115\\n8-1 Schematic diagram of wetland system at Areata, CA.129\\n8-2 Schematic diagram of Phase 1 2 wetland systems at West Jackson County, MS.132\\n8-3 Schematic diagram of Phase 3 wetland expansion at West Jackson County, MS.132\\n8-4 Schematic diagrams of the wetland system at Gustine, CA.136\\n8-5 Schematic diagram of the wetland system at Ouray, CO.140\\n8-6 Schematic of Minoa, NY, VSB system.142\\n8-7 Schematic diagram of typical VSB (one of three) at Mesquite, NV.145\\n8-8 Schematic of VSB system at Mandeville, LA.147\\n8-9 Schematic of VSB system at Sorrento, LA.151\\nVIII", "height": "4283", "width": "3142", "jp2-path": "constructedwetla00nati_0014.jp2"}, "15": {"fulltext": "List of Tables\\n1-1. Types of Wetlands in the NADB.3\\n1-2. Types of Wastewater Treated and Level of Pretreatment for NADB Wetlands.3\\n1-3. Size Distribution of Wetlands in the NADB.4\\n1-4. Distribution of Wetlands in the NADB by State/Province.4\\n1- 5. Start Date of Treatment Wetlands in the NADB.4\\n2- 1 Characteristics of Plants for Constructed Wetlands.14\\n2-2 Factors to Consider in Plant Selection.15\\n2- 3 Characteristics of Animals Found in Constructed Wetlands.16\\n3- 1 Typical Constructed Wetland Influent Wastewater.30\\n3-2 Size Distributions for Solids in Municipal Wastewater.31\\n3-3 Size Distribution for Organic and Phosphorus Solids in Municipal Wastewater.31\\n3-4 Fractional Distribution of BOD, COD, Turbidity and TSS in the Oxidation Pond Effluent and\\nEffluent from Marsh Cell 5.34\\n3-5 Background Concentrations of Contaminants of Concern in FWS Wetland Treatment System Effluents.35\\n3- 6 Wetland Oxygen Sources and Sinks.41\\n4- 1 Loading and Performance Data for Systems Analyzed in This Document.56\\n4-2 Trace Metal Concentrations and Removal Rates, Sacramento Regional Wastewater Treatment Plant.63\\n4-3 Fractional Distribution of BOD, COD and TSS in the Oxidation Pond Effluent and Effluent from\\nMarsh Cell 5.64\\n4-4 Background Concentrations of Water Quality Constituents of Concern in FWS Constructed Wetlands.70\\n4-5 Examples of Change in Wetland Volume Due to Deposition of Non-Degradable TSS (V ss and\\nPlant Detritus (V d Based on 100 Percent Emergent Plant Coverage.74\\n4-6 Lagoon Influent and Effluent Quality Assumptions.77\\n4- 7 Recommended Design Criteria for FWS Constructed Wetlands.83\\n5- 1 Hydraulic Conductivity Values Reported in the Literature.92\\n5-2 Comparison of VSB Areas Required for BOD Removal Using Common Design Approaches.97\\n5-3 Data from Las Animas, CO VSB Treating Pond Effluent.100\\n5-4 Summary of VSB Design Guidance.106\\n7-1 Cost Comparison of 4,645m 2 Free Water Surface Constructed Wetland and Vegetated Submerged Bed.121\\n7-2 Technical and Cost Data for Wetland Systems Included in 1997 Case Study Visitations.121\\n7-3 Clearing and Grubbing Costs for EPA Survey Sites.122\\n7-4 Excavation and Earthwork Costs for EPA Survey Sites.122\\n7-5 Liner Costs for EPA Survey Sites.123\\n7-6 Typical Installed Liner Costs for 9,300m 2 Minimum Area.123\\n7-7 Media Costs for VSBs from EPA Survey Sites.124\\n7-8 Costs for Wetland Vegetation and Planting from EPA Survey Sites.124\\n7-9 Costs for Inlet and Outlet Structures from EPA Sites.124\\n7-10 Range of Capital Costs for a 0.4 ha Membrane-Lined VSB and FWS Wetland.126\\n7-11 Annual O M Costs at Carville, LA (570m 3 /d) Vegetated Submerged Bed.127\\n7-12 Annual O M Costs for Constructed Wetlands, Including All Treatment Costs.127\\nIX", "height": "4307", "width": "3198", "jp2-path": "constructedwetla00nati_0015.jp2"}, "16": {"fulltext": "List of Tables (cont.)\\n8-1 Summary of Results, Phase 1 Pilot Testing, Areata, CA.130\\n8-2 Long-Term Average Performance, Areata WWTP.131\\n8-3 Wetland Water Quality, West Jackson County, MS.134\\n8-4 Performance Results in Mature Vegetated vs Immature Vegetated FWS Cells, Gustine, CA.138\\n8-5 Wetland Effluent Characteristics, Gustine, CA.139\\n8-6 BOD TSS Removal for Ouray, CO.141\\n8-7 Village of Minoa VSB Construction Costs.143\\n8-8 Summary Performance, Mesquite, NV, VSB Component.146\\n8-9 Monthly Effluent Characteristics, Mesquite, NV, VSB Component.146\\n8-10 Water Quality Performance, Mandeville, LA, Treatment System (June Sept., 1991).149\\n8-11 Water Quality Performance, Mandeville, LA, Treatment System (Jan. 1996 July 1997). 150\\n8-12 VSB Effluent Water Quality, Sorrento, LA.152\\nx", "height": "4283", "width": "3142", "jp2-path": "constructedwetla00nati_0016.jp2"}, "17": {"fulltext": "Acknowledgements\\nMany people participated in the creation of this manual. Technical direction throughout the\\nmulti-year production process was provided by USEPA\u00e2\u0080\u0099s National Risk Management Research\\nLaboratory (NRMRL). Technical writing was carried out in several stages, but culminated into a\\nfinal product as a cooperative effort between the NRMRL and the contractors named below.\\nSignificant technical reviews and contributions based on extensive experience with constructed\\nwetlands were made by a number of prominent practitioners. Technical review was provided by\\na group of professionals with extensive experience with the problems specific to small commu\u00c2\u00ac\\nnity wastewater treatment systems. The production of the document was also a joint effort by\\nNRMRL and contractual personnel. All of these people are listed below:\\nPrimary Authors and Oversight Committee\\nDonald S. Brown, Water Supply and Water Resources Division, NRMRL, Cincinnati, OH\\nJames F. Kreissl, Technology Transfer and Support Division, NRMRL, Cincinnati, OH\\nRobert A. Gearheart, Humboldt University, Areata, CA\\nAndrew P. Kruzic, University of Texas at Arlington, Arlington, TX\\nWilliam C. Boyle, University of Wisconsin, Madison, Wl\\nRichard J. Otis, Ayres Associates, Madison, Wl\\nMajor Contributors/Authors\\nSherwood C. Reed, Environmental Engineering Consultants, Norwich, VT\\nRichard Moen, Ayres Associates, Madison, Wl\\nRobert Knight, Consultant, Gainesville, FL\\nDennis George, Tennessee Technological University, Cookeville, TN\\nMichael Ogden, Southwest Wetlands Group, Inc., Santa Fe, NM\\nRonald Crites, Brown and Caldwell, Sacramento, CA\\nGeorge Tchobanoglons, Consultant, Davis, CA\\nContributing Writers/Production Specialists\\nIan Clavey, CEP Inc., Cincinnati, OH\\nVince lacobucci, CEP Inc., Cincinnati, OH\\nJulie Hotchkiss, CEP Inc., Cincinnati, OH\\nPeggy Heimbrock, TTSD NRMRL, Cincinnati, OH\\nStephen E. Wilson, TTSD NRMRL, Cincinnati, OH\\nDenise Ratliff, TTSD NRMRL, Cincinnati, OH\\nBetty Kampsen, STD NRMRL, Cincinnati, OH\\nTechnical Reviewers\\nArthur H. Benedict, EES Consulting, Inc., Bellevue, WA\\nPio Lombardo, Lombardo Associates, Inc., Newton, MA\\nRao Surampalli, USEPA- Region VII, Kansas City, KS\\nRobert K. Bastian, USEPA Office of Wastewater Management, Washington, DC\\nXI", "height": "4307", "width": "3198", "jp2-path": "constructedwetla00nati_0017.jp2"}, "18": {"fulltext": "", "height": "4283", "width": "3142", "jp2-path": "constructedwetla00nati_0018.jp2"}, "19": {"fulltext": "Chapter 1\\nIntroduction to the Manual\\n1.1. Scope\\nConstructed wetlands are artificial wastewater treatment\\nsystems consisting of shallow (usually less than 1 m deep)\\nponds or channels which have been planted with aquatic\\nplants, and which rely upon natural microbial, biological,\\nphysical and chemical processes to treat wastewater. They\\ntypically have impervious clay or synthetic liners, and en\u00c2\u00ac\\ngineered structures to control the flow direction, liquid de\u00c2\u00ac\\ntention time and water level. Depending on the type of sys\u00c2\u00ac\\ntem, they may or may not contain an inert porous media\\nsuch as rock, gravel or sand.\\nConstructed wetlands have been used to treat a variety\\nof wastewaters including urban runoff, municipal, indus\u00c2\u00ac\\ntrial, agricultural and acid mine drainage. However, the\\nscope of this manual is limited to constructed wetlands\\nthat are the major unit process in a system to treat munici\u00c2\u00ac\\npal wastewater. While some degree of pre- or post- treat\u00c2\u00ac\\nment will be required in conjunction with the wetland to\\ntreat wastewater to meet stream discharge or reuse re\u00c2\u00ac\\nquirements, the wetland will be the central treatment com\u00c2\u00ac\\nponent.\\nThis manual discusses the capabilities of constructed\\nwetlands, a functional design approach, and the manage\u00c2\u00ac\\nment requirements to achieve the designed purpose. This\\nmanual also attempts to put the proper perspective on the\\nappropriate use of constructed wetlands. For some appli\u00c2\u00ac\\ncations, they are an excellent option because they are low\\nin cost and in maintenance requirements, offer good per\u00c2\u00ac\\nformance, and provide a natural appearance, if not more\\nbeneficial ecological benefits. However, because they re\u00c2\u00ac\\nquire large land areas, 4 to 25 acres per million gallons of\\nflow per day, they are not appropriate for some applica\u00c2\u00ac\\ntions. Constructed wetlands are especially well suited for\\nwastewater treatment in small communities where inex\u00c2\u00ac\\npensive land is available and skilled operators are hard to\\nfind.\\n1.2 Terminology\\nA brief discussion of terminology will help the reader dif\u00c2\u00ac\\nferentiate between the constructed wetlands discussed in\\nthis manual and other types of wetlands. Wetlands are\\ndefined in Federal regulations as \u00e2\u0080\u009cthose areas that are in\u00c2\u00ac\\nundated or saturated by surface or ground water at a fre\u00c2\u00ac\\nquency and duration sufficient to support, and that under\\nnormal circumstances do support, a prevalence of veg\u00c2\u00ac\\netation typically adapted for life in saturated soil condi\u00c2\u00ac\\ntions. Wetlands generally include swamps, marshes, bogs\\nand similar areas.\u00e2\u0080\u009d (40 CFR 230.3(t)) Artificial wetlands\\nare wetlands that have been built or extensively modified\\nby humans, as opposed to natural wetlands which are\\nexisting wetlands that have had little or no modification by\\nhumans, such as filling, draining, or altering the flow pat\u00c2\u00ac\\nterns or physical properties of the wetland. The modifica\u00c2\u00ac\\ntion or direct use of natural wetlands for wastewater treat\u00c2\u00ac\\nment is discouraged and natural wetlands are not dis\u00c2\u00ac\\ncussed in this manual (see discussion of policy issues in\\nSection 1.7.2).\\nAs previously defined, constructed wetlands are artifi\u00c2\u00ac\\ncial wetlands built to provide wastewater treatment. They\\nare typically constructed with uniform depths and regular\\nshapes near the source of the wastewater and often in\\nupland areas where no wetlands have historically existed.\\nConstructed wetlands are almost always regulated as\\nwastewater treatment facilities and cannot be used for\\ncompensatory mitigation (see Section 1.7.2). Some EPA\\ndocuments refer to constructed wetlands as constructed\\ntreatment wetlands to avoid any confusion about their pri\u00c2\u00ac\\nmary use as a wastewater treatment facility (USEPA,\\n1999). Constructed wetlands which provide advanced\\ntreatment to wastewater that has been pretreated to sec\u00c2\u00ac\\nondary levels, and also provide other benefits such as\\nwildlife habitat, research laboratories, or recreational uses\\nare sometimes called enhancement wetlands.\\nConstructed wetlands have been classified by the lit\u00c2\u00ac\\nerature and practitioners into two types. Free water sur\u00c2\u00ac\\nface (FWS) wetlands (also known as surface flow wet\u00c2\u00ac\\nlands) closely resemble natural wetlands in appearance\\nbecause they contain aquatic plants that are rooted in a\\nsoil layer on the bottom of the wetland and water flows\\nthrough the leaves and stems of plants. Vegetated sub\u00c2\u00ac\\nmerged bed (VSB) systems (also known as subsurface\\nflow wetlands) do not resemble natural wetlands because\\nthey have no standing water. They contain a bed of media\\n(such as crushed rock, small stones, gravel, sand or soil)\\nwhich has been planted with aquatic plants. When prop\u00c2\u00ac\\nerly designed and operated, wastewater stays beneath\\nthe surface of the media, flows in contact with the roots\\nand rhizomes of the plants, and is not visible or available\\nto wildlife.\\n1", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0019.jp2"}, "20": {"fulltext": "The term \u00e2\u0080\u009cvegetated submerged bed\u00e2\u0080\u009d is used in this manual\\ninstead of subsurface flow wetland because it is a more ac\u00c2\u00ac\\ncurate and descriptive term. The term has been used previ\u00c2\u00ac\\nously to describe these units (WPCF, 1990; USEPA, 1994).\\nSome VSBs may meet the strict definition of a wetland, but a\\nVSB does not support aquatic wildlife because the water\\nlevel stays below the surface of the media, and is not condu\u00c2\u00ac\\ncive to many of the biological and chemical interactions that\\noccur in the water and sediments of a wetland with an open\\nwater column. VSBs have historically been characterized as\\nconstructed wetlands in the literature, and so they are in\u00c2\u00ac\\ncluded in this manual.\\nConstructed wetlands should not be confused with cre\u00c2\u00ac\\nated or restored wetlands, which have the primary function\\nof wildlife habitat. In an effort to mimic natural wetlands, the\\nlatter often have a combination of features such as varying\\nwater depths, open water and dense vegetation zones, veg\u00c2\u00ac\\netation types ranging from submerged aquatic plants to\\nshrubs and trees, nesting islands, and irregular shorelines.\\nThey are frequently built in or near places that have histori\u00c2\u00ac\\ncally had wetlands, and are often built as compensatory miti\u00c2\u00ac\\ngation. Created and restored wetlands for habitat or com\u00c2\u00ac\\npensatory mitigation are not discussed in this manual.\\nFinally, the term vertical flow wetland is used to describe a\\ntypical vertical flow sand or gravel filter which has been\\nplanted with aquatic plants. Because successful operation\\nof this type of system depends on its operation as a filter (i.e.\\nfrequent dosing and draining cycles), this manual does not\\ndiscuss this type of system.\\n1.3 Relationship to Previous EPA\\nDocuments\\nSeveral Offices or Programs within USEPA have published\\ndocuments in recent years on the subject of constructed\\nwetlands. Some examples of publications and their USEPA\\nsponsors are:\\nDesign Manual: Constructed Wetlands and Aquatic Plant\\nSystems for Municipal Wastewater Treatment (1988)\\n(Office of Research and Development, Cincinnati, OH,\\nEPA 625-1 -88-022)\\nSubsurface Flow Constructed Wetlands for Wastewa\u00c2\u00ac\\nter Treatment: A Technology Assessment (1993) (Office\\nof Wastewater Management, Washington, DC, EPA 832-\\nR-93-008)\\nHabitat Quality Assessment of Wetland Treatment Sys\u00c2\u00ac\\ntems (3 studies in 1992 and 1993) (Environmental Re\u00c2\u00ac\\nsearch Lab, Corvallis, OR, EPA600-R-92-229, EPA600-\\nR-93-117, EPA 600-R-93-222)\\nConstructed Wetlands for Wastewater Treatment and\\nWildlife Habitat: 17 Case Studies (1993) (Office of Waste-\\nwater Management, Washington, DC, EPA 832-R-93-\\n005)\\nGuidance for Design and Construction of a Subsur\u00c2\u00ac\\nface Flow Constructed Wetland (August 1993) (USEPA\\nRegion VI, Municipal Facilities Branch)\\nA Handbook of Constructed Wetlands (5 volumes,\\n1995) (USEPA Region III with USDA, NRCS, ISBN 0-\\n16-052999-9)\\nConstructed Wetlands for Animal Waste Treatment: A\\nManual on Performance, Design, and Operation With\\nCases Histories (1997) (USEPA Gulf of Mexico Pro\u00c2\u00ac\\ngram)\\nFree Water Surface Wetlands for Wastewater Treat\u00c2\u00ac\\nment: A Technology Assessment (1999) (Office of\\nWastewater Management, Washington, DC, EPA/832/\\nR-99/002)\\nSome information presented in this manual may contra\u00c2\u00ac\\ndict information presented in these other documents. Some\\ncontradictions are the result of new information and un\u00c2\u00ac\\nderstanding developed since the publication of earlier docu\u00c2\u00ac\\nments; some contradictions are the result of earlier mis\u00c2\u00ac\\nconceptions about the mechanisms at work within con\u00c2\u00ac\\nstructed wetlands; and some contradictions are the result\\nof differing opinions among experts when insufficient in\u00c2\u00ac\\nformation exists to present a clear answer to issues sur\u00c2\u00ac\\nrounded by disagreement. As stated previously, this manual\\nattempts to put an environmental engineering perspective\\non the use, design and performance of constructed wet\u00c2\u00ac\\nlands as reflected by the highest quality data available at\\nthis time. In areas where there is some disagreement\\namong experts, this manual assumes a conservative ap\u00c2\u00ac\\nproach based on known treatment mechanisms which fit\\nexisting valid data.\\n1.4 Wetlands Treatment Database\\nThrough a series of efforts funded by the USEPA, a\\nWetlands Treatment Database, \u00e2\u0080\u009cNorth American Wetlands\\nfor Water Quality Treatment Database or NADB\u00e2\u0080\u009d (USEPA,\\n1994) has been compiled which provides information about\\nnatural and constructed wetlands used for wastewater\\ntreatment in North America. Version 1 of the NADB was\\nreleased in 1994 and contains information for treatment\\nwetlands at 174 locations in over 30 US states and Cana\u00c2\u00ac\\ndian provinces. Information includes general site informa\u00c2\u00ac\\ntion, system specific information (e.g., flow, dimensions,\\nplant species), contact people with addresses and phone\\nnumbers, literature references, and permit information. It\\nalso contains some water quality data (BOD, TSS, N-se-\\nries, P, DO, and fecal conforms), but the data is not of uni\u00c2\u00ac\\nform quantity and quality, which makes it inappropriate for\\ndesign or modeling purposes.\\nVersion 2 of the NADB is currently undergoing Agency\\nreview and contains information on treatment wetlands at\\n245 locations in the US and Canada. Because each loca\u00c2\u00ac\\ntion may have multiple wetland cells, there are over 800\\nindividual wetland cells identified in Version 2. Besides\\nexpanding the number of wetland locations from Version\\n1, Version 2 also contains information regarding vegeta\u00c2\u00ac\\ntion, wildlife, human use, biomonitoring and additional water\\nquality data. As with Version 1, the data is not adequate\\nfor design or modeling.\\n2", "height": "4283", "width": "3142", "jp2-path": "constructedwetla00nati_0020.jp2"}, "21": {"fulltext": "Data did not exist or were incomplete for many of the\\nwetlands included in the NADB. Only existing informa\u00c2\u00ac\\ntion was collected for the NADB; no new measurements\\nwere made. Therefore, the NADB is very useful for ob\u00c2\u00ac\\ntaining general information about the status of con\u00c2\u00ac\\nstructed wetlands usage, as well as the locations of\\noperating systems and people to contact. However, it is\\nnot useful as a source of water quality data for wetland\\ndesign or prediction of treatment performance.\\nTables 1.1 through 1.4 give an overview of Version 2 of\\nthe NADB. The size range and median size are shown in\\nseveral tables to give the reader a feel for the size of each\\ntype of wetland. The median size is shown because there\\nare a few very large wetlands in some of the groups, which\\nmakes the median size more characteristic of the group\\nthan the mean size.\\nTables 1.1 and 1.2 group the wetlands by type of wet\u00c2\u00ac\\nland and type of wastewater being treated, respectively. In\\ngeneral FWSs are larger than VSBs, with the median size\\nof FWS wetlands being twice that of VSBs. The summary\\nstatistics for \u00e2\u0080\u009cother water\u00e2\u0080\u009d wetlands in Table 1.2 are some\u00c2\u00ac\\nwhat misleading because they are influenced by the large\\nEverglades Nutrient Removal project in Florida.\\nTable 1-1. Types of Wetlands in the NADB\\nType of Wetland\\nQty.\\nMin.\\nSize (hectares)\\nMedian\\nMax.\\nConstructed Wetlands\\n205\\n0.0004\\n0.8\\n1406\\nFree Water Surface\\n138\\n0.0004\\n1\\n1406\\nMarsh*\\n125\\n0.0004\\n1\\n1406\\nOther\\n13\\n0.08\\n3\\n188\\nVegetated Submerged Bed (all Marsh)\\n49\\n0.004\\n0.5\\n498\\nCombined FWS VSB (all Marsh)\\n8\\n0.1\\n0.4\\n17\\nOther or Not Classified\\n10\\n0.01\\n1\\n14\\nNatural Wetlands (all Free Water Surface)\\n38\\n0.2\\n40\\n1093\\nForest\\n18\\n1\\n40\\n204\\nMarsh\\n16\\n0.2\\n33\\n1093\\nOther or Not Classified\\n4\\n6\\n64\\n494\\nNot Classified 2\\nMarshes are characterized by soft-stemmed herbaceous plants, including emergent species, such as cattails, floating species, such as water lilies,\\nand submerged species, such as pondweeds. (Niering, 1985)\\nTable 1-2. Types of Wastewater Treated and Level of Pretreatment for NADB Wetlands\\nSize (hectares)\\nWastewater Type Pretreatment\\nQty.\\nMin.\\nMedian\\nMax.\\nAgricultural\\n58\\n0.0004\\n0.1\\n47\\nNone\\n8\\nPrimary\\n35\\nFacultative\\n14\\nNot classified\\n1\\nIndustrial\\n13\\n0.03\\n10\\n1093\\nPrimary\\n1\\nFacultative\\n2\\nSecondary\\n6\\nAdvanced Secondary\\n1\\nNot classified\\n3\\nMunicipal\\n159\\n0.004\\n2\\n500\\nPrimary\\n9\\nFacultative\\n78\\nSecondary\\n49\\nAdvanced Secondary\\n9\\nTertiary\\n4\\nOther\\n4\\nNot classified\\n6\\nStormwater\\n6\\n0.2\\n8\\n42\\nNone\\n4\\nSecondary\\n1\\nOther\\n1\\nOther Water\\n7\\n3\\n376\\n1406\\nNone\\n4\\nPrimary\\n1\\nFacultative\\n1\\nSecondary\\n1\\nNot classified\\n2\\n3", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0021.jp2"}, "22": {"fulltext": "Table 1.3 groups all the wetlands, regardless of type of\\nwetland or wastewater being treated, by size. In terms of\\narea, the majority of the wetlands are less than 10 hect\u00c2\u00ac\\nares (25 acres), and almost 90% are less than 100 hect\u00c2\u00ac\\nares (250 acres). In terms of design flow rate, the majority\\nare less than 1000 m3/d (about 0.25 mgd), and 82% are\\nless than 4060 m3/d (1 mgd).\\nTable 1.4 groups all the wetlands, regardless of type of\\nwetland or wastewater being treated, by location. Treat\u00c2\u00ac\\nment wetlands are located in 34 US states and 6 Cana\u00c2\u00ac\\ndian provinces. The number of wetlands per state is prob\u00c2\u00ac\\nably more a function of having an advocate for treatment\\nwetlands in the state than climate or some other favorable\\ncondition.\\nTable 1-3. Size Distribution of Wetlands in the NADB\\nArea (hectares) Design Flow (m3/d)\\nSize\\nRange\\nCumulative\\nPercentage\\nSize\\nRange\\nCumulative\\nPercentage\\nless than 1\\n46\\nless than 10\\n19\\nless than 10\\n75\\nless than 100\\n31\\nless than 100\\n93\\nless than 1000\\n62\\nless than 1000\\n99\\nless than 10,000\\n93\\nTable 1-4. Distribution of Wetlands in the NADB by State/Province\\nState or Province*\\nNumber of\\nWetlands\\nMin.\\nSize (hectares)\\nMedian\\nMax.\\nSD\\n42\\n0.3\\n2\\n134\\nFL\\n24\\n0.2\\n44.5\\n1406\\nAR\\n21\\n0.3\\n0.8\\n4\\nKY\\n19\\n0.01\\n0.1\\n5\\nLA\\n15\\n0.02\\n0.3\\n17\\nMS\\n11\\n0.02\\n0.9\\n101\\nCA\\n9\\n0.1\\n14\\n59\\nAL\\n8\\n0.04\\n0.2\\n6\\nONT\\n8\\n0.02\\n0.09\\n0.4\\nMD\\n5\\n0.1\\n0.2\\n2\\nOR\\n5\\n0.1\\n4\\n36\\nSC\\n5\\n20\\n36\\n185\\nIN\\n4\\n0.002\\n0.12\\n1\\nMl\\n4\\n5\\n56.5\\n110\\nMO\\n4\\n0.04\\n0.25\\n37\\nNY\\n4\\n0.03\\n0.25\\n2\\nPA\\n4\\n0.01\\n0.055\\n0.2\\nTX\\n4\\n0.1\\n0.2\\n0.5\\nAZ\\n3\\n2\\n38\\n54\\nGA\\n3\\n0.01\\n0.3\\n0.4\\nND\\n3\\n14\\n17\\n33\\nNVS\\n3\\n0.1\\n0.1\\n0.4\\nTN\\n3\\n0.1\\n0.2\\n0.3\\nWl\\n3\\n0.01\\n6\\n156\\nALB, IA, ME, MN,\\nNC, NM, NV, QUE\\n2\\nCT, IL, MA, NJ, NWT,\\nPEI, VA, WA\\n1\\n*Two-letter abbreviations are states; three-letter abbreviations are\\nprovinces.\\n1.5 History\\nKadlec and Knight (1996) give a good historical account\\nof the use of natural and constructed wetlands for waste-\\nwater treatment and disposal. As they point out, natural\\nwetlands have probably been used for wastewater disposal\\nfor as long as wastewater has been collected, with docu\u00c2\u00ac\\nmented discharges dating back to 1912. Some early con\u00c2\u00ac\\nstructed wetlands researchers probably began their efforts\\nbased on observations of the apparent treatment capacity\\nof natural wetlands. Others saw wastewater as a source\\nof water and nutrients for wetland restoration or creation.\\nResearch studies on the use of constructed wetlands for\\nwastewater treatment began in Europe in the 1950 s, and\\nin the US in the late 1960 s. Research efforts in the US\\nincreased throughout the 1970 s and 1980 s, with signifi\u00c2\u00ac\\ncant Federal involvement by the Tennessee Valley Authority\\n(TVA) and the U.S. Department of Agriculture in the late\\n1980 s and early 1990 s. USEPA has had a limited role in\\nconstructed wetlands research which might explain the\\ndearth of useful, quality-assured data.\\nStart dates for constructed wetlands in the NADB are\\nshown in Table 1.5, with the start dates for natural wet\u00c2\u00ac\\nlands used for treatment included for comparison. The table\\nshows that the use of FWS wetlands and VSBs in North\\nAmerica really began in the early and latel980 s, respec\u00c2\u00ac\\ntively, and the number continues to increase. No new natu\u00c2\u00ac\\nral wetland treatment systems have begun since 1990, and\\nat least one-third of the natural wetland treatment systems\\nincluded in the NADB are no longer operating.\\n1.6 Common Misconceptions\\nMany texts and design guidelines for constructed wet\u00c2\u00ac\\nlands, in addition to those listed above sponsored by the\\nvarious offices of USEPA, have been published since\\nUSEPA\u00e2\u0080\u0099s 1988 design manual (EC/EWPCA (1990); WPCF\\n(1990); Tennessee Valley Authority (1993); USDA (1993);\\nReed, et al (1995); Kadlec and Knight (1996); Campbell\\nand Ogden (1999)). Also, a number of international con\u00c2\u00ac\\nferences have been convened to present the findings of\\nconstructed wetlands research from almost every conti\u00c2\u00ac\\nnent (Hammer (1989); Cooper and Findlater (1990); Moshiri\\nTable 1-5. Start Date of Treatment Wetlands in the NADB\\nType\\nbefore\\n1950\\n1950 s\\n60 s\\n1970 s\\n\u00e2\u0080\u009880-\u00e2\u0080\u009884\\n\u00e2\u0080\u009885-\u00e2\u0080\u009889\\n1990 s\\n(latest*)\\nConstructed,\\nFWS\\n1\\n0\\n3\\n8\\n33\\n85\\n(\u00e2\u0080\u009896)\\nConstructed,\\nVSB\\n0\\n0\\n0\\n0\\n21\\n31\\n(\u00e2\u0080\u009894)\\nConstructed,\\nhybrid\\n0\\n0\\n0\\n1\\n4\\n6\\n(\u00e2\u0080\u009894)\\nNatural,\\nFWS\\n4\\n3\\n9\\n5\\n8\\n1\\n(\u00e2\u0080\u009890)\\nYear of last wetland included in database for this type of wetland other\\nwetlands may have started after this date, but are not in the database.\\n4", "height": "4283", "width": "3142", "jp2-path": "constructedwetla00nati_0022.jp2"}, "23": {"fulltext": "(1993); IAWQ (1994)(1995) (1997)). However, in spite of\\nthe great amount of resources devoted to constructed wet\u00c2\u00ac\\nlands, questions and misconceptions remain about their ap\u00c2\u00ac\\nplication, design, and performance. This section briefly de\u00c2\u00ac\\nscribes four common misconceptions; further discussion of\\nthese items is found in other chapters.\\nMisconception #1: Wetland design has been well-charac\u00c2\u00ac\\nterized by published design equations. Constructed wetlands\\nare complex systems in terms of biology, hydraulics and water\\nchemistry. Furthermore, there is a lack of quality data of suf\u00c2\u00ac\\nficient detail, both temporally and spatially, on full-scale con\u00c2\u00ac\\nstructed wetlands. Due to the lack of data, designers have\\nbeen forced to derive design parameters by aggregating per\u00c2\u00ac\\nformance data from a variety of wetlands, which leads to\\nuncertainties about the validity of the parameters. Data from\\nwetlands with detailed research studies with rigorous quality\\ncontrol (QC) might be combined with data from wetlands\\nwith randomly collected data with little QC. Data from small\\nwetlands with minimal pretreatment might be combined with\\ndata from large wetlands used for polishing secondary efflu\u00c2\u00ac\\nent. Additional problems with constructed wetlands data in\u00c2\u00ac\\nclude: lack of paired influent-effluent samples; grab samples\\ninstead of composited samples; lack of reliable flow or de\u00c2\u00ac\\ntention time information; and lack of important incidental in\u00c2\u00ac\\nformation such as temperature and precipitation. The result\u00c2\u00ac\\ning data combinations, completed to obtain larger data sets,\\nhave sometimes been used to create regression equations\\nof questionable value for use in design. Finally, data from\\nconstructed wetlands treating relatively high quality (but in\u00c2\u00ac\\nadequately characterized) wastewater has sometimes been\\nused to derive design parameters for more concentrated\\nmunicipal treatment applications, which is less than assur\u00c2\u00ac\\ning for any designer.\\nMisconception #2: Constructed wetlands have aerobic as\\nwell as anaerobic treatment zones. Probably the most com\u00c2\u00ac\\nmon misconception concerns the ability of emergent wet\u00c2\u00ac\\nland plants to transfer oxygen to their roots. Emergent aquatic\\nplants are uniquely suited to the anaerobic environment of\\nwetlands because they can move oxygen from the atmo\u00c2\u00ac\\nsphere to their roots. Research has shown that some oxy\u00c2\u00ac\\ngen \u00e2\u0080\u009cleaks\u00e2\u0080\u009d from the roots into the surrounding soils (Brix,\\n1997). This phenomenon, and early work with natural and\\nconstructed wetlands that treated wastewater with a low\\noxygen demand, has led to the assumption that significant\\naerobic micro-sites exist in all wetland systems. Some con\u00c2\u00ac\\nstructed wetlands literature states or implies that aerobic bio\u00c2\u00ac\\ndegradation is a significant treatment mechanism in fully\\nvegetated systems, which has led some practitioners to be\u00c2\u00ac\\nlieve that wetlands with dense vegetation, or many sources\\nof \u00e2\u0080\u009cleaking\u00e2\u0080\u009d oxygen, are in fact aerobic systems. However,\\nthe early work with tertiary or polishing wetlands is not di\u00c2\u00ac\\nrectly applicable to wetlands treating higher strength waste-\\nwater because it fails to account for the impacts of the waste-\\nwater on the characteristics of the wetland. Treatment mecha\u00c2\u00ac\\nnisms that function under light loads are impaired or over\u00c2\u00ac\\nwhelmed due to changes imparted by the large oxygen de\u00c2\u00ac\\nmand of more contaminated municipal wastewater. Field\\nexperience and research have shown that the small amount\\nof oxygen leaked from plant roots is insignificant compared\\nto the oxygen demand of municipal wastewater applied at\\npractical loading rates.\\nMisconception #3: Constructed wetlands can remove sig\u00c2\u00ac\\nnificant amounts of nitrogen. Related to the misconception\\nabout the availability of oxygen in constructed wetlands is\\nthe misconception about the ability of constructed wetlands\\nto remove significant amounts of nitrogen. Harvesting re\u00c2\u00ac\\nmoves less than 20% of influent nitrogen (Reed, et al,1995)\\nat conventional loading rates. This leaves nitrification and\\ndenitrification as the primary removal mechanisms. If it is\\nassumed that wetlands have aerobic zones, it then follows\\nthat nitrification of ammonia to nitrate should occur. Further\u00c2\u00ac\\nmore, if the aerobic zone surrounds only the roots of the\\nplants, it then follows that anaerobic zones dominate, and\\ndenitrification of nitrate to nitrogen gas should also occur.\\nUnfortunately, the nitrogen-related misconceptions have been\\nresponsible for the failure of several constructed wetlands\\nthat were built to remove or oxidize nitrogen. Because anaero\u00c2\u00ac\\nbic processes dominate in both VSBs and fully vegetated\\nFWS wetlands, nitrification of ammonia is unlikely to occur\\nin the former and will occur only if open water zones are\\nintroduced to the latter. Constructed wetlands can be de\u00c2\u00ac\\nsigned to remove nitrogen, if sufficient aerobic (open water)\\nand anaerobic (vegetated) zones are provided. Otherwise,\\nconstructed wetlands should be used in conjunction with other\\naerobic treatment processes that can nitrify to remove nitro\u00c2\u00ac\\ngen.\\nMisconception #4: Constructed wetlands can remove sig\u00c2\u00ac\\nnificant amounts of phosphorus. Phosphorus removal in con\u00c2\u00ac\\nstructed wetlands is limited to seasonal uptake by the plants,\\nwhich is not only minor compared to the phosphorus load in\\nmunicipal wastewater, but is negated during the plants\u00e2\u0080\u0099 se\u00c2\u00ac\\nnescence, and to sorption to influent solids which are cap\u00c2\u00ac\\ntured, soils or plant detritus, all of which have a limited ca\u00c2\u00ac\\npacity. Two problems have been associated with phospho\u00c2\u00ac\\nrus data in the literature. First, some phosphorus removal\\ndata has been reported in terms of percent removal. How\u00c2\u00ac\\never, many of the early phosphorus studies were for natural\\nwetlands or constructed wetlands that received wastewater\\nwith a low phosphorus concentration. Because of low influ\u00c2\u00ac\\nent concentrations, removal of only a single mg/L of phos\u00c2\u00ac\\nphorus was reported as a large percent removal. Second,\\nfor studies evaluating the performance of newly constructed\\nwetlands, phosphorus removal data will be uncharacteristic\\nof long-term performance. New plants growing in a freshly\\nplanted wetland will uptake more phosphorus than a mature\\nwetland, which will have phosphorus leaching from dying\\n(senescent) plants as well as uptake by growing plants. Also,\\nnewly placed soils or media will have a greater phosphorus\\nsorption capacity than a mature system which will have most\\nsorption sites already saturated.\\n1.7 When to Use Constructed Wetlands\\n1.7.1 Appropriate Technology for Small\\nCommunities\\nAppropriate technology is defined as a treatment sys\u00c2\u00ac\\ntem which meets the following key criteria:\\n5", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0023.jp2"}, "24": {"fulltext": "Affordable Total annual costs, including capital, op\u00c2\u00ac\\neration, maintenance and depreciation are within the\\nuser\u00e2\u0080\u0099s ability to pay.\\nOperable Operation of the system is possible with\\nlocally available labor and support.\\nReliable Effluent quality requirements can be con\u00c2\u00ac\\nsistently meet.\\nUnfortunately, many rural areas of the U.S. with small\\ntreatment plants (usually defined as treating less than 3,800\\nm3/d (1 mgd)) have failed to consider this appropriate tech\u00c2\u00ac\\nnology definition, and have often adopted inappropriate\\ntechnologies such as activated sludge. In 1980, small,\\nactivated sludge systems constituted 39% of the small\\npublicly owned treatment facilities (GAO, 1980). Recent\\ninformation from one state showed that 73% of all treat\u00c2\u00ac\\nment plants of less than 3,800m3/d capacity used some\\nform of the activated sludge process. Unfortunately, the\\nactivated sludge process is considered by almost all U.S.\\nand international experts to be the most difficult to operate\\nand maintain of the various wastewater treatment concepts.\\nPresently, small treatment plants constitute more than 90%\\nof the violations of U.S. discharge standards. At least one\\nU.S. state, Tennessee, has required justification for the use\\nof activated sludge package plants for very small treat\u00c2\u00ac\\nment plant applications (Tennessee Department of Public\\nHealth, 1977).\\nSmall community budgets become severely strained by\\nthe costs of their wastewater collection and treatment fa\u00c2\u00ac\\ncilities. Inadequate budgets and poor access to equipment,\\nsupplies and repair facilities preclude proper operation and\\nmaintenance (O M). Unaffordable capital costs and the\\ninability to reliably meet effluent quality requirements add\\nup to a prime example of violating the prior criteria for ap\u00c2\u00ac\\npropriate technology. Unfortunately, no consideration for\\nreuse, groundwater recharge, or other alternatives to\\nstream discharge has heretofore been common, except in\\na few states where water shortages exist.\\nPresently there are a limited number of appropriate tech\u00c2\u00ac\\nnologies for small communities which should be immedi\u00c2\u00ac\\nately considered by a community and their designer. These\\ninclude stabilization ponds or lagoons, slow sand filters,\\nland treatment systems, and constructed wetlands. All of\\nthese technologies fit the operability criterion, and to vary\u00c2\u00ac\\ning degrees, are affordable to build and reliable in their\\ntreatment performance. Because each of these technolo\u00c2\u00ac\\ngies has certain characteristics dNd requirements for pre-\\nand post- treatment to meet a certain effluent quality, they\\nmay be used alone or in series with others depending on\\nthe treatment goals.\\nFor example, the designer may wish to supplement sta\u00c2\u00ac\\nbilization ponds with a tertiary system to meet reuse or\\ndischarge criteria consistently. Appropriate stabilization\\npond upgrading methods to meet effluent standards in\u00c2\u00ac\\nclude FWS wetlands, which can provide the conditions for\\nenhanced settling to attain further reduction of fecal\\ncoliforms and removal of the excess algal growth which\\ncharacterizes pond system effluents. FWS wetlands are\\nnormally used after ponds because of their ability to handle\\nthe excess algal solids generated in the ponds. Although\\nVSBs have been employed after ponds, excess algal sol\u00c2\u00ac\\nids have caused problems at some locations, thus defeat\u00c2\u00ac\\ning the operability factor in the appropriate technology defi\u00c2\u00ac\\nnition. VSBs are more appropriately applied behind a pro\u00c2\u00ac\\ncess designed to minimize suspended and settleable sol\u00c2\u00ac\\nids, such as a septic or Imhoff tank or anaerobic lagoon.\\nConstructed wetlands may also require post-treatment\\nprocesses, depending on the ultimate goals of the treat\u00c2\u00ac\\nment system. More demanding effluent requirements may\\nrequire additional processes in the treatment train or may\\ndictate the use of other processes altogether. For example,\\nthe ability of constructed wetlands to remove nitrogen and\\nphosphorus has frequently been overestimated. Two ap\u00c2\u00ac\\npropriate technologies that readily accomplish ammonium\\noxidation are intermittent and recirculating sand filters.\\nThere is at least one case study of the successful use of a\\nrecirculating gravel filter in conjunction with a VSB (Reed,\\net al, 1995 FWS systems can both nitrify and denitrify,\\nthus removing significant portions of nitrogen from the\\nwastewater, by alternating fully vegetated and open water\\nzones in proper proportions. If the municipal facility is re\u00c2\u00ac\\nquired to have significant phosphorus removal (e.g., to at\u00c2\u00ac\\ntain 1 mg/L from a typical influent value of 6 to 7 mg/L),\\nconstructed wetlands will need to be accompanied by some\\nprocess or processes that can remove the phosphorus.\\nIn conclusion, constructed wetlands are an appropriate\\ntechnology for areas where inexpensive land is generally\\navailable and skilled labor is less available. Whether they\\ncan be used essentially alone or in series with other ap\u00c2\u00ac\\npropriate technologies depends on the required treatment\\ngoals. Additionally, they can be appropriate for onsite sys\u00c2\u00ac\\ntems where local regulators call for and allow systems other\\nthan conventional septic tank soil absorption systems.\\n1.7.2 Policy and Permitting Issues\\nAn interagency workgroup, including representatives\\nfrom several Federal agencies, is presently developing\\nGuiding Principles for Constructed Treatment Wetlands:\\nProviding Water Quality and Wildlife Habitat (USEPA,\\n1999). The essence of the current draft of the guidelines is\\nthat constructed treatment wetlands will:\\nreceive no credit as mitigation wetlands;\\nbe subject to the same rules as treatment lagoons\\nregarding liner requirements;\\nbe subject to the same monitoring requirements as\\ntreatment lagoons;\\nshould not be constructed in the waters of the United\\nStates, including existing natural wetlands; and\\nwill not be considered Waters of the United States\\nupon abandonment if the first and the fourth condi\u00c2\u00ac\\ntions are met.\\n6", "height": "4283", "width": "3142", "jp2-path": "constructedwetla00nati_0024.jp2"}, "25": {"fulltext": "The guidance encourages use of local plant species and\\nexpresses concern about permit compliance during lengthy\\nstartup periods and vector attraction and control issues.\\nTo avoid additional permitting and regulatory require\u00c2\u00ac\\nments, constructed wetlands should be designed as a treat\u00c2\u00ac\\nment process and built in uplands as opposed to wetlands\\nor flood plains, i.e., outside of waters of the U.S.. Consider\\nthe following from the draft guidelines.\\nIf your constructed treatment wetland is constructed\\nin an existing water of the U.S., it will remain a water\\nof the U.S. unless an individual CWA section 404 per\u00c2\u00ac\\nmit is issued which explicitly authorizes it as an ex\u00c2\u00ac\\ncluded waste treatment system designed to meet the\\nrequirements of the CWA.... Once constructed, if your\\ntreatment wetland is a water of the U.S., you will need\\na NPDES permit for the discharge of pollutants... into\\nthe wetland.... [Additionally,] if you wish to use a de\u00c2\u00ac\\ngraded wetland for wastewater treatment and plan to\\nconstruct water control structures, such as berms or\\nlevees, this construction will... require a Section 404\\npermit. Subsequent maintenance may also require a\\npermit.\\nAs stated in the guidelines:\\nIf the constructed wetland is abandoned or is no longer\\nbeing used as a treatment system, it may revert to a\\nwater of the U.S. if... the following conditions exist:\\nthe system has wetland characteristics (i.e., hydrol\u00c2\u00ac\\nogy, soils, vegetation) and it is either (1) an interstate\\nwetland, (2) is adjacent to another water of the U.S.\\n(other than waters which are themselves wetlands),\\nor (3) if it is an isolated intrastate water which has a\\nnexus to interstate commerce (e.g., it provides habitat\\nfor migratory birds).\\nNone of preceding discussion precludes designing and\\nbuilding a wetland which provides water reuse, habitat or\\npublic use benefits in addition to wastewater treatment.\\nConstructed wetlands built primarily for treatment will gen\u00c2\u00ac\\nerally not be given credit as compensatory mitigation to\\nreplace wetland losses. However, in limited cases, some\\nparts of a constructed wetland system may be given credit,\\nespecially if additional wetland area is created beyond that\\nneeded for treatment purposes. Also, current policy en\u00c2\u00ac\\ncourages the use of properly treated wastewater to restore\\ndegraded wetlands. For example, restoration might be\\npossible if:\\n1 the source water meets all applicable water qual\\nity standards and criteria, (2) its use would result in a net\\nenvironmental benefit to the aquatic system\u00e2\u0080\u0099s natural\\nfunctions and values, and if applicable, (3) it would help\\nrestore the aquatic system to its historical condition.\\nPrime candidates for restoration may include wetlands\\nthat were degraded or destroyed through the diversion\\nof water supplies,... For example, in the arid west, there\\nare often historic wetlands that no longer have a reliable\\nwater source due to upstream water allocations or sink\u00c2\u00ac\\ning groundwater tables. Pre-treated effluent may be the\\nonly source of water available for these areas and their\\ndependent ecosystems.... EPA has developed regional\\nguidance to assist dischargers and regulators in dem\u00c2\u00ac\\nonstrating a net ecological benefit from maintenance of\\na wastewater discharge to a waterbody.\\nThis discussion of policy and permitting issues is very\\ngeneral and regulatory decisions regarding these issues\\nare made on a case-by-case basis. Planners and design\u00c2\u00ac\\ners should seek guidance from State and Regional regu\u00c2\u00ac\\nlators about site specific constructed wetland criteria in\u00c2\u00ac\\ncluding location, discharge requirements, and possible\\nlong-term monitoring requirements.\\n1.7.3 Other Factors\\nProbably the most important factor which impacts all\\naspects of constructed wetlands is their inherent aesthetic\\nappeal to the general public. The desire of people to have\\nsuch an attractive landscape enhancement treat their\\nwastewater and become a valuable addition to the com\u00c2\u00ac\\nmunity is a powerful argument when the need for waste-\\nwater treatment upgrading becomes a matter of public\\ndebate. The appeal of constructed wetlands makes the\\nneed to accurately assess the capability of the technology\\nso important and so difficult. The engineering community\\noften fails to appreciate this inherent appeal, while the\\nenvironmental community often lacks the understanding\\nof treatment mechanisms to appreciate the limitations of\\nthe technology. The natural attraction of constructed wet\u00c2\u00ac\\nlands and the potential for other aesthetic benefits may\\nsometimes offset the treatment or cost advantages of other\\ntreatment options, and public opinion may dictate that a\\nconstructed wetland is the preferred option. In other situa\u00c2\u00ac\\ntions, constructed wetlands will be too costly or unable to\\nproduce the required effluent water quality, and the de\u00c2\u00ac\\nsigner will have to convince the public that wetlands are\\nnot a viable option, in spite of their inherent appeal.\\nThe use of constructed wetlands as a treatment tech\u00c2\u00ac\\nnology carries some degree of risk for several reasons.\\nFirst, as noted in a review of constructed wetlands for\\nwastewater treatment by Cole (1998), constructed wetlands\\nare not uniformly accepted by all state regulators or EPA\\nregions. Some authorities encourage the use of constructed\\nwetlands as a proven treatment technology, due in part to\\nthe misconceptions noted in Section 1.6. Others still con\u00c2\u00ac\\nsider them to be an emerging technology. As with any new\\ntreatment technology, uniform acceptance of constructed\\nwetlands will take some time. Other natural treatment pro\u00c2\u00ac\\ncesses which are now generally accepted, such as slow\\nrate or overland flow land treatment systems, went through\\na similar course of variable acceptance.\\nSecond, although there is no evidence of harm to wild\u00c2\u00ac\\nlife using constructed wetlands, some regulators have ex\u00c2\u00ac\\npressed concern about constructing a system which will\\ntreat wastewater while it attracts wildlife. Unfortunately,\\nthere has not been any significant research conducted on\\nthe risks to wildlife using constructed wetlands. Although\\n7", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0025.jp2"}, "26": {"fulltext": "they are a distinctly different type of habitat, the lack of\\nevidence of risks to wildlife using treatment lagoon sys\u00c2\u00ac\\ntems for many years suggests that there may not be a\\nserious risk for wetlands treating municipal wastewater.\\nOf course, if a wetland is going to treat wastewater with\\nhigh concentrations of known toxic compounds, the de\u00c2\u00ac\\nsigner will need to use a VSB system or incorporate fea\u00c2\u00ac\\ntures in a FWS wetland which restrict access by wildlife.\\nFinally, as noted earlier, due to the lack of a large body\\nof scientifically valid data, the design process is still em\u00c2\u00ac\\npirical, that is, based upon observational data rather than\\nscientific theories. Due to the variability of many factors at\\nconstructed wetlands being observed by researchers (e.g.,\\nclimatic effects, influent wastewater characteristics, design\\nconfigurations, construction techniques, and O M prac\u00c2\u00ac\\ntices), there will continue to be disagreement about some\\ndesign and performance issues for some period of time.\\n1.8 Use of This Manual\\nChapters 1,2,7 and 8 provide information for non-tech-\\nnical readers, such as decision-makers and stakeholders,\\nto understand the capabilities and limitations of constructed\\nwetlands. These chapters provide the type of information\\nrequired to question designers and regulators in the pro\u00c2\u00ac\\ncess of determining how constructed wetlands may be used\\nto expand, upgrade or develop wastewater treatment in\u00c2\u00ac\\nfrastructure.\\nChapters 3 through 6 provide information for technical\\nreaders, such as design engineers, regulators and plan\u00c2\u00ac\\nners, to plan, design, build and manage constructed wet\u00c2\u00ac\\nlands as part of a comprehensive plan for local and re\u00c2\u00ac\\ngional management of municipal wastewater collection,\\ntreatment, and reuse.\\nChapter 2 describes constructed wetland treatment sys\u00c2\u00ac\\ntems and their identifiable features. It answers the most\\nfrequently asked questions about these systems and in\u00c2\u00ac\\ncludes a glossary of terms which are used in this manual\\nand generally in discussion of constructed wetland sys\u00c2\u00ac\\ntems. There are brief discussions of other aquatic treat\u00c2\u00ac\\nment systems that are in use or are commercially avail\u00c2\u00ac\\nable and an annotated introduction to specific uses for\\nconstructed wetlands outside the purview of this manual.\\nChapter 3 discusses the treatment mechanisms occur\u00c2\u00ac\\nring in a constructed wetland to help the reader under\u00c2\u00ac\\nstand the most important processes and what climatic con\u00c2\u00ac\\nditions and other physical phenomena most affect these\\nprocesses. A basic understanding of the mechanisms in\u00c2\u00ac\\nvolved will allow the reader to more intelligently interpret\\ninformation from other literature sources as well as infor\u00c2\u00ac\\nmation in chapters 4 and 5 of this manual.\\nChapters 4, 5, and 6 describe the design, construction,\\nstartup and operational issues of constructed wetlands in\\nsome detail. It will be apparent to the reader that there are\\npresently insufficient data to create treatment models in\\nwhich there can be great confidence. Most data in the lit\u00c2\u00ac\\nerature has been generated with inadequate quality as\u00c2\u00ac\\nsurance and control (Qa/Qc), and most research studies\\nhave not measured or focused on documentation of key\\nvariables which could explain certain performance char\u00c2\u00ac\\nacteristics. Chapters 4 and 5 use the existing data of suffi\u00c2\u00ac\\ncient quality to create a viable approach to applicability\\nand design of both FWS and VSB systems and sets prac\u00c2\u00ac\\ntical limits on their performance capabilities. Chapter 6\\ndeals with the practical issues of construction and start-up\\nof these systems which have been experienced to date.\\nChapter 7 contains cost information for constructed wet\u00c2\u00ac\\nlands. Subsequent to standardizing the costs to a specific\\ntime, it becomes clear that local conditions and require\u00c2\u00ac\\nments can dominate the costs. However, the chapter does\\nprovide a reasonable range of expected costs which can\\nbe used to evaluate constructed wetlands against other\\nalternatives in the facility planning stage. Also, there is\\nsufficient information presented to provide the user with a\\nrange of unit costs for certain components and to indicate\\nthose components that dominate system costs and those\\nthat are relatively inconsequential.\\nChapter 8 presents eight case studies to allow readers\\nto become familiar with sites that have used constructed\\nwetlands and their experiences. The systems in this chap\u00c2\u00ac\\nter are not ones which are superior to other existing facili\u00c2\u00ac\\nties, but they are those which have been observed and\\nfrom which lessons can be learned by the reader about\\neither successful or unsuccessful design practices.\\n1.9 References\\nBrix, H. 1997. Do Macrophytes Play a Role in Constructed\\nTreatment Wetlands?. Water Science Technology,\\nVol 35, No. 5, pp.11-17.\\nCampbell, C.S. and M.H. Ogden. 1999. Constructed Wet\u00c2\u00ac\\nlands in the Sustainable Landscape. John Wiley and\\nSons, New York, New York.\\nCole, Stephen. 1998. The Emergence of Treatment Wet\u00c2\u00ac\\nlands. Environmental Science Technology, Vol. 3,\\nNo.5, pp 218A-223A.\\nCooper, P.F., and B.C. Findlater, eds. 1990. Constructed\\nWetlands in Water Pollution Control. Pergamon Press,\\nNew York, New York.\\nEC/EWPCA. 1990. European Design and Operations\\nGuidelines for Reed Bed Treatment Systems. Prepared\\nfor the EC/EWPCA Expert Contact Group on Emer\u00c2\u00ac\\ngent Hydrophyte Treatment Systems. P.F. Cooper, ed.,\\nEuropean Community/European Water Pollution Con\u00c2\u00ac\\ntrol Association.\\nGovernment Accounting Office. 1980. Costly wastewater\\ntreatment plants fail to perform as expected. CED-81-\\n9. Washington, D.C.\\nHammer, D.A., ed. 1989. Constructed Wetlands for Waste-\\nwater Treatment. Lewis Publishers, Inc. Chelsea,\\nMichigan.\\n8", "height": "4283", "width": "3142", "jp2-path": "constructedwetla00nati_0026.jp2"}, "27": {"fulltext": "IAWQ. 1992. Proceedings of international conference on\\ntreatment wetlands, Sydney, Australia. Water Science\\nTechnology. Vol. 29, No. 4.\\nIAWQ. 1995. Proceedings of international conference on\\ntreatment wetlands, Guangzhou, China. Water Science\\nTechnology. Vol. 32, No. 3.\\nIAWQ. 1997. Proceedings of international conference on\\ntreatment wetlands, Vienna, Austria. Water Science\\nTechnology. Vol. 35, No. 5.\\nKadlec, R.H. and R.L. Knight. 1996. Treatment Wetlands.\\nCRC Press LLC. Boca Raton, FL.\\nMoshiri, L., ed. 1993. Constructed Wetlands for Water Qual\u00c2\u00ac\\nity Improvement. Lewis Publishers, Inc., Chelsea, Ml.\\nNiering, W.A. 1985. Wetlands. Alfred A. Knopf, Inc., New\\nYork, NY.\\nReed, S.C., R.W. Crites, and J.E. Middlebrooks. 1995.\\nNatural Systems for Waste Management and Treat\u00c2\u00ac\\nment. Second edition. McGraw-Hill, Inc., New York,\\nNY.\\nTennessee Department of Public Health. 1977. Regula\u00c2\u00ac\\ntions for plans, submittal, and approval; Control of con\u00c2\u00ac\\nstruction; Control of operation. Chapter 1200-4-2, State\\nof Tennessee Administrative Rules. Knoxville, TN.\\nTennessee Valley Authority. 1993. General Design, Con\u00c2\u00ac\\nstruction, and Operation Guidelines: Constructed Wet\u00c2\u00ac\\nlands Wastewater Treatment Systems for Small Us\u00c2\u00ac\\ners Including Individual Residences. G.R. Steiner and\\nJ.T. Watson, eds. 2nd edition. TVA Water Management\\nResources Group. TVA/WM--93/10. Chattanooga, TN.\\nU.S. Department of Agriculture. 1995. Handbook of Con\u00c2\u00ac\\nstructed Wetlands. Svolumes. USDA-Natural Re\u00c2\u00ac\\nsources Conservation Service/US EPA-Region III/\\nPennsylvania Department of Natural Resources.\\nWashington, D.C.\\nU.S. Environmental Protection Agency. 1988. Design\\nManual: Constructed Wetlands and Aquatic Plant Sys\u00c2\u00ac\\ntems for Municipal Wastewater Treatment. EPA/625/\\n1-88/022. US EPA Office of Research and Develop\u00c2\u00ac\\nment, Cincinnati, OH.\\nU.S. Environmental Protection Agency. 1993. Subsurface\\nFlow Constructed Wetlands for Wastewater Treatment:\\nA Technology Assessment. S.C. Reed, ed., EPA/ 832/\\nR-93/008. US EPA Office of Water, Washington, D.C.\\nU.S. Environmental Protection Agency. 1994. Wetlands\\nTreatment Database (North American Wetlands for\\nWater Quality Treatment Database). R.H. Kadlec, R.L.\\nKnight, S.C. Reed, and R.W. Ruble eds., EPA/600/C-\\n94/002. US EPA Office of Research and Development,\\nCincinnati, OH.\\nU.S. Environmental Protection Agency. 1999. Final Draft\\nGuiding Principles for Constructed Treatment Wetlands:\\nProviding Water Quality and Wildlife Habitat. Developed\\nby the Interagency Workgroup on Constructed Wetlands\\n(U.S. Environmental Protection Agency, Army Corps of\\nEngineers, Fish and Wildlife Sen/ice, Natural Resources\\nConservation Services, National Marine Fisheries Ser\u00c2\u00ac\\nvice, and Bureau of Reclamation). Final Draft 6/8/1999.\\nhttp://www.epa.gov/owow/wetlands/constructed/\\nguide.html\\nWater Pollution Control Federation. 1990. Natural Systems\\nfor Wastewater Treatment. Manual of Practice FD-16,\\nS.C. Reed, ed., Water Pollution Control Federation,\\nAlexandria, VA.\\n9", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0027.jp2"}, "28": {"fulltext": "Chapter 2\\nIntroduction to Constructed Wetlands\\n2.1 Understanding Constructed Wetlands\\nConstructed wetlands are wastewater treatment systems\\ncomposed of one or more treatment cells in a built and\\npartially controlled environment designed and constructed\\nto provide wastewater treatment. While constructed wet\u00c2\u00ac\\nlands have been used to treat many types of wastewater\\nat various levels of treatment, the constructed wetlands\\ndescribed in this manual provide secondary treatment to\\nmunicipal wastewater. These are treatment systems that\\nreceive primary effluent and treat it to secondary effluent\\nstandards and better, in contrast to enhancement systems\\nor polishing wetlands, which receive secondary effluent\\nand treat it further prior to discharge to the environment.\\nThis distinction emphasizes the degree of treatment more\\nthan the means of treatment, because the constructed\\nwetlands described in this manual receive higher-strength\\nwastewater than the polishing wetlands that have been\\nwidely used as wastewater treatment systems for the last\\n20 years.\\nWhile constructed wetlands discussed in this manual\\nprovide secondary treatment in a community\u00e2\u0080\u0099s wastewa\u00c2\u00ac\\nter treatment system, this technology also can be used in\\ncombination with other secondary treatment technologies.\\nFor example, a constructed wetland could be placed up\u00c2\u00ac\\nstream in the treatment train from an infiltration system to\\noptimize the cost of secondary treatment. In other uses,\\nconstructed wetlands could discharge secondary effluent\\nto enhancement wetlands for polishing. Constructed wet\u00c2\u00ac\\nlands are not recommended for treatment of raw waste-\\nwater. Figure 2-1 portrays a hypothetical wastewater treat\u00c2\u00ac\\nment train utilizing constructed wetlands in series.\\nThe distinction between constructed wetlands for sec\u00c2\u00ac\\nondary treatment and enhancement systems for tertiary\\ntreatment is critical in understanding the limitations of ear\u00c2\u00ac\\nlier accounts of wetland-based treatment systems and\\ndatabases of system performance. Most of the commonly\\navailable information on constructed wetland treatment\\nsystems is derived from data gathered at many larger pol\u00c2\u00ac\\nishing wetlands and a relatively few smaller constructed\\nwetlands for secondary treatment. In the past, largely un\u00c2\u00ac\\nverified data from these disparate sources has been ag\u00c2\u00ac\\ngregated, statistically rendered, and then applied as guid\u00c2\u00ac\\nance for constructed wetland systems, with predictably\\ninconsistent results. In contrast, guidance offered in this\\nmanual is drawn from reliable research data and practical\\napplication in constructed wetlands for secondary treat\u00c2\u00ac\\nment of higher-strength municipal wastewater.\\nConstructed wetlands comprise two types of systems\\nthat share many characteristics but are distinguished by\\nthe location of the hydraulic grade line. Design variations\\nfor both types principally affect shapes and sizes to fit site-\\nspecific characteristics and optimize construction, opera\u00c2\u00ac\\ntion, and performance. Both types of constructed wetlands\\ntypically may be fitted with liners to prevent infiltration,\\ndepending on local soil conditions and regulatory require\u00c2\u00ac\\nments.\\nFree water surface (FWS) constructed wetlands closely\\nresemble natural wetlands in appearance and function, with\\na combination of open-water areas, emergent vegetation,\\nvarying water depths, and other typical wetland features.\\nFigure 2-2 illustrates the main components of a FWS con\u00c2\u00ac\\nstructed wetland. Atypical FWS constructed wetland con\u00c2\u00ac\\nsists of several components that may be modified among\\nvarious applications but retain essentially the same fea\u00c2\u00ac\\ntures. These components include berms to enclose the\\ntreatment cells, inlet structures that regulate and distribute\\ninfluent wastewater evenly for optimum treatment, various\\ncombinations of open-water areas and fully vegetated sur\u00c2\u00ac\\nface areas, and outlet structures that complement the even\\ndistribution provided by inlet structures and allow adjust\u00c2\u00ac\\nment of water levels within the treatment cell. Shape, size,\\nand complexity of design often are functions of site char\u00c2\u00ac\\nacteristics rather than preconceived design criteria.\\nVegetated submerged bed (VSB) wetlands consist of\\ngravel beds that may be planted with wetland vegetation.\\nFigure 2-3 provides a schematic drawing of a VSB sys\u00c2\u00ac\\ntem. Atypical VSB system, like the FWS systems described\\nabove, contains berms and inlet and outlet structures for\\nregulation and distribution of wastewater flow. In addition\\nto shape and size, other variable factors are choice of treat\u00c2\u00ac\\nment media (gravel shape and size, for example) as an\\neconomic factor, and selection of vegetation as an optional\\nfeature that affects wetland aesthetics more than perfor\u00c2\u00ac\\nmance.\\nThe apparent simplicity and natural function of con\u00c2\u00ac\\nstructed wetlands may obscure the complexity of interac-\\n10", "height": "4283", "width": "3142", "jp2-path": "constructedwetla00nati_0028.jp2"}, "29": {"fulltext": "Figure 2-1. Constructed wetlands in wastewater treatment train\\nFloating and Submerged Floating and Emergent\\nInlet Settling Zone Emergent Plants Growth Plants Plants\\nZone 1\\nFully Vegetated\\nD O.\\nH 0.75 m\\nZone 2\\nOpen-Water Surface\\nD O. B\\nH 1.2 m\\nZone 3\\nFully Vegetated\\nD.O. B\\nH 0.75 m\\nFigure 2-2. Elements of a free water surface (FWS) constructed wetland\\nPretreated\\n(Settled)\\nInfluent\\nFigure 2-3. Elements of a vegetated submerged bed (VSB) system\\n11", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0029.jp2"}, "30": {"fulltext": "tions required for effective wastewater treatment. Unlike\\nnatural wetlands, constructed wetlands are designed and\\noperated to meet certain performance standards. Once a\\nconstructed wetland is designed and becomes operational,\\nthe system requires regular monitoring to ensure proper\\noperation. Based on monitoring results, these systems may\\nneed minor modifications, in addition to routine manage\u00c2\u00ac\\nment, to maintain optimum performance.\\nIn this chapter, a basic understanding of constructed\\nwetland ecology is presented for planners, policy makers,\\nlocal government officials, and others involved in the ap\u00c2\u00ac\\nplication of constructed wetlands for wastewater treatment.\\nBasic ecological components and functions of wetlands\\nare briefly described to bring readers to a common level of\\nunderstanding, but detailed descriptions are purposely\\nomitted for the sake of focus and relative correlation to\\ntreatment performance. To enhance one\u00e2\u0080\u0099s knowledge of\\nwetland ecology, many publications are commonly avail\u00c2\u00ac\\nable. For designers and operators, general knowledge of\\nwetland ecology is assumed, and detailed information on\\nconstructed wetlands is offered in succeeding chapters.\\nWhile municipal wastewater treatment systems utilizing\\nconstructed wetlands modeled on the functions of natural\\nwetlands systems are the focus of this manual, related\\nsystems utilizing components of natural wetland systems\\nalso are briefly described. In addition, constructed wetlands\\nfor on-site domestic wastewater systems and non-munici\u00c2\u00ac\\npal wastewater treatment are introduced.\\nBecause VSB wetlands are not dependent on wetland\\nvegetation for treatment performance and do not require\\nopen-water areas, portions of this chapter describe de\u00c2\u00ac\\nsign and management considerations that pertain only to\\nFWS wetlands. For reference purposes, important terms\\nare highlighted in bold type and are explained in a glos\u00c2\u00ac\\nsary at the end of the chapter.\\n2.2 Ecology of Constructed Wetlands\\nConstructed wetlands are ecological systems that com\u00c2\u00ac\\nbine physical, chemical, and biological processes in an\\nengineered and managed system. Successful construc\u00c2\u00ac\\ntion and operation of an ecological system for wastewater\\ntreatment requires a basic knowledge and understanding\\nof the components and the interrelationships that compose\\nthe system.\\nThe treatment systems of constructed wetlands are\\nbased on ecological systems found in natural wetlands. A\\nmain distinction between constructed wetlands and natu\u00c2\u00ac\\nral wetlands is the degree of control over natural processes.\\nFor example, a constructed wetland operates with a rela\u00c2\u00ac\\ntively stable flow of water through the system, in contrast\\nto the highly variable water balance of natural wetlands,\\nmostly due to the effects of variable precipitation. As a re\u00c2\u00ac\\nsult, wetland ecology in constructed wetlands is affected\\nby continuous flooding and concentrations of total sus\u00c2\u00ac\\npended solids (TSS), biochemical oxygen demand (BOD),\\nand other wastewater constituents at consistently higher\\nlevels than would otherwise occur in nature.\\nIn a constructed wetland, most of the inflow is a predict\u00c2\u00ac\\nable volume of wastewater discharged through sewers.\\nLesser volumes of precipitation and surface runoff are sub\u00c2\u00ac\\nject to seasonal and annual variations. Losses from these\\nsystems can be calculated by measuring outflow and esti\u00c2\u00ac\\nmating evapotranspiration as well as by accounting for\\nseepage in unlined systems. Even with predictable inflow\\nrates, however, modeling the water balance of constructed\\nwetlands must comprehend weekly and monthly variations\\nin precipitation and runoff and the effects of these vari\u00c2\u00ac\\nables on wetland hydraulics, especially detention time re\u00c2\u00ac\\nquired for treatment. See Chapter 3 for a more thorough\\ndiscussion of modeling concerns.\\nTemperature variations also affect the treatment perfor\u00c2\u00ac\\nmance of constructed wetlands, although not consistently\\nfor all wastewater constituents. Treatment performance for\\nsome constituents tends to decrease with colder tempera\u00c2\u00ac\\ntures, but BOD and TSS removal through flocculation, sedi\u00c2\u00ac\\nmentation, and other physical mechanisms is less affected.\\nIn colder months, the absence of plant cover would allow\\natmospheric reaeration and solar insolation to occur with\u00c2\u00ac\\nout the shading and surface covering that plant cover pro\u00c2\u00ac\\nvides during the growing season. Ice cover is another sea\u00c2\u00ac\\nsonal variable that affects constructed wetlands by alter\u00c2\u00ac\\ning wetland hydraulics and restricting solar insolation, at\u00c2\u00ac\\nmospheric reaeration, and biological activity; however, the\\ninsulating layer provided by ice cover would slow down\\nthe rate and degree of cooling in the water column but\\nwould not affect physical processes such as settling, filtra\u00c2\u00ac\\ntion, and flocculation. Plant senescence and decay also\\ndecreases under ice cover, with a corresponding decrease\\nin effluent BOD.\\n2.3 Botany of Constructed Wetlands\\nSuccessful performance of constructed wetlands de\u00c2\u00ac\\npends on ecological functions that are similar to those of\\nnatural wetlands, which are based largely on interactions\\nwithin plant communities. Research has confirmed that\\ntreatment of typical wastewater pollutants (TSS and BOD)\\nin FWS constructed wetlands generally is better in cells\\nwith plants than in adjoining cells without plants (Bavor et\\nal., 1989; Burgoon et al., 1989; Gearheart et al., 1989;\\nThut, 1989). However, the mechanisms by which plant\\npopulations enhance treatment performance have yet to\\nbe determined fully. Some authors have hypothesized a\\nrelationship between plant surface area and the density\\nand functional performance of attached microbial popula\u00c2\u00ac\\ntions (EPA, 1988; Reed et al., 1995), but demonstrations\\nof this relationship have yet to be proven.\\nPlant communities in constructed wetlands undergo sig\u00c2\u00ac\\nnificant changes following initial planting. Very few con\u00c2\u00ac\\nstructed wetlands maintain the species composition and\\ndensity distributions envisioned by their designers. Many\\nof these changes are foreseeable, and many have little\\napparent effect on treatment performance. Other changes,\\nhowever, may result in poor performance and the conse\u00c2\u00ac\\nquent need for increased management. The following sec\u00c2\u00ac\\ntions summarize basic principles of plant ecology that may\\naid in understanding of constructed wetlands.\\n12", "height": "4283", "width": "3142", "jp2-path": "constructedwetla00nati_0030.jp2"}, "31": {"fulltext": "2.3.1 Wetland Microbial Ecology\\nIn any wetland, the ecological food web requires micro\u00c2\u00ac\\nscopic bacteria, or microbes, to function in all of its com\u00c2\u00ac\\nplex transformations of energy. In a constructed wetland,\\nthe food web is fueled by influent wastewater, which pro\u00c2\u00ac\\nvides energy stored in organic molecules. Microbial activ\u00c2\u00ac\\nity is particularly important in the transformations of nitro\u00c2\u00ac\\ngen into varying biologically useful forms. In the various\\nphases of the nitrogen cycle, for example, different forms\\nof nitrogen are made available for plant metabolism, and\\noxygen may be either released or consumed. Phosphorus\\nuptake by plants also is dependent in part on microbial\\nactivity, which converts insoluble forms of phosphorus into\\nsoluble forms that are available to plants. Microbes also\\nprocess the organic (carbon) compounds, and release\\ncarbon dioxide in the aerobic areas of a constructed wet\u00c2\u00ac\\nland and a variety of gases (carbon dioxide, hydrogen sul\u00c2\u00ac\\nfide, and methane) in the anaerobic areas. Plants, plant\\nlitter, and sediments provide solid surfaces where micro\u00c2\u00ac\\nbial activity may be concentrated.\\nMicrobial activity varies seasonally in cold regions, with\\nlesser activity in colder months, although the performance\\ndifferential in warm versus cold climates is less in full-scale\\nconstructed wetlands than in small-scale, controlled ex\u00c2\u00ac\\nperiments (Wittgren and Maehlum, 1996), apparently be\u00c2\u00ac\\ncause of the multiplicity of physical, chemical, and biologi\u00c2\u00ac\\ncal transformations taking place simultaneously over a\\nlarger contiguous area.\\n2.3.2 Algae\\nAlgae are ubiquitous in wet habitats, and they inevitably\\nbecome components of FWS systems. While algae are a\\nmajor component in certain treatment systems (for ex\u00c2\u00ac\\nample, lagoons), algae can affect treatment performance\\nof FWS constructed wetlands significantly. As a result, the\\npresence of algae must be anticipated in the design stage.\\nAlgae in open areas, especially in areas of submergent\\nvegetation, can form a living canopy that blocks sunlight\\nfrom penetrating the water column to that vegetation, which\\nresults in reduced dissolved oxygen (DO) levels. The pres\u00c2\u00ac\\nence of open, unshaded water near the outlet of a con\u00c2\u00ac\\nstructed wetland typically promotes seasonal blooms of\\nphytoplanktonic algal species, which results in elevated\\nconcentrations of suspended solids and particulate nutri\u00c2\u00ac\\nent forms in the effluent.\\nSeveral floating aquatic plant species, especially duck\u00c2\u00ac\\nweed, have very high rates of primary production, which\\nresult in large quantities of biomass and trapped nonliving\\nelements accumulating within the fully vegetated portion\\nof the FWS wetland and pond systems (Table 2-1). Water\\nhyacinth can also perform well in pond systems in tropical\\nclimates to enhance TSS and algal removal. However, both\\nspecies block sunlight and lower DO levels by eliminating\\natmospheric re aeration at the water/air interface.\\nHigh growth rates of these plants have led to special\u00c2\u00ac\\nized wastewater treatment systems that use these plants\\nfor harvesting nutrients from wastewater. The disadvan\u00c2\u00ac\\ntages of harvesting these plants arise from their low\\nsolids (typically less than 5% on a wet-weight basis) and\\nthe consequent need for drying prior to disposal, which\\nsimultaneously creates secondary odor and water-quality\\nproblems. For disposal, harvested duckweed, which has a\\nhigh protein content, typically has been incorporated into\\nagricultural soils as green manure, and water hyacinths\\nhave been partially dried and landfilled or allowed to de\u00c2\u00ac\\ncompose in a controlled environment to produce methane\\nas a useful by-product. However, numerous attempts to\\ndemonstrate beneficial and cost-effective by-product re\u00c2\u00ac\\ncovery have been mostly unsuccessful under North Ameri\u00c2\u00ac\\ncan social and economic conditions.\\n2.3.3 Emergent Herbaceous Plants\\nEmergent herbaceous wetland plants are very impor\u00c2\u00ac\\ntant structural components of wetlands. Their various ad\u00c2\u00ac\\naptations allow competitive growth in saturated or flooded\\nsoils. These adaptations include one or more of the fol\u00c2\u00ac\\nlowing traits: lenticels (small openings through leaves and\\nstems) that allow air to flow into the plants; aerenchymous\\ntissues that allow gaseous convection throughout the length\\nof the plant, which provides air to plant roots; special mor\u00c2\u00ac\\nphological growth structures, such as buttresses, knees,\\nor pneumatophores, that provide additional root aeration;\\nadventitious roots for absorption of gases and plant nutri\u00c2\u00ac\\nents directly from the water column; and extra physiologi\u00c2\u00ac\\ncal tolerance to chemical by-products resulting from growth\\nin anaerobic soil conditions.\\nThe primary role of emergent vegetation in FWS sys\u00c2\u00ac\\ntems is providing structure for enhancing flocculation, sedi\u00c2\u00ac\\nmentation, and filtration of suspended solids through ide\u00c2\u00ac\\nalized hydrodynamic conditions. Emergent wetland plant\\nspecies also play a role in winter performance of FWS\\nconstructed wetlands by insulating the water surface from\\ncold temperatures, trapping falling and drifting snow, and\\nreducing the heat-loss effects of wind (Wittgren and\\nMaehlum, 1996).\\nLimited information is available to demonstrate signifi\u00c2\u00ac\\ncant or consistent effects of plant species selection on\\nconstructed wetland performance. For example, in two simi\u00c2\u00ac\\nlar FWS treatment cells at the Iron Bridge Wetland in\\nFlorida, the major difference between the cells was the\\ndominant plant species. Bulrush appeared to perform\\nnearly the same as cattail in treatment of BOD, TSS, total\\nnitrogen (TN), and total phosphorus (TP). As research and\\napplication of constructed wetlands have expanded, docu\u00c2\u00ac\\nmentation of actual performance differences between\\nemergent marsh plant species in constructed wetlands has\\nbecome increasingly less valuable to constructed wetland\\ndesigners.\\nThe wetland designer is strongly encouraged to seek\\ninformation from experienced local wetland practitioners\\nwhen selecting emergent herbaceous species to ensure\\nselection of locally successful species. Table 2-2 provides\\nguidelines for initial selection and establishment of plant\\nspecies adapted to wetland environments.\\n13", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0031.jp2"}, "32": {"fulltext": "Table 2.1 Characteristics of plants for constructed wetlands\\nGeneral Types\\nof Plants\\nGeneral Characteristics\\nand Common Examples\\nFunction or Importance\\nto Treatment Process\\nFunction or Importance\\nfor Habitat\\nDesign Operational\\nConsiderations\\nFree-Floating\\nAquatic\\nRoots or root-like structures\\nsuspended from floating\\nleaves. Will move about with\\nwater currents. Will not stand\\nerect out of the water.\\nCommon duckweed (Lemna),\\nBig duckweed (Spirodela).\\nPrimary purposes are nutrient\\nuptake and shading to retard\\nalgal growth. Dense floating mats\\nlimit oxygen diffusion from the\\natmosphere. Duckweed will be\\npresent as an invasive species.\\nDense floating mats limit\\noxygen diffusion from the\\natmosphere and block\\nsunlight from submerged\\nplants. Plants provide shelter\\nand food for animals.\\nDuckwood is a natural\\ninvasive species in\\nNorth America. No\\nspecific design is\\nrequired.\\nRooted Floating\\nAquatic\\nUsually with floating leaves,\\nbut may have submerged\\nleaves. Rooted to bottom.\\nWill not stand erect out of the\\nwater. Water lily (Nymphea),\\nPennywort (Hydrocotyle).\\nPrimary purposes are providing\\nstructure for microbial attachment\\nand releasing oxygen to the water\\ncolumn during daylight hours.\\nDense floating mats limit oxygen\\ndiffusion from the atmosphere.\\nDense floating mats limit\\noxygen diffusion from the\\natmosphere and block\\nsunlight from submerged\\nplants. Plants provide\\nshelter and food for animals.\\nWater depth must be\\ndesigned to promote\\nthe type of plant (i.e.\\nfloating, submerged,\\nemergent) desired\\nwhile hindering other\\ntypes of plants.\\nSubmerged\\nAquatic\\nUsually totally submerged;\\nmay have floating leaves.\\nRooted to bottom. Will not\\nstand erect in air. Pondweed\\n(Potamogeton), Water weed\\n(Elodea).\\nPrimary purposes are provioing\\nstructure for microbial attachment,\\nand providing oxygen to the water\\ncolumn during daylight hours.\\nPlants provide shelter and\\nfood for animals (especially\\nfish).\\nRetention time in open\\nwater zone should be\\nless than necessary\\nto promote algal\\ngrowth which can\\ndestroy these plants\\nthrough sunlight\\nblockage.\\nEmergent\\nAquatic\\nHerbaceous (i.e. non-woody).\\nRooted to the bottom. Stand\\nerect out of the water. Tolerate\\nflooded or saturated conditions.\\nCattail (Typha), Bulrush\\n(Scirpus), Common Reed\\n(Phragmites).\\nPrimary purpose is providing\\nstructure to induce enhanced\\nflocculation and sedimentation.\\nSecondary purposes are shading\\nto retard algal growth, windbreak\\nto promote quiescent conditions for\\nsettling, and insulation during winter\\nmonths.\\nPlants provide shelter and\\nfood for animals. Plants\\nprovide aesthetic beauty for\\nhumans.\\nWater depths must be\\nin the range that is\\noptimum for the\\nspecific species\\nchosen (planted).\\nShrubs\\nWoody, less than 6 m tall.\\nTolerate flooded or saturated\\nsoil conditions. Dogwood\\n(Cornus), Holly (Ilex).\\nTreatment function is not defined:\\nit is not known if treatment data\\nfrom unsaturated or occasionally\\nsaturated phytoremediation sites\\nin upland areas is applicable to\\ncontinuously saturated wetland\\nsites.\\nPlants provide shelter and\\nfood for animals (especially\\nbirds). Plants provide aesthetic\\nbeauty for humans.\\nPossible perforation of\\nliners by roots.\\nTrees\\nWoody, greater than 6 m tall.\\n(same as for shrubs)\\n(same as for shrubs)\\n(same as for shrubs)\\nTolerate flooded or saturated\\nsoil conditions. Maple (Acer).\\nWillow (Salix).\\n2.3.4 Plant Nutrition and Growth Cycles\\nWetland plants require optimum environmental condi\u00c2\u00ac\\ntions in each phase of their life cycles, including germina\u00c2\u00ac\\ntion and initial plant growth, adequate nutrition, normal\\nseasonal growth patterns, and rates of plant senescence\\nand decay. For more detailed information on wetland plant\\necology, the nonbiologist is referred to the wetland ecol\u00c2\u00ac\\nogy text by Mitsch and Gosselink (1993) and portions of\\nthe constructed wetland text by Kadlec and Knight (1996).\\nA wide variety of references describe growth cycles, tim\u00c2\u00ac\\ning of seed release, overwintering ability, energy cycling,\\nand other characteristics and processes that provide wet\u00c2\u00ac\\nland plant species with a competitive advantage in their\\nnatural habitats; the reader is referred to other sources for\\ndetailed information. An overview of important character\u00c2\u00ac\\nistics follows.\\nEmergent herbaceous wetland species planted early in\\nthe growing season in temperate climates generally multi\u00c2\u00ac\\nply by vegetative reproduction to a maximum total stand\u00c2\u00ac\\ning biomass in late summer or early fall within a single\\ngrowing season. This biomass may represent multiple\\ngrowth and death periods for individual plants during the\\ncourse of the growing season, or it may represent a single\\nemergence of plant structures, depending on the species.\\nFor many species, seeds are produced along with maxi\u00c2\u00ac\\nmum standing crop and released with maturation in the\\nfall for early germination in the spring.\\n14", "height": "4283", "width": "3142", "jp2-path": "constructedwetla00nati_0032.jp2"}, "33": {"fulltext": "Table 2.2 Factors to Consider in Plant Selection (adapted from Thunhorst, 1993)\\nFactors\\nConsult local experts\\nNative species\\nInvasive or aggressive\\nspecies\\nTolerant of high\\nnutrient load\\nComments\\nThe number of professional wetland scientists, practitioners, and plant nurseries has increased dramatically in the\\npast 10 years. Help from an experienced, local person should be available from a variety of sources, including\\ngovernment agencies and private companies.\\nUsing plants that grow locally increases the likelihood of plant survival and acceptance by local officials.\\nPlants that have extremely rapid growth, lack natural competitors, or are allelopathic* can crowd out all other spe\u00c2\u00ac\\ncies and destroy species diversity. State or local agencies may ban the use of some species.\\nUnlike natural wetlands, constructed wetlands will receive a continuous inflow of wastewater with high nutrient\\nconcentrations. Plants that can not tolerate this condition will not survive.\\nTolerant of continuous Unlike natural wetlands, which may experience periodic or occasional dry periods, constructed wetlands will\\nflooding receive a continuous inflow of wastewater. Plants that require periodic or occasional drying as part of their\\nreproductive cycle will not survive.\\nGrowth characteristics Perennial plants are generally preferred over annual plants because plants will continue growing in the same area\\nand there is no concern about seeds being washed or carried away. For emergent species, persistent plants are\\ngenerally preferred over semi- or non-persistent plants because the standing plant material provides added\\nshelter and insulation during the winter season.f\\nAvailable form for planting Costs of obtaining and planting the plants will vary depending on the form of planting material, which may be\\navailable in a variety of forms depending on the plant species. Entire plant forms (e.g. bare root plants or plugs) will\\nusually cost more than partial plant material (e.g. seeds or rootstock), but the plant supplier may guarantee a\\nhigher survival rate.T\\nRate of growth\\nSlower growing plants will require a greater number of plants, planted closer together, at start-up to obtain the\\nsame density of plant coverage in the initial growing season.\\nWildlife benefits\\nIf the wetland is to be used for habitat, plants that provide food, shelter/cover and nesting/nursery for the desired\\nanimals should be chosen.\\nPlant diversity Mono-cultures of plants are more susceptible to decimation by insect or disease infestations; catastrophic\\ninfestations will temporarily affect treatment performance. Greater plant diversity will also tend to encourage a\\ngreater diversity of animals.\\nAllelopathic plants that have harmful effects on other plants by secreting toxic chemicals\\nt Perennial aboveground portion dies, but below-ground portion remains dormant and sprouts in the next growing season.\\nAnnual entire plant dies and reproduction is only by seed produced before the plant dies.\\nPersistent aboveground dead portions remain upright through the dormant season.\\nSemi-persistent aboveground dead portions may remain standing for some part of the dormant season before falling into clumps.\\nNon-persistent aboveground dead portions decay and wash away at the end of the growing season.\\nt Bare root plant seedling with soil washed from roots. Plug seedling with soil still on roots. Rootstock piece of underground stem (rhizome).\\nFor some species with high lignin content, particularly\\ncattail, bulrush, and common reed, much of the plant re\u00c2\u00ac\\nmains standing as dead biomass that slowly decays dur\u00c2\u00ac\\ning the winter season. In FWS systems, this standing dead\\nbiomass provides additional structure for enhanced floc\u00c2\u00ac\\nculation and sedimentation that is important in wetland\\ntreatment performance throughout the annual cycle. Dead\\nbiomass, both standing and fallen, also is important to root\\nviability under flooded, winter conditions because of the\\ninsulating layer it provides, in addition to its contribution to\\nthe internal load on the system.\\nLike all plants, wetland plants require many macro- and\\nmicronutrients in proper proportions for healthy growth.\\nWhile municipal wastewater can supply adequate quanti\u00c2\u00ac\\nties of these limiting nutrients, other types of wastewater,\\nincluding industrial wastewater, acid mine drainage, and\\nstormwater, may not.\\nNitrogen and phosphorus are key nutrients in the life\\ncycles of wetland plants. However, plant uptake of nitro\u00c2\u00ac\\ngen and phosphorus is not a significant mechanism for\\nremoval of these elements in most wetlands receiving par\u00c2\u00ac\\ntially treated municipal wastewater because nitrogen and\\nphosphorus are taken up and released in the cycle of plant\\ngrowth and death. Nonetheless, undecomposed litter from\\ndead biomass provides storage for phosphorus, metals,\\nand other relatively conservative elements (Kadlec and\\nKnight, 1996).\\nWhile uptake rates of nitrogen and phosphorus are po\u00c2\u00ac\\ntentially high, harvesting plant biomass to remove these\\nnutrients has been limited to floating aquatic plant com\u00c2\u00ac\\nmunities, in which the plants can be harvested with only\\nbrief altering of system performance. Although common\\nreed is harvested annually from certain European con\u00c2\u00ac\\nstructed wetlands as a by-product (and not for nutrient re\u00c2\u00ac\\nduction), full-scale constructed wetlands where plants are\\n15", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0033.jp2"}, "34": {"fulltext": "routinely harvested have not been documented in the\\nUnited States.\\n2.4 Fauna of Constructed Wetlands\\nThe role that animal species may play in constructed\\nwetlands is a consideration for management of FWS wet\u00c2\u00ac\\nlands. Animals typically compose less biomass than do\\nwetland plants, but animals are able to alter energy and\\nmass flows disproportionately to their biomass contribu\u00c2\u00ac\\ntion. During outbreaks of insect pests in constructed wet\u00c2\u00ac\\nlands, for example, entire marshes and floating aquatic\\nplant systems can be defoliated, which interrupts mineral\\ncycles and upsets water-quality treatment performance.\\nIn another example, the rooting action of bottom-feeding\\nfish (primarily carp) causes sediment resuspension, which\\naffects performance of constructed wetlands in removing\\nsuspended solids and associated pollutants. The presence\\nof large seasonal waterfowl populations has had similar\\nresults in constructed wetlands at Columbia, Missouri, and\\nelsewhere. In VSB wetlands, only avian species play a\\nsignificant role.\\nWhile wildlife species play generally positive, second\u00c2\u00ac\\nary roles in constructed wetlands, their presence also may\\ngenerate unintended consequences. Bird species common\\nto wetland environments, for example, typically attract\\nbirdwatchers, who may provide public support for munici\u00c2\u00ac\\npalities and industries employing this treatment technol\u00c2\u00ac\\nogy. The presence of the public at constructed wetlands\\nfor secondary treatment, however, necessitates manage\u00c2\u00ac\\nment efforts to ensure adequate protection from human\\nhealth and safety risks presented by exposure to primary\\neffluent (see also section 2.6). Conversely, regulatory con\u00c2\u00ac\\ncern for potentially vulnerable wildlife species has impeded\\nplans for constructed wetlands at certain sites and for cer\u00c2\u00ac\\ntain wastewaters with toxic constituents.\\nFree water surface wetlands closely resemble the ecol\u00c2\u00ac\\nogy of natural wetlands and aquatic habitats, and they in\u00c2\u00ac\\nevitably attract animal species that rely on wet environ\u00c2\u00ac\\nments during some or all of their life history. All animal\\ngroups are represented in constructed wetlands: protozo\u00c2\u00ac\\nans, insects, mollusks, fish, amphibians, reptiles, birds, and\\nmammals. Table 2-3 summarizes animal species that may\\nbe found in constructed wetlands.\\n2.5 Ecological Concerns for Constructed\\nWetland Designers\\nWetland ecology is integral to the success of constructed\\nwetlands because of their complexity and their accessibil\u00c2\u00ac\\nity to wildlife. While the ecology of VSB systems relates\\nmore to its subsurface than its surface environment, wet\u00c2\u00ac\\nland plants and other surface features that are character\u00c2\u00ac\\nistic of VSB wetlands also require consideration.\\nTable 2.3 Characteristics of Animals Found in Constructed Wetlands\\nMembers of Group Commonly Found in Function or Importance to Treatment\\nAnimal Group Treatment Wetlands Process Design Operational Considerations\\nInvertebrates,\\nincluding\\nprotozoa,\\ninsects, spiders,\\nand crustaceans\\nA wide variety will be present, but diversity\\nand populations will vary seasonally and\\nspatially.\\nUndoubtedly play a role in\\nchemical and biological cycling and\\ntransformations and in supporting food\\nweb for higher organisms, but exact\\nfunctions have not been defined\\nMosquito control must be considered;\\nmono-cultures of plants are more\\nsusceptible to decimation by insect\\ninfestations.\\nFish\\nSpecies adapted to living at or near the\\nsurface (mosquitofish, mudminnow);\\nspecies adapted to living in polluted\\nwaters (bowfin, catfish, killifish, carp).\\nConsumers of insects and decaying\\nmaterial (e.g. mosquitofish eat\\nmosquito larvae).\\nAnaerobic conditions will limit\\npopulations; nesting areas required;\\nbottom-feeders can uproot plants and\\nresuspend sediments.\\nAmphibians and\\nReptiles\\nFrogs, alligators, snakes, turtles\\nConsumers of lower organisms\\nTurtles have an uncanny ability to fall\\ninto water control structures and to\\nget caught in pipes, so turtle exclusion\\ndevices are needed; monitoring of\\ncontrol structures and levees for\\ndamage or obstruction is needed.\\nBirds\\nA wide variety (35-63 species are\\npresent, including forest and prairie\\nspecies as well as waterfowl, but\\ndiversity and populations vary\\nseasonally and spatially.\\nConsumers of lower organisms\\nHeavy use, especially by migratory\\nwaterfowl, can contribute to pollutant\\nload on a seasonal basis.\\nMammals\\nSmall rodents (shrews, mice, voles);\\nlarge rodents (rabbits, nutria, muskrats,\\nbeaver); large grazers (deer); large\\ncarnivores (opossums, raccoons, foxes).\\nConsumers of plants and lower\\norganisms\\nNutria and muskrat populations can\\nreach nuisance levels, removing\\nvegetation and destroying levees;\\nstructural controls and animal\\nremoval may be required.\\nMcAllister, 1992, 1993a, 1993b\\n16", "height": "4283", "width": "3142", "jp2-path": "constructedwetla00nati_0034.jp2"}, "35": {"fulltext": "Constructed wetlands invariably attract wildlife, a factor\\nthat must be considered in the design and management of\\nconstructed wetlands. As components of an ecological\\ncommunity, animals in general perform vital ecological func\u00c2\u00ac\\ntions in constructed wetlands. Specific roles of animals in\\nthe development and operation of constructed wetlands,\\nhowever, are not well researched. Experience has shown\\nthat many animals are beneficial elements in constructed\\nwetlands, but many other are nuisance species. Proper\\nattention to desirable and undesirable wildlife species, as\\nwell as primary and ancillary functions of constructed wet\u00c2\u00ac\\nlands, will aid the success of a constructed wetland.\\n2.5.1 Primary and Ancillary Functions of\\nConstructed Wetlands\\nPrimary functions of most constructed wetlands include\\nwater storage and water-quality improvement. Some of\\nthese constructed wetlands are designed intentionally for\\nground water recharge. Numerous other functions attrib\u00c2\u00ac\\nuted to natural wetlands are important in constructed wet\u00c2\u00ac\\nlands and are described in succeeding chapters.\\nAncillary functions include primary production of organic\\ncarbon by plants; oxygen production through photosyn\u00c2\u00ac\\nthesis; production of wetland herbivores, as well as preda\u00c2\u00ac\\ntor species that range beyond the wetland boundaries;\\nreduction of export of organic matter and nutrients to down\u00c2\u00ac\\nstream ecosystems; and creation of cultural values in terms\\nof educational and recreational resources. One or more of\\nthese ancillary functions may be an important goal in some\\nconstructed wetland projects. For detailed descriptions of\\nancillary functions, the reader is referred to information\\npresented elsewhere (Feierabend, 1989; Sather, 1989;\\nKnight, 1992).\\n2.5.2 Wildlife Access Controls\\nSuccessful wildlife management in FWS wetlands re\u00c2\u00ac\\nquires maintaining a balance between attracting benefi\u00c2\u00ac\\ncial species and controlling pest species (EPA, 1993a).\\nWhile most wildlife species in wetlands are attractive but\\noften unnoticed, many species are attractive for aesthetic\\nreasons but are impediments to the success of constructed\\nwetlands. Nuisance species in constructed wetlands in\u00c2\u00ac\\nclude burrowing rodents, especially beavers, nutria, and\\nmuskrats, which burrow through berms and levees and\\nconsume beneficial emergent vegetation; mosquitoes,\\nwhich cause annoyance and health concerns; and certain\\nbottom-feeding fish, such as carp, which uproot aquatic\\nvegetation and cause increases in effluent TSS and asso\u00c2\u00ac\\nciated pollutants by stirring up sediments and resuspend\u00c2\u00ac\\ning them in the water column. Waterfowl in large numbers\\nalso may be undesirable because they cause similar prob\u00c2\u00ac\\nlems, and their nutrient-rich droppings place additional\\ndemands on the water-quality performance of constructed\\nwetlands.\\nControl of wildlife access in constructed wetlands is highly\\nsite-specific; as a result, control measures must be based\\non geographic location, nuisance species, wetland design,\\nand preferred levels of management. Control methods are\\napplied throughout the planning, construction, and opera\u00c2\u00ac\\ntion of constructed wetland projects. Control of carp, for\\nexample, can be anticipated during design and managed\\nwith winter drawdown of water levels and subsequent in-\\ndepth freezing in northern climates. Also effective is draw\u00c2\u00ac\\ndown and physical removal of stranded individuals, but\\nthis method is more labor intensive and less effective in\\neradicating carp populations. Large rodents can be\\nscreened out of culverts to limit access and prevent dam\u00c2\u00ac\\nming; however, trapping and physical removal may be\\nneeded to prevent burrowing and subsequent undermin\u00c2\u00ac\\ning of banks and other damage. For waterfowl control, lim\u00c2\u00ac\\nited open-water areas will discourage many species, but\\ntreatment requirements will dictate the size and use of these\\nzones. Netting suspended over unavoidable open-water\\nareas can prevent their use for feeding, but this method\\ndeviates from the intent to incorporate natural methods of\\nwildlife control.\\nWetland wildlife species frequently have home ranges\\nwell outside the borders of an individual constructed wet\u00c2\u00ac\\nland cell; consequently, they can become a public resource\\nthat may need to be protected and promoted for reasons\\nunrelated to their perceived value to constructed wetlands.\\nAlthough the values of constructed wetlands for wildlife\\nhabitat may be subject to public and scientific debate, this\\ntopic nonetheless must be considered in all project phases\\nto determine optimum design and management features\\nto promote or discourage the presence of wildlife (Knight,\\n1997; Worrall et al., 1996).\\n2.5.3 Mosquito Habitat Controls\\nMosquitoes may be integral components of the ecologi\u00c2\u00ac\\ncal food web, but mosquitoes generally are considered a\\npest species. While a constructed wetland\u00e2\u0080\u0099s attractiveness\\nto wildlife may be regarded as a benefit to the human com\u00c2\u00ac\\nmunity, the potential for breeding mosquitoes can be an\\nobstacle to permitting, funding, and other steps essential\\nto the siting of a constructed wetland.\\nSeveral methods of mosquito control can be employed\\nin the planning, construction, and operation of constructed\\nwetlands. Predation is one means. Mosquito fish have been\\nfound to be effective in reducing mosquito populations when\\nhabitat conditions are optimized by manipulating water lev\u00c2\u00ac\\nels and when channels are kept free of dead vegetation.\\nDrawdown of water levels aids mosquito fish spawning in\\nspring and provides the fish with better access to mos\u00c2\u00ac\\nquito larvae during mosquito breeding season (Dill, 1989).\\nIn warm climates, mosquito fish habitat must be monitored\\nfor excessive water temperatures and fluctuations in efflu\u00c2\u00ac\\nent strength and content. Bats and several avian species\\nalso are effective predators, but planning and managing\\noptimum conditions have yet to be standardized.\\nIn the planning and construction stages, management\\nof mosquito habitat can be enabled with steep slopes on\\nwater channels that reduce standing water area in shallow\\nareas. In contrast to this design is the use of more natural,\\nundulating banks that have been popular in polishing wet-\\n17", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0035.jp2"}, "36": {"fulltext": "lands. This natural appearance is more visually appealing\\nbut is ineffective for mosquito-control purposes. A channel\\nprofile that has been effective in mosquito control is a steep\u00c2\u00ac\\nsided channel flanked by relatively flat aprons leading out\u00c2\u00ac\\nward to steep-sided banks (Dill, 1989). This profile allows\\nthe facility operator to draw down water levels to the lower\\nchannel during the mosquito-breeding season. Figure 2-4\\nillustrates this design. With standing water eliminated from\\nemergent vegetation in the shallow flanks of the channel,\\ndeeper water in the lower channel provides an environ\u00c2\u00ac\\nment more conducive to mosquito predation by fish spe\u00c2\u00ac\\ncies. Flexible drainage capability is essential to this means\\nof control.\\nWater spray systems also have been used for mosquito\\ncontrol, but such mechanical systems are inconsistent with\\nthe passive nature of constructed wetlands, which utilize\\nnatural systems to accomplish wastewater treatment and\\nmanage ancillary concerns.\\nVegetation management is another approach to mos\u00c2\u00ac\\nquito control, especially in the absence of water-level con\u00c2\u00ac\\ntrol features (Dill, 1989). Taller vegetation especially needs\\nmanagement. Cattails and bulrushes, for example, tend to\\nfall over late in the growing season, which creates condi\u00c2\u00ac\\ntions favorable for mosquito reproduction in the following\\ngrowing season, as well as unfavorable conditions for pre\u00c2\u00ac\\ndation by mosquito fish (Martin and Eldridge, 1989). Chan\u00c2\u00ac\\nnels planted with lower-growing vegetation and cleared\\nannually of dead standing stock can reduce mosquito popu\u00c2\u00ac\\nlations and optimize predation, providing that this vegeta\u00c2\u00ac\\ntion imparts the same structural role beneath the water\\nsurface.\\nLarvicide is a proven means of active mosquito control\\nwhen employed in conjunction with other management\\ntechniques. A bacterium (Bacillus sphaericus) has been\\nfound effective in reducing culex mosquitoes, one of the\\nmost common species in the United States. Tests have\\nindicated that a commercial larvicide containing the bacte\u00c2\u00ac\\nria may be capable of eliminating most of the populations\\nof culex in treatment lagoons (WaterWorld, 1996). The\\nconcentrated bacteria in powdered form is applied to stand\u00c2\u00ac\\ning water as a coating on granulated corncobs, which\\nquickly releases protein crystals and bacteria spores to\\nthe water surface. Upon ingestion, the bacteria enter mos\u00c2\u00ac\\nquito larvae tissues through pores in the gut wall and mul\u00c2\u00ac\\ntiply rapidly, and the infected larvae typically die within two\\ndays. However, fully vegetated zones are more difficult to\\ntreat than open water zones or lagoons.\\n2.6 Human Health Concerns\\nMany studies of constructed wetlands\u00e2\u0080\u0099 biological effec\u00c2\u00ac\\ntiveness and attractiveness to humans for aesthetic and\\ncultural reasons have focused on polishing wetlands that\\nreceive secondary effluent, which are outside the focus of\\nthis manual. At many of these successful polishing wet\u00c2\u00ac\\nlands for tertiary treatment, interpretive centers and signage\\ninvite visitors, and boardwalks and naturalists guide them\\nthrough the outdoor experience. Constructed wetlands that\\nreceive primary effluent for secondary treatment, on the\\nother hand, may not be visitor-friendly places, and human\\nvisitors may best enjoy them from the periphery for sev\u00c2\u00ac\\neral reasons.\\nPartially treated wastewater in a constructed wetland for\\nsecondary treatment, despite the proven effectiveness of\\nthis ecological approach to treatment, presents essentially\\nthe same risks to human health as wastewater in primary\\ntreatment and lagoons. Risk of dermal contact and pos\u00c2\u00ac\\nsible transmission of disease is equally unappealing in FWS\\nwetlands for secondary treatment as it is in open lagoons.\\nThis concern is distinguished from human interaction with\\nFigure 2-4. Profile of a three-zone FWS constructed wetland cell\\n18", "height": "4283", "width": "3142", "jp2-path": "constructedwetla00nati_0036.jp2"}, "37": {"fulltext": "polishing systems, where influent wastewater has already\\nmet effluent quality requirements which are set by regula\u00c2\u00ac\\ntory authorities.\\nIn constructed wetlands receiving primary effluent, hu\u00c2\u00ac\\nman exposure to wastewater is a greater concern at the\\ninlet end of the system, where influent has achieved pri\u00c2\u00ac\\nmary treatment only. Lesser concern for human exposure\\nis warranted at the outlet end, where wastewater has been\\ntreated to the quality of secondary treatment or better, which\\nis the quality of wastewater entering the polishing wetlands\\nthat have been popular for environmental awareness and\\neducation activities.\\nAs a result, humans must be considered an unwanted\\nspecies in most areas of FWS wetlands treating municipal\\nwastewater to meet secondary treatment (defined as 30\\nmg/L of BOD and TSS). Nonetheless, constructed wet\u00c2\u00ac\\nlands can serve as recreational areas and outdoor labora\u00c2\u00ac\\ntories, especially at the outlet end where wastewater has\\nbeen treated to secondary effluent standards. Management\\nconsiderations may include the public\u00e2\u0080\u0099s access, percep\u00c2\u00ac\\ntions, and exposure to health threats (Knight, 1997). To\\neffectively address these concerns, fencing, signage, and\\nother controls must be considered in the proposal stage\\nas well as in design and operation of the system.\\nMosquito populations may represent merely an annoy\u00c2\u00ac\\nance factor to be managed, as described above, but some\\nspecies of mosquitoes also carry a health risk that must\\nbe addressed. In warmer climates, including the southern\\nUnited States, the encephalitis mosquito (Culex tarsalis)\\nthrives in the extended breeding season provided by con\u00c2\u00ac\\nstructed wetlands, but water-level manipulation and mos\u00c2\u00ac\\nquito fish predation in the two-tiered pond design described\\npreviously have been effective in controlling these mos\u00c2\u00ac\\nquito populations (Dill, 1989). The two-tiered design allows\\nwater levels to be drawn down to concentrate prey spe\u00c2\u00ac\\ncies (mosquitoes) in smaller areas for more efficient con\u00c2\u00ac\\nsumption by predators (mosquito fish).\\nMost of the health concerns described above do not apply\\nto VSB systems, in which wastewater typically is not ex\u00c2\u00ac\\nposed at the land surface.\\n2.7 On-site System Applications\\nOn-site constructed wetland systems may also be ap\u00c2\u00ac\\nplied to wastewater treatment and disposal at individual\\nproperties. On-site constructed wetlands generally utilize\\nthe same technologies as the municipal VSB systems de\u00c2\u00ac\\nscribed in this manual, and they share with municipal sys\u00c2\u00ac\\ntems the advantages of cost-effectiveness and low-main\u00c2\u00ac\\ntenance requirements. However, on-site constructed wet\u00c2\u00ac\\nlands are distinguished typically by final effluent discharge\\nto soils instead of surface water. For purposes of this dis\u00c2\u00ac\\ncussion, on-site constructed wetland systems treat septic\\ntank effluent, or primary effluent, in small-scale VSB sys\u00c2\u00ac\\ntems for subsurface disposal to soils.\\nOn-site constructed wetlands also differ from municipal\\nsystems in scale. On-site constructed wetlands typically\\noccupy only a few hundred square feet. Municipal VSB\\nsystems may serve hundreds of residential, commercial,\\nand industrial properties, while on-site systems would serve\\na single home or several residences in a cluster.\\nAn on-site VSB system typically consists of a lined VSB\\nthat receives primary effluent from a septic tank, and in\\nsome designs, a second VSB that receives effluent from\\nthe upstream VSB system. The second VSB can be un\u00c2\u00ac\\nlined to allow treated wastewater to infiltrate to soil for dis\u00c2\u00ac\\nposal. Variations of this treatment train include use of\\nsupplemental absorption trenches to facilitate soil absorp\u00c2\u00ac\\ntion and direct surface discharge with or without subse\u00c2\u00ac\\nquent disinfection. Each VSB typically is planted with wet\u00c2\u00ac\\nland vegetation.\\nApplied studies and research experiments of on-site\\nconstructed wetland systems have shown adequate treat\u00c2\u00ac\\nment performance for most wastewater constituents, in\u00c2\u00ac\\ncluding BOD, TSS, and fecal coliforms, with variations in\\nperformance for removal of ammonia nitrogen (Burgan and\\nSievers, 1994; Huang et al., 1994; Johns et al., 1998;\\nMankin and Powell, 1998; Neralla et al., 1998; White and\\nShirk, 1998).\\n2.8 Related Aquatic Treatment Systems\\nSeveral types of aquatic treatment systems have been\\nconstructed to treat municipal and other wastewaters, and\\nmost of these systems fall outside the definition of con\u00c2\u00ac\\nstructed wetlands discussed in this manual. These other\\ntypes of systems are briefly described to provide the reader\\nwith additional background and references to source ma\u00c2\u00ac\\nterial.\\nPolishing wetlands have been used also to remove trace\\nmetals, including cadmium, chromium, iron, lead, manga\u00c2\u00ac\\nnese, selenium, and zinc in a variety of situations. The\\nprimary removal mechanism for metals in wastewater ap\u00c2\u00ac\\npears to be sedimentation. Plant uptake results in deposi\u00c2\u00ac\\ntion of metals to soil via plant roots and requires harvest of\\nplants to partially remove metals from the system. In some\\ncases, however, effluent concentrations of metals have\\nexceeded influent levels, apparently due to evaporation of\\nwastewater.\\nOne proprietary treatment system, which among its many\\nmanifestations has used both FWS-like and VSB-like treat\u00c2\u00ac\\nment units as part of its treatment train, is known as the\\nAdvanced Ecologically Engineered System (AEES), or\\n\u00e2\u0080\u009cLiving Machine.\u00e2\u0080\u009d This system incorporates conventional\\ntreatment system components, including sedimentation/\\nanaerobic bioreactors, extended aeration, clarifiers, fixed-\\nfilm reactors, and a final clarifier, sometimes with a VSB\\nfor polishing, in a greenhouse setting. The AEES was ap\u00c2\u00ac\\nplied to four demonstration projects funded with federal\\ngrants. The four projects underwent evaluation of treat\u00c2\u00ac\\nment performance for various wastewater types and set\u00c2\u00ac\\ntings (e.g., raw wastewater in a moderate climate, raw\\nwastewater at higher flow rates in a colder climate, in situ\\nwater-quality improvements to pond water, and polishing\\n19", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0037.jp2"}, "38": {"fulltext": "of secondary effluent). One of the demonstration projects\\nalso was evaluated by an independent firm under contract\\nto the U.S. EPA (EPA, 1997b). Results of performance\\nevaluations indicated that wastewater treatment met per\u00c2\u00ac\\nformance goals for certain wastewater constituents; other\\ngoals were unmet. Although this technology is presented\\nby its developers as a type of natural system, the use of\\nwetland plants appears to influence aesthetics more than\\ntreatment performance. The reader is directed to other\\nsources for further information (EPA, 1993b; EPA, 1997b;\\nLiving Technologies, 1996; Reed et al., 1995; Todd and\\nJosephson, 1994).\\nFloating macrophyte systems rely only partially on treat\u00c2\u00ac\\nment processes provided by wetlands and require mecha\u00c2\u00ac\\nnized components to achieve the intended treatment per\u00c2\u00ac\\nformance. Larger duckweed systems and water hyacinth\\nsystems utilize mechanical systems to remove floating\\nmacrophytes. Both have been employed to treat waste-\\nwater by removing some of the wastewater constituents,\\nprimarily BOD and TSS. In both systems, removal of plants\\nusually requires additional mechanical systems for drying,\\ndisposal, and other residuals handling (Zirschky and Reed,\\n1988).\\n2.9 Frequently Asked Questions\\n1. What are constructed wetlands?\\nThe term \u00e2\u0080\u009cconstructed wetlands\u00e2\u0080\u009d refers to a technol\u00c2\u00ac\\nogy designed to employ ecological processes found\\nin natural wetland ecosystems. These systems uti\u00c2\u00ac\\nlize wetland plants, soils, and associated microorgan\u00c2\u00ac\\nisms to remove contaminants from wastewater. As\\nwith other natural biological treatment technologies,\\nwetland treatment systems are capable of providing\\nadditional benefits. They are generally reliable sys\u00c2\u00ac\\ntems with no anthropogenic energy sources or chemi\u00c2\u00ac\\ncal requirements, a minimum of operational require\u00c2\u00ac\\nments, and large land requirements. The treatment\\nof wastewater using constructed wetland technology\\nalso provides an opportunity to create or restore wet\u00c2\u00ac\\nlands for environmental enhancement, such as wild\u00c2\u00ac\\nlife habitat, greenbelts, passive recreation associated\\nwith ponds, and other environmental amenities.\\n2. What are wetland treatment systems?\\nThe term \u00e2\u0080\u009cwetland treatment system\u00e2\u0080\u009d generally re\u00c2\u00ac\\nfers to two types of passive treatment systems. One\\ntype of system is a free water surface (FWS) con\u00c2\u00ac\\nstructed wetland, which is a shallow wetland with a\\ncombination of emergent aquatic plants (cattail, bul\u00c2\u00ac\\nrush, reeds, and others), floating plants (duckweed,\\nwater hyacinth, and others), and submergent aquatic\\nplants (sago pondweed, widgeon grass, and others).\\nA FWS wetland may have open-water areas domi\u00c2\u00ac\\nnated by submergent and floating plants, or it may\\ncontain islands for habitat purposes. It may be lined\\nor unlined, depending on regulatory and/or perfor\u00c2\u00ac\\nmance requirements. These systems exhibit com\u00c2\u00ac\\nplex aquatic ecology, including habitat for aquatic\\nand wetland birds.\\nA second type of system is termed \u00e2\u0080\u009cvegetated sub\u00c2\u00ac\\nmerged bed (VSB)\u00e2\u0080\u009d and is known to many as a sub\u00c2\u00ac\\nsurface flow wetland. A VSB is not an actual wet\u00c2\u00ac\\nland because it does not have hydric soils. Emer\u00c2\u00ac\\ngent wetland plants are rooted in gravel, but waste-\\nwater flows through the gravel and not over the\\nsurface. This system is also shallow and contains\\nsufficiently large gravel to permit long-term subsur\u00c2\u00ac\\nface flow without clogging. Roots and tubers (rhi\u00c2\u00ac\\nzomes) of the plants grow into pore spaces in the\\ngravel. Most current data indicate that these sys\u00c2\u00ac\\ntems perform as well without plants as with plants;\\nas a result, wetland ecology is not a critical factor\\nin VSB systems.\\n3. Are constructed wetlands reliable? What do they\\ntreat?\\nConstructed wetlands are an effective and reliable\\nwater reclamation technology if they are properly\\ndesigned, constructed, operated, and maintained.\\nThey can remove most pollutants associated with\\nmunicipal and industrial wastewater and stormwater\\nand are usually designed to remove contaminants\\nsuch as biochemical oxygen demand (BOD) and\\nsuspended solids. Constructed wetlands also have\\nbeen used to remove metals, including cadmium,\\nchromium, iron, lead, manganese, selenium, zinc,\\nand toxic organics from wastewater.\\n4. How does a constructed wetland treat wastewa\u00c2\u00ac\\nter?\\nA natural wetland acts as a watershed filter, a sink\\nfor sediments and precipitates, and a biogeochemi\u00c2\u00ac\\ncal engine that recycles and transforms some of\\nthe nutrients. A constructed wetland performs the\\nsame functions for wastewater, and a constructed\\nwetland can perform many of the functions of con\u00c2\u00ac\\nventional wastewater treatment trains (sedimenta\u00c2\u00ac\\ntion, filtration, digestion, oxidation, reduction, ad\u00c2\u00ac\\nsorption, and precipitation). These processes oc\u00c2\u00ac\\ncur sequentially as wastewater moves through the\\nwetland, with wastewater constituents becoming\\ncomingled with detritus of marsh plants.\\n5. What is the difference between treatment and en\u00c2\u00ac\\nhancement wetlands?\\nConstructed wetlands generally are designed to\\ntreat municipal or industrial effluents as well as\\nstormwater runoff. Enhancement marshes, or pol\u00c2\u00ac\\nishing wetlands, are designed to benefit the com\u00c2\u00ac\\nmunity with multiple uses, such as water reclama\u00c2\u00ac\\ntion, wildlife habitat, water storage, mitigation banks,\\nand opportunities for passive recreation and envi\u00c2\u00ac\\nronmental education. Both types of wetland sys\u00c2\u00ac\\ntems can be designed as separate systems, or\\n20", "height": "4283", "width": "3142", "jp2-path": "constructedwetla00nati_0038.jp2"}, "39": {"fulltext": "important attributes of each can be integrated into\\na single design with multiple treatment and en\u00c2\u00ac\\nhancement objectives.\\n6. Can a constructed wetland be used to meet a sec\u00c2\u00ac\\nondary effluent standard?\\nBoth FWS and VSB constructed wetlands can be\\nused to meet a 30/30 mg/L BOD and TSS discharge\\nstandard. It is not advisable to put raw wastewater\\ninto a constructed wetland.\\n7. Can a constructed wetland be used to meet an\\nadvanced secondary/tertiary discharge standard?\\nWith sufficient pretreatment and wetland area, FWS\\nconstructed wetlands can meet discharge standards\\nof less than 10 mg/L BOD, TSS, and TN on a\\nmonthly average basis. Many examples of FWS\\nwetland systems meeting these standards on a\\nmonthly average basis can be found in the United\\nStates (EPA, 1999). VSB systems have been used\\nextensively in England for polishing secondary ef\u00c2\u00ac\\nfluents and treating effluent from combined sani\u00c2\u00ac\\ntary and storm sewers. In the U.S., they have gen\u00c2\u00ac\\nerally not performed well in consistently reaching\\nadvanced treatment goals with primary treatment\\ninfluent.\\n8. How much area is required for constructed wet\u00c2\u00ac\\nlands?\\nAs a general rule, a constructed wetland receiving\\nwastewater with greater degrees of pretreatment\\n(for example, primary clarification, oxidation pond,\\ntrickling filter, etc.) requires less area than a con\u00c2\u00ac\\nstructed wetland receiving higher-strength waste-\\nwater. Historically, constructed wetlands designers\\nhave employed from 2 to over 200 acres/MGD (4\\nto 530 L/m 2 -d). However, there is no generic an\u00c2\u00ac\\nswer to the question since it depends on the efflu\u00c2\u00ac\\nent criteria to be met and buffer areas required.\\n9. Do these systems have to be lined?\\nThe requirement for liners in constructed wetlands\\ndepends on each state\u00e2\u0080\u0099s regulatory requirements\\nand/or the characteristics of surface and subsur\u00c2\u00ac\\nface soils. In a general sense, if soils are porous\\n(e.g., sands), well-drained, and contain small\\namounts of loams, clays, and silts, lining is likely to\\nbe a requirement for constructed wetlands. On the\\nother hand, if soils are poorly drained and composed\\nmostly of clays, then lining might not be required.\\nThese systems would tend to produce a layer of\\npeat on the bottom that would reduce infiltration with\\ntime. The concept of a \u00e2\u0080\u009cleaky wetland,\u00e2\u0080\u009d which may\\ntake advantage of natural processes to purify waste-\\nwater as it moves downward through soil to re\u00c2\u00ac\\ncharge the ground water, may be considered a po\u00c2\u00ac\\ntential benefit in certain areas.\\n10. What is the role of the plants in constructed wet\u00c2\u00ac\\nlands?\\nIn FWS constructed wetlands, plants play several\\nessential roles. The most important function of\\nemergent and floating aquatic plants is providing a\\ncanopy over the water column, which limits produc\u00c2\u00ac\\ntion of phytoplankton and increases the potential\\nfor accumulation of free-floating aquatic plants (e.g.,\\nduckweed) that restrict atmospheric reaeration.\\nThese conditions also enhance reduction of sus\u00c2\u00ac\\npended solids within the FWS constructed wetland.\\nEmergent plants play a minor role in taking up ni\u00c2\u00ac\\ntrogen and phosphorus. The effect of litter fall from\\nprevious growing seasons as it moves through the\\nwater column and eventually decomposes into hu\u00c2\u00ac\\nmic soil and lignin particles may be significant in\\nterms of effluent quality.\\nThe role of plants in VSB systems is not clear. Ini\u00c2\u00ac\\ntially it was believed that translocation of oxygen\\nby plants was a major source of oxygen to microbes\\ngrowing in the VSB media, and therefore plants\\nwere critical components in the process. However,\\nside-by-side comparisons of planted and unplanted\\nsystems have not confirmed this belief. Neverthe\u00c2\u00ac\\nless, planted VSB systems are more desirable aes\u00c2\u00ac\\nthetically than unplanted horizontal rock-filter sys\u00c2\u00ac\\ntems, and plants do not appear to hinder perfor\u00c2\u00ac\\nmance of VSB systems.\\n11. How much time is needed for a constructed wet\u00c2\u00ac\\nland to become fully operational and meet discharge\\nrequirements?\\nFor FWS wetland systems, several growing sea\u00c2\u00ac\\nsons may be needed to obtain the optimum veg\u00c2\u00ac\\netative density necessary for treatment processes.\\nThe length of this period is somewhat dependent\\non the original planting density and the season of\\nthe initial planting. Effluent quality has been ob\u00c2\u00ac\\nserved to improve with time, suggesting that veg\u00c2\u00ac\\netation density and accumulated plant litter play an\\nimportant role in treatment effectiveness.\\nVSB systems also require more than one growing\\nseason to achieve normal wetland plant densities.\\nHowever, the time required for VSB systems to\\nbecome fully operational is considerably less than\\nFWS systems because of the minor role of plants\\nin the treatment process. Development of the mi\u00c2\u00ac\\ncrobial biomass in the media of a VSB system typi\u00c2\u00ac\\ncally requires from three to six months.\\n12. How long can a FWS wetland operate before ac\u00c2\u00ac\\ncumulated plant material and settled solids need to\\nbe removed?\\nFWS wetland systems receiving oxidation pond\\neffluent may operate for 10 to 15 years without the\\nneed to remove accumulated litter and settled\\n21", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0039.jp2"}, "40": {"fulltext": "nondegradable influent solids. Treatment capaci\u00c2\u00ac\\nties of these wetlands have not shown a decrease\\nin treatment effectiveness with time. However, it is\\nassumed that further experience will reveal that\\nthere is a finite period of accumulation that will re\u00c2\u00ac\\nsult in the need to remove solids. In both types of\\nsystems, the bulk of the solids accumulation oc\u00c2\u00ac\\ncurs at the influent end of the system. As a result,\\nsolids may need to be removed from only a portion\\nof the system that may be as small as 10 to 25% of\\nthe surface area.\\n13. How much effort is required to operate and main\u00c2\u00ac\\ntain a constructed wetland?\\nThese systems require a minimum of operational\\ncontrol. Monthly or weekly inspection of weirs and\\nweekly sampling typically are required at the efflu\u00c2\u00ac\\nent end, and periodic sampling between multiple\\ncells is recommended.\\nMaintenance of constructed wetlands generally is\\nlimited to the control of unwanted aquatic plants\\nand control of disease vectors, especially mosqui\u00c2\u00ac\\ntoes. Harvesting of plants generally is not required,\\nbut annual removal or thinning of vegetation or re\u00c2\u00ac\\nplanting of vegetation may be needed to maintain\\nflow patterns and treatment functions.\\nEffective vector control can be achieved by appro\u00c2\u00ac\\npriately applying integrated pest management prac\u00c2\u00ac\\ntices, such as introducing mosquito fish or provid\u00c2\u00ac\\ning habitat for mosquito-eating birds and bats. Bi\u00c2\u00ac\\nmonthly monitoring of mosquito larvae and pupae\\nand applications of larvacides may be required on\\nan as-needed basis.\\nSediment accumulation typically is not a problem\\nin a well-designed and properly operated con\u00c2\u00ac\\nstructed wetland, thus partial dredging is required\\nonly rarely.\\nThese tasks would require approximately one day\\nper week of labor for a wetland system treating a\\nflow of one million gallons per day (MGD) (3,880\\nm 3 /d) or less, and monitoring may be the most de\u00c2\u00ac\\nmanding task.\\n14. Do constructed wetlands produce odors?\\nConventional wastewater treatment processes pro\u00c2\u00ac\\nduce odors mostly associated with anaerobic de\u00c2\u00ac\\ncomposition of human waste and food waste found\\nin sewage. These odors usually are concentrated\\nin areas of small confinement and point discharges,\\nlike influent pump stations, anaerobic digesters, and\\nsludge-handling processes. Wetlands, in contrast,\\nincorporate normal processes of decomposition\\nover a relatively large area, potentially diluting odors\\nassociated with the natural decomposition of plant\\nmaterial, algae, and other biological solids. How\u00c2\u00ac\\never, wetland treatment systems receiving septic\\ntank and primary effluents can release anaerobic\\nodors around the inlet piping, and both types are\\ngenerally anaerobic, which makes odor generation\\na major operational concern.\\n15. Are mosquitoes a potential problem with con\u00c2\u00ac\\nstructed wetlands? If so, how are they managed?\\nMosquitoes generally are not a problem in properly\\ndesigned and operated VSB systems. However,\\nmosquitoes can be a problem in FWS constructed\\nwetlands. If a FWS wetland is designed with suffi\u00c2\u00ac\\ncient open water (40 to 60% of the surface area) to\\npermit effective control with mosquito fish, and in\u00c2\u00ac\\nlet and outlet weirs are placed to allow level control\\nand drainage of wetland cells, the potential for\\nmosquito populations to thrive is reduced. This lat\u00c2\u00ac\\nter concept provides for isolation of various wet\u00c2\u00ac\\nland cells to allow them to be drained and/or to al\u00c2\u00ac\\nlow predators and mosquitoes to become concen\u00c2\u00ac\\ntrated in pools and channels.\\nAlong with these physical factors, the development\\nof a balanced ecosystem that includes other aquatic\\ninvertebrates (beetles), aquatic insects (dragon flies\\nand damsel flies), fish (top-feeding minnows, stick\u00c2\u00ac\\nlebacks, gobis, and others), birds (swallows, ducks,\\nand others), and mammals (bats) will help main\u00c2\u00ac\\ntain acceptable levels of mosquitoes. Under these\\nconditions, the mosquito is simply a component in\\na balanced food web. If an imbalance develops,\\nthen intervention with certain biological and chemi\u00c2\u00ac\\ncal agents may be required.\\nA successful intervention method has been the use\\nof Bti, a bacterium spore that interferes with devel\u00c2\u00ac\\nopment of the adult. In essence, Bti kills the larva\\nvia physical actions. Several applications over the\\nmosquito season are needed to interfere with the\\nmosquito\u00e2\u0080\u0099s natural growth cycle, which may be three\\nto four months in length. Other larvacides, such as\\nmethoprene, are chemicals that are not selective\\nfor certain stages of mosquitoes\u00e2\u0080\u0099 life cycle.\\nAdulticides also are not selective for life cycles but\\ncould be used at critical times.\\nIn general, proper design that supports a healthy\\nwetland ecosystem produces conditions that main\u00c2\u00ac\\ntain sufficiently low mosquito populations.\\n16. What is the present level of application of this tech\u00c2\u00ac\\nnology?\\nAs of late 1999, more than 200 communities in the\\nUnited States were reported to be utilizing con\u00c2\u00ac\\nstructed wetlands for wastewater treatment. Most\\nof these communities use wetlands for polishing\\nlagoon effluent. In addition, communities in a wide\\nrange of sizes use this technology, including large\\ncities such as Phoenix, Arizona, and Orange\\n22", "height": "4283", "width": "3142", "jp2-path": "constructedwetla00nati_0040.jp2"}, "41": {"fulltext": "County, Florida. For the most part, however, FWS\\ntechnology has been utilized by small- to medium\u00c2\u00ac\\nsized communities ranging from 5,000 to 50,000 in\\npopulation.\\nEven though constructed wetlands for municipal\\nwastewater treatment have been around for as long\\nas 40 years, there have been widespread problems\\nin their performance with respect to nitrogen trans\u00c2\u00ac\\nformations and removal as well as phosphorus re\u00c2\u00ac\\nmoval (WRC, 2000). This manual has been cre\u00c2\u00ac\\nated to help future owners and designers avoid\\nunrealistic expectations from these systems.\\n17. Can these systems operate at elevations other than\\nsea level?\\nFWS and VSB systems are found in a wide range\\nof elevations extending, for example, from the\\ndesert Southwest to New England, and from the\\nsoutheast United States to the Rocky Mountains\\nand Pacific coast regions. The common wetland\\nplants used in these systems are found in all areas\\nof the United States and Canada. There is no in\u00c2\u00ac\\nherent biological or ecological basis for these types\\nof systems to not work in the normal range of physi\u00c2\u00ac\\nographic conditions in the United States, Canada,\\nand Mexico.\\n18. Can constructed wetlands work in cold tempera\u00c2\u00ac\\ntures?\\nConstructed wetlands are found in a wide range of\\nclimatological settings, including cold climates\\nwhere ice forms on the surface for four to six months\\nof the year. For example, these systems are found\\nin Canada, North Dakota, Montana, Vermont, Colo\u00c2\u00ac\\nrado, and other cold-climate areas. Special con\u00c2\u00ac\\nsiderations must be included in the design of these\\nsystems for the formation of an ice layer and the\\neffect of cold temperatures on mechanical systems,\\nsuch as the influent and effluent works. The ab\u00c2\u00ac\\nsence of living plants that have died back for the\\nwinter and the presence of a layer of ice approxi\u00c2\u00ac\\nmately 0.5 to 1.0 ft. thick have not been shown to\\nseverely affect the secondary treatment capabili\u00c2\u00ac\\nties of these systems. Nitrogen transformation and\\nremoval is, however, impaired during very cold pe\u00c2\u00ac\\nriods.\\n19. Can you receive full treatment benefits from a con\u00c2\u00ac\\nstructed wetland that also provides ancillary ben\u00c2\u00ac\\nefits such as wildlife habitat?\\nMultiple benefits can accrue from a FWS con\u00c2\u00ac\\nstructed wetland if it is properly sited and designed.\\nFor example, FWS wetlands that have a significant\\nportion of surface area occupied by submergent\\naquatic plants and deeper water have been found\\nto produce higher-quality effluent and provide\\ngreater habitat value than other configurations. This\\nopen space is used by aquatic fowl for feeding,\\naccess to refugia, and as a source of fresh water.\\nThe same submerged aquatic plants that provide\\nwastewater treatment also serve as a food source\\nfor aquatic birds and mammals.\\nBecause reduced human health risk is associated\\nwith tertiary treatment or \u00e2\u0080\u009cpolishing\u00e2\u0080\u009d wetlands, they\\nhave commonly enjoyed full recreational access to\\nthe FWS systems, but they provide minimal removal\\nof several key pollutants in comparison to the treat\u00c2\u00ac\\nment wetlands that are the focus of this manual.\\nTherefore, human access to these systems entails\\ngreater health risks because the wastewater is ac\u00c2\u00ac\\ntively being treated. The wildlife and other natural\\necological populations may be equally abundant in\\nthese systems as in the polishing systems, but hu\u00c2\u00ac\\nman access may be restricted, at least in the inlet\\nenvirons.\\nThe potential for ancillary benefits is reduced with\\nVSB systems. Depending on its size and degree of\\nvegetation, a VSB system could provide wildlife\\nhabitat. VSB wetlands also can be used for envi\u00c2\u00ac\\nronmental education and awareness activities.\\n2.10 Glossary\\nAbiotic Nonbiological processes or treatment mechanisms\\nin a constructed wetland.\\nAdsorption Adherence by chemical or physical bonding\\nof a pollutant to a solid surface.\\nAdventitious roots provide a competitive advantage to a\\nplant by growing from stems into the surrounding air\\n(around terrestrial plants) or water (around aquatic plants)\\nbefore entering the soil substrate to provide additional up\u00c2\u00ac\\ntake or absorption directly from the surrounding medium.\\nAerenchymous tissues in aquatic plants provide for trans\u00c2\u00ac\\nfer of gases within a plant. In wastewater treatment sys\u00c2\u00ac\\ntems, emergent aquatic plants rely on aerenchymous tis\u00c2\u00ac\\nsues for transfer of oxygen to their roots.\\nAerobic processes in wastewater treatment systems take\\nplace in the presence of dissolved oxygen.\\nAlgae are single-celled to multicelled organisms that rely\\non photosynthesis for growth. Most algae are classified as\\nplants.\\nAnaerobic processes in wastewater treatment systems\\ntake place in the absence of dissolved oxygen and instead\\nrely on molecular oxygen available in decomposing com\u00c2\u00ac\\npounds.\\nAspect ratio The length of a constructed wetland divided\\nby its width (LVW).\\nAtmospheric reaeration introduces atmospheric oxygen\\ninto the water at the water\u00e2\u0080\u0099s surface, which provides dis\u00c2\u00ac\\nsolved oxygen to the aquatic environment.\\n23", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0041.jp2"}, "42": {"fulltext": "Autotrophic Types of reactions that generally require only\\ninorganic reactants; for example, nitrification.\\nBiochemical oxygen demand (BOD) is the demand for\\ndissolved oxygen that decomposition of organic matter\\nplaces on a wastewater treatment process. BOD as ex\u00c2\u00ac\\npressed in milligrams per liter (mg/L) is used as a mea\u00c2\u00ac\\nsure of wastewater organic strength and as a measure of\\ntreatment performance. This constituent is represented\\nthroughout the text of this manual as \u00e2\u0080\u009cBOD,\u00e2\u0080\u009d which stands\\nfor the U.S. standard 5-day BOD test result.\\nBiomass is the total amount of living material, including\\nplants and animals, in a unit volume.\\nBiotic is a term which implies microbiological or biological\\nmechanisms of treatment.\\nBOD removal is the lowering of demand for dissolved oxy\u00c2\u00ac\\ngen required for biological decomposition processes in the\\nwater column; hence, BOD removal can be accomplished\\nby biological decomposition in open-water zones and by\\nflocculation and sedimentation in fully vegetated zones and\\nin VSBs.\\nBulrush is the common name for a number of plants of\\nthe genus Scirpus found in wetlands. Several species of\\nbulrush commonly used in constructed wetlands thrive in\\nthe wide range of environmental conditions in constructed\\nwetlands, including varying levels of water depth and qual\u00c2\u00ac\\nity. The large, terete bulrush species include S. validus, S.\\ncalifornicus, and S. acutus, all of which form dense stands\\nwith large numbers of round-sectioned stems that main\u00c2\u00ac\\ntain an upright posture for one or more years. Other spe\u00c2\u00ac\\ncies of Scirpus include the three-square varieties, such as\\nS. americanus (olynei), S. fluviatilis, and S. robustus, which\\noffer tolerance to salinity, a variety of color shades, and\\nattractiveness to various animal species.\\nCanopy Uppermost or tallest vegetation in a plant com\u00c2\u00ac\\nmunity.\\nCattail is the common name for a number of plants of the\\ngenus Typha that are common in constructed wetlands in\\nthe United States, with at least three species predominant:\\nT. latifolia, T. domingensis, and T. angustifolia. Along with\\ntheir hybridized forms, these species occupy numerous\\nwater-depth and water-quality niches within constructed\\nwetlands. The wetland designer is advised to consult local\\nbotanists and geographic references to determine which\\nlocal cattail species or hybrid is best adapted to the spe\u00c2\u00ac\\ncific water quality, water depth, and substrate planned for\\na constructed wetland.\\nCommon reed (Phragmites) probably is the most widely\\nused plant in constructed wetlands on a worldwide basis,\\nbut it typically is not used in the United States. Although\\nthis plant has excellent growth characteristics in very shal\u00c2\u00ac\\nlow constructed wetlands, it is an invasive species in some\\nnatural wetlands, and its transport and intentional intro\u00c2\u00ac\\nduction to some localities are discouraged. Common reed\\nis considered to offer little value as food or habitat for wet\u00c2\u00ac\\nland wildlife species (Thunhorst, 1993).\\nConstructed wetlands are wastewater treatment systems\\nthat rely on physical, chemical, and biological processes\\ntypically found in natural wetlands to treat a relatively con\u00c2\u00ac\\nstant flow of pretreated wastewater.\\nDeciduous Woody plants that shed their leaves in cold\\nseasons.\\nDentrification Biotic conversion of nitrate-nitrogen to ni\u00c2\u00ac\\ntrogen gases.\\nDetritus Loose, dead leaves and stems from dead veg\u00c2\u00ac\\netation.\\nDike A wall of mounded soil that contains or separates\\nconstructed wetlands from surrounding areas. Dissolved\\noxygen (DO) is required in the water column of a waste-\\nwater treatment system for aerobic biochemical processes\\nthat take place in constructed wetlands.\\nDominant plant species The plant species that exerts a\\ncontrolling influence on the function of the entire plant com\u00c2\u00ac\\nmunity.\\nDuckweed Duckweed naturally moves on a large water\\nsurface by movement induced by wind action unless it is\\nprotected from the wind and held in place by dense stands\\nof emergent plants (e.g., macrophytes) or artificial barri\u00c2\u00ac\\ners. In FWS systems, this results in dense growths of duck\u00c2\u00ac\\nweed within the fully vegetated zones. Duckweed effec\u00c2\u00ac\\ntively seals the water surface and prevents atmospheric\\nreaeration. This action combined with the inherent oxygen\\ndemand of the incompletely treated municipal wastewater\\nresults in anaerobic conditions in these fully vegetated\\nzones.\\nEmergent herbaceous wetland plants grow rooted in the\\nsoil, with plant structures extending above the surface of\\nthe water. These plants are herbaceous by virtue of their\\nrelatively decomposable (leafy) plant structures, but they\\nalso have sufficient internal structure to maintain their up\u00c2\u00ac\\nright growth, even without the support of surrounding wa\u00c2\u00ac\\nters. Most emergent wetland plants grow with or without\\nthe presence of surface water; however, they generally\\ngrow in shallow water near the banks of a water body.\\nEmergent vegetation (see macrophytes).\\nEvapotranspiration Loss of water to the atmosphere\\nthrough water surface and vegetation.\\nExotic species A plant not indigenous to the region.\\nFecal coliform A common measure for pathogenicity of\\nwastewater. This analytical test reveals the number of these\\ntypes of organisms in counts/100 milliliters (#/100mL)\\nFiltration is the process of filtering influent solids from the\\nwastewater and typically is provided by plant stems and\\nleaves and other vegetation in the water column.\\n24", "height": "4283", "width": "3142", "jp2-path": "constructedwetla00nati_0042.jp2"}, "43": {"fulltext": "Floating aquatic plants are commonly found in FWS sys\u00c2\u00ac\\ntems, including water hyacinth Eichhornia crassipes),\\nduckweed Lemna spp., Spirodela spp., and Wolffia spp.),\\nwater fern Azolla carotiniana and Salvinia rotundifolia),\\nand water lettuce Pistia stratiotes). Also common are\\nrooted plants growing in a floating form, including penny\u00c2\u00ac\\nwort Hydrocotlyle spp.), water lily Nymphaea spp.), frog s\\nbit (Limnobium spongia), spatterdock (Nuphar spp.), and\\npondweed Potemogeton spp.).\\nFloating aquatic systems are in essence shallow basins\\ncovered with floating aquatic plants. One type of plant that\\ncan remain in place is the water hyacinth, but it is very\\nsensitive to other than tropical temperatures and is con\u00c2\u00ac\\nsidered to be an invasive species. Duckweed has been\\nheld in place with artificial barriers in these types of sys\u00c2\u00ac\\ntems.\\nFlocculation is the process of very small particles of mat\u00c2\u00ac\\nter clumping together to reach a collectively larger size. In\\nwastewater treatment processes, flocculation typically ag\u00c2\u00ac\\nglomerates colloidal particulates into larger, settleable sol\u00c2\u00ac\\nids that are then removed by sedimentation processes.\\nFree water surface (FWS) wetlands are constructed wet\u00c2\u00ac\\nlands that provide wastewater treatment through floccula\u00c2\u00ac\\ntion and sedimentation during the flow of wastewater\\nthrough stands of aquatic plants growing in shallow water.\\nIn some FWS wetlands, there are also open areas where\\naerobic bio-oxidation complements the physical removal\\nprocesses. FWS systems resemble natural wetlands in\\nfunction and appearance. FWS systems have also been\\ntermed \u00e2\u0080\u009csurface flow systems.\u00e2\u0080\u009d\\nFunction refers to the purpose, role, or actions expected\\nof constructed wetlands in the process of wastewater treat\u00c2\u00ac\\nment. Function is expressed in terms of expected results,\\nsuch as nutrient uptake, removal of TSS and BOD, main\u00c2\u00ac\\ntenance of dissolved oxygen in open water zones, and\\nreduction of wastewater constituents to acceptable levels,\\nwaterfowl habitat, and water storage.\\nHabitat value The suitability of an area to support a given\\nspecies.\\nHerbaceous Plant material that has no woody parts.\\nHerbivores are members of the animal kingdom that con\u00c2\u00ac\\nsume plant matter.\\nHydric soils, or wetland soils, exhibit distinct chemical and\\nphysical changes that result from periodic inundation and\\nsaturation. Flooding and subsequent decomposition and\\noxidation of soil chemicals typically result in anaerobic soil\\nconditions.\\nHydrophyte Any plant growing in a soil that is deficient in\\noxygen.\\nIndigenous species Species of plants that are native to\\nan area.\\nInorganics Compounds that do not contain organic car\u00c2\u00ac\\nbon.\\nLagoons are also called stabilization ponds, oxidation\\nponds, etc. In conventional wastewater treatment systems,\\nthey typically are used to provide intermediate treatment\\nof wastewater through a variety of physical, chemical, and\\nbiological processes.\\nLimiting nutrient is the nutrient that controls a particular\\nplant\u00e2\u0080\u0099s growth. When present in insufficient amounts rela\u00c2\u00ac\\ntive to a given plant\u00e2\u0080\u0099s needs, a limiting nutrient limits that\\nplant\u00e2\u0080\u0099s growth.\\nLimnetic The open water zone of a FWS system where\\nlight can penetrate to induce photosynthesis.\\nMacrophytes are plants that are readily visible to the un\u00c2\u00ac\\naided eye and include vascular or higher plants. Vascular\\nplants include mosses, ferns, conifers, monocots, and di\u00c2\u00ac\\ncots. Macrophytes also may be categorized by a variety of\\necological growth forms.\\nMarsh A common term applied to treeless wetlands.\\nMicrobes or microorganisms are microscopic organisms\\n(only viewed with a microscope), such as bacteria, proto\u00c2\u00ac\\nzoans, and certain species of algae, which are respon\u00c2\u00ac\\nsible for many of the biochemical transformations neces\u00c2\u00ac\\nsary in wastewater treatment processes.\\nNitrification Biotic conversion of ammonium nitrogen to\\nnitrite and nitrate-nitrogen.\\nNuisance species Plants that detract from or interfere with\\nthe designated purpose(s) of constructed wetlands.\\nOn-site constructed wetland systems are wastewater\\nsystems for treatment and disposal at the site where waste-\\nwater is generated. For example, a residential septic sys\u00c2\u00ac\\ntem is an on-site system.\\nOrganics Compounds that contain organic carbon (also\\nvolatile solids).\\nOxygen demand Generally expressed through relatively\\nhigh BOD concentrations, the property of municipal waste-\\nwater that removes dissolved oxygen from the water col\u00c2\u00ac\\numn.\\nPhotosynthesis is the conversion of sunlight into organic\\nmatter by plants through a process of combining carbon\\ndioxide and water in the presence of chlorophyll and light,\\nwhich releases oxygen as a by-product.\\nPhytoplankton are algae that are microscopic in size\\nwhich float or drift in the upper layer of the water column\\nand depend on photosynthesis and the presence of phos\u00c2\u00ac\\nphorus and nitrogen in the water.\\nPneumatophores are structures that provide air channels\\nfor emergent plants growing in water environments.\\nPolishing wetlands are designed to provide tertiary treat\u00c2\u00ac\\nment to secondary effluent to meet performance standards\\n25", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0043.jp2"}, "44": {"fulltext": "required by National Pollutant Discharge Elimination Sys\u00c2\u00ac\\ntem (NPDES) permits. Design considerations for polish\u00c2\u00ac\\ning wetlands are outside the scope of this manual.\\nPrimary effluent is the product of primary treatment of\\nwastewater that typically involves settling of solids in a\\ncontainment structure, such as a septic tank, settling pond,\\nor lagoon.\\nPrimary production is the production of biomass (organic\\ncarbon) by plants and microscopic algae, typically through\\nphotosynthesis, as the first link in the food chain.\\nPrimary treatment of wastewater is a settling process for\\nremoval of settleable solids from wastewaters.\\nRhizome Root-like stem that produces roots and stems to\\npropogate itself in a surrounding zone.\\nSecondary effluent is wastewater that has undergone sec\u00c2\u00ac\\nondary treatment and is discharged to the environment or\\nreceives further treatment in tertiary treatment processes.\\nSecondary treatment continues the process begun in pri\u00c2\u00ac\\nmary treatment by removing certain constituents, such as\\nbiochemical oxygen demand (BOD) and total suspended\\nsolids (TSS) from primary effluent to prescribed treatment\\nlevels; typically, 30 mg/L in the United States.\\nSediment Organic and mineral particulates that have\\nsettled from the overlying water column (also sludge).\\nSeepage Loss of water from a constructed wetland to the\\nsoil through infiltration below the system. Senescence is\\nthe phase at the end of a plant\u00e2\u0080\u0099s life that leads to death\\nand, finally, decay.\\nSolar insolation refers to the amount of solar radiation\\nthat reaches the constructed wetland. Solar radiation in\\nthe summer months may play an important role in photo\u00c2\u00ac\\nsynthesis in open-water zones of a FWS system.\\nStanding biomass in a constructed wetland is the total\\namount of plant material that stands erect. This term typi\u00c2\u00ac\\ncally is used as \u00e2\u0080\u009cdead standing biomass\u00e2\u0080\u009d to refer to dead,\\nstanding plants, in contrast to green plants and plant litter\\ncomposed of broken and fallen dead plant parts.\\nStructure refers to the form and amount of living and\\nnonliving components of an ecosystem. For example,\\nemergent vegetation provides the structure to perform\\nwetland functions. Wetland structure is expressed in\\nqualitative terms such as species of flora and fauna, or\\ntype of wetland such as marsh, bog, or bottomland for\u00c2\u00ac\\nest.\\nSubmerged aquatic plants or submergent vegetation\\nare rooted plants that grow in open water zones within\\nthe water column of an aquatic environment (compare to\\nemergent aquatic plants) and provide dissolved oxygen\\nfor aerobic biochemical reactions. They lie below the wa\u00c2\u00ac\\nter surface, except for flowering parts in some species.\\nSubsurface flow (SF) wetlands (see vegetated sub\u00c2\u00ac\\nmerged bed (VSB) systems).\\nTertiary treatment (see polishing wetlands).\\nTotal nitrogen (TN) is the sum of all the forms of nitrogen,\\nincluding nitrate, nitrite, ammonia, and organic nitrogen in\\nwastewater, and is typically expressed in milligrams per\\nliter (mg/L).\\nTotal phosphorus (TP) is a measure of all forms of phos\u00c2\u00ac\\nphorus in wastewater, typically expressed in milligrams per\\nliter (mg/L).\\nTotal suspended solids (TSS) are particulate matter in\\nwastewater consisting of organic and inorganic matter that\\nis suspended in the water column. The numeric value is\\nprovided by specific analytical test. Typically, municipal\\nwastewaters include the settleable solids and some por\u00c2\u00ac\\ntion of the colloidal fraction.\\nVascular plant Plant that readily conducts water, miner\u00c2\u00ac\\nals and foods throughout its boundaries.\\nVegetated submerged bed (VSB) systems provide waste-\\nwater treatment in filter media that is not directly exposed\\nto the atmosphere but may be slightly influenced by the\\nroots of surface vegetation. VSB systems also have been\\ntermed subsurface flow (SF) wetlands, rock reed filters,\\nsubmerged filters, root zone method, reed bed treatment\\nsystems, and microbial rock plant filters. In this manual,\\nthe term \u00e2\u0080\u009cvegetated submerged bed systems\u00e2\u0080\u009d is used be\u00c2\u00ac\\ncause gravel beds rather than hydric soils are the support\\nmedia for wetland plants; as a result, the systems are not\\ntruly wetlands.\\nVegetative reproduction is the process of asexual repro\u00c2\u00ac\\nduction, in which new plants develop from roots, stems,\\nand leaves of the parent plant.\\nWastewater treatment is the process of improving the\\nquality of wastewater. The term can refer to any parts\\nor all parts of the process by which raw wastewater is\\ntransformed through biological, biochemical, and physi\u00c2\u00ac\\ncal means to reduce contaminant concentrations to pre\u00c2\u00ac\\nscribed levels prior to release to the environment. A\\nwastewater treatment process typically consists of pri\u00c2\u00ac\\nmary, secondary, and tertiary treatment.\\nWetland hydraulics refers to movement of water\\nthrough constructed wetlands, including volumes,\\nforces, velocities, rates, flow patterns, and other char\u00c2\u00ac\\nacteristics.\\nWoody plants are plants that produce bark and vascu\u00c2\u00ac\\nlar structures that are not leafy in nature. Woody plants\\nhave trunks, stems, branches, and twigs that allow them\\nto occupy a greater variety of available niches than her\u00c2\u00ac\\nbaceous plants can occupy. General terms that describe\\ncategories of woody plants found in wetlands are shrubs,\\ntrees (canopy or subcanopy), and woody vines.\\n26", "height": "4283", "width": "3142", "jp2-path": "constructedwetla00nati_0044.jp2"}, "45": {"fulltext": "Wrack Plant debris carried by water.\\nZooplankton Microscopic and small animals that live in\\nthe water column.\\n2.11 References\\nArizona Department of Environmental Quality (ADEQ).\\n1995. Arizona guidance manual for constructed wet\u00c2\u00ac\\nlands for water quality improvement. Prepared by\\nR. L. Knight, R. Randall, M. Girts, J.A. Tress, M.\\nWilhelm, and R.H. Kadlec. ADEQ TM 95-1.\\nArmstrong, W. 1978. Root aeration in the wetland envi\u00c2\u00ac\\nronment. In: D.D. Hook and R.M.M. Crawford (eds.)\\nPlant life in anaerobic environments. Ann Arbor, Ml:\\nAnn Arbor Science, Chapter 9, pp. 269-297.\\nBavor, H.J., D.J. Roser, P.J. Fisher, and I.C. Smalls.\\n1989. Performance of solid-matrix wetland systems\\nviewed as fixed-film bioreactors. In: D.A. Hammer\\n(ed.) Constructed wetlands for wastewater treat\u00c2\u00ac\\nment, municipal, industrial, and agricultural.\\nChelsea, Ml: Lewis Publishers, Chapter 39k, pp.\\n646-656.\\nBurgan, M.A. and D.M. Sievers. 1994. On-site treatment\\nof household sewage via septic tank and two- stage\\nsubmerged bed wetland. In: Proceedings of the Sev\u00c2\u00ac\\nenth International Symposium on Individual and\\nSmall Community Sewage Systems. American So\u00c2\u00ac\\nciety of Agricultural Engineers, Atlanta, GA: pp. 77-\\n84.\\nBurgoon, P.S., K.R. Reddy, and T.A. DeBusk. 1989. Do\u00c2\u00ac\\nmestic wastewater treatment using emergent plants\\ncultured in gravel and plastic substrates. In: D.A.\\nHammer (ed.) Constructed wetlands for wastewa\u00c2\u00ac\\nter treatment, municipal, industrial, and agricultural.\\nChelsea, Ml: Lewis Publishers, Chapter 38f, pp.\\n536-541.\\nDennison, M.S. and J.F. Berry. 1993. Wetlands: guide\\nto science, law, and technology. Park Ridge, NJ:\\nNoyes Publications, 439 pp.\\nDill, C.H. 1989. Wastewater wetlands: user friendly mos\u00c2\u00ac\\nquito habitats. In: D.A. Hammer (ed.) Constructed\\nwetlands for wastewater treatment, municipal, in\u00c2\u00ac\\ndustrial, and agricultural. Chelsea, Ml: Lewis Pub\u00c2\u00ac\\nlishers, Chapter 39m, pp. 664-667.\\nFeierabend, J.S. 1989. Wetlands: the lifeblood of wild\u00c2\u00ac\\nlife. In: D.A. Hammer (ed.) Constructed wetlands\\nfor wastewater treatment, municipal, industrial, and\\nagricultural. Chelsea, Ml: Lewis Publishers, Chap\u00c2\u00ac\\nter 7, pp. 107-118.\\nFriend, M. 1985. Wildlife health implications of sewage\\ndisposal in wetlands. In: P.J. Godfrey, E.R. Kaynor,\\nS. Pelczarski, and J. Benforado (eds.) Ecological\\nconsiderations in wetlands treatment of municipal\\nwastewaters. New York, NY: Van Nostrand Reinhold,\\nChapter 17, pp. 262-269.\\nGearheart, R.A., F. Klopp, and G. Allen. 1989. Con\u00c2\u00ac\\nstructed free surface wetlands to treat and receive\\nwastewater: pilot project to full scale. In: D.A. Ham\u00c2\u00ac\\nmer (ed.) Constructed wetlands for wastewater treat\u00c2\u00ac\\nment, municipal, industrial, and agricultural.\\nChelsea, Ml: Lewis Publishers, Chapter 8, pp. 121\\n137.\\nHammer, D.A. 1992. Creating freshwater wetlands. Boca\\nRaton, FL: Lewis Publishers, 298 pp.\\nHuang, J., R.B. Renau, Jr., and C. Hagedorn. 1994. Con\u00c2\u00ac\\nstructed wetlands for domestic wastewater treat\u00c2\u00ac\\nment. In: Proceedings of the Seventh International\\nSymposium on Individual and Small Community\\nSewage Systems. American Society of Agricultural\\nEngineers, Atlanta, GA, pp. 66-76.\\nJohns, M.J., B.J. Lisidar, A.L. Kenimer, and R.W. Weaver.\\n1998. Nitrogen fate in a subsurface flow constructed\\nwetland for on-site wastewater treatment. In: Proceed\u00c2\u00ac\\nings of the Eighth National Symposium on Individual\\nand Small Community Sewage Systems. American\\nSociety for Agricultural Engineers, Orlando, FL, pp.\\n237-246.\\nKadlec, R.H. and R.L. Knight. 1996. Constructed wetlands.\\nBoca Raton, FL: Lewis Publishers, 893 pp.\\nKadlec, R.H., D.A. Hammer, and M.A. Girts. 1990. A total\\nevaporative constructed wetland treatment system. In:\\nP.F. Cooper and B.C. Findlater (eds.) Constructed wet\u00c2\u00ac\\nlands in water pollution control. Oxford, UK: Pergamon\\nPress, pp. 127-138.\\nKent, D.M. 1994. Applied wetlands science and technol\u00c2\u00ac\\nogy. Boca Raton, FL: Lewis Publishers, 436 pp.\\nKnight, R.L. 1992. Ancillary benefits and potential prob\u00c2\u00ac\\nlems with the use of wetlands for nonpoint source pol\u00c2\u00ac\\nlution control. Ecological Engineering, 1:97-113.\\nKnight, R.L. 1997. Wildlife habitat and public use benefits\\nof constructed wetlands. In: R. Haberl, R. Perfler, J.\\nLaber, and P. Cooper (eds.) Wetland systems for wa\u00c2\u00ac\\nter pollution control 1996. Water Science Technol\u00c2\u00ac\\nogy 35(5). Oxford, UK: Elsevier Science Ltd., pp. 35-\\n43.\\nKroodsma, D.E. 1978. Habitat values for nongame wet\u00c2\u00ac\\nland birds. In: P.E. Greeson, J.R. Clark, and J.E. Clark\\n(eds.) Wetland functions and values: The state of our\\nunderstanding. Minneapolis, MN: American Water\\nResources Association, pp. 320-326.\\nLiving Technologies, Inc. 1996. Interim performance re\u00c2\u00ac\\nport for the South Burlington, Vermont \u00e2\u0080\u009cLiving Ma\u00c2\u00ac\\nchine,\u00e2\u0080\u009d January-August 1996. Burlington, VT: Living\\nTechnologies, Inc., September 1996.\\n27", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0045.jp2"}, "46": {"fulltext": "Majumdar, S.K., R.P. Brooks, F.J. Brenner, and R.W.\\nTiner (eds.) 1989. Wetlands ecology and conserva\u00c2\u00ac\\ntion: Emphasis in Pennsylvania. Easton, PA: The\\nPennsylvania Academy of Science, 394 pp.\\nMankin, K.R. and G. M. Powell. 1998. Onsite rock-plant\\nfilter monitoring and evaluation in Kansas. In: Pro\u00c2\u00ac\\nceedings of the Eighth National Symposium on In\u00c2\u00ac\\ndividual and Small Community Sewage Systems.\\nAmerican Society for Agricultural Engineers, Or\u00c2\u00ac\\nlando, FL, pp. 228-236.\\nMarble, A.D. 1992. A guide to wetland functional de\u00c2\u00ac\\nsign. Boca Raton, FL: Lewis Publishers, 222 pp.\\nMartin, C.V. and B.F. Eldridge. 1989. California\u00e2\u0080\u0099s expe\u00c2\u00ac\\nrience with mosquitoes in aquatic wastewater treat\u00c2\u00ac\\nment systems. In: D.A. Hammer (ed.) Constructed\\nwetlands for wastewater treatment, municipal, in\u00c2\u00ac\\ndustrial, and agricultural. Chelsea, Ml: Lewis Pub\u00c2\u00ac\\nlishers, pp. 393-398.\\nMcAllister, L.S. 1992. Habitat quality assessment of two\\nwetland treatment systems in Mississippi\u00e2\u0080\u0094A pilot\\nstudy. EPA/600/R-92/229. U.S. Environmental Pro\u00c2\u00ac\\ntection Agency, Environmental Research Laboratory,\\nCorvallis, OR. November 1992.\\nMcAllister, L.S. 1993a. Habitat quality assessment of\\ntwo wetland treatment systems in the arid west\u00e2\u0080\u0094A\\npilot study. EPA/600/R-93/117. U.S. Environmental\\nProtection Agency, Environmental Research Labo\u00c2\u00ac\\nratory, Corvallis, OR. July 1993.\\nMcAllister, L.S. 1993b. Habitat quality assessment of\\ntwo wetland treatment systems in Florida\u00e2\u0080\u0094A pilot\\nstudy. EPA/600/R-93/222. U.S. Environmental Pro\u00c2\u00ac\\ntection Agency, Environmental Research Laboratory,\\nCorvallis, OR. November 1993.\\nMerritt, A. 1994. Wetlands, industry wildlife: A manual\\nof principles and practices. Gloucester, UK: The\\nWildfowl Trust, 182 pp.\\nMitsch, W.J. and J.G. Gosselink. 1993. Wetlands. 2d\\ned. New York, NY: Van Nostrand Reinhold, 722 pp.\\nNeralla, S., R.W. Weaver, and B.J. Lesikar. 1998. Plant\\nselection for treatment of septic effluent in subsur\u00c2\u00ac\\nface wetlands. In: Proceedings of the Eighth Na\u00c2\u00ac\\ntional Symposium on Individual and Small Commu\u00c2\u00ac\\nnity Sewage Systems. American Society for Agri\u00c2\u00ac\\ncultural Engineers, Orlando, FL, pp. 247-253.\\nNiering, W.A. 1985. Wetlands. New York, NY: Alfred A.\\nKnopf, 638 pp.\\nPayne, N.F. 1992. Techniques for wildlife habitat man\u00c2\u00ac\\nagement of wetlands. New York, NY: McGraw-Hill.\\nPost, Buckley, Schuh Jernigan, Inc. 1993. Compli\u00c2\u00ac\\nance and performance review for the City of\\nOrlando\u00e2\u0080\u0099s easterly wetland treatment system. Pre\u00c2\u00ac\\npared for the City of Orlando, FL.\\nReed, S.C., R.W. Crites, and E.J. Middlebrooks. 1995.\\nNatural systems for waste management and treat\u00c2\u00ac\\nment. 2d ed. New York, NY: McGraw-Hill, 433 pp.\\nReed, S.C., J. Salisbury, L. Fillmore, and R. Bastian.\\n1996. An evaluation of the \u00e2\u0080\u009cLiving Machine\u00e2\u0080\u009d waste-\\nwater treatment concept. In: Proceedings, WEFTEC\\n*96, 69th Annual Conference and Exhibition, Dal\u00c2\u00ac\\nlas, TX. Water Environment Federation, Alexandria,\\nVA, October 1996.\\nSather, J.H. 1989. Ancillary benefits of wetlands con\u00c2\u00ac\\nstructed primarily for wastewater treatment. In: D.A.\\nHammer (ed.) Constructed wetlands for wastewa\u00c2\u00ac\\nter treatment, municipal, industrial, and agricultural.\\nChelsea, Ml: Lewis Publishers, Chapter 28a, pp.\\n353-358.\\nSchueler, T.R. 1992. Design of stormwater wetland sys\u00c2\u00ac\\ntems: Guidelines for creating diverse and effective\\nstormwater systems in the mid-Atlantic region.\\nAnacostia Restoration Team, Metropolitan Washing\u00c2\u00ac\\nton Council of Governments, Washington, DC. 133\\npp.\\nSnoddy, E.L., G.A. Brodie, D.A. Hammer, and D.A.\\nTomljanovich. 1989. Control of the armyworm,\\nSimyra henrici (Lepidoptera: Noctuidae), on cattail\\nplantings in acid drainage constructed wetlands at\\nWidows Creek Steam-Electric Plant. In: D.A. Ham\u00c2\u00ac\\nmer (ed.) Constructed wetlands for wastewater treat\u00c2\u00ac\\nment, municipal, industrial, and agricultural.\\nChelsea, Ml: Lewis Publishers, Chapter 421, pp.\\n808-811.\\nStowell, R., S. Weber, G. Tchobanoglous, B.A. Wilson,\\nand K.R. Townzen. 1985. Mosquito considerations\\nin the design of wetland systems for the treatment\\nof wastewater. In: P.J. Godfrey, E.R. Kaynor, S.\\nPelczarski, and J. Benforado (eds.) Ecological con\u00c2\u00ac\\nsiderations in wetlands treatment of municipal\\nwastewaters. New York, NY: Van Nostrand Reinhold,\\nChapter 3, pp. 38-47.\\nThunhorst, G.A. 1993. Wetland planting guide for the\\nnortheastern United States: Plants for wetland cre\u00c2\u00ac\\nation, restoration, and enhancement. St. Michaels,\\nMD: Environmental Concern, Inc., 179 pp.\\nThut, R.N. 1989. Utilization of artificial marshes for treat\u00c2\u00ac\\nment of pulp mill effluents. In: D.A. Hammer (ed.)\\nConstructed wetlands for wastewater treatment, mu\u00c2\u00ac\\nnicipal, industrial, and agricultural. Chelsea, Ml:\\nLewis Publishers, Chapter 19, pp. 239-244.\\nTodd, J. and B. Josephson. 1994. Living machines:\\nTheoretical foundations and design precepts.\\nFalmouth, MA: Ocean Arks International.\\n28", "height": "4283", "width": "3142", "jp2-path": "constructedwetla00nati_0046.jp2"}, "47": {"fulltext": "U.S. Environmental Protection Agency (EPA). 1988. Design\\nmanual: Constructed wetlands and aquatic plant sys\u00c2\u00ac\\ntems for municipal wastewater treatment. Center for\\nEnvironmental Research Information, Cincinnati, OH.\\nU.S. Environmental Protection Agency (EPA). 1993a. Con\u00c2\u00ac\\nstructed wetlands for wastewater treatment and wildlife\\nhabitat. EPA 832-R-005. Office of Water, Washington,\\nDC.\\nU.S. Environmental Protection Agency (EPA). 1993b. Sub\u00c2\u00ac\\nsurface flow constructed wetlands for wastewater treat\u00c2\u00ac\\nment: A technology assessment. EPA 832-R-93-008.\\nOffice of Water, Washington, DC.\\nU.S. Environmental Protection Agency (EPA). 1997a. Re\u00c2\u00ac\\nsponse to Congress on use of decentralized wastewa\u00c2\u00ac\\nter treatment systems. EPA 832-R-97-001 b. Office of\\nWater, Washington, DC.\\nU.S. Environmental Protection Agency (EPA). 1997b. Re\u00c2\u00ac\\nsponse to Congress on the AEES \u00e2\u0080\u009cLiving Machine\u00e2\u0080\u009d\\nWastewater Treatment Technology. EPA 832-R-97-002.\\nOffice of Water, Washington, DC.\\nU.S. Environmental Protection Agency (EPA). 1999. Free\\nwater surface wetlands for wastewater treatment: A tech\u00c2\u00ac\\nnology assessment. EPA 832/R-99/002. Office of Wa\u00c2\u00ac\\nter, Washington, DC.\\nVisher, S.S. 1954. Climatic atlas of the United States. Cam\u00c2\u00ac\\nbridge, MA: Harvard University Press.\\nVymazal, J. 1995. Algae and element cycling in wetlands.\\nBoca Raton, FL: Lewis Publishers, 689 pp.\\nWater Research Commission (South Africa). 2000. Con\u00c2\u00ac\\nstructed wetlands: The answer to small scale wastewa\u00c2\u00ac\\nter treatment in South Africa.\\nWaterWorld. 1996. Product focus, June.\\nWeller, M.W. 1978. Management of freshwater marshes for\\nwildlife. In: R.E. Good, D.F. Whigham, and R.L. Simpson\\n(eds.) Freshwater wetlands: Ecological processes and\\nmanagement potential. New York, NY: Academic Press,\\npp. 267-284.\\nWhite, K.D. and C.M. Shirk. 1998. Performance and design\\nrecommendations for on-site wastewater treatment us\u00c2\u00ac\\ning constructed wetlands. In: Proceedings of the Eighth\\nNational Symposium on Individual and Small Commu\u00c2\u00ac\\nnity Sewage Systems. American Society for Agricultural\\nEngineers, Orlando, FL, pp. 195-201.\\nWilliams, C.R., R.D. Jones, and S.A. Wright. 1996. Mosquito\\ncontrol in a constructed wetland. In: Proceedings,\\nWEFTEC \u00e2\u0080\u009896, 69th Annual Conference and Exposition,\\nDallas, TX. Water Environment Federation, Alexandria,\\nVA, October 1996, pp. 333-344.\\nWittgren, H.B. and T. Maehlum. 1996. Wastewater con\u00c2\u00ac\\nstructed wetlands in cold climates. In: R. Haberl, R.\\nPerfler, J. Laber, and P. Cooper (eds.) Water Science\\nTechnology 35(5), Wetland systems for water pollution\\ncontrol 1996. Oxford, UK: Elsevier Science Ltd., pp. 45-\\n53.\\nWolverton, B.C. 1987. Aquatic plants for wastewater treat\u00c2\u00ac\\nment: An overview. In: K.R. Reddy and W.H. Smith (eds.)\\nAquatic plants for water treatment and resource recov\u00c2\u00ac\\nery. Orlando, FL: Magnolia Publishing, pp. 3-15.\\nWorrall, P, K.J. Peberdy, and M.C. Millett. 1996. Constructed\\nwetlands and nature conservation. In: R. Haberl, R.\\nPerfler, J. Laber, and P. Cooper (eds.) Water Science\\nTechnology 35(5), Wetland systems for water pollution\\ncontrol 1996. Oxford, UK: Elsevier Science Ltd., pp. 205-\\n213.\\nZirschky, J. and S.C. Reed. 1988. The use of duckweed for\\nwastewater treatment. Journal of the Water Pollution\\nControl Foundation, 60:1253-1258.\\n29", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0047.jp2"}, "48": {"fulltext": "Chapter 3\\nRemoval Mechanisms and Modeling Performance of\\nConstructed Wetlands\\n3.1 Introduction\\nConstructed wetlands are highly complex systems that\\nseparate and transform contaminants by physical, chemi\u00c2\u00ac\\ncal, and biological mechanisms that may occur simulta\u00c2\u00ac\\nneously or sequentially as the wastewater flows through\\nthe system. In a qualitative sense, the processes that oc\u00c2\u00ac\\ncur are known, but in only a few cases have they been\\nadequately measured to provide a more quantitative as\u00c2\u00ac\\nsessment. The predominant mechanisms and their se\u00c2\u00ac\\nquence of reaction are dependent on the external input\\nparameters to the system, the internal interactions, and\\nthe characteristics of the wetland. The external input pa\u00c2\u00ac\\nrameters most often of concern include the wastewater\\nquality and quantity and the system hydrological cycle.\\nTypical characteristics of municipal wastewaters most\\noften treated in constructed wetlands are described in Table\\n3-1. The emphasis of this manual is on the treatment of\\nmunicipal wastewater with the objectives of achieving tar\u00c2\u00ac\\nget levels of suspended solids, organic matter, pathogens,\\nand in some instances, nutrients (specifically total nitro\u00c2\u00ac\\ngen) and heavy metals. Wastewaters that will be consid\u00c2\u00ac\\nered include septic tank effluent, primary effluent, pond\\neffluents, and some secondary effluents from overloaded\\nor poorly controlled systems. Table 3-1 shows that the char\u00c2\u00ac\\nacter of the wastewater is dependent on pretreatment and\\nTable 3-1. Typical Constructed Wetland Influents\\nConstituent\\n(mg/L)\\nSeptic Tank\\nEffluent 1\\nPrimary\\nEffluent 2\\nPond\\nEffluent 3\\nBOD\\n129-147\\n40-200\\n11-35\\nSol. BOD\\n100-118\\n35-160\\n7-17\\nCOD\\n310-344\\n90-400\\n60-100\\nTSS\\n44-54\\n55-230\\n20-80\\nVSS\\n32-39\\n45-180\\n25-65\\nTN\\n41-49\\n20-85\\n8-22\\nnh 3\\n28-34\\n15-40\\n0.6-16\\nno 3\\n0-0.9\\n0\\n0.1-0.8\\nTP\\n12-14\\n4-15\\n3-4\\nOrthoP\\n10-12\\n3-10\\n2-3\\nFecal coli (log/100ml)\\n5.4-6.0\\n5.0-7.0\\n0.8-5.6\\nEPA (1978), 95% confidence interval. Prior to major detergent\\nreformulations which reduce P species by -50%.\\n2 Adapted from Metcalf and Eddy, (1991) assuming typical removal by\\nprimary sedimentation-soluble BOD 35 to 45% total.\\n3 EPA (1980).\\nmay contain both soluble and particulate fractions of or\u00c2\u00ac\\nganic and inorganic constituents in reduced or oxidized\\nforms. As will be seen later, these characteristics play an\\nimportant role in the major mechanisms of removal.\\nThe two major mechanisms at work in most treatment\\nsystems are liquid/solid separations and constituent trans\u00c2\u00ac\\nformations. Separations typically include gravity separa\u00c2\u00ac\\ntion, filtration, absorption, adsorption, ion exchange, strip\u00c2\u00ac\\nping, and leaching. Transformations may be chemical, in\u00c2\u00ac\\ncluding oxidation/reduction reactions, flocculation, acid/\\nbase reactions, precipitation, or a host of biochemical re\u00c2\u00ac\\nactions occurring under aerobic, anoxic, or anaerobic con\u00c2\u00ac\\nditions. Both separations and transformations may lead to\\ncontaminant removal in wetlands but often only result in\\nthe detention of the contaminant in the wetland for a pe\u00c2\u00ac\\nriod of time. There may be changes in the contaminant\\ncomposition that will effectively achieve treatment objec\u00c2\u00ac\\ntives, such as the biochemical transformation of organic\\ncompounds to gases such as C0 2 or CH 4 A biochemical\\ntransformation, however, may produce biomass or organic\\nacids that may not achieve the treatment objective if these\\nmaterials escape in the effluent. In the case of biomass, it\\nmay escape as volatile suspended solids, or it may un\u00c2\u00ac\\ndergo further bacterial reaction, which may result in the\\nleaching of a soluble carbon compound back into the wa\u00c2\u00ac\\nter column.\\nThe remainder of this chapter will review potential mecha\u00c2\u00ac\\nnisms that may be at work in constructed wetlands. These\\nreactions may occur in the water column, on the surfaces\\nof plants, within the litter and detritus accumulating at the\\nwetland surface or on the bottom, or within the root zone\\nof the system. The reactions unique to the wetland type\\nwill also be delineated.\\n3.2 Mechanisms of Suspended Solids\\nSeparations and Transformations\\n3.2.1 Description and Measurement\\nSuspended solids in waters are defined by the method\\nof analysis. Standard Methods (1998) defines total sus\u00c2\u00ac\\npended solids as those solids retained on a standard glass\\nfiber filter that typically has a nominal pore size of 1.2pm.\\nThe type of filter holder, the pore size, porosity, area and\\nthickness of the filter, and the amount of material depos-\\n30", "height": "4283", "width": "3142", "jp2-path": "constructedwetla00nati_0048.jp2"}, "49": {"fulltext": "ited on the filter are the principal factors affecting the sepa\u00c2\u00ac\\nration of suspended from dissolved solids. As a result, the\\nmeasurement reported for total suspended solids may in\u00c2\u00ac\\nclude particle sizes ranging from greater than 100|im to about\\n1 pm. Soluble (dissolved) solids would therefore include col\u00c2\u00ac\\nloidal solids smaller than 1 pm and molecules in true solu\u00c2\u00ac\\ntion. A classical method of solids classification by size would\\ninclude the following:\\nSettleable Solids 100pm\\nSupracolloidal Solids 1 -100pm\\nColloidal Solids 10-3-1 pm\\nSoluble Solids 10-3pm\\nSolids are also classified as volatile or fixed, again based\\non the method of analysis. Standard Methods (1998) de\u00c2\u00ac\\nfines a volatile solid as one that ignites at 550\u00c2\u00b0C. Although\\nthe method is intended to distinguish between organic sol\u00c2\u00ac\\nids and inorganic solids, it is not precise since volatile solids\\nwill include losses due to the decomposition or volatilization\\nof some mineral salts depending on the time of exposure to\\nthe ignition temperature.\\nWastewater influents to wetlands may contain significant\\nquantities of suspended solids (Table 3-1). The composition\\nof these solids is quite different, however. Septic tank and\\nprimary effluents will normally contain neutral density colloi\u00c2\u00ac\\ndal and supracolloidal solids emanating from food wastes,\\nfecal materials, and paper products. Pond effluent suspended\\nsolids are likely to be predominantly algal cells. All three will\\nbe high in organic content. Size distribution is also different\\namong the waste streams. Tables 3-2 and 3-3 present infor\u00c2\u00ac\\nmation on size distributions of suspended solids, organic\\nmatter, and phosphorus in domestic wastewaters with vari\u00c2\u00ac\\nous levels of pretreatment. It should be noted that methods\\ndiffered between investigators on estimating size ranges.\\nHigh settleable fractions are not surprising for raw wastewa\u00c2\u00ac\\nter samples or for the pond effluent containing algal cells. It\\nis important to note the association of organic matter and\\nphosphorus with the various solid fractions.\\nTable 3-2. Size Distributions for Solids in Municipal Wastewater\\nType of Sample\\nby Weight)\\nSize Range\\n(fxm)\\nPrimary Eff. 1\\nPrimary Eft. 2\\nPrimary Eff. 3\\nRaw Sewage 4\\nRaw Sewage 5\\n10 3\\n_\\n_\\n_\\n31\\n48\\n10 3 -1.0\\n20\\n22(10-30)\\n14\\n9\\n1.0-12\\n54\\n35(24-51)\\n12\\n26\\n43(30-60)\\n1.0-100\\n81\\n24\\n18\\n100\\n19\\n31\\n23\\nLevine et al. (1984).\\n2 Tchobanoglous et al. (1983).\\n3 Gearheart, etal. (1993).\\n4 Heukelekian and Balmat (1959).\\n5 Rickert and Hunter ((1972).\\nTable 3-3. Size Distribution for Organic and Phosphorus Solids in Municipal Wastewater\\nType of Solids\\nby Weight)\\nSize Range\\n(nm)\\nOrganic\\nSolids\\n(primary\\neffluent)\\nOrganic\\nSolids 2\\n(primary\\neffluent)\\nOrganic\\nSolids 2\\n(primary\\neffluent)\\nOrganic\\nSolids 2\\n(primary\\neffluent)\\nOrganic\\nSolids 2\\n(primary\\neffluent)\\nOrganic\\nSolids 3\\n(raw\\nsewage)\\nTotal\\nPhos. 4\\n(primary\\neffluent)\\nTotal\\nPhos. 4\\n(primary\\neffluent)\\n10 3\\n9\\n_\\n_\\n_\\n_\\n42\\n_\\n_\\n0.1\\n51\\n50\\n25\\n35\\n17.2\\n15.7\\n10-M.0\\n11\\n0.1-1.0\\n8\\n19\\n2\\n1\\n54.6\\n67.0\\n1.0-12\\n34\\n26\\n13\\n13\\n7.1 5\\n6 T\\n12\\n7\\n5\\n60\\n41\\n21.0\u00c2\u00ae\\n8.5\\n1.0-100\\n15\\n20\\n100\\n28\\n27\\nMunch et al. (1980).\\n2 Levine et al. (1991).\\n3 Rickert and Hunter (1972).\\n\u00e2\u0080\u009cLevine et al. (1984).\\n5 Range: 1-5 /urn\\n6 Range: 5 //m\\n31", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0049.jp2"}, "50": {"fulltext": "3.2.2 Suspended Solids in Free Water\\nSurface Wetlands\\nTotal suspended solids are both removed and produced\\nby natural wetland processes. The predominant physical\\nmechanisms for suspended solids removal are flocculation/\\nsedimentation and filtration/interception, whereas suspended\\nsolids production within the wetland may occur due to death\\nof invertebrates, fragmentation of detritus from plants, pro\u00c2\u00ac\\nduction of plankton and microbes within the water column or\\nattached to plant surfaces, and formation of chemical pre\u00c2\u00ac\\ncipitates such as iron sulfide. Figure 3-1 illustrates the most\\nimportant of these processes as they occur in a FWS sys\u00c2\u00ac\\ntem. Resuspension of solids may occur due primarily to tur\u00c2\u00ac\\nbulence created by animals, high inflows, or winds. A brief\\ndiscussion of some of these processes and how they may\\naffect free water surface systems follows.\\n3.2.2.1 Discrete and Flocculant Settling\\nTypically, particulate settling produced by gravity may\\nbe categorized as discrete or flocculant settling. Both sepa\u00c2\u00ac\\nration processes exploit the properties of particle size, spe\u00c2\u00ac\\ncific gravity, shape, and fluid specific gravity and viscosity.\\nDiscrete settling implies that the particle settles indepen\u00c2\u00ac\\ndently and is not influenced by other particles or changes\\nin particle size or density. A mathematical expression for\\nthe terminal settling velocity of the discrete particle may\\nbe derived from Newton\u00e2\u0080\u0099s Law. Under laminar flow condi\u00c2\u00ac\\ntions, which exist in fully vegetated zones of a FWS and in\\nVSBs, the velocity of a spherical particle can be estimated\\nby Stokes\u00e2\u0080\u0099 Law, which states that the settling velocity is\\ndirectly proportional to the square of the nominal diameter\\nand the difference in particle and fluid densities and is in\u00c2\u00ac\\nversely proportional to fluid viscosity. Drag on the particle\\nthat influences settling velocity is affected by particle shape,\\nfluid/particle turbulence, and fluid viscosity.\\nWhereas discrete settling can be estimated given the\\nindependent variables discussed previously, flocculant\\nsettling cannot be so easily determined, requiring experi\u00c2\u00ac\\nmental measurement. It occurs as the result of particle\\ngrowth and, perhaps, change in characteristics overtime.\\nAs a result, particle settling velocity typically increases with\\ntime. Flocculent settling is promoted by the relative move\u00c2\u00ac\\nment of target particles in such a fashion as to cause an\\neffective collision. This relative velocity (velocity gradient)\\nis often calculated as G, the mean velocity gradient, which\\nis a function of power input, dynamic viscosity, and system\\nvolume (Camp and Stein, 1943). Effective velocity gradi-\\nDuckweed, Floating Litter Detritus\\nSettled TSS Detritus from Plants\\nDissolved Oxygen \u00c2\u00ab0 (Anoxic)\\nFully Vegetated Zone\\nRemovals due to Flocculation,\\nSedimentation, Adsorption and\\nAnaerobic Reactions, Primarily\\nAtmospheric\\nReaeration\\n-WAr\\nBOD Oxidation\\nNH 4 -N-^N0 3 -N\\nSolar\\nRadiation\\nSubmerged Vegetation\\nDissolved Oxygen +++(Aerobic)\\nOpen Water Zone\\nTransformations by Aerobic Biological\\nTreatment, Primarily\\nPathogen Kill by Sunlight Time\\nFigure 3-1. Mechanisms that dominate FWS systems\\n32", "height": "4283", "width": "3142", "jp2-path": "constructedwetla00nati_0050.jp2"}, "51": {"fulltext": "ents for flocculation range from 10 to 75 sec- 1 Floccula\u00c2\u00ac\\ntion may occur naturally, as when fresh water flows into\\nsaline water forming a delta, or it may require chemical\\n(coagulant) addition. It may affect large particles (100pm\\nto 1000pm) of low to moderate specific gravity (1.001 to\\n1.01) and small particles (1.0pm to 10pm) with high spe\u00c2\u00ac\\ncific gravity (1.5 to 2.5). The formation of larger flocculant\\nparticles is dependent on the electric charge on the par\u00c2\u00ac\\nticle surface. Like electrical charges on the double layer\\nsurrounding particles may produce particle stability that\\nhinders attachment even if collisions take place. This\\ncharge is sensitive to the composition of the fluid. Adsorp\u00c2\u00ac\\ntion of solutes to the surface occurs as a result of a variety\\nof binding mechanisms, which may eventually result in the\\ndestabilization of the particles and result in particle adhe\u00c2\u00ac\\nsion. There has been little work done on the evaluation of\\nnatural flocculation phenomena with primary effluent or\\nalgal cells. The existence of emergent plant stems in FWS\\nwetlands will promote effective velocity gradients for par\u00c2\u00ac\\nticle collisions, but the adhesion of these particles would\\nbe dependent on surface properties that would be influ\u00c2\u00ac\\nenced by water column quality.\\nIn wetland systems treating primary or septic tank efflu\u00c2\u00ac\\nents (or secondary effluents), particle sizes are mostly in\\nthe colloidal to low supracolloidal range (Table 3-2). Typi\u00c2\u00ac\\ncally sedimentation processes will remove material larger\\nthan about 50pm with specific gravity of about 1.20. The\\nremaining particles are normally the lower density materi\u00c2\u00ac\\nals. Using Stokes\u00e2\u0080\u0099 Law to approximate discrete settling\\nvelocity, particles ranging from 1.0pm to 10pm with a spe\u00c2\u00ac\\ncific gravity ranging from 1.01 to 1.10 will settle at a rate of\\nfrom 0.3 to 4 x 10~ 4 m/d. Typical hydraulic loads to FWS\\nwetlands are in the range of 0.01 to 0.5 m/d (note that the\\nhydraulic load is equivalent to the mean settling velocity of\\na particle that will be removed exactly at that loading). As\u00c2\u00ac\\nsuming the higher settling velocity of 0.3 m/d and a typical\\nFWS system velocity of 50 m/d and depth of 0.8m, the\\nlarger particles would settle by gravity in approximately\\n2.7 days, or 133 m along the wetland longitudinal axis.\\nThe smaller, less dense particles would require over 200\\ndays and a length of over 11,000 m. Therefore it can be\\nconcluded that the larger, denser particles could be re\u00c2\u00ac\\nmoved in the primary zone of a wetland based on simple\\ndiscrete settling theory (see Chapter 4 for more details on\\ndesign). The smaller, neutral-density particles, which make\\nup a significant fraction of septic tank and primary effluent,\\nare not likely removed in this primary zone by simple dis\u00c2\u00ac\\ncrete sedimentation, but may be flocculated due to the\\nvelocity gradients imposed by emergent plant stems in the\\nwater column. It is also possible that some particles may\\nbe intercepted by angular emergent plant tissue as would\\noccur in settling basins equipped with plate or tube set\u00c2\u00ac\\ntlers. Clearly, removal of TSS by a FWS wetland is more\\ncomplex than predicted by discrete settling theory. There\\nis currently insufficient transect data available on waste-\\nwater influents of interest to develop a rational separation\\nmodel, either qualitatively or quantitatively, for TSS removal\\nfrom primary or septic tank effluents in FWS systems.\\nFor wetland systems receiving pond effluents, the pri\u00c2\u00ac\\nmary source of suspended solids for much of the season\\nis algal cells. These cells include green algae, pigmented\\nflagellates, blue-greens, and diatoms. Sizes range from\\nIp to lOOiim, and shapes may range from coccoid to fila\u00c2\u00ac\\nmentous. Specific gravity of actively growing algal cells\\nmay be close to that of water insofar as they must remain\\nsuspended high up within the water column in order to\\nsurvive. Flotation may be accomplished by gas vacuoles\\n(blue-green algae), gelatinous sheathes, or shapes that\\nincrease particle drag. It is believed that wind-induced tur\u00c2\u00ac\\nbulence and vertical water motion greatly influence algae\\ndistribution in ponds (Bella, 1970). Motile algae are not\\ntypically predominant in wastewater pond systems. Once\\nalgal cells die for lack of nutrients and/or sunlight, they\\nlose this flotation characteristic and will settle. Settling ve\u00c2\u00ac\\nlocities range from 0.0 to 1.0 m/s (typically, 0.1 to 0.3 m/s)\\ndepending on species and physiological condition\\n(Hutchinson, 1967). It is likely that many of these cells will\\nbe removed by sedimentation in wetlands covered by\\nemergent vegetation providing shading and reducing wind\\naction. Flocculation of the cells within the wetland is also\\npossible although little experimental evidence has been\\npresented to date. Table 3-4 was generated by Gearheart\\nand Finney (1996), and it represents the only known appli\u00c2\u00ac\\ncation of the particle-size theory to show that colloidal frac\u00c2\u00ac\\ntions are flocculated in FWS systems (see Chapter 4 for\\nfurther explanation). Figure 3-2 illustrates the removal of\\nTSS observed for a fully vegetated FWS wetland treating\\npond effluent. Attempts to settle algae from ponds in open\\nsettling basins have not been successful, however, likely\\ndue to the presence of light and wind action.\\n3.2.2.2 Filtration/Interception\\nFiltration, in the usual sense of this unit process, is not\\nlikely to be significant in surface wetlands. Stems from\\nemergent plants are too far apart to effect significant en\u00c2\u00ac\\ntrapment of the particle sizes found in influent to these\\nwetlands. Furthermore, plant litter and detritus at the sur\u00c2\u00ac\\nface and bottom of the wetland are high in void fraction\\nsuch that filtration is not likely an important mechanism.\\nOn the other hand, interception and adhesion of particles\\non plant surfaces could be significant mechanisms for re\u00c2\u00ac\\nmoval. The efficiency of particle collection would be de\u00c2\u00ac\\npendent on particle size, velocity, and characteristics of\\nthe particle and the plant surfaces that are impacted. In\\nwetlands, plant surfaces in the water column are coated\\nwith an active biofilm of periphyton. This biofilm can ad\u00c2\u00ac\\nsorb colloidal and supracolloidal particles as well as ab\u00c2\u00ac\\nsorb soluble molecules. Depending on the nature of the\\nsuspended solids, they may be metabolized and converted\\nto soluble compounds, gases, and biomass or may physi\u00c2\u00ac\\ncally adhere to the biofilm surfaces to eventually be\\nsloughed off into the surrounding water column. Similar\\nreactions may occur in the surface detritus or at the surficial\\nbottom sediment. To date, there have been no definitive\\nstudies reported on the importance of this mechanism in\\nsuspended solids removal in free surface wetlands.\\n3.2.2.3 Resuspension\\nIn FWS wetlands, velocity induced resuspension is mini\u00c2\u00ac\\nmal. Water velocities are too low to resuspend settled par-\\n33", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0051.jp2"}, "52": {"fulltext": "Table 3-4. Fractional Distribution of Bod, COD, Turbidity, and SS in the Oxidation Pond Effluent and Effluent from Marsh Cell 5 (Gearheart and\\nFinney, 1996)\\nBOD\\nCOD\\nTurbidity\\nSS\\nmg/I\\nmg/I\\nNTU\\nMG/L\\nOxidation Pond\\nFraction\\nTotal\\n27.5\\n100\\n80\\n100\\n11.0\\n100\\n31.0\\n100\\nSettleable\\n3.7\\n13\\n5\\n6\\n2.5\\n23\\n5.8\\n19\\nSupracolloidal\\n13.7\\n50\\n23\\n29\\n5.3\\n48\\n25.2\\n81\\nColloidal, soluble\\n10.1\\n37\\n52\\n65\\n3.2\\n29\\nMarsh Fraction\\nTotal\\n4.8\\n100\\n50\\n100\\n3.9\\n100\\n2.3\\n100\\nSettleable\\n0\\n0\\n0\\n0\\n0.6\\n15\\n0.3\\n13\\nSupracolloidal\\n1.2\\n24\\n4\\n8\\n1.6\\n42\\n2.0\\n87\\nColloidal, soluble\\n3.6\\n76\\n46\\n92\\n1.7\\n43\\nFigure 3-2. Weekly transect TSS concentration for Areata cell 8 pilot receiving oxidation pond effluent (EPA, 1999)\\ntides from bottom sediments or from plant surfaces. Fur\u00c2\u00ac\\nthermore, fully vegetated wetlands provide excellent sta\u00c2\u00ac\\nbilization of sediments by virtue of sediment detritus and\\nroot mats. The reintroduction of settled solids in wetlands\\nis most likely due to gas-lift in vegetated areas or\\nbioturbation or wind-induced turbulence in open water ar\u00c2\u00ac\\neas. Wetland sediments and microdetritus are typically near\\nneutral buoyancy, flocculant, and easily disturbed.\\nBioturbation by fish, mammals, and birds can resuspend\\nthese materials and lead to increases in wetland suspended\\nsolids. The oxygen generated by algae and submerged\\nplants, nitrogen oxides and nitrogen gas from denitrifica\u00c2\u00ac\\ntion, or methane formed in anaerobic process may cause\\nflotation of particulates (Kadlec and Knight, 1996).\\nAs discussed previously, the generation of new biom\u00c2\u00ac\\nass by primary production or through the metabolism of\\ninfluent wastewater constituents will eventually result in\\nthe return of some suspended materials back into the wa\u00c2\u00ac\\nter column. The magnitude of wetland particulate cycling\\nis large, with high internal levels of gross sedimentation\\nand resuspension, and almost always overshadows influ\u00c2\u00ac\\nent TSS loading in natural or tertiary treatment wetlands.\\nThe effluent TSS from a wetland rarely results directly from\\nnonremovable TSS in the influent wastewater and is often\\ndictated by the wetland processes that generate TSS in\\nthe wetland. Typical background TSS concentrations ex\u00c2\u00ac\\npected in FWS wetlands appear in Table 3-5. It should be\\nnoted that large expanses of open wetland prior to dis-\\n34", "height": "4283", "width": "3142", "jp2-path": "constructedwetla00nati_0052.jp2"}, "53": {"fulltext": "charge structures could result in unusually high effluent\\nTSS concentrations due to the production of excessive\\namounts of algae and induced high levels of wildlife activi\u00c2\u00ac\\nties that could produce effluent variations as typified in Fig\u00c2\u00ac\\nure 3-3.\\nHigh incoming TSS or organic loading will result in a\\nmeasurable increase in bottom sediments near the inlet\\nstructure (Van Oostrom and Cooper, 1990; EPA, 1999).\\nHowever, no FWS treatment wetland has yet required\\nmaintenance because of sediment accumulation, includ\u00c2\u00ac\\ning some that have been in service for over 20 years.\\n3.2.3 Suspended Solids in Vegetated\\nSubmerged Beds\\nOne of the primary intermediate mechanisms in the re\u00c2\u00ac\\nmoval of suspended solids by VSB systems is the floccu\u00c2\u00ac\\nlation and settling of colloidal and supracolloidal particu\u00c2\u00ac\\nlates. These systems are relatively effective in TSS removal\\nbecause of the relatively low velocity and high surface area\\nin the VSB media. VSBs act like horizontal gravel filters\\nand thereby provide opportunities for TSS separations by\\ngravity sedimentation (discrete and flocculant), straining\\nand physical capture, and adsorption on biomass film at\u00c2\u00ac\\ntached to gravel and root systems. Clogging of the filter\\nmedia has been of some concern especially with high TSS\\nloading, but documentation of this phenomenon has not\\nbeen forthcoming. The accumulation of recalcitrant or\\nslowly degradable solids may eventually lead to increased\\nheadlosses near the influent end of the system. Design\\nfeatures to overcome this are described in Chapter 5.\\nThe importance of vegetation in VSB systems has been\\ndebated for some time. Several recent studies have com\u00c2\u00ac\\npared pollutant removal performance of planted and\\nunplanted VSB systems and have shown no significant dif\u00c2\u00ac\\nference in performance (Liehr, 2000; Young et al., 2000).\\nThe importance of plant type has also been evaluated\\n(Gersberg et al., 1986; Young et al., 2000). Maximum root\\nlength and growth rates have been reported. Although some\\ninvestigators claimed that certain treatment goals are likely\\nto benefit from certain plants, these claims have not been\\nsustained by others (Young et al., 2000). The extension of\\nroot system within the gravel bed is dependent on system\\nloading, plant type, climate, and wastewater characteristics,\\namong other variables. It appears that a dominant fraction\\nof the flow passes below the root system in VSB facilities.\\nThe role of root surfaces in TSS removal has not been proven\\nexperimentally.\\nThe contributions of internal biological processes to ef\u00c2\u00ac\\nfluent TSS is likely similar to that found in FWS systems,\\nalthough algal contributions should be negligible.\\nResuspension of separated solids is not likely since sys\u00c2\u00ac\\ntem velocities are low and scouring should not be signifi\u00c2\u00ac\\ncant. Furthermore, bioturbation in these systems should\\nbe minimal. Background concentrations for VSB systems\\nhave not yet been definitively documented with reliable\\ninformation.\\n3.3 Mechanisms for Organic Matter\\nSeparations and Transformations\\n3.3.1 Description and Measurement\\nOrganic matter in wastewater has been measured in a\\nnumber of ways over the years. Because the organic frac\u00c2\u00ac\\ntion in wastewater is often complex and the concentra\u00c2\u00ac\\ntions of the individual components relatively low, analyses\\nTable 3-5. Background Concentrations of Contaminants of Concern in FWS Wetland Treatment System Effluents\\nConstituent\\nRange (mg/L)\\nTypical (mg/L)\\nFactors Governing Value\\nReference\\nTSS\\n2-5\\n3\\nPlant types, coverage,\\nClimate, wildlife\\nReed et al.,1995;\\nKadlec and Knight, 1996\\nBOD 5\\n2-8\\n5\\nPlant types, coverage,\\nClimate, plant density\\nReed et al., 1995\\nGearheart, 1992\\nBOD 5 2\\n5-12\\n10\\nPlant types, coverage,\\nClimate, plant density\\nKadlec and Knight, 1996\\nTN\\n1-3\\n2\\nPlant types, coverage,\\nClimate, oxic/anoxic\\nKadlec and Knight, 1996;\\nReed et al., 1995\\nNH -N\\n4\\n0.2-1.5\\n1.0\\nPlant types, coverage,\\nClimate, oxic/anoxic\\nKadlec and Knight, 1996;\\nReed et al., 1995\\nTP\\n0.1-0.5\\n0.3\\nPlant types, coverage,\\nClimate, soil type\\nKadlec and Knight, 1996;\\nReed et al., 1995\\nFecal Coli CFU/100 ml\\n50-5,000\\n200\\nPlant types, coverage,\\nClimate, wildlife\\nWatson et al, 1987;\\nGearheart et al., 1989\\nWetland system with significant open water and submergent vegetation\\n2 Wetland system fully covered by emergent vegetation\\n35", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0053.jp2"}, "54": {"fulltext": "O)\\nE\\no\\no\\nCD\\nc\\nD\\n3\\nLU\\nJuly-91 July-92\\nJuly-93 July-94 July-95 July-96 July-97\\nDate\\nFigure 3-3. Variation in effluent BOD at the Areata enhancement marsh (EPA, 1999)\\nare often performed on the aggregate amount of organic\\nmatter comprising organic constituents with common char\u00c2\u00ac\\nacteristics. Methods for total organic carbon (TOC) and\\nvolatile solids (VS) measure the total amount of organic\\nmatter present. Chemically oxidizable organic matter is\\noften measured as Chemical Oxygen Demand (COD),\\nexpressed in units of oxygen, and biodegradable organic\\nmatter is determined by the Biochemical Oxygen Demand\\n(BOD) procedure. All of these aggregate methods have a\\nplace in assessing pollutant levels in water, but none will\\nprovide information on specific organic molecules or their\\nfate in treatment processes. As a result, any qualitative or\\nquantitative model attempting to express mechanistic be\u00c2\u00ac\\nhavior of organic matter in a system is an empirical model\\nbased on observation of the parameter of interest. In wet\u00c2\u00ac\\nlands, physical, chemical, and biochemical reactions will\\ntransform and/or separate organic matter, often leading to\\ndifferent species of organic molecules. Thus the BOD (or\\nCOD, or TOC) of the influent to a wetland does not mea\u00c2\u00ac\\nsure the same organic constituents that appear in the ef\u00c2\u00ac\\nfluent. This phenomenon is no different than what has al\u00c2\u00ac\\nready been discussed for TSS.\\nMost regulatory agencies today establish wastewater\\ndischarge permit limits based on BOD values; thus much\\nof the data available is expressed as that parameter. It is\\ndifficult to use BOD in mass balance calculations insofar\\nas it is a dynamic measure conducted over a finite time\\n(usually five days) and at a specified temperature (usually\\n20\u00c2\u00b0C). One can use it to estimate roughly the oxygen re\u00c2\u00ac\\nquirements for aerobic systems if the rate of oxygen de\u00c2\u00ac\\nmand exertion (expressed by the biodegradation constant,\\nk) is known. To further complicate the use of this param\u00c2\u00ac\\neter, the analysis of BOD may or may not include the ni\u00c2\u00ac\\ntrogenous oxygen demand (NOD), which may be ex\u00c2\u00ac\\npressed concurrently or simultaneously with the carbon\u00c2\u00ac\\naceous oxygen demand. Thus primary influent BOD may\\nmeasure carbonaceous organic matter, whereas effluent\\nfrom the wetland may include both carbonaceous and ni\u00c2\u00ac\\ntrogenous (ammonia) matter depending on the system.\\nTable 3-1 presents typical values of total and soluble BOD\\nfor primary and septic tank effluents as well as lagoon ef\u00c2\u00ac\\nfluents. Values of COD and VSS (volatile suspended sol\u00c2\u00ac\\nids) are also provided. There is no simple way to relate\\nBOD and COD values for wastewater insofar as the differ\u00c2\u00ac\\nences that exist between degradable and chemically oxi\u00c2\u00ac\\ndizable fractions.\\n3.3.2 Organic Matter in Free Water\\nSurface Wetlands\\n3.3.2.1 Physical Separations of Organic Matter\\nTable 3-4 illustrates that influents typically received by\\nFWS systems contain some particulate organic matter. A\\nsignificant amount of the influent from septic and primary\\neffluents is in the dissolved and colloidal fraction as would\\nbe expected, whereas pond effluents may contain a size\u00c2\u00ac\\nable fraction of supracolloidal material represented by al\u00c2\u00ac\\nga! cells. Separation of particulate organic matter would\\noccur by the same mechanisms as those described for\\nTSS. It is not uncommon to find organic matter removal in\\nthe influent end of a FWS system that parallels TSS re\u00c2\u00ac\\nmoval. Figure 3-4 illustrates predominant organic matter\\nseparations and transformations that occur in FWS sys\u00c2\u00ac\\ntems. As noted in section 3.3.2.2, biochemical transforma\u00c2\u00ac\\ntions of the entrapped and settled organic matter will greatly\\ninfluence the apparent removal of total organic matter within\\nthe water column.\\nSoluble organic matter may also be removed by a num\u00c2\u00ac\\nber of separation processes. Adsorption/absorption (the\\nmovement of contaminants from one phase to another) is\\nan important process affecting some organic molecules.\\nThe process is often referred to as sorption to cover both\\nadsorption and absorption processes in natural systems\\nbecause the exact manner in which partitioning to the sol\u00c2\u00ac\\nids occurs is often not known. Partitioning of organic mat\u00c2\u00ac\\nter between solids can be understood and predicted to\\n36", "height": "4283", "width": "3142", "jp2-path": "constructedwetla00nati_0054.jp2"}, "55": {"fulltext": "some degree using physiochemical properties of the or\u00c2\u00ac\\nganic (e.g., water solubility, octanol-water partition coeffi\u00c2\u00ac\\ncient). Sorption is often described by an isotherm\\n(Freundlich) relationship. The degree of sorption and its\\nrate are dependent on the characteristics of both the or\u00c2\u00ac\\nganic and the solid. In wetlands, the important solid sur\u00c2\u00ac\\nfaces would include the plant litter and detritus occurring\\nat the wetland surface or on the bottom and plant stems\\nand leaves often covered by a periphyton biofilm. The sorp\u00c2\u00ac\\ntion process may be reversible or irreversible depending\\non the organic and solid. Sorbents may eventually become\\n\u00e2\u0080\u009csaturated\u00e2\u0080\u009d with sorbate although often the sorbed organic\\nis biochemically transformed, renewing the sorbent capac\u00c2\u00ac\\nity. Many of the wetland solid surfaces are also renewed\\nby continuous turnover of biomass that makes up the ma\u00c2\u00ac\\njor component of the sorbent. It is believed that sorption\\nprocesses play an important role in organic separation in\\nwetlands, but the processes have not been adequately\\nquantified at this time.\\nVolatilization may also account for loss of certain organ\u00c2\u00ac\\nics. In this reaction, the organic partitions to the air. The\\npropensity for a given compound to move from liquid to\\ngaseous phase is measured by Henry\u00e2\u0080\u0099s constant. The\\nhigher the value for a compound, the more likely it will par\u00c2\u00ac\\ntition to the gaseous phase. Generally, organic matter en\u00c2\u00ac\\ntering a wetland receiving pretreatment will not contain sig\u00c2\u00ac\\nnificant quantities of volatile compounds (VOCs). Faculta\u00c2\u00ac\\ntive lagoons have been shown to remove 80 to 96% of\\nvolatile organics from municipal wastewater (Hannah et\\nal., 1986). However, some of these organic materials may\\nbe produced by biological transformations. Precipitation\\nreactions with organic matter found in wetland influents\\nhave not been documented for municipal wastewater.\\n3.3.2.2 Biological Conversions of Organic\\nMatter\\nThe Biochemistry\\nBiochemical conversions are important mechanisms\\naccounting for changes in concentration and composition\\nof biodegradable organic matter in wetlands. They may\\naccount for removal of some organic constituents by vir\u00c2\u00ac\\ntue of mineralization or gasification and the production of\\norganic matter through synthesis of new biomass. Organ\u00c2\u00ac\\nisms will consume organic matter (and inorganic matter\\nas well) in order to sustain life and to reproduce. The or\u00c2\u00ac\\nganic matter in wastewater serves as an energy source as\\nwell as a source of molecular building blocks for biomass\\nsynthesis. The reactions occurring therefore are ones that\\nprepare the molecule for use by the organism or are di\u00c2\u00ac\\nrectly involved in the extraction of energy or incorporation\\nof building blocks in the synthesis reaction. End products\\nof the reaction are waste products of the system. These\\nDIC Dissolved Inorganic Carbon\\nVOC Volatile Organic Carbon\\nPIC Particulate Inorganic Carbon\\nFigure 3-4. Carbon transformations in a FWS wetland\\n37", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0055.jp2"}, "56": {"fulltext": "reactions include oxidation/reduction processes, hydroly\u00c2\u00ac\\nsis, and photolysis.\\nSince energy is a key element in the biochemical sys\u00c2\u00ac\\ntem, the reaction is classified as chemotrophic or pho-\\ntotrophic depending on whether the reaction utilizes a\\nchemical source of energy or light energy. The environ\u00c2\u00ac\\nment greatly influences the energetics of the reaction that\\nis driven by electron transfers. If the element at the end of\\nthis set of transfers is oxygen, the reaction is referred to as\\nan aerobic reaction. Aerobic metabolism requires dissolved\\noxygen and results in the most efficient conversion of bio\u00c2\u00ac\\ndegradable materials to mineralized end products, gases,\\nand biomass. Anoxic (anaerobic respiration) reactions use\\nnitrates, carbonates, or sulfates as terminal electron ac\u00c2\u00ac\\nceptors (in place of oxygen). Terminal electron acceptors\\nare subsequently reduced in these reactions, producing\\nend products such as nitrogen oxides, free nitrogen, sul\u00c2\u00ac\\nfur, thiosulfate, and so forth. These reactions are typically\\nless efficient (biomass produced per unit substrate utilized)\\nthan aerobic reactions and produce mineralized end prod\u00c2\u00ac\\nucts and gases, but less biomass per unit of substrate con\u00c2\u00ac\\nverted. Anaerobic metabolism takes place in the absence\\nof dissolved oxygen and uses organic matter as the termi\u00c2\u00ac\\nnal electron acceptor as well as the electron donor. These\\ntransformations are the least efficient of the biochemical\\nreactions and will not result in the reduction in BOD (or\\nCOD) unless hydrogen or methane is produced, since elec\u00c2\u00ac\\ntrons released in the oxidation of the organic are passed\\nto electron acceptors (reduced products such as alcohols\\nand organic acids) that remain in the medium. The only\\nenergy loss in the system is that due to microbial ineffi\u00c2\u00ac\\nciencies.\\nThe transformations described previously rely on chemi\u00c2\u00ac\\ncal energy to drive them. A very important transformation\\nthat takes place in open water areas of FWS wetlands uses\\nsunlight energy to drive the reaction (photosynthesis). In\\nthese reactions, inorganic carbon (C0 2 and carbonates) is\\nsynthesized to form biomass (primary production), releas\u00c2\u00ac\\ning oxygen. Thus both oxygen and organic matter are pro\u00c2\u00ac\\nduced within the system.\\nThe previous reactions and their stoichiometry, equilib\u00c2\u00ac\\nrium, and rates are dependent on environmental variables\\nincluding dissolved oxygen, temperature, oxidation/reduc\u00c2\u00ac\\ntion potential, and chemical characteristics, to name a few.\\nAn excellent reference on microbial metabolism in waste-\\nwater systems can be found in Grady and Lim (1980).\\nThe Organisms\\nBiochemical reactions of importance in FWS constructed\\nwetlands are carried out by a large number of organism\\nclasses. They may be classified based on their position in\\nthe energy or food chain (producers, consumers, or de\u00c2\u00ac\\ncomposers) or on their life form or habitat. A classical de\u00c2\u00ac\\nscription relative to a wetland habitat would include\\nBenthos\u00e2\u0080\u0094organisms attached or resting on the bot\u00c2\u00ac\\ntom within the plant litter and detritus or living within\\nthe sediments\\nPeriphyton\u00e2\u0080\u0094both plants and animals attached to stems\\nand leaves of rooted plants\\nPlankton\u00e2\u0080\u0094floating plants or animals whose move\u00c2\u00ac\\nments are generally dictated by currents\\nNeuston\u00e2\u0080\u0094plants or animals resting or swimming on\\nthe wetland surface\\nNekton\u00e2\u0080\u0094swimming organisms able to navigate at will\\nAlthough no quantitative assessments have been re\u00c2\u00ac\\nported, it is believed that the decomposers (bacteria, acti-\\nnomycetes, and fungi) play the most important role in wet\u00c2\u00ac\\nlands relative to the removal of organic matter by way of\\nmineralization and gasification. They are associated with\\nall habitats listed. They are also responsible for the syn\u00c2\u00ac\\nthesis of biomass and the production of organic metabolic\\nend products that may leach into the water column. These\\norganisms are often classified as aerobic, facultative, or\\nanaerobic, depending on the type of reactions that they\\nperform. They may also be classified with respect to their\\nsource of energy and the type of chemical compound that\\nthey use as a source of carbon.\\nThe primary producers generate organic residues within\\nthe wetland and add dissolved oxygen to the system. They\\nalso play an important role in the removal and recycling of\\nnutrients in the wetland. The macrophytes will also pre\u00c2\u00ac\\nvent incoming radiation from entering the water column.\\nThis shading will affect the growth of plant periphyton, phy\u00c2\u00ac\\ntoplankton, and submerged macrophytes, will interfere with\\nsurface mass transfer of oxygen, and will moderate wet\u00c2\u00ac\\nland water temperatures. These rooted plants provide sig\u00c2\u00ac\\nnificant submerged surfaces for growth of periphyton. The\\nsubmerged surface area provided by selected FWS veg\u00c2\u00ac\\netation varies from 2.2 to 6.5 m 2 /m 2 for a wetland 0.5 m\\ndeep, depending on plant species and coverage (EPA,\\n1999).\\nOxygen Transfer to FWS Wetlands\\nOxygen is a critical element in the biochemical transfor\u00c2\u00ac\\nmation of organic matter (as well as other compounds to\\nbe described later). As briefly discussed previously, bio\u00c2\u00ac\\nchemical reactions that use dissolved oxygen (DO) are\\nefficient processes and yield mineralized end products. An\\naerobic environment is highly desirable in wastewater treat\u00c2\u00ac\\nment systems in which the target is effective removal of\\nBOD. There are three possible sources of DO in wetland\\nsystems\u00e2\u0080\u0094surface aeration, photosynthesis, and plant oxy\u00c2\u00ac\\ngen transfer.\\nWhen a gas is dissolved in water, the process is gener\u00c2\u00ac\\nally treated as a mass transfer occurring over four steps\\n(two-film theory). It presumes a thin but finite gaseous and\\nliquid film at the air-water interface. The gas must pass\\nthrough the bulk gas phase, then through the gas film, to\\nthe liquid film, and then into the bulk liquid. For oxygen,\\nthe liquid film is the rate-limiting step and controls the rate\\nof mass transfer, although for a quiescent water body, the\\nbulk liquid transport may control the process. By use of\\nFick\u00e2\u0080\u0099s Law, the diffusional process can be modeled pro-\\n38", "height": "4283", "width": "3142", "jp2-path": "constructedwetla00nati_0056.jp2"}, "57": {"fulltext": "ducing the commonly used oxygen mass transfer relation\u00c2\u00ac\\nship:\\ndC/dt K L a (C s -C) 3 1\\nWhere C concentration of oxygen in water (M/L 3\\nt time (T)\\nK L a overall mass transfer coefficient for oxy\u00c2\u00ac\\ngen in water (1/T)\\nC s steady-state oxygen saturation concentra\u00c2\u00ac\\ntion in water (M/L 3\\nC o the dissolved oxygen concentration in the\\nbulk water (M/L 3\\nThis equation indicates that the rate of oxygenation is\\ndependent on the overall mass transfer coefficient, the\\nsteady-state DO saturation concentration for oxygen in\\nwater, and the bulk water DO. Generic symbols for mass\\n(M), time (T), and length (L) are employed for units. The\\nvalue of K L a is a function of the physical characteristics of\\nthe wetland. For typical FWS systems, isotropic turbulence\\nwould occur whereby there is neither a significant velocity\\ngradient nor shearing stress. For this system, the value of\\nK L a would be a direct function of wetland velocity and the\\noxygen molecular diffusion coefficient and an indirect func\u00c2\u00ac\\ntion of system depth (O\u00e2\u0080\u0099Connor and Dobbins, 1958) ac\u00c2\u00ac\\ncording to the following equation:\\nK 2 [D l U] 1/2 H 3/2 (3-2)\\nWhere K, surface reaeration coefficient (1/T)\\nD l oxygen molecular diffusion coefficient (L 2 /T)\\nU velocity of flow (L/T)\\nH depth (L)\\nAn estimate of surface aeration in an open water zone\\nof a FWS system can be made assuming a typical wet\u00c2\u00ac\\nland water velocity of 30 m/d and a depth of 0.3 m. At\\n20\u00c2\u00b0C, the mass transfer coefficient would be approximately\\n0.43/d. Assuming a bulk wetland water DO of 0 mg/L, the\\nmass transfer of oxygen would be about 3.9 mg/L/d or 1.2\\ng/m 2 /d. For more realistic values of the water DO, the trans\u00c2\u00ac\\nfer would range from 0.5 to 0.9 g/m 2 /d. These numbers\\ncompare favorably with values reported by the TVA, which\\nrange from 0.50 to 1.0 g/m 2 /d (Watson et al., 1987). These\\nopen water-zone values will be higher than would be ob\u00c2\u00ac\\nserved in wetlands with plant cover because plant debris,\\nfloating plants, and emergent plant surfaces impede mass\\ntransfer across the surface. In the open zones, the bulk\\nwater DO (which might approach 0 mg/L) would not be the\\nsame as the DO near the water surface (which might ap\u00c2\u00ac\\nproach saturation during the daylight hours). See Figure\\n3-5 for a submergent plant (open water) zone, which illus\u00c2\u00ac\\ntrates the inaccuracy that would result in assuming a DO\\nof 0 mg/L in the bulk water column. The actual DO values\\nin Figure 3-5 are from polishing FWS applications and are\\ntherefore higher than would be expected in a treatment\\nFWS system. Actually, a value near zero DO is normal in\\nfully vegetated or emergent zones (Figure 3-5b) of these\\nlatter systems.\\nOxygen will also be transferred to the wetland by virtue\\nof photosynthesis carried out by phytoplankton, periphy\u00c2\u00ac\\nton, and submerged plants. The general relationship for\\nphotosynthesis of green plants implies that approximately\\n2.5 g of oxygen would be evolved per g of carbon fixed as\\ncell mass. In the absence of sunlight energy, oxygen would\\nbe consumed by these plants in respiration. Presuming\\nhighly productive conditions, about 1.0 g C/m 2 /d may be\\nproduced during daylight hours resulting in a generation\\nof 2.5 g 0 2 /m 2 /d (Lewin, 1962). One may deduce a some\u00c2\u00ac\\nwhat larger value presuming typical net primary produc\u00c2\u00ac\\ntion of a wetland to be about 4.0 g total biomass/m 2 /d\\n(Mitsch and Gosselink, 1993) and about 1.0 g 0 2 /g net\\nbiomass produced by photosynthesis. These numbers\\nimply that in open areas where sufficient photosynthesis\\nmight occur, oxygen should be available for aerobic oxi\u00c2\u00ac\\ndation within the water column, at least during part of the\\nday. Active plant respiration during the evening may com\u00c2\u00ac\\npletely negate the oxygenation estimated during daylight\\nhours, however. The DO concentrations have been docu\u00c2\u00ac\\nmented for both emergent and submergent plant zones in\\nthe Areata tertiary/polishing/enhancement marsh system\\n(Figure 3-5). Clearly, the submergent plant zone provided\\nmore DO by virtue of greater photosynthesis and surface\\naeration. This figure also clearly demonstrates that the\\nbulk water column is not mixed with respect to DO, being\\nhighest at the surface where atmospheric reaeration and\\nphotosynthesis are predominant. Rose and Crumpton\\n(1996) have demonstrated the effects of emergent mac\u00c2\u00ac\\nrophyte stands and open water in a prairie wetland. They\\nfound that the emergent sites had low DO concentrations\\nand were almost always anoxic, whereas sites at the edge\\nof the stand had higher DO concentrations, with signifi\u00c2\u00ac\\ncant increases in DO during the daylight hours. The open\\nwater areas consistently exhibited higher values of DO\\nwith diurnal changes up to 10 mg/L. These results are\\nconsistent with the presumption that emergent stands pro\u00c2\u00ac\\nvided a heavy canopy cover, along with small floating\\nplants and plant litter that obscured light penetration and\\nsubsequent photsynthesis and also affected surface aera\u00c2\u00ac\\ntion. The plant litter stands at the margin were open and\\nallowed light penetration, encouraging photosynthesis by\\nperiphyton, phytoplankton, and submerged plants. Open\\nareas allowed even more opportunity for photosynthesis\\nas well as surface aeration.\\nThe role of rooted, emergent plants on oxygen transfer\\nto the wetland system is subject to controversy. Because\\nthese wetland plants are typically rooted in soils that are\\nanaerobic, they have evolved special airways to allow the\\nefficient movement of atmospheric oxygen to the root sys\u00c2\u00ac\\ntem. Dead and broken plant shoots may also allow for trans\u00c2\u00ac\\nport of some oxygen to the root zone. There is a sufficient\\nbody of evidence to show that significant amounts of oxy\u00c2\u00ac\\ngen are transported down these passages and that other\\ngases, such as carbon dioxide, hydrogen, and methane,\\nmay pass upward through these same channels. Gas trans\u00c2\u00ac\\nfer is the result of humidity-, thermally-, and/or Venturi-in\u00c2\u00ac\\nduced convective flow as well as diffusion. Gas exchange\\nthrough the root surface is by diffusion. Although photo-\\n39", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0057.jp2"}, "58": {"fulltext": "a) Vertical distribution of DO in a submergent\\nplant zone of the Areata Enhancement Marsh\\nO)\\ng\\nO\\no\\nGearheart-6\\nGearheart-4\\nGearheart-2\\nmiddle\\nbottom\\nb) Vertical distribution of DO in an emergent\\nplant zone of the Areata Enhancement Marsh\\nFigure 3-5. Dissolved oxygen distribution in emergent and submergent zones of a tertiary FWS (EPA, 1999)\\nsynthesis does not seem to enhance the concentration of\\noxygen in the shoots, sunlight can cause convection to\\nincrease because light amplifies the degree of stomatal\\nopenings in the leaves, and higher temperatures cause\\nsteeper diffusion gradients for gases (Armstrong and\\nArmstrong, 1990). A large proportion of the oxygen enter\u00c2\u00ac\\ning the plant is vented to the atmosphere instead of being\\nused in plant respiration or effluxed to the root system.\\nA number of studies have been made on the transport of\\noxygen by plants. Only one field study has been reported\\non an operating wetland (Brix and Schierup, 1990). They\\nfound that for Phragmites in both FWS and VSB systems,\\nthe oxygen transported almost exactly balanced respira\u00c2\u00ac\\ntion by the plants. The range of values reported by other\\ninvestigators is 0 to 28.6 g 0 2 /m 2 /d, whereas rates of 0 to 3\\ng 0 2 /m 2 /d were found in 15 of the 23 studies. Kadlec and\\nKnight (1996) pointed out that studies to date infer that\\noxygen transfer measurements made from BOD and am\u00c2\u00ac\\nmonium losses are not accurate. At present, it seems rea\u00c2\u00ac\\nsonable to presume that plant oxygen transfer is not an\\nimportant source of oxygen in most wetland systems.\\nThe DO concentration found in FWS systems is depen\u00c2\u00ac\\ndent on the rate of oxygen transfer and the rate of oxygen\\nuptake. If one equals the other, system DO will remain\\nconstant. If respiration exceeds transfer, DO values will\\nfall to zero and anaerobic conditions will prevail. The prin\u00c2\u00ac\\nciple consumers of oxygen (respiration) in wetlands include\\nmicroorganisms that consume oxygen during normal ex\u00c2\u00ac\\nogenous and endogenous respiration and plants that carry\\nout respiration when sunlight energy is unavailable as an\\nenergy source. Sources of oxygen requirements will in\u00c2\u00ac\\nclude those from influent organic matter, stored organic\\nmatter in living biomass (endogenous respiration), dead\\nplant litter at the surface and bottom of the wetland, dead\\nperiphyton and plankton suspended in the water column\\nor residing at the wetland surface or within the benthal\\ndeposits, and influent ammonium nitrogen. One factor that\\nshould be considered in wetland design is the determina\u00c2\u00ac\\ntion of an oxygen balance. A mass balance on oxygen is\\ndifficult to perform in FWS systems owing to the highly\\ncomplex and dynamic characteristics of the system. An\\nestimate of influent oxygen demand (carbonaceous and\\nnitrogenous) is possible, but uptake due to plant respira\u00c2\u00ac\\ntion and decomposition of plant carbon is more difficult to\\npredict (Table 3-6). The sources of oxygen are also diffi\u00c2\u00ac\\ncult to quantify as discussed previously. Total coverage of\\nwetlands by emergent plants results in little reliable oxy\u00c2\u00ac\\ngenation (some oxygen will likely be produced by periphy\u00c2\u00ac\\nton near the water surface, but quantification of this is un\u00c2\u00ac\\nreliable at the present time). Use of open areas to pro\u00c2\u00ac\\nmote photosynthesis by submerged plant and plankton\\nappears to be a logical approach, but again, quantitative\\nestimates of transfer are difficult to assess based on cur\u00c2\u00ac\\nrent data. It should be emphasized that DO is not a steady\\nvalue in wetlands but will vary in a diurnal fashion with\\nphotosynthesis. It is not unrealistic to presume that wide\\nfluctuations in DO will occur, especially in active systems.\\nAs will be described later, the DO concentration will also\\nchange along the wetland length as demands and sup\u00c2\u00ac\\nplies change.\\nFWS Biological Fleactions\\nInfluent particulate organic matter may be entrapped\\nwithin biofilms attached to emergent plant surfaces or ac\u00c2\u00ac\\ncumulated on the wetland floor within the plant litter and\\nsediments (Figure 3-4). Experience suggests that much of\\nthis material is accumulated very close to the influent struc-\\n40", "height": "4283", "width": "3142", "jp2-path": "constructedwetla00nati_0058.jp2"}, "59": {"fulltext": "Table 3-6. Wetland Oxygen Sources and Sinks\\nProcess\\nSource\\nFWS\\nSink\\nVSB\\nSource Sink\\nReaeration\\no\\nPhotosynthesis\\nPlant 0 2 Transpiration\\nInfluent BOD ult (oxid./endog.)\\n(t)\\n(t)\\nInfluent NH.\\n(t)\\nPlant Respiration\\n(t)\\nPlant Decomposition\\n(t)\\nmay be estimated in some instances\\n(t) May be calculated for wetland system\\nture. In addition, particulate organic matter deriving from\\ndead plant litter accumulates on the floor of the wetland as\\nwell as in surface mats. The quantity of this material is\\ndependent on the species of plants growing in the area\\nand their coverage. Emergent plant communities have\\nhigher potential production rates than submerged commu\u00c2\u00ac\\nnities (Wetzel, 1983). The accumulated organic debris at\\nthe wetland floor degrades at different rates depending on\\nthe composition of the organic matter. Influent particulate\\norganic matter from primary settling or septic tank efflu\u00c2\u00ac\\nents is easily degradable in most environments. Algal cells\\nfrom pond effluents are biologically less available. Emer\u00c2\u00ac\\ngent macrophytes produce much more structural material\\n(lignin, cellulose, and hemicellulose) than do submerged\\nand floating leafed plants, and this material degrades rela\u00c2\u00ac\\ntively slowly (Godschalk and Wetzel, 1978).\\nMuch of the particulate organic matter would be hydro\u00c2\u00ac\\nlyzed, producing lower molecular weight organic com\u00c2\u00ac\\npounds that are more soluble in water, which leach back\\ninto the water column and contribute to the soluble BOD\\ndownstream. In the presence of oxygen, these compounds\\nwould be oxidized by microbes to C0 2 oxidized forms of\\nnitrogen and sulfur, and water. Under anaerobic conditions,\\nthese compounds may be converted to low molecular\\nweight organic acids and alcohols. Under strict anaerobic\\nconditions, methanogenesis may occur whereby these\\ncompounds are converted to gaseous end products of CH 4\\nC0 2 and H 2 In the presence of sulfates, sulfur-reducing\\nmicrobes will convert these low molecular weight organic\\ncompounds to C0 2 and sulfide. Either of these anaerobic\\nreactions will essentially remove organic matter from the\\nsystem. As the degradability of the material decreases,\\nthe decomposition rates slow and the nature of the meta\u00c2\u00ac\\nbolic end products change. It has been suggested that\\nsoluble organic matter has a half-life of about three days\\nwhile organic sediment may exhibit a half-life on the order\\nof four months (EPA, 1999). The rates of degradation are\\nalso temperature dependent. Thus sediment organic mat\u00c2\u00ac\\nter may accumulate during the colder months and be more\\nrapidly degraded in the spring when water temperatures\\nrise. This increase in degradation will result in an increase\\nin soluble organic matter released to the water column and\\na concomitant increase in oxygen demand, a phenomenon\\nthat has also been observed in facultative ponds for nearly\\na century.\\nThe result of these metabolic activities is that (1) organic\\nmatter concentrations (and oxygen demand) may increase\\ndownstream as particulate organic material is solubilized,\\n(2) the effect of temperature on observed organic matter\\nremoval may not be as significant in wetlands as would be\\npredicted by typical temperature correction relationships\\nfor biochemical reactions, and (3) the organic matter re\u00c2\u00ac\\nsidual downstream is a combination of recalcitrant organic\\nmatter in the influent, likely very small, soluble organic\\ncompounds released from plant decomposition and par\u00c2\u00ac\\nticulate organic matter released from dead plant and mi\u00c2\u00ac\\ncrobial materials.\\nThe source of the soluble fraction of organic matter in\\nthe wetland is, as has been stated, influent to the system\\nand soluble material released from the decomposition of\\ninfluent particulate matter and dead plant and microbial\\ntissue. This soluble material is most likely sorbed onto plant\\nsurface biofilms, although a fraction may be sorbed onto\\nbiomass suspended in the water column, and still another\\nfraction will diffuse to the debris at the wetland floor or\\nsurface. The sorbed organic matter will be metabolized by\\norganisms associated with the biofilms. The metabolic\\npathway and the end products of this metabolism will be\\ndependent on the presence or absence of oxygen. As pre\u00c2\u00ac\\nviously described, areas of the wetland populated with\\ndense emergent macrophytes can supply only a small frac\u00c2\u00ac\\ntion of the oxygen necessary to satisfy demand. Typical\\nwetland profiles in these areas suggest that most of the\\nwater column is anoxic, as are the sediments below (small\\nmicrosites containing oxygen may be found adjacent to\\nactive plant roots). The degree of anoxia would be depen\u00c2\u00ac\\ndent on the organic and nutrient load to the wetland area.\\nOpen areas of wetland (containing submerged plants) and\\nthe margins adjacent to emergent macrophyte coverage\\ndo demonstrate aerobic conditions throughout the wetland\\ndepth (again, dependent on organic and nutrient load and\\ntype of vegetation).\\nAs described previously, the mechanisms that regulate\\ndissolved organic matter removal in wetlands include bio\u00c2\u00ac\\ndegradation, sorption, and photolysis. Different operative\\nmechanisms may act on different types of organic matter.\\nAs a result, fundamental mechanisms should be consid\u00c2\u00ac\\nered in wetland designs and operation to enhance removal\\nprocesses. Wetlands receiving municipal wastewater pond\\neffluents may, for example, produce a net increase in dis\u00c2\u00ac\\nsolved organic matter (Barber et al., 1999). Details of de\u00c2\u00ac\\nsign strategies for FWS systems based on these observa\u00c2\u00ac\\ntions are found in Chapter 4.\\n3.3.3 Organic Matter in Vegetated\\nSubmerged Beds\\nVegetative submerged beds act as fixed-film bioreactors.\\nAs described in section 3.2.3, the actual role of plants in\\nthese beds is controversial. Some research (Gersberg et\\nal., 1986) has claimed effective results with selected spe\u00c2\u00ac\\ncies, but these claims have not been substantiated by oth\u00c2\u00ac\\ners. The presence of a root structure would provide addi-\\n41", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0059.jp2"}, "60": {"fulltext": "tional surface for biofilm attachment. Macrophytes may also\\ncontribute some oxygen to the granular bed as previously\\ndescribed. Based on that review, rates of oxygen trans\u00c2\u00ac\\nport by macrophytes range from 0 to 3 g 0 2 /m 2 /d. How\u00c2\u00ac\\never, it has been found that root penetration in the bed is\\nonly partial, and there is a significant amount of flow under\\nthe root zone. Furthermore, plant oxygen transfer would\\nbe unreliable for a significant portion of the year due to\\nplant senescence.\\nParticulate organic matter is removed in VSB systems\\nby mechanisms similar to suspended solids separation in\\nhorizontal gravel beds with the same media size. The sepa\u00c2\u00ac\\nrated solids from the influent wastewater and plant litter\\nwould undergo decomposition much the same way as oc\u00c2\u00ac\\ncurs in FWS systems. Hydrolysis will generate soluble\\ncompounds. Those compounds and soluble organic mat\u00c2\u00ac\\nter from the influent to the system or cycled from solids\\ndecomposition will most likely sorb to biofilm surfaces at\u00c2\u00ac\\ntached to the media, plant roots, and plant litter accumu\u00c2\u00ac\\nlated at the bed surface or within the interstices of the\\nmedia. Oxygen sources to the VSB would be limited to\\nsome small amount of surface aeration and plant-medi\u00c2\u00ac\\nated transport. The thatch that accumulates at the bed\\nsurface would inhibit or at least slow down surface trans\u00c2\u00ac\\nport. It is possible that some aerobic metabolism would\\noccur in these beds, but the predominant biological mecha\u00c2\u00ac\\nnism is likely to be facultative/anaerobic. Typical values of\\nDO in VSB systems are very low 0.1 mg/L). In VSB sys\u00c2\u00ac\\ntems where ORP has been measured, values were typi\u00c2\u00ac\\ncally quite low, indicating strong reducing conditions\\n(Lienard, 1987). Thus the predominant metabolic pathways\\nare most likely anaerobic. As described previously, the\\nanaerobic pathways leading to BOD removal from the sys\u00c2\u00ac\\ntem would be methanogenesis, sulfate reduction, or deni\u00c2\u00ac\\ntrification, all yielding gaseous end products. These reac\u00c2\u00ac\\ntions are temperature dependent and therefore are likely\\nto slow down or cease in winter months. As discussed pre\u00c2\u00ac\\nviously, the processes will resume as the water warms up,\\nand high releases of gaseous end products and soluble\\norganic matter may occur. Some clogging of the bed may\\noccur due to accumulation of slowly degradable and re\u00c2\u00ac\\ncalcitrant solids. Low-loaded systems may exhibit some\\naerobic reactions, especially near the effluent end of the\\nprocess. Residual effluent BOD from VSB systems is likely\\nto be somewhat more consistent than that from FWS sys\u00c2\u00ac\\ntems because of the presence of less plant matter in the\\nwater column.\\n3.4 Mechanisms of Nitrogen Separations\\nand Transformations\\n3.4.1 Description and Measurement\\nIn waters and wastewater, the forms of nitrogen of great\u00c2\u00ac\\nest interest are, in order of decreasing oxidation state, ni\u00c2\u00ac\\ntrate, nitrite, ammonia, and organic nitrogen. All nitrogen\\nforms are reported in wastewater as nitrogen, N. All of these\\nforms, including nitrogen gas (N 2 are biochemically\\ninterconvertible and are components of the nitrogen cycle.\\nAnalytically, organic nitrogen and ammonia can be deter\u00c2\u00ac\\nmined together, and are termed \u00e2\u0080\u009cTotal Kjeldahl nitrogen\u00e2\u0080\u009d\\n(TKN). Organic nitrogen in wastewater includes proteins,\\npeptides, nucleic acids, and urea. Organic nitrogen may\\nbe found in both soluble and particulate forms. The other\\nnitrogen species are water soluble. Ammonia nitrogen may\\nbe found in the un-ionized form, NH 3 or the ionized form,\\nNH 4 depending on water temperature and pH. The ion\u00c2\u00ac\\nized form is predominant in wetlands. At 25\u00c2\u00b0C and a pH of\\n7.0, the un-ionized ammonia is approximately 0.6%.\\nThe discharge of nitrogen to receiving surface and\\nground water sources is of concern for a number of rea\u00c2\u00ac\\nsons. Excessive accumulation of nitrogen in surface wa\u00c2\u00ac\\nters can lead to ecological imbalances that may cause\\novergrowth of plants and animals, leading to water quality\\ndegradation (eutrophication). High concentration of the un\u00c2\u00ac\\nionized ammonia species are toxic to fish and other aquatic\\nlife. Nitrate and nitrite nitrogen constitute a public health\\nconcern, primarily related to methemoglobinemia and car\u00c2\u00ac\\ncinogenesis. Ammonia nitrogen may deplete dissolved\\noxygen in natural waters by way of microbial nitrification\\nreactions. As a result, discharge permits may be written to\\ncontrol any or all species of nitrogen. Most commonly,\\nammonia or total nitrogen are the target pollutants speci\u00c2\u00ac\\nfied depending on the receiving stream. Typical concen\u00c2\u00ac\\ntrations of the nitrogen species found in primary, septic\\ntank, and treatment pond effluents are shown in Table 3-1.\\nIt should be noted that whereas primary and septic tank\\neffluents would contain organic nitrogen and ammonia,\\ntreatment ponds may contain either reduced or oxidized\\nforms of nitrogen depending on loading and season of the\\nyear. Organic nitrogen in the latter systems would be pri\u00c2\u00ac\\nmarily associated with algal cells. It is important to note\\nthat when evaluating the performance of wetlands relative\\nto nitrogen, both total nitrogen and the species of nitrogen\\nare important. Mass balances must be conducted on total\\nnitrogen species, not on just one or two forms, to generate\\nmeaningful data.\\n3.4.2 Nitrogen in Free Water Surface\\nSystems\\n3.4.2.1 Physical Separation of Nitrogen\\nSpecies\\nThere are a number of separation processes that will\\naffect nitrogen species in wetlands. Nitrogen associated\\nwith suspended solids (organic nitrogen) may be removed\\nby many of the processes described earlier for the removal\\nof TSS including flocculation, sedimentation, filtration, and\\ninterception processes (Figure 3-6). Sorption of both par\u00c2\u00ac\\nticulate and soluble organic nitrogen may occur on biofilms\\nassociated with emergent macrophytes, plant litter, or other\\ndetritus at the FWS surface or on the bottom. Ion exchange\\nof ammonium (NH 4 by clay minerals in the wetland soils\\nmay play a role in nitrogen separation if this species either\\ndiffuses into the soil layer or is biologically produced by\\nthe ammonification of organic nitrogen solids located in\\nthe benthal layer. The exchange capacity of the clay min\u00c2\u00ac\\nerals would be important in this assessment. It must be\\nemphasized that the exchange mineral would have limited\\n42", "height": "4283", "width": "3142", "jp2-path": "constructedwetla00nati_0060.jp2"}, "61": {"fulltext": "Sediment\\nPON Particulate Organic Nitrogen\\nDON Dissolved Organic Nitrogen\\nFigure 3-6. Nitrogen transformations in FWS wetlands\\nlong-term capacity unless regeneration by chemical or bio\u00c2\u00ac\\nchemical action takes place. It is not likely that ion exchange\\nwould play an important or dependable role in nitrogen\\nremoval after a start-up period in most wetland systems.\\nFurthermore, the native soil layer is buried under detritus\\nand plant litter within a period of time, thereby isolating\\nthese clay minerals from the wetland system. Ammonia\\n(NH 3 gas may also be removed from the system by strip\u00c2\u00ac\\nping. As discussed previously, the quantity of un-ionized\\nammonia at neutral pH values is low, but during active\\nphotosynthesis in open water zones, pH values may rise\\nto values as high as 8.0 to 8.5 depending on water alkalin\u00c2\u00ac\\nity. At that pH, the fraction of NH 3 (NH 3 /NH 4 may increase\\nto 20 to 25% at 20\u00c2\u00b0C. If surface turbulence is high due to\\nwind action, significant losses of nitrogen may occur in\\nthese open water areas if ammonia concentrations are\\nhigh. Few, if any, well-controlled studies have been con\u00c2\u00ac\\nducted to examine the importance of volatilization losses\\nin FWS systems with open areas.\\n3.4.2.2 Biologically Mediated Transformations\\nof Nitrogen Species\\nAmmonification\\nAlmost half of the municipal wastewater nitrogen con\u00c2\u00ac\\ntent, as received at the treatment facility, is in the organic\\nnitrogen form. The rest has usually already been converted\\nto ammonium-nitrogen (EPA, 1993) in the sewer. The bio\u00c2\u00ac\\nlogical transformation of organically combined nitrogen to\\nammonium nitrogen during organic matter degradation is\\nreferred to as ammonification, hydrolysis, or mineraliza\u00c2\u00ac\\ntion. The process occurs under aerobic and anaerobic\\nconditions, but has been described as slower for the latter\\nby Mitsch and Gosselink (1993). Other environmental en\u00c2\u00ac\\ngineering literature, however, does not support any differ\u00c2\u00ac\\nence in rates under varying oxygen states because of their\\nprimary dependence on enzymatic pathways. The rate of\\nthis process is primarily dependent on pH and tempera\u00c2\u00ac\\nture, increasing with increased temperatures. Municipal\\nwastewaters have been demonstrated to be fully hydro\u00c2\u00ac\\nlyzed in 19 hours at temperatures of 11\u00c2\u00b0 to 14\u00c2\u00b0C (Bayley\\net al., 1973). Once the ammonium is formed, it can be\\nabsorbed by plants through their root systems, immobi\u00c2\u00ac\\nlized by ion exchange in the sediments, solubilized and\\nreturned to the water column, volatilized as gaseous am\u00c2\u00ac\\nmonia, anaerobically converted back to organic matter by\\nmicrobes, absorbed by phytoplankton/floating aquatic\\nmacrophytes in the water column, or aerobically nitrified\\nby aerobic microorganisms.\\nNitrification\\nIn the presence of dissolved oxygen, microbes in the\\nwater column or within the biofilms may convert ammo\u00c2\u00ac\\nnium to nitrite and nitrate nitrogen in a two-step process.\\nIn this process about 4.3g of 0 2 are required per g ammo\u00c2\u00ac\\nnium nitrogen oxidized to nitrate and 7.14 g of alkalinity as\\nCaC0 3 are consumed. The process is temperature and\\npH dependent (EPA, 1993). The reaction may take place\\nin an aerobic water column by suspended bacteria and\\n43", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0061.jp2"}, "62": {"fulltext": "within any aerobic biofilms. Nitrate is not immobilized by\\nsoil minerals and remains in the water column or pore water\\nof the sediments. It may be absorbed by plants or microbes\\nin assimilatory nitrate reduction (converted to biomass via\\nammonium) or may undergo dissimilatory nitrogenous ox\u00c2\u00ac\\nide reduction (nitrate reduction pathways referred to as\\ndenitrification).\\nDenitrification\\nDissimilatory nitrate reduction or denitrification is car\u00c2\u00ac\\nried out by microorganisms under anaerobic (anoxic) con\u00c2\u00ac\\nditions, with nitrate as the terminal electron acceptor and\\norganic carbon as the electron donor (EPA, 1993). That is\\nto say, the reaction occurs in the absence of oxygen and\\nrequires an organic carbon source. The products of deni\u00c2\u00ac\\ntrification are N 2 and N 2 0 gases that will readily exit the\\nwetlands. The denitrification reaction occurs primarily in\\nthe wetland sediments and in the periphyton films in the\\nwater column below fully vegetated growth where DO is\\nlow and available carbon is high. The minimum carbon to\\nnitrate-nitrogen ratio for denitrification would be about 1 g\\nC/g N0 3 -N. Decomposing wetland plants and plant root\\nexudates are potential sources of biodegradable organic\\ncarbon for this purpose. These sources are most readily\\navailable at the beginning of senescence. Organic carbon\\nwill be consumed (satisfying some oxygen demand: ap\u00c2\u00ac\\nproximately 2.86 g 0 2 per g nitrate nitrogen reduced) and\\nalkalinity is produced (approximately 3.0 g CaC0 3 alkalin\u00c2\u00ac\\nity per g nitrate nitrogen reduced). The process is tem\u00c2\u00ac\\nperature and pH dependent. Denitrification in the sediments\\nmay supply N 2 for fixation by bacteria and for plant uptake\\nin the root zone (nitrogen fixation) if the system is nitro\u00c2\u00ac\\ngen-poor. The remainder will remain in equilibrium with N 2\\nin the water column. The nitrogen gas in the water phase\\nmay be available for nitrogen fixation by some periphyton\\nand phytoplankton. There will also be an air-water inter\u00c2\u00ac\\nchange of N 2 The losses to the air represent nitrogen\\nlosses from the system, and these are greater in open water\\nthan in fully vegetated zones.\\nNitrogen Fixation\\nNitrogen gas may be converted to organic nitrogen by\\nway of selected organisms that contain the enzyme nitro-\\ngenase. The reaction may be carried out aerobically or\\nanaerobically by bacteria and blue-green algae. Nitrogen\\nfixation occurs in the overlying water in FWS open water\\nzones, in the sediment, in the oxidized rhizosphere of the\\nplants, and on the leaf and stem surfaces of plants (Reddy\\nand Graetz, 1988). It may be a significant source of nitro\u00c2\u00ac\\ngen in natural wetlands but is not important in systems\\ntreating wastewater in which nitrogen is plentiful.\\nPlant Uptake (Assimilation)\\nWetland plants will assimilate nitrogen as an important\\npart of their metabolism. Inorganic nitrogen forms are re\u00c2\u00ac\\nduced by the plant to organic nitrogen compounds used\\nfor plant structure. During the growing season, there is a\\nhigh rate of uptake of nitrogen by emergent and submerged\\nvegetation from the water and sediments. Increased im\u00c2\u00ac\\nmobilization of nutrients by microbes and uptake by algae\\nand epiphytes also lead to a retention of inorganic forms\\nof nitrogen in the wetland. Estimates of net annual nitro\u00c2\u00ac\\ngen uptake by emergent wetland plant species vary from\\n0.5 to 3.3 gN/m 2 /yr (Burgoon et al., 1991). Reeds and bul\u00c2\u00ac\\nrushes are at the lower end of this range, whereas cattails\\nare at the higher end. Estimates for epiphytes and microbes\\nin wetland systems have not been found. During the ac\u00c2\u00ac\\ntive growth period, a significant amount of the total plant\\nnitrogen is in the stems and leaves above the sediments.\\nDuring senescence, the nitrogen translocates back to the\\nroots and rhizomes for storage. However, a substantial\\nportion of the nitrogen is lost to the water column through\\nlitter fall and subsequent leaching. This generally leads to\\na net export of nitrogen in the fall and early spring. The\\nextent of recycling of nitrogen within the wetland is depen\u00c2\u00ac\\ndent on nitrogen loading to the system. Treatment wetland\\nsystems are considered as eutrophic wetlands with ex\u00c2\u00ac\\ncessive nutrient levels. As a result, intrasystem cycling is\\nless important to the treatment process than it would be if\\nthe hydrologic regime were more varied (Twinch and\\nAshton, 1983).\\n3.4.2.3 Nitrogen in Free Water Surface\\nWetlands\\nFigure 3-6 illustrates the highly complex series of reac\u00c2\u00ac\\ntions for nitrogen in FWS systems. Particulate organic ni\u00c2\u00ac\\ntrogen entering the wetland as wastewater influent or pro\u00c2\u00ac\\nduced in the wetland by plants is separated. It may be\\nfound associated with biofilms attached to plant structures\\nin the water column, the wetland sediment, or in floating\\nlitter and detritus. The biodegradable compounds will be\\nammonified by aerobic or anaerobic organisms associated\\nwith the biofilms and sediment surfaces. The recalcitrant\\norganic nitrogen will accumulate and eventually become a\\npart of the deep sediments.\\nAmmonium released from the particulate organic nitro\u00c2\u00ac\\ngen in the sediments is available to the emergent and sub\u00c2\u00ac\\nmerged macrophytes as an important nutrient. Uptake\\noccurs during the growing season, which increases the\\nconcentration gradient and the release of more ammonium.\\nExcess ammonia may remain in reserve in the sediment\\nand leach from the sediment into the water column, where\\nit may undergo biological oxidation (nitrification) under\\naerobic conditions. Release of ammonium into the water\\ncolumn in the fall and early spring is not an unusual phe\u00c2\u00ac\\nnomenon in wetlands. The leached ammonium may be\\ntaken up by epiphytes or plankton found in the water col\u00c2\u00ac\\numn or be attached to emergent and floating plants. Nitri\u00c2\u00ac\\nfication of ammonium requires DO and is therefore limited\\nto areas of the wetland where oxygen is available. There\\nmay be some nitrification occurring adjacent to plant rhi\u00c2\u00ac\\nzomes where oxygen leaks from the plant. The relative\\nimportance of this pathway in wetlands is minor in treat\u00c2\u00ac\\nment wetlands because most sediments below emergent\\ncanopies are anaerobic. Little nitrification would be ex\u00c2\u00ac\\npected in these regions of the wetland. In the water col-\\n44", "height": "4283", "width": "3142", "jp2-path": "constructedwetla00nati_0062.jp2"}, "63": {"fulltext": "umn near the surface in open areas, oxygenation may be\\nsufficient to ensure significant nitrification. The important\\nvariable in sizing an open water zone of a FWS system for\\nnitrification is organic plus nitrogenous loading. More pre\u00c2\u00ac\\ncisely, it is the oxygen demand loading (carbonaceous plus\\nnitrogenous oxygen demand [CBOD NOD]) to each wet\u00c2\u00ac\\nland zone that will dictate whether oxygen is present. Typi\u00c2\u00ac\\ncally, nitrification will not be initiated until a majority of the\\norganic compounds have been removed. Thus, nitrifica\u00c2\u00ac\\ntion in the water column would not be expected in the ini\u00c2\u00ac\\ntial settling zone, but could occur in subsequent open wa\u00c2\u00ac\\nter/aerobic zones.\\nThe nitrate produced by nitrification or introduced with\\nthe system influent (e.g., from oxidation ponds achieving\\nnitrification) may be taken up by periphyton or plankton.\\nSmall amounts produced within any aerobic sediments\\nwould be taken up by plant roots or may diffuse upward\\ninto the water phase. Under anaerobic conditions and in\\nthe presence of organic matter, microbes associated with\\nattached biofilms or suspended in the water column may\\nconvert nitrate to nitrogen gases (NO N 2 via denitrifica\u00c2\u00ac\\ntion. Some nitrate will also diffuse into tne sediments where\\nit is available for plant uptake or can be denitrified as well.\\nMoving downstream from the wetland influent, the reac\u00c2\u00ac\\ntions of nitrogen could be expected to occur sequentially\\nsuch that total nitrogen levels should drop in the settling\\nzone (owing to separation of organic nitrogen), followed\\nby ammonia release, nitrification, and denitrification. Plants\\nwill attenuate this sequence by releases and uptake\\nthroughout the annual growth/senescence cycle. Systems\\nloaded at a level such that oxygen demand exceeds oxy\u00c2\u00ac\\ngen supply will not exhibit significant nitrification. Seasonal\\nchange as well as influent variability will greatly impact\\nsystem performance. Highly nitrified influent from pretreat\u00c2\u00ac\\nment systems may provide excellent nitrogen removal\\nduring warm seasons when sufficient organic matter is\\navailable (primarily from plant decomposition) for denitrifi\u00c2\u00ac\\ncation. Nitrogen release may be significant in fall and early\\nspring seasons during plant senescence and death. The\\nbackground nitrogen values found in Table 3-5 reflect con\u00c2\u00ac\\ntributions by internal recycling of nitrogen within the sys\u00c2\u00ac\\ntem.\\nIn open water zones of FWS systems, elevated pH and\\nwater temperature may enhance NH3-N volatization to the\\ndegree that it becomes a significant removal mechanism.\\nThis mechanism has been shown to reach levels as high\\nas 50% or more under optimum conditions in stabilization\\nponds, but FWS open water zones are smaller in size,\\ntherefore minimizing this pathway under normal conditions\\n(EPA, 1983).\\nWastewater discharge permits are normally written so\\nas to limit effluent ammonia concentrations (either sea\u00c2\u00ac\\nsonally or all year) or total nitrogen concentrations. For\\nammonia removal, the processes that will achieve effec\u00c2\u00ac\\ntive removal include plant uptake, nitrification, volatiliza\u00c2\u00ac\\ntion, and ion exchange. The latter two typically have only\\nminor impact in most FWS systems. Plant uptake is sea\u00c2\u00ac\\nsonal and requires harvesting prior to plant senescence.\\nFortunately, seasonal nitrogen uptakes may parallel am\u00c2\u00ac\\nmonia restrictions in those cases in which these restric\u00c2\u00ac\\ntions are based on summer oxygen demands and/or cer\u00c2\u00ac\\ntain game fish maximization. Generally, the designer must\\nbe concerned with achieving reliable ammonia removal by\\nmeans of nitrification. This may be achieved at low load\u00c2\u00ac\\ning (oxygen demand) with sequencing closed and open\\nwetland areas (See Chapter 4). It should be noted that\\nnitrification is temperature dependent, so that rates will sig\u00c2\u00ac\\nnificantly slow in winter months, especially in colder cli\u00c2\u00ac\\nmates.\\nNitrogen removal may be achieved by plant uptake/har\u00c2\u00ac\\nvesting, nitrification/denitrification, volatilization, and ion\\nexchange. Again, the latter two are considered to be of\\nminor consequence in most FWS systems. Plant uptake\\nand harvesting requires careful system management and\\ncan be costly. The requirement for denitrification requires\\nnitrification as explained previously plus adequate decay\u00c2\u00ac\\ning plant organic carbon in a region free of dissolved oxy\u00c2\u00ac\\ngen. Sequential designs are also best to achieve this goal\\n(See Chapter 4). Note that temperature affects both nitrifi\u00c2\u00ac\\ncation and denitrification so that rates can be significantly\\nreduced during the colder months, which may control de\u00c2\u00ac\\nsign requirements.\\n3.4.3 Nitrogen in Vegetated Submerged\\nBeds\\nAs described in section 3.3.3, VSB systems incorporate\\nanaerobic fixed-film biological reactions. Organic nitrogen\\ntrapped within the bed will undergo ammonification. The\\nreleased ammonia may be available for plant uptake de\u00c2\u00ac\\npending on the location of plant roots. Flow below the plant\\nroots will carry ammonium downstream. Plant uptake (0.03\\nto 0.3 g/m 2 /d) of nitrogen is low compared to typical nitro\u00c2\u00ac\\ngen loading to VSB systems. As described previously, de\u00c2\u00ac\\npendence on plant uptake for nitrogen removal requires\\nharvesting and is not effective during plant senescence\\nand death.\\nOxygen sources in VSB systems are negligible, and it is\\nmost likely there will be insufficient oxygen to promote re\u00c2\u00ac\\nliable nitrification in all but the most lowly loaded systems.\\nAny nitrification occurring may be found in the root zone\\nadjacent to rhizomes or near the bed surface where some\\nsurface oxygen transfer might occur. If nitrification occurs,\\nit would occur downstream where oxygen demand is low\u00c2\u00ac\\nest.\\nConventional VSB systems would seem to be well suited\\nfor denitrification of nitrified influents. These beds are\\nanaerobic. However, they require a supply of organic car\u00c2\u00ac\\nbon from decomposing plant residue entrapped within the\\nbed or aerobically decomposed products of plant biomass\\nat the bed surface, which may also leach into the anaero\u00c2\u00ac\\nbic zones during rainfall events. The supply of carbon is\\nseasonal, however, since it would be highest after plant\\nsenescence. Low temperature will slow the process dur\u00c2\u00ac\\ning the winter months.\\n45", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0063.jp2"}, "64": {"fulltext": "From this discussion, it is clear that conventional VSB\\nsystems do not represent reliable, cost-effective systems\\nfor ammonia removal. To improve, the loading to the sys\u00c2\u00ac\\ntem would necessarily have to be low. Nitrogen removal\\nfrom well-nitrified influents to the system may be possible,\\nbut seasonal availability of carbon may create carbon limi\u00c2\u00ac\\ntations that should be considered in the design (See Chap\u00c2\u00ac\\nter 5).\\n3.5 Mechanisms of Phosphorus\\nSeparations and Transformations\\n3.5.1 Description and Measurement\\nPhosphorus occurs in natural waters and wastewater\\nprimarily as phosphates. They are classified as orthophos\u00c2\u00ac\\nphates, condensed (pyro-, meta-, and poly-) phosphates,\\nand organically bound phosphates. They may be in solu\u00c2\u00ac\\ntion or particulate form. Organic phosphates are formed\\nprimarily by biological processes and are found in raw\\nwastewater as food residues and body wastes and in\\ntreated wastewater as living or nonliving biota (e.g., algae\\nand bacteria from treatment ponds). Inorganic phospho\u00c2\u00ac\\nrus found in wastewater most often comes from various\\nforms of personal and commercial cleaning solutions or\\nfrom the treatment of boiler waters. Storm waters carry\\ninorganic forms of phosphorus from fertilizers into com\u00c2\u00ac\\nbined sewers. Classification of phosphorus is based on a\\nvariety of analytical methods. The typical concentrations\\nof phosphates in influent wastewaters to a treatment wet\u00c2\u00ac\\nland appear in Table 3-1. Modern P concentrations are\\n-50% of those shown for septic tank effluent in this table.\\nTable 3-3 indicates that the major fraction of these phos\u00c2\u00ac\\nphate forms are in the colloidal range, and Munch et al.\\n(1980) indicated that 80% of the phosphate was split al\u00c2\u00ac\\nmost equally between colloidal and supracolloidal fractions.\\nPhosphorus is one of the most important elements in\\necosystems. It is often the major limiting nutrient in fresh\u00c2\u00ac\\nwater systems. Since there is no important gaseous com\u00c2\u00ac\\nponent in the biogeochemical cycle, phosphorus tends to\\nmove to the sediment sink in natural systems and become\\nscarce in the ecosystem. In fact, it is the accretion of min\u00c2\u00ac\\neral phosphates and biomass in the sediment that is the\\nprimary mechanism for phosphorus removal in the wet\u00c2\u00ac\\nland environment.\\n3.5.2 Phosphorus in Free Water Surface\\nSystems\\n3.5.2.1 Physical/Chemical Separations of\\nPhosphorus\\nParticulate phosphate may be deposited onto the FWS\\nsystem sediment by sedimentation or entrapped within the\\nemergent macrophyte stem matrix and attached (sorbed)\\nonto biofilms (Figure 3-7). Soluble phosphate may be\\nsorbed onto plant biofilms in the water column, onto biofilms\\nin the floating plant litter, or onto the wetland sediments.\\nThe exchange of soluble phosphate between sediment\\npore water and the overlying water column by diffusion\\nand sorption/desorption processes is a major pathway for\\nsoluble phosphates in wetlands. In the sediment pore wa\u00c2\u00ac\\nter, these phosphates may be precipitated as the insoluble\\nferric, calcium, and aluminum phosphates or adsorbed onto\\nclay particles, organic peat, and ferric and aluminum ox\u00c2\u00ac\\nides and hydroxides. The precipitation as calcium phos\u00c2\u00ac\\nphates occurs at pH values above 7 and may occur within\\nthe sediment pore water or in the water column near ac\u00c2\u00ac\\ntive phytoplankton growth where pH values may rise well\\nabove 7. The sorption of phosphorus on clays involves\\nboth the chemical bonding of the negatively charged phos\u00c2\u00ac\\nphates with positively charged clay and the substitution of\\nphosphates for silicates in the clay matrix (Stumm and\\nMorgan, 1970). Phosphate can be released (desorbed)\\nfrom the metal complexes depending on the redox poten\u00c2\u00ac\\ntial of the sediment. Under anoxic conditions, for example,\\nthe ferric compound is reduced to the more soluble fer\u00c2\u00ac\\nrous compound and phosphate is released. Phosphates\\nmay also be released from ferric and aluminum phosphates\\nunder anoxic conditions by hydrolysis. Phosphate sorbed\\nto clays and hydrous oxides may also be resolubilized\\nthrough the exchange of anions. The release of phosphate\\nfrom insoluble salts will also occur if the pH decreases as\\na result of the biological formation of organic acids, nitrates,\\nor sulfates. Over time, however, a significant fraction of\\nthe initially removed phosphate will become bound within\\nthe sediments and lost to the system. At the start-up of a\\nFWS system (possibly for more than one year), the phos\u00c2\u00ac\\nphorus removal will be abnormally high owing to the initial\\nreactions with the soils of the wetland. This removal mecha\u00c2\u00ac\\nnism is finite and essentially disappears after this period.\\n3.5.2.2 Biological Transformations of\\nPhosphates\\nDissolved organic phosphate and insoluble inorganic and\\norganic phosphate are not usually available to plants until\\ntransformed to a soluble inorganic form. These transfor\u00c2\u00ac\\nmations may take place in the water column by way of\\nsuspended microbes and in the biofilms on the emergent\\nplant surfaces and in the sediments. Uptake of phosphates\\nby microorganisms, including bacteria, algae, and duck\u00c2\u00ac\\nweed, acts as a short-term, rapid-cycling mechanism for\\nsoluble and insoluble forms. Cycling through the growth,\\ndeath, and decomposition process returns most of the\\nphosphate back into the water column. Some phosphate\\nis lost in the process due to long-term accretion in newly\\nformed sediments. Uptake by the macrophytes occurs in\\nthe sediment pore water by the plant root system. The\\nestimate of net annual phosphorus uptake by emergent\\nwetland species varies from 1.8 to 18 g P/m 2 /y (Burgoon\\net al., 1991). The cycle of uptake and release is similar to\\nthat of the microbes, but these reactions operate over a\\nlonger time scale of months to years. Uptake occurs dur\u00c2\u00ac\\ning the growth phase of the plant and release occurs dur\u00c2\u00ac\\ning plant senescence and death in the late summer and\\nfall, followed by decomposition in the plant litter. Again,\\nsome phosphate is lost to the system through accretion\\nprocesses within the sediments.\\n3.5.2.3 FWS System Reactions\u00e2\u0080\u0094Phosphate\\nSustainable phosphate removal in a FWS system in\u00c2\u00ac\\nvolves the accretion and burial of phosphate within the\\n46", "height": "4283", "width": "3142", "jp2-path": "constructedwetla00nati_0064.jp2"}, "65": {"fulltext": "Figure 3-7. Phosphorus cycling in a FWS wetland (adapted from Twinch and Ashton, 1983)\\nwetland sediments (Figure 3-7). Phosphate cycling and\\nstorage involves a complex set of processes with a num\u00c2\u00ac\\nber of forms of phosphate. Insoluble organic and inorganic\\nphosphates are settled or captured on solid surfaces within\\nthe water column or in the wetland sediments or floating\\nlitter. Many of these insoluble forms may be chemically\\nand biologically transformed to available forms of phos\u00c2\u00ac\\nphate for uptake by macrophytes, epiphytes, and floating\\nplants. The phosphate taken up by these biological sys\u00c2\u00ac\\ntems is recycled back into the system and is subsequently\\navailable for other organisms or may leave the system\\nthrough the water column. The undecomposed portion of\\nthe biological growths may accumulate and thereby be\\nremoved from the system as accreted sediment. This ma\u00c2\u00ac\\nterial along with any recalcitrant phosphate separated from\\nthe water column and accumulated within the sediment\\nrepresents the total net phosphate removal from the sys\u00c2\u00ac\\ntem.\\nPhosphate removal in FWS systems follows a seasonal\\npattern in most temperate climate conditions. The form of\\nphosphate, the type and density of the aquatic plants, the\\nphosphate loading rate, and the climate determine the\\npattern and amount of phosphate removed from the wet\u00c2\u00ac\\nland over any given time period. Aquatic plants serve as\\nthe seasonal reservoir for phosphate as they take up\\nsoluble reactive phosphate (SRP) during the growing sea-\\ni son. There is a finite amount of SRP that can be incorpo\u00c2\u00ac\\nrated in the aquatic plants, epiphytes, and plankton in the\\nwater column. In climates where senescing of plants oc\u00c2\u00ac\\ncurs in the fall, the majority of the phosphorus taken up will\\nbe released back into the water column (Figure 3-8). In\\nthis figure, during the second year Marsh 1 received tap\\nwater without phosphorus, whereas Marsh 3 received\\nwastewater at a loading rate of 0.15 kg P/ha/d throughout.\\nRelease in excess of influent phosphorus is noted in the\\nMarsh 3 effluent in the fall. The effluent phosphorus exhib\u00c2\u00ac\\nited for Marsh 1 is the result of release from the standing\\ncrop developed the year before. Note a background re\u00c2\u00ac\\nsidual phosphorus concentration of about 0.5 mg/L SRP\\nfor this system. Maximum removal of phosphate was found\\nto be about 1.5 mg/L at a loading of less than 1.5 kg P04/\\nha/d and reduced to negligible 0.2 mg/L) at loadings\\nabove 5 (Gearheart, 1993). This maximum is consistent\\nwith the theory of Stumm (1975), which suggested approxi\u00c2\u00ac\\nmately 20% of influent P could be removed under an equi\u00c2\u00ac\\nlibrium condition in a lake.\\n3.5.3 Phosphorus in Vegetative\\nSubmerged Beds\\nThe removal of phosphate from VSB systems relies on\\naccretion of phosphorus from decomposing plants and from\\nseparated, recalcitrant phosphate from the influent to the\\nprocess. Phosphate loading to these systems is large rela\u00c2\u00ac\\ntive to plant uptake, and reliable sustained removal by har\u00c2\u00ac\\nvesting of plants prior to senescence would not provide\\nsignificant removal. Accretion of partially decomposed plant\\ntissue may provide some additional removal of phospho\u00c2\u00ac\\nrus. Cycling of phosphorus will produce seasonal effluent\\nvariations similar to those seen for FWS systems. Some\\nminerals associated with the media can provide tempo-\\n47", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0065.jp2"}, "66": {"fulltext": "rary removal by means of precipitation/exchange/sorption\\nmechanisms, but these effects would be short term 1\\nyear) and dependent on the source of the granular materi\u00c2\u00ac\\nals.\\n3.6 Mechanisms of Pathogen Separations\\nand Transformations\\n3.6.1 Description and Measurement\\nWaterborne pathogens including helminthes, protozoans,\\nfungi, bacteria, and viruses are of great concern in assess\u00c2\u00ac\\ning water quality. Since routine examination for pathogenic\\norganisms is not recommended because of cost and the\\nlow numbers of a specific pathogen present at any given\\ntime, indicator organisms are used. The most common in\u00c2\u00ac\\ndicators of the level of waterborne pathogen contamina\u00c2\u00ac\\ntion in water are the coliform group. Today, the fecal coliform\\ntest is considered to be a better indicator of human fecal\\ncontamination than the more general total coliform proce\u00c2\u00ac\\ndure. Even so, the fecal coliform test is not specific and\\ncan produce false positive results for human contamina\u00c2\u00ac\\ntion, since these organisms are excreted by a number of\\nwarm-blooded animals including those residing in wetland\\nenvironments. Fecal streptococci analysis may also be\\nused as an additional indicator of fecal pollution. Together\\nwith the fecal coliform test, these two procedures are some\u00c2\u00ac\\ntimes used to discriminate between human and other warm\u00c2\u00ac\\nblooded animals. Table 3-1 indicates typical ranges of the\\nindicator organisms in typical influents to treatment wet\u00c2\u00ac\\nland systems.\\nSeparation of pathogens (and indicators) from the water\\ncolumn does not in itself mean that the organisms are no\\nlonger viable. They may be released from the matrix to\\nwhich they are attached and become available again in\\nthe water column as infectious agents. The true removal\\nof pathogens is only achieved by rendering them nonvi-\\nable.\\n3.6.2 Fate in Constructed Wetlands\\nPathogens (and indicators) entering wetlands may be\\nincorporated within the TSS or may be found as suspen\u00c2\u00ac\\nsions in the influent wastewater. Those associated with\\nTSS would be separated from the water column by the\\nsame mechanisms as discussed for TSS (sedimentation,\\ninterception, and sorption). Once separated, the viable\\norganisms may be released from the solid matrix and be\\nretained within the biofilm or sediment pore-water, or they\\nmay be reentrained into the water column. Regardless of\\ntheir location, they must compete with the consortium of\\norganisms surrounding them. As intestinal organisms, they\\nwill normally require a rich substrate and high temperature\\nto favorably compete. Most will not survive in this compe\u00c2\u00ac\\ntition. They will also be destroyed by predation or, if near\\nthe open water surface, by UV irradiation.\\nRemoval of pathogens (indicators) in wetlands appears\\nto be correlated with TSS removal and hydraulic residence\\ntimes (Gearheart et al., 1999; Gersberg et al., 1989). Few\\nstudies have been performed on the effect of wetlands on\\nspecific pathogens, but Gearheart has found similar re\u00c2\u00ac\\nmovals to FC with Salmonella and MS2 coliphage. Many\\npathogens are more sensitive to the wetland environment\\nthan indicators, but some viruses and protozoans (spores)\\nmay be more resistant. Erratic results have been reported\\non viruses, and mechanisms affecting their removal may\\nbe different than those that destroy indicators.\\nCO\\ng\\nV\\n3\\nQ.\\no\\nDate\\nFigure 3-8. Phosphorus pulsing in pilot cells in Areata; Marsh 1 received tap water until June 1982 (no phosphorus load), while Marsh 3 received\\noxidation pond effluent (Gearheart, 1993)\\n48", "height": "4283", "width": "3142", "jp2-path": "constructedwetla00nati_0066.jp2"}, "67": {"fulltext": "It is significant to note that indicator organisms and per\u00c2\u00ac\\nhaps pathogens may be generated within the wetland. Thus\\nbackground levels of indicators will be found even in natu\u00c2\u00ac\\nral wetland systems (see Table 3-5). These background\\nlevels are variable, influenced by season and other opera\u00c2\u00ac\\ntional parameters of the system (Figure 3-9). It should be\\nnoted that in general these indicator organisms are not\\nfrom human sources. However, constructed wetlands are\\nunlikely to consistently meet stringent effluent fecal coliform\\npermit levels. Therefore, regulators may require disinfec\u00c2\u00ac\\ntion of treatment wetland effluents prior to discharge.\\nGearheart (1998) consistently attained an FC count of less\\nthan 2/100 mL with UV disinfection of FWS effluent.\\n3.7 Mechanisms of Other Contaminant\\nSeparations and Transformations\\n3.7.1 Metals\\nWhile some metals are required for plant and animal\\ngrowth in trace quantities (barium, beryllium, boron, chro\u00c2\u00ac\\nmium, cobalt, copper, iodine, iron, magnesium, manga\u00c2\u00ac\\nnese, molybdenum, nickel, selenium, sulfur, and zinc),\\nthese same metals may be toxic at higher concentrations.\\nOther metals have no known biological role and may be\\ntoxic at even very low concentrations (e.g., arsenic, cad\u00c2\u00ac\\nmium, lead, mercury, and silver) (Gersberg et al., 1984;\\nCrites et al., 1997). Influent wastewater to wetlands may\\ncarry metals as soluble or insoluble species.\\nMetals entering wetlands as insoluble suspended solids\\nare separated from the water column in a manner similar\\nto TSS. Depending on pH and redox potential, these in\u00c2\u00ac\\nsoluble species may be resolubilized and returned to the\\nliquid phase. Important removal mechanisms for metals\\ninclude cation exchange and chelation with wetland soils\\nand sediments, binding with humic materials, precipitation\\nas insoluble salts of sulfides, carbonates, and\\noxyhydroxides, and uptake by plants, algae, and bacteria.\\nThe chemically bound metals may eventually become bur\u00c2\u00ac\\nied in the anoxic sediments where sulfides occur. These\\nbound metals are often not bio-available and remain re\u00c2\u00ac\\nmoved from the system. If sediments are disturbed or re\u00c2\u00ac\\nsuspended and moved to oxic regions of the wetland, se\u00c2\u00ac\\nquestered metals may resolubilize.\\nMetals may be incorporated into the wetland biomass\\nby way of the primary production process. For macro\u00c2\u00ac\\nphytes, metals are taken up through the root system and\\ndistributed through the plant. The extent of uptake is de\u00c2\u00ac\\npendent on the metal species and plant type. Gersberg et\\nal. (1984), found only minor uptake by plants in VSB sys\u00c2\u00ac\\ntems, while others claim that metals can be found on root\\nsurfaces due to precipitation and adsorption. The accu\u00c2\u00ac\\nmulation of heavy metals was found to be variable in a\\nmarsh in New Jersey receiving wastewater (Simpson et\\nal., 1981; 1983). Cadmium, copper, lead, nickel, and zinc\\nhad accumulated in the litter at the end of the growing sea\u00c2\u00ac\\nson in much higher concentrations than in the live vegeta\u00c2\u00ac\\ntion. Other studies have shown that metals like cadmium,\\nchromium, copper, lead, mercury, nickel, and zinc can be\\nsequestered by wetland soils and biota or both (Mitsch\\nand Gosselink, 1993). The high uptake of selenium by biota\\nin a wetland marsh receiving irrigation waters was dis\u00c2\u00ac\\ncussed in Hammer (1992), but some could have been vola\u00c2\u00ac\\ntilized. Studies have shown that some algae will seques\u00c2\u00ac\\nter selected metals (Kadlec and Knight, 1996). Floating\\nplants such as duckweed have been shown to be excel\u00c2\u00ac\\nlent accumulators of cadmium, copper, and selenium, but\\nonly moderate accumulators for chromium and poor accu\u00c2\u00ac\\nmulators for nickel and lead (Zayed et al., 1998). A review\\nof metal removal in wetlands is found in Kadlec and Knight\\n(1996).\\n10,000\\no\\no\\nD\\nn\\nE\\n3\\nC,\\no\\nc\\nD\\n3\\n3=\\nLU\\n1,000\\n100\\n100 1,000\\nInfluent FC (number/100 mL)\\ni-r\\n10,000 100,000 1 000,000\\nFigure 3-9. Influent versus effluent FC for the TADB systems (EPA, 1999)\\n49", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0067.jp2"}, "68": {"fulltext": "At the present time there is insufficient long-term data\\non full-scale constructed wetlands to provide a reliable\\nestimate of performance on the removal of metals from\\nwastewater. However, in VSBs and in fully vegetated FWS\\nsystems, the anaerobic conditions are conducive to retain\u00c2\u00ac\\ning most metals with the settled TSS and minimizing\\nresolubilization. Similarly, the actual removals will be af\u00c2\u00ac\\nfected by the speciation of the influent metals.\\n3.7.2 Other Organic Compounds\\nThere is concern about the fate of many trace organic\\ncompounds in the environment. These include pesticides,\\nfertilizers, process chemicals, and others that fall under\\nthe category of priority pollutants. The fate of these com\u00c2\u00ac\\npounds in wetlands is dependent on the properties of the\\ncompound, the characteristics of the wetland, the species\\nof plants, and other environmental factors. The most im\u00c2\u00ac\\nportant separation and transformation mechanisms in\u00c2\u00ac\\nvolved include volatilization, sedimentation/interception,\\nbiodegradation, adsorption, and uptake. These mecha\u00c2\u00ac\\nnisms have been discussed previously. Recalcitrant organ\u00c2\u00ac\\nics that have been separated may accumulate in the wet\u00c2\u00ac\\nland sediments. Some may be taken up by plants and be\\nreturned to the system upon plant decomposition. Biodeg\u00c2\u00ac\\nradation of some organic compounds may result in com\u00c2\u00ac\\npletely mineralized end products, or the process may pro\u00c2\u00ac\\nduce end products that may be more toxic than the parent\\ncompound. At this time, there is insufficient data available\\non full-scale wetland systems to evaluate how effective\\nthey are in the long-term removal and destruction of most\\npriority pollutants. Based on pretreatment performance,\\noxidation or facultative lagoons remove a high %age of\\nvolatile and semivolatile organic compounds (Hannah et\\nal., 1986), resulting in low influent concentrations to the\\nFWS system that follows, while primary sedimentation is\\nless effective and results in higher influent concentrations\\nof both to subsequent VSB systems.\\n3.8 Constructed Wetland Modeling\\n3.8.1 Modeling Concepts\\nThe modeling of wastewater treatment operations and\\nprocesses has long been of interest to environmental en\u00c2\u00ac\\ngineers. This interest stems primarily from a need to quan\u00c2\u00ac\\ntify the performance of the process and a desire to opti\u00c2\u00ac\\nmize the design and operation of the treatment facility.\\nModeling of many of the treatment processes used today\\nhas met with only partial success primarily because of the\\nlack of rigor in most models. This is due to the enormous\\ncomplexity of the reaction mechanisms that may take place\\nwithin many of these systems and with the difficulty in char\u00c2\u00ac\\nacterizing the constituents within the wastewater. Con\u00c2\u00ac\\nstructed wetlands fall in this category of a highly complex\\nsystem in which a multiplicity of reactions and reaction\\nmechanisms occur, even in the simplest of systems. Ad\u00c2\u00ac\\nsorption, sedimentation, flocculation, biological catalysis,\\nprecipitation, exchange, and diffusional processes are but\\na few of the important functional mechanisms that may\\ncontrol the removal of a given constituent. Furthermore,\\nthese mechanisms are dependent on a number of physi\u00c2\u00ac\\ncal, chemical, and biological variables within the system\\n(e.g., temperature, redox potential, pH, plant density, etc.).\\nIt is apparent that in a highly complex system such as\\nthe constructed wetland, the quantification of all specific\\nrate-controlling mechanisms seems unlikely. The transient\\nnature of the influent wastewater characteristics and the\\nlack of substantial control over the process undoubtedly\\nwill result in frequent changes of the rate-controlling mecha\u00c2\u00ac\\nnisms of the process.\\nIn developing a model for any process, the first question\\nthat should be asked is, \u00e2\u0080\u009cWhat is the value of modeling\\nthis particular system?\u00e2\u0080\u009d Currently, the design engineer may\\nbe using empirical models that assist in interpolating infor\u00c2\u00ac\\nmation from lab-scale or pot-scale studies. The major prob\u00c2\u00ac\\nlem is scale-up, and most of the designer\u00e2\u0080\u0099s time is spent\\non concerns about operating conditions within rather nar\u00c2\u00ac\\nrow ranges in order to meet permit requirements. Added\\nto that is the ever-present shortcoming of analytical and\\nsampling methods. The answer to the question would ap\u00c2\u00ac\\npear to be that there is little value in developing more em\u00c2\u00ac\\npirical curve-fitting models for the process. The design\\nengineer might be well advised at the present time to de\u00c2\u00ac\\nvelop performance parameters, curves, and operational\\ncharts that could be used for the plants under investiga\u00c2\u00ac\\ntion. If a deterministic model of mechanistic proportions is\\nto be developed, it needs to be developed through a se\u00c2\u00ac\\nries of rigorous processes ensuring that it is, in fact, a true\\nmodel of the process.\\nWriting a mechanistic, mathematical model is generally\\neasier than verifying it. That is not to say that conceiving\\nand writing the model is trivial, but rather to emphasize the\\ndifficulty in giving the model a fair chance to fail the experi\u00c2\u00ac\\nmental test. Note that the emphasis is on a chance for\\nverification failure rather than a chance to pass. Thus an\\ninvestigator\u00e2\u0080\u0099s problem of ownership of a particular model\\npresents itself, which is not easily subjugated to the scien\u00c2\u00ac\\ntific issue of fairly and rigorously testing the model.\\nThe experimental learning process is basically iterative\\nand consists of successive and repeated use of the se\u00c2\u00ac\\nquence. Box and Hunter (1965), although not the first to\\nnote this important underlying pattern in experimentation,\\nhave best exploited the pattern and developed strategies\\nfor experimentation that efficiently lead one through the\\ncycle and advise one in determining the details of subse\u00c2\u00ac\\nquent cycles. One such cycle is illustrated in Figure 3-10.\\nIn environmental engineering, a field that relies heavily on\\nempirical methods, the unavoidable long-term character\\nof the experiments required for a system, such as a con\u00c2\u00ac\\nstructed wetland, has resulted in many different individu\u00c2\u00ac\\nals conducting rather inefficient iterations of different parts\\nof the problem. As a result, the development of a rigorous\\nmodel of the process, or parts of it, has not been achieved\\nas is true with many of the wastewater treatment processes\\ndesigned today.\\nOf particular importance in the iterative sequence are\\nthe steps of design and analysis. In this context, design is\\n50", "height": "4283", "width": "3142", "jp2-path": "constructedwetla00nati_0068.jp2"}, "69": {"fulltext": "Model\\ni\\nReliable and Pertinent\\nData\\n4\\nParametric Estimates\\ni\\nQuality of Fit\\ni\\nAdequacy of Model\\nI I\\nYes No\\ni\\nExperimentation\\nFigure 3-10. Adaptive model building\\ndevising experiments suggested by the current status of\\nthe process that will most likely improve an understanding\\nof it. Analysis would be the examination of the data in such\\na manner as to discover how far conjectures are born out\\nand spark modified or new conjectures when the old ones\\nare found wanting. Both engineering and statistics play an\\nimportant role in the process.\\n3.8.2 Status of Wetland Modeling\\nWhat is the status of model building for constructed wet\u00c2\u00ac\\nlands at this time? There are a number of ways one might\\nclassify models. One classification would include linguis\u00c2\u00ac\\ntic models, stochastic models, and deterministic models.\\nLinguistic, or word, models are qualitative and have as their\\nmain advantage the capability of representing incomplete\\nstates of knowledge not explicitly represented by the other\\ntwo types of models. Stochastic models of processes are\\nthe result of data-driven, top-down approaches to model\u00c2\u00ac\\ning and can reflect information contained in the data used\\nto prepare them. These models are useful but are data\\nintensive and require that the data be representative of\\nthe behavior of the process that they are designed to model.\\nDeterministic models, both empirical and mechanistic, are\\neither built from the bottom up based on first principles or\\nresult from careful observation of phenomena. They are\\nrobust and general, and are effective provided that the data\\nare available to support the theory and to calibrate the\\nmodel.\\nAn examination of the literature on constructed wetlands\\nsuggests that all three of these models have been pro\u00c2\u00ac\\nposed or used. Yet it is worth noting that none have really\\nmet the test of the iterative process. There are very few\\nfull-scale studies of constructed wetlands that have pro\u00c2\u00ac\\nvided a database sufficient to demonstrate success or fail\u00c2\u00ac\\nure of a given model. Most studies lack sufficient spatial\\nand temporal sampling to even identify whether a model\\nfails the experimental test of verification. In an effort to pro\u00c2\u00ac\\nvide more data, investigators use databases from a num\u00c2\u00ac\\nber of sites. Site-to-site variability makes this process sus\u00c2\u00ac\\npect. Quality control on the data collected is also of con\u00c2\u00ac\\ncern. For the most part, the data fit to constructed wet\u00c2\u00ac\\nlands is regressed from empirical models, and fit is ex\u00c2\u00ac\\npressed in terms of the coefficient of determination, R 2 It\\nis important to note that a high value of R 2 does not assure\\na valid relation nor does a low value mean that the model\\nis useless. It is often stated that R 2 explains a certain pro\u00c2\u00ac\\nportion of the variability in the observed response. If the\\ndata were from a well-designed controlled experiment, with\\nproper replication and randomization, it is reasonable to\\ninfer that a significant association of the variation in y with\\nvariation in the level of x is a causal effect of x. If, however,\\nas in the case of most wetland data, the data are observa\u00c2\u00ac\\ntional, there is a high risk of a causal relationship being\\nwrong. With observational data, there can be many rea\u00c2\u00ac\\nsons for associations among variables, only one of which\\nexhibits causality. Totally spurious correlations, often with\\n51", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0069.jp2"}, "70": {"fulltext": "high R 2 values, can arise when unrelated variables are\\ncombined.\\nOften rival models may be tentatively considered for a\\nconstructed wetland process. It is not uncommon to find\\nthat more than one model can be calibrated to fit the data\\nand give residual errors that are acceptable. In some cases,\\nthe selection of the seemingly acceptable model is of little\\npractical consequence over the range of interest. In other\\ncases, knowing which model is better may throw light on\\nfundamental questions about reaction mechanisms and\\nother phenomena under investigation. A fundamental con\u00c2\u00ac\\ncept in model discrimination is that rival models often di\u00c2\u00ac\\nverge noticeably only at extreme conditions. Thus extremes\\nmust be evaluated to provide useful statistical information.\\nModels must be put into jeopardy of failing. An excellent\\ndiscussion of this may be found in Berthouex and Brown\\n(1994).\\nIn summary, it appears premature, given the lack of qual\u00c2\u00ac\\nity-assured data, for designers of constructed wetlands to\\nrely on regressed empirical models. The problem is one of\\nextrapolation of these mostly \u00e2\u0080\u009cblack box\u00e2\u0080\u009d models from site\\nto site and extension of the model outside of the database.\\nExamination of the wide variation in parameter values (re\u00c2\u00ac\\naction coefficients, background concentrations, etc.) sug\u00c2\u00ac\\ngests that fitting data to simplistic models may be insuffi\u00c2\u00ac\\ncient at this time to provide reliable design information in\\nmost cases. Currently the design of these systems should\\nbe based on design parameters (e.g., hydraulic loading,\\nnitrogen loading, detention time, etc.) and operating crite\u00c2\u00ac\\nria that are required to meet a specific effluent limitation.\\nThis is not a novel approach, but has been used for many\\ndecades by environmental engineers in the design of highly\\ncomplex unit processes including the activated sludge pro\u00c2\u00ac\\ncess and waste stabilization ponds. Only when a carefully\\ndesigned series of iterative studies have been conducted,\\nand data based on quality-controlled specifications have\\nbeen analyzed, can rigorous models be provided for use\\nin wetland system design.\\nCurrently there is a North American Database (NADB)\\non wetlands that has been relied on for purposes of wet\u00c2\u00ac\\nland design. Efforts have been made to refine that data\u00c2\u00ac\\nbase to improve reliability. What is urgently needed at this\\ntime is an effective plan for the design of studies that will\\nprovide a comprehensive understanding of the processes\\nthat occur within wastewater wetlands. Efforts have already\\nbeen made to mathematically model some of the wetland\\nprocesses based on first principles. These models should\\nserve as the starting point for the adaptive iterative pro\u00c2\u00ac\\ncess as described in Figure 3-10. The experimental de\u00c2\u00ac\\nsign should include extensive, quality-assured, transect\\ndata at numerous selected sites (spatial variations) over\\nan extended period of time (temporal variations). Charac\u00c2\u00ac\\nterization of the wastewater must include both particulate\\nand soluble fractions of contaminants and must ensure\\nquality control of both sampling and analyses. Character\u00c2\u00ac\\nization of the wetland is also important and should include\\ndata on residence time distribution of flow, geometry, plant\\nspecies and distribution, monolithic zone coverage and\\ndistribution, and so forth. Once this database is developed,\\nthe iterative modeling of this very complex system can\\nbegin in earnest. Given the number of years of constructed\\nwetland experience, such efforts are generally overdue.\\n3.9 References\\nArmstrong, J. and W. Armstrong. 1990. Light enhanced\\nconnective throughflow increases oxygenation in rhi\u00c2\u00ac\\nzomes rhizospheres of Phragmites australis (Cav.).\\nTrin. Ex. Steud., New Phytologist, 114:121.\\nBarber, L., et al. 1999. Transformation of dissolved organic\\ncarbon in constructed wetland systems. Project Re\u00c2\u00ac\\nport, U.S. Dept. Interior, Bureau of Reclamation.\\nBayley, R.W., E.V. Thomas, and P.F. Cooper. 1973. Some\\nproblems associated with the treatment of sewerage\\nby non-biological processes. In: Applications of new\\nconcepts in physical-chemical wastewater treatment.\\nW.W. Eckenfelder and L.K. Cecil (eds.). Oxford, UK:\\nPergamon Press, pp. 119-132.\\nBella, D. 1970. Simulating the effect of sinking and vertical\\nmixing of algae population dynamics. J. Water Poll.\\nCont. Fed. 42(2):R140.\\nBerthouex, P.M. and L. Brown. 1994. Statistics for envi\u00c2\u00ac\\nronmental engineers. Boca Raton, FL: Lewis Publica\u00c2\u00ac\\ntions Inc., 287 pp.\\nBox G.E.P. and W.G. Hunter. 1965. The experimental study\\nof physical mechanisms. Technometrics, 7:23.\\nBrix, H. and H. Schierup. 1990. Soil oxygenation in con\u00c2\u00ac\\nstructed reed beds: The role of macrophyte and soil-\\natmosphere interface oxygen transport. In: P.F. Coo\u00c2\u00ac\\nper and B.C. Findlater (eds.) Proceedings of interna\u00c2\u00ac\\ntional conference on use of constructed wetlands in\\nwater pollution control. Oxford, UK: Pergamon Press.\\nBurgoon, P.S., K.R. Reddy, T.A. DeBusk, and B. Koopman.\\n1991. Vegetated submerged beds with artificial sub\u00c2\u00ac\\nstrates. II: N and P Removal. Journal ASCE-EED,\\n117(4):408-424.\\nCamp, T.R. and P.C. Stein. 1943. Velocity gradients and\\ninternal work in fluid motion. J. Boston Soc. Civ. Eng.,\\n30:209.\\nCrites, R.W., et al. 1997. Removal of metals and ammonia\\nin constructed wetlands. Water Environment Research,\\n69(2).\\nGearheart, R.A. 1993. Phosphorus removal in constructed\\nwetlands. Paper No. AC93-023-001. Presented at the\\n66th Annual WEFTEC Meeting, Anaheim, CA.\\nGearheart, R.A. 1998. The use of free surface constructed\\nwetland as an alternative process treatment train to\\nmeet unrestricted water reclamation standards. In:\\nAWT98 Proceedings, p. 559.\\n52", "height": "4283", "width": "3142", "jp2-path": "constructedwetla00nati_0070.jp2"}, "71": {"fulltext": "Gearheart, R.A. and B.A. Finney. 1996. Criteria for design\\nof free surface constructed wetlands based upon a\\ncoupled ecological and water quality model. In: Pro\u00c2\u00ac\\nceedings of 5th International Conference on Wetland\\nSystems for Water Pollution Control. IAWQ, Vienna,\\nAustria.\\nGearheart, R.A., et al. 1983. City of Areata marsh pilot\\nproject, effluent quality results\u00e2\u0080\u0094System design and\\nmanagement. Project No. C-06-2270. State Water\\nResources Control Board, Sacramento, CA.\\nGearheart, R.A., F. Klopp, and G. Allen. 1989. Constructed\\nfree water surface wetlands to treat and receive waste-\\nwater: Pilot project to full scale. In: Constructed wet\u00c2\u00ac\\nlands for wastewater treatment, D.A. Flammer (ed.)\\nChelsea, Ml: Lewis Publishers, Inc., pp. 121-137.\\nGearheart, R.A., et al. 1999 [In draft]. Free water surface\\nwetlands for wastewater treatment: A technology as\u00c2\u00ac\\nsessment. U.S. Environmental Protection Agency, Of\u00c2\u00ac\\nfice of Water Management, U.S. Bureau of Reclama\u00c2\u00ac\\ntion, Phoenix, AZ.\\nGersberg, R.M., et al. 1984. The removal of heavy metals\\nby artificial wetlands. In: Proceedings Water Reuse\\nSymposium, III. Vol. 2. AWWA Research Foundation,\\np. 639.\\nGersberg, R.M., et al. 1986. Role of aquatic plants in waste-\\nwater treatment by artificial wetlands. Water Research\\n20(3):363.\\nGersberg, R.M., R.A. Gearheart, and M. Ives. 1989. Patho\u00c2\u00ac\\ngen removal in constructed wetlands. In: Proceedings\\nfrom First International Conference on Wetlands for\\nWastewater Treatment. Chattanooga, TN, June 1988.\\nAnn Arbor, Ml: Ann Arbor Press.\\nGodschalk, G.L. and R.G. Wetzel. 1978. Decomposition\\nin littoral zones of lakes. In: R.E. Good et al. (eds.)\\nFreshwater wetlands: ecological process and manage\u00c2\u00ac\\nment potential. New York, NY: Academic Press.\\nGrady, Jr., C.P.L. and H.C. Lim. 1980. Biological wastewa\u00c2\u00ac\\nter treatment\u00e2\u0080\u0094Theory applications. New York, NY:\\nMarcel Dekker, Inc.\\nHammer, D.A. 1992. Creating freshwater wetlands.\\nChelsea, Ml: Lewis Publishers, Inc., 298 pp.\\nHannah, S.A., B.M. Austern, A.E. Eralp, and R.H. Wise.\\n1986. Comparative removal of toxic pollutants by 6\\nwastewater treatment processes. Jour. WPCF,\\n58(1):27-34.\\nHeukelekian, H. and J.L. Balmat. 1959. Chemical compo\u00c2\u00ac\\nsition of the particulate fractions of domestic sewage.\\nSewage Ind. Wastes, 31 (4):413.\\nHutchinson, G. 1967. A treatise on limnology. Vol. 2. New\\nYork, NY: John Wiley Sons.\\nKadlec, R.H. and R.L. Knight. 1996. Treatment wetlands.\\nBoca Raton, FL: Lewis-CRC Press.\\nLevine, A.D., G. Tchobanoglous, and T. Asano. 1984. Char\u00c2\u00ac\\nacterizations of the size distribution of contaminants\\nin wastewater: Treatment and reuse implication. 57th\\nAnnual Conference Water Pollution Control Federa\u00c2\u00ac\\ntion, New Orleans, LA.\\nLevine, A.D., G. Tchobanoglous, and T. Asano. 1991. Size\\ndistribution of particulate contaminants in wastewater\\nand their impact on treatability. Wat. Res., 25(8):911\\n922.\\nLewin, R.A. (ed.) 1962. Physiology biochemistry of al\u00c2\u00ac\\ngae. New York, NY: Academic Press, 751 pp.\\nLiehr, S.K. 2000. Constructed wetlands treatment of high\\nnitrogen landfill leachate. WERF Report No. 94-IRM-\\nU. NCSU.\\nLienard, A. 1987. Domestic wastewater treatment in tanks\\nwith emergent hydrohoytes: Latest results of a recent\\nplant in France. Water Sci. Tech., 19(12):373-375.\\nMetcalf and Eddy. 1991. Wastewater engineering. 3d ed.\\nNew York, NY: McGraw-Hill, Inc.\\nMitsch, W.J. and J.G. Gosselink. 1993. Wetlands. New\\nYork, NY: Van Nostrand Reinhold.\\nMunch R., C.P. Hwang, and T.H. Lackie. 1980. Wastewa\u00c2\u00ac\\nter fractions add to total treatment picture. Water Sew.\\nWks., 127:49-54.\\nO\u00e2\u0080\u0099Connor, D.J. and W.E. Dobbins. 1958. Mechanism of\\nreaeration in natural streams. Trans. Amer. Soc. Civil\\nEng., 123:641.\\nReddy, K.R. and D.A. Graetz. 1988. Carbon and nitrogen\\ndynamics in wetland soils. In: D.D. Hook et al. (eds.)\\nThe ecology and management of wetlands. Vol. I. Port\u00c2\u00ac\\nland OR: Timber Press, p. 307.\\nReed, S.C., R.W. Crites, and E.J. Middlebrook. 1995. Natu\u00c2\u00ac\\nral systems for waste management and treatment. 2d\\ned. New York, NY: McGraw-Hill.\\nRickert, D.A. and J.V. Hunter. 1972. Colloidal matter in\\nwastewater secondary effluents. J. Water Pollution\\nControl Federation, 44(1):134.\\nRose, C. and W.G. Crumpton. 1996. Effects of emergent\\nmacrophytes and dissolved oxygen dynamics in a prai\u00c2\u00ac\\nrie pothole wetland. Wetlands, 16(4):495.\\nSimpson R. L., et al. 1981. Dynamics of nitrogen, phos\u00c2\u00ac\\nphorus, and heavy metals in Delaware River freshwa\u00c2\u00ac\\nter tidal wetland. U.S. Environmental Protection\\nAgency, Final Report, Corvallis Environmental Re\u00c2\u00ac\\nsearch Lab, Corvallis, OR.\\nI\\n53", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0071.jp2"}, "72": {"fulltext": "Table 4-1. Loading and Performance Data for Systems Analyzed in this Document (DMDB).\\nConstituent\\nMin\\nPollutant Loading\\nRate (kg/ha-day)\\nMean\\nMax\\nMin\\nInfluent (mg/L)\\nMean\\nMax\\nMin\\nEffluent (mg/L)\\nMean\\nMax\\nBOD,\\n2.3\\n51\\n183\\n6.2\\n113\\n438\\n5.8\\n22\\n70\\nTSS\\n5\\n41\\n180\\n12.7\\n112\\n587\\n5.3\\n20\\n39\\nnh 4 -n\\n0.3\\n5.8\\n16\\n3.2\\n13.4\\n30\\n0.7\\n12\\n23\\nTKN\\n1.0\\n9.5\\n20\\n8.7\\n28.3\\n51\\n3.9\\n19\\n32\\nTP\\n0.56\\n1.39\\n2.41\\n0.68\\n2.42\\n3.60\\nFC\\n42000\\n73000\\n250000\\n112\\n403\\n713\\nBOD Biochemical Oxygen Demand (5 day)\\nTSS Total Suspended Solids\\nNH 4 -N Ammonia Nitrogen\\nTKN Total Kjeldahl Nitrogen\\nTP Total Phosphorus\\nFC Fecal Coliform, cfu/IOOmL\\nance of constituents, e.g., not all systems reported all con\u00c2\u00ac\\nstituents.\\n4.1.3 BOD Performance\\nThe relationship between average biochemical oxygen\\ndemand (BOD) loading and average BOD effluent con\u00c2\u00ac\\ncentration for the studied systems is shown in Figure 4-1.\\nThere is a general trend between increased BOD loading\\nand increased effluent concentration up to the highest load\u00c2\u00ac\\ning of 183 kg/ha-day if only the fully vegetated designs are\\ntaken into account. The figure reveals considerable efflu\u00c2\u00ac\\nent variation for a given BOD loading and shows consider\u00c2\u00ac\\nable variation in effluent quality at the lower BOD loading\\nrates. The effect of the background BOD, due to release\\nfrom previously settled influent TSS and plant decomposi\u00c2\u00ac\\ntion is especially evident in systems with low loading rates.\\nFigure 4-2 illustrates the internal BOD load which occurs\\nfrom the partial anaerobic digestion of previously settled\\norganic solids and plant exudates and other byproducts of\\nanaerobic biodegradation. The portion of that internal load\u00c2\u00ac\\ning which is due to the plant detritus has been measured\\nand is illustrated in Figure 4-3. Since anaerobic processes\\nare extremely sensitive to temperature, these internal load\u00c2\u00ac\\nings begin in the spring as water temperature rises and\\ncontinue until the backlog of settleable organics and plant\\ndetritus accumulated over the winter is exhausted. Plant\\nexudates and senescent byproducts occur in their own\\ncycles which provide internal loading to the system in a\\ndynamic manner. Background BOD concentrations can\\nrange up to almost 10 mg/L.\\nA more conservative analysis of Figure 4-1 indicates that\\na fully vegetated FWS should not be loaded above 40 kg\\nBOD/ha-d if a secondary effluent BOD standard (30 mg/L)\\nis to be met. Restricting the analysis to open water FWS\\nsystems indicates that loadings up to 45 kg/ha-d yielded\\neffluent BOD of less than 20 mg/L, and loadings up to 130\\nkg/ha-d always met this quality. However, there is only one\\ndata point above 45 kg/ha-d and it is at 130 kg/ha-d. The\\nopen water FWS systems which permit reaeration and\\naerobic oxidation should be designed for an areal loading\\nof no more than 60 kg/ha-d to consistently attain an efflu\u00c2\u00ac\\nent BOD of 30 mg/L until more performance data are ob\u00c2\u00ac\\ntained. Coincidently, Stowell (1988) recommended an up\u00c2\u00ac\\nper limit of 60 to 70 kg BOD/ha-d to prevent odors from an\\nFWS system. Open water FWS systems loaded below 45\\nkg/ha-d can be expected to attain effluent BODs of 20 mg/\\nL or less. Analysis of the TADB yields a similar maximum\\nareal BOD loading rate of 50 kg/ha-d without differentia\u00c2\u00ac\\ntion between fully vegetated and open water FW systems\\n(EPA, 1999).\\n4.1.4 TSS Performance\\nThe effectiveness of FWS treatment wetlands to remove\\ntotal suspended solids (TSS) is recognized as one of their\\nprincipal advantages. Over a range of loadings from 5 to\\n180 kg/ha-day, there are several relationships between\\nloading and effluent TSS quality with the DM data, as shown\\nin Figure 4-4. Under a fairly narrow range of solids load\u00c2\u00ac\\nings, (up to 30 kg/ha-d) secondary effluent TSS concen\u00c2\u00ac\\ntrations 30 mg/L) can be attained with fully vegetated\\nsystems. Since physical processes dominate the removal\\nof TSS, similar designs should produce similar effluent\\nqualities. Analysis of the TADB (EPA, 1999) yields similar\\nmaximum loading.\\nTSS removal is most pronounced in the inlet region of a\\nFWS constructed wetland. Generally, the influent TSS from\\noxidation pond systems are removed in the first 2 to 3 days\\nof the nominal hydraulic retention time in fully vegetated\\nzones near the inlet (Gearheart.et al, 1989; Reed, et al,\\n1995; Kadlec and Knight, 1996). Enhanced settling and\\nflocculation processes account for most of this removal,\\nand the overall removal efficiency is a function of the ter\u00c2\u00ac\\nminal settling velocity of the influent and flocculated sol\u00c2\u00ac\\nids. Long-term removal of detrital material will likely be re\u00c2\u00ac\\nquired 10-15 years into operation. The separated solids\\nundergo anaerobic decomposition, releasing soluble dis\u00c2\u00ac\\nsolved organic compounds and gaseous by-products, car\u00c2\u00ac\\nbon dioxide and methane gas, to the water column. Figure\\n4-2 shows the reduction of total and soluble BOD and TSS\\nthrough a pilot project wetland cell. Approximately 80% of\\nthe TSS is removed in the first two days of theoretical HRT\\nprimarily due to enhanced sedimentation and flocculation.\\n56", "height": "4283", "width": "3142", "jp2-path": "constructedwetla00nati_0072.jp2"}, "73": {"fulltext": "80\\n70\\nV\\n60\\nQ\\nO\\nCD\\nc\\nD\\n3\\nLU\\n50\\n40\\n30\\n20\\nV\\nV\\nV\\n10\\n0\\no\\no\\nV\\n00\\no\\no\\nvv\\nV\\nV\\no\\nV\\nV Fully Vegetated\\nO Significant Open Area\\n0\\n50\\n100\\n150\\nBOD Load (kg/ha*day)\\nFigure 4-1. BOD effluent vs. areal loading (DMDB)\\nFigure 4-2. Release of soluble BOD during early stage\\n200\\n57", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0073.jp2"}, "74": {"fulltext": "Percent Dry Weight of Standing Crop to\\nWater Column\\nFigure 4-3. Annual detritus BOD load Scripus and Typha assuming 15,000 kg/Ha standing crop (Gearheart Finney, 1996)\\n50\\n40\\nV\\n05\\nE.\\nCO\\nCO\\nc\\na\\n3\\n30\\n20\\n10\\nV\\nV\\no\\no\\noo\\nV\\nV\\n0\\nV\\no\\nV\\no O\\nV\\nT\\n50\\no\\nV\\no\\nV\\no\\nV Fully Vegetated\\nO Significant Open Area\\n1 1\\n100 150\\nTSS Load (kg/ha-day)\\nFigure 4-4. TSS loading vs. TSS in effluent (DMDB)\\n200\\n58", "height": "4283", "width": "3142", "jp2-path": "constructedwetla00nati_0074.jp2"}, "75": {"fulltext": "Subsequently, the removal essentially ceases without sub\u00c2\u00ac\\nsequent open zones which can provide conditioning and\\ntransformation processes which may improve overall re\u00c2\u00ac\\nmoval of TSS attainable by the system.\\nA closer analysis of the DMDB again shows that TSS\\nloadings can be higher for FWS systems with open-water\\nzones. Only one very small site with such zones exceeded\\nsecondary effluent TSS standards (30 mg/L), and it was\\nloaded at more than 90 kg/ha-d. Below a loading of 30 kg/\\nha-d an effluent of 20 mg/L of TSS was consistently achiev\u00c2\u00ac\\nable. It is therefore recommended that in addition to that\\nareal loading limitation a maximum loading of 50 kg/ha-d\\nbe employed to attain an effluent of 30 mg/L of TSS until\\nmore performance data can be obtained.\\n4.1.5 Nitrogen Performance\\nAny discussion of nitrogen species in FWS constructed\\nwetlands must be predicated by a return to first principles,\\nas described in Chapter 3. Given the numerous transfor\u00c2\u00ac\\nmation possibilities and the dearth of removal mechanisms,\\nthere are only a few meaningful explanations. Influent ni\u00c2\u00ac\\ntrogen for the typical applications of this manual will be\\nprimarily in the form of ammonia-nitrogen (NFI4-N) with a\\nsignificant organic nitrogen (ON) contribution. Approxi\u00c2\u00ac\\nmately 10 to 15% of the oxidation pond effluent TSS due\\nto algae is organic nitrogen (Balmer and Vik, 1978). Since\\nboth are measured by the total Kjeldahl nitrogen (TKN)\\ntest, it becomes the likely standard of areal loading analy\u00c2\u00ac\\nsis. Any discussion of just one species (typically, NH4-N)\\nis of little value and often misleading to readers.\\nAnother key discussion point is the inherent inability of\\nfully vegetated FWS systems to nitrify a typical FWS influ\u00c2\u00ac\\nent, as described in the preceding paragraph, within a prac\u00c2\u00ac\\ntical number of days of HRT. During periods of senescence\\nwhen fully vegetated zones become partially open-water\\nzones, different mechanisms of treatment can replace\\nthese which dominate during the normal growing season,\\nif the climate can sustain them. This is further reinforce\u00c2\u00ac\\nment for the fact that there are few absolutes in natural\\nsystems. Sadly, these conditions are rarely recognized or\\nadequately described and measured, making use of most\\nexisting data sets open to some question. However, in this\\nanalysis the fact that a system is classified as either fully\\nvegetated or as having significent open-water zones aids\\nin explaining many anomolies.\\n4.1.5.1 TKN Performance\\nFigure 4-5 illustrates that for a fully vegetated FWS which\\nreceives 30 to 50 mg/L of TKN the effluent exceeds 24\\nmg/L since the only removal mechanism is sedimentation\\n35\\nCT\\nE\\nz\\nc\\n4\\n3\\nLU\\n30\\n25\\n20\\n15\\n10\\n5\\nV\\nv\\nv\\nv\\nv\\nV\\nV\\nooo\\nT\\n5\\nT\\n10\\nT\\n15\\nV Fully Vegetated\\nO Significant Open Area\\n20\\n25\\nTKN Load (kg/ha-day)\\nFigure 4-5. Effluent TKN vs. TKN loading\\n59", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0075.jp2"}, "76": {"fulltext": "of organic nitrogen (ON). One more lightly loaded (3.3 kg/\\nha-d) fully vegetated system did produce an effluent TKN\\nof about 9 mg/L. The three open-water zone systems were\\nall lightly loaded 2.8 kg/ha-d) and produced effluent TKN\\nof about 4 mg/L. Since these latter designs offer a mecha\u00c2\u00ac\\nnism to transform the TKN to nitrate-nitrogen (N03 -N),\\nwhich could subsequently be removed through denitrifica\u00c2\u00ac\\ntion, they could conceivably be loaded more heavily and\\nstill meet a stringent total nitrogen standard (e.g., 10 mg/\\nL). No more heavily loaded systems were indicated in the\\nDMDB. The TADB analysis (EPA, 1999) did indicate that\\nany FWS system which received a TKN loading of less\\nthan 3.3 kg/ha-d could meet an effluent TKN of less than\\n10 mg/L, but does not subdivide results into the two\\nsubcatagories used herein. Arcata\u00e2\u0080\u0099s open-water-zone sys\u00c2\u00ac\\ntems have been able to maintain effluent total nitrogen (TN)\\nbelow 5 mg/L at loadings of up to 3 kg TN/ha-d (Gearheart,\\n1995) through the denitrification provided near the FWS\\nsystem outlet which is fully vegetated. Maximum TKN load\u00c2\u00ac\\nings to sustain an effluent TKN of less than 10 mg/L can\\nconservatively be set at 5 kg/ha-d until more data are made\\navailable. This only applies to open water FWS systems,\\nwhile fully vegetated systems are limited to only a small\\npercentage of TKN removal due to the settling of organic\\nnitrogen particulate matter.\\n4.1.5.2 Denitrification\\nThe extent of nitrate removal via denitrification is de\u00c2\u00ac\\npendent on the extent of the prior conversion of TKN to\\nN03-N, a labile carbon or other energy source and anaero\u00c2\u00ac\\nbic/anoxic conditions in the water column. Therefore, deni\u00c2\u00ac\\ntrification, which converts N03-N to gaseous end prod\u00c2\u00ac\\nucts which can leave the constructed wetland, is best suited\\nto a fully vegetated condition. Further, any N03-N which\\nenters a FWS wetland is likely to be quickly removed, while\\nany nitrate formation (nitrification), which occurs in the\\nopen-water zones of the FWS can be removed near the\\nfully vegetated outlet zone if the conditions noted above\\nare met. The DMDB offers no assistance in that all the\\nsystems which had nitrate-nitrogen in their influent had it\\nat very low concentrations (average 2.47 mg/L), even\\nthough effluent concentrations were lower (average 2.22\\nmg/L).\\nGearheart (1995) reports that the carbon produced from\\ndecaying macrophytes is sufficient to denitrify 100 mg N03-\\nN/L in an FWS and that the reaction rate is temperature\\ndependent, signifying its biological nature. Reed, et al\\n(1995) and Crites and Tchobanoglous (1998) also indicate\\nthat FWS systems have the capablility to denitrify, but they\\noffer no specific examples. Therefore, denitrification should\\nbe feasible in FWS systems as long as there is sufficient\\ndetention time in fully vegetated zones with anaerobic/an\u00c2\u00ac\\noxic conditions.\\n4.1.5.3 Ammonia Nitrogen Performance\\nAlso, as noted previously, ammonia-nitrogen (NH4-N)\\nlimits are often specified for treatment facilities in their\\nNPDES permit. However, the level of effluent ammonia in\\nan FWS constructed wetland effluent bears only a tenu\u00c2\u00ac\\nous relationship to its influent NH4-N concentration. The\\nnormal case will find that all influent nitrogen is measured\\nas TKN, and that this total will be divided between organic\\nnitrogen and NH4-N. It is likely that this total nitrogen will\\nbe reduced in any FWS owing to the loss of organic nitro\u00c2\u00ac\\ngen due to enhanced settling. In the DMDB the average\\nTKN removal was 32%, while the fully vegetated systems\\nreported 28%. This difference is not larger because the\\nopen-water FWS systems were few in number and were\\nall loaded more lightly. Although one can plot the effluent\\nNH4-N vs NH4-N loading from the DMDB, the data dem\u00c2\u00ac\\nonstrate no useful relationship. Therefore, unless a FWS\\nis designed for very low TKN loadings with an ample open-\\nwater zone to nitrify the influent, there is no meaningful\\nchance to meet any NH4-N effluent standard which is sig\u00c2\u00ac\\nnificantly lower 30%) than the influent concentration.\\n4.1.5.4 Other Nitrogen Performance\\nSince total nitrogen is the sum of all forms of nitrogen, it\\nwill be reduced through nitrification/denitrification, the loss\\nof organic nitrogen due to flocculation and sedimentation\\nand plant uptake of NH4-N. Since some of this settled frac\u00c2\u00ac\\ntion will return to the mainstream as the settled organics\\npartially digest and the plant uptake will return due to se\u00c2\u00ac\\nnescence, the total nitrogen budget should be evaluated\\non an annual basis. The returned nitrogen will likely be in\\nthe same two forms (organic and ammonia-nitrogen) as\\nthe normal influent TN load, making this internal load very\\ncompatible with the external load. Given the transformability\\nof individual nitrogen components between each other\\nbased on the conditions existing at different locations in\\nthe FWS wetland, the designer needs to provide passive\\ncontrols(e.g..depth and vegetation patterns) if he or she\\nwishes to remove a substantial portion of the incoming ni\u00c2\u00ac\\ntrogen load.\\n4.1.6 Total Phosphorus Performance\\nOnly 4 of the DMDB systems measured TP loadings and\\neffluent quality, as shown in Figure 4-6. While some ap\u00c2\u00ac\\nproximate comparisons can be made, the need to sepa\u00c2\u00ac\\nrate the inorganic phosphorus performance from the or\u00c2\u00ac\\nganic particulate phosphorus performance makes the lack\\nof DM data impossible to utilize effectively, therefore, the\\nTA database (EPA.1999) is used for an approximate analy\u00c2\u00ac\\nsis.\\nFigure 4-7 shows that over a range of loading up to 4.5\\nkg/ha-day at the TADB sites, total phosphorus effluent con\u00c2\u00ac\\ncentration generally increased with loading (USEPA, 1999).\\nAt the lower loading rates 0.55 kg/ha-d), however, the\\neffluent phosphorus concentration was less than 1.5 mg/\\nL. The fractional distribution of TP in municipal wastewa\u00c2\u00ac\\nter previously treated by lagoons is variable and has not\\nbeen well documented. Balmer and Vik (1978) found fil\u00c2\u00ac\\ntered P/total P to be 20-25%, but the flocculation and sedi\u00c2\u00ac\\nmentation superiority of the initial FWS fully vegetated zone\\nwill remove a significant of those forms which enter as\\nsupracolloidal and settleable solids. Gearheart (1993) has\\nperformed extensive studies on the Areata FWS systems\\nand found a relationship between areal loading and phos-\\n60", "height": "4283", "width": "3142", "jp2-path": "constructedwetla00nati_0076.jp2"}, "77": {"fulltext": "Effluent TP (mg/L)\\n4\\n3.5\\n2.5\\n2\\n1.5\\n1\\n0 0.5 1 1.5 2 2.5 3\\nTP Load (kg/ha*day)\\nFigure 4-6. Effluent TP vs. TP areal loading\\nFigure 4-7. Average total phosphorus loading rate vs. total phosphorus effluent concentration for TADB wetland systems\\n61", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0077.jp2"}, "78": {"fulltext": "phorus removal. An upper limit of 1.5 mg/L removal of or\u00c2\u00ac\\nthophosphates was found at loadings of less than 1.5 kg/\\nha-d and a hydraulic retention time (HRT) of at least 15\\ndays. HRTs of less than 7 days yielded a maximum re\u00c2\u00ac\\nmoval of 0.7 mg/L of orthophosphate, as shown in Figure\\n4-8.\\nThe phosphorus cycle of uptake during the growing sea\u00c2\u00ac\\nson and release during senescence and the initial sub\u00c2\u00ac\\nstantial uptake of phosphorous by the soil of the FWS fur\u00c2\u00ac\\nther confounds short-time studies of phosphorus transfor\u00c2\u00ac\\nmations and removal. As a final issue in this conundrum,\\nthe particulate fractionation and chemical speciation of the\\ninfluent phosphorus will also have some impact on trans\u00c2\u00ac\\nformations and fate of P. Therefore, long-term studies which\\ndifferentiate between P forms and document vegetation\\ncondition, climate, temperature and other pertinent water\\nquality parameters are necessary to provide meaningful\\ninformation for future FWS system designers, but the an\u00c2\u00ac\\nnual P removal by these systems is quite limited based on\\nmechanistic evaluations and controlled studies.\\n4.1.7 Fecal Coliform Performance\\nOnly four systems in the DMDB reported fecal coliform\\n(FC) data, and three of those were fully vegetated sys\u00c2\u00ac\\ntems. The average removal was just over 2 logs, from\\n72,700/1 OOmL to 400/100ml. The TADB (EPA, 1999) re\u00c2\u00ac\\nsults are shown in Figure 4-9 which offers no obvious rela\u00c2\u00ac\\ntionship between inlet and outlet concentrations. Figure 4-\\n10 (Gearheart, 1989) shows results from the Areata pilot\\nstudy which demonstrate that flocculation/sedimentation\\nis the primary FC removal mechanism for fully vegetated\\ncells or zones. This figure is especially valuable in light of\\nthe world literature on FC dieoff in lagoons which identify\\nsolar radiation as the primary disinfection mechanism\\n(Mara, 1975). Such a mechanism can be effective in open-\\nwater zones of the FWS, but the same mechanisms which\\nremove settleable and colloidal solids in fully vegetated\\nzones are responsible for FC removal in those zones.\\nFigure 4-8. Retention Time vs. Orthophosphate Removal (mg/I)\\nEstimates of the internal addition of background fecal\\ncoliform by wildlife in treatment wetlands are provided by\\nthose systems that receive disinfected influent. For ex\u00c2\u00ac\\nample, the Areata Enhancement Wetland received chlori\u00c2\u00ac\\nnated effluent, and during the period 1990-1997\\n(Gearheart,et al,1998), the effluent FC was less than 500\\nMPN/1 OOmL about 80% of the time. This is a system with\\nlarge open-water zones that supports a wide variety and\\nhigh population of aquatic birds and mammals. Higher lev\u00c2\u00ac\\nels of background FC levels are found during the fall and\\nwinter bird migration period. A similar study on the same\\nsystem during 1995-1996 showed that the effluent mean\\nwas 40 CFU/IOOmL, was less than 300 CFU/IOOmL over\\n90 percent of the time, and on no occasion exceeded 500\\nCFU/1 OOmL. Studies of MS-2 coliphage showed similar (2\\nlogs) removal to that which was obtained with FC\\n(Gearheart, 1995).\\nThe considerable temporal variability in the effluent mi\u00c2\u00ac\\ncroorganism counts produced by treatment wetlands and\\nconventional treatment technologies suggests the use of\\ngeometric averaging to determine monthly mean values\\nfrom daily or weekly measurements. Even with geometric\\nmeans, individual monthly values are frequently 10 times\\nlarger or smaller than the long-term mean for many treat\u00c2\u00ac\\nment wetlands, possibly due to wildlife habitat features.\\nThis implies that at sites which have strict FC restrictions,\\nthe ability to disinfect the FWS effluent is required.\\n4.1.8 Metals Other Particulate-Oriented\\nPollutants\\nWhile some metals are required for plant and animal\\ngrowth in trace quantities (barium, boron, chromium, co\u00c2\u00ac\\nbalt, copper, iodine, iron, magnesium, manganese, mo\u00c2\u00ac\\nlybdenum, nickel, selenium, sulfur, and zinc), these same\\nmetals may be toxic at higher concentrations. Other met\u00c2\u00ac\\nals may be toxic at even very low concentrations (e.g. ar\u00c2\u00ac\\nsenic, cadmium, lead, mercury, and silver) (Gearheart,\\n1993).\\nInformation from FWS treatment wetlands indicates that\\na fraction of the incoming metal load will be trapped and\\neffectively removed through sequestration with settleable\\nsuspended solids and soils. For many metals, the limited\\ndata indicate that concentration reduction efficiency and\\nmass reduction efficiency correlate with TSS reduction.\\nWetland background metal concentrations and internal\\nprofiles are not well known. It has been shown that chro\u00c2\u00ac\\nmium levels higher than 0.1 mg/L and copper levels higher\\nthan 1.0 mg/L have detrimental effects on a floating duck\u00c2\u00ac\\nweed species (Lemna gibba). Table 4-2 shows metal con\u00c2\u00ac\\ncentration data obtained from a constructed wetland dem\u00c2\u00ac\\nonstration project in Sacramento, where disinfected acti\u00c2\u00ac\\nvated sludge effluent was applied to parallel 1.44 acre cells,\\neach with a hydraulic loading of 65 m3/ha-d and similar\\nplant density.\\nThe valence and form of each metal was not determined,\\nbut nickel and arsenic appeared to be the most resistent\\nto removal (SCRSD, 1998). Several researchers have stud-\\n62", "height": "4283", "width": "3142", "jp2-path": "constructedwetla00nati_0078.jp2"}, "79": {"fulltext": "10,000 1\\no\\no\\n0)\\nn\\nE\\n3\\nC,\\no\\nc\\n0\\n_3\\n5=\\nLU\\n1,000\\n100\\n1\\n10\\n100 1,000 10,000 100,000 1 000,000\\nInfluent FC (number/100 mL)\\nFigure 4-9. Average influent FC concentration vs. FC effluent concentration for TADB wetland systems\\n10 5\\n10 4\\n1,000\\n100\\nFigure 4-10. Areata pilot Cell 8, TSS, BOD, FC\\nTable 4-2. Trace Metal Concentrations and Removal Rates, Sacramento Regional Wastewater\\nTreatment Plant (SCRSD, 1998).\\nRemoval\\nMetal\\nInfluent (mg/L)\\nEffluent (mg/L)\\nRate\\nMin\\nMean\\nMax\\nMin\\nMean\\nMax\\nSilver\\n0.25\\n0.29\\n0.32\\n0.02\\n0.03\\n0.03\\n90\\nArsenic\\n2.00\\n2.23\\n2.60\\n1.50\\n2.20\\n3.10\\n1.3\\nCadmium\\n0.040\\n0.077\\n0.140\\n0.005\\n0.009\\n0.019\\n88\\nChromium\\n0.50\\n1.05\\n1.40\\n0.50\\n0.77\\n3.10\\n27\\nCopper\\n4.60\\n8.62\\n17.00\\n1.60\\n4.04\\n7.00\\n19\\nMercury\\n0.0084\\n0.0105\\n0.0144\\n0.0021\\n0.0031\\n0.0041\\n71\\nNickel\\n4.30\\n8.23\\n23.00\\n4.10\\n8.96\\n20.00\\nLead\\n0.25\\n0.58\\n1.20\\n0.05\\n0.14\\n0.26\\n55\\nAntimony\\n0.40\\n0.41\\n0.42\\n0.12\\n0.15\\n0.20\\n63\\nSelenium\\n0.50\\n0.50\\n0.50\\n0.50\\n0.50\\n0.50\\nZinc\\n6.4\\n26.2\\n34.0\\n1.30\\n3.53\\n8.70\\n70\\n63", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0079.jp2"}, "80": {"fulltext": "ied particle sizes vs removal rates. Most have concentrated\\non urban mechanical wastewater treatment systems.\\nOdegaard (1987) noted that except for nickel 50 to 75% of\\nthe incoming metals (zinc, copper, chromium, lead, and\\ncadmium) in the wastewater were associated with the TSS.\\nHannah, et al, (1986) showed that facultative lagoons re\u00c2\u00ac\\nmoved 40 to 80% of metals, including nickel. The sum\u00c2\u00ac\\nmary of these and other studies is that most metals, with\\nthe exception of nickel, boron, selenium, and arsenic, tend\\nto associate with removable solids fractions. Gearheart and\\nFinney (1996) evaluated particle size removals of oxida\u00c2\u00ac\\ntion pond effluent in a FWS wetland (see Table 4-3). Their\\nresults show that the settleable solids 100 m) portion\\nof BOD, COD and TSS are essentially completely removed,\\nthe supracolloidal 1 to 100 m) fraction is 80 to 90% re\u00c2\u00ac\\nmoved, while the remaining 1 m) fractions are less im\u00c2\u00ac\\npacted.\\n4.1.9 Stochastic Variability\\nFree water surface (FWS) treatment wetlands demon\u00c2\u00ac\\nstrate the same type of water quality variability typical of\\nother complex biological treatment processes. While inlet\\nconcentration pulses are frequently dampened through the\\nlong hydraulic and solids retention times of the treatment\\nwetland, there is always significant spatial and temporal\\nvariability in wetland water pollutant concentrations. The\\nstochastic character of rainfall and the periodicity and sea\u00c2\u00ac\\nsonal fluctuation in ET contribute to much of this variability\\nin the concentrations in wetland effluents. Better design\\nand operational factors could reduce some of the variation\\nseen in systems to date. Each site and its unique climatol\u00c2\u00ac\\nogy require the designer to consider the effect these vari\u00c2\u00ac\\nables will have on the sizing, depth, and configuration of\\nthe system.\\n4.2 Wetland Hydrology\\nThe hydrology of FWS wetlands is considered by many\\nto be the most important factor in maintaining wetland struc\u00c2\u00ac\\nture and function, determining species composition, and\\nTable 4-3. Fractional Distribution of BOD, COD and TSS in the\\nOxidation Pond Effluent and Effluent from Marsh Cell 5\\n(Gearheart and Finney, 1996)\\nBOD COD TSS\\nmg/L\\nmg/L\\nmg/L\\nOxidation Pond\\nFraction\\nTotal\\n27.5\\n100\\n80\\n100\\n31.0\\n100\\nSettleable\\n3.7\\n13\\n5\\n6\\n5.8\\n19\\nSupracolloidal\\n13.7\\n50\\n23\\n29\\n25.2\\n81\\nColloidal-soluble\\n10.1\\n37\\n52\\n65\\nMarsh Fraction\\nTotal\\n4.8\\n100\\n50\\n100\\n2.3\\n100\\nSettleable\\n0\\n0\\n0\\n0\\n0.3\\n13\\nSupracolloidal\\n1.2\\n24\\n4\\n8\\n2.0\\n87\\nColloidal-soluble\\n3.6\\n76\\n46\\n92\\ndeveloping a successful wetlands project (Mitsch and\\nGosselink, 1993). The following section describes the most\\ncommon method for characterizing wetland hydrology: the\\ndevelopment of a wetland water balance.\\n4.2.1 Wetland Water Balance\\nThe wetland water balance quantifies the hydrologic\\nbalance between inflows, outflows, and internal gains and\\nlosses of water to a wetland, in relation to the wetland vol\u00c2\u00ac\\nume or storage capacity. The sources of water to a FWS\\nconstructed wetland are wastewater inflow and precipita\u00c2\u00ac\\ntion, snowmelt and direct runoff from the wetland catch\u00c2\u00ac\\nment (i.e. berms and roads). Water losses from a FWS\\nconstructed wetland occur through the outlet, evapotrans-\\npiration, infiltration, and bank storage (wicking). A thorough\\nunderstanding of the dynamic nature of the wetland water\\nbalance, and how this balance affects pollutants, is useful\\nin the planning and design of FWS constructed wetlands.\\nAn overall wetland water balance is the first step in de\u00c2\u00ac\\nsigning a FWS constructed wetland, and should be com\u00c2\u00ac\\npleted prior to the actual design steps described later in\\nthis chapter. At a minimum, a detailed monthly or seasonal\\nwater balance, which considers all potential water losses\\nand gains, should be conducted for any proposed FWS\\nconstructed wetland. An annual water balance may miss\\nimportant seasonal wetland water gains or losses, such\\nas heavy periods of winter precipitation or high summer\\nevapotranspiration rates, which can affect FWS constructed\\nwetland pollutant effluent concentrations. Water balances\\nperformed over shorter time periods than monthly will cap\u00c2\u00ac\\nture additional information about the dynamics of a wet\u00c2\u00ac\\nlands hydrology, but the increased cost of data acquisition\\nwill not generally be justified.\\nThe wetland water balance for a FWS constructed wet\u00c2\u00ac\\nland can be expressed in generic units (L=length; T=time)\\nas:\\nQ 0 Q f Q sm -Q b Q e (P+ET+I)A W (4-1)\\ndt\\nwhere:\\nA w wetland water surface area (L 2\\nET evapotranspiration rate (L/T),\\nI infiltration to groundwater (L/T),\\nP precipitation rate (L/T),\\nQ b berm loss rate (L 3 /T),\\nQ c catchment runoff rate (L 3 /T),\\nQ o wastewater inflow rate (L 3 /T),\\nQ e wetland outflow rate (L 3 /T),\\nQ sm snowmelt rate (L 3 /T),\\nt time (T), and\\nV w water volume or storage in wetland (L 3\\nThe impact of wet weather and snowmelt on the waste-\\nwater inflow (Q o is external to the water balance.\\nSome of the terms in Equation 4-1 may be deemed in\u00c2\u00ac\\nsignificant and can be neglected, simplifying calculations\\nand data collection requirements. For example, ground-\\n64", "height": "4283", "width": "3142", "jp2-path": "constructedwetla00nati_0080.jp2"}, "81": {"fulltext": "water infiltration (I) and berm losses (Q b can be neglected\\nif the wetland is lined with an impermeable barrier, and the\\nsnowmelt (Q sm is only important in certain locations.\\n4.2.2 Wastewater Inflow\\nThe daily wastewater inflow flow rate (Q o will almost\\nalways be the primary inflow into a FWS constructed wet\u00c2\u00ac\\nland. If the FWS wetland is being added to an existing\\nwastewater treatment process, wastewater flow rates may\\nalready be measured. If the wastewater flow rates and\\nvariability are not known, they can be estimated using con\u00c2\u00ac\\nventional engineering methods. Examples of variable\\nwastewater flows include seasonal peaks from vacation\\ncommunities and seasonal high infiltration and inflow rates\\ninto collection systems.\\n4.2.3 Precipitation, Snowmelt, and\\nCatchment Runoff\\nDepending on the time period of the water balance, daily,\\nmonthly or seasonal precipitation and snowmelt data may\\nbe required. Precipitation inflows into a wetland come from\\ndirect precipitation (P) onto the wetland surface area and\\nrunoff from the wetland catchment (Q c Snowmelt\\n(Q )accounts for the amount of water entering the wet-\\nlana from melting snow from the wetland catchment. The\\neffects of precipitation on the wetland water balance are\\nnormally significant, while snowmelt can be seasonably\\nsignificant only in certain climates. Q c is a significant factor\\nonly in the rarest of circumstances. c\\n4.2.4 Wastewater Outflow\\nThe wastewater outflow (Q e corresponds to the amount\\nof treated wastewater leaving the FWS constructed wet\u00c2\u00ac\\nland over a specified time period. Wastewater outflow re\u00c2\u00ac\\nflects the balance between inflows, additional water gains\\nand losses, and the change in storage of the FWS con\u00c2\u00ac\\nstructed wetland.\\n4.2.5 E vapotranspiration\\nWetland evapotranspiration (ET) is the combined water\\nloss due to evaporation from the water surface and tran\u00c2\u00ac\\nspiration from wetland vegetation. The loss of water from\\nET affects the wetland in two ways. It increases the hy\u00c2\u00ac\\ndraulic retention time by removing water, and can concen\u00c2\u00ac\\ntrate certain pollutants, especially conservative dissolved\\nconstituents. For non-conservative constituents, such as\\nBOD, an increase in the hydraulic retention time may pro\u00c2\u00ac\\nvide a modified removal rate which can either partially off\u00c2\u00ac\\nset or enhance the concentrating effects of ET.\\nSpecific ET rates have proven difficult to accurately\\nmeasure in FWS wetlands. As a consequence, it is com\u00c2\u00ac\\nmon practice in wetland design to assume that wetland\\nET rates are equivalent to some percentage of open water\\nor pan evaporation rates. Kadlec and Knight (1996) rec\u00c2\u00ac\\nommend that ET be assumed equal to 70 to 80% of Class\\nA pan evaporation in fully vegetated FWS systems. Reed,\\net al, (1995) suggest 80% of the pan rate. Since ET rates\\nin FWS systems may vary from those in open waters to\\nthose in fully vegetated zones, an overall average rate may\\nbe useful. A rate of 70 to 75% of the pan rate is a reason\u00c2\u00ac\\nable assumption since the two are not significantly differ\u00c2\u00ac\\nent. Maximum ET rates have been found in smaller wet\u00c2\u00ac\\nlands or wetland test cells with small area to perimeter\\nratios (Gearheart, et al, 1993). ET rates of up to 5 mm/d\\nare found in the southern U.S., and Qe may approach zero\\nduring these periods (EPA, 1999).\\n4.2.6 Infiltration and Berm Losses\\nInfiltration (I) is the loss of water that occurs into the bot\u00c2\u00ac\\ntom soils or berms of a FWS constructed wetland. If\\npresent, infiltration decreases the outlet flow rate, effec\u00c2\u00ac\\ntively increasing the water retention time and increasing\\nthe potential for constituent removal. Constituent reduc\u00c2\u00ac\\ntion may be further improved by the loss of soluble pollut\u00c2\u00ac\\nants into the soil as the water infiltrates. Infiltration tends\\nto reduce with time as clogging of soil pores progresses\\n(Middlebrooks, et al, 1982). If the FWS constructed wet\u00c2\u00ac\\nland is lined with some type of impermeable barrier, infil\u00c2\u00ac\\ntration can be neglected in the water balance. If not, siting\\non more permeable soils might endanger ground water\\nquality.\\n4.2.7 Wetland Volume\\nThe outlet in a FWS constructed wetland generally con\u00c2\u00ac\\nsists of a control structure that can regulate water depths\\nin the wetland. Increasing or decreasing water levels\\nchanges the wetland volume, which influences the water\\nbalance by providing more or less storage capacity. The\\nwetland volume (V w or storage capacity directly influences\\nthe time required for the wastewater to pass through the\\nwetland. Water storage capacity can be increased to off\u00c2\u00ac\\nset the effects of high seasonal precipitation or evapotrans\u00c2\u00ac\\npiration. Since FWS constructed wetlands have a continu\u00c2\u00ac\\nous wastewater inflow and some form of outlet water level\\ncontrol, water surface elevations do not change signifi\u00c2\u00ac\\ncantly, unless the wetland operation and maintenance\\nschedule dictates water level fluctuations. The type of\\nemergent aquatic plants in each region of an FWS is pri\u00c2\u00ac\\nmarily determined by the depth of the FWS in that zone.\\nFor the most part 1.2m (4 feet) is considered the maxi\u00c2\u00ac\\nmum seasonal water depth for fully vegetated sections of\\nthe wetland. Normal operating depths vary from 0.5 to\\n0.75m 1.7 to 2.5 feet) depending on the types of plants\\nand types of physical substrate.\\n4.3 Wetland Hydraulics\\nFrom a design perspective, wetland hydraulics defines\\nthe movement of water through a FWS constructed wet\u00c2\u00ac\\nland. A FWS constructed wetland with poor hydraulic de\u00c2\u00ac\\nsign can be problematic in terms of effluent water quality,\\nodors, and vector nuisances. This section first defines some\\nbasic wetland hydraulics terms, and then briefly summa\u00c2\u00ac\\nrizes basic wetland hydraulic principles.\\n65", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0081.jp2"}, "82": {"fulltext": "4.3.1 Wetland Hydraulics Terminology\\nand Definitions\\n4.3.1.1 Water Depth\\nWater depth is an important physical measure for the\\ndesign, analysis, and operation and maintenance of FWS\\nconstructed wetlands. The ability to vary water depth in a\\nFWS constructed wetland is one operational control avail\u00c2\u00ac\\nable to operators to manipulate wetland performance.\\nThe actual water depth at all locations in a FWS con\u00c2\u00ac\\nstructed wetland will generally not be known with a high\\ndegree of accuracy due to basin bottom irregularities. In\\naddition, the water depth in the wetland may decrease due\\nto the buildup of peat from the deposition of detritus and\\nsettled solids buildup. Increasing the water depth by chang\u00c2\u00ac\\ning the outlet weir elevation can help offset decreases in\\nwater depth. This slow-rate change progresses with time\\nfrom the inlet toward the outlet. Detrital plant material builds\\nup on and under the water surface of any vegetated zone,\\nespecially the initial vegetated zone. Wetlands operating\\nfor 15 years have documented a 0.08 -0.12m (3 to 5 inch)\\ndepth change due to plant detritus along the initial veg\u00c2\u00ac\\netated zone in an FWS wetland. The largest accumulation\\nwas in the inlet region (Kadlecik, 1996).\\nEstimated operating water depths for FWS constructed\\nwetlands in the NADB (1993) have ranged from approxi\u00c2\u00ac\\nmately 0.1 to over 2.0m (0.3 to 6+ feet) with typical depths\\nof 0.15 0.60m (0.5 to 2 feet). Operating depths are gen\u00c2\u00ac\\nerally different for the area with emergent plants (0.6 m)\\nthan those areas with submergent plants (1.2m). Since\\nmost of the NADB systems were designed to be fully veg\u00c2\u00ac\\netated, these depths are less than one would expect in the\\nfuture. For some calculations the average water depth (h)\\ncan be used, as it represents the average water depth over\\nthe total wetland surface area (A w\\n4.3.1.2 Volume\\nThe volume (Vw) of a FWS constructed wetland is the\\npotential quantity of water (neglecting vegetation, litter and\\npeat) that could be stored in the wetland basin. The wet\u00c2\u00ac\\nland water volume can be determined by multiplying aver\u00c2\u00ac\\nage water depth (h) by area (AJ:\\nV w (AJ(h) (4-2)\\n4.3.1.3 Wetland Porosity or Void Fraction\\nIn a FWS wetland, the vegetation, settled solids, litter\\nand peat occupy a portion of the water column, thereby\\nreducing the space available for water. The porosity of a\\nwetland (e), or void fraction, is the fraction of the total vol\u00c2\u00ac\\nume available through which water can flow. Wetland po\u00c2\u00ac\\nrosity has proven difficult to accurately measure in the field.\\nAs a result, wetland porosity values listed in the literature\\nare highly variable. For example, Reed, et al (1995) and\\nCrites and Tchobanoglous (1996) suggest wetland poros\u00c2\u00ac\\nity values ranging from 0.65 to 0.75 for fully vegetated\\nwetlands, for dense to less-mature wetlands, respectively.\\nKadlec and Knight (1996) report that average wetland po\u00c2\u00ac\\nrosity values are usually greater than 0.95, and e 1.0\\ncan be used as a good approximation. Gearheart (1997)\\nfound porosity values in the range of 0.75 in dense mature\\nportions of the Areata wetland. For hydrological design, an\\naverage porosity value should be used which is based on\\nthe areal percent of open water zones (non-emergent veg\u00c2\u00ac\\netation) to vegetated zones. For example, a wetland with\\n50% open water (e =1.0) and 50% emergent vegetation\\n(e 0.75), would have an average e 0.875.\\nThe overall effects of decreasing porosity are to reduce\\nthe wetland volume available for water, which reduces the\\nretention time of water within the wetland, and to increase\\nflocculation of colloidal material which improves removal\\nby sedimentation. It is recommended that a porosity value\\nof 0.65 to 0.75 for fully vegetated zones be used in FWS\\nconstructed wetland design calculations, with lower val\u00c2\u00ac\\nues for the most densely vegetated areas. A value of e\\n1.0 should be used for wetland open water zones. The\\nuse of conservative average porosity values provides a\\nfactor of safety, and results in a more conservative design.\\n4.3.1.4 Average Wastewater Flow\\nThe average wastewater flow accounts for the effects of\\nwater gains and losses (precipitation, evapotranspiration\\nand infiltration) that occur in a FWS constructed wetland.\\nDefining Q o as the FWS influent flow rate and Q e as the\\nFWS effluent flow rate, the average wastewater flow rate\\nis expressed as:\\nn _ Qo Qe\\nVave 2 (4-3)\\nIf actual wastewater inflow and outflow are known, these\\nvalues can be used in Equation 4-3. If only one of these\\nflows has been measured, a water balance can be con\u00c2\u00ac\\nducted to determine the other. If neither are known, a wa\u00c2\u00ac\\nter balance can be useful to show the relationship between\\nthe two under the extreme circumstances of operation.\\n4.3.1.5 Hydraulic Retention Time\\nThe nominal hydraulic retention time (HRT) is defined\\nas the ratio of the useable wetland water volume to the\\naverage flow rate (Q ave The theoretical hydraulic reten\u00c2\u00ac\\ntion time as t can be calculated as:\\nt-(VJ(e)/Q\u00e2\u0080\u009e (4-4)\\nThe flow rate used in the hydraulic retention time calcu\u00c2\u00ac\\nlation can be the average wetland flow (Q ave or the maxi\u00c2\u00ac\\nmum or minimum flows, depending on the a purpose of the\\ncalculation.\\n4.3.1.6 Hydraulic Loading Rate\\nThe hydraulic loading rate (q) is the volumetric flow rate\\ndivided by the wetland surface area and represents the\\ndepth of water distributed to the wetland surface over a\\nspecified time interval. The hydraulic loading rate can be\\nwritten as:\\nq Q\u00e2\u0080\u009e (4-5)\\n66", "height": "4283", "width": "3142", "jp2-path": "constructedwetla00nati_0082.jp2"}, "83": {"fulltext": "where q has units of L/T. Generally the hydraulic load\u00c2\u00ac\\ning rate is determined using the wastewater inflow (Q o\\n4.3.2 Water Conveyance\\nWater conveyance in FWS wetlands is hydraulically com\u00c2\u00ac\\nplex, varying in both space and time due to wetland veg\u00c2\u00ac\\netation and litter, changing inflow conditions, and the sto\u00c2\u00ac\\nchastic nature of hydrologic events.\\nWhen designing a constructed wetland, it is necessary\\nto understand how water moves through the wetland, and\\nhow this water movement influences various design con\u00c2\u00ac\\nsiderations.\\n4.3.2.1 Ideal versus Actual Flow in a FWS\\nConstructed Wetland\\nThough plug flow is generally assumed for the purposes\\nof FWS constructed wetland design, actual wetland flow\\nhydraulics do not follow an ideal plug flow model. The de\u00c2\u00ac\\nviation from plug flow of an existing FWS constructed wet\u00c2\u00ac\\nland can be determined through the use of tracer tests.\\nOne result of a tracer test is the determination of the aver\u00c2\u00ac\\nage tracer retention time, which is defined as the centroid\\nof the response curve, as shown in Figure 4-11. The aver\u00c2\u00ac\\nage tracer retention time is equal to the active water vol\u00c2\u00ac\\nume (V w (e) divided by the average volumetric flow rate\\n(Q ave and thus represents a direct measure of actual re\u00c2\u00ac\\ntention time. Results from some tracer studies have shown\\nthat the hydraulic characteristics of a FWS constructed\\nwetland can be approximated by a series of 4 to 6 equally\\nsized complete mix reactors (Kadlec and Knight, 1996; and\\nCrites and Tchobanoglous, 1998). In other studies, the\\ncomplete mix reactor model has resulted in a poor fit to\\nthe data, and other models have been more successful.\\nFigure 4-11 shows the observed tracer concentration from\\none wetland cell of the Sacramento Regional Wastewater\\nTreatment Plant Demonstration Wetlands Project com\u00c2\u00ac\\npared to the predicted tracer concentrations using the fi\u00c2\u00ac\\nnite state model first suggested by Hovorka (1961). The\\nfinite stage model integrates components of completely\\nmixed, plug flow, and off line storage addition/feedback\\ninto one hydraulic model. Coefficients are unique for each\\ngeometry, planting pattern, etc. For any given site with\\nappropriate data the finite stage model gives the best fit of\\nthe tracer data. This method was first applied to FWS sys\u00c2\u00ac\\ntems at the Areata pilot studies (Gearheart, et al, 1983)\\nand has subsequently been applied to the Sacramento\\nsystem (Dombeck, 1998). The value of multiple cells and\\nperiodic open-water zones have been recognized for mini\u00c2\u00ac\\nmizing short-circuiting by numerous authors.\\n4.3.2.2 Hydraulic Gradient in a FWS\\nConstructed Wetland\\nFor FWS constructed wetlands, some assessment of the\\nenergy loss or head loss from inlet to outlet is necessary\\nto ensure that the wetland is designed to handle all poten\u00c2\u00ac\\ntial flows without creating significant backwater problems,\\nsuch as flooding the inlet structures or overtopping berms.\\nIt has historically been assumed that Manning s equation,\\nwhich defines flow in open channels, can be adapted to\\nFigure 4-11. Tracer response curve for Sacramento Regional Wastewater Treatment Plant Demonstration Wetlands Project Cell 7 (SERSD, 1998).\\n67", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0083.jp2"}, "84": {"fulltext": "estimate head loss in FWS wetlands. By assuming that\\nthe submerged wetland vegetation, peat and litter provides\\nmore frictional resistance to flow than the wetland bottom\\nand sides, Manning s equation has been adapted as fol\u00c2\u00ac\\nlows:\\nwhere:\\nv average flow velocity (L/T),\\nn Manning\u00e2\u0080\u0099s resistance coefficient (T/L 1/3\\nh average wetland depth (L), and\\nS hydraulic gradient or slope of water surface (L/L).\\nIn the above equation, the average wetland depth and\\nwater surface slope is fairly easily estimated, and the av\u00c2\u00ac\\nerage velocity (v) is defined as the average flow (Q di\u00c2\u00ac\\nvided by the available average cross sectional area (A v )(e),\\nor (Width)(depth)(e). The determination of Manning s re\u00c2\u00ac\\nsistance coefficient (n) is not as straightforward. In wet\u00c2\u00ac\\nlands, the vegetation and litter providing resistance to wa\u00c2\u00ac\\nter flow is distributed throughout the water column, with\\nsettled particles and detritus on the bottom and a thicker\\nthatch level at the top. Thus, n should be a function of the\\nwater depth as well as the resistance of specific surfaces.\\nMeasurements of n in operating wetlands range from ap\u00c2\u00ac\\nproximately 0.3 to 1.1 s/m 1/3 with the higher numbers cor\u00c2\u00ac\\nresponding to water depths less than 0.2 m (Kadlec and\\nKnight, 1996). Reed, et al, (1995) use an equation to esti\u00c2\u00ac\\nmate n at 0.2m depth to vary from 1 to 14 s/m 1/3 Linsley,\\net.al., (1982) offer a series of values for n from0.024 to\\n0.112. A default value of 0.1 to 0.5 is suggested for those\\nwishing to pursue this issue. Atypical solution provided in\\nCrites and Tchobanoglous (1996) is a slope of 1 in 10,000,\\nor 1cm in 100 meters. Since multiple cells are recom\u00c2\u00ac\\nmended as good design practice to minimize short-circuit\u00c2\u00ac\\ning and to maximize treatment performance, the above\\nanalysis is superfluous for most applications where aspect\\nratios (length/width) are within suggested limits of 3:1 to\\n5:1, or even larger.\\n4.4 Wetland System Design and Sizing\\nRationale\\n4.4.11ntroduction\\nAs FWS constructed wetlands became recognized as a\\nviable wastewater treatment process, FWS design mod\u00c2\u00ac\\nels soon followed. These models were intended to aid en\u00c2\u00ac\\ngineers/designers in the process of FWS wetland design\\nand performance assessment. To date, a number of wet\u00c2\u00ac\\nland design methods have been proposed for predicting\\nconstituent removals in FWS wetlands. These may be\\nfound with explanation in Reed, et al, (1995), Kadlec and\\nKnight, (1996) and Crites and Tchobanoglous, (1998). The\\ndesign models and methods have been used to attempt to\\npredict the fate of BOD, TSS, TN, NH 4 N0 3 TP and fecal\\ncoliforms in a FWS system.\\nFree water surface constructed wetlands have usually\\nbeen modeled as attached growth biological reactors, in\\nwhich the plants and detrital material uniformly occupy the\\nentire volume of the wetland.\\nThe current trend in wetland design modeling is the de\u00c2\u00ac\\nvelopment of simple mass balance or input/output mod\u00c2\u00ac\\nels. These simplified models do not explicitly account for\\nthe many complex reactions that occur in a wetland, either\\nin the water column or at interfaces such as the water/\\nsediment interface. Instead, all reactions are lumped into\\none overall biological reaction rate parameter that can be\\nestimated from collected FWS wetland performance data.\\nAt this stage of wetland understanding, more complex and\\ntheoretical wetland models which explicitly describe the\\nkinetics of known wetland processes may not be possible\\ndue to severe limitations in almost all of the existing wet\u00c2\u00ac\\nlands data.\\n4.4.2 Existing Models\\nIn essence the types of models that have been used in\\nFWS constructed wetland design are known as plug-flow-\\nreactor (PFR) models.. One assumes horizontally based (lin\u00c2\u00ac\\near) kinetics (Reed, et al,1995; Crites and Tchobanoglous,\\n1998), while the other assumes vertical (areal) kinetics\\n(Kadlec and Knight, 1996). Several varieties of these mod\u00c2\u00ac\\nels exist. Some assume average kinetic rate constants, while\\nothers assume retarded kinetic rate constants. All provide a\\nlist of effluent background concentrations below which an\\nFWS cannot dependably attain and specific default values\\nfor temperature adjustments to correct kinetic rate constants.\\nSome suggest monthly multipliers for average computed\\ndesign performance. Some include safety factors within the\\nequation while others apply them to the model result. All as\u00c2\u00ac\\nsume first-order biological kinetics, despite the fact that the\\ninitial fully vegetated treatment zone is anaerobic, and none\\nof these models can account for a sequencing, i.e., fully veg\u00c2\u00ac\\netated and open-water zones in sequence, design which is\\nrecommended herein for better performance. Recently, one\\nof the primary model creators has also noted the inadequacy\\nof these models (Kadlec, 2000). Readers are referred to\\nKadlec and Knight (1996), Reed, et al, (1995), and Crites\\nand Tchobanoglous (1998) for details. For the purpose of\\nthis manual, i.e., providing secondary (BOD=SS =30mg/l)\\nand advanced secondary treatment of municipal wastewa\u00c2\u00ac\\nters, none of these equations alone are able to accurately\\npredict the performance of a multi-zone FWS constructed\\nwetland. Even if they could be calibrated \u00e2\u0080\u009cto fit\u00e2\u0080\u009d a specific set\\nof data their non-deterministic basis belies their ability to fit\\nother circumstances of operation.\\n4.4.3 Areal Loading Rates\\nThe areal loading rate method specifies a maximum load\u00c2\u00ac\\ning rate per unit area for a given constituent. These meth\u00c2\u00ac\\nods are common in the design of oxidation ponds and land\\ntreatment systems. Areal loading rates can be used to give\\nboth planning level and final design sizing estimates for\\nFWS systems from projected pollutant mass loads. For\\nexample, knowing the areal BOD loading rate, the expected\\nBOD effluent concentration can be estimated or compared\\nto the long term average performance data of other well-\\ndocumented, full-scale operating systems.\\n68", "height": "4283", "width": "3142", "jp2-path": "constructedwetla00nati_0084.jp2"}, "85": {"fulltext": "In section 4.1 each pollutant was discussed based on\\nareal loading vs. effluent concentration based on the\\nDMDB, the TADB, specific studies and mechanistic evalu\u00c2\u00ac\\nations of other sources of information. Areal loading does\\nnot always correlate to a reasonable design basis, espe\u00c2\u00ac\\ncially with regard to nutrients and pathogen removal, and\\nother mechanistic explanations are necessary. However,\\nif typical municipal wastewaters are to be treated which\\nhave total and filtered pollutant fractionation which are rea\u00c2\u00ac\\nsonably consistent from site to site, a rational design ap\u00c2\u00ac\\nproach can be deduced for those parameters which can\\nbe removed during the enhanced flocculation/sedimenta\u00c2\u00ac\\ntion which occurs in the initial fully vegetated zone of a\\nFWS constructed wetland. Therefore, based on Figures\\n4-1 and 4-4 the following areal loadings can be employed\\nfor this initial zone (zone 1) of the FWS\\nParameter Zone 1 Areal Loading Effluent Concentration\\nBOD 40 kg/ha-d 30 mg/L\\nTSS 30 kg/ha-d 30 mg/L\\nThe relative areal loadings imply that unless the pre\u00c2\u00ac\\ntreatment process were to have a BOD concentration of\\ngreater than 1.3 times the TSS concentration, the latter\\nwould be the critical loading rate for the fully vegetated\\nzone if secondary standards are to be met by a fully veg\u00c2\u00ac\\netated FWS system.\\nIf the FWS system were to have significant open areas\\nbetween fully vegetated zones, a better effluent quality\\ncould be attained at areal loadings, based on the entire\\nFWS system area (AJ:\\nParameter Areal Loading Effluent Concentration\\nBOD 45 kg/ha-d 20 mg/L\\n60 kg/ha-d 30 mg/L\\nTSS 30 kg/ha-d 20 mg/L\\n50 kg/ha-d 30 mg/L\\nThese loadings are based on the entire system area,\\nnot just zone 1. Therefore, with open-water zones which\\nprovide aerobic transformations and removal opportuni\u00c2\u00ac\\nties, a better effluent quality is achievable than with a fully\\nvegetated FWS system. Although there are insufficient data\\nat this time to eliminate the need to provide effluent disin\u00c2\u00ac\\nfection, more disinfection interferences are removed which\\nwould facilitate that step. Conversely, the open water zones\\nwould attract wildlife to a greater degree, and the impacts\\ncreated by their activities. Similarly, the need to and the\\npower required to reaerate the final effluent will at the least\\nbe reduced. The advantages of this design concept have\\nbeen described by Gearheart and Finney (1996) to include\\nreduced \u00e2\u0080\u009cbackground\u00e2\u0080\u009d BOD concentrations in the effluent\\nowing to the aerobic biological removals in the open-water\\nzones. As with the fully vegetated systems, the TSS areal\\nloading is more critical. With more quality data these limit\u00c2\u00ac\\ning loadings could be shown to be conservative, especially\\nthe BOD loading for attaining secondary effluent standards\\nwith open-water FWS systems.\\n4.5 Design\\n4.5.1 Design Sizing and Performance\\nMechanisms\\nIf a pretreatent system already exists, the type of influ\u00c2\u00ac\\nent characterization necessary has already been dis\u00c2\u00ac\\ncussed, but at a minimum all pollutants which are of con\u00c2\u00ac\\ncern to the NPDES permitting authority should be mea\u00c2\u00ac\\nsured as both total and filtered through a standardized glass\\nfiber filter prior to analysis. Ideally, a particle-size distribu\u00c2\u00ac\\ntion analysis of the type described in Crites and\\nTchobanoglous (1998) could be performed for all critical\\npollutants to aid the designer in predicting what level of\\nremovals of each pollutant are likely to be attained by an\\nFWS or other treatment processes. If the pretreatment\\nsystem does not exist, the designer will need to perform a\\nvariety of investigations as described in several engineer\u00c2\u00ac\\ning texts (e.g., Crites and Tchobanoglous,1998; WEF,\\n1998).\\nA primary supposition of this manual is that a FWS con\u00c2\u00ac\\nstructed wetland is most likely to treat effluent from a sta\u00c2\u00ac\\nbilization or oxidation pond or from primary-treated (settled)\\nmunicipal wastewater. After the designer determines overall\\nsize of the FWS system from these BOD and TSS areal\\nloading rates, he or she can return to evaluate the fate of\\nother constituents.\\nIf the total and filtered analyses are available, it is a rea\u00c2\u00ac\\nsonable approximation to assume that the filtered analy\u00c2\u00ac\\nsis represents a rough approximation of effluent quality\\nattainable from treatment zone 1 (fully vegetated zone)\\ngiven that the filter pores are generally a bit larger than the\\nspecific particle sizes indicated for the \u00e2\u0080\u009ccolloidal/soluble\u00e2\u0080\u009d\\nfraction in Table 4-3. Internal loads in the soluble form\\nshould also be added to this fraction in estimation of zone\\n1 effluent(see Figure 4-2 and 4-3). For more stringent ef\u00c2\u00ac\\nfluent requirements than those cited above for BOD and\\nTSS, the designer should look at alternative polishing pro\u00c2\u00ac\\ncesses such as land treatment or slow sand filtration.\\nWhile a few physical and chemical processes occur uni\u00c2\u00ac\\nformly over the entire wetland volume, many of the most\\nimportant treatment processes occur in a sequential man\u00c2\u00ac\\nner and the wetland must be designed to accommodate\\nthis characteristic. For example, TSS removal and removal\\nof associated BOD, Org N and P, metals, etc., occur in the\\ninitial portion of the cell, while the subsequent zones can\\nimpact certain soluble constituents. Given sufficient dis\u00c2\u00ac\\nsolved oxygen in open (unvegetated) areas, soluble BOD\\nremoval and nitrification of ammonia can occur. If insuffi\u00c2\u00ac\\ncient oxygen is present, soluble BOD is very slowly re\u00c2\u00ac\\nmoved by anaerobic processes. Wetland design must also\\nconsider the background level, or expected lower limit, of\\nwater quality constituents in the FWS wetland effluent (see\\nTable 4-4). Particulate and soluble constituents are inter\u00c2\u00ac\\nnally produced as a part of the normal decomposition and\\ntreatment processes occurring in a constructed wetland.\\nWildlife contribute fecal coliform and additional organic\\ncompounds. During periods of intense activity, wildlife also\\n69", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0085.jp2"}, "86": {"fulltext": "stir up settled solids contributing to an increase in turbid\u00c2\u00ac\\nity, TSS, and BOD. Table 4-4 shows the typical background\\nlevels for the constituents of interest recommended for\\nusers of this document. Designs requiring effluent quality\\nclose to the values in Table 4-4 must be aware of the natu\u00c2\u00ac\\nral fluctuations about the mean values, as shown in Figure\\n4-12. For more details on the numerical values in the table,\\nthe reader is urged to refer to Reed, et al, (1995), Kadlec\\nand Knight, 1996, and Gearheart, 1992.\\nA similar approach to the one suggested here for de\u00c2\u00ac\\nsigning FWS wetlands, referred to as the sequential\\nmodel has been developed by Gearheart and Finney\\n(1999). The overall approach of the model is to consider\\nthe dominant physical and biological processes respon\u00c2\u00ac\\nsible for determining effluent quality from each distinctive\\narea or zone of the constructed wetland and allow the de\u00c2\u00ac\\nsigner to specify areal requirements and wetland depth for\\neach of these specific functions. This methodology recog\u00c2\u00ac\\nnizes that while some of the constituent transformations\\nand removal mechanisms are to some degree occurring\\nsimultaneously throughout the wetland, the majority of the\\nremoval occurs in a sequential fashion, with one process\\nor mechanism providing the products for the next process\\nor mechanism. The total area required for treatment is then\\na sum of each of the zones required to reach a specific\\neffluent objective. This approach allows the designer to\\nsequentially determine the range of effluent characteris\u00c2\u00ac\\ntics which are attainable in a given definable zone before\\nentering a subsequent reactor (zone) which has known\\ntreatment capabilities.\\nTable 4-4. Background Concentrations of Water Quality Constituents\\nof Concern in FWS Constructed Wetlands\\nRange Typical\\nParameter (mg/L) (mg/L) Factors governing\\nTSS\\n2-5\\n3\\nPlant types, plant coverage, climate,\\nwildlife activity\\nBOD\\n2-8\\n5\\nPlant types, plant coverage, plant\\ndensity, climate, wildlife activity\\nBOD 2\\n5-12\\n10\\nPlant types, plant coverage, plant\\ndensity, climate\\nTN\\n1 -3\\n2\\nPlant types, plant coverage, climate,\\noxic/anoxic conditions\\nNFF-N\\n4\\n0.2- 1.5\\n1\\nPlant types, plant coverage, climate,\\noxic/anoxic conditions\\nTP\\nsoil\\n0.1 -0.5\\n0.3\\nPlant types, plant coverage, climate,\\ntype\\nFC 3\\n50 5000\\n200\\nPlant types, plant coverage, climate,\\nwildlife activity\\nFWS with open water and submergent and floating aquatic macro\u00c2\u00ac\\nphytes.\\n2 Fully vegetated with emergent macrophytes and with a minimum of\\nopen water.\\n2 Measured in cfu/100 ml\\nThe sequential model approach recognizes that all the\\ntreatment objectives beyond secondary require a minimum\\nof three general wetland compartments (see Figure 4-\\n13): (1) an initial compartment where the bulk of the floc\u00c2\u00ac\\nculation and sedimentation will occur, (2) an aerobic com\u00c2\u00ac\\npartment where soluble BOD reduction and nitrification can\\noccur, and (3) a vegetated polishing compartment where\\nfurther reductions in TSS and associated constituents and\\nnitrogen (via denitrification) can occur. Permanent phos\u00c2\u00ac\\nphorus removal in wetlands is generally small and is largely\\nthe result of phosphorus adsorption to solids and plant\\ndetritus. Sedimentation and pathogen reduction are related\\nto detention time in zone 1, to retention time and tempera\u00c2\u00ac\\nture in zone 2, and to retention time in zone 3. As noted\\nearlier, the notion of compartments is artificial as the treat\u00c2\u00ac\\nment processes overlap in time and space, and no spe\u00c2\u00ac\\ncific physical compartment is necessarily implied. However,\\nseparation of an FWS into a series of single-function zones\\n(cells) with individual outlet controls is not an unattractive\\nconcept.\\nA rational overview of the FWS system is depicted in\\nFigure 4-14. It illustrates that the primary mechanisms in\\nzone 1, which is fully vegetated and anaerobic throughout\\nits depth during the growing season, are sedimentation\\nand flocculation, as determined by transect measurements\\nof dissolved oxygen and pollutant concentrations. Any ex\u00c2\u00ac\\ntension of the HRT in zone 1 beyond approximately 2 days\\nat Qmax would be essentially wasteful since the anaero\u00c2\u00ac\\nbic conditions will not result in any significant further re\u00c2\u00ac\\nmoval of soluble constituents and flocculation sedimenta\u00c2\u00ac\\ntion has been effectively completed. The TSS and associ\u00c2\u00ac\\nated constituents (particulate BOD, organic nitrogen and\\nphosphorous, metals and certain semivolatile organic com\u00c2\u00ac\\npounds) have also reached this same status. Volatile or\u00c2\u00ac\\nganics are likely to be removed from the wastewater dur\u00c2\u00ac\\ning the collection or oxidation pond treatment processes\\n(Hannah, et al, 1986), while most semivolatiles are removed\\nwith the solids in the oxidation pond or in zone 1 of the\\nFWS system.\\nFor many years it has been recognized that effluent floc\u00c2\u00ac\\nculation is primarily a function of energy input from either\\nexternal sources or internal hydrodynamic forces, and that\\nreduced Reynolds\u00e2\u0080\u0099 Numbers (Re) induce optimal sedimen\u00c2\u00ac\\ntation of particles. Over the past several decades this phe\u00c2\u00ac\\nnomena has been applied in the development of hydrody\u00c2\u00ac\\nnamic devices which accomplish excellent flocculation and/\\nor sedimentation without moving parts, such as pipe mix\u00c2\u00ac\\ners and flocculators, tube and plate settlers, and pebble\\nbed and wedgewire outlet devices for clairifers. Flow\\nthrough the emerging vegetation is extremely tortuous and\\nis accompanied by a very small hydraulic radius. The\\nReynolds Number (Re) is a direct function of the hydraulic\\nradius (diameter, if the path were round (as in a pipe). If\\nthe Re falls in a range which corresponds to laminar flow,\\nsedimentation is maximized. Re is several thousand in large\\nbasins, and even larger in non-vegetated ponds. No direct\\nmeasurements of Re or laminar flow have been made at\\nthe time of this writing, but analogous results from studies\\n70", "height": "4283", "width": "3142", "jp2-path": "constructedwetla00nati_0086.jp2"}, "87": {"fulltext": "150\\nO)\\nS\\nQ\\no\\nCO\\n\u00e2\u0080\u0094Q\u00e2\u0080\u0094\\nMean\\n-0-\\nMedian\\n\u00e2\u0080\u0094A\u00e2\u0080\u0094\\nMinimum\\nMaximum\\n70\\nDistance from Influent (m)\\nFigure 4-12. Mean, median, minimum and maximum transect BOD 5 data for Areata Pilot Cell 8\\nFloating and\\nInlet Settling Zone Emergent Plants\\nSubmerged\\nGrowth Plants\\nFloating and Emergent\\nPlants\\nZone 1\\nFully Vegetated\\nD.O.\\nH 0.75 m\\nZone 2\\nOpen-Water Surface\\nD.O.\\nFI 1.2 m\\nZone 3\\nFully Vegetated\\nD.O.\\nH 0.75 m\\nFigure 4-13. Elements of a free water surface (FWS) constructed wetland\\n71", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0087.jp2"}, "88": {"fulltext": "Zone 1\\nZone 2\\nZone 3\\nFigure 4-14. Generic removal of pollutants in 3-zone FWS system\\nof tube settlers and particle-size removals support this\\ntheory, given the large amount of wetted surface available.\\n(Sparham, 1970). This concept also supports the use of\\nfully vegetated areas immediately preceding outlet weirs.\\nIn zone 2, which is primarily open-water, the natural\\nreaeration processes are supplemented by submerged\\nmacrophytes during daylight periods to elevate dissolved\\noxygen in order to oxidize carbonaceous compounds\\n(BOD) to sufficiently low levels to facilitate nitrification of\\nthe NH 4 -N to N0 3 -N. These processes require large\\namounts of oxygen and time in a passive system (no me\u00c2\u00ac\\nchanical assistance). The maximum HRT in zone 2 is gen\u00c2\u00ac\\nerally limited to about 2 to 3 days before unwanted algal\\nblooms occur. Therefore, more than one open zone may\\nbe required to complete these reactions. If so, the result\\nwould be a five (or more) zone design since each open\\nzone would be followed by a fully vegetated zone. The\\nreactions in zone 2 are essentially the same as in a facul\u00c2\u00ac\\ntative lagoon. Therefore, the equations which apply to those\\nsystems might offer reasonable approximations to the rate\\nof transformations occurring in this open-water zone. There\u00c2\u00ac\\nfore, the first-order Marais and Shaw (1961) equation for\\nfecal coliform dieoff could be applied as an approximation,\\nalong with its temperature dependancy:\\nCo (l tK p N\\nwhere: Co influent FC concentration, cfu/100 ml\\nCe effluent FC concentration, cfu/100 ml\\nN number of open-water zones in the\\nFWS\\nt HRT (T)\\nK fecal coliform removal rate constant\\n(T 1\\n2.6 1 19) T 20 4 8\\nwhere: T temperature, \u00c2\u00b0C\\nBOD removal in the open-water zone should also follow\\nexisting equations such as (Crites and Tchobanoglous,\\n1998);\\nw (4-9)\\nCo (l tK p N\\n72", "height": "4283", "width": "3142", "jp2-path": "constructedwetla00nati_0088.jp2"}, "89": {"fulltext": "where:\\nC BOD, mg/L\\nKb specific BODs removal rate constant\\n(T 1\\nKb 0.15 (1.04) 1 20 (4-10)\\nTherefore, in analyzing Figure 4-14 the downward stope\\nin FC and BOD in zone 2 can be approximated through\\nthe above equations, without considering offsets from wild\u00c2\u00ac\\nlife. As noted previously, the nitrifying bacteria can prolif\u00c2\u00ac\\nerate and convert ammonia-nitrogen to nitrate(N0 3 -N) and\\nwill be the primary nitrogen transformation role of zone 2.\\nHowever, the carbonaceous BOD must be low enough to\\nallow these reactions to occur. In rotating biological\\ncontactors this concentration of BOD is about 15 mg/I\\n(USEPA, 1993). As noted by Gearheart (1992) increasing\\nthe size of the open-water zone generally increases dis\u00c2\u00ac\\nsolved oxygen, pH, and N0 3 -N, while decreasing soluble\\nBOD and ammonium.\\nU.K.\u00e2\u0080\u0099s Department of Environment has studied lagoon\\nsystems treating similar quality influent to that of zone 2.\\nThey have noted that algal growth generally starts to oc\u00c2\u00ac\\ncur between days 2 and 3 (UK, 1973). Algal growth can\\nraise pH, interfere with FC kill and the growth of submerged\\nplants, increase NH 3 -N volatilization, and induce phospho\u00c2\u00ac\\nrus precipitation. Also, the additional biomass and precipi\u00c2\u00ac\\ntates that must be removed in zone 3 will add to the inter\u00c2\u00ac\\nnal loading on the FWS system. The primary goal of the\\nopen-water zone is to provide dissolved oxygen to remove\\nBOD and convert NH 4 -N to N0 3 -N. Therefore, the optimium\\nsizing of this zone would be an HRT of 2 to 3 days. Assum\u00c2\u00ac\\ning a Q max /Q ave of 2, the designer might choose an HRT of\\n2 days at x Q max or an HRT of 3 days at Q ave Climate would\\nlikely be the final criterion, with the larger size favored in\\nnorthern areas and the smaller in southern ones.\\nThe third zone is fully vegetated like zone 1 and has a\\nsimilar function. Zone 3, like zone 1 is also capable of deni\u00c2\u00ac\\ntrification if the influent flow contains N0 3 -N. Where oxida\u00c2\u00ac\\ntion pond pretreatment of municipal wastewaters is em\u00c2\u00ac\\nployed, zone 1 of the FWS system is not generally required\\nto denitrify, but zone 3 will if zone 2 induces nitrification.\\nThe primary energy source for successful denitrification is\\nthe release of organic substrates from the detritus from\\ndecaying plants. However, partially digested, previously\\nremoved organics may also be available. Denitrifying bac\u00c2\u00ac\\nteria perform only under anaerobic conditions and best\\nwhen attached to large surface areas, e.g., plants. Denitri\u00c2\u00ac\\nfication, like nitrification, is temperature-sensitive. Nitrifi\u00c2\u00ac\\ncation and denitrification are greatly impaired when water\\ntemperatures are reduced below 10\u00c2\u00b0C. Gearheart (1992)\\nshowed total inorganic nitrogen in the Areata Marsh to be\\nreduced from 25 to 5 mg/L. In 1995 he demonstrated pilot-\\nscale removal of N0 3 -N from 130 mg/L to 6 mg/L using no\\nsupplemental carbon sources in 80 hours at 15\u00c2\u00b0C. The\\nprimary limitation in a three-zone FWS system designed\\nto remove nitrogen is the rate of nitrification in the open-\\nwater zone. If the open-water zone succeeds in nitrifying\\nthe NH 4 -N, the system should be able to denitrify it. Reed,\\net al, (1995) indicate that denitrification should require less\\nthan one day hydraulic retention time (HRT) for denitrifica\u00c2\u00ac\\ntion from municipal wastewater concentrations to an efflu\u00c2\u00ac\\nent requirement of 10 mg/L. Kadlec and Knight (1996)\\nfound that 1 to 2 days should suffice to reach 90% N0 3 -N\\nremoval. Therefore the previously- stated requirement for\\nzone 3 (HRT of 2 days) should meet this retention require\u00c2\u00ac\\nment and ensure significant denitrification. WEF Manual\\nof Practice FD-16 (1990) indicates that the denitrification\\nrate can be as high as 10 kg/ha-d. Loadings must be within\\nthe limits of available labile carbon to proceed at the maxi\u00c2\u00ac\\nmum rate.\\nAs with zone 1 there is additional, temporary nutrient (N\\nand P) removal by plant uptake in zone 3, which may be\\nsignificant at certain times during the year, while release\\nof most of these nutrients occurs at other times. These\\nplant effects can mask the effects of other processes which\\ncould be impacting the system performance at the same\\ntimes. Unfortunately, there are insufficient data to fully quan\u00c2\u00ac\\ntify the nutrient cycle for each zone of the FWS system.\\n4.5.2 Total Suspended Solids Removal\\nDesign Considerations\\nSince prior discussion indicates that TSS removal (rather\\nthan BOD removal) drives the sizing process, there is a\\nneed to provide further discussion of the mechanisms in\u00c2\u00ac\\nvolved and their implications on design. Treatment mecha\u00c2\u00ac\\nnisms which dominate in the vegetated inlet zone of a FWS\\nconstructed wetland volume are flocculation, sedimenta\u00c2\u00ac\\ntion and anaerobic decomposition. Discrete and flocculent\\nsettling occurs as the wastewater flows through the initial\\nfully vegetated zone. Since the FWS was likely preceded\\nby an oxidation pond where most discrete settling has oc\u00c2\u00ac\\ncurred already, the enhanced settling in zonel is mostly\\ndue to flocculation of large supracolloidal solids in pas\u00c2\u00ac\\nsage through the emergent vegetation. The processes are\\ngenerally not temperature dependent and occur at rela\u00c2\u00ac\\ntively high hydraulic loading rates. TSS removal rates of\\n40 to 60% are common with a q of 0.06 m/day to 0.27 m/\\nday, but relative removals are more accurately determined\\nby influent characteristics and the hydrodynamics of the\\ninitial vegetated zone.\\nThe majority of incoming solids are removed in this ini\u00c2\u00ac\\ntial settling volume. Hyacinth and duckweed systems are\\nsimilar to (but not as good as) zone 1 of an FWS in the\\nhydrodynamics which promote excellent flocculation and\\nsedimentation. The mechanisms of the fully vegetated zone\\n1 can be estimated from the use of particle size distribu\u00c2\u00ac\\ntion analysis. Generally, wastewaters have been analyzed\\nin form size ranges:\\nSettleable 100 pm)\\nSupracolloidal (1 to 100 |im)\\nColloidal (0.001 to 1 pm)\\nDissolved 0.001 pm)\\n73", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0089.jp2"}, "90": {"fulltext": "Only one study has employed this approach (Gearheart\\nand Finney, 1996) with oxidation ponds followed by FWS\\nconstructed wetland treatment. The results shown in Table\\n4-3, clearly demonstrate the essentially complete removal\\nof the settleable fraction (100% for BOD and 95% for TSS)\\nand progressively reduced removal of the supracolloidal\\n(91 of BOD and 92% of TSS) and colloidal (66% of BOD)\\nfractions. This progression runs counter to the frequently\\nnoted biological reaction rate vs particle size relationship\\n(Levine, et. al., 1991). Therefore, the primary mechanism\\nfor removal of TSS and associated pollutants (BOD, or\u00c2\u00ac\\nganic nutrients, metals and toxic organics) is not biologi\u00c2\u00ac\\ncal in nature. This would appear to be reinforced by the\\nlack of dissolved oxygen, high oxygen demand, and the\\nslow nature of anaerobic biological reactions which are\\nthe predominant biological mechanisms.\\nThe solids that are removed undergo incomplete anaero\u00c2\u00ac\\nbic decomposition (acidification) resulting in a release of\\nnitrogen, phosphorus, and carbon in the form of volatile\\nfatty acids. The amount of accumulated internal load de\u00c2\u00ac\\npends on the length of time the water temperature stays\\nbelow 5-10\u00c2\u00b0C since this material does not undergo signifi\u00c2\u00ac\\ncant decomposition until the water temperature increases\\nabove this threshold value. The longer the uninterrupted\\nperiod of less than 5-10\u00c2\u00b0C, the greater the initial load and\\nits effect on dissolved BOD at temperatures above this\\nthreshold. In most temperate North American climates, the\\nrelease of this accumulated organic material expresses\\nitself mostly in the late spring and in the early summer,\\nsimilar to oxidation pond spring turnover Some of these\\nimpacts are noted by the comments within Figure 4-14,\\nwhich show how some of these phenomena might impact\\nremoval patterns.\\nNon-degradeable material is removed, accumulates and\\nis compressed forming an organic layer of biologically re\u00c2\u00ac\\ncalcitrant material in the sediments of zone 1. The layer is\\nthicker near the influent end of the wetland and gets shal\u00c2\u00ac\\nlower in the direction of flow. This delta of accumulated\\nsolid material can eventually reduce the HRT and the avail\u00c2\u00ac\\nable solids storage volume of the wetland. These losses\\nare also acerbated by accumulated plant detritus. These\\naccumulated solids sludge or biosolids will occasion\u00c2\u00ac\\nally need to be removed and managed, e.g., directly land\\napplied and plowed under as a soil amendment or through\\nsome other method as directed by the regulatory authori\u00c2\u00ac\\nties.\\nThe reduction in wetland volume due to settled solids,\\nliving plants and plant detritus can be significant over the\\nlong term. The rate of accumulation of settled suspended\\nsolids is a function of the water temperature, mass of influ\u00c2\u00ac\\nent TSS the effectiveness of TSS removal, the decay\\nrate of the volatile fraction of the TSS, and the settled TSS\\nmass which is non-volatile. The plant detritus buildup is a\\nfunction of the standing crop and the decay rate of the\\nplant detritus. Accumulation for emergent vegetated areas\\nof the Areata enhancement wetlands was measured to be\\napproximately 12 mm/year of detritus on the bottom due\\nto plant breakdown and 12 to 25 mm/year of litter forming\\na thatch on the surface (Kadlecik, 1996). The volume of\\nthe living plants, specifically the volume of the emergent\\nplants, ranged from 0.005 m 3 /m 2 (low stem density, water\\ndepth of 0.3 m) to 0.078 m 3 /m 2 (high stem density, water\\ndepth of 0.75 m). This accumulation is more or less con\u00c2\u00ac\\nstant from year to year as the wetland matures. The total\\nvolume reduction under the initial vegetated zone can be\\nestimated using a mass balance equation:\\nV r [(VJ(t) (V d )(t)]A w (4-11)\\nwhere:\\nV r volume reduction over period of analysis (m 3\\nV ss volume reduction due to non-volatile TSS and\\nnon-degradable volatile TSS accumulation\\n(m 3 /ha-yr),\\nV d volume reduction due to non-volatile detrital\\naccumulation as A function of annual production\\n(m 3 /ha-yr),\\nA w fully vegetated wetland area (ha),\\nt w period of analysis usually (years).\\nThe loss of volume per hectare over a ten year period\\nfor a 1 hectare fully vegetated FWS wetland zone with a\\ndepth of 0.75 m can be estimated by use of this equation.\\nBased on information in Middlebrooks, et al, (1982) and\\nCarre, et al, (1990) a reasonable default value for V when\\ntreating raw wastewater in lagoons) would be 200 to 400\\nm 3 /ha-yr (2 to 4 cm/yr). Therefore, a conservative default\\nvalue of 150 m 3 /ha-yr can be used. One hundred percent\\ncoverage of emergent vegetation was measured to con\u00c2\u00ac\\ntribute 120 m 3 /ha- yr of bottom detritus, and 120 m 3 /ha-yr\\nof surface litter with a standing crop volume of 412 m 3 /ha.\\nSubstituting into the equation for a 10-year analysis yields:\\nVr =[150)(10) (240)(10)] 1.0 3,900m 3\\nTable 4-5 provides additional examples of wetland vol\u00c2\u00ac\\nume loss due to TSS and plants detritus. Based on the\\nactual Areata experience, it is clear that use of equation 4-\\n11 is a conservative means of estimating volume reduc\u00c2\u00ac\\ntion from TSS deposition and detrital accumulation.\\nUsing the initial fully vegetated zone volume (V,) and\\nadding the standing crop (V c the total loss of volume can\\nbe estimated by addition to be 4,312 m 3 Since the original\\nvolume is area (10,000 m 2 times depth(0.75 m) or 7,500\\nm 3 the total loss of volume would be 4,312/10,000 or 43%.\\nThis corresponds to a new porosity (e) of 0.57. As noted\\nearlier dense, mature stands of emergent plants are as\u00c2\u00ac\\nsumed to have a porosity of about 0.65.\\nTable 4-5. Examples of Change in Wetland Volume Due to Deposition\\nof Non-Degradable TSS (V ss and Plant Detritus (V d Based\\non 100% Emergent Plant Coverage (Gearheart, et al, 1998)\\nInfluent TSS.\\n(mg/L)\\nv s\\n50% removal\\n(m 3 /yr)ha)\\n75% removal\\nV d (m 3 /ha/yr)\\n40\\n75\\n113\\n240\\n60\\n80\\n112\\n150\\n168\\n225\\n240\\n240\\n74", "height": "4283", "width": "3142", "jp2-path": "constructedwetla00nati_0090.jp2"}, "91": {"fulltext": "The accumulation computed above indicate that the call\\nis nearly ready for residual solids removal, as its excess\\nstorage capacity is essentially used up. However, the Areata\\nfacility for which the accumulation measurements were\\nmade is still performing well after 12 years (USEPA, 1999).\\nThe loss of volume and porosity computed by the previ\u00c2\u00ac\\nous method is obviously conservative, but illustrates how\\none could conservatively estimate the loss of porosity in\\nthe initial settling zone.\\nWhen designing the primary wetland cell treating oxida\u00c2\u00ac\\ntion pond effluent the designer should consider this cumu\u00c2\u00ac\\nlative problem by increasing the depth of the inlet zone\\n(up to 1 .Om) to lengthen the period before solids removal\\nwould be required. The designer should also provide for\\neasily accessible solids removal in this zone. There may\\nbe a need to harvest vegetation and related detritus to\\nmaintain fully vegetated and open-water areas in proper\\nproportion. Such controlled harvesting may be extended\\ninto the fully vegetated zones to reduce the apparent loss\\nof effective treatment volume and delay the need to re\u00c2\u00ac\\nmove accumulated solids.\\nThe fully vegetated, anaerobic zone 1 of the FWS wet\u00c2\u00ac\\nland should be designed based upon the average maxi\u00c2\u00ac\\nmum monthly flow rate (G max to assure the potential for\\neffective removal of solids during periods of high flow. To\\nfacilitate solids removal and handling, this initial compart\u00c2\u00ac\\nment should be designed as at least two equally sized\\nwetlands with a 0.6 to 0.9 m operating depth, which can\\nbe operated in parallel. This would allow taking one cell\\nout of operation for maintenance work such as for solids\\nremoval, vegetation removal, or replanting.\\n4.5.3 Design Examples\\nDesign Example 1 BOD and TSS to meet secondary\\neffluent requirements\\nDesign a FWS wetland to treat lagoon effluent to meet a\\nmonthly average 30 mg/I BOD and TSS discharge objec\u00c2\u00ac\\ntive. The community has a design population of 50,000\\npeople with an average annual design flow of 18,920 m 3\\nday (5 MGD) (Q ave Use design loading factors from sec\u00c2\u00ac\\ntions 4.4 and 4.5* to meet a 30 mg/I BOD and TSS effluent\\nstandard. Since a single fully vegetated FWS system can\\nbe employed with maximum areal loading rates for these\\nsystems are 40 kg BOD/ha-d and 30 kg TSS/ha-d. Facul\u00c2\u00ac\\ntative lagoon effluent typically averages from 30 to 40 mg\\nBOD/L and 40 to 100 mg TSS/L, with the latter being much\\nmore variable due to seasonal algal growth and spring and\\nfall overturn periods (WEF, 1998; Middlebrooks, et al,\\n1982). For this example the average FWS influent BOD is\\n50 mg/I at Q ave (18,920 m 3 /d), while the average TSS is 70\\nmg/L at this flow. At the maximum monthly flow (Q max of 2\\nx Q ave the BOD is 40 mg/L and TSS is 30 mg/L.\\nI! Step 1 Apply areal loading rates(ALR) to average (Q ave\\nand maximum monthly flow (Q^J conditions to iden\u00c2\u00ac\\ntify the critical conditions for sizing of the facility.\\nALR Q Co/A w (4-12)\\nwhere:\\nALR areal loading rates: BOD 40 kg /ha-d ;TSS\\n30 kg /ha-d\\nQ0 incoming flow rate, in m 3 /d\\nCO influent concentration, in mg/L\\nA total area of FWS, in ha\\nw 9\\nwhich for BOD yields:\\nfor Q ave A w (18,920 m 3 /d)(1000 L/m 3 )(50 mg/L)/ (40\\nkg/ha-d)(106 mg/kg) 24 ha\\nfor Q max A w (37,840) (40)/ (40) (106) 38 ha\\nSimilarly, for TSS:\\nfor Q ave A w (18,920) (70)/(30)(106) 44 ha\\nfor Q max A w (37,840)(30)/(30)(106) 38 ha\\nTherefore, the limiting condition is the TSS loading at\\naverage flow conditions, where 44 hectares are required\\nto meet secondary effluent standards with a fully vegetated,\\nsingle-zone FWS system. However, it has been previously\\nshown that open water zones permit higher areal loading\\nrates (from section 4.4), so the sizing can be recomputed\\non that basis following the same procedure. From that\\nanalysis, with BOD and TSS loading rates of 60 and 50\\nkg/ha-d, respectively, the critical condition is still the aver\u00c2\u00ac\\nage flow condition and the TSS areal loading, but with a\\nrequirement of 26 ha instead of 44 ha.\\nStep 2 Determine the theoretical HRT(days) using equa\u00c2\u00ac\\ntion 4-4, assuming h 0.6 m and e 0.75 in veg\u00c2\u00ac\\netated zones (1 and 3) and h 1.2 m and e 1.0 in\\nthe open zone (2). The combined estimate is an aver\u00c2\u00ac\\nage depth of 0.8 m and an average e 0.8. Therefore,\\nthe first estimate is for overall HRT, followed by indi\u00c2\u00ac\\nvidual cell estimates.\\nf\u00c2\u00b0 r Q ave _ Vvve _ Aw h _\\nQave Qave\\n(26 ha)(l 0,000 m 2 ha)(0.8 m)(0.80)\\n18,920 m 3 d\\n8.9 days\\nfor 9\u00e2\u0084\u00a2, 1 4-5 days\\nThis last calculation implies that at the maximum monthly\\nflow the overall HRT may not be adequate for the neces\u00c2\u00ac\\nsary treatment mechanisms to perform. If these relatively\\nequal-sized zones are employed as a first approximation,\\nthere would be less than one day of theoretical HRT in\\neach at this maximum flow condition. For zone 1 the mini\u00c2\u00ac\\nmum HRT at Q max should be about 2 days, making 4 days\\nat Q\\nave\\nFor zone 2 there is an upper limit which depends on\\nclimate and temperature. In this example, the concept is\\n75", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0091.jp2"}, "92": {"fulltext": "that the open-water area will have an HRT exceeding that\\nwhich is required for an algal bloom, creating a significant\\nadditional loading on zone 3. The time required for this\\ncondition varies with temperature, e.g., shorter in hotter\\nclimates. For most U.S. conditions a maximum HRT of\\nabout 2 to 3 days should avoid most blooms. On the other\\nhand, the longer the HRT in zone 2, the better the reduc\u00c2\u00ac\\ntion in soluble organics, ammonia-nitrogen and fecal\\nconforms. Therefore, the designer should consider isola\u00c2\u00ac\\ntion of this zone from the fully-vegetated zones that pre\u00c2\u00ac\\ncede and follow it and provide some flexibility in HRT con\u00c2\u00ac\\ntrol independent of the other zones to optimize this zone\u00e2\u0080\u0099s\\ntreatment performance. For this exercise a minimum HRT\\nof 2 days is chosen, making the average HRT 4 days at\\naverage flow.\\nZone 3 should be provided the same design consider\u00c2\u00ac\\nations as zone 1, since it functions in the same manner.\\nDepending on the performance of zone 2, it may also pro\u00c2\u00ac\\nvide denitrification in addition to flocculation and sedimen\u00c2\u00ac\\ntation. Therefore, it should have approximately the same\\nHRT as zone 1.\\nThe minimum HRT at Q max is therefore 2 2 2 6\\ndays, and the average 12 days with the assumptions cho\u00c2\u00ac\\nsen in this example. This would then require (using equa\u00c2\u00ac\\ntion 4-4)an overall wetland area of:\\nA w (t)(Q)/(h)(e)\\n(12 d)(18,920 m 3 /d) (0.8 m)(0.80)(10,000 m 2 /ha)\\n35 ha\\nings to meet these effluent concentrations are 45 kg BOD\\n/ha-d and 30 kg TSS /ha-d. Using the same influent condi\u00c2\u00ac\\ntions in the first example, the steps of preliminary sizing\\nare the same.\\nStep 1 Apply areal loading to determine the FWS system\u00e2\u0080\u0099s\\ncritical sizing conditions using equation 4-12.\\nBOD: at Q ava A w\\nat Q\u00e2\u0084\u00a2.. A\\nTSS: at Q a a A a\\nal Q\u00e2\u0084\u00a2,- A\\nThe limiting condition is again the TSS loading at Q ave\\nwhere 44 hectares are required. This is a larger require\u00c2\u00ac\\nment than in the previous example, as would be expected\\nsince more stringent effluent requirements are being met.\\nStep 2 Determine the theoretical HRT (t) required for the\\nentire 3-zone FWS system and each specific zone\\nusing equation 4-4, assuming an overall average depth\\n(h) of 0.8 m and an overall porosity (e) of 0.8.\\nf Q _ (44 ha)(l 0,000 m 2 ha)(0.8 m)(0.8)\\nave 19,920 m 3 /d\\n14.9 days\\n(18.920) (50)(1000)/(45)(106)\\n21 ha\\n(37.840) (40)(1000)/(45)(106)\\n34 ha\\n(18.920) (70)(1000)/(30)(106)\\n44 ha\\n(37.840) (30)(1000)/(30)(106)\\n38 ha\\nApplying the normal additional area for buffers and set\u00c2\u00ac\\nbacks of 1.25 to 1.4, the total area required for the FWS\\nfacility is 45 ha (135 acres).\\nStep 3. Configuration\\nforQ ma, t 7.4 days\\nReturning to individual zones and assuming an equal\\nminimum HRT in each, equation 4-4 is used in dimension\u00c2\u00ac\\ning at maximum flow conditions:\\nGiven the high TSS of the influent stream and the po\u00c2\u00ac\\ntential for short circuiting, the system should be designed\\nwith two parallel treatment trains of a minimum of three\\ncells in each. The first cells in each train should normally\\neach get 50% of the flow and may have a deeper (1.0 m)\\ninlet area directly adjacent to the inlet structure to handle\\nany discrete solids settling which might occur at this loca\u00c2\u00ac\\ntion. This design option would add approximately one day\\nto the overall HRT, and would only be chosen in situations\\nwhere pretreatment is likely to allow escape of readily settle-\\nable particulates. Multiple cells allow for redistribution of\\nthe primary cell effluent in the subsequent cell which re\u00c2\u00ac\\nduces short-circuiting. Flexible intercell piping will facili\u00c2\u00ac\\ntate maintenance without a major reduction in the neces\u00c2\u00ac\\nsary HRT to produce satisfactory effluent quality. Aspect\\nratios of the cells should be greater than 3:1 and adapted\\nto the site contours and restrictions. Additional treatment\\nwill likely be required after the FWS system to meet fecal\\ncoliform and dissolved oxygen permit requirements.\\nDesign Example 2 BOD and TSS 20mg/L Effluent\\nRequirements\\nTo meet this effluent quality an open-water zone will be\\nrequired in the FWS. From Section 4.4.3 the critical load\u00c2\u00ac\\n(2.5 d)(37,840 m 3 d)\\n2 (1.0)(1.2 m)( 10,000 m 2 ha)\\n7.9 ha\\nTherefore, the area for zones 1 and 3 are:\\nA 3 =A, (44 7.5 )/2\\n18 ha\\nThe overall FWS system area, including buffers, would\\nbe about 58 hectares (145 acres).\\nStep 3 Configuration\\nAgain the use of parallel trains is encouraged for all the\\nsame reasons as noted in the previous example. Parallel\\ntrains of 3 cells in each are recommended which allow any\\nsingle cell in a train to be removed from service with trans\u00c2\u00ac\\nfer of its influent to the same zone cell.\\nBy using an aspect ratio in the range of 3 to 5:1 and j\\ncomplete-cell-width inlets and outlets the intercellular trans- 1\\nfers should be simplified.\\n76", "height": "4267", "width": "3142", "jp2-path": "constructedwetla00nati_0092.jp2"}, "93": {"fulltext": "Design Example 3 Estimating from examples 1 and 2.\\nFor design example 1, if the influent to the FWS system\\nwas facultative lagoon effluent, it would be reasonable to\\nexpect the characterization in Table 4-6,with cognizence\\nthat the impact of climate and season on the performance\\nof lagoons and the characteristics of municipal wastewa\u00c2\u00ac\\nters vary by orders of magnitude. However, the numbers\\nin the table are within the normally expected ranges. To\\ntest the areal loading information presented earlier in this\\nchapter, the loading factors for each chemical constituent\\ncan be computed using equation 4-12. These yield aTKN\\nloading of 10.8 kg/ha-d for example 1 and 8.6 kg/ha-d for\\nexample 2. Similarly, the TP loadings are 2.7 kg/ha-d and\\n2.1 kg/ha-d for examples 1 and 2, respectively.\\nComparing these loadings to Figure 4-5, it is impossible\\nto accurately predict effluent quality for example 1, but it\\nappears that little removal could be expected had the origi\u00c2\u00ac\\nnal fully vegetated approach been taken. Mechanistically,\\nthe primary mechanisms which are available for TKN re\u00c2\u00ac\\nmoval in zone 1 are flocculation and sedimentation of or\u00c2\u00ac\\nganic N. Since there are only 4 mg/L of organic N the real\u00c2\u00ac\\nistic maximum expectation would be a removal of all but 1\\nmg/L, while the NH 4 -N may be mostly assimilated by the\\nplants during the active growing rate computed for this\\nexample, but most would be returned to the water column\\nduring senescence. Therefore, the effluent TKN could av\u00c2\u00ac\\nerage anywhere between about 15 and 20 mg/L,depending\\non the season, and an overall removal of about 2 to 3 mg/\\nL. With the final open-water design of this example, it is\\nnot possible to predict removal without more data from\\nopen-zoned systems. As in example 2, the three-zone FWS\\nis likely to produce an effluent TKN of greater than 4 mg/L\\nsince all three such systems on the figure were loaded at\\na lower rate. Actual removal would depend upon nitrifica\u00c2\u00ac\\ntion accomplished in zone 2, which would be a function of\\ntemperature, HRT and dissolved oxygen in that zone. Since\\nthe TKN loading rate is about 4 to 5 times the highest one\\nin the figure for open water systems, a conservative ap\u00c2\u00ac\\nproach might be that one-fourth of the nitrogen might be\\nnitrified in the open zone and denitrified in zone 3. This\\nwould yield an additional 4 mg/L to the 3 assumed for ex\u00c2\u00ac\\nample 1. This would yield a removal of 7 mg/L and an ef\u00c2\u00ac\\nfluent TN of about 13 mg/L which could vary from about 10\\nto 16 mg/L during the year depending on plant condition\\nand temperature. Conversely, the systems shown in the\\nfigure may have had excess capacity in zone 2 to fully\\nnitrify all the ammonium-nitrogen and the same effluent\\nconcentration for the lightly loaded open-water systems\\ncould also be attained. By having an open-water zone\\nwhere nitrification can occur, the inherent denitrification ca-\\nTable 4-6. Lagoon Influent and Effluent Quality Assumptions.\\nParameter\\nRaw Wastewater\\nLagoon Effluent\\nTKN(mg/L)\\n40\\n20\\nNH 4 -N(mg/L)\\n10\\n16\\nTP(mg/L)\\n7\\n5\\nFC(#/100ml)\\n106\\n104\\npability of the subsequent fully-vegetated zone creates a\\npotent opportunity for nitrogen control. It is also feasible\\nin the open-water zone to enhance NH3 volatilization, but\\nthis mechanism is less likely to be significant owing to the\\nlimited size of zone 2 which may not permit increased pH\\nwhich would enhance volatilization. Such estimates are\\nextremely tenuous until more data is generated on higher\\nloadings to these open water FWS systems, and in the\\ninterim the designer would be wise to perform pilot studies\\nwhere nitrogen limits are part of effluent permit require\u00c2\u00ac\\nments.\\nAreal loading data on total phosphorus (TP) in Figure 4-\\n6 are inconclusive. The TADB (USEPA, 1999) would sug\u00c2\u00ac\\ngest that these example loadings could produce an efflu\u00c2\u00ac\\nent of 3.0 to 4.5 mg/L. At the loadings indicated in these\\nexamples, the data of Gearheart (1993) would allow for an\\noverall annual average removal of approximately one mg/\\nL. This would provide a similar effluent for both examples\\nof about 4 mg/L. The dominant removal mechanisms in\\nboth examples are flocculation and sedimentation of or\u00c2\u00ac\\nganic phosphorus, but plant uptake and release will cause\\nthe effluent to vary from background levels in the growth-\\nphase to levels at or above the influent concentration dur\u00c2\u00ac\\ning the senescent-phase. This discussion does not include\\nthe startup-phase where TP removal will occur for several\\nmonths until the soil\u00e2\u0080\u0099s phosphorus adsorption capacity is\\nreduced to an equilibrium level by satisfaction of the soil\u00e2\u0080\u0099s\\ncalcium, aluminum and iron adsorption sites and comple\u00c2\u00ac\\ntion of the initial growth phase of the plants.\\nFecal coliform (FC) removal is limited by the natural back\u00c2\u00ac\\nground which is depicted in Table 4-4. Figure 4-10 shows\\nthat FC removal is based on enhanced sedimentation and\\nflocculation in the fully-vegetated zone of an FWS. There\u00c2\u00ac\\nfore, approximately one log (90%) of removal can be safely\\nestimated in that zone. With an open-water zone, the FWS\\ncan take advantage of the natural solar disinfection which\\nis described in the international lagoon literature (Mara,\\n1975). This additional kill of FC is limited by the HRT in the\\nopen-water zone and is a temperature-dependent func\u00c2\u00ac\\ntion with first-order kinetics. Time limitation and single-cell\\nhydraulics will likely limit additional kill to about one log.\\nSince in zone 3 FC removal would be by sedimentation,\\nless than one additional log of removal could be expected.\\nBased on the prior analyses the total removal for ex\u00c2\u00ac\\namples 1 and 2 would be 2+ logs of kill, with an expected\\neffluent FC count of 100/100ml. A fully vegetated system\\nwhich has no open zone would likely remove somewhere\\nbetween 1 and 2 logs to produce an effluent with several\\nhundred FC/100ml. Both would experience a natural varia\u00c2\u00ac\\ntion about those means as discussed earlier in the chap\u00c2\u00ac\\nter. One major reason for periodic increases will be wildlife\\nattraction to open water zones. However, with the require\u00c2\u00ac\\nment that the outlet be located at the terminus of the sub\u00c2\u00ac\\nsequent fully-vegetated zone 3, the impacts of wildlife\\nshould be minimized. However, some spikes of fecal\\ncoliform may still be evident.\\nAs noted earlier, the impact of the example designs on\\nmetals and toxic organics will vary also. Most metals will\\n77", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0093.jp2"}, "94": {"fulltext": "likely be removed with the TSS by physical means, and\\neffluent metals will probably be similar in ratio to the two\\nTSS effluent concentrations. The average pond effluent\\nhad a TSS of 70 mg/I and the two FWS designs should\\nyield 30mg/L and 20mg/L, respectively. Therefore, design\\nexamples 1 and 2 should remove about 70% of the heavy\\nmetals. Since each metal reacts differently this type of\\nanalysis has little meaning. Typically, nickel, boron, sele\u00c2\u00ac\\nnium and arsenic are more resistent to removal by sedi\u00c2\u00ac\\nmentation than most of the other commonly measured\\nmetals. A similar discusion can be provided with regard to\\nsemi-volatile toxic organic compounds. Both classes of\\npollutants may be associated with certain effluent particle-\\nsize fractions, which will cause them to follow the removal\\npatterns discussed earlier in concert with Table 4-3.\\n4.6 Design Issues\\nThis subsection describes issues that are important in\\nthe design and layout of a FWS constructed wetland.\\nThese design issues are separate from wetland area de\u00c2\u00ac\\nterminations already described. However, it is important\\nfor the engineer/designer to understand that design issues\\nand wetland area determinations are both important. The\\ndesign issues outlined here are intended to maximize the\\ntreatment potential of FWS constructed wetlands and may\\nimpact the wetland area determined from the wetland siz\u00c2\u00ac\\ning steps, which should be considered the starting point\\nfor a FWS constructed wetland design. Many of the de\u00c2\u00ac\\nsign issues outlined below are based on experience with\\nFWS constructed wetland systems currently in operation.\\n4.6.1 Wetland Layout\\n4.6.1.1 Site Topography\\nIn many cases, the topography of the site will dictate the\\ngeneral shape and configuration of the FWS constructed\\nwetland. On sloping sites, for example, constructing the\\nlong dimension of the wetland parallel to the existing ground\\ncontours helps minimize grading requirements. With proper\\ndesign, sloped sites can reduce pumping costs by taking\\nadvantage of the existing hydraulic gradients.\\n4.6.1.2 Aspect (length to width) Ratio\\nThe aspect ratio (AR) or length to width ratio (L/W), of a\\nFWS wetland system is defined as the average length di\u00c2\u00ac\\nvided by the average width, and can be expressed as:\\nwhere:\\nL average length of wetland system, and\\nW average width of wetland system.\\nFWS constructed wetlands have been designed with ARs\\nfrom less than 1:1 to over 90:1. Generally, FWS constructed\\nwetlands are designed and built with an AR greater than\\n1:1. It has been suggested that wetlands with higher ARs\\nhelp to minimize short circuiting, and force the wetland to\\nmore closely conform to plug flow hydraulics (Gearheart,\\n1996: Dombeck, 1998). However, results of dye studies\\non existing FWS constructed wetlands have shown that\\nmany wetlands deviate from ideal plug flow hydraulics in\u00c2\u00ac\\ndependent of the AR. For wetland systems with very high\\nlength to width ratios, careful consideration needs to be\\ngiven to headloss and hydraulic gradient considerations\\nto avoid overflows of confining dikes near the influent end.\\nUse of equation 4-6 and the material in section 4.3.2.2 will\\npermit the designer forced to use high AR cells to evaluate\\neach assumption and make corrections as necessary.\\nWhen conducting a hydraulic grade line analysis to deter\u00c2\u00ac\\nmine if the backwater is at an acceptable elevation near\\nthe inlet, the outlet level is normally assumed to be at the\\nmidpoint.\\n4.6.1.3 Wetland configuration\\nThe shape of a FWS constructed wetland can be highly\\nvariable depending on site topography, land configuration,\\nand surrounding land use activities. FWS constructed wet\u00c2\u00ac\\nlands have been configured in a number of shapes, in\u00c2\u00ac\\ncluding rectangles, polygons, ovals, kidney shapes, and\\ncrescent shapes. There is no data that supports one FWS\\nconstructed wetland shape as being superior in terms of\\nconstituent removal and effluent quality, over another\\nshape. However, any wetland shape needs to be designed\\nand configured following the general guidelines of this re\u00c2\u00ac\\nport. Design concerns such as hydraulic retention time,\\nshort-circuiting, headloss, inlet/outlet structures, and inter\u00c2\u00ac\\nnal and surface configurations can significantly impact\\nwetland effluent quality.\\n4.6.1.4 Multiple cells\\nIt has been shown in both the design of oxidation ponds\\nand FWS constructed wetlands, that a number of cells in\\nseries can consistently produce a higher quality effluent.\\nThis is based upon the hydrodynamic characteristics that\\nconstituent mass is gathered at the outlet end of one cell,\\nand redistributed to the inlet of the next cell. This process\\nalso minimizes the short circuiting effect of any one unit,\\nand maximizes the contact area in the subsequent cell.\\nFor treatment and water quality purposes, it is recom\u00c2\u00ac\\nmended that a FWS constructed wetland should consist\\nof a minimum of three cells in series. Open water zones\\nhave also been used to redistribute flows, but their value\\nin this regard has been overshadowed by their other at\u00c2\u00ac\\ntributes.\\nLarge wetland cells can have internal berms running\\nparallel to the flow direction, effectively creating smaller\\nparallel cells with better hydraulic properties. Multiple cells\\nwith appropriate piping between them offer greater opera\u00c2\u00ac\\ntional flexibility. In the event that a wetland cell needs to be\\ntaken off line for maintenance reasons, the remaining cell\\nor cells can remain operational. This is made even more\\nimportant if cells are sized to coincide with zoning. Com\u00c2\u00ac\\npletely vegetated and completely open cells are easier to\\nmaintain and are more flexible when sequencing or inde\u00c2\u00ac\\npendent cell HRT adjustments or maintenance is required.\\n78", "height": "4267", "width": "3142", "jp2-path": "constructedwetla00nati_0094.jp2"}, "95": {"fulltext": "4.6.2 Internal Wetland Components\\n4.6.2.1 Open water/Vegetation ratio\\nThe location of emergent vegetation, the type and den\u00c2\u00ac\\nsity of this vegetation, and the climate as it relates to plant\\nsenescence are important factors in the design of a FWS\\nconstructed wetland. Providing adequate open water ar\u00c2\u00ac\\neas is an important, but often overlooked, component in\\nthe design and implementation of FWS constructed wet\u00c2\u00ac\\nlands (Gearheart, 1986; Hammer, 1996; Hamilton, 1994,\\nStefan et a!., 1995). Open water is defined as a wetland\\nsurface which is not populated by emergent vegetation\\ncommunities, but may contain submergent aquatic plants\\nas well as unconsolidated groupings of floating aquatic\\nplants. Historically, many FWS constructed wetlands were\\ndesigned and built as fully vegetated basins with no desig\u00c2\u00ac\\nnated open water areas. Many of these systems proved\\nproblematic with very low or no water column dissolved\\noxygen, that resulted in odor production and vector prob\u00c2\u00ac\\nlems.\\nNatural wetlands generally contain a mix of open water\\nand emergent vegetation areas. The open water areas\\nprovide many functions such as oxygenation of the water\\ncolumn from atmospheric reaeration, submerged macro\u00c2\u00ac\\nphytes, and algal photosynthesis. They also permit preda\u00c2\u00ac\\ntion of mosquito larvae by fish and other animals and pro\u00c2\u00ac\\nvide habitat and feeding areas for waterfowl. Open water\\nareas in FWS constructed wetlands will not only provide\\nthe same functions as for natural wetlands, but will also\\nprovide the opportunity for increased soluble BOD reduc\u00c2\u00ac\\ntion and nitrification of wastewater because of the increase\\nin oxygen levels. It is recommended that a FWS constructed\\nwetland not be fully vegetated, but should include some\\nopen water areas. Open water areas in a FWS constructed\\nwetland will result in a more complex, dynamic, and self-\\nsustaining wetland ecosystem, that better mimics a natu\u00c2\u00ac\\nral wetland. Open water wetlands have lower background\\nBOD than fully vegetated wetlands (see Table 4-4), which\\nreflects their improved treatment potential.\\nThe ratio of open water to emergent vegetation depends\\non land availability, costs, and the function and goals of\\nthe FWS constructed wetland system. Generally speak\u00c2\u00ac\\ning zones 1 and 3 should be 100% vegetated with the zone\\n2 surface having 50% to 100% open water. If denitrifica\u00c2\u00ac\\ntion is required, the 3rd zone which is 100% vegetated will\\naccomplish it.. The open-water zones with an HRT in ex\u00c2\u00ac\\ncess of 3 days may invite algal blooms. As long as this\\nzone is followed by a fully vegetated zone with an HRT of\\n2 or more days, this should not represent a problem be\u00c2\u00ac\\nyond increased biomass management requirements.\\nThe most effective method used for creating open water\\nareas in a single cell is to excavate a zone that is deep\\nenough to prevent emergent vegetation colonization and\\nmigration. Some have periodically raised water levels to a\\ndepth that limits emergent vegetation growth, but this is\\noperationally demanding and may have negative treatment\\nimpacts. The type of dominant macrophyte (i.e., emer\u00c2\u00ac\\ngent or submergent) can be controlled by controlling the\\noperating depth. Water column depths greater than ap\u00c2\u00ac\\nproximately 1.25 to 1.5 meters planted with submergents\\nsuch as Potomogeton spp., will not rapidly be encroached\\nupon by emergent macrophytes like bulrushes reeds, and\\ncattails. If the water column depth is between 0.5 to 1.0\\nmeters and planted with emergent vegetation, such as\\nbulrush and cattails, they will prevail over submergents\\nand most other emergents by filling in the surface area\\nthrough rhizome and tuber propagation. The seasonal\\nchange in water levels (hydroperiod) is also a determinant\\nin establishing various aquatic macrophyte communities.\\nDue to the lack of shading, significant blooms of algae\\ncan occur in large open water areas, which can have nega\u00c2\u00ac\\ntive effects on effluent quality. To help minimize the poten\u00c2\u00ac\\ntial for algal growth, open water areas should be designed\\nfor less than 2 to 3 days hydraulic retention time. In gen\u00c2\u00ac\\neral, the growth cycle of algae is approximately 7 days, so\\nproviding open water areas with less than 2-3 days reten\u00c2\u00ac\\ntion time will help minimize algal growth in the open-water\\nzone of the wetland. Sufficient standing crops of\\nsubmergent macrophytes may also limit algal regrowth in\\nthese zones. Conversely, excessive algal growth may im\u00c2\u00ac\\npair the performance of the submergent macrophytes by\\nlimiting the solar energy which reaches them.\\nGuidelines for designing a FWS constructed wetland in\\nterms of vegetated covering are as follows: Begin with an\\nemergent vegetation zone covering the volume used in\\nthe first 2 days of retention time at maximum monthly flow\\n(Q max to provide for influent solids flocculation and sepa\u00c2\u00ac\\nration.. The emergent zone should be followed by an open\\nwater zone covering days 3 and 4 in the retention time\\nsequence at Q max The open water zone should be designed\\nto facilitate production of dissolved oxygen to meet CBOD\\nand NBOD demands. The final 2 days of hydraulic reten\u00c2\u00ac\\ntion volume at Q max should be an emergent wetland to\\nreduce any solids (algae, bacteria, etc.) generated in the\\nopen water and to supply carbon (decomposing plant ma\u00c2\u00ac\\nterial) and anoxic conditions for denitrification. It is also\\nrecommended that this final stand of emergent vegetation\\nbe as close as possible to the outlet of a FWS constructed\\nwetland. This provides a final level of protection just be\u00c2\u00ac\\nfore the effluent leaves the wetland to minimize the impact\\nof wildlife on effluent quality. This recommendation may\\nheighten the maintenance requirements for the outlet de\u00c2\u00ac\\nvice, but it will result in less variability in the effluent qual\u00c2\u00ac\\nity.\\n4.6.2.2 Inlet Settling Zone\\nDepending on the pretreatment process, a substantial\\nportion of the incoming settleable and suspended solids\\nmay be removed by discrete settling in the inlet region of a\\nFWS constructed wetland. For example, if the FWS sys\u00c2\u00ac\\ntem is to follow an existing treatment facility which is prone\\nto produce high concentrations of settleable TSS, an inlet\\nsettling zone should be used. If the pretreatment facility\\ndoes a good job of solids capture, but has a high concen\u00c2\u00ac\\ntration of soluble constituents, an inlet settling zone is of\\n79", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0095.jp2"}, "96": {"fulltext": "no value. Given that FWS systems are generally preceded\\nby lagoon systems which seasonally produce large TSS\\nconcentrations, primarily due to algal mass, the need for\\nan inlet settling zone would be marginal since algal solids\\nwill require flocculation and sunlight restriction before be\u00c2\u00ac\\ncoming settleable.\\nIf an inlet settling zone should be desired, it should be\\nconstructed across the entire width of the wetland inlet. A\\nrecommended guideline is to design a settling zone which\\nprovides approximately 1 day hydraulic retention time at\\nthe average wastewater flow rate, as most settleable and\\nsuspended solids are removed within this time period. The\\nsettling zone should be deep enough to provide adequate\\naccumulation and storage of settled solids, but shallow\\nenough to allow the growth of emergent vegetation, such\\nas bulrush and cattails. Recommended depth is approxi\u00c2\u00ac\\nmately 1 meter.\\nMost accumulated organic solids will slowly decay and\\nreduce in volume. This decay is one of the two major\\nsources of internal loading and background constituents\\nin the effluent. However, at some time in the future the\\nremaining accumulated solids will need to be removed from\\nthe settling zone.\\n4.6.2.3 Inlet/Outlet Structures\\nPlacement and type of inlet and outlet control structures\\nare critical in FWS constructed wetlands to ensure treat\u00c2\u00ac\\nment effectiveness and reliability. To effectively minimize\\nshort-circuiting in a FWS constructed wetland, two goals\\nconcerning cell inlet/outlet structures are critical: (1) uni\u00c2\u00ac\\nform distribution of inflow across the entire width of the\\nwetland inlet, and (2) uniform collection of effluent across\\nthe total wetland outlet width. Both of these should mini\u00c2\u00ac\\nmize localized velocities, thus reducing potential\\nresuspension of settled solids. It is important that any out\u00c2\u00ac\\nlet structure be designed so that the wetland can be com\u00c2\u00ac\\npletely drained, if required. Some of the common types of\\nwetland inlet/outlet systems in use today, and general\\nguidelines regarding their design are further discussed in\\nChapter 6.\\nDepending on the type of wastewater influent, the inlet\\nstructure discharge point could be located below or above\\nthe wetland water surface. Perforated pipe inlet/outlet struc\u00c2\u00ac\\ntures can be difficult to operate and maintain when they\\nare fully submerged. All inlet distribution systems should\\nbe accessible for cleaning and inspection by using\\ncleanouts.\\nOutlet structures represent an operational control fea\u00c2\u00ac\\nture that directly affect wetland effluent quality. It is impor\u00c2\u00ac\\ntant that outlet structures facilitate a wide range of operat\u00c2\u00ac\\ning depths. By adjusting the outlet structure, both the wa\u00c2\u00ac\\nter depth and hydraulic retention time can be increased or\\ndecreased. This and the need to accommodate cell drain\u00c2\u00ac\\nage usually results in locating the outlet manifold at the\\nbottom of the outlet zone. The differences in water quality\\nbetween water depths can also be highly variable. An outlet\\nstructure design which allows for maximum flexibility of\\ncollection depths may be desirable, but may not always\\nbe compatible with collection devices that minimize short-\\ncircuiting. With this type of design, the outlet structure can\\nbe adjusted to draw wetland effluent from the water depth\\nwith the best water quality. This alternative design usually\\ninvolves multiple drop boxes with openings at different\\ndepths. In most cases however the uniform collector set\\nat the bottom is favored owing to its inherent advantages\\nin terms of improved effluent quality and facilitation of cell\\ndrainage.\\nTwo types of inlet/outlet structures are commonly used\\nin FWS constructed wetlands. For small or narrow (high\\nAR) wetlands, perforated PVC pipe can be used for both\\ninlet and outlet structures. The length of pipe should be\\napproximately equal to the wetland width, with uniform\\nperforations (orifices) drilled along the pipe. The size of\\nthe pipes, and size and spacing of the orifices will depend\\non the wastewater flow rate and the hydraulics of the inlet/\\noutlet structures. It is important that the orifices be large\\nenough to minimize clogging with solids. Perforated pipes\\ncan be connected to a manifold system by a flexible tee\\njoint, which allows the pipes to be adjusted up or down. In\\nsome cases wetland designers with this type of inlet/outlet\\nstructure will cover the perforated pipes with gravel to pro\u00c2\u00ac\\nvide more uniform distribution or collection of flows. This\\ntype of inlet/outlet structure requires periodic inspection,\\nsome operation and maintenance to maintain equal flow\\nthrough the pipe, and access at the end to clean clogged\\norifices.\\nFor larger wetland systems, multiple weirs or drop boxes\\nare generally used for inlet and outlet structures. Weirs or\\ndrop boxes are generally constructed of concrete, but\\nsmaller PVC boxes are also available. These structures\\nshould be located no further apart than every 15 m (center\\nto center) across the wetland inlet width, with a preferred\\nspacing of 5 to 10 m. The same spacing requirements apply\\nfor the outlet weirs or drop boxes. Depending on the source\\nof the wastewater influent, the inlet weirs or drop boxes\\ncan be connected by a common manifold pipe. Whatever\\nthe configuration, it is important that the manifold pipes\\nand weirs be hydraulically analyzed to attain reasonably\\nuniform distribution. Simple weir or drop box type inlet struc\u00c2\u00ac\\ntures are relatively easy to operate and maintain.\\nWeir overflow rates have not been considered in the\\ndesign of most wetlands. Weir loading rates of existing\\nwetlands are significantly higher than those required in\\nmost biological solids removal processes (i.e., 120 to 190\\nm 3 /m.d (WEF, 1998). Excess weir rates can cause high\\nwater velocities near the outlet which could entrain solids\\nwhich would otherwise be removed from the effluent.\\nTherefore, weir loading rates should be designed to meet\\nthe above range for best performance until more quantita\u00c2\u00ac\\ntive data are generated.\\n4.6.2.4 Baffles\\nBaffles are internal structures installed either perpen\u00c2\u00ac\\ndicular or parallel to the direction of flow. Baffles can be\\n80\\nids,", "height": "4267", "width": "3142", "jp2-path": "constructedwetla00nati_0096.jp2"}, "97": {"fulltext": "effective in reducing short-circuiting, for mixing waters of\\ndifferent depths, and for improved flocculation performance.\\nProperly designed and placed open water zones can also\\nact as baffles by allowing mixing and redistribution of waste-\\nwater before it enters into the next wetland vegetated zone.\\nThe use of baffles depends on cell configurations, aspect\\nratios, treatment goals, and permit compliance. In general,\\nexcept for special circumstances unforseen in typical mu\u00c2\u00ac\\nnicipal wastewater treatment application the use of such\\nstructures is not recommended. However, their use in cor\u00c2\u00ac\\nrecting problems which are due to hydraulic flow difficul\u00c2\u00ac\\nties (short circuiting, dead zones, etc.) make them useful\\nto the operator-owner.\\n4.6.2.5 Recirculation\\nRecirculation is the process of introducing treated efflu\u00c2\u00ac\\nent back to the inlet or to some other internal location of\\nthe wetland. Recycling effluent can decrease influent con\u00c2\u00ac\\nstituent concentrations and increase dissolved oxygen\\nconcentrations near the inlet. The increased dissolved\\noxygen concentrations can help reduce inlet odors, lower\\nBOD, and enhance nitrification potential in open-water\\nzones. If recirculation is to be considered, the effects of\\nrecirculation on the wetland water balance and wetland\\nhydraulics need to be analyzed. In general, the ability to\\nrecycle, like the ability to drain each cell, could be consid\u00c2\u00ac\\nered part of the need to have flexible piping multiple cells,\\nand multiple trains of cells. The value of recirculation has\\nnot been shown to date to be a major factor in improving\\nFWS performance.\\n4.6.2. 6 Flow Measuring Devices\\nMany existing wetland systems do not have accurate\\nflow measuring devices. Even if accurate estimates of in\u00c2\u00ac\\nflows and/or outflows to the treatment plant are known,\\ninternal flow distribution to individual wetland cells is not\\nknown or measured. Without accurate flow measurements\\nto individual wetland cells, it is impossible to determine\\ninternal flow rates, average velocities, and hydraulic re\u00c2\u00ac\\ntention times for each cell, thus making system perfor\u00c2\u00ac\\nmance adjustments difficult. It is recommended that some\\ntype of flow measuring device be either installed in or avail\u00c2\u00ac\\nable to be installed in each cell of a FWS constructed wet\u00c2\u00ac\\nland. This includes separate flow measuring devices on\\neach inlet for multiple wetland cell configurations. Some\\nexamples of flow measuring devices include simple 90 g V-\\nnotch or rectangular weirs, and more sophisticated Parshall\\nflumes for larger systems. Depending on the size and lay\u00c2\u00ac\\nout of the wetland, cell inlet/outlet structures should be\\ndesigned to be compatible with available flow measuring\\ndevices.\\n4.6.3 Pretreatment Requirements\\nExamples of treatment that should precede FWS con\u00c2\u00ac\\nstructed wetlands include all types of stabilization ponds\\nand primary sedimentation systems. The use of wetlands\\nto polish secondary effluent to less than 10 mg/I BOD and\\nTSS has been documented, but is not covered in detail\\nhere. The reader is directed to USEPA (1999) for guid\u00c2\u00ac\\nance in these applications. The effluent entering a FWS\\nconstructed wetland should be free from floatable and large\\nsettleable solids, and excessive levels of oil and grease.\\nAlso important to a FWS constructed wetland is the in\u00c2\u00ac\\ncoming metal concentrations. While a FWS constructed\\nwetland does remove and immobilize many heavy metals\\nalong with the TSS, excessive influent concentrations could\\nresult in residuals which are unacceptable for subsequent\\nland application. A source reduction program and/or an\\nindustrial waste pretreatment ordinance are required if\\nexcessive metals concentrations are present in the raw\\nwastewater.\\n4.7 Construction/Civil Engineering Issues\\nSpecific construction/civil engineering design issues that\\nshould be considered early in the planning and design\\nphase of a FWS constructed wetland project include site\\ntopography and soils, berm construction, impermeable liner\\nmaterials, wetland vegetation substrate, and internal drain\u00c2\u00ac\\nage. Many of these issues should be considered during\\nthe site selection process, as they may become difficult or\\ncostly to correct later in the actual design and construction\\nphases of the project. The construction/civil engineering\\nrequirements for a FWS constructed wetland are similar\\nto other earthen water quality management systems such\\nas oxidation ponds, and are discussed in Chapter 6 and in\\nUSEPA (1983) and Middlebrooks, et al (1982).\\n4.7.1 Site Topography and Soils\\nIn general, level land with clay soils affords the optimal\\nphysical setting for a FWS constructed wetland. Potential\\nwetland sites with other physical conditions can be used,\\nbut may require more substantial engineering, earthwork,\\nconstruction requirements, and liners. In order to overcome\\nsite limitations, the cost of a FWS constructed wetland will\\nalso increase proportionally as the wetland site further\\ndeviates from optimal site conditions.\\nFWS constructed wetlands can be built on sites with a\\nwide range of topographic relief. Construction costs are\\nlower for flat sites since sloped sites require more grading\\nand berm construction. Site topography will generally dic\u00c2\u00ac\\ntate the basic shape and configuration of the FWS con\u00c2\u00ac\\nstructed wetland.\\nThe principal soil considerations in siting and implement\u00c2\u00ac\\ning a FWS constructed wetland are the infiltration capacity\\nof the soils and their suitability as berm material and wet\u00c2\u00ac\\nland vegetation substrate. In most cases FWS constructed\\nwetlands are required to meet stringent infiltration restric\u00c2\u00ac\\ntions depending on the state regulations for groundwater\\nprotection. An exception are wetland systems designed to\\nincorporate infiltration as part of the treatment and dis\u00c2\u00ac\\ncharge process. In these cases, the underlying soil must\\nhave infiltration rates compatible with the design discharge\\nrates. If native site soils are not suitable, separate infiltra\u00c2\u00ac\\ntion trenches can be added to increase the infiltration sur\u00c2\u00ac\\nface area. In some cases, it will be necessary to import\\nberm and/or bottom materials or use synthetic liners (see\\nChapter 6) to prevent infiltration.\\n81", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0097.jp2"}, "98": {"fulltext": "Interior berms containing FWS wetland cells should be\\nbuilt with up to 3:1 side slopes as the soil characteristics\\nallow. A minimum freeboard of 0.6 m above the peak flow\\noperating depth in the wetland is required. For wetlands\\nthat will receive exceptionally high peak inflows, additional\\nfreeboard may be required to ensure that berm overtop\u00c2\u00ac\\nping does not occur. Additional freeboard may also be de\u00c2\u00ac\\nsigned to accommodate long-term solids and peat buildup\\nduring the operation of the wetland, and to allow appropri\u00c2\u00ac\\nate water depths to be maintained as sludge builds up in\\nthe initial cells over time.\\nAll FWS-cell external berms should have a minimum top\\nwidth of 3 m, which provides an adequate road width for\\nmost standard service vehicles. In some cases, internal\\nberms can have smaller top widths, as routine operation\\nand maintenance can be carried out by small motorized\\nvehicles, such as ATVs. Road surfaces should be an all\\nweather type, preferably gravel, which also minimizes di\u00c2\u00ac\\nrect runoff into the wetland.\\nBerm integrity is critical to the long term operational ef\u00c2\u00ac\\nfectiveness of FWS constructed wetlands. Common berm\\nfailure causes include burrowing by mammals, such as\\nbeaver nutria and muskrat, and holes from root penetra\u00c2\u00ac\\ntion by trees and other vegetation growing on or near the\\nberms. Several design features can eliminate and/or mini\u00c2\u00ac\\nmize these problems. A thin impermeable wall, or internal\\nlayer of gravel, can be installed during construction, which\\nwill minimize mammal burrowing and/or root penetration.\\nPlanting the berm using vegetation with a shallow root sys\u00c2\u00ac\\ntem can also be effective. Unlike oxidation ponds, berm\\nerosion in fully vegetated zones and/or cells from wave\\naction is generally not a concern due to the dampening\\neffect of the wetland vegetation. However, in larger cells\\nwith open zones it could be an issue, and stabilization pond\\ntexts should be consulted for solutions (Middlebrooks, et\\nal, 1982)(USEPA, 1983).\\nIn the design and site selection process, an important\\nconsideration is the amount of additional area required for\\nberms. In general, the higher the aspect ratio for a FWS\\nconstructed wetland, the more area that will be required\\nfor the berms and for the entire wetland system. This in\u00c2\u00ac\\ncrease in required total wetland area to accommodate\\nberms is more pronounced for smaller wetlands than for\\nlarger wetlands. A factor of 1.2 to 1.4 times the cell area is\\nusually employed to determine the total site area for the\\nFWS system.\\n4.7.2 Impermeable Liner Materials\\nA concern with FWS constructed wetlands is the poten\u00c2\u00ac\\ntial loss of water from infiltration and contamination of\\ngroundwater below the wetland site. While there are some\\nwetland applications where infiltration is desirable, the\\nmajority of the applications require some type of barrier to\\nprevent groundwater contamination. Under ideal condi\u00c2\u00ac\\ntions, the wetland site will consist of natural soils with low\\npermeability that restrict infiltration. However, many wet\u00c2\u00ac\\nlands have been constructed on sites where soils have\\nhigh permeability. In these cases, some type of liner or\\nbarrier will likely be required to minimize infiltration. Liner\\nrequirements can also add significantly to the construction\\ncost of a FWS constructed wetland.\\nExisting natural soils with permeability less then approxi\u00c2\u00ac\\nmately 10~ 6 cm/s are generally adequate as an infiltration\\nbarrier. For site soils with higher permeabilities, some type\\nof liner material will likely be required. Some examples of\\nwetland liner materials include imported clay fill, bentonite\\nsoil layers, chemical treatment of existing soils, asphalt,\\nand synthetic membrane liners such as PVC or HDPE. In\\nsome instances, it will be possible to compact the existing\\nsite soils to acceptable permeability. Due to their ability to\\nbe placed in shaped wetland cells, clay liners are gener\u00c2\u00ac\\nally a more sustainable component of the wetland than\\nsynthetic membrane liners. Whatever liner material is cho\u00c2\u00ac\\nsen, an important consideration is to provide adequate soil\\ncover and depth that protects the liner from incidental dam\u00c2\u00ac\\nage and root penetration from the wetland vegetation (see\\nChapter 6).\\n4.7.3 Soil Substrates for Plants\\nAquatic macrophytes generally reproduce asexually by\\ntuber runners. Soils with high humic and sand components\\nare easier for the tubers and runners to migrate through,\\nand plant colonization and growth is more rapid. The soil\\nsubstrate for wetland vegetation should be agronomic in\\nnature (e.g. loam), well loosened, and at least 150 mm (6\\ninches) deep. Depending on the liner material, deeper soil\\nsubstrates may be required to protect the liner. If this type\\nof soil layer exists at the site, it should be saved. After the\\nwetland basin, berms and other earthen structures are\\nconstructed, and the liner is installed (if required), the origi\u00c2\u00ac\\nnal soil substrate can be placed back into the excavated\\nregion. To meet soil specifications, it may be necessary to\\namend the saved soils with other materials.\\nWhile soils such as loam and silt are good for plant\\ngrowth, they can allow large vegetation mats to float when\\nlarge water level fluctuations occur in the wetland. Float\u00c2\u00ac\\ning vegetation mats can significantly alter the treatment\\ncapabilities of FWS constructed wetlands by allowing\\nwastewater to flow between the floating mats and substrate,\\nnot in contact with any vegetation treatment media. To cir\u00c2\u00ac\\ncumvent this potential problem, denser soil substrates such\\nas a sandy loam, or a loam gravel mix can be used. This\\nwill be more important in FWS constructed wetlands where\\nlarge water depth fluctuations will be part of the operation\\nand maintenance procedure.\\n4.7.4 Internal Drainage and Flexible\\nPiping\\nIn the event a FWS constructed wetland needs to be\\ndrained, the wetland bottom should have a slope of 1% or\\nless. Drainage may be required for maintenance reasons\\nsuch as liner repair, sludge removal, vegetation manage\u00c2\u00ac\\nment, and berm repair. Deeper channels may be employed\\nto allow for drainage and/or continued use when serial cells\\nare taken out of service. Channels can also be used to\\n82", "height": "4267", "width": "3142", "jp2-path": "constructedwetla00nati_0098.jp2"}, "99": {"fulltext": "connect deeper open water areas where these are part of\\na larger cell, rather than separate cells. In general the more\\ncomplete the intercellular piping, the greater the opera\u00c2\u00ac\\ntional flexibility is for the entire system.\\n4.8 Summary of Design Recommendations\\nA summary of the design recommendations for FWS\\nwetland treatment systems is presented in Table 4-7. As\\nmore quality-assured data become available allowable\\npollutant areal loadings will likely be revised.\\nTable 4-7. Recommended Design Criteria for FWS Constructed\\nWetlands\\nParameter\\nDesign Criteria\\nEffluent Quality\\nBOD 20 or 30 mg/L\\nTSS 20 or 30 mg/L\\nPretreatment\\nOxidation Ponds (lagoons)\\nDesign Flows\\nQ max (maximum monthly flow) and\\nQ\u00e2\u0084\u00a2 (average flow)\\nMaximum BOD Loading\\n(to entire system) to Meet:\\n20 mg/L: 45 kg/ha-d\\n30 mg/L: 60 kg/ha-d\\nMaximum TSS Loading\\n(to entire system) to Meet:\\n20 mg/L: 30 kg/ha-d\\n30 mg/L: 50 kg/ha-d\\nWater Depth\\n0.6 0.9 m Fully vegetated zones\\n1.2-1,5m Open-water zones\\n1.0m Inlet settling zone\\n(optional)\\nMinimum HRT (at Qmax)\\nin Zone 1 (and 3)\\n2 days fully vegetated zone\\nMaximum HRT (at Qave)\\nin Zone 2\\n2 3 days open-water zone\\n(climate dependent)\\nMinimum Number of Cells\\n3 in each train\\nMinimum Number of Trains\\n2 (unless very small)\\nBasin Geometry (Aspect Ratio)\\nOptimum 3:1 to 5:1, but subject to\\nsite limitations\\nAR 10:1 may need to calculate\\nbackwater curves\\nInlet Settling Zone Use\\nWhere pretreatment fails to retain\\nsettleable particulates\\nInlet\\nOutlet\\nUniform distribution across cell inlet\\nzone\\nUniform collection across cell outlet\\nzone\\nOutlet Weir Loading\\n200 m3/m-d\\nVegetation\\nEmergent\\nTypha or Scirpus (native species\\npreferred)\\nSubmerged\\nPotamogeton, Elodea, etc (see\\nchapter 2).\\nTable 4-7. Continued\\nParameter\\nDesign Criteria\\nDesign Porosities\\n0.65 for dense emergents in fully\\nvegetated zones\\n0.75 for less dense stand of\\nemergents in same zones\\n1.0 for open-water zones\\nCell Hydraulics\\nEach cell should be completely\\ndrainable\\nFlexible intercell piping to allow for\\nrequired maintenance\\nIndependent, single-function cells\\ncould maximize treatment\\n4.9 References\\nBalmer, P. and B.Vik.. 1978. \u00e2\u0080\u009cDomestic Wastewater Treat\u00c2\u00ac\\nment with Oxidation Ponds in Combination with Chemi\u00c2\u00ac\\ncal Precipitation,\u00e2\u0080\u009c Prog. Water Tech, Vol 10, No. 5-6,\\npp867-880.\\nCarre, J., M. P. Loigre, and M. Leages 1990. \u00e2\u0080\u009cSludge Re\u00c2\u00ac\\nmoval from Some Wastewater Stabilization Ponds.\u00e2\u0080\u009d\\nWater Science Technology, Vol 22, No 3-4, pp 247-\\n252.\\nCole, S. 1988. The Emergence of Treatment Wetlands\\nES T. Vol 3, No. 5, pp. 218-223.\\nCrites, R.W., and G. Tchobanoglous. 1998. \u00e2\u0080\u009cSmall and De\u00c2\u00ac\\ncentralized Wastewater Management Systems, WCB\\nMcGraw-Hill, NY.\\nDombeck, G. 1998. Sacramento Regional Wastewater\\nTreatment Plant Demonstration Wetland Project. 1997\\nAnnual Report, Nolte and Associates, Sacramento, Ca.\\nFrankenbach, R.l and J.S Meyer. 1999. Nitrogen Removal\\nin A Surface Flow Wetland Wastewater Treatment Wet\u00c2\u00ac\\nlands, 1999, Wetlands, Volume la, No. 2, June 1999\\npp.403-412.\\nGearheart, R.A., and B. Finney. 1999. \u00e2\u0080\u009cThe Use of Free\\nSurface Constructed Wetlands as An Alternative Pro\u00c2\u00ac\\ncess Treatment Train to Meet Unrestricted Water Rec\u00c2\u00ac\\nlamation Standards\u00e2\u0080\u009d, Wat. Sci. Tech. Vol. 40, No. 4-5,\\npp. 375-382.\\nGearheart, R.A., B. A. Finney, M. Lang, and J. Anderson.\\n1998. \u00e2\u0080\u009cA Comparison of System Planning, Design and\\nSizing Methodologies for Free Water Surface Con\u00c2\u00ac\\nstructed Wetlands\u00e2\u0080\u009d. 6th International Conference on\\nWetland Systems for Water Pollution Control.\\nGearheart, R.A. and B. A. Finney. 1996. Criteria for De\u00c2\u00ac\\nsign of Free Surface Constructed wetlands Based\\nUpon a Coupled Ecological and Water Quality Model.\\nPresented at the Fifth International Conference on\\nWetland Systems for Water Pollution Control, Vienna,\\nAustria.\\n83", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0099.jp2"}, "100": {"fulltext": "Gearheart, R. A. 1995. Watersheds Wetlands Wastewa\u00c2\u00ac\\nter Management. In Natural and Constructed Wetlands\\nfor Wastewater Treatment. Ramadori, R., L. Cingolani,\\nand L. Cameroni, eds., Perugia, Italy, pp 19-37.\\nGearheart, R. A. 1993. \u00e2\u0080\u009cPhosphorus Removal in Constructed\\nWetlands\u00e2\u0080\u009d. Presented at the 66th WEF Conference and\\nExposition, Anaheim, Ca.\\nGearheart, R.A. 1992. Use of Constructed Wetlands to Treat\\nDomestic Wastewater, City of Areata, California\u00e2\u0080\u009d, Wat.\\nSci. Tech., Vol. 26, No. 7-8, pp. 1625-1637.\\nGearheart, R.A., F. Klopp, and G. Allen. 1989. Constructed\\nFree Surface Wetlands to Treat and Receive Wastewa\u00c2\u00ac\\nter Pilot Project to Full Scale, In D.A. Hammer (ed.) Con\u00c2\u00ac\\nstructed Wetlands for Wastewater Treatment, pp. 121-\\n137, Lewis Publisher, Inc., Chelsea, Ml\\nGearheart, R.A., B. A. Finney, S. Wilbur, J. Williams, and D.\\nHall. 1984. \u00e2\u0080\u0098The Use of Wetland Treatment Processes\\nin Water Reuse\u00e2\u0080\u009d, Future of Water Reuse, Volume 2, Pro\u00c2\u00ac\\nceedings of Symposium III Water Reuse, AWWA Re\u00c2\u00ac\\nsearch Foundation, pp. 617-638.\\nGearheart, R.A., S. Wilbur, J. Williams, D. Hull, B. A. Finney,\\nand S. Sundberg. 1983. City of Areata Marsh Pilot\\nProject: effluent quality results-system design and man\u00c2\u00ac\\nagement. Final report. Project No. C-06-2270, State\\nWater Resources Control Board, Sacramento, CA.\\nGregg, J., and A. Horne. 1993. Short-term Distribution and\\nFate of Trace Metals in a Constructed Wetland Receiv\u00c2\u00ac\\ning Treated Municipal Wastewater Environmental En\u00c2\u00ac\\ngineering and Health Sciences Laboratory Report No.\\n93-4. University of California, Berkeley, CA.\\nHammer, D, 1992, Creating Freshwater Wetlands Lewis\\nPublishers, Chelsea, Ml\\nHannah, S.A, B.M. Austern, A.E. Eralp, and R.H. Wise, 1986.\\nJournal WPCF, Vol 55, No 1, pp 27-34.\\nHovorka, R.B. 1961. An Asymmetric Residence-time Distri\u00c2\u00ac\\nbution Model for Flow Systems, Dissertation, Case In\u00c2\u00ac\\nstitute of Technology.\\nKadlec. R.H. 2000. The Inadequecy of First-Order Treatment\\nWetland Models. Ecological Engineering, vol. 15, pp 105-\\n109;\\nKadlec, R.H. and R.L. Knight. 1996. Treatment Wetlands.\\nBoca Raton, FL: Lewis-CRC Press.\\nKadlecik, L. 1996. Organic Content of Wetland Soils, Areata\\nEnhancement Marsh, Special Project, ERE Department\\nWetland Workshop.\\nLevine, A. D., G. Tchobanoglous and T. Asano, 1991. Size\\nDistributions of Particulate Contaminants in Wastewa\u00c2\u00ac\\nter and Their Impact on Treatability. Water Research,\\nVol. 25, No 8, pp. 911-922.\\nLinsley, R.K. Jr., M.A. Kohler, and J.L.H. Paulhus, 1982.\\nHydrology for Engineers, 3rd Ed., McGraw-Hill, NY.\\nMara, D.D. 1975 Proposed Design for Oxidation Ponds in\\nHot climates. Journal ASCE-EE, Vol.101, No 2, pp 296-\\n300.\\nMarais, C. V. R., and V. A. Shaw. 1961. A Rational Theory for\\nthe Design of Sewage Stabilization Ponds in Central and\\nSouth Africa. Transactions South African Institute of Civil\\nEngineers, Vol. 3, pp. 205ff.\\nMiddlebrooks, E. J., C. E. Middlebrooks, T. H. Reynolds, G.Z.\\nWatters, S.C. Reed, and D.B.George. 1982. Wastewa\u00c2\u00ac\\nter Stabilization Lagoon Design, Performance and Up\u00c2\u00ac\\ngrading, MacMillen, New York, NY.\\nMitsch, W.J. and J.G. Gosselink.1993. Wetlands. Van\\nNostrand Reinhold, NY.\\nNADB (North American Treatment Wetland Database). 1993.\\nElectronic database created by R. Knight, R. Ruble, R.\\nKadlec, and S. Reed for the U.S. Environmental Protec\u00c2\u00ac\\ntion Agency. Cincinnati, OH.\\nOdegaard, H. 1987. Particle Separation in Wastewater Treat\u00c2\u00ac\\nment. In Proceedings EWPCA 7th European Sewage\\nand Refuse Symposium, pp. 351-400.\\nReckhow, K., and S. S. Qian. 1994. Modeling Phosphorus\\nTrapping in Wetlands Using General Models. Water\\nResources Research, Vol. 30, No. 11, pp. 3105-3114.\\nReddy, K. R., and W.R. De Busk. 1987. Nutrient Storage\\nCapabilities of Aquatic and Wetland Plants for Water\\nTreatment and Resource Recovery. Magnolia Pub., Inc.,\\nOrlando, FL.\\nReed, S. C., R. Crites, and E. J. Middlebrooks, 1995 Natu\u00c2\u00ac\\nral Systems for Waste Management and Treatment,\\nMcGraw-Hill, San Francisco, Ca.\\nReed, S.C., R.W. Crites, and E.J. Middlebrooks. 1995. Natu\u00c2\u00ac\\nral Systems for Waste Management and Treatment. 2nd\\nEd., McGraw-Hill, NY.\\nSartoris, J., J. Thullen, L. Barber, and D. Salas. 1999. Inves\u00c2\u00ac\\ntigation of Nitrogen Transformations in a Southern Cali\u00c2\u00ac\\nfornia Constructed Wastewater Treatment Wetland, Eco\u00c2\u00ac\\nlogical Engineering, Vol 14, pp. 49-65.\\nSCRSD. 1998. Constructed Wetlands Demonstration Project.\\n1997 Annual Report, Sacramento, CA.\\nSparham, V.R. 1970. \u00e2\u0080\u009cImproved Settling Tank Efficiency by\\nUpward Flow Clarification,\u00e2\u0080\u009d JWPCF, Vo. 42, No 5, pp\\n801-811.\\nTchobanoglous, G., R. W. Crites, R.A. Gearheart, and S. C.\\nReed. 2000. A Review of Treatment Kinetics for Con\u00c2\u00ac\\nstructed Wetlands. Presented to WEF Specialty Con\u00c2\u00ac\\nference Disinfection, 2000. New Orleans, LA.\\n84", "height": "4267", "width": "3142", "jp2-path": "constructedwetla00nati_0100.jp2"}, "101": {"fulltext": "Tchobanoglous, G., F. Meitski, K. Thompson and T.H.\\nChadwick. 1989. Evolution and Performance of\\nCity of San Diego Pilot-Scale Aquatic Wastewa\u00c2\u00ac\\nter Treatment System Using Water Hyacinths.\\nResearch Journal WPCF, Vol 61, No. 11-12, pp\\n1625-1655.\\nTchobanoglous, G. and E. D. Schroeder. 1985. Wa\u00c2\u00ac\\nter Quality: Characteristics, Modeling, Modifica\u00c2\u00ac\\ntion. Addison-Wesley, Reading, MA.\\nUnited Kingdom, Dept, of Environment. 1973. Treat\u00c2\u00ac\\nment of Secondary Sewage Effluent in Lagoons.\\nNotes on Water Pollution #63. London, U.K.\\nUnited States Environmental Protection Agency.\\n1999. FWS Wetlands for Wastewater Treatment:\\nA Technology Assessment. EPA 832/R-99/002.\\nOffice of Water, Washington, DC.\\nU.S. Environmental Protection Agency. 1988. Design\\nManual. Constructed Wetlands and Aquatic Plant\\nSystems for Municipal Wastewater Treatment.\\nEPA/625/1 -88/022. Cincinnati, OH.\\nU.S. Environmental Protection Agency, 1983. Design\\nManual Municipal Wastewater Stabilization\\nPonds. EPA/625/1-83-015. Cincinnati, OH.\\nU.S. Environmental Protection Agency, 1993.\\nManual: Nitrogen Control. USEPA Publication No.\\nEPA/625/R-93/010. Cincinnati, OH.\\nWater Environment Federation, 1998. Design of Mu\u00c2\u00ac\\nnicipal Wastewater Treatment Plants, 4th Ed,\\nMOP#8. Alexandria, VA.\\nWater Environment Federation, 1990. Natural Sys\u00c2\u00ac\\ntems for Wastewater Treatment. MOP FD-16, Al\u00c2\u00ac\\nexandria, VA.\\n85", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0101.jp2"}, "102": {"fulltext": "Chapter 5\\nVegetated Submerged Bed Systems\\n5.1 Introduction\\nThe pollutant removal performance of vegetated sub\u00c2\u00ac\\nmerged bed (VSB) systems depends on many factors in\u00c2\u00ac\\ncluding influent wastewater quality, hydraulic and pollut\u00c2\u00ac\\nant loading, climate, and the physical characteristics of the\\nsystem. The main advantage of a VSB system over a free\\nwater surface (FWS) wetland system is the isolation of the\\nwastewater from vectors, animals and humans. Concerns\\nwith mosquitoes and pathogen transmission are greatly\\nreduced with a VSB system. Properly designed and oper\u00c2\u00ac\\nated VSB systems may not need to be fenced off or other\u00c2\u00ac\\nwise isolated from people and animals. Comparing con\u00c2\u00ac\\nventional VSB systems to FWS systems of the same size,\\nVSB systems typically cost more to construct, primarily\\nbecause of the cost of media (Reed et al., 1985). Because\\nof costs, it is likely that the use of the conventional VSB\\nsystems covered in this manual will be limited to individual\\nhomes, small communities, and small commercial opera\u00c2\u00ac\\ntions where mosquito control is important and isolation fenc\u00c2\u00ac\\ning would not be practical or desirable.\\nA conventional VSB system is described in Chapter 2\\nand depicted in Figure 2-3. The typical components in\u00c2\u00ac\\nclude (1) inlet piping, (2) a clay or synthetic membrane\\nlined basin, (3) loose media filling the basin, (4) wetland\\nvegetation planted in the media, and (5) outlet piping with\\na water level control system. The vast majority of VSB sys\u00c2\u00ac\\ntems have used continuous and saturated horizontal flow,\\nbut several systems in Europe have used vertical flow.\\nAlternative VSB systems are defined here as VSBs that\\nhave been modified to improve their treatment performance\\n(George et al., 2000, Young et al., 2000, Behrends et al.,\\n1996). Typical modifications involve some type of cyclic\\nfilling and draining of the system to improve the oxygen\\ninput into the media. The potential improvement in perfor\u00c2\u00ac\\nmance with alternative VSB systems is offset to some de\u00c2\u00ac\\ngree by a more complex and expensive operating system.\\nIt is too early to predict whether alternative VSB designs\\nwill prove to be more cost effective or practical than con\u00c2\u00ac\\nventional VSB systems, although they appear to provide\\nsignificantly better removal of certain pollutants.\\nThis chapter will discuss VSB systems that treat (1) septic\\ntank and primary sedimentation effluents, (2) pond efflu\u00c2\u00ac\\nents, and (3) secondary and non-algal pond effluents. The\\nmost common VSB systems in the U.S. treat septic tank\\nand pond effluents for BOD and TSS removal. In Europe,\\nVSB systems are most often used to treat septic tank ef\u00c2\u00ac\\nfluents, although they have also been used extensively in\\nthe U.K. for polishing activated sludge and RBC effluents,\\nand for treating combined sewer bypass flows (Cooper,\\n1990, Green and Upton, 1994).\\nThis chapter provides a summary of the theoretical and\\npractical considerations in the design of conventional VSB\\nsystems. VSB systems, like other natural treatment sys\u00c2\u00ac\\ntems, are less understood than highly-engineered waste\\ntreatment systems because they (1) have more variable,\\ncomplex, and less controllable flow patterns, (2) have re\u00c2\u00ac\\naction rates and sites within the system that vary with time\\nand location, and (3) are subject to the inconsistencies of\\nclimate and growth patterns. This complexity makes the\\ndevelopment and use of design equations based on ideal\u00c2\u00ac\\nized reactor and reaction kinetic theory difficult, if not im\u00c2\u00ac\\npractical and unrealistic. Furthermore, because pollutant\\nremoval performance can be quite variable, designs must\\nbe conservative if a guaranteed effluent quality is required.\\n5.2 Theoretical Considerations\\n5.2.1 Potential Value of Wetland Plants in\\nVSB Systems\\nIn several recent studies that have compared the pollut\u00c2\u00ac\\nant removal performance of planted and unplanted VSB\\nsystems, it has been found that plants do not have a major\\nimpact on performance (Young et al, 2000, George et al.,\\n2000, Liehr et al., 2000). There is however significant cost\\nand time associated with the establishment and mainte\u00c2\u00ac\\nnance of the wetland plants in a VSB system. Neverthe\u00c2\u00ac\\nless, planted systems have a significant aesthetic advan\u00c2\u00ac\\ntage over unplanted systems and may be of value as wet\u00c2\u00ac\\nland habitat in some cases. Unfortunately, the aesthetic\\nvalue of plants and the value of VSB wetland systems as\\nwetland habitat are difficult to quantify, and no mitigation\\ncredit is given by the USEPA for the habitat value they\\nprovide. In the following sections the potential value of\\nwetland plants in VSB systems is discussed in more de\u00c2\u00ac\\ntail.\\n5.2.1.1 Type of Wetland Plants\\nSeveral studies have attempted to determine if pollutant\\nremoval performance differs with various types of wetland\\n86", "height": "4267", "width": "3142", "jp2-path": "constructedwetla00nati_0102.jp2"}, "103": {"fulltext": "plants (Gersberg et al., 1986, Young et al., 2000). Although\\nsome researchers have claimed a relationship, these\\nclaims have not been substantiated by others (Gersberg\\net al., 1986).\\nIt is not clear if it is desirable to maintain a single plant\\nspecies, or a prescribed collection of plant species, for any\\ntreatment purpose. Single plant (monoculture) systems are\\nmore susceptible to catastrophic plant death due to pre\u00c2\u00ac\\ndation or disease (George et al., 2000). It is generally as\u00c2\u00ac\\nsumed that multiple plant and native plant systems are\\nless susceptible to catastrophic plant death, although no\\nstudies have confirmed this assumption. Plant invasion and\\nplant dominance further complicate the issue; in several\\ncases researchers have found that, with time and without\\noperator intervention, one of the planted species or an in\u00c2\u00ac\\nvader species has become the dominant species in all or\\npart of the system (Young et al., 2000, Liehr et al., 2000).\\nThis occurs less frequently and more slowly in VSB sys\u00c2\u00ac\\ntems than in FWS systems.\\nThe impact of wetland plants on pollutant removal per\u00c2\u00ac\\nformance appears to be minimal based on current knowl\u00c2\u00ac\\nedge, so the selection of plants species should be based\\non aesthetics, impacts on operation, and long-term plant\\nhealth and viability in a given geographical area. Local\\nwetland plants experts should be consulted when making\\nthe selection.\\n5.2.1.2 Plant Mediated Gas Transfer\\nWetland plants can facilitate gas transfer both into and\\nout of the wastewater of a VSB system. The focus of most\\nstudies has been oxygen transfer into the wastewater.\\nHowever, methane and other dissolved gases in the waste-\\nwater can be transferred out of the wastewater by wetland\\nplants. The mechanisms of plant-mediated gas transfer\\nare described in detail in Chapter 3. The potential amount\\nof oxygen transferred by plant roots into the wastewater\\ndepends on many factors including dissolved oxygen con\u00c2\u00ac\\ncentration in the wastewater, root depth in the wastewater,\\nair and leaf temperatures, and plant growth status (rapid\\ngrowth vs. senescence). Most studies to determine the\\nrates of plant-mediated oxygen transfer have been per\u00c2\u00ac\\nformed in laboratory microcosms or mesocosms under\\ncontrolled conditions.(George et al., 2000, Liehr, et al.,\\n2000) It is not clear if these results are transferable to full-\\nscale systems.\\nBased on a review of the literature, the likely rate of oxy\u00c2\u00ac\\ngen transfer is between zero and 3.0 g-0 2 /m 2 -d (0 0.6\\nlbs/1000 ft 2 -d). While this maximum value is within the BOD\\nloading range of lightly loaded VSB systems, (3 g/m 2 -d\\n30 kgBOD/ha-d 27 lb BOD/ac-d), there is very little evi\u00c2\u00ac\\ndence to support the assumption that plants add signifi\u00c2\u00ac\\ncant amounts of oxygen to VSB systems. Typical values\\nof dissolved oxygen in VSB systems are very low 1 .Omg/\\nL), but because of the difficulty in obtaining an accurate in-\\nsitu oxygen reading, the actual values are probably even\\nlower. In VSB systems where oxidation-reduction poten\u00c2\u00ac\\ntial (ORP) has been measured, values were typically quite\\nnegative, indicating strong reducing conditions.\\nUnplanted systems have been found to perform as well\\nas planted systems in both BOD and ammonia nitrogen\\nremoval (George et al., 2000, Liehr et al., 2000, Young, et\\nal., 2000). Furthermore, investigations of root depth and\\nflow pathways have found that the roots do not fully pen\u00c2\u00ac\\netrate to the bottom of the media and there is substantially\\nmore flow under the root zone than through it (Young et\\nal., 2000, George et al., 2000, Bavor et al. 1989, Fisher,\\n1990, DeShon et al., 1995, Sanford et al., 1995a 1995b,\\nSanford, 1999, Rash and Liehr, 1999, Breen and Chick,\\n1995, Bowmer, 1987). The oxygen supply from the roots\\nis also likely to be unreliable due to yearly plant senes\u00c2\u00ac\\ncence, plant die-off due to disease and pests, and vari\u00c2\u00ac\\nable plant coverage from year to year. Considering all of\\nthese factors, it is recommended that designers assume\\nwetland plants provide no significant amounts of oxygen\\nto a VSB system.\\nPlants will also affect the other potential source of oxy\u00c2\u00ac\\ngen to VSBs the direct oxygen transfer from the atmo\u00c2\u00ac\\nsphere to the wastewater. Researchers at TVA have esti\u00c2\u00ac\\nmated oxygen transfer from the atmosphere to be between\\n0.50 and 1.0 g-0 2 /m 2 -d (0.1-0.2 lbs/1000 ft 2 -d) (Behrends\\net al., 1993). Decomposing plant matter on top of the me\u00c2\u00ac\\ndia would likely cause even lower rates of oxygen trans\u00c2\u00ac\\nport into the wastewater because the plant matter acts as\\na diffusion barrier and, ultimately, an oxygen demand.\\n5.2.1.3 Nutrient and Metals Removal by\\nWetland Plants\\nWetland plants take up macro-nutrients (such as N and\\nP) and micro-nutrients (including metals) through their roots\\nduring active plant growth. At the beginning of plant se\u00c2\u00ac\\nnescence most of the nutrients are translocated to the rhi\u00c2\u00ac\\nzomes and roots. A significant proportion of the nutrients\\nmay also be exuded from the plant (Gearheart et al., 1999).\\nEstimates of net annual nitrogen and phosphorus uptake\\nby emergent wetland species vary from 12 to 120 gN/m 2 -y\\nand 1.8 to 18 gP/m 2 -y respectively (Reddy and DeBusk,\\n1985). Reeds and bulrush are at the lower end of both\\nranges while cattails are at the higher end. These esti\u00c2\u00ac\\nmates are based on annual growth rates and nutrient con\u00c2\u00ac\\ncentrations of the whole plant, but since in a VSB system\\nonly the shoots can be harvested, the values should be\\nreduced by at least 50%. Plant uptake of metals can also\\nbe estimated by this method. To maximize nutrient removal\\nby the plants in a VSB system, shoot harvesting must be\\ndone before senescence. Harvesting of wetland plants is\\nnot recommended during the growing season because the\\nwarm temperatures may cause plant stress, substantial\\nstem death, and significant delay in re-growth in some\\nwetland plants (George, et al., 2000).\\nThe expected maximum removal rates of nitrogen, phos\u00c2\u00ac\\nphorus and metals by direct plant uptake and harvesting\\nare small compared to typical loadings in VSB systems.\\nFurthermore, nitrogen, phosphorus and metals removal by\\nplant uptake will vary with time. Most of the nutrient up\u00c2\u00ac\\ntake occurs during rapid plant growth in the spring and\\nsummer, and if the plant is not harvested before senes-\\n87", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0103.jp2"}, "104": {"fulltext": "cence a significant portion of the plant-sequestered nutri\u00c2\u00ac\\nents are released back into the water. Therefore, unless\\nthe nutrient removal standards for a VSB system are also\\nvariable and synchronous with plant uptake and release,\\nthe presence of plants may be more harmful than helpful\\nin meeting nutrient removal standards. Finally, it is unlikely\\nthat the nutrients or metals removal obtained by harvest\u00c2\u00ac\\ning are worth the considerable time and labor required to\\nharvest and reuse or dispose of the biomass.\\n5.2.1.4 Plant-Supplied Carbon Sources for\\nDenitrification\\nBecause of the inherent anaerobic conditions associ\u00c2\u00ac\\nated with VSB systems, they are good candidates for deni\u00c2\u00ac\\ntrification. The likely limiting factor for denitrification in VSB\\nsystems is biodegradable organic carbon. The value of\\nplant-supplied organic carbon for denitrification in a VSB\\nsystem depends on the wastewater COD to nitrogen ratio\\nand the forms of nitrogen in the influent to the system.\\nPlant-supplied organic carbon is most important in VSB\\nsystems treating nitrate-rich influents deficient in biode\u00c2\u00ac\\ngradable organic carbon such as effluents from nitrifying\\nactivated sludge plants. The minimum COD to nitrate-ni\u00c2\u00ac\\ntrogen ratio for denitrification is 2.3 g-C0D/g-N0 3 -N. Since\\noxygen is used preferentially over nitrate as the electron\\nacceptor by the microbes that carry out denitrification, the\\nrequired C0D/N0 3 -N ratio can be significantly higher if any\\noxygen is present in the system.\\nDecomposing wetland plants and plant root exudates\\nare potential sources of biodegradable organic carbon for\\ndenitrification but are also sources of organic nitrogen,\\nwhich is easily converted to ammonia. Plant root exudates\\nof organic carbon and nitrogen are the largest at the be\u00c2\u00ac\\nginning of senescence. Because of the predominantly\\nanaerobic conditions in VSB systems, decomposition of\\nplant biomass within the media of a VSB system will likely\\nprovide more organic carbon (and ammonia) to the waste-\\nwater than will decomposition of the plant biomass on top\\nof the media, which takes place in largely aerobic condi\u00c2\u00ac\\ntions. Some of the decomposition products of biomass on\\ntop of the media (including nitrates) are transported into\\nthe wastewater by precipitation infiltration.\\nIn one study of a VSB system treating a nitrified second\u00c2\u00ac\\nary effluent, nitrate removal improved from 30% to 80%\\nwhen mulched biomass including straw, wetland plants,\\nand grass was applied to the top of the media (Gersberg\\net al., 1983). Another study with a VSB system treating a\\nnitrified landfill leachate found that nitrate removal was lim\u00c2\u00ac\\nited by biodegradable organic carbon (Liehr et al., 2000).\\n5.2.1.5 Plant Role in Thermal Insulation\\nOne potential advantage of a planted over an unplanted\\nVSB system is the role of plants in providing thermal insu\u00c2\u00ac\\nlation to the wastewater during cold weather. Dead plant\\nbiomass on top of the media helps to limit both convective\\nheat losses from the wastewater and infiltration of melted\\nsnow into the wastewater. Two researchers have devel\u00c2\u00ac\\noped methods to estimate the effect of plants in prevent\u00c2\u00ac\\ning heat loss from the wastewater of a VSB system (Reed\\net al., 1995, Smith et al., 1997). However, it is not clear\\nhow important this factor is in pollutant removal perfor\u00c2\u00ac\\nmance because 1) it has not been shown that planted VSB\\nsystems perform better than unplanted systems, even in\\nwinter, and 2) the dead plant material on top of the media\\nalso acts as a barrier to oxygen transfer and a potential\\nsource of biodegradable carbon and nutrients to the waste-\\nwater.\\n5.2.1.6 Plant Impact on Hydraulic Conductivity\\n(Clogging) and Detention Time\\nSeveral VSB systems have experienced conditions\\ncalled \u00e2\u0080\u009csurfacing\u00e2\u0080\u009d where a portion of the wastewater flows\\non top of the media. Surfacing (1) creates conditions fa\u00c2\u00ac\\nvorable for odors and mosquito breeding, (2) creates a\\npotential health hazard for persons and animals that may\\ncome into contact with the wastewater, and (3) reduces\\nthe hydraulic retention time (HRT) and performance of a\\nVSB system. Surfacing occurs whenever the hydraulic\\nconductivity of the media is not sufficient to transport the\\ndesired flow within the usable headloss of the media. The\\nusable headloss is defined by the difference in the eleva\u00c2\u00ac\\ntions of the outlet piping and the top of the media. Surfac\u00c2\u00ac\\ning can result from a number of factors including (1) poor\\ndesign of the system inlet and outlet piping, (2) an inaccu\u00c2\u00ac\\nrate estimate of the clean hydraulic conductivity of the\\nmedia, (3) improper construction, and (4) an inaccurate\\nestimate of the reduction in hydraulic conductivity, or \u00e2\u0080\u009cclog\u00c2\u00ac\\nging\u00e2\u0080\u009d, that will occur due to solids accumulation and/or\\ngrowth of plant roots. Several researchers have found that\\nclogging was the most severe within the first 1/4 to 1/3 of\\nthe system (Young et al., 2000, George et al., 2000, Bavor\\net al. 1989, Fisher, 1990, Sapkota and Bavor, 1994, Tan\u00c2\u00ac\\nner and Sukias, 1995, Tanner et al., 1998). The hydraulic\\nconductivity was found to be less restricted and fairly uni\u00c2\u00ac\\nform over the remaining length of the system.\\nBased on studies in Europe during the 1980s, some re\u00c2\u00ac\\nsearchers proposed that plant roots significantly increased\\nthe hydraulic conductivity in VSBs with soil media by open\u00c2\u00ac\\ning up preferential pathways for the wastewater flow\\n(Kickuth, 1981). Later studies of these systems found that\\na significant portion of flow occurred on top of the soil (Coo\u00c2\u00ac\\nper et al., 1989). Based on recent studies, the presence of\\nplant roots in the gravel media of a VSB system will have a\\nnegative effect on hydraulic conductivity (George et al.,\\n2000, Young et al., 2000, DeShon et al., 1995, Sanford et\\nal., 1995a and 1995b, Breen and Chick, 1995). Research\u00c2\u00ac\\ners at TTU compared the reduction in void volume due to\\nroot and non-root solids. They estimated that the reduc\u00c2\u00ac\\ntion in void volume due to root solids (2 8%) was much\\nlarger than the reduction in void volume due to non-root\\nsolids (0.1 0.4%). Even though the overall estimated re\u00c2\u00ac\\nduction in void volume was small, there was a 98% reduc\u00c2\u00ac\\ntion in hydraulic conductivity.\\nThe primary functions of a plant\u00e2\u0080\u0099s roots are to supply\\nwater and nutrients and to physically anchor or support\\nthe above-ground portions on the plants. Water and nutri-\\n88", "height": "4267", "width": "3142", "jp2-path": "constructedwetla00nati_0104.jp2"}, "105": {"fulltext": "ents will be plentiful at all depths of a VSB, so the plant\\nroots will typically penetrate only 15 25 cm (6\u00e2\u0080\u009c -10 as\\nneeded to anchor the plant. In most VSB systems the plant\\nroots do not fully penetrate the entire depth of the media\\nand the reduction in hydraulic conductivity in the root zone\\nresults in the creation of \u00e2\u0080\u009cshort-circuiting\u00e2\u0080\u009d under the root\\nzone, and more flow through the portion of the media with\u00c2\u00ac\\nout roots (Bavor et al., 1989, Fisher, 1990, DeShon et al.,\\n1995, Sanford et al., 1995a and 1995b, Sanford, 1999,\\nRash and Liehr, 1999, Tanner and Sukias, 1995, Breen\\nand Chick, 1995). This situation may also lead to the cre\u00c2\u00ac\\nation of stagnant zones within the media dead volume\\nwhich results in lower actual HRTs as the water preferen\u00c2\u00ac\\ntially flows through a smaller volume of the media. The\\ndecrease in HRT will depend in part on the fraction of the\\ndepth that is occupied by the roots; that is, deeper beds\\nwill have more a greater proportion of the media that is not\\nimpacted by roots.\\nFrom tracer studies, researchers have found significant\\ndifferences between actual and theoretical HRTs in their\\nVSB systems and attributed it to dead volume in the upper\\nzone of the media where the majority of the roots grow\\n(Liehr et al., 2000, Young et al., 2000, Bavor et al., 1989,\\nFisher, 1990, DeShon et al., 1995, Sanford et al., 1995a\\nand 1995b, Breen and Chick, 1995). However, the re\u00c2\u00ac\\nsearchers at TTU did not find a significant reduction in HRT\\nin three of the cells they studied. (George et al., 2000)\\nThe researchers at North Carolina State University\\n(NCSU) attributed part of the dead volume in their sys\u00c2\u00ac\\ntems to stratification of the water caused by less dense\\nrain water infiltration ponding within the media on top of\\nhigher density leachate. This phenomenon has also been\\nreported by others (DeShon et al., 1995, Sanford et al.,\\n1995a and 1995b, Sanford,1999, Rash and Liehr, 1999).\\nNCSU found that the short-circuiting was greater in an\\nunplanted VSB system than in a planted system. While\\nrain water ponding may be a problem with some VSB sys\u00c2\u00ac\\ntems, the effect at NCSU was magnified by the relatively\\nlarge catchment area (due to the shallow side slopes used\\nin the system) and the salinity of the leachate. The CU\\nresearchers performed two sets of tracer studies in the\\nthree cells of the Minoa system. The first set was performed\\nin the clean media of each cell before planting. The sec\u00c2\u00ac\\nond set was performed after plant establishment on the\\none cell that was half planted and half unplanted. From\\nthe first study they concluded that there was short circuit\u00c2\u00ac\\ning through the lower media and dead volume resulting in\\nthe actual HRTs being only 75% of the theoretical values,\\neven in the clean media. They attributed these results to\\nmedia compaction during construction and intermixing of\\nthe upper pea gravel with the lower larger media. From\\nthe second tracer study they concluded that plants roots,\\nwhich penetrated only half of the media depth, resulted in\\nmore short circuiting and dead volume than in the unplanted\\nmedia. Tanner Sukias (1995) also reported more accu\u00c2\u00ac\\nmulation of solids in the root zone, which further contrib\u00c2\u00ac\\nuted to preferential flow around the root zone.\\n5.2.2 Removal Mechanisms\\n5.2.2.1 BOD and TSS\\nVSB systems have been used for secondary treatment\\n(i.e. 30 mg/L of BOD and TSS) for a variety of wastewa\u00c2\u00ac\\nters including: primary and septic tank effluents; pond ef\u00c2\u00ac\\nfluent; and effluents from activated sludge, RBC, and trick\u00c2\u00ac\\nling filter systems that don\u00e2\u0080\u0099t consistently meet secondary\\nstandards. As discussed in Chapter 3, the primary mecha\u00c2\u00ac\\nnisms for BOD and TSS removal are flocculation, settling,\\nand filtration of suspended and large colloidal particles.\\nVSB systems are effective for TSS and BOD because of\\nrelatively low flow velocities and a high amount of media\\nsurface area. They typically do better at TSS removal, be\u00c2\u00ac\\ncause TSS removal is a completely physical mechanism,\\nwhile BOD removal is more complex. Larger biodegrad\u00c2\u00ac\\nable particles that have been quickly removed by physical\\nmechanisms will be degraded over time and be converted\\ninto particles in the soluble and small colloidal size range.\\nAs such they become an internal \u00e2\u0080\u009csource\u00e2\u0080\u009d of BOD as they\\ndegrade and reenter the water. Some material is also in\u00c2\u00ac\\ncorporated into microbial biomass.\\nSome material will accumulate in a VSB, but the amount\\nof long term solids accumulation is unknown. Tanner and\\nSukias (1995) reported finding less solids accumulation\\nthan would be expected based on the load in the influent\\nwastewater. Researchers at Richmond, Australia (Bavor\\net al., 1989, Fisher, 1990) found that most solids were re\u00c2\u00ac\\nmoved in the initial section of the VSB and that the \u00e2\u0080\u009csolids\\naccumulation front\u00e2\u0080\u009d stabilized after a year and did not ad\u00c2\u00ac\\nvance. These findings support the idea that trapped mate\u00c2\u00ac\\nrial will degrade over time. VSB systems treating pond\\nwastewater are likely to accumulate more solids, and be\\nmore susceptible to clogging, because TSS in pond waste-\\nwater is predominantly algae, which are slightly less bio\u00c2\u00ac\\ndegradable and degrade more slowly than typical primary\\nor secondary wastewater solids.\\nBOD and TSS in the effluent from a VSB are probably\\nnot materials that have passed through the VSB, but rather\\nare converted or internally produced material. As such it is\\nlikely to be quite different in size or composition from influ\u00c2\u00ac\\nent BOD and TSS. For example, the influent TSS in the\\nLas Amimas system were predominantly algal cells, but\\nthere were almost no algal cells in the effluent even thought\\nthe effluent TSS averaged 30 mg/L (Richard Synder,\\n1994).\\nTrue BOD removal only occurs when the material caus\u00c2\u00ac\\ning the BOD is completely converted by anaerobic biologi\u00c2\u00ac\\ncal processes to gaseous end products. The two most likely\\nanaerobic pathways are methane fermentation and sul\u00c2\u00ac\\nfate reduction. Because methane fermentation is severely\\ninhibited at temperatures below 10\u00c2\u00b0C, sulfate reduction\\nprobably predominates for soluble BOD removal during\\ncolder months. However, seasonal performance does not\\nvary as much as would be expected based on the typical\\ntemperature dependence of biological reactions. A likely\\nexplanation, illustrated in Figure 5-1, is that biodegradable\\nparticles that are physically removed during colder months\\n89", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0105.jp2"}, "106": {"fulltext": "BOD (mg/L) TSS (mg/L)\\nFigure 5-1. Seasonal cycle in a VSB\\n90", "height": "4267", "width": "3142", "jp2-path": "constructedwetla00nati_0106.jp2"}, "107": {"fulltext": "are degraded more slowly and accumulate (Kadlec and\\nKnight, 1996). As the temperature warms up the rate of\\ndegradation of trapped particles increases, leading to a\\nreduction of accumulated solids and a release of BOD.\\nThis theory would explain why summer BOD removal rates,\\nbased on influent BOD loading, do not appear to be sig\u00c2\u00ac\\nnificantly greater than winter removal rates. The need for\\ninsulation of the surface of VSB systems in northern cli\u00c2\u00ac\\nmates has been discussed, but the need has not been\\nquantified (Jenssen, etal, 1993).\\nAlternative VSB systems should achieve higher oxygen\\ntransfer rates, so BOD removal should improve because\\naerobic biological processes will become more prevalent.\\nHowever, microbial biomass production should also in\u00c2\u00ac\\ncrease, which may lead to increased clogging problems.\\nThe potential of alternative VSB systems for TSS and BOD\\nremoval is unclear, but performance at Minoa, NY has been\\nvery good (Reed and Giarrusso, 1999).\\n5.2.2.2. Nitrogen\\nSeveral conventional VSB systems have been designed,\\nbuilt and operated to remove ammonia from various waste-\\nwaters. While partial ammonia removal has been achieved\\nin some systems, the removals have been less than pre\u00c2\u00ac\\ndicted (George et al., 2000, Liehr et al., 2000, Young et al.,\\n2000). Ammonia can be removed by microbial reactions\\nor plant uptake. Because VSB systems are predominantly\\nanaerobic, microbial removal via nitrification is very lim\u00c2\u00ac\\nited. As discussed in Section 5.2.1.3, plant uptake is also\\nvery limited. Very lightly loaded systems have achieved\\npartial ammonia removal (George et al., 2000,1999; Young\\net al., 2000), but if ammonia removal is required, a sepa\u00c2\u00ac\\nrate ammonia removal process should be used in conjunc\u00c2\u00ac\\ntion with a VSB system.\\nThe predominantly anaerobic condition of VSB systems\\nseems well suited for microbial removal of nitrate via deni\u00c2\u00ac\\ntrification, but there are relatively few studies to document\\ntheir use for this specific purpose (Gersberg, et al, 1983;\\nStengel and Schultz-Hock, 1989). Systems treating well\\noxidized secondary effluents or other carbon limited waste-\\nwaters may have inadequate carbon for denitrification to\\nproceed efficiently (Liehr et al., 2000). Systems treating\\nwastewaters with more carbon, and that have achieved\\npartial nitrification, typically achieve almost complete deni\u00c2\u00ac\\ntrification (George et al., 2000, Young et al., 2000). Crites\\nand Tchobanoglous (1998) suggest that significant denitri\u00c2\u00ac\\nfication of municipal wastewaters can occur in VSB sys\u00c2\u00ac\\ntems at a detention time of 2 to 4 days, but Stengel and\\nSchultz-Hock (1989) demonstrated with methanol addition\\nthat denitrification was carbon limited.\\nAlternative VSB systems should achieve higher oxygen\\ntransfer rates, so they should be more efficient at ammo\u00c2\u00ac\\nnia removal via nitrification (George et al., 2000, Reed\\nGiarusso, 1999, Behrends et al., 1996, May et al., 1990)\\nand less efficient for nitrate removal via denitrification than\\nconventional VSBs.\\n5.3 Hydrology\\n5.3.1 Evapotransporation and\\nPrecipitation Impacts\\nThe avoidance of surfacing is a major design criterion\\nand high amounts of precipitation or snowmelt can increase\\nthe flow in a VSB system. In climates with extended peri\u00c2\u00ac\\nods of precipitation or heavy snowmelt, the runoff from the\\ntotal catchment area that drains into the VSB must be es\u00c2\u00ac\\ntimated and included in the design flow. Evapotransporation\\n(ET) decreases the hydraulic loading and will not contrib\u00c2\u00ac\\nute to surfacing.\\nExcept in very wet climates, flows from precipitation\\nevents will probably not adversely affect performance be\u00c2\u00ac\\ncause VSB systems have a relatively small surface area\\n(compared to FWS wetlands) and effluent controls should\\nbe sufficient to prevent surfacing. Precipitation dilutes pol\u00c2\u00ac\\nlutants in the system, temporarily raises the water level,\\nand decreases the HRT, while ET concentrates pollutants,\\ntemporarily lowers the water level, and increases the HRT.\\nET rates will vary depending on plant species and density,\\nbut rates from 1.5 to 2 times the pan evaporation rate have\\nbeen reported in the literature (refs). Except in very wet or\\ndry climates, the two results are probably offsetting, re\u00c2\u00ac\\nducing the overall impact on water level and effluent val\u00c2\u00ac\\nues. Unfortunately, the specific effects of ET and precipi\u00c2\u00ac\\ntation on VSB performance are not documented because\\ngood estimates of ET and precipitation are hard to obtain,\\nand precise influent and effluent flow measurements are\\nseldom available, even in research systems.\\n5.3.2 Water Level Estimation\\nAn important step in the design process is to estimate\\nthe elevation of the water surface throughout the VSB to\\nensure that surfacing of the wastewater does not occur.\\nAs in all gravity flow systems the water level in a VSB sys\u00c2\u00ac\\ntem is controlled by the outlet elevation and the hydraulic\\ngradient, or slope, which is the drop in the water level\\n(headloss) over the length from the inlet to the outlet. The\\nrelationship between flow through a porous media and the\\nhydraulic gradient is typically described by the general form\\nof Darcy\u00e2\u0080\u0099s Law (Eq. 5.1). This form assumes laminar flow\\nthrough media finer than coarse gravel, and many authors\\nhave modified it for other applications including other me\u00c2\u00ac\\ndia and turbulent flow. However, use of the general form\\nwithout modification is recommended as sufficient to esti\u00c2\u00ac\\nmate the water level within a VSB.\\nQ (K)(A)(S) (K)(W)(DJ(dh/dL)\\nor, for a defined length of the VSB,\\n(5-1)\\ndh (Q)(L) (K)(W)(D w\\n(5-2)\\nwhere Q= flow rate, m 3 /d\\nK hydraulic conductivity, m 3 /m 2 -d, or m/d\\nA cross-sectional area normal to wastewater flow, m 2\\nC (W)(DJ\\nwhere W width of VSB, m\\nD w water depth, m\\n91", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0107.jp2"}, "108": {"fulltext": "L length of VSB, m\\ndh head loss (change in water level) due to flow re\\nsistance, m\\nS dh/dL hydraulic gradient, m/m\\nThe water level at the inlet of a VSB will rise to the level\\nrequired to overcome the head loss in the entire VSB.\\nTherefore, the VSB must be designed to prevent surfac\u00c2\u00ac\\ning. K for an operating VSB varies with time and location\\nwithin the media and will have a major impact on the head\\nloss. K is very difficult to determine because it is influenced\\nby factors that cannot be easily accounted for, including\\nflow patterns (affected by preferential flow and short cir\u00c2\u00ac\\ncuiting), and clogging (affected by changes in root growth/\\ndeath and solids accumulation/degradation). Therefore, a\\nvalue must be assumed for design purposes. Typical val\u00c2\u00ac\\nues for various sizes of rock and gravel are shown in Table\\n5-1. Several of the references listed in Table 5-1 also noted\\nthat K was much less in the initial 1/4 to 1/3 of the VBS\\nthan in the remainder of the bed. Based on the studies\\nlisted in Table 5-1 and many observed cases of surfacing\\nin VSB systems, the following conservative values are rec\u00c2\u00ac\\nommend for the long-term operating K values:\\ninitial 30% of VSB K 1 of clean K\\nfinal 70% of VSB K 10% of clean K.\\n5.3.3 Hydraulic Retention Time and\\nContaminant Dispersion\\nThe theoretical HRT in any reactor is defined as the liq\u00c2\u00ac\\nuid volume of the reactor divided by the flow rate through\\nit. The liquid volume in a VSB system is difficult to accu\u00c2\u00ac\\nrately determine because of the loss of pore volume to\\nroots and other accumulated solids, such as recalcitrant\\nbiomass and chemical precipitates. The lost pore volume\\nwill vary with both location in the VSB and time, both sea\u00c2\u00ac\\nsonally and yearly, because of root growth and decay, and\\nsolids accumulation and degradation. Preferential flow (see\\nsection 5.2.1.6) as illustrated in Figure 5-2 will also have a\\ndirect impact on HRT and has not been correlated with\\nchanges in pore volume. For design purposes the volume\\noccupied by roots and other solids is assumed to be insig\u00c2\u00ac\\nnificant and the theoretical HRT is estimated using the\\naverage flow (including precipitation and ET for very wet\\nor dry climates) through the system, the system dimen\u00c2\u00ac\\nsions, the operating water level, and the initial (clean) po\u00c2\u00ac\\nrosity of the media, which is either estimated or experi\u00c2\u00ac\\nmentally determined.\\nThe actual HRT has been frequently reported to be 40-\\n80% less than the theoretical HRT (based on pore vol\u00c2\u00ac\\nume) either due to loss of pore volume, dead volume, or\\npreferential flow (Fisher, 1990, Sanford et al., 1995b,\\nBhattarai and Griffin, 1998, Batchelor and Loots, 1997,\\nRash and Liehr, 1999, Tanner and Sukias, 1995, Breen\\nand Chick, 1995, Tanner et al., 1998, Bowmer, 1987). A\\nrough approximation of the liquid volume can be deter\u00c2\u00ac\\nmined by measuring the volume of water drained from an\\noperating bed, but water held in small pores or adhering to\\nbiomass will remain in the system. Draining will also not\\nbe able to account for preferential flow. Tracer studies are\\nrecommended as a more realistic measure of the HRT in\\na VSB system, using one of a variety of tracers (Young et\\nal., 2000, Young et al., 2000, George et al., 2000, Netter\\nTable 5-1. Hydraulic Conductivity Values Reported in the Literature.\\nSize and type\\nof Media\\n\u00e2\u0080\u009cCleanTDirty\u00e2\u0080\u009d\\nK (m/d)\\nType of Wastewater\\n(Typical TSS, mg/L) 2\\nLength of\\nOperation\\nNotes References\\n5-10 mm gravel\\n34,000/12,000\\n2\u00c2\u00b0 effluent (100)\\n2 years\\nK 12,000 is for downstream portion (last 80 m) of VSB\\n5-10 mm gravel\\n34,000/900\\n2\u00c2\u00b0 effluent (100)\\n2 years\\nK 900 is for inlet zone (first 20 m) of VSB\\nBavor et al (1989), Fisher (1990), Bavor Schulz\\n(1993)\\n17 mm creek rock\\n100,000/44,000\\nnutrient solution (neg)\\n4 months\\nneg negligible TSS\\n6 mm pea gravel\\n21,000/9000\\nnutrient solution (neg)\\n4 months\\nMacmanus et al (1992), DeShon et al (1995)\\n30-40 mm coarse gravel\\nNR/1000\\n2\u00c2\u00b0 effluent (30 w/a)\\n2 years\\nw/a with algae; pond effluent; gravel bed only-\\nno plants\\n5-14 mm fine gravel\\nNR/12,000\\n2\u00c2\u00b0 effluent (30 w/a)\\n2 years\\ncoarse gravel is first 6m of bed; fine is last 9 m of\\nbed Sapkota Bavor (1994)\\n20-40 mm coarse gravel\\nNR/NR\\nlandfill leachate (neg)\\n26 months\\nfor coarse gravel, headloss was controlled by\\noutlet, not K\\n5 mm pea gravel\\n6200/600\\nlandfill leachate (neg)\\n26 months\\nSanford et al (1995a 1995b), Sanford (1999),\\nSurface et al (1993)\\n19 mm rock\\n120,000/3000\\nseptic tank effluent (50)\\n7 months\\nGeorge et al (2000)\\n14 mm fine gravel\\n15,000/see note\\naerated pond (60 w/a)\\n2 years\\nK of combined gravel (fine overlaid coarse) was\\n22 mm coarse gravel\\n64,000/see note\\naerated pond (60 w/a)\\n2 years\\n2000 at 50 m from inlet; 27,000 at 300 m from inlet\\nKadlec Watson (1993), Watson et al (1990)\\nType as defined in the reference(s)\\n2 neg negligible; w/a with algae\\n92", "height": "4267", "width": "3142", "jp2-path": "constructedwetla00nati_0108.jp2"}, "109": {"fulltext": "Wetland Plants\\nJntlet _YT\\nOutlet\\nZone\\nIntlet\\nZone\\n0.6m\\nNot to Scale Dimensions Are \u00e2\u0080\u009cTypical\u00e2\u0080\u009d\\nFigure 5-2. Preferential Flow in a VSB\\nand Bischofsberger, 1990, Fisher, 1990, Netter 1994,\\nSanford et al., 1995b, Bhattarai and Griffin, 1998, Bowmer,\\n1987).\\nSome of the current design equations for VSB systems\\nassume plug flow conditions. However, tracer studies per\u00c2\u00ac\\nformed on VSB systems have found significant amounts\\nof dispersion as shown in Figure 5-3 (Sanford et al., 1995b,\\nBhattarai and Griffin, 1998, Liehr et al., 2000, George et\\nal., 2000). Based on current data it appears that VSB sys\u00c2\u00ac\\ntems can not be accurately modeled as either plug flow or\\ncomplete mix reactors. The simplest model that can pro\u00c2\u00ac\\nvide a reasonable fit to the tracer curves is a series of\\nequal volume complete mix reactors. However, while this\\nmodel may mathematically fit the tracer data, it does not\\nrealistically represent physical flow through porous media.\\nIntuitively it would seem that a plug flow reactor with dis\u00c2\u00ac\\npersion would most closely represent the actual conditions\\nin a VSB. This model allows greater flexibility in determin\u00c2\u00ac\\ning a fit of the tracer data but typically results in a complex\\nmathematical model of pollutant removal. Estimates of the\\ndispersion number for VSB systems have ranged from\\n0.050 to 0.31 (George et al., 2000, Bhattarai and Griffin,\\n1998), with greater numbers for systems with small length-\\nwidth ratios. Dispersion numbers less than 0.025 are in\u00c2\u00ac\\ndicative of near-plug flow conditions while values above\\n0.20 indicate a high degree of dispersion. The modeling of\\nflow and dispersion is complicated by the non-uniformity\\nof flow and pore volume in space and time as previously\\ndiscussed, and by other factors including precipitation and\\nET.\\nAt this point in time there appears to be little justification\\nfor using complex flow models, because of a lack of data\\nand the unpredictable and constantly varying conditions\\nwithin a VSB.\\n5.4 Basis of Design\\n5.4.1 Introduction\\nAttempting to fully describe pollutant removal in VSB\\nsystems is at least as complex as trying to describe VSB\\nhydraulics. Many authors have examined several relation\u00c2\u00ac\\nships as a model for pollutant removal, including zero and\\nfirst order reactions in both plug flow and complete mix\\nreactor models. None of the relationships were found to\\nreasonably fit of the all data that are available. Further\u00c2\u00ac\\nmore, data from VSB systems are typified by a wide vari\u00c2\u00ac\\nability, as would be expected of dynamic natural systems\\nthat are influenced by many factors. This variability is evi\u00c2\u00ac\\ndent in the plots of TSS, BOD, TKN and TP data in this\\nsection. Data scatter is not reduced by comparing pollut\u00c2\u00ac\\nant removal with a variety of factors (e.g. area, volume,\\nHRT, percent removals or loading rate), or by normalizing\\nthe data (C e /C 0 Expected trends, such as temperature\\ndependence for BOD removal or better removal with lower", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0109.jp2"}, "110": {"fulltext": "D)\\nE\\nc\\no\\nfc\\nk-\\nc\\na\\no\\nc\\no\\no\\nE\\n3\\nFigure 5-3. Lithium Chloride Tracer Studies in a VSB System (George et al., 2000)\\npollutant loading, are often not apparent due to the scatter\\nof the data. Therefore, the design approach recommended\\nhere is to use the maximum pollutant loading rates that\\nhave been shown to meet discharge standards. This ap\u00c2\u00ac\\nproach yields a much more conservative design than other\\ncommon design approaches. As additional quality data be\u00c2\u00ac\\ncomes available in the future, it may be possible to extend\\nthese conservative loading rates with confidence.\\nTwo types of pollutant loading rates were considered,\\nan areal loading rate (ALR), g/m 2 -d, and a volumetric load\u00c2\u00ac\\ning rate (VLR), g/m 3 -d. Both ALRs and VLRs have been\\nused by researchers to describe VSB performance. ALR\\nis calculated by multiplying the influent flow rate (m 3 /d) by\\nthe influent pollutant concentration (mg/L g/m 3 and di\u00c2\u00ac\\nviding by the surface area of the VSB system (m 2 Be\u00c2\u00ac\\ncause sedimentation, plant growth and oxygen transfer are\\ntheoretically dependent on the surface area, ALR may be\\na characteristic parameter for some pollutants. VLR is cal\u00c2\u00ac\\nculated by multiplying the influent flow rate (m 3 /d) by the\\ninfluent pollutant concentration (mg/L g/m 3 and divid\u00c2\u00ac\\ning by the pore volume of the VSB system (m 3 Because\\nthe removal of certain pollutants could be dependent on\\nthe HRT, the VLR could be a characteristic parameter for\\nsome pollutants. However, because the actual saturated\\npore volume is seldom known and the HRT may not be\\ndirectly related to the pore volume due to preferential flow,\\nthe utility of VLR for design purposes is limited. Also, a\\ncomparison of Figures 5-4 through 5-7, which are typical\\nof scatter for all pollutants, shows that data scatter is not\\nreduced by the use of VLR. Therefore, the design recom\u00c2\u00ac\\nmendations in this chapter are based on ALRs.\\nFinally, because the type of pre-treatment has a major\\nimpact on the characteristics of the wastewater being\\ntreated, the following discussions are organized by the type\\nof wastewater being treated: septic tank and primary efflu\u00c2\u00ac\\nents, pond effluents, and secondary treatment effluents.\\n5.4.2 TSS and BOD Removal for Septic\\nTank and Primary Effluents\\nTwo recent studies, one conducted by Tennessee Tech\u00c2\u00ac\\nnological University (TTU) and one conducted by Clarkson\\nUniversity (CU) at the Village of Minoa, New York, have\\nprovided the majority of data used to establish the design\\nrecommendations for this section (George et al., 2000,\\nYoung et al., 2000). These two studies were chosen be\u00c2\u00ac\\ncause their research objectives were to provide design in\u00c2\u00ac\\nformation, they utilized several VSBs with different mea\u00c2\u00ac\\nsured loadings, and the data are of good quantity and qual\u00c2\u00ac\\nity. Influents in the TTU and CU studies were respectively\\na low strength septic tank effluent and a fairly typical pri\u00c2\u00ac\\nmary effluent. Each data point in the following figures rep\u00c2\u00ac\\nresents a quarterly average of biweekly (every 2 weeks)\\nsampling for the TTU data, and a quarterly average of at\\nleast two monthly samples for the CU data. The results\\nfrom one other VSB system treating septic tank effluent\\nstudied by University of Nebraska Lincoln (UNL) research\u00c2\u00ac\\ners are also included in these figures (Vanier Dahab,\\n1997). After reviewing the literature, no other studies with\\n94", "height": "4267", "width": "3142", "jp2-path": "constructedwetla00nati_0110.jp2"}, "111": {"fulltext": "50\\n40\\no) 30\\nE\\nTTU1\\nA TTU2\\nTTU3\\nUNL\\nCU\\nNADB\\nTSS Areal Loading Rate (g/m2-d)\\nFigure 5-4. Effluent TSS vs areal loading rate\\n50\\n40\\n30\\nO)\\nE\\nCO\\nco\\n20\\n3=\\n111\\n10\\n0\\n7^2\\nn\\nr*\\no\\n\u00e2\u0080\u0094i\u00e2\u0080\u0094\\n100\\nTTU1\\nA TTU2\\nTTU3\\nUNL\\nCU\\n\u00e2\u0080\u0094i-1-1\\n200 300 400\\nTSS Volumetric Loading Rate (g/m3-d)\\n500\\n600\\nFigure 5-5. Effluent TSS vs volumetric loading rate\\n95", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0111.jp2"}, "112": {"fulltext": "c\\nd)\\nJ3\\n3\\nLU\\n70\\n60\\n50\\ng 40\\nQ\\no\\nCD\\nTTU1\\nA\\nTTU2\\nTTU3\\nUNL\\nCU\\nNADB\\nBOD Areal Loading Rate (g/m2-d)\\nFigure 5-6. Effluent BOD vs areal loading rate\\nO\\nO\\nm\\nc\\n1\\nI3\\nLU\\nBOD Volumetric Loading Rate (g/m3-d)\\nFigure 5-7. Effluent BOD vs volumetric loading rate\\n96", "height": "4267", "width": "3142", "jp2-path": "constructedwetla00nati_0112.jp2"}, "113": {"fulltext": "septic tank or primary wastewater were found to have data\\nwith similar quality and quantity as these three studies.\\nData from the NADB for VSBs treating primary effluent,\\nsome of which are of unknown quality, are also shown in\\nFigures 5-4 and 5-6.\\nTSS removal is quite good; effluent TSS was consis\u00c2\u00ac\\ntently less than 30 mg/L at TSS ALRs as high as 20 g/m 2\\nd (Figure 5-4). The two data points in Figure 5-4 that are\\nabove 30 mg/L are from systems at TTU that were inten\u00c2\u00ac\\ntionally overloaded to failure, and are not typical. Other\\nresearchers have reported plugging of the surface of the\\nmedia (as opposed to clogging of the pore volume) when\\nexcessively high TSS loadings were applied (Tanner\\nSukias, 1995, Tanner et al., 1998, van Oostrom Cooper,\\n1990). Additional data may extend these limited ALRs when\\nit becomes available. However, it should be noted that the\\ntypical sustained influent TSS concentrations for the data\\nplotted in these figures were less than 100 mg/L. It is rec\u00c2\u00ac\\nommended that TSS ALR be limited to 20 g/m 2 -d, based\\non the maximum monthly influent TSS. This would corre\u00c2\u00ac\\nspond to a loading of 2 cm/d for an influent concentration\\nof 100 mg/L of TSS, 4 cm/d for an influent concentration of\\n50 mg/L of TSS, and so on.\\nBOD removal is not as good as TSS removal, so the size\\nof a VSB designed to meet secondary treatment standards\\nwill generally be controlled by the requirements for BOD re\u00c2\u00ac\\nmoval. Effluent BOD values were found to periodically ex\u00c2\u00ac\\nceed 30 mg/L at BOD ALRs greater than 6 g/m 2 -d (Figure 5-6).\\nIt is recommended that BOD ALR be limited to 6 g/m 2 -d,\\nbased on the maximum monthly influent BOD, to produce\\na maximum effluent BOD of 30 mg/L. Table 5-2 compares\\nthe size of a VSB designed with this ALR compared to the\\nsize of VSBs designed using several common approaches.\\nAs expected the other design approaches result in VSB\\nsystems significantly smaller than that using the conser\u00c2\u00ac\\nvative design approach presented here.\\n5.4.3 Nutrient Removal for Septic Tank\\nand Primary Effluents\\nMost of the organic nitrogen in septic tank and primary\\neffluents is associated with suspended solids that are easily\\nremoved in VSB systems. It is generally assumed that the\\norganic nitrogen will be converted to ammonia in VSB sys\u00c2\u00ac\\ntems, but spiked concentrations of urea (a soluble form of\\norganic nitrogen) were often not completely converted in\\none study (George et al., 2000). Ammonia removal in VSB\\nsystems is severely oxygen limited, and it is inversely re\u00c2\u00ac\\nlated to the ultimate (carbonaceous and nitrogenous) BOD\\nloading. Also, the conversion of organic nitrogen into am\u00c2\u00ac\\nmonia via ammonification or hydrolysis masks any attempt\\nto relate ammonia removal to other design factors. For this\\nreason Total Kjeldahl Nitrogen (TKN) data rather than\\nammonia data are presented in Figure 5-8. The TKN re\u00c2\u00ac\\nmoval performance is generally poor and highly variable.\\nTherefore, VSB systems should not be used alone to treat\\npre-settled municipal wastewaters if significant amounts\\nof ammonia must be consistently removed.\\nAlthough the data are not presented here, if any nitrate\\nis produced in VSB systems treating septic tank and pri\u00c2\u00ac\\nmary effluents, it is likely that the nitrate will be removed\\nby denitrification.\\nTable 5-2. Comparison of VSB Area Required for BOD Removal Using Common Design Approaches.\\nDesign criteria\\nFlow (Q) 400 m 3 /d (105,680 gpd)\\nInfluent BOD 5 (Ci) 125 mg/L\\nEffluent BOD 5 (Ce) 30 mg/L\\nDesign\\nApproach\\nRate\\nConstant\\nLoading\\nConstant\\nOther Factors\\nRequired\\nArea\\nm 2 (ac)\\nThis Manual\\n6 g/m 2 -d\\n(54 Ib/ac-d)\\n8,330 (2.0)\\nEuropean\\n(Cooper, 1990)\\nK BO o 0Vd\\n5710(1.4)\\nKadlec\\nKnight\\n(1996)\\n180 m/yr\\n(590 ft/yr)\\nBackground Concentration 2 10 mg/L\\n1420 (0.4)\\nReed, etal.\\n(1995)\\nTemperature\\nDependent 2\\nK10 0.62/d\\nK20 1.104/d\\nWater Depth 1 0.4 m (16\\nMedia Porosity\u00e2\u0080\u0099 0.38\\nat 10\u00c2\u00b0C, 6090 (1.5)\\nat 20\u00c2\u00b0C, 3400 (0.8)\\nTVA (1993)\\n5.3 g/m 2 -d\\n(48 Ib/ac-d)\\nDerived from TVA design\\nAssumes septic tank effluent\\n9430 (2.3)\\n\u00e2\u0080\u0099Values chosen by user; these are not necessarily the values recommended by the design\u00e2\u0080\u0099s author.\\n2 Values calculated per instructions of design\u00e2\u0080\u0099s author.\\n97", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0113.jp2"}, "114": {"fulltext": "50\\n40\\nt A\\nA\\nA\\nL\\nO)\\nE\\nc\\nd)\\nLU\\n30\\n20\\n10\\n4 t\\n1U\u00c2\u00bb 4\\n0\\n2\\nT-\\n4\\n\u00e2\u0080\u0094i\u00e2\u0080\u0094\\n10\\nTTU1\\nA TTU2\\nTTU3\\nT UNL\\nCU\\n\u00e2\u0080\u0094t\u00e2\u0080\u0094\\n12\\n0\\n6 8\\nTKN Areal Loading Rate (g/m2-d)\\n14\\nFigure 5-8. Effluent TKN vs areal loading rate\\nAlthough phosphorus is partially removed in VSB sys\u00c2\u00ac\\ntems treating septic tank and primary effluents, VSBs are\\nnot very effective for long-term phosphorus removal (Fig\u00c2\u00ac\\nure 5-9). It should be noted that the phosphorus data shown\\nin Figure 5-9 are from VSB systems that are relatively new,\\nwhen it can be assumed that the phosphorus precipitation\\nand adsorption capacity of the media would be at its great\u00c2\u00ac\\nest. Because plant uptake of phosphorus is quite small\\ncompared to typical loadings (Reed, et al, 1995; Crites\\nTchobanoglous, 1998), the phosphorus removal capacity\\nwill decrease with time. Estimates of realistic long-term\\nphosphorus removal by plant harvesting is limited to about\\n0.055 g/m 2 -d (0.5 Ib/ac-d) (Crites Tchobanoglous, 1998).\\nVSB systems should not be expected to remove phospho\u00c2\u00ac\\nrus on a long-term basis.\\n5.4.4 TSS, BOD and Nutrient Removal for\\nPond Effluents\\nThere is much less quality data comparable to the TTU\\nand CU studies for VSB systems treating pond effluents.\\nData from a study conducted at three experimental VSB\\nsystems at Las Animas, Colorado by Colorado State Uni\u00c2\u00ac\\nversity (Richard Synder, 1994) were used to support\\ndesign recommendations for VSB systems treating pond\\neffluents (Table 5-3). The pollutant removal performance\\nfor the Las Animas VSBs treating oxidized pond effluent\\nwas not as good as the performance of the TTU and CU\\nsystems. NABD data for VSBs treating pond effluent (Fig\u00c2\u00ac\\nure 5-10), which are not as reliable as the Las Animas\\ndata, show similar performance. Several of the NABD sys\u00c2\u00ac\\ntems have experienced surfacing caused by clogging of\\nthe media surface (as opposed to clogging of the pore vol\u00c2\u00ac\\nume) by algae.\\nFor Las Animas, the average TSS ALR was 6.2 g/m 2 -d\\n(55 Ib/ac-d) and produced an overall average effluent TSS\\nof 35 mg/L. The average BOD ALR was 2.0 g/m 2 -d (18 lb/\\nac-d) and produced an overall average effluent BOD of 25\\nmg/L. There was essentially no nitrogen or phosphorus\\nremoval on average in the three VSBs. The poor overall\\npercent removal of BOD of 35% might be related to the\\nrelatively high concentrations of algal cells in the influent\\nduring several months of each year. The measured BOD\\nof pond effluent typically does not account for the true BOD\\nof algal cells because algal cells degrade more slowly than\\nother organic matter.\\nA VSB system in Mesquite, Nevada has been used since\\n1992 in parallel with overland flow and oxidation ditch sys\u00c2\u00ac\\ntems to treat an aerated pond effluent. One year of monthly\\ndata for the Mesquite system is summarized in Chapter 8.\\nOver the one-year sampling period the effluent BOD aver\u00c2\u00ac\\naged 29 mg/L when loaded at an average BOD ALR of 2.5\\ng/m 2 -d (22 Ib/ac-d). Better BOD and TSS removals than at\\nLas Animas and Mesquite are reported in a 1993 EPA re\u00c2\u00ac\\nport for several VSB systems treating pond algal effluents.\\nHowever, the sparse amount of data of unproven quality\\nrepresented by the average values given in the report is\\n98", "height": "4267", "width": "3142", "jp2-path": "constructedwetla00nati_0114.jp2"}, "115": {"fulltext": "3.5\\nc\\na\\n3\\nLU\\n3\\n2.5\\n2\\n1.5\\n1\\n0.5\\n0\\n4\\nA\\n_\u00e2\u0080\u00a2. 1\\nTTU1\\nTTU2\\nTTU3\\nCU\\ni\\nl-1-1-1-r\\n0 0.2 0.4 0.6 0.8 1 1.2\\nTP Areal Loading Rate (g/m2-d)\\nFigure 5-9. Effluent TP vs areal loading rate\\ninadequate to use with confidence. Sapkota and Bavor\\n(1994) report similar TSS removal, but do not report BOD\\nremoval.\\nThe upgrading of pond effluent with rock filters is similar\\nto the use of VSBs after ponds. However, because of vari\u00c2\u00ac\\nable results from rock filters, their use is generally cau\u00c2\u00ac\\ntioned due to a lack of reliable design information (Reed,\\net al, 1995). Performance of rock filters is also plagued by\\nH S generation and high effluent ammonia. Illinois requires\\neffluent aeration and recommends disinfection before dis\u00c2\u00ac\\ncharge for pond rock filter systems. Because of the limited\\ndata and uncertainty about similar rock filter systems, VSB\\nsystems are not recommended for treating pond effluents\\nif the system must consistently meet a 30/30 standard.\\n5.4.5 BOD, TSS and Nutrient Removal for\\nSecondary and Non-algal Pond\\nEffluents\\nThere are very few quality-assured data available from\\nVSB systems in the U.S. treating secondary effluents. The\\n1993 U.S. EPA report included data collected over a three\\nmonth period from three systems. Additional data from one\\nof these systems, Mandeville, LA, is included in Chapter\\n8. The Mandeville VSB treats an aerated lagoon effluent\\nwhich has little or no algae. The average influent BOD and\\nTSS were 40 and 16 mg/L, respectively. The average ef\u00c2\u00ac\\nfluent BOD and TSS were 5 and 3 mg/L, respectively at a\\nBOD ALR of 7.9 g/m2-d (70 Ib/ac-d).\\nRepresentatives from Severn Trent Water, Ltd., have\\nreported on the performance of VSB reed bed systems\\ntreating activated sludge and RBC effluents in small treat\u00c2\u00ac\\nment plants (less than 2000 people) in the U.K. (Green\\nand Upton, 1994). The goal for these VSB systems is to\\nprovide additional treatment of secondary effluents so that\\nthey consistently meet discharge limitations, which can vary\\nfrom 30/20 to 15/10 TSS/BOD. Essentially these systems\\nserve as aesthetic and sometimes economical substitutes\\nfor tertiary filters for small treatment plants. In some cases\\nin the U.K. they have been used to treat storm water by\u00c2\u00ac\\npass flows at secondary treatment plants. While the Severn\\nTrent systems typically remove some nitrogen and phos\u00c2\u00ac\\nphorus, they are not capable of meeting typical discharge\\nstandards for nutrients in the U.S. The primary design ba\u00c2\u00ac\\nsis used by Severn Trent is a hydraulic surface loading\\nrate of 0.20 m 3 /m 2 -d (5 gpd/sq ft) for the average daily flow\\n(Green and Upton, 1994). This value is derived from the\\ndesign recommendation of the European task group on\\nVSB systems (Cooper, 1990). For systems with an aver\u00c2\u00ac\\nage influent BOD 40 mg/L, this results in average areal\\nBOD loading of less than 8.0 g/m 2 -d (71 Ib/ac-d). Typical\\nsystems are 0.6 m (24 in) deep, 0.4 m wide per m 3 /d (5 ft\\nper 1000 gpd) of flow, and 12.5 m (41 ft) long.\\nBased on the success of the Mandeville and Severn Trent\\nsystems, it appears that VSB systems can be effectively\\nused to help small secondary systems consistently meet\\nsecondary effluent standards. The recommended approach\\n99", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0115.jp2"}, "116": {"fulltext": "Table 5-3. Data from Las Animas, CO VSB Treating Pond Effluent.\\nTime\\nPeriod 1\\nInf. TSS\\nmg/L\\nEff. TSS\\nmg/L\\nInf. BOD\\nmg/L\\nEff. BOD\\nmg/L\\nInf. TKN\\nmg/L\\nEff. TKN\\nmg/L\\nInf. TP\\nmg/L\\nEff. TP\\nmg/L\\nCell 1\\nWinter 91\\n89.7\\n43.0\\n26.7\\n37.5\\nND\\nND\\n1.57\\n1.9\\nSrping 92\\n146.0\\n28.7\\n34.0\\n22.7\\n7.2\\n11.4\\n1\\n1.67\\nSummer 92\\n178.0\\n41.7\\n49.7\\n29.0\\n6.1\\n8.7\\n1.17\\n1.68\\nFall 92\\n223.0\\n34.3\\n54.0\\n30.0\\n7.3\\n10.7\\n1.47\\n1.9\\nWinter 92\\n50.0\\n34.3\\n33.7\\n32.7\\n14.1\\n14.0\\n2.25\\n2.3\\nSpring 93\\n66.0\\n24.0\\n41.0\\n32.0\\n16.1\\n16.3\\n2.55\\n2.6\\nSummer 93\\n95.3\\n33.3\\n30.0\\n9.3\\n3.9\\n5.3\\n0.67\\n0.78\\nFall 93\\n127.0\\n38.0\\n40.3\\n16.0\\n4.0\\n3.4\\n0.65\\n0.6\\nAverage\\n121.9\\n34.7\\n38.7\\n26.2\\n8.4\\n10.0\\n1.42\\n1.68\\nCell 2\\nWinter 91\\n89.7\\n51.0\\n26.7\\n37.0\\nND\\nND\\n1.57\\n2.57\\nSrping 92\\n146.0\\n34.0\\n34.0\\n35.0\\n7.2\\n14.1\\n1\\n2.37\\nSummer 92\\n178.0\\n43.3\\n49.7\\n29.3\\n6.1\\n9.0\\n1.17\\n1.72\\nFall 92\\n223.0\\n26.0\\n54.0\\n40.0\\n7.3\\n8.8\\n1.47\\n1.78\\nWinter 92\\n50.0\\n33.0\\n33.7\\n29.7\\n14.1\\n14.2\\n2.25\\n2.28\\nSpring 93\\n66.0\\n26.7\\n41.0\\n35.3\\n16.1\\n15.2\\n2.55\\n2.68\\nSummer 93\\n95.3\\n27.0\\n30.0\\n15.0\\n3.9\\n5.5\\n0.67\\n0.82\\nFall 93\\n127.0\\n33.3\\n40.3\\n21.3\\n4.0\\n4.8\\n0.65\\n0.65\\nAverage\\n121.9\\n34.3\\n38.7\\n30.3\\n8.4\\n10.2\\n1.42\\n1.86\\nCell 3\\nWinter 91\\n89.7\\n46.0\\n26.7\\n11.3\\nND\\nND\\n1.57\\n1.47\\nSrping 92\\n146.0\\n47.0\\n34.0\\n22.0\\n7.2\\n5.4\\n1\\n1.43\\nSummer 92\\n178.0\\n33.3\\n49.7\\n20.3\\n6.1\\n9.6\\n1.17\\n1.62\\nFall 92\\n223.0\\n41.3\\n54.0\\n27.0\\n7.3\\n8.1\\n1.47\\n1.72\\nWinter 92\\n50.0\\n34.3\\n33.7\\n25.7\\n14.1\\n13.0\\n2.25\\n2.2\\nSpring 93\\n66.0\\n23.7\\n41.0\\n29.7\\n16.1\\n13.9\\n2.55\\n2.53\\nSummer 93\\n95.3\\n29.3\\n30.0\\n8.3\\n3.9\\n4.7\\n0.67\\n0.82\\nFall 93\\n127.0\\n34.3\\n40.3\\n8.0\\n4.0\\n5.6\\n0.65\\n0.55\\nAverage\\n121.9\\n36.2\\n38.7\\n19.0\\n8.4\\n8.6\\n1.42\\n1.54\\nEach of the values in the table is the average of three monthly samples.\\nBOD or TSS Areal Loading Rate (g/m2-d)\\nNADB Systems Treating Pond Effluent\\nFigure 5-10. NADB VSBs Treating Pond Effluent\\n100", "height": "4267", "width": "3142", "jp2-path": "constructedwetla00nati_0116.jp2"}, "117": {"fulltext": "is to limit the BOD ALR to a maximum monthly value of 8\\ng/m2-d (71 Ib/ac-d). However, VSB systems are not rec\u00c2\u00ac\\nommended as a remedy for inadequately operated acti\u00c2\u00ac\\nvated sludge systems. Process upsets in poorly operated\\nactivated sludge systems can quickly fill a VSB system\\nwith mixed liquor solids, resulting in surface flow due to\\nclogging of the media.\\n5. 4.6 Metals Removal for AII Types of\\nWastewater\\nMetals are removed in a VSB by two primary mecha\u00c2\u00ac\\nnisms. First, because many metals (e.g. Zn, Cr, Pb, Cd,\\nFe, Al) are associated with particles (Heukelekian Balmat,\\n1959; SWEP, 1985), the high efficiency of particulate sepa\u00c2\u00ac\\nration in a VSB should remove these metals accordingly.\\nSecond, sulfide precipitation occurs due to the reduction\\nof sulfates to sulfides in the absence of nitrate, and ren\u00c2\u00ac\\nders some metals insoluble, resulting in significant remov\u00c2\u00ac\\nals, as described in Reed, etal (1995) for Cu, Cd, and Zn.\\nAs long as the system ORP remains low, which is likely\\ngiven the anaerobic nature of VSBs, it is unlikely that met\u00c2\u00ac\\nals precipitated in the sulfide form will re-enter the water\\ncolumn (Bounds, et al, 1998; Reed, et al, 1995). Some\\nmetals such as Ni and Cd are more mobile and less likely\\nto be removed, but they are not normally present in toxic\\nquantities in municipal wastewater.\\nThere is relatively little data on metals removal by VSB\\nsystems and no known information from long-term stud\u00c2\u00ac\\nies. Gersberg et al. (1984) found significant removal of Cu,\\nZn and Cd, and determined that plant uptake was respon\u00c2\u00ac\\nsible for only 1 of the Cu and Zn removal. In a study with\\na VSB system treating a landfill leachate, researchers found\\nonly a small increase in the Pb, Cd, and Cu levels on root\\nsurfaces, and no increase in any of the metals measured\\nin any plant tissue compared to plants from a control sys\u00c2\u00ac\\ntem (Peverly et al., 1995). They concluded that the in\u00c2\u00ac\\ncreased metal concentrations on the root surface was due\\nto metal precipitation and adsorption. Metal removal by\\nplant uptake should not be counted on in any VSB system\\nover the long term.\\n5.4.7 Pathogen Remo val for AII Types of\\nWastewater\\nWhile pathogens will be partially removed in a VSB sys\u00c2\u00ac\\ntem, a disinfection step after the VSB will normally be re\u00c2\u00ac\\nquired to meet discharge limits. Researchers in Nebraska\\nfound a three log reduction in fecal coliforms from 10 6 to\\n10 3 /100mL in a VSB system treating a septic tank effluent\\n(Vanier and Dahab, 1997). Gersberg et al. (1989) found a\\ntwo log reduction in total coliforms in a VSB system treat\u00c2\u00ac\\ning primary effluent. The coliform removal in two VSB sys\u00c2\u00ac\\ntems in England treating secondary effluents varied be\u00c2\u00ac\\ntween 40% and 99%, but effluent values did not meet dis\u00c2\u00ac\\ncharge requirements (Griffin et al., 1998). Fecal coliform\\nreductions were typically two logs (1 x 10 6 to 1 x 10 4 /1 OOmL)\\nin several experimental VSB systems in Tennessee, ex\u00c2\u00ac\\ncept for two cells operated in a fill and drain mode. These\\nfill and drain cells achieved a three log reduction with the\\nsame influent wastewater (George et al., 2000). For de\u00c2\u00ac\\nsign purposes a two log reduction is a reasonable esti\u00c2\u00ac\\nmate of VSB performance.\\n5.5 Design Considerations\\n5.5 .1 Media Size and Hardness\\nThe media of a VSB system perform several functions;\\nthey (1) are rooting material for vegetation, (2) help to\\nevenly distribute/collect flow at the inlet/outlet, (3) provide\\nsurface area for microbial growth, and (4) filter and trap\\nparticles. For successful plant establishment, the upper\u00c2\u00ac\\nmost layer of media should be conducive to root growth. A\\nvariety of media sizes and materials have been tried, but\\nthere is no clear evidence that points to a single size or\\ntype of media, except that the media should be large\\nenough that it will not settle into the void spaces of the\\nunderlying layer. It is recommended that the planting me\u00c2\u00ac\\ndia not exceed 20 mm (3/4 in) in diameter, and the mini\u00c2\u00ac\\nmum depth should be 100 mm (4 in).\\nThe media in the inlet and outlet zones (see Figure 5-\\n11) should be between 40 and 80 mm (1.5-3 in) in diam\u00c2\u00ac\\neter to minimize clogging and should extend from the top\\nto the bottom of the system. The inlet zone should be about\\n2 m long and the outlet zone should be about 1 m long.\\nThese zones with larger media will help to even distribute\\nor collect the flow without clogging. The use of gabions\\n(wire rock baskets used for bank stabilization) to contain\\nthe larger media simplifies construction. Gabions may also\\nmake it easier to remove and clean the inlet zone media if\\nit becomes clogged.\\nAny portion of the media that is wetted is a surface on\\nwhich microbes grow and solids settle and/or accumulate.\\nMedia in VSBs have ranged from soil to 100 mm (4 in.)\\nrock. Experience with soil and sand media shows that it is\\nvery susceptible to clogging and surfacing of flows, even if\\ninfluent TSS concentrations are minimal, so soil or sand\\nmedia should be avoided. Gravel and rock media have\\nbeen used successfully, with smaller diameter media be\u00c2\u00ac\\ning more susceptible to clogging, and larger media more\\ndifficult to handle during construction or maintenance.\\nCrushed limestone can be used, but is not recommended\\nfor VSB systems because of the potential for media breakup\\nand dissolution under the strongly reducing environment\\nof a VSB, which can lead to clogging. Media with high iron\\nor aluminum will have more sites for phosphorus binding\\nand should enhance phosphorus removal, but only during\\nthe first few months of operation. The limited removal ca\u00c2\u00ac\\npability is probably not worth an added expense if it is not\\navailable locally at a reasonable cost. Alternative media\\nsuch as shredded tires, plastic trickling filter media, ex\u00c2\u00ac\\npanded clay aggregates and shale with potentially high\\nphosphorus absorptive capacity have been used, but there\\nis inadequate data to make a recommendation for or\\nagainst their use.\\nThere does not appear to be a clear advantage in pollut\u00c2\u00ac\\nant removal with different sized media in the 10 to 60 mm\\n(3/8 2 in.) range. Therefore, it is recommended that the\\n101", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0117.jp2"}, "118": {"fulltext": "Media Surface\\nk\\nE\\nCD\\nO\\nf\\nInlet\\nZone\\nTreatment Zone\\nOutlet\\nZone\\nZone 1\\nZone 2\\n2 m\\n30% of Length\\n70% of Length\\n1 m\\nOutlet\\nSide View\\nFigure 5-11. Proposed Zones in a VSB\\naverage diameter of the treatment zone media be between\\n20 and 30 mm (3/4 1 in.) in diameter as a compromise\\nbetween the potential for clogging and ease of handling.\\nTo minimize settling of the media smooth, rounded media\\nwith a Mohs hardness of 3 or higher is recommended if it\\nis available locally at a reasonable cost. Based on the data\\nin Table 5-1, the hydraulic conductivity of the 20 30 mm\\ndiameter clean media is assumed to be 100,000 m/d.\\n5.5.2 Slopes\\nThe top surface of the media should be level or nearly\\nlevel for easier planting and routine maintenance. Theo\u00c2\u00ac\\nretically, the bottom slope should match the slope of the\\nwater level to maintain a uniform water depth throughout\\nthe VSB. However, because the hydraulic conductivity of\\nthe media varies with time and location, it is not practical\\nto determine the bottom slope this way, and the bottom\\nslope should be designed only for draining the system,\\nand not to supplement the hydraulic conductivity of the\\nVSB. A practical approach is to uniformly slope the bottom\\nalong the direction of flow from inlet to outlet to allow for\\neasy draining when maintenance in required. No research\\nhas been done to determine an optimum slope, but a slope\\nof 1/2 to 1% is recommended for ease of construction and\\nproper draining (Chalk Wheale, 1989). Care should be\\ntaking when grading the bottom slope to eliminate low\\nspots, channels and side-to-side sloping which will pro\u00c2\u00ac\\nmote dead volume or short-circuiting.\\nThe slope of the berms containing a VSB should be as\\nsteep as possible, consistent with the soils, construction\\nmethods and materials. Shallow side slopes create larger\\nareas which capture and route precipitation into the VSB,\\nwhich may be detrimental to system performance. Also,\\nthe site should be graded to keep off-site runoff out of the\\nVSB.\\n5.5.3 Inlet and Outlet Piping\\nThe inlet piping must be designed to minimize the po\u00c2\u00ac\\ntential for short-circuiting and clogging in the media, and\\nmaximize even flow distribution. For VSBs with length-width\\nratios less than one, additional care must be taken to spread\\nthe influent across the whole width of the VSB. Standard\\nhydraulic design principles and structures (e.g. adjustable\\nweirs and orifices) are used to split, balance evenly dis\u00c2\u00ac\\ntribute flows (WEF, 1998). The recommended method to\\nevenly distribute flows is to use reducing tees or 90 de\u00c2\u00ac\\ngree elbows which can be rotated on the header (see Chap\u00c2\u00ac\\nter 6). The main advantage of a rotating fitting is that it\\nallows the operator to easily adjust the distribution of the\\ninfluent, which may help in reducing media clogging. When\\nthe potential for public access exists, a cover over the in\u00c2\u00ac\\nfluent distribution system must be used. Possible covers\\ninclude half sections of pipe or cavity chambers, as used\\nin leach fields. If piping with orifices is used to distribute\\nflows instead of a pipe with rotating fittings, it is necessary\\nto minimize the headloss in the distribution piping so that\\nthe headloss through the orifices controls the flow. This\\nrequirement limits the number and size of orifices used,\\nand makes the distribution piping large enough so that the\\nvelocity in it is low. The orifices should be evenly spaced\\nat a distance approximately equal to 10% of the cell width.\\nFor example, a system 20 m (65 ft) wide should have ori\u00c2\u00ac\\nfices placed every 2 m (6.5 ft). If poor design causes waste-\\nwater to always discharge through only some of the ori\u00c2\u00ac\\nfices, clogging of the media or accumulation of a surface\\n102", "height": "4267", "width": "3142", "jp2-path": "constructedwetla00nati_0118.jp2"}, "119": {"fulltext": "layer of solids near those orifices can become a problem,\\nespecially for an influent with relatively high suspended\\nsolids, such as pond effluent. Finally, the inlet piping should\\nbe designed to allow for inspection and clean-out by the\\noperator.\\nThe outlet piping must be designed to minimize the po\u00c2\u00ac\\ntential for short-circuiting, to maximize even flow collec\u00c2\u00ac\\ntion, and to allow the operator to vary the operating water\\nlevel and drain the bed. For VSBs with length-width ratios\\nless than one, additional care must be taken to collect the\\ninfluent from the whole width of the VSB. A collection header\\nwith orifices that is placed across the entire width of the\\nbottom of the VSB is recommended to promote even flow.\\nThe collection header should be designed with the same\\nhydraulic principles used for inlet distribution piping. Slot\u00c2\u00ac\\nted or perforated drainage pipe can be used if the collec\u00c2\u00ac\\ntion header is not too long, but properly sized and spaced\\norifices in a large diameter collection header allow a de\u00c2\u00ac\\nsigner to use a longer collection header and still achieve\\nbalanced flow collection. The recommended maximum dis\u00c2\u00ac\\ntance between orifices in the collection header is 10% of\\nthe cell width. The relative potential for clogging with slot\u00c2\u00ac\\nted or perforated drainage pipe versus a longer collection\\nheader with fewer orifices is unknown. Finally, the outlet\\npiping should be designed to allow for clean-out by the\\noperator.\\nA simple device to adjust the water level in a separate,\\ncovered, outlet box is recommended to achieve variable\\nwater level control (see Chapter 6). It is recommended that\\nthere be only one collection header and adjustable-level\\ndevice per cell of a multiple cell VSB system. The adjust\u00c2\u00ac\\nable device should allow the operator to flood the VSB to a\\ndepth of 50 mm (2 in.) above the surface of the media (for\\nhelp in weed control), and to draw-down or drain the cell\\nfor maintenance.\\n5.5.4 System Depth, Width and Length\\nThe impact of water depth on pollutant removal is not\\nclear. One problem with almost all published information\\non VSB systems is that even though the media depth may\\nbe known, the actual operating water level is not known.\\nThe TTU study found slightly better BOD removal with\\ngreater media depth, when comparing 45 cm (18 in) with\\n30 cm (12 in) systems operated at same areal loading, but\\nit is unclear if this was due only to the increased HRT. No\\nother study has tested this result or determined the opti\u00c2\u00ac\\nmum depth for a VSB system (George et al., 2000). One\\nstudy suggested that total root penetration of the media\\nwas critical to pollutant removal and recommended that\\nsystem depth be set equal to the maximum root depth of\\nthe wetland species to be used in the VSB (Gersberg et al.\\n1983). However, as discussed previously, plants supplied\\nwith abundant nutrients near the surface will not neces\u00c2\u00ac\\nsarily grow roots to their maximum depth. As a safety fac\u00c2\u00ac\\ntor Kadlec and Knight (1996) recommend allowing room\\nfor solids accumulation in the bottom of the VSB, but the\\nneed for this has not been proven. Typical average media\\ndepths in VSB systems have ranged from 0.3 to 0.7 m (12\\nto 28 in.), and various researchers have recommended\\ndepths from 0.4 to 0.6 m (16 to 24 in.).\\nAs discussed previously there is evidence for preferen\u00c2\u00ac\\ntial flow below the root zone through media with a higher\\nconductivity. In order to minimize this flow, a shallower\\ndepth would be required. On the other hand, a shallower\\ndepth may require a greater area to achieve a desired HRT.\\nUntil future studies provide better information on optimum\\nwater depth, it is recommended to use a design maximum\\nwater depth (at the inlet of the VSB) of 0.40 m (16 in.). The\\ndepth of the media will be defined by the level of the waste-\\nwater at the inlet and should be about 0.1 m (4 in.) deeper\\nthan the water.\\nThe overall width of a treatment system using VSBs is\\ndefined by Darcy\u00e2\u0080\u0099s Law, which is a function of the flow,\\nALR, water depth and hydraulic conductivity. The width of\\na individual VSB is set by the ability of the inlet and outlet\\nstructures to uniformly distribute and collect the flow with\u00c2\u00ac\\nout inducing short-circuiting. The recommended maximum\\nwidth in a TVA design manual is 61 m (200 ft.). If the de\u00c2\u00ac\\nsign produces a larger value, the user should divide the\\nVSB into several cells that do not exceed 61 m in width. As\\ndiscussed previously, several researchers have noted that\\nmost BOD and TSS is removed in the first few meters of a\\nVSB, but some recommend minimum lengths ranging from\\n12 to 30 m (40 to 100 ft) to prevent short-circuiting. The\\nrecommended minimum length for this manual is 15 m (50\\nft).\\nAlthough much has been made of the aspect (length-\\nwidth) ratio in early constructed wetlands literature, the only\\nprerequisite for treatment is the area as defined by the\\nALR. A study by Bounds, et.al. (1998) found that there was\\nno significant difference in TSS or CBOD removal in three\\nparallel VSB systems with aspect ratios of 4:1, 10:1, and\\n30:1. In all three systems the majority of TSS and CBOD\\nwas removed in the first third on the VSB. Removals were\\nalso unaffected by stressing the systems with large hy\u00c2\u00ac\\ndraulic spikes and intermittent loading. The TTU study also\\nfound no significant difference in systems with 1:4 and 4:1\\naspect ratios (George et al., 2000). Therefore, the aspect\\nratio is not a factor in the overall design. However, the rec\u00c2\u00ac\\nommended values for maximum width and minimum length\\ndiscussed previously will tend to result in individual VSB\\ncells with an length-width ratio between 1:1 and 1:2.\\n5.6 Design Example for a VSB Treating\\nSeptic Tank or Primary Effluent\\nThe design has two basic assumptions. First, the total\\nVSB has four zones (see Figure 5-11). The inlet and outlet\\nzones were discussed in section 5.5.1. Based on the lit\u00c2\u00ac\\nerature as discussed previously, the initial treatment zone\\nwill (1) occupy about 30% of the total area, (2) perform\\nmost of the treatment, and (3) have a big decrease in hy\u00c2\u00ac\\ndraulic conductivity (use K 1 of clean K). The final treat\u00c2\u00ac\\nment zone will occupy the remaining 70% of the area and\\nhave little change in hydraulic conductivity (use K 10%\\nof clean K). The second basic assumption is that Darcy\u00e2\u0080\u0099s\\n103", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0119.jp2"}, "120": {"fulltext": "Law, while not exact, it is good enough for design pur\u00c2\u00ac\\nposes. The sizing of the initial and final treatment zones\\nfollows these steps:\\n1) determine the surface area, using recommended\\nALR\\n2) determine the width, using Darcy\u00e2\u0080\u0099s Law\\n3) determine the length and headloss of the initial treat\u00c2\u00ac\\nment zone, using Darcy\u00e2\u0080\u0099s Law\\n4) determine the length and headloss of the final treat\u00c2\u00ac\\nment zone, using Darcy\u00e2\u0080\u0099s Law\\n5) determine bottom elevations, using bottom slope\\n6) determine water elevations throughout the VSB,\\nusing headloss\\n7) determine water depths, accounting for bottom slope\\nand headloss\\n8) determine required media depth\\n9) determine the number of VSB cells\\nFor this example the following values are given:\\nMaximum Monthly Flow (Q) 200 m 3 /d\\nMaximum Monthly Influent (CO) BOD 100 mg/L\\n100 g/m 3\\nMaximum Monthly Influent (CO) TSS 100 mg/L 100\\ng/m 3\\nRequired discharge limits 30 mg/L BOD and TSS\\nRecommended values for VSBs (see Table 5-4) are:\\nALR for BOD 6 g/m 2 -d\\nALR for TSS 20 g/m 2 -d\\nUse washed, rounded media 20-30 mm in diameter,\\nclean K 100,000 m/d\\nHydraulic conductivity of initial treatment zone (K)\\n1 of 100,000 1000 m/d\\nHydraulic conductivity of final treatment zone (K\\n10% of 100,000 10,000 m/d\\nBottom slope (s) _% 0.005\\nDesign water depth at inlet (D w0 0.4 m\\nDesign water depth at beginning of final treatment zone\\n(D J 0.4 m\\nDesign media depth (D m 0.6 m\\nMaximum allowable headloss through initial treatment\\nzone (dti) 10% of D m 0.06 m\\n5.6.1 Determine the Surface Area (As) for\\nBoth Pollutants\\nA=(Q)(C 0 )/ALR\\nFor BOD, A s (200 m 3 /d)(100 g/m 3 6 g/m 2 -d 3333 m 2\\nFor TSS, A s (200 m 3 /d)(100 g/m 3 20 g/m 2 -d 1000 m 2\\nUse the larger area requirement, or 3333 m 2\\nThe surface area for the initial treatment zone (A sj\\n(30%) (3333 m 2 1000 m 2\\nThe surface area for the final treatment zone (A s(\\n(70%) (3333 m 2 2333 m 2\\n5.6.2 Determine the Width\\nDetermine the minimum width (W) needed to keep the\\nflow below the surface, using Darcy\u00e2\u0080\u0099s Law (Eq. 5-1) and\\nrecommended values for the initial treatment zone.\\nQ (K)(W)(D w0 )(dh/L)\\nwhere: L length of initial treatment zone (A sj (W)\\nSubstitute and rearrange equation to solve for W:\\nW 2 (Q)(A si (K)(dh.)(D w0 (5-3)\\nFor this example:\\nW 2 (200 m 3 /d)(1000 m 2 (1000 m/d)(0.06 m)(0.4 m)\\n8333 m 2\\nW =91.3 m\\nThis is the width for which the headloss equals 0.06 m,\\ngiven all the parameters as defined. The designer must\\nuse a width equal to or greater than this to ensure that the\\nheadloss is less than or equal to the design value.\\n5.6.3 Determine the Length and Headloss\\n(Eq. 5-2) of the Initial Treatment\\nZone (L)\\nL (A sj (W) (1000 m 2 (91.3 m) 11.0 m\\nThis is the length for which the headloss equals 0.06 m,\\ngiven all the parameters as defined. The designer must\\nuse a length less than or equal to this to ensure that the\\nheadloss is less than or equal to the recommended value.\\ndh j= (Q)(L) (K)(W)(DJ (200 m 3 /d)(11.0 m) (1000\\nm/d)(91.3 m)(0.4 m) 0.06 m\\n5.6.4 Determine the Length and Headloss\\nof the Final Treatment Zone (L)\\nL, (A,) (W) (2333 m 2 (91.3 m) 25.6 m\\nThis is the length where the total area of the VSB will be\\nexactly equal to the value set by the ALR. The designer\\nmust use a length equal to or greater than this to ensure\\n104", "height": "4267", "width": "3142", "jp2-path": "constructedwetla00nati_0120.jp2"}, "121": {"fulltext": "that the surface area is equal to or greater than the recom\u00c2\u00ac\\nmended value.\\ndh,= (Q)(L f (K f )(W)(D wf (200 m 3 /d)(25.6 m)\\n(10,000 m/d)(91.3 m)(0.4 m) 0.01 m\\n5.6.5 Determine Bottom Elevations\\nE be elevation of bottom at outlet 0 (reference point\\nfor all elevations)\\nE bf elevation of bottom at beginning of final treatment\\nzone (s)(L f (0.005)(25.6 m) 0.13 m\\nE b0 elevation of bottom at inlet (s)(L L\\n(0.005)(11.0 m +25.6 m) 0.18 m\\n5.6.6 Determine the Water Surface\\nElevations\\nE^ elevation of water surface at beginning of final\\ntreatment zone\\nE bf 0.13 m 0.4 m 0.53 m (D^ 0.4 m\\nwas an initial recommended value)\\nE a elevation of water surface at outlet E dh\\nwe wf f\\n0.53 m 0.01 m 0.52 m\\nE elevation of water surface at inlet E dh\\nw0 wf i\\n0.53 m 0.06 m 0.59 m\\n5.6.7 Determine Water Depths\\nD w0 depth of water at inlet E w0 E b0 0.59 m 0.18\\nm 0.41 m (about equal uTdesign D w0 so okay.)\\nD wf depth of water at beginning of final treatment\\nzone\\nE^ E bf 0.53 m 0.13 m 0.40 m (equal to\\ndesign D^, so okay.)\\nD we depth of water at outlet E we E be 0.52 m 0\\nwe 0.52 m\\n5.6.8 Determine the Media Depth\\nThe media depth will depend on whether the designer\\nwants a level media surface, or a minimum depth-to-water\\n(DJ throughout the VSB.\\na) If a level surface is desired, the elevation must be\\ngreater than the highest water elevation, which is at the\\ninlet, E _ 0.59 m. A media elevation set at 0.65 m would\\nbe reasonable, and the following media depths and Dtw\u00e2\u0080\u0099s\\nresult:\\nD m0 depth of media at inlet 0.65 m E b0 0.65 m\\n0.18 m 0.47 m\\nD depth of media at beginning of final treatment\\nzone 0.65 m E bf 0.65 m 0.13 m 0.52 m\\nD me depth of media at outlet 0.65 m 0 0.65 m\\nD tw0 depth-to-water at inlet 0.65 m E w0 0.65 m\\n0.59 m 0.06 m\\nD tw( depth-to-water at beginning of final treatment\\nzone 0.65 m E 0.65 m 0.53 m 0.12 m\\nwf\\nD, a depth-to-water at outlet 0.65 m E,= 0.65 m\\ntwo 1 we\\n0.52 m 0.13 m\\nThe depth-to-water is small at the inlet (0.06 m) and the\\ndesigner may want to add an additional layer of media in\\nthe first few meters of the initial treatment zone as an added\\nprecaution against surfacing, even though the design ALR\\nand K values is very conservative. The resulting D tw in the\\nfinal treatment zone would be 0.12 to 0.13 m, which should\\nnot inhibit the growth of aquatic species.\\nb) If a constant depth-to-water throughout the VSB is\\ndesired (e.g. 0.1 m), then the media depth would be calcu\u00c2\u00ac\\nlated as follows:\\nE m0 elevation of media surface at inlet E w0 0.1 m\\n0.59 m 0.1 m 0.69 m\\nE mf elevation of media surface at beginning of final\\ntreatment zone\\nE 0.1 m 0.53 m 0.1 m 0.63 m\\nw(\\nE elevation of media surface at outlet E +0.1\\nme we\\nm 0.52 m 0.1 m 0.62 m\\nD m0 depth of media at inlet E m0 E b0 0.69 m\\n0.18 m 0.51 m\\nD mf depth of media at beginning of final treatment\\nzone E E 0.63 m 0.13 m 0.56 m\\nmf bf\\nD depth of media at outlet E 0 0.52 m 0\\n0.52 m\\nThis approach would result in a drop in the media sur\u00c2\u00ac\\nface of (0.69 m 0.51 m) of 0.18 m over the 11.0 m length\\nof the initial treatment zone (slope 1.6%), which would\\nprobably not impair operation and maintenance activities.\\n5.6.9 Determine Number of VSB Cells\\nIt is recommended that at least two VSBs be used in\\nparallel in all but the smallest systems, so that one of the\\nVSBs can be taken out of service for maintenance or re\u00c2\u00ac\\npairs without causing serious water quality violations. In\\nthis example, the total size of the VSB system is 91.3 m\\nwide by 36.6 m long. Therefore, use two VSBs, each 46 m\\nwide and 37 m long could be used. Other combinations of\\nlength and width that have the required surface area will\\nalso work as long as the hydraulics conditions are meet.\\nAlso remember that inlet and outlet zones will add to the\\noverall length of the VSB.\\n105", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0121.jp2"}, "122": {"fulltext": "Table 5-4. Summary of VSB Design Guidance.\\nRecommended for use after primary\\nsedimentation (e.g. septic tank, Imhoff\\ntank, primary clarifier) VSBs not\\nrecommended for use after ponds\\nPretreatment because of problems with algae\\nSurface Area\\nBased on desired effluent quality and areal loading rates as follows:\\nBOD\\nBOD\\nTSS\\nTKN\\nTP\\n6 g/m 2 -d (53.5 Ib/ac-d) to attain 30 mg/L\\neffluent\\n1.6 g/m 2 -d (14.3 Ib/ac-d) to attain 20 mg/L\\neffluent\\n20 g/m2-d (178 Ib/ac-d) to attain 30 mg/L\\neffluent\\nUse another treatment process in\\nconjunction with VSB\\nVSBs not recommended for phosphorus\\nremoval\\nDepth\\nMedia (typical) 0.5 0.6 m (20 24 in.)\\nWater (typical) 0.4 0.5 m (16 20 in.)\\ncoming the inadequate purification capacity of certain soils.\\nThey view VSBs as passive systems with low operation\\nand maintenance requirements.\\nA review of various on-site VSB design guidelines by\\nMankin and Powell (1998) revealed that there was a large\\nvariation among the designs. Recommended depth var\u00c2\u00ac\\nied from 0.3 to 0.8 m (1 to 2.5 ft), with the great majority\\nbetween 0.3 and 0.5 m (1 and 1.5 ft). For a three bedroom\\nhouse typical VSB areas varied from 10 m 2 to 100 m 2\\n(104 to 1088 ft 2 HRTs varied from 1.3 to 6.5 d, and length-\\nwidth ratio varied from 71:1 to 1.8:1. Median values were\\na depth of 0.45 m (1.5 ft), area of 30 m 2 (315 ft 2 and HRT\\nof 4.7 d. Gravel size guidelines varied from 0.65 cm (0.25\\nin.) to 7.5 cm (3.0 in.)\\nThese authors sampled three typical VSB systems in\\nKansas and compared them with other reported data. De\u00c2\u00ac\\nspite employing a larger than average area, the units failed\\nto meet a 30/30 BOD/TSS requirement at two of the three\\nsites.\\nLength\\nWidth\\nBottom slope\\nAs calculated (see design example);\\nminimum of 15 m (49 ft)\\nAs calculated (see design example);\\nmaximum of 61 m (200 ft)\\n0.5- 1%\\nTop slope\\nlevel or nearly level\\nHydraulic Conductivity\\nFirst 30% of length 1% of clean K\\nLast 70% of length 10% of clean K\\nGiven the general lack of operation and maintenance\\nrequirements and the potential aesthetic appearance of\\nVSB systems, their attractiveness to local and state regu\u00c2\u00ac\\nlators is quite predictable. As a passive system potentially\\ncapable of meeting a 30/30 BOD/TSS requirement, they\\nhave obvious advantages over mechanical systems which\\nrequire a significant management program and electrical\\nsupport to function satisfactorily. Also, their general reli\u00c2\u00ac\\nability, when compared to mechanical systems, offers ad\u00c2\u00ac\\nditional protection against clogging of the soil\u00e2\u0080\u0099s infiltrative\\nsurface.\\nMedia\\nAll media should be washed clean of fines and debris; more rounded\\nmedia will generally have more void spaces; media should be resistant\\nto crushing or breakage.\\nInlet zone 40 80 mm (1.5 3.0 in)\\n(1st 2 m (6.5 ft)]\\nTreatment zone 20 30 mm (3/4 -1 in) [use clean K\\n100,000, if actual K not known]\\nOutlet zone 40 80 mm (1.5 3.0 in)\\n[last 1 m (3.2 ft)]\\nPlanting media 5 20 mm (1/4 3/4 in)\\n[top 10 cm (4 in.)]\\nMiscellaneous Use at least 2 VSBs in parallel\\nUse adjustable inlet device with\\ncapability to balance flows\\nUse adjustable outlet control device with\\ncapability to flood and drain system\\n5.7 On-site Applications\\nA number of states, including Louisiana, Kentucky, Kan\u00c2\u00ac\\nsas, Arkansas, Texas and Indiana, have used VSBs for\\non-site wastewater management. Kentucky alone lists over\\n4000 such installations (Thom et al., 1998). Most of these\\nstates have adopted VSBs as a pretreatment step prior to\\nsoil infiltration in an effort to protect groundwater by over-\\nBased on the VSB design guidance presented previously,\\na three bedroom home would require a VSB of 100 m 2\\nassuming six persons and a BOD loading of 100 g/cap-d.\\nAs expected, due to the conservative nature of the design\\napproach presented in this chapter, this area is at the high\\nend of the areas found by Mankin and Powell (1998).\\nThere should be minimal deviation from the recommen\u00c2\u00ac\\ndations of Table 5-4, except that simplified inlet and outlet\\nconfigurations, appropriate for small on-site systems, can\\nbe used. As with larger VSBs, some means of post-aera\u00c2\u00ac\\ntion and disinfection will be required if surface discharge is\\ncontemplated. Discharge to soil infiltration is more likely,\\nand soil absorption guidelines provided by the State will\\napply.\\n5.8 Alternative VSB Systems\\nAlternative VSB systems are those that operate with\\nsome schedule of filling and draining the media. Fill and\\ndrain VSB systems are similar to sequencing batch reac\u00c2\u00ac\\ntors, intermittent sand filters, or overland flow systems in\\nthat the flow into a single cell of a system is intermittent.\\nDraining a VSB system is a simple way to introduce more\\noxygen into the media. Clearly plants are playing a lesser\\nrole in these systems and they are inherently quite differ\u00c2\u00ac\\nent from a natural wetland. Nevertheless they are discussed\\nhere because they have been identified as constructed\\n106", "height": "4267", "width": "3142", "jp2-path": "constructedwetla00nati_0122.jp2"}, "123": {"fulltext": "wetlands and have evolved from conventional VSB sys\u00c2\u00ac\\ntems. They are more complex to operate than a conven\u00c2\u00ac\\ntional VSB system.\\nOne of the first and more unconventional alternative VSB\\nsystems was developed in England and tested in England\\nand Egypt in the late 1980s (May et al., 1990). The sys\u00c2\u00ac\\ntem, called a gravel bed hydroponic system, is very simi\u00c2\u00ac\\nlar to an overland flow process except that the wastewater\\nflows through 8-10 cm (3-4 in) of gravel. Loading is typi\u00c2\u00ac\\ncally intermittent except when denitrification is desired.\\nResearchers at TTU (1999) experimented with alternat\u00c2\u00ac\\ning fill and drain VSB wetlands for one year in 1994 and\\ncompared the results to conventional VSBs in side by side\\ntesting. The alternating fill and drain cells followed a con\u00c2\u00ac\\nventional VSB cell. Effluent from the fill and drain cells was\\nrecycled back to the conventional cell. They found some\\nimprovement in nitrogen removal but overall the results\\nwere not as good as they had expected.\\nResearchers at TVA have developed (and patented) a\\nsystem in which the wastewater is quickly drained from\\none wetland cell and pumped into a second parallel cell\\n(Behrends, et al., 1996). The draining and filling occurs\\nwithin 2 hours and then the process is reversed; the sec\u00c2\u00ac\\nond cell is drained quickly and the first cell is refilled. The\\nreciprocating flow process is repeated continuously, with\\na small amount of influent continually added to the first\\ncell and a fraction of the wastewater continually drawn from\\nthe second cell as effluent. The reciprocating two cell sys\u00c2\u00ac\\ntem was compared with a conventional two cell system for\\nsix months in side by side testing in late 1995 and early\\n1996 at Benton, Tennessee. Continued operation of both\\ntwo-cell pairs in the reciprocating mode has continued since\\nMay of 1996. Comparing conventional operation to the\\nreciprocating mode, the reciprocating mode produced sig\u00c2\u00ac\\nnificantly lower effluent BOD and ammonia nitrogen.\\nOne of the most studied full-scale VSB systems is lo\u00c2\u00ac\\ncated at the Village of Minoa in New York State (see Chap\u00c2\u00ac\\nter 9). Two New York State agencies and the USEPA pro\u00c2\u00ac\\nvided grant funds to the Village for incorporation of sev\u00c2\u00ac\\neral special features in the VSB system and for a research\\nand technology transfer study of the system by research\u00c2\u00ac\\ners at Clarkson University, Potsdam, NY. The system was\\noriginally designed and operated as a conventional VSB\\nsystem, but during 15 months treating a primary effluent,\\nthe system performed very poorly compared to its design\\nexpectations. Faced with numerous complaints from\\nnearby residents about hydrogen sulfide odors, the opera\u00c2\u00ac\\ntors started operating the system with occasional draw\u00c2\u00ac\\ndown periods to control odors. The drawdown significantly\\nreduced odors. In April 1997, when the experimental plan\\nfor the system called for the three cells to operated in se\u00c2\u00ac\\nries, the Minoa operators decided to increase the flow by\\n100% and change the operation to a fill and drain mode.\\nThe fill and drain operation included a resting period dur\u00c2\u00ac\\ning the drained condition and continuous operation for some\\ntime after filling. The fill and drain operation eliminated the\\nhydrogen sulfide odors and also resulted in a significant\\nimprovement in the effluent quality. However, the opera\u00c2\u00ac\\ntors were not satisfied with the improved performance and\\nexperimented further. In 1998 they changed the operation\\nto a mode that continued to the writing of this manual. Two\\nof the wetland cells operate in a parallel fill and drain mode\\nvery similar to sequencing batch reactors. The third cell is\\noperated in a conventional mode but in series with the first\\ntwo cells. This mode of operation has resulted in an addi\u00c2\u00ac\\ntional significant improvement in effluent quality over the\\nprevious fill and drain mode of operation. See section 9.8\\nfor a more detailed description of the operation and the\\nresults.\\nWithin the last five years, several unsaturated vertical\\nflow systems have been constructed and tested in Europe.\\nMost have been used for tertiary treatment of secondary\\neffluents but they have also been used for treating septic\\ntank and sugar beet processing effluents. They appear to\\nperform significantly better than conventional VSB systems.\\nRecommended design loadings are approximately twice\\nthat for conventional VSB systems.\\n5.9 References\\nBatchelor, A. and R Loots. 1997. A critical evaluation of a\\npilot scale subsurface flow wetland: 10 years after com\u00c2\u00ac\\nmissioning. Water Science Technology, 35(5):337-343.\\nBavor, H.J., D.J. Roser, RJ. Fisher, and I.C. Smalls. 1989.\\nPerformance of solid-matrix wetland systems viewed as\\nfixed-film bioreactors. In: D.A. Hammer (ed.) Constructed\\nWetlands for Wastewater Treatment. Chelsea, Ml: Lewis\\nPublishers, pp. 646-656.\\nBavor, H.J. and T.J. Schulz. 1993. Sustainable suspended\\nsolids and nutrient removal in large-scale, solid matrix,\\nconstructed wetland systems. In: G.A. Moshiri (ed.) Con\u00c2\u00ac\\nstructed wetlands for water quality improvement. Boca\\nRaton, FLLewis Publishers, pp. 219-225.\\nBehrends, L.L., Coonrod, H.S., Bailey E. and M.J. Bulls. 1993.\\nOxygen Diffusion Rates in Reciprocating Rock Biofilters:\\nPotential Applications for Subsurface Flow Constructed\\nWetlands, In: Proceedings Subsurface Flow Constructed\\nWetlands Conference, August 16-17, 1993, University\\nof Texas at El Paso.\\nBehrends, L.L., F. J. Sikora, H.S. Coonrod, E. Bailey and C.\\nMcDonald. 1996. Reciprocating Subsurface-Flow Con\u00c2\u00ac\\nstructed Wetlands for Removing Ammonia, Nitrate, and\\nChemical Oxygen Demand: Potential for Treating Do\u00c2\u00ac\\nmestic, Industrial and Agricultural Wastewater. Vol 5, Pp\\n251-263. In: Proceedings of the Water Environment\\nFederation 69th Annual Conference. Dallas, TX.\\nBhattarai, R.R. and D.M. Griffin, Jr. 1998. Results of tracer\\ntests in rock plant filters. Department of Civil Engineer\u00c2\u00ac\\ning, Louisiana Tech University, Ruston, LA.\\nBounds, H.C., J. Collins, Z. Liu, Z. Qin, andT.A. Sasek. 1998.\\nEffects of length-width ratio and stress on rock-plant fil\u00c2\u00ac\\nter operation. Small Flow Journal, 4(1 ):4-14.\\n107", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0123.jp2"}, "124": {"fulltext": "Bowmer, K.H. 1987. Nutrient removal from effluents by\\nan artificial wetland: influence of rhizosphere aera\u00c2\u00ac\\ntion and preferential flow studied using bromide and\\ndye tracers. Water Research, 21 (5):591-599.\\nBreen, P.F. and A.J. Chick. 1995. Rootzone dynamics\\nin constructed wetlands receiving wastewater: a\\ncomparison of vertical and horizontal flow systems.\\nWater Science Technology, 32(3):281-290.\\nChalk, E. and G. Wheale. 1989. The root-zone process\\nat Holtby Sewage Treatment Works. Journal IWEM,\\n3:201-207.\\nCooper, P.F. 1990. European Design and Operations\\nGuidelines for Reed Bed Treatment Systems, Rep.\\nUI17, Water Research Centre, Swindon, U.K.\\nCooper, P.F., J.A. Hobson and S. Jones. 1989. Sewage\\nTreatment by Reed Bed Systems. Journal of the In\u00c2\u00ac\\nstitution of Water and Environmental Management.\\n3 (1) 60.\\nCrites, R. and G.Tchobanoglous. 1998. Small and de\u00c2\u00ac\\ncentralized wastewater management systems. San\\nFrancisco, CA: McGraw-Hill.\\nDahab, M.F. and R.Y. Surampalli. 1999. Predicting Sub\u00c2\u00ac\\nsurface Flow constructed Wetlands Performance: A\\nComparison of Common Design Models. In: Pro\u00c2\u00ac\\nceedings of the Water Environment Federation 72th\\nAnnual Conference. New Orleans, LA.\\nDeShon, G.C., A.L. Thompson, and D.M. Sievers. 1995.\\nHydraulic properties and relationships for the de\u00c2\u00ac\\nsign of subsurface flow wetlands. Presented at Ver\u00c2\u00ac\\nsatility of Wetlands in the Agricultural Landscape\\nConference, Tampa, FL, Sept. 17-20, 1995.\\nFisher, P.J. 1990. Hydraulic characteristics of con\u00c2\u00ac\\nstructed wetlands at Richmond, NSW, Australia. In:\\nP.F. Cooper and B.C. Findlater (eds.) Constructed\\nWetlands in Water Pollution Control. Oxford, UK:\\nPergamon Press, pp. 21-31.\\nGearheart, R.A. 1998. Use of FWS constructed wetlands\\nas an alternative process treatment train to meet\\nunrestricted water reclamation standards. Presented\\nat AWT-98, Advanced Wastewater Treatment, Re\u00c2\u00ac\\ncycling and Reuse, Milan, Italy, pp. 559-567.\\nGearheart, R.A. et al. 1999. Free water surface wet\u00c2\u00ac\\nlands for wastewater treatment: a technology as\u00c2\u00ac\\nsessment. USEPA, Office of Water Management, US\\nBureau of Reclamation, City of Phoenix, AZ.\\nGeorge, D.B. et al. 2000. Development of guidelines\\nand design equations for subsurface flow con\u00c2\u00ac\\nstructed wetlands treating municipal wastewater.\\nUSEPA, Office of Research and Development, Cin\u00c2\u00ac\\ncinnati, OH.\\nGersberg, R.M., B.V. Elkins and C.R. Goldman. 1983.\\nNitrogen Removal in Artificial Wetlands. Water Re\u00c2\u00ac\\nsearch 17 (9) 1009.\\nGersberg, R.M. et al. 1984. The Removal of Heavy Met\u00c2\u00ac\\nals by Artificial Wetlands, In: Proc Water Reuse\\nSymp. Ill, Vol 2, AWWA Research Foundation, 639.\\nGersberg, R.M., et al. 1986. Role of Aquatic Plants in\\nWastewater Treatment by Artificial Wetlands. Wa\u00c2\u00ac\\nter Research 20 (3) 363.\\nGersberg, R.M., Gearheart, R.A., and M. Ives. 1989.\\nPathogen Removal in Constructed Wetlands, Proc.\\nFrom First International Conference on Wetlands for\\nWastewater Treatment, Chattanooga, TN, June\\n1988, Ann Arbor Press.\\nGreen, M.B. and J. Upton. 1994. Constructed Reed\\nBeds: A Cost-Effective Way to Polish Wastewater\\nEffluents for Small Communities. Water Env. Res.\\n66 (3) 188.\\nGriffin, P., B. Green and A.Pritchard. 1998. Pathogen\\nRemoval in Subsurface Flow Constructed Reed\\nBeds. In: Proceedings of the Water Environment\\nFederation 71st Annual Conference. Orlando, FL.\\nHeukelekian, H. and J.L. Balmat. 1959. Chemical com\u00c2\u00ac\\nposition of the particulate fractions of domestic sew\u00c2\u00ac\\nage. Sewage Industrial Wastes, 81:413-423.\\nJenssen, P.T. M. Muehlan, and T. Kregstad. 1993. Po\u00c2\u00ac\\ntential use of constructed wetlands for wastewater\\ntreatment in northern environments. In: Proceedings\\nof 2nd International Conference on Design and Op\u00c2\u00ac\\neration of Small Wastewater Treatment Plants, pp.\\n193-200.\\nKadlec, R.H. and R.L. Knight. 1996. Treatment Wet\u00c2\u00ac\\nlands. Boca Raton, FL: Lewis-CRC Press.\\nKadlec, R.H. and J.T. Watson. 1993. Hydraulics and sol\u00c2\u00ac\\nids accumulation in a gravel bed treatment wetland.\\nIn: G.A. Moshiri (ed.) Constructed wetlands for wa\u00c2\u00ac\\nter quality improvement. Boca Raton, FL:Lewis Pub\u00c2\u00ac\\nlishers, pp. 227-235.\\nKickuth, R. 1981. Abwasserreinigung in mosaikmatrizen\\naus aeroben und anaerobenteilbezirken. In: F.\\nMoser (Ed), Grundlagen der Abwassereinigung, pp\\n639-665.\\nKing, A.C., C.A. Mitchell, and T. Howes. 1997. Hydrau\u00c2\u00ac\\nlic tracer studies in a pilot scale subsurface flow con\u00c2\u00ac\\nstructed wetland. Water Science Technology,\\n35(5): 189-196.\\nLiehr, R.K. et al. 2000. Constructed wetlands treatment\\nof high nitrogen landfill leachate. Project Number\\n94-IRM-U, Water Environment Research Founda\u00c2\u00ac\\ntion, Alexandria, VA.\\n108", "height": "4267", "width": "3142", "jp2-path": "constructedwetla00nati_0124.jp2"}, "125": {"fulltext": "Macmanus, B.E., A.L. Thompson, and D.M. Sievers.\\n1992. Predicting water mounding in subsurface rock\\nbed wetlands. Presented at the Mid-Central Con\u00c2\u00ac\\nference of the American Society of Agricultural En\u00c2\u00ac\\ngineers, St. Joseph, MO, March 13-14, 1992.\\nMankin, K.R. and G.M. Powell. 1998. Onsite rock-plant\\nfilter monitoring and evaluation in Kansas. In: Pro\u00c2\u00ac\\nceedings of 8th National Symposium on Individual\\nand Small Community Sewage Systems, ASAE, St.\\nJoseph, Ml.\\nMay, E., J.E. Bulter, M.G. Ford, R.F. Ashworth, J.S. Wil\u00c2\u00ac\\nliams and M.M.M. Baghat. 1990. Comparison of\\nChemical and Microbiological Processes in Gravel\\nBed Hydroponic (GBH) Systems for Sewerage\\nTreatment. In: Constructed Wetlands in Water Pol\u00c2\u00ac\\nlution Control. Cooper and Findlater (Eds)\\nPergamon Press U.K.\\nNetter, R. and W. Bischofsberger. 1990. Hydraulic in\u00c2\u00ac\\nvestigations on planted soil filters. In: P.F. Cooper\\nand B.C. Findlater (eds.) Constructed Wetlands in\\nWater Pollution Control. Oxford, UK: Pergamon\\nPress, pp. 11-20.\\nNetter, R. 1994. Flow characteristics of planted soil fil\u00c2\u00ac\\nters. Water Science Technology, 29(4):37-44.\\nOdegaard, M. 1987. Particle separation in wastewater\\ntreatment. In: Proceedings of 7th European Sew\u00c2\u00ac\\nage and Refuse Symposium, EWPCA, pp. 351-400.\\nPeverly, J.H., J.M. Surface and T. Wang. 1995. Growth\\nand Trace Metal Absorption by Phragmites austra\u00c2\u00ac\\nlis in Wetlands constructed for Landfill Leachate\\nTreatment. Ecological Engineering 5, 21.\\nRash, J.K. and S.K. Liehr. 1999. Flow pattern analysis\\nof constructed wetlands treating landfill leachate.\\nWater Science Technology, 40(3):309-315.\\nReedy, K.R. and W.F. DeBusk. 1985. Nutrient removal\\npotential of selected aquatic macrophytes. J. Envi\u00c2\u00ac\\nronmental Quality, 19:261.\\nReed, S.C., R.W. Crites and E.J. Middlebrooks. 1995.\\nNatural Systems for Waste Management and Treat\u00c2\u00ac\\nment. 2nd Ed. NY: McGraw Hill.\\nReed, S.C. and S. Giarrusso. 1999. Sequencing Op\u00c2\u00ac\\neration Provides Aerobic Conditions in a Con\u00c2\u00ac\\nstructed Wetland. In: Proceedings of the Water En\u00c2\u00ac\\nvironment Federation 72th Annual Conference. New\\nOrleans, LA.\\nRichard, M. and J. Snyder. 1994. Results of the pilot\\nwetlands study at Las Amimas, CO. Report to the\\nCity of Las Animas, Colorado State University, CO.\\nSanford, W.E., T.S. Steenhuis, J-Y. Parlange, J.M. Sur\u00c2\u00ac\\nface, and J.H. Peverly. 1995a. Hydraulic conductiv\u00c2\u00ac\\nity of gravel and sand as substrates in rock-reed\\nfilters. Ecological Engineering, 4:321-336.\\nSanford, W.E., T.S. Steenhuis, J.M. Surface, and J.H.\\nPeverly. 1995b. Flow characteristics of rock-reed fil\u00c2\u00ac\\nters for treatment of landfill leachate. Ecological Engi\u00c2\u00ac\\nneering, 5:37-50.\\nSanford, W.E. 1999. Substrate type, flow characteristics,\\nand detention times related to landfill leachate treat\u00c2\u00ac\\nment efficiency in constructed wetlands. In: G.\\nMulamootil, E.A. McBean, and F. Rovers (eds.) Con\u00c2\u00ac\\nstructed wetlands for the treatment of landfill leachate.\\nBoca Raton, FL:Lewis Publishers, pp. 47-56.\\nSapkota, D.P. and H.J. Bavor. 1994. Gravel bed filtration\\nas a constructed wetland component for the reduction\\nof suspended solids from maturation pond effluent.\\nWater Science Technology, 29(4):55-66.\\nSmith, I.D., G.N. Bis, E.R. Lemon and L.R, Rozema. 1997.\\nA Thermal Analysis of a Sub-surface, Vertical Flow\\nConstructed Wetland. Wat. Sci. Tech. 35 (5) 55.\\nStengel, E. and Schultz-Hock, R. 1989. Denitrification in\\nartificial wetlands. In: D.A. Hammer (ed.) Constructed\\nWetlands for Wastewater Treatment. Chelsea, Ml:\\nLewis Publishers, pp. 484-492.\\nSurface, J.M., J.H. Peverly, T.S. Steenhuis, and W.E.\\nSanford. 1993. Effect of season, substrate composi\u00c2\u00ac\\ntion, and plant growth on landfill leachate treatment in\\na constructed wetland. In: G.A. Moshiri (ed.) Con\u00c2\u00ac\\nstructed wetlands for water quality improvement. Boca\\nRaton, FL:Lewis Publishers, pp. 461-472.\\nTanner, C.C. and J.P. Sukias. 1995. Accumulation of or\u00c2\u00ac\\nganic solids in gravel-bed constructed wetlands. Wa\u00c2\u00ac\\nter Science Technology, 32(3):229-239.\\nTanner, C.C., J.P.S. Sukias, and M.P. Upsdell. 1998. Or\u00c2\u00ac\\nganic matter accumulation during maturation of gravel-\\nbed constructed wetlands treating farm dairy waste-\\nwaters. Water Research, 32(10):3046-3054.\\nThom, W.O., Y.T. Yang, and J.S. Dinger. 1998. Long-term\\nresults of residential constructed wetlands. In: Proceed\u00c2\u00ac\\nings of 8th National Symposium on Individual and Small\\nCommunity Sewage Systems, ASAE, St. Joseph, Ml.\\nUSEPA. 1993. Subsurface Flow Constructed Wetlands for\\nWastewater Treatment, A Technology Assessment.\\nEPA 832-R-93-008.\\nVanier, S.M. and M.F. Dahab. 1997. Evaluation of Subsur\u00c2\u00ac\\nface Flow Constructed Wetlands for Small Commu\u00c2\u00ac\\nnity Wastewater Treatment in the Plains. In: Proceed\u00c2\u00ac\\nings of the Water Environment Federation 70th An\u00c2\u00ac\\nnual Conference. Chicago, IL.\\nvan Oostrom, A.J. and R.N. Cooper. 1990. Meat process\u00c2\u00ac\\ning effluent treatment in surface-flow and gravel-bed\\n109", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0125.jp2"}, "126": {"fulltext": "constructed wastewater wetlands. In: P.F. Cooper and\\nB.C. Findlater (eds.) Constructed Wetlands in Water\\nPollution Control. Oxford, UK: Pergamon Press, pp.\\n321-332.\\nWatson, J.T., K.D. Choate, and G.R. Steiner. 1990. Per\u00c2\u00ac\\nformance of constructed wetland treatment systems\\nat Benton, Hardin, and Pembroke, Kentucky, during\\nthe early vegetation establishment phase. In: P.F. Coo\u00c2\u00ac\\nper and B.C. Findlater (eds.) Constructed Wetlands in\\nWater Pollution Control. Oxford, UK: Pergamon Press,\\npp. 171-182.\\nWEF. 1998. Manual of Practice #8. Water Environment\\nFederation, Alexandria, VA.\\nYoung, T.C., A.G. Collins, and T.L. Theis. 2000. Subsur\u00c2\u00ac\\nface flow wetland for wastewater treatment at Minoa,\\nNY. Report to NYSERDA and USEPA, Clarkson Uni\u00c2\u00ac\\nversity, NY.\\n110", "height": "4267", "width": "3142", "jp2-path": "constructedwetla00nati_0126.jp2"}, "127": {"fulltext": "Chapter 6\\nConstruction, Start-up, Operation, and Maintenance\\n6.1 Introduction\\nConstructed wetland systems require infrequent opera\u00c2\u00ac\\ntion and maintenance activities to achieve performance\\ngoals if they are designed and constructed properly. This\\nchapter discusses construction details, start-up procedures,\\nand operation and maintenance activities for both free water\\nsurface wetlands and vegetated submerged beds.\\n6.2 Construction\\nConstruction of wetland systems primarily involves com\u00c2\u00ac\\nmon earth moving, excavating, backfilling, and grading.\\nMost of the equipment and procedures are the same as\\nthose employed for construction of lagoons, shallow ponds,\\nand similar containment basins. However, there are as\u00c2\u00ac\\npects that require special attention to ensure flow through\\nthe wetland is uniform over the design treatment volume.\\nAlso, establishment of vegetation is unique to the basin\\nconstruction and not always within the repertoire of con\u00c2\u00ac\\nstruction contractors. It is the intent of this section to pro\u00c2\u00ac\\nvide guidance on these special and unique aspects of\\nwetland construction.\\n6.2.1 Basin Construction\\nThe basic containment structure of constructed wetlands\\nconsists of berms and liners. The structural and watertight\\nintegrity of the liner and surrounding berm are critical. Fail\u00c2\u00ac\\nure of either will result in loss of water, risk of ground water\\npollution, and possible loss of plants due to the decline of\\nthe water level in the wetland.\\n6.2.1.1 Basin Layout\\nThe topography of the site will dictate the general shape\\nand configuration of the wetland. Constructing the wetland\\non sloping sites with the long axis along the contour will\\nminimize the grading requirements. With proper layout, long\\nsloping sites can reduce pumping costs by taking advan\u00c2\u00ac\\ntage of the available fall.\\n6.2.1.2 Site Preparation\\nClearing and grubbing, rough grading, and berm con\u00c2\u00ac\\nstruction use the same procedures, techniques, and equip\u00c2\u00ac\\nment used for lagoons and conventional water contain\u00c2\u00ac\\nment basins. If possible, it is desirable to balance the cut\\nand fill on the site to avoid the need for remote borrow pits\\nor soil disposal. If agronomic-quality topsoil exists on the\\nsite, it should be stripped and stockpiled. In the case of\\nFWS wetlands, the topsoil can be utilized as the rooting\\nmedium for the emergent vegetation and revegetation of\\nthe berm surfaces. A soil-rooting medium is not required\\nfor VSB systems.\\nTo meet its performance expectations, it is critically im\u00c2\u00ac\\nportant for the water to flow uniformly through the entire\\nwetland area. Severe short-circuiting of flow can result from\\nimproper grading or nonuniform subgrade compaction. The\\noperating water depth may be 60 cm (2 ft) or less, so ir\u00c2\u00ac\\nregularities in the bottom surface can induce preferential\\nflow paths. Specified tolerances for grading will depend\\non the size of the wetland. A very large FWS wetland of\\nseveral thousand acres cannot afford the effort to fine grade\\nto very close tolerances. Therefore, the wetland should be\\nsubdivided into several smaller cells or the design should\\nincorporate a sizing safety factor to compensate for po\u00c2\u00ac\\ntential short-circuiting. For smaller wetlands of a few hun\u00c2\u00ac\\ndred hectares or less, it is usually cost effective to specify\\ncloser grading tolerances. Bottom grades are an impor\u00c2\u00ac\\ntant consideration when converting existing lagoons to wet\u00c2\u00ac\\nlands. Because of the design depths in lagoons, careful\\ngrading of the bottom may not have been required. In many\\ncases in which conversions were made without careful\\nregrading, significant short-circuiting has occurred that re\u00c2\u00ac\\nduced the wetland treatment performance.\\nUniform compaction of the subgrade is also important to\\nprotect the liner integrity from subsequent construction\\nactivity (i.e., liner placement, soil placement for FWS wet\u00c2\u00ac\\nlands, gravel placement for VSB systems) and from stress\\nwhen the wetland is filled. The loading on the liner is ap\u00c2\u00ac\\nproximately 2,200 kg/m 2 (450 lbs/ft 2 including the plant\\nmass. Short-circuiting of flow through a FWS wetland also\\ncan result from ruts and low areas in the subgrades. The\\nsubgrade should be uniformly compacted to the same lev\u00c2\u00ac\\nels used for native soils in road subgrades.\\nFine grading and compaction of the native subgrade soils\\nalso depends on the liner requirements. Most wetland cells\\nare graded level from side to side and either level or with a\\nslight slope in the direction of flow. Wetlands are often con\u00c2\u00ac\\nstructed with a bottom slope of 1% or less which is suffi\u00c2\u00ac\\ncient to drain the cell if and when maintenance is required.\\nIll", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0127.jp2"}, "128": {"fulltext": "6.2.1.3 Berms\\nBerms in constructed wetlands contain water within spe\u00c2\u00ac\\ncific flow paths. Exterior berms are designed to prevent\\nunregulated flow releases. Interior berms are used to aug\u00c2\u00ac\\nment flow distribution. External berms are typically built to\\nprovide 0.6 to 1 m (2-3 ft) of freeboard with a width at\\nleast 3 m (10 ft) at the top to permit service vehicle ac\u00c2\u00ac\\ncess. The amount of freeboard should be enough to con\u00c2\u00ac\\ntain a given storm rainfall amount. Side slopes should be\\na maximum of 3:1; however, slopes of 2:1 have been used\\nfor internal side slopes, particularly when liners or erosion\\ncontrol blankets are used. Access ramps into each cell of\\nthe system should be shallow enough for maintenance\\nequipment to enter. All berms should be constructed in\\nconformance with standard geotechnical considerations,\\nfor they may be subject to local dam safety regulations.\\nDesign considerations for internal berms, however, are less\\ncritical since they are not designed for water containment.\\nSee Figure 6-1 for typical design features of constructed\\nwetland berms.\\nShort-circuiting around the edges of cells has been ex\u00c2\u00ac\\nperienced in some FWS wetlands where vegetation on the\\nberm slope is absent. This is a particular problem if syn\u00c2\u00ac\\nthetic liners are used. The liners do not provide a good\\nrooting medium and so may remain bare. The open water\\ngap between the berm and the vegetated area in the wet\u00c2\u00ac\\nland proper provides a preferential flow path. A soil layer\\ncan be placed on the berm side slope to establish vegeta\u00c2\u00ac\\ntion, but the slope is very susceptible to erosion, particu\u00c2\u00ac\\nlarly near the water line. The soil loss from erosion will\\nhave the added impact of reducing the detention time in\\nthe wetland. This has not been a problem in clay-lined\\nwetlands because the clay provides a good rooting me\u00c2\u00ac\\ndium.\\n6.2.1.4 Liners\\nLiners used for wetlands are the same as those typically\\nused for lagoons and ponds. The materials include:\\nPolyvinyl chloride (PVC)\\nPolyethylene (PE)\\nPolypropylene\\nMost systems typically use 30 mil polyvinyl chloride\\n(PVC) or high-density polyethylene (HDP). These may be\\nprefabricated for small, individual-residence wetlands, but\\nGrassed Berm\\n3:1 typical)\\nFigure 6-1. Examples of constructed wetland berm construction\\n112", "height": "4267", "width": "3142", "jp2-path": "constructedwetla00nati_0128.jp2"}, "129": {"fulltext": "they are usually constructed in place using conventional\\nprocedures for assembly, joint bonding, and anchoring.\\nLiners also may include scrims, which are more costly. The\\nscrim is a woven nylon or polypropylene net embedded in\\nplastic or surrounding bentonite. Plastic liners with scrims\\nare marketed under trade names such as Hypalon or XR-\\n5. Several good resources are available for liner applica\u00c2\u00ac\\ntion and selection (EPA, 1993; EPA, 1994; Rumer and\\nMitchell, 1996).\\nLiner punctures must be prevented during placement and\\nsubsequent construction activity. If the subgrade contains\\nsharp stones, a geotextile fabric should be placed beneath\\nthe liner. A geotextile fabric or a layer of sand approximately\\n5 cm (2 in) thick should be placed on top of the liner if\\ncrushed rock is used in a VSB system. The engineer should\\nspecify that the liner installer provides written approval of\\nthe condition of the subgrade as a condition prior to liner\\ninstallation.\\nMany membrane liners currently used require protec\u00c2\u00ac\\ntion from ultraviolet solar radiation. Conventional methods\\ncan be used to achieve protection, but VSB systems should\\nnot use a soil cover as UV protection since erosion may\\nwash soil into the bed and result in local media clogging.\\nRiprap material consisting of aggregate approximately 8-\\n15 cm (3-6 in) in size is recommended for this application.\\nThis larger riprap will reduce the potential for weeds to\\nbecome established and spread into the wetland. It can\\nalso withstand foot traffic for the life of the system.\\nClay liners also have been used. Manufactured liners\\nusing bentonite are common. The bentonite may be mixed\\nwith the native soils and compacted, or it may be in the\\nform of pads or blankets consisting of bentonite between\\ntwo scrims of finely woven polypropylene or polyethylene.\\nNative soils may be used if they have sufficiently high\\nclay content to achieve the necessary permeability. Usu\u00c2\u00ac\\nally the state regulatory agency will specify the acceptable\\npermeability. Typically, the clay liner must be 0.3 m (1 ft) or\\nmore in thickness to provide the necessary hydraulic bar\u00c2\u00ac\\nrier. In the case of a FWS, the surface of the clay layer\\nshould be well compacted to discourage root penetration\\nby the emergent vegetation as the wetland matures.\\n6.2.1.5 Inlet and Outlet Structures\\nInlet and outlet structures distribute the flow into the\\nwetland, control the flow path through the wetland, and\\ncontrol the water depth. Multiple inlets and outlets spaced\\nacross either end of the wetland are essential to ensure\\nuniform influent distribution into and flow through the wet\u00c2\u00ac\\nland. These structures help to prevent \u00e2\u0080\u009cdead zones\u00e2\u0080\u009d where\\nexchange of water is poor, resulting in wastewater deten\u00c2\u00ac\\ntion times that can be much less than the theoretical de\u00c2\u00ac\\ntention times.\\nIn small- to medium-sized wetlands, perforated or slot\u00c2\u00ac\\nted manifolds running the entire wetland width typically are\\nused for both the inlets and outlets. Sizes of the mani\u00c2\u00ac\\nfolds, orifice diameters, and spacing are a function of the\\nprojected flow rate. For example, the first cell of the FWS\\nwetland in West Jackson County, Ml, is designed for an\\naverage flow of 2,270 m 3 /d (600,000 gpd). It uses a 300\\nmm (12 in)-diameter PVC manifold for the inlet that ex\u00c2\u00ac\\ntends the full 76 m (250 ft) width of the cell. The manifold\\nis perforated with 50 mm (2 in)-diameter orifices on 3 m\\n(10 ft) centers. It rests on a concrete footing to ensure sta\u00c2\u00ac\\nbility and discharges to a 150 mm (6 in)-thick layer of coarse\\naggregate. A single inlet would not be suitable for a wide\\nwetland cell such as this because it would not be possible\\nto achieve uniform flow across the cell. Multiple weir boxes\\ncould be used as an alternative. Splitter boxes using \u00e2\u0080\u009cV\u00e2\u0080\u009d\\nnotched weirs or other methods can be used to divide the\\ninfluent flow equally between the individual weir boxes.\\nThe weir boxes also can be used for measuring the influ\u00c2\u00ac\\nent flow. Examples of these types of structures can be found\\nin irrigation engineering textbooks.\\nWhere possible, the inlet manifold should be installed in\\nan exposed position to allow access by the operator for\\nflow adjustment and maintenance. Several alternatives to\\nthe simple drilled orifice can be used for flow distribution\\ncontrol. See Figure 6-2 for examples of inlet manifolds.\\nIn cold climates where extended periods of freezing\\nweather are possible or where public exposure is an is\u00c2\u00ac\\nsue, a submerged inlet is necessary. In these instances,\\nthe simple perforated inlet manifold is used. Since it is not\\npossible to adjust the level of the submerged manifolds\\nafter construction is completed, extra effort should be ex\u00c2\u00ac\\npended to compact and grade the inlet and outlet zones to\\nlimit subsequent settling. It may be necessary to support\\nthe manifold on concrete footings where the underlying\\nsoils are potentially unstable. An accessible cleanout should\\nbe provided at each end of the submerged manifold to\\nallow flushing if the manifold becomes clogged. Shut-off\\ndevices should be provided on all inlets to permit mainte\u00c2\u00ac\\nnance or resting of the wetland.\\nIn FWS wetlands, the encroachment of adjacent emer\u00c2\u00ac\\ngent vegetation may clog the manifold outlets with plant\\nlitter and detritus. This problem may be eliminated by con\u00c2\u00ac\\nstructing a deep water zone approximately 1-1.3 m (3-4\\nft) deeper than the bottom of the rest of the wetland. The\\nopen area should be limited to 1 m (3 ft) in width. The\\nmanifold also can be enclosed in a berm of coarse riprap\\n8-15 cm (3-6 in) in size. The coarse riprap inhibits plant\\ngrowth. The open water design, however, allows easier\\naccess to the manifold for maintenance, but may encour\u00c2\u00ac\\nage wildlife visitation and the potential effluent quality deg\u00c2\u00ac\\nradation that accompanies it.\\nOutlet structures help to control uniform flow through the\\nwetland as well as the operating depth. If submerged out\u00c2\u00ac\\nlet manifolds are used, they must be connected to a level\\ncontrol device that permits the operator to adjust the water\\ndepth in the wetland. This device can be an adjustable\\nweir or gate, a series of stop logs, or a swiveling elbow\\n(Figure 6-3).\\nAn alternative to submerged manifolds for inlet and out\u00c2\u00ac\\nlet structures is multiple weir or drop boxes. These are\\n1\\n13", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0129.jp2"}, "130": {"fulltext": "Cleanout (both ends)\\n3E\\n\u00c2\u00aeo o\u00c2\u00b0\\noU\\nfig\\n\u00c2\u00b0o\u00c2\u00b0\\notf\\no9o\\n0 OoQ\\n96\\nrr fl\\n0\\n\u00c2\u00b0lo 0\\n0 o 0\\no ?o\\ndo 0\\n0\\n0\\nControl Valve\\na) Submerged Perforated Pipe\\nSettled\\nSewage\\nuPVC Pipe\\nV.*\\nReed Bed\\no\\n0\\nWire Mesh Gabions\\nWire Mesh Gabion\\nwith 60 100mm Stones\\nb) Gabion Feed\\nLevel Surface\\nSoil Cover over Liner\\nReed Bed\\nBack-filled\\nwith Stones\\nk\\n90\u00c2\u00b0 Tees with O Ring Seals Inlet\\nWire Mesh Gabion (optional)\\nwith 60 100mm Stones\\nc) Swivel Tee\\nFigure 6-2. Examples of constructed wetland inlet designs\\n114", "height": "4267", "width": "3142", "jp2-path": "constructedwetla00nati_0130.jp2"}, "131": {"fulltext": "Outlet\\nAdjustable\\nWeir\\nDebris\\nScreen\\nAdjustable Weir\\nOutlet\\nDebris\\nScreen\\na) Adjustable Weir\\nWire Mesh Gabion (optional)\\nwith 60 100mm Stones\\nWire Mesh Gabion (optional)\\nwith 60 100mm Stones\\nSlotted Pipe\\nCollector\\nO Ring Joint\\nc) 90\u00c2\u00b0 Elbow Arrangement\\nLiner\\nSlotted Pipe\\nCollector\\nb) Interchangeable Section\\nInterchangeable Section\\nof Pipe Fits O Ring Socket\\nFigure 6-3. Outlet devices\\n115", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0131.jp2"}, "132": {"fulltext": "usually constructed of concrete, either cast in place or pre\u00c2\u00ac\\nfabricated. Several boxes must be installed across the width\\nof the wetland to ensure uniform flow through the wetland.\\nPreferred spacing varies from 5 to 10 m (15-30 ft) but may\\nbe as much as 15 m (50 ft) on center depending on the\\nwidth of the wetland cell. Overflow rates should be limited\\nto 200 m 3 /m-d (16,000 gpd/ft 2 Drop boxes do require a\\ndeep water zone immediately around them to minimize\\nvegetation encroachment. In northern climates, the boxes\\nare more susceptible to freezing than are submerged mani\u00c2\u00ac\\nfolds.\\nDebris screens may be placed in front of FWS wetland\\noutlets. In Figure 6-3 there is an example of their place\u00c2\u00ac\\nment in the outlet. The emergent vegetation in the wetland\\nwill drop many leaves, and storm events can uproot entire\\nplants that float to the collection manifolds or outlet struc\u00c2\u00ac\\ntures. The screens will prevent the debris from clogging\\nthe downstream piping or treatment processes or impair\u00c2\u00ac\\ning effluent quality.\\n6.2.1.6 Media\\nA soil or finer-rock medium is necessary as a matrix in\\nboth FWS wetlands and VSB systems for supporting emer\u00c2\u00ac\\ngent vegetation. In FWS wetlands, a layer of soil at least\\n15 cm (6 in) deep is placed on the compacted bottom or\\nliner to create the rooting medium for the intended emer\u00c2\u00ac\\ngent vegetation. This soil can be the topsoil removed dur\u00c2\u00ac\\ning initial site preparation and grading or can be imported.\\nAny loamy soil with acceptable agronomic properties is\\nsuitable.\\nIn VSB systems, the media provide the matrix for water\\nflow as well as the planting medium. Gravel is the most\\ncommonly used media, but sand, crushed rock, and plas\u00c2\u00ac\\ntic media also have been used (Kadlec and Knight, 1996).\\nLarge gravel media are typically recommended to prevent\\nclogging, whereas a smaller media layer can be used on\\ntop of a bed of larger gravel to provide a better rooting\\nmedia (see Chapter 5).\\nMost local sand and gravel suppliers have concrete ag\u00c2\u00ac\\ngregate available that can be screened for the coarse frac\u00c2\u00ac\\ntions to provide an acceptable media for VSB systems.\\nThe media should be washed to eliminate soil and other\\nfines that can contribute to media clogging. Rounded river\\ngravel is recommended over sharp-edged crushed rock\\nbecause of the looser packing that the rounded rock pro\u00c2\u00ac\\nvides. Hard, durable stone (river gravel or crushed stone)\\nis recommended. Crushed limestone, which is soft and\\neasily disintegrates, should be avoided.\\n6.2.2 Vegetation Establishment\\nVegetation and its litter is necessary for successful per\u00c2\u00ac\\nformance of FWS wetlands and contributes aesthetically\\nto the appearance of both FWS wetlands and VSB sys\u00c2\u00ac\\ntems. Establishing this vegetation is probably the least fa\u00c2\u00ac\\nmiliar aspect of wetland construction for most contractors.\\nIn recent years, a number of specialty firms have emerged\\nwith the expertise for selecting and planting the vegetation\\nin these systems. Employing one of these firms is recom\u00c2\u00ac\\nmended for large projects if the construction contractor\\ndoes not have prior wetland experience.\\n6.2.2.1 Species Selection and Sources\\nFor wastewater treatment, macrophytes selected for\\nplanting should (1) be active vegetative colonizers with\\nspreading rhizome systems, (2) have considerable biom\u00c2\u00ac\\nass or stem densities to achieve maximum velocity gradi\u00c2\u00ac\\nent and enhanced flocculation and sedimentation, and (3)\\nbe a combination of species that will provide coverage over\\nthe broadest range of water depths encountered (Allen et\\nal., 1990).\\nWetland plants can be purchased from nurseries, col\u00c2\u00ac\\nlected in the wild, or grown for a specific project. No gen\u00c2\u00ac\\neral recommendation can be made as to the best source\\nof plants for a particular project. However, wild collected\\nplants are usually the most desirable because they are\\nmore closely adapted to local environmental conditions,\\ncan be planted with limited storage, and offer a greater\\ndiversity. For large projects, commercial seedlings may be\\nthe most cost-effective alternative. The seedlings are sup\u00c2\u00ac\\nplied in suitable planting condition that allows use of me\u00c2\u00ac\\nchanical agricultural equipment for planting.\\n6.2.2.2 Planting\\nEstablishing vegetation in a constructed wetland involves\\nplanting a suitable propagule at the appropriate time. Whole\\nplants or dormant rhizomes and tubers are typically planted.\\nSeeding has not been particularly successful because of\\nstratification requirements of wetland seed and loss of seed\\nfrom water action.\\nIn temperate climates, the prime planting period begins\\nafter dormancy has begun in the fall and ends after the\\nfirst third of the summer growing season has passed. The\\nplanting period for herbaceous vegetation is broader than\\nfor woody plants. Early spring growing-season plantings\\nhave been the most successful (Allen et al., 1990).\\nPlanting seedlings or clumps is the simplest method.\\nSome experience is necessary wittwhizomes to identify\\nthe node of the future shoot, which must be planted up\u00c2\u00ac\\nward. Special anchoring may be necessary when the plant\u00c2\u00ac\\ning medium is soft, plants are buoyant, or erosion will dis\u00c2\u00ac\\nturb the system. The soil should be maintained in a moist\\ncondition after planting. The water level can be increased\\nslowly as new shoots develop and grow. The water level\\nmust never be higher than the tips of the green shoots or\\nthe plants will die.\\nThe macrophyte planting density can be as close as 0.3\\nm (1 ft) centers or as much as 1 m (3 ft). The higher the\\ndensity, the more rapid will be the development of a ma- I\\nture and completely functional wetland system. However, I\\nhigh density plantings will increase construction costs sig\u00c2\u00ac\\nnificantly. If planted on 1 m (3 ft) centers, a wetland sys- i\\ntern will take at least two full growing seasons to approach\\nequilibrium and optimal plant-related performance objec-\\n116", "height": "4267", "width": "3142", "jp2-path": "constructedwetla00nati_0132.jp2"}, "133": {"fulltext": "tives. FWS wetlands should be planted more densely ow\u00c2\u00ac\\ning to the role of the plants in the treatment process. How\u00c2\u00ac\\never, it may not be economical to plant very large FWS\\nwetlands on 1 m (3 ft) centers if the total wetland area is\\nintended to cover several thousand hectares. In such\\ncases, plantings should be done in separate bands ex\u00c2\u00ac\\ntending the full width of the wetland cells to interrupt pref\u00c2\u00ac\\nerential flow of wastewater through the cells. VSB systems\\ncan be planted less densely.\\nWater must be provided during the initial growth period.\\nThis can be complicated in large FWS wetlands because\\nit may not be possible to plant the entire surface in a cell at\\none time. If mechanical equipment is used for planting,\\nthe unplanted areas should be kept dry until planting is\\ncomplete. Since the bottom is sloped toward the discharge\\nend, planting should start at the outlet and proceed toward\\nthe inlet. Sprinklers and shallow flooding have been used\\nto keep the planted areas wet. If planting by hand, the whole\\narea can be flooded with a few centimeters of water. The\\nwater depth can be increased gradually as the plant shoots\\ngrow until the design level is reached. If the FWS wetland\\nis designed to treat a high-strength influent such as pri\u00c2\u00ac\\nmary treated wastewater, a cleaner water source or dilut\u00c2\u00ac\\ning the wastewater with storm water or well water is rec\u00c2\u00ac\\nommended for the initial planting and growth period so the\\nplants are not overly stressed. If the intended influent is\\nclose to secondary quality, it can be used immediately. If\\nan acceptable agronomic soil has not been used as the\\nrooting media, a preliminary application of commercial fer\u00c2\u00ac\\ntilizers may be necessary. Use of fertilizers should be care\u00c2\u00ac\\nfully considered, however, because of the potential impacts\\nof the nutrients that might escape in the effluent to the\\nreceiving water.\\nIn VSB systems, it is typical practice to flood the wetland\\ncell to the surface of the media prior to planting and to\\nmaintain that level until significant growth has occurred.\\nLater, the water level is lowered to the intended operating\\nlevel. If the wetland is designed to treat septic tank or pri\u00c2\u00ac\\nmary effluent, clean water is recommended for the plant\u00c2\u00ac\\ning phase. The high oxygen demand of the wastewater\\ncould inhibit initial plant growth. After a few weeks of plant\\ngrowth, wastewater can be introduced. A layer of straw or\\nhay mulch 15 to 20 cm (6-8 in) in thickness should be\\nplaced on the gravel surface to protect the new plants from\\nthe high summer surface temperatures that can occur on\\nbare gravel surfaces. The mulch also is useful for provid\u00c2\u00ac\\ning thermal insulation during the first winter of operation in\\nnorthern climates.\\n6.3 Start-up\\nStart-up periods for FWS wetlands are necessary to\\nestablish the flora and fauna associated with the treatment\\nprocesses. The start-up period will vary in length depend\u00c2\u00ac\\ning on the type of design (FWS wetlands or VSB systems),\\nthe characteristics of the influent wastewater, and the sea\u00c2\u00ac\\nson of year. In FWS wetlands, the start-up period should\\n1 be sufficient for the vegetation to become well established\\nif the treatment objectives are to be met. The start-up pe\u00c2\u00ac\\nriod for VSB systems is less critical since its performance\\nis less dependent on vegetation.\\n6.3.1 Free Water Surface Wetlands\\nFWS wetlands will not attain optimum performance lev\u00c2\u00ac\\nels until the vegetation and litter are fully developed and at\\nequilibrium. The time required to reach this point is a func\u00c2\u00ac\\ntion of the planting density and season of the year. A wet\u00c2\u00ac\\nland with a high density planting that is started in the spring\\nis likely to be fully developed by the end of the second\\ngrowing season. A wetland with a low density planting\\nstarted in late fall in a northern climate may require three\\nyears or more to achieve its intended treatment perfor\u00c2\u00ac\\nmance.\\nUnder ideal conditions, start-up of a FWS wetland should\\nbe delayed six weeks after planting to provide sufficient\\ntime for the emergent plants to acclimatize and grow above\\nthe working water level. When this is not possible, start-up\\nmust control the water level at less than plant height. How\u00c2\u00ac\\never, such rapid start-up will risk damage to the new plants\\nand may prolong the time required for the system to reach\\noptimum performance.\\nWhen start-up is initiated, the water level must be gradu\u00c2\u00ac\\nally raised to the design level by adjusting the flow control\\ndevice at the outlet of each cell. This is done to allow the\\ntops of the emerging vegetation to remain above water. If\\nthe influent is high strength, such as primary or septic tank\\neffluent, it may be necessary to dilute the influent with clear\\nwater or recycle treated effluent to slowly increase the\\npollutant loadings to the wetland until the vegetation is\\nacclimatized.\\nDuring the start-up period, the operator should inspect\\nthe wetland several times per week. Plant health and\\ngrowth should be observed, berms and dikes inspected\\nfor structural problems, water levels adjusted, and mos\u00c2\u00ac\\nquito emergence noted. In large areas of a FWS system\\nwhere growth of the vegetation has failed, the macrophytes\\nshould be replanted to avoid the risk of short-circuiting of\\nflow. The experience developed during this period will be\\nhelpful in determining the inspection frequency that will be\\nrequired during the mature phase of the wetland.\\nTreatment performance during the start-up period may\\nnot be representative of long-term expectations. Poorly\\nestablished FWS wetlands with minimal vegetation will not\\nperform acceptably. Influent TSS and associated pollut\u00c2\u00ac\\nants will not be properly removed. Large open areas will\\npermit algae blooms. The system will not perform differ\u00c2\u00ac\\nently from a maturation pond, in that only pathogen kill will\\nlikely occur. Removal efficiency of TSS and its associated\\npollutants can be expected to improve as the plant canopy\\ndevelops and increases in density. Removals of ammonia\\nand phosphorus may be greater during the start-up period\\nthan after equilibrium is reached in new FWS wetlands,\\nwhich have a new soil surface and rapidly growing veg\u00c2\u00ac\\netation. Both conditions provide a rapid but short-term re\u00c2\u00ac\\nmoval of these nutrients. Adsorption sites on soil particles\\n117", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0133.jp2"}, "134": {"fulltext": "can take up both ammonia and phosphorus, and the nutri\u00c2\u00ac\\nent uptake by the plants during the rapid growing phase\\ncan be significant. Within one or two years of start-up, how\u00c2\u00ac\\never, removal of phosphorus will decline. Removal of am\u00c2\u00ac\\nmonia nitrogen will decline also unless the system is a\\nFWS with substantial open areas.\\n6.3.2 Vegetated Submerged Bed Systems\\nTreatment in VSB systems is primarily BOD and TSS\\nremoval through the trapping of particulate material in the\\nmedia. Some BOD removal may be reintroduced from bio\u00c2\u00ac\\nchemical methanogenisis of captured organic solids in the\\nanaerobic environment. Biological denitrification also may\\noccur if nitrates are present in the influent. Plants may take\\nup nutrients in the wastewater, but this is usually not sig\u00c2\u00ac\\nnificant. Phosphorus removal during the start-up period will\\noccur, but typically becomes minor as chemical exchange\\nsites on the media are filled. Since the plants play an in\u00c2\u00ac\\nsignificant role in the treatment performance, equilibrium\\nshould be reached in less than one year unless high-ca\u00c2\u00ac\\npacity media is employed.\\nDuring the start-up period, the operator is primarily re\u00c2\u00ac\\nsponsible for adjusting the water level in the wetland. Typi\u00c2\u00ac\\ncally, the VSB systems will be filled to the surface of the\\nmedia at the end of planting. As the plants begin to root,\\nthe water level can be gradually lowered to the design\\noperating level. It may be necessary to add fertilizer dur\u00c2\u00ac\\ning this period until sufficient nutrients are made available\\nby the addition of wastewater.\\n6.4 Operation and Maintenance\\nConstructed wetlands are \u00e2\u0080\u009cnatural\u00e2\u0080\u009d systems. As a result,\\noperation is mostly passive and requires little operator in\u00c2\u00ac\\ntervention. Operation involves simple procedures similar\\nto the requirements for operation of a facultative lagoon.\\nThe operator must be observant, take appropriate actions\\nwhen problems develop, and conduct required monitoring\\nand operational monitoring as necessary. The most criti\u00c2\u00ac\\ncal items in which operator intervention is necessary\\nareAdjustment of water levels\\nMaintenance of flow uniformity (inlet and outlet struc\u00c2\u00ac\\ntures)\\nManagement of vegetation\\nOdor control\\nControl of nuisance pests and insects\\nMaintenance of berms and dikes\\n6.4.1 Water Level and Flow Control\\nWater level and flow control are usually the only opera\u00c2\u00ac\\ntional variables that have a significant impact on a well-\\ndesigned constructed wetland\u00e2\u0080\u0099s performance. Changes in\\nwater levels affect the hydraulic residence time, atmo\u00c2\u00ac\\nspheric oxygen diffusion into the water phase, and plant\\ncover. Significant changes in water levels should be in\u00c2\u00ac\\nvestigated immediately, as they may be due to leaks,\\nclogged outlets, breached berms, storm water drainage,\\nor other causes.\\nSeasonal water level adjustment helps to prevent freez\u00c2\u00ac\\ning in the winter. In cold climates, the water levels should\\nbe raised approximately 50 cm (18 in) in late fall until an\\nice sheet develops. Once the water surface is completely\\nfrozen, the water levels can be lowered to create an insu\u00c2\u00ac\\nlating air pocket under the ice and snow cover to maintain\\nhigher water temperatures in the wetland (Kadlec and\\nKnight, 1996; Grits and Knight, 1990). This procedure is\\nused for both FWS wetlands and VSB systems.\\n6.4.2 Maintenance of Flow Uniformity\\nMaintaining uniform flow across the wetland through in\u00c2\u00ac\\nlet and outlet adjustments is extremely important to achieve\\nthe expected treatment performance. The inlet and outlet\\nmanifolds should be inspected routinely and regularly ad\u00c2\u00ac\\njusted and cleaned of debris that may clog the inlets and\\noutlets. Debris removal and removal of bacterial slimes\\nfrom weir and screen surfaces will be necessary. Sub\u00c2\u00ac\\nmerged inlet and outlet manifolds should be flushed peri\u00c2\u00ac\\nodically. Additional cleaning with a high-pressure water\\nspray or by mechanical means also may become neces\u00c2\u00ac\\nsary.\\nInfluent suspended solids will accumulate near the in\u00c2\u00ac\\nlets to the wetland. These accumulations can decrease\\nhydraulic detention times. Over time, accumulation of these\\nsolids will require removal. VSB systems cannot be\\ndesludged easily without draining and removing the me\u00c2\u00ac\\ndia. Therefore, VSB systems should not be considered for\\ntreating wastewaters with high suspended-solids loads,\\nsuch as facultative pond effluents, which have high algal\\nconcentrations.\\n6.4.3 Vegetation Management\\nRoutine maintenance of the wetland vegetation is not\\nrequired for systems operating within their design param\u00c2\u00ac\\neters and with precise bottom-depth control of vegetation.\\nWetland plant communities are self-maintaining and will\\ngrow, die, and regrow each year. Plants will naturally spread\\nto unvegetated areas with suitable environments (e.g.,\\ndepth within plant\u00e2\u0080\u0099s range) and be displaced from areas\\nthat are environmentally stressful. Operators must control\\nspreading into open water areas that are intended by de\u00c2\u00ac\\nsign to be aerobic zones through harvesting.\\nThe primary objective in vegetation management is to\\nmaintain the desired plant communities where they are\\nintended to be within the wetland. This is achieved through\\nconsistent pretreatment process operation, small, infre\u00c2\u00ac\\nquent changes in the water levels, and harvesting plants\\nwhen and where necessary. Where plant cover is deficient,\\nmanagement activities to improve cover may include wa\u00c2\u00ac\\nter level adjustment, reduced loadings, pesticide applica\u00c2\u00ac\\ntion, and replanting.\\nHarvesting and litter removal may be necessary depend\u00c2\u00ac\\ning on the design of the system. Plant removal from some\\n118", "height": "4267", "width": "3142", "jp2-path": "constructedwetla00nati_0134.jp2"}, "135": {"fulltext": "FWS wetlands may be required to meet the treatment\\ngoals, but a well-designed and well-operated VSB system\\nshould not require routine harvesting. Harvesting of\\nPhragmites at the height of the growing season and just\\nbefore the end of the growing season does help to remove\\nsome nitrogen from the system, but phosphorus removal\\nis limited (Suzuki et al., 1985). Winter burning of vegeta\u00c2\u00ac\\ntion can be used to control pests.\\n6.4.4 Odor Control\\nOdors are seldom a nuisance problem in properly loaded\\nwetlands. Odorous compounds emitted from open water\\nareas are typically associated with anaerobic conditions,\\nwhich can be created by excessive BOD and ammonia\\nloadings. Therefore, reducing the organic and nitrogen\\nloadings can control odors. Alternatively, aerobic open\\nwater zones interspersed in areas between fully vegetated\\nzones introduce oxygen to the system. Turbulent flow struc\u00c2\u00ac\\ntures such as cascading outfall structures and channels\\nwith hydraulic jumps, which are employed to introduce\\noxygen into the system effluent, can generate serious odor\\nproblems through stripping of volatile compounds such as\\nhydrogen sulfide, if the constructed wetland has failed to\\nremove these constituents.\\n6.4.5 Control of Nuisance Pests and\\nInsects\\nPotential nuisances and vectors that may occur in FWS\\nwetlands include burrowing animals, dangerous reptiles,\\nmosquitoes, and odors. An infestation of burrowing ani\u00c2\u00ac\\nmals such as muskrats and nutria can seriously damage\\nvegetation in a system. These animals use both cattails\\nand bulrushes as food and nesting materials. These ani\u00c2\u00ac\\nmals can be controlled during the design phase by de\u00c2\u00ac\\ncreasing the slope on berms to 5:1 or using a coarse riprap.\\nTemporarily raising the operating water level may also dis\u00c2\u00ac\\ncourage the animals. Live trapping and release may be\\nsuccessful, but in most cases it has been necessary to\\neliminate the animals. Fencing has had little success.\\nDangerous reptiles are common in the southeastern\\nstates. The most common are snakes, particularly the water\\nmoccasin, and alligators. It is difficult to control these ani\u00c2\u00ac\\nmals directly. Warning signs, fencing, raised boardwalks,\\nand mowed hiking trails can be used to minimize human\\ncontact with the animals. Operators should be made aware\\nof the dangers and preventive actions that can be taken to\\navoid dangerous situations.\\nMosquito control is a critical issue in FWS wetlands. In\\nwarm climates, wetlands have been seeded with mosquito\\nfish (Gambusia) and dragonfly larvae to control mosqui\u00c2\u00ac\\ntoes. Mosquito fish also can be used in northern climates,\\nbut they need to be restocked each year. However, mos\u00c2\u00ac\\nquito fish have difficulty reaching all parts of the wetland\\nwhen the accumulation of litter is too dense, particularly if\\ncattails are grown. Other natural control methods have in\u00c2\u00ac\\ncluded erecting bat and bird houses. Desirable birds in\u00c2\u00ac\\nclude purple martins and swallows. Bacterial larvicides,\\nBTI (Bacillus thuringiensis israelensis), and BS Bacillus\\nsphaericus) have been used successfully in a number of\\nwetlands.\\n6.4.6 Maintenance of Berms and Dikes\\nBerms and dikes require mowing, erosion control, and\\nprevention of animal burrows and tree growth. When the\\nwetland is operated at a shallow depth, periodic removal\\nof tree seedlings from the wetland bed may be necessary.\\nIf the trees are allowed to reach maturity, they may shade\\nout the emergent vegetation and with it the necessary con\u00c2\u00ac\\nditions to enhance flocculation, sedimentation, and deni\u00c2\u00ac\\ntrification.\\n6.5 Monitoring\\nRoutine monitoring is essential in managing a wetland\\nsystem. In addition to regulatory requirements, inflow and\\noutflow rates, water quality, water levels, and indicators of\\nbiological conditions should be regularly monitored and\\nevaluated. Monitoring of biological conditions includes\\nmeasurement of microbial populations and monitoring\\nchanges in water quality, percent cover of dominant plant\\nspecies, and benthic macroinvertebrate and fish popula\u00c2\u00ac\\ntions at representative stations. Overtime, these data help\\nthe operator to predict potential problems and select ap\u00c2\u00ac\\npropriate corrective actions.\\n6.6 References\\nAllen, H.H., G.J. Pierce, and R. Van Wormer. 1990. Consider\u00c2\u00ac\\nations and techniques for vegetation establishment in con\u00c2\u00ac\\nstructed wetlands. In: D.A. Hammer (ed.) Constructed wet\u00c2\u00ac\\nlands for wastewater treatment, municipal, industrial and\\nagricultural. Chelsea, Ml: Lewis Publishers, Inc.\\nGrits, M.A. and R.L. Knight. 1990. Operations optimization. In:\\nD.A. Hammer (ed.) Constructed wetlands for wastewater\\ntreatment, municipal, industrial and agricultural. Chelsea,\\nMl: Lewis Publishers, Inc.\\nKadlec, R.H. and R.L. Knight. 1996. Treatment wetlands. Boca\\nRaton, FL: CRC Press LLC.\\nRumer and Mitchell, 1996. Assessment of barrier containment\\ntechnologies. NTIS report PB 96-180583.\\nSuzuki, T., A.G. Wathugala, and Y. Kurihara. 1985. Preliminary\\nstudies on making use of Phragmites australis for the re\u00c2\u00ac\\nmoval of nitrogen, phosphorus, and COD from the waste\\nwater. UNESCO\u00e2\u0080\u0099s Man and Biosphere Programme in Ja\u00c2\u00ac\\npan, Coordinating Committee on MAB Programme, pp. 95-\\n99.\\nU.S. Environmental Protection Agency (EPA). 1993. Report of\\nworkshop on geosynthetic clay liners. EPA/600/R-93/171.\\nOffice of Research and Development, Washington, DC.\\nU.S. Environmental Protection Agency (EPA). 1994. Seminar\\nPublication: Design, operation, and closure of municipal\\nsolid waste landfills. EPA/625/R-94/008. Office of Re\u00c2\u00ac\\nsearch and Development, Cincinnati, OH.\\n119", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0135.jp2"}, "136": {"fulltext": "Chapter 7\\nCapital and Recurring Costs of Constructed Wetlands\\n7.1 Introduction\\nThe major items included in capital costs of constructed\\nwetlands are\\nLand costs\\nSite investigation\\nClearing and grubbing\\nExcavation and earthwork\\nLiner\\nMedia\\nPlants\\nInlet structures\\nOutlet structures\\nFencing\\nMiscellaneous piping, pumps, etc.\\nEngineering, legal, and contingencies\\nContractor\u00e2\u0080\u0099s overhead and profit\\nMost of these costs are directly dependent on the de\u00c2\u00ac\\nsign treatment area of the system, and the unit costs for\\nalmost all are essentially the same for FWS and VSB sys\u00c2\u00ac\\ntems. The major difference between the two concepts is\\nthe media cost (Table 7-1). In the case of a VSB, a 60 cm\\n(2 ft) depth of gravel typically fills the bed, whereas the\\nmedium for a FWS wetland consists of 15 cm (6 in) or\\nmore of topsoil used as growth media for the wetland veg\u00c2\u00ac\\netation.\\n7.2 Construction Costs\\n7.2.1 Total Construction Costs\\nThe cost data in this report were obtained from site vis\u00c2\u00ac\\nits to nine operational constructed wetland systems and\\nfrom related published sources. The nine systems were\\nAreata, CA; Gustine, CA; Mesquite, NV; Ouray, CO; West\\nJackson County, MS; Mandeville, LA; Sorrento, LA;\\nCarville, LA; and Ten Stones, VT. This group includes four\\nFWS wetlands and five VSBs with design flows ranging\\nfrom 0.3 to 175 L/s (6,700 gpd to 4 mgd). The start-up\\ndates for these subsystems range from 1986 (Areata, CA)\\nto 1997 (Ten Stones, VT). In order to provide a common\\nbase for comparison, all costs have been adjusted with\\nthe appropriate Engineering News Record (ENR) Construc\u00c2\u00ac\\ntion Cost Index (CCI) factor to August 1997 (ENR CCI\\n5854).\\nUnfortunately, it is not possible to extract the individual\\nline-item construction costs listed in Table 7-1 for most\\nexisting wetland systems because their construction con\u00c2\u00ac\\ntracts were let as lump sum bids for entire projects. In many\\ncases, the situation is further confounded since the lump\\nsum bids also may include preliminary treatment compo\u00c2\u00ac\\nnents, pumping stations, and community collection sys\u00c2\u00ac\\ntems. In addition, local conditions and site characteristics\\nalso significantly affect wetland system costs. VSB wet\u00c2\u00ac\\nlands in southern Louisiana, for example, pay a high price\\nfor imported gravel since none is available locally. Some\\nexisting wetland systems were converted from existing la\u00c2\u00ac\\ngoon cells. In these cases, the costs for clearing and grub\u00c2\u00ac\\nbing and excavation and earthwork would be minimal. As\\na result of these factors, it is not possible to derive general\\nnationally applicable cost-per-hectare unit cost. The best\\nthat can be achieved is a range of costs that may be use\u00c2\u00ac\\nful for an order-of-magnitude preliminary estimate.\\nTable 7-2 presents a summary of technical and cost data\\nfor the nine constructed wetland systems included in the\\nEPA case study visitations. The costs listed in the table\\nare the estimated construction costs for the wetland com\u00c2\u00ac\\nponent in each system at the time the system was con\u00c2\u00ac\\nstructed. It is difficult to draw general conclusions from the\\ndata because of the many variables involved. The sys\u00c2\u00ac\\ntems listed were designed with different design models and\\nprocedures to achieve different water quality goals, so the\\nrelationship between the treatment areas provided and the\\ndesign flow rates is not meaningful. The only nearly con\u00c2\u00ac\\nsistent factor is that land costs were zero in all cases ex\u00c2\u00ac\\ncept Ouray, CO, because the land was already in the pos\u00c2\u00ac\\nsession of the system owner. The costs given are based\\non actual construction costs and do not include a factor for\\nsystem design or site investigation. In most cases, the site\\ninvestigation costs for these nine systems were minimal\\n120", "height": "4267", "width": "3142", "jp2-path": "constructedwetla00nati_0136.jp2"}, "137": {"fulltext": "Table 7-1. Cost Comparison of 4,645 m 2 Free Water Surface Constructed Wetland and Vegetated Submerged Bed\\nFree Water Vegetated\\nSurface Wetland Submerged Bed\\nItem\\nUnits\\nUnit Price\\nTotal Cost\\nof Total\\nTotal Cost\\nof Total\\nExcavation/\\nCompaction\\nm 3\\n$2.30\\n13,000\\n19.4\\n13,000\\n10.7\\nSoil (45 cm)\\nm 3\\n$1.30\\n2,800\\n4.2\\nna\\nGravel (60 cm)\\nm 3\\n$20.95\\nNa\\n51,900\\n42.6\\nLiner (30 mil PC)\\nm 2\\n$3.75\\n19,250\\n28.7\\n19,250\\n15.8\\nPlants\\nEach\\n$0.60\\n7,500\\n(60 cm o.c.)\\n11.2\\n13,330\\n(45 cm o.c.)\\n10.9\\nPlumbing\\nLump sum\\n7,500\\n11.2\\n7,500\\n6.1\\nControl Structures\\nLump sum\\n7,000\\n10.4\\n7,000\\n5.7\\nOther\\nLump sum\\n10,000\\n67,050\\n14.9\\n100.0\\n10,000\\n121,980\\n8.2\\n100.0\\n4,645 m 2 50,000 ft 2\\nTable 7-2. Technical and Cost Data for Wetland Systems Included in 1997 Case Study Visitations\\nLocation\\nStartup\\nDate\\nArea\\n(hectares)\\nFlow\\n(m 3 /s)\\nNo.\\nCells\\nLiner\\nBerm\\nConst 2\\nLand\\nCost\\nConst.\\nCost\\n$/m 2\\nAdj. Cost 3\\n$/m 2\\nFree Water Surface Wetlands\\nAreata, CA\\n1986\\n3.0\\n66.2\\n3\\nNo\\nNo\\n$0\\n$225,000\\n7.43\\n10.12\\nGustine, CA\\n1987\\n9.8\\n22.8\\n24\\nNo\\nYes\\n$0\\n$882,000\\n9.04\\n12.27\\nOuray, CO\\n1993\\n0.9\\n8.7\\n4\\nYes\\nYes\\n$55,000\\n$108,500\\n12.16\\n13.02\\nW.J.C. MS\\n1997\\n20.2\\n54.8\\n7\\nNo\\nYes\\n$0\\n$700,000\\n3.44\\n3.44\\nVegetated Submerged Beds\\nCarville, LA\\n1986\\n0.3\\n3.4\\n1\\nNo\\nYes\\n$0\\n$100,000\\n38.64\\n52.64\\nMandeville.LA\\n1990\\n2.3\\n34.2\\n3\\nNo\\nNo\\n$0\\n$590,000\\n26.05\\n32.18\\nMesquite, NV\\n1991\\n1.9\\n9.1\\n12\\nNo\\nNo\\n$0\\n$515,000\\n27.13\\n32.83\\nSorrento, LA\\n1991\\n0.07\\n1.14\\n1\\nNo\\nYes\\n$0\\n$75,000\\n103.44\\n125.18\\nTen Stones, VT\\n1997\\n0.04\\n0.16\\n2\\nYes\\nYes\\n$0\\n$40,000\\n84.66\\n89.66\\n\u00e2\u0080\u0099A \u00e2\u0080\u0098No\u00e2\u0080\u0099 response is compacted native soil or pre-existing pavement\\n2 A \u00e2\u0080\u0098No\u00e2\u0080\u0099 response had pre-existing lagoon berms\\nAdjusted to August, 1997 costs (ENR CCI 5854)\\nHectares 2.47 acres; m 3 /s 22.83 mgd; m 2 10.76 ft 2\\nsince information pertaining to soil characteristics and ground\\nwater conditions was already available.\\nThere is some evidence of economy of scale in the tabulated\\ndata; the 20.2-hectare (50-acre) FWS wetland expansion at West\\nJackson County, MS, is the largest system listed and had the\\nlowest unit cost. Contributing factors are believed to be the lack\\nof a liner and minimal berm construction because of the small\\nnumber of relatively large cells selected for this project (seven\\ncells). Ouray, CO, had the highest unit costs listed for FWS wet\u00c2\u00ac\\nlands. This system required the use of a membrane liner and\\nhad significant construction costs for berms because of the num\u00c2\u00ac\\nber of small cells, in this case four cells on 0.89 hectares (2.2\\nacres). The system at Gustine, CA, shows a higher unit cost\\nthan Areata, CA, primarily due to the extra berm construction\\ninvolved. Other sources indicate that the cost per hectare for\\nlarge FWS systems is about one-third the cost of smaller FWS\\nwetlands, similar to the range presented in Table 7-2. The con\u00c2\u00ac\\nstruction costs for FWS wetlands might therefore range from\\nabout $34,600 per hectare to $237,200 per hectare ($14,000/\\nacre to $96,000/acre in 1997$), depending on the size of the\\nsystem, the number of cells and berms, and the need for a mem\u00c2\u00ac\\nbrane liner. The size of the system will depend on the water-\\nquality goals and local climatic conditions. Additional costs will\\ninclude any site investigation and engineering design, pre- and/\\nor post-treatment components, means for transferring waste-\\nwater to the treatment site and effluent from the site, and land\\ncosts.\\nEconomy of scale is apparent for the five VSB systems listed\\nin Table 7-2. The average unit cost for the two smallest sys\u00c2\u00ac\\ntems is at least twice that of the three larger systems. An-\\n121", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0137.jp2"}, "138": {"fulltext": "other major factor in these cost differences is due to the\\nsignificant differences in the local costs of the rock and\\ngravel media used. Sorrento, LA, for example, used\\ncrushed limestone imported from Mexico because speci\u00c2\u00ac\\nfied aggregate was not available in that part of Louisiana.\\nIn comparison, Mesquite, NV, used available media from\\na nearby gravel pit. Local gravel also was available for the\\nTen Stones, VT, system, but the system is conservatively\\ndesigned for the cold winter climate and has a higher unit\\ncost than Mesquite, NV. If the Sorrento costs are omitted,\\nthe construction costs for VSB wetlands may range from\\n$321,200 per hectare to $897,000 per hectare ($130,000/\\nacre to $363,000/acre in 1997$), depending on the size of\\nthe system, the need for a liner, and the local costs of gravel.\\nThe size of the system will depend primarily on the water-\\nquality goals and to a lesser degree on local climatic con\u00c2\u00ac\\nditions. Additional costs will include any site investigation\\nand engineering design, pre- and/or post-treatment com\u00c2\u00ac\\nponents, means for transferring wastewater to and/or from\\nthe treatment site, and land costs. These costs for VSB\\nwetlands are significantly higher than the highest costs cited\\nfor FWS wetlands.\\n7.2.2 Geotechnical Investigations\\nOnly four of the systems listed in Table 7-2 did not utilize\\nany preliminary geotechnical investigations. Three of these,\\nAreata, CA; Gustine, CA; and Mesquite, NV, utilized exist\u00c2\u00ac\\ning lagoon cells, and the underlying soil conditions were\\npresumably already known. The fourth system, Ten Stones,\\nVT, was relatively small, and the state regulatory agency\\nrequired a membrane liner regardless of the underlying\\nsoil characteristics, so a geotechnical investigation was\\nnot considered necessary. The other five systems utilized\\nsome shallow borings to verify expected soil conditions at\\nthe wetland site. The only system that retained cost data\\nfor this activity was Mandeville, LA, where approximately\\n$15,000 was allocated in 1989 for site surveys and soil\\nborings in the wetland area. The updated cost for survey\u00c2\u00ac\\ning and soil borings at the Mandeville wetland site would\\nbe about $2,720 per hectare ($1,100/acre) in 1997$.\\n7.2.3 Clearing and Grubbing\\nThree of the systems listed in Table 7-2 required clear\u00c2\u00ac\\ning and grubbing as part of their site preparation. Techni\u00c2\u00ac\\ncal details and related costs are listed in Table 7-3. The\\ncost data in Table 7-3 are compatible with experience in\\nthe general construction industry. Costs for clearing and\\ngrubbing on relatively level land can range from $4,940\\nper hectare ($2,000/acre) for brush and some small trees\\nto $12,355 per hectare ($5,000/acre) for a tree-covered\\nsite. Campbell and Ogden (1999) indicate southwestern\\ncosts at $2,965 per hectare ($1,200/acre).\\n7.2.4 Excavation and Earthwork\\nExcavation and earthwork typically includes grading the\\nwetland site to finished grade, constructing berms and\\naccess ramps, and in the case of FWS wetlands, reserv\u00c2\u00ac\\ning and replacing topsoil in the bed to serve as the vegeta\u00c2\u00ac\\ntion growth medium. Table 7-4 summarizes available cost\\ndata from the 1997 survey.\\nAn economy of scale is expected for earthwork costs\\nand is evident in the data for the small Ten Stones, VT,\\nproject where excavation costs were three times greater\\nthan the larger municipal-sized systems. All three sites\\nlisted were on relatively level land, with soils ranging from\\nclay at West Jackson County, MS, to silty loam at Ten\\nStones, VT. The average cost for the two municipal sys-\\nTable 7-3. Clearing and Grubbing Costs for EPA Survey Sites\\nLocation\\nSite Area\\n(hectares)\\nTotal\\nCost\\nCost\\nHectare\\nAdj. Cost 1\\n($/hectare)\\nWest Jackson Co., MS 2\\n20.2\\n$100,000\\n$4940\\n4940\\nSorrento, LA 3\\n1.6\\n$7,000\\n$4325\\n5235\\nOuray, CO 4\\n2.0\\n$22,700\\n$11,120\\n12,050\\nAdjusted to August, 1997 (ENR CCI 5854\\n2 Ground cover: brush and sparse tree seedlings\\n3 Ground cover: brush\\n4 Ground cover: trees\\nHectares 2.47 acres\\nTable 7-4. Excavation and Earthwork Costs for EPA Survey Sites\\nSite Area Quantity Total\\nLocation (hectares) (m 3 Cost\\n$/Hectare\\n$/m 3\\nAdj. Cost\\n($/m 3\\nW. Jackson Co., MS\\n20.2\\n52,000\\n$408,000\\n20,165\\n7.85\\n8.29\\nGustine, CA\\n9.7\\n34,400\\n$200,000\\n20,600\\n5.81\\n8.03\\nTen Stones, VT\\n0.04\\n355\\n$8,200\\n184,200\\n23.16\\n23.16\\nAdjusted to August, 1997 (ENR CCI 5854\\nHectares 2.47 acres\\nm 3 1.31 yd 3\\n122", "height": "4267", "width": "3142", "jp2-path": "constructedwetla00nati_0138.jp2"}, "139": {"fulltext": "terns shown is about $8.17 per cubic meter ($6.25/yd 3\\nAbout one-third of that cost could be assigned to excava\u00c2\u00ac\\ntion of the wetland bed to grade (on relatively level land),\\nwith the remainder for berm and ramp construction and\\nreservation and replacement of topsoil for the FWS sys\u00c2\u00ac\\ntem. Campbell and Ogden (1999) suggest $1.96 to $3.27\\nper cubic meter ($1.50 to $2.50/yd 3 as a default value for\\npreliminary estimates.\\n7.2.5 Liner Costs\\nA variety of materials, including the in situ native soils,\\nhave been used as liner material depending on the re\u00c2\u00ac\\nquirements of the regulatory agencies. The majority of the\\nsystems listed in Table 7-2 utilized the existing on-site soils\\nfor their liner material. Two of the remaining systems listed\\nin Table 7-2 used plastic membrane liners. Table 7-5 sum\u00c2\u00ac\\nmarizes these costs. These costs reflect the economy of\\nscale available for larger systems. The unit cost at Ouray\\nwas $5.27 per m 2 ($0.49/ft 2 while $10.01 per m 2 ($0.93/\\nft 2 was found at Ten Stones (1997$). Ouray used a 30-mil\\nHDPE liner, and Ten Stones used a prefabricated 30-mil\\nPVC liner. Other liner materials are also available, and typi\u00c2\u00ac\\ncal large system costs for some of these are presented in\\nTable 7-6. Where soils are rocky, a geotextile fabric or layer\\nof sand may be necessary beneath the synthetic liner to\\nprotect it from punctures. The liner will add $0.54 to $0.86/\\nm 2 ($0.05 to $0.08/ft 2 to the costs presented in Table 7-6.\\nThe costs of compaction and testing of clay liners can ex\u00c2\u00ac\\nceed $3.23/m 2 ($0.30/ft 2\\nTable 7-5. Liner Costs for EPA Survey Sites\\nLocation\\nTreatment Area\\n(hectares)\\nTotal Cost/\\nCost Hectare 1\\nAdj. Cost 2\\n($/hectare)\\nOuray, CO\\nTen Stones, VT\\n1.36 3\\n0.045\\n$64,000 $46,930\\n$4,500 $100,175\\n52,725\\n100,175\\nRepresents cost per hectare of treatment area. Actual liner area is\\nlarger to cover berms, etc.\\n2 Adjusted to August, 1997 (ENR CCI 5854)\\n3 Lined area at Ouray, CO includes lagoons and wetland cells.\\nHectares 2.47 acres 10,000 m 2\\nTable 7-6. Typical Installed Liner Costs for 9,300 Square Meter\\n(100,000 ft 2 Minimum Area\\nLiner Material $/m 2\\nBentonite (9.8 kg/m 2 and harrowed in place)\\n0.52-0.60\\nClay impregnated geosynthetic\\n0.37-0.60\\nAsphalt concrete\\n0.60-0.75\\nButyl rubber (50 mm thickness)\\n0.60\\nPVC (30 mil)\\n0.28-0.40\\nHDPE (40 mil)\\n0.35-0.40\\nHypalon (30 mil\\n0.55\\nHypalon (60 mil)\\n0.60-0.70\\nPPE (30 mil)\\n0.58-0.60\\nReinforced PPE (30 mil)\\n0.65\\nXR-5\\n0.85-0.92\\nm 2 10.76 ft 2\\n7.2.6 Media Costs\\nThe media in a FWS wetland are the soils placed on top\\nof the prepared bottom of the bed which serve as the growth\\nmedium for the emergent vegetation in the system. A simi\u00c2\u00ac\\nlar layer of topsoil is also usually applied to the berm slopes\\nto allow their revegetation. Placement of these soil layers\\nis usually included in the earthwork costs previously dis\u00c2\u00ac\\ncussed.\\nThe media used in a VSB are the gravel or rock placed\\nin the bed. They serve to support the growth of the vegeta\u00c2\u00ac\\ntion and to provide physical filtration, flocculation, sedimen\u00c2\u00ac\\ntation, and surfaces for attached microbial growth and ad\u00c2\u00ac\\nsorption to occur. Several different sizes of rock and gravel\\ncan be used in these systems. At the sites visited in the\\nEPA study, medium-sized gravel, 20-25 mm in diameter\\n(0.75-1 in), was used for treatment. Coarser rock, 40-50\\nmm in diameter (1.5-2 in), was used to surround the inlet\\nand outlet manifolds, and a layer of pea gravel, 5-10 mm\\nin diameter (1/4-3/8 in), was sometimes used to cap the\\ngravel in the treatment bed. Coarse stone, 10-15 cm in\\ndiameter (4-6 in), is sometimes used to cover the exposed\\nliner on the side slopes and to reduce the risk of burrowing\\nanimals. The unit cost of these materials depends on the\\nsize of the material, the volume needed, and the distance\\nfrom the source to the wetland site. The media is usually\\nthe most expensive part of the construction of a VSB, po\u00c2\u00ac\\ntentially representing 40 to 55% of total construction costs\\n(Table 7-1). Table 7-7 summarizes the costs for these ma\u00c2\u00ac\\nterials as derived from the 1997 site visitations.\\nThe local availability of gravel and the transport distance\\nto the VSB site are the key factors influencing media costs.\\nAs a result, the cost data in Table 7-7 should only be used\\nfor preliminary estimates. Local sources should be con\u00c2\u00ac\\ntacted for a detailed construction cost estimate. Based on\\nthe data in Table 7-7, the media costs (for the main bed)\\nrange from $74,130 to $133,440 per hectare ($30,000 to\\n$54,000/acre) depending on the local availability of suit\u00c2\u00ac\\nable material.\\n7.2.7 Plants and Planting Costs\\nPlant materials sometimes can be obtained locally by\\ncleaning drainage ditches. It is also possible to develop an\\non-site nursery at the wetland construction site if there is\\nsufficient advance time, or grow plant sprigs or seedlings\\nfrom seed and transplant these to the wetland cells. A large\\nand expanding number of commercial nurseries also exist\\nand can supply a large variety of plant species for these\\nwetlands systems. The majority of the systems listed in\\nTable 7-2 were planted with commercial nursery stock.\\nSmall systems are typically planted by hand; large sys\u00c2\u00ac\\ntems can use mechanical planters, and nursery-grown\\nsprigs or plant seedlings are advantageous for the pur\u00c2\u00ac\\npose. Hydroseeding has been successful with Typha seeds\\n(Gearheart et al., 1998). Table 7-8 summarizes available\\ncost data for plants and planting from the 1997 survey sites.\\nCampbell and Ogden (1999) quote a range of $0.50 to\\n$1.00 per plant in place as a default value, while Gearheart\\net al. (1998) estimate $12,355 per hectare ($5,000/acre)\\nfor a total planting cost.\\n123", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0139.jp2"}, "140": {"fulltext": "Table 7-7. Media Costs for VSBs from EPA Survey Sites\\nMedia Size\\nMedia Depth\\nMedia Quantity\\nCost\\nCost\\nAdj. Cost 1\\nLocation\\n(mm)\\n(m)\\n(m 3 /hectare)\\n($/m 3\\n(S/hectare)\\n($/hectare)\\nMesquite, NV\\nBed: 10-25\\n0.8\\n8,140\\n10.99\\n89,380\\n108,230\\nCarville, LA\\nTop: 20\\n0.15\\n1,525\\n27.14\\n41,325\\n44,735\\nBed: 40-75\\n0.60\\n6,100\\n20.21\\n123,160\\n133,320\\nTen Stones, VT\\nTop: 10\\n0.15\\n1,523\\n25.07\\n38,180\\n38,180\\nBed: 20-25\\n0.60\\n6,095\\n12.01\\n73,180\\n73,180\\nOutlets: 50\\n0.60\\n725\\n7.85\\n5,680\\n5,680\\nRipRap: 100\\n0.12\\n445\\n18.31\\n8,130\\n8,130\\nAdjusted to August, 1997 (ENR CCI 5854)\\nm 3 /hectare 1.89 yd 3 /acre\\nTable 7-8. Costs for Wetland Vegetation and Planting from EPA Survey Sites\\nPlant\\nAdj. Planting\\nPlant\\nDensity\\nPlanting\\nPlant Cost\\nPlanting Cost\\nCost\\nLocation\\nType\\n(no./hectare)\\nMethod\\n($/plant)\\n($/hectare)\\n($/hectare)\\nTen Stones, VT\\nCattails\\n35,830\\nHand\\n0.23\\nNot available\\nNot available\\nBulrush\\n35,830\\nHand\\n0.23\\nNot available\\nNot available\\nMandeville, LA\\nBulrush\\n15,000\\nHand\\nNot available\\n2,965\\n3,670\\nCarville, LA\\nPickerel Weed\\n34,595\\nHand\\nLocal sources\\n2,470\\n3,370\\nArrowhead\\n34,595\\nHand\\nLocal sources\\n2,470\\n3,370\\nSorrento, LA\\nNone\\nNone\\nNone\\nNone\\nNone\\nNone\\nGustine, CA\\nBulrush\\n46,950\\nMechanical\\nNot available\\n3,460\\n4,595\\nCattails\\n11,860\\nMechanical\\nNot available\\n1,975\\n2,695\\nOuray, CO\\nCattails\\n13,465\\nHand\\nLocal sources\\nNot available\\nNot available\\nBulrush\\n13,465\\nHand\\nLocal sources\\nNot available\\nNot available\\nWest Jackson Co., MS\\nCattails\\n11,860\\nMechanical\\n0.38\\n4,450\\n4,450\\nMesquite, NV\\nBulrush\\nNot available\\nHydroseeding\\nNot available\\nNot available\\nNot available\\nAreata, CA\\nBulrush\\n9,885\\nHand\\nNot available\\nNot available\\nNot available\\n\u00e2\u0080\u0099Adjusted to August, 1997 costs (ENR CCI\\n5854)\\nTable 7-9. Costs for Inlet and Outlet Structures from EPA Survey Sites\\nLocation Structure Type Weir Type\\nCost\\n($/structure)\\nAdj. Cost 1\\n($/structure)\\nWest Jackson Co., MS\\nConcrete box\\nBolted plate\\n2,500\\n2,500\\nCarville, LA\\nConcrete box\\nShear Gate\\n3,900\\n4,400\\nGustine, CA\\nConcrete box\\nStop log\\n1,125\\n1,500\\nTen Stones,VT\\n100 mm PVC manifold\\nNone\\n1,500\\n1,500\\nAdjusted to August, 1997 (ENR CCI 5854)\\n7.2.8 Cost of Inlet and Outlet Structures\\nThe inlet and outlet structures for most small- to moder\u00c2\u00ac\\nate-sized wetland systems are typically some variation of\\na perforated manifold pipe. Large wetland systems typi\u00c2\u00ac\\ncally use multiple drop or weir boxes for both inlets and\\noutlets. Adjustable water level outlet structures should be\\nused to control the water level in the wetland cell. If the\\noutlet is a pipe manifold, a water level-control structure\\nmust be added, which should cost about the same as a\\nweir box. Table 7-9 summarizes the available cost data\\nfrom the 1997 survey.\\n7.2.9 Piping, Equipment, and Fencing\\nCosts\\nThese items include the piping to transfer the wastewa\u00c2\u00ac\\nter to the wetland, the piping from the wetland to a dis-\\n124", "height": "4267", "width": "3142", "jp2-path": "constructedwetla00nati_0140.jp2"}, "141": {"fulltext": "charge point, and any pumps required for either of those\\npurposes. Fencing is typically installed around all munici\u00c2\u00ac\\npal wastewater treatment systems, but has not usually been\\nrequired around the smaller VSB wetland beds due to the\\nlow risk of public contact and exposure to the wastewater.\\nNone of these features are unique to wetland systems,\\nand costs for these items were not available at the sites\\nincluded in the 1997 EPA survey.\\n7.2.10 Miscellaneous Costs\\nThese costs include engineering design and legal fees,\\nconstruction contingencies, and profit and overhead for the\\nconstruction contractor. These costs are not unique to\\nwetland systems and are usually expressed as a percent\u00c2\u00ac\\nage of the total construction costs when preparing an esti\u00c2\u00ac\\nmate. Mobilization and bonding are also typically included\\nin the construction costs. Typical values for miscellaneous\\ncosts are as follow:\\nMobilization, 5% of direct costs\\nBonds, 3% of direct costs\\nEngineering design services, 15% of capital costs\\nConstruction services and start-up, 10% of capital costs\\nContractor\u00e2\u0080\u0099s overhead and profit, 15% of capital costs\\nContingencies, 15% of capital costs\\nThe following example illustrates the application of these\\nfactors. Assume direct project construction costs (i.e., la\u00c2\u00ac\\nbor, materials, equipment, etc.) are $300,000, therefore:\\nDirect construction costs\\n$300,000\\nMobilization, 5%\\n$15,000\\nBonds, 3%\\n$9,000\\nCapital cost of construction\\n$324,000\\nEngineering, 15%\\n$48,600\\nStart-up, 10%\\n$32,400\\nOverhead, profit and contingencies, 30%\\n$97,200\\nTotal capital costs\\n$502,200\\n7.2.11 Construction Cost Summary\\nThe major cost factors for both VSB and FWS wetlands\\nare compared in Table 7-10. The tabulated data are drawn\\nfrom previous tables for an assumed 0.405 hectare (one\\nacre) wetland with a membrane liner. The cost data are in\\nterms of dollars per hectare, and the percentage data are\\npercent of total cost. The latter can be used to determine\\nwhich system components are likely to be the most ex\u00c2\u00ac\\npensive. The cost data shown do not include the costs of\\nthe land, mobilization, fencing, landscaping, pre- or post\u00c2\u00ac\\ntreatment units, or the transfer piping to and from the wet\u00c2\u00ac\\nland site, and should only be used for preliminary, order-\\nof-magnitude cost estimates.\\nThe cost of gravel media for the VSB is the most expen\u00c2\u00ac\\nsive item in Table 7-10, followed by the membrane liner for\\nboth types of wetlands. The cost of the gravel media in the\\nVSB controls the cost regardless of the type of liner used.\\nIf site conditions allow for the compaction of native clay\\nsoil to produce an acceptable ground water barrier in lieu\\nof a synthetic membrane liner, then the liner costs can be\\neliminated. In this case, perforated pipe manifolds for inlet\\nand outlet structures are used instead of concrete weir\\nboxes.\\n7.3 Operation and Maintenance Costs\\nThe operation and maintenance of constructed wetland\\nsystems designed for wastewater treatment are relatively\\nsimple and require minimal time. They are similar to, but\\nsomewhat more than, the O M requirements for a facul\u00c2\u00ac\\ntative pond. Most of the operator\u00e2\u0080\u0099s time at a wetland treat\u00c2\u00ac\\nment system is spent servicing pumps, headworks, disin\u00c2\u00ac\\nfection, and other conventional components in the process.\\nAnimal (i.e., nutria, muskrats) control, vector (mosquitoes)\\ncontrol, and NPDES monitoring are probably the most time-\\nconsuming aspects of wetland operation and maintenance.\\nCrites and Ogden (1998) report the operating costs for FWS\\nconstructed wetlands and VSBs range from $0.10 to $0.30\\nand $0.04 to $0.08, respectively, per 3,785 L (1,000 gal) of\\ntreated water.\\nAt the FWS wetland system at Ouray, CO, the O M re\u00c2\u00ac\\nquirements for the wetland are as follows:\\nCheck berms for animal\\ndamage and erosion\\nOnce per week\\nCheck and clean effluent\\ndebris screens\\nOnce per week\\nObserve and adjust water\\nlevels and flow rates\\nOnce per month\\nRemove sludge from inlet\\nzone\\nAs required\\nFlush manifold pipes\\nAs required\\nMosquito control\\nAs required by local\\nhealth authorities\\nThe 1997 monthly operating costs for the complete treat\\nment system (aerated lagoon, FWS, chlorination/dechlori\\nnation) at Ouray, CO, were\\nPower for lagoon aerators\\n$1,400\\nLagoon sludge removal and disposal 800\\nMiscellaneous supplies\\n125\\nNPDES laboratory tests\\n300\\nWages\\n1,083\\nTotal\\n$3,708\\n125", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0141.jp2"}, "142": {"fulltext": "Table 7-10. Range of Capital Costs for a 0.4 Hectare (Membrane Lined VSB and FWS Wetland)\\nItem Vegetated Submerged Bed (VSB) Free Water Surface (FWS)\\nLow Cost Range\\nHigh Cost Range\\nLow Cost Range\\nHigh Cost Range\\nCost\\nPercent\\nCost\\nPercent\\nCost\\nPercent\\nCost\\nPercent\\n($/hectare)\\nof Total\\n($/hectare)\\nof Total\\n($/hectare)\\nof Total\\n($/hectare)\\nof Total\\nSurvey/Geotechnic\\n2,718\\n1.2\\n5,436\\n1.3\\n2,718\\n1.9\\n5,436\\n2.1\\nClear Grub 2\\n4,942\\n2.2\\n12,355\\n3.0\\n4,942\\n3.4\\n12,355\\n4.8\\nEarthwork 3\\n18,039\\n8.1\\n29,900\\n7.3\\n18,039\\n12.4\\n29,900\\n11.7\\nMembrane Liner 4\\n30 mil PVC\\n37,807\\n16.9\\n43,243\\n37,807\\n26.1\\n43,243\\n40 mil PE\\n43,243\\n48,432\\n43,243\\n48,432\\n40 mil PPE\\n53,869\\n59,305\\n53,869\\n59,305\\n45 mil Reinf. PPE\\n64,494\\n69,931\\n64,494\\n69,931\\n60 mil Hypalon\\n69,931\\n80,803\\n69,931\\n80,803\\nXR-5\\n102,301\\n113,174\\n27.5\\n102,301\\n113,174\\n44.4\\nMedia\\n129,483 s\\n57.8\\n199,413 s\\n48.5\\n16,062\u00c2\u00ae\\n11.1\\n20,015\u00c2\u00ae\\n7.8\\nPlants Planting 7\\n8,649\\n3.9\\n17,297\\n4.2\\n8,649\\n6.0\\n17,297\\n6.8\\nControl Structures\\n4,942\u00c2\u00ae\\n2.2\\n16,062\\n3.9\\n39,537 9\\n27.3\\n39,600\\n15.5\\nPlumbing Fencing\\n17,297\\n7.7\\n17,297\\n4.2\\n17,297\\n11.9\\n17,297\\n6.8\\nTotals:\\n233,877\\n100\\n410,935\\n100\\n145,050\\n100\\n255,012\\n100\\nAdjusted to 1997 dollars (ENR CCI 5854)\\n^Clearing and grubbing costs are higher for sites with large trees\\n3 Earthwork (excavation and compaction) costs are typically 2.00 to 3.25 per m 3 A 0.9 m deep excavation was assumed.\\n4 For rocky soils, add 5,435 to 8,645 per hectare to the costs presented. For a site employing a minimum of 9,300 m 2 of liner, deduct 5,435. Delete\\nthe costs for the liner if native clay liner is used.\\n5 Reported cost range is for 60 cm of gravel media with 15 cm of pea gravel. Gravel costs typically range from 17 to 26 per m 3 within 20 miles of the\\nproject. Longer delivery distances will increase the cost.\\n6 Assumes 15 cm of topsoil over the wetland bottom.\\nPlanting costs are typically 0.50 to 1.00 per plant. Values shown are for planting at 2.5 sq. ft centers. Adjust cost if different spacing is used.\\n8 122 m of 100 mm diameter PVC manifold plus one water level control box\\n9 Eight concrete weir box structures for inlets/outlets\\n,0 Uses 30 mil PVC liner\\nUses XR-5 liner\\n0.405 ha 1 acre\\nThe tasks specifically related to the wetland components\\nare estimated to require about 16 hours per month or about\\n$3,000 per year. On an areal basis, this equates to $3,370\\nper hectare per year ($1,364/acre per year) for this 0.89-\\nhectare (2.2-acre) wetland system. These wetland costs rep\u00c2\u00ac\\nresent about 7% of the total O M costs for the entire treat\u00c2\u00ac\\nment process. If more rigorous testing than the minimal\\nNPDES testing were required, then monitoring could become\\nthe most expensive cost of all O M categories shown.\\nThe annual O M expenses at the VSB system in Carville,\\nLA (0.15 mgd), are shown in Table 7-11. At Carville, the an\u00c2\u00ac\\nnual costs directly associated with the wetland components\\nare estimated to be $650 per year or $2,500 per hectare per\\nyear ($1,015/acre per year). These costs are about 6% of\\nthe total O M costs for the entire treatment system.\\nThe 1996 O M costs for the Gustine, CA, sewer depart\u00c2\u00ac\\nment were about $433,275, which included bond repayment,\\nengineering fees, and other contractual services. A single\\nmajor expense was $152,402 for electrical power for pumps\\nand the lagoon aerators. The direct O M costs for the sewer\\nsystem, the lagoons, and the wetland were $280,873. Since\\nthe wetland O M tasks at Gustine are similar to those previ\u00c2\u00ac\\nously described for Ouray and Carville, it can be assumed\\nthat the cost percentage determined at those systems is also\\napplicable at Gustine. Using a 7% factor, the annual wetland\\nO M costs at Gustine would be $19,661 or approximately\\n$2,025 per hectare per year ($819/acre per year).\\nAt Areata, CA, it is estimated that the O M tasks directly\\nrelated to the wetlands require 20 minutes of operator time\\nper day or 122 hours per year. The major tasks are weir\\nadjustments and berm inspections. At an assumed cost of\\n$30 per hour (including benefits, incidentals, and support\\ncosts), the annual O M costs for the Areata wetlands would\\nbe $1,205 per hectare per year ($488/acre per year).\\nFor the small system at Ten Stones, VT (6,700 gpd), one-\\nhalf hour per month is estimated to inspect the system and\\npumps and to adjust water levels if necessary. These efforts\\nwill be voluntary on the part of the corporation members, so\\nthere will be no actual cost for the service. However, if a\\ncontractual service were retained at the previously assumed\\nrate of $30 per hour, the annual maintenance costs would\\nbe $4,043 per hectare per year ($1,636/acre per year).\\nThe remainder of the systems included in the 1997 EPA\\nSurvey (West Jackson County, MS; Mandeville, LA; Mes\u00c2\u00ac\\nquite, NV; and Sorrento, LA) did not have recorded data for\\nseparate wetland O M costs, and estimates were not pro\u00c2\u00ac\\nvided. Table 7-12 summarizes the O M cost data that was\\navailable.\\nIt is not possible to divide the total annual O M costs shown\\nin Table 7-12 into ranked categories for the major O M tasks.\\nThe major O M tasks are visual inspections of the berms\\nand of plant health, and adjustments in water levels and other\\nflow-control structures as required. Both nutria and musk-\\n126", "height": "4267", "width": "3142", "jp2-path": "constructedwetla00nati_0142.jp2"}, "143": {"fulltext": "Table 7-11. Annual O M Costs at Carville, LA (570 m 3 /d) Veg\u00c2\u00ac\\netated Submerged Bed\\nAnnual Cost\\nItem (1997$)\\nElectricity\\nLagoon aerators\\n4,080\\nUV disinfection\\n316\\nMiscellaneous\\n350\\nMaintenance\\nRepair berms (30 man-hours)\\n478\\nMaintain UV system (60 man-hours)\\n956\\nBerm grass cutting (50 man-hours)\\n797\\nParts Supplies\\nAerators\\n230\\nUV System\\n800\\nFlow meter\\n25\\nNPDES Monitoring\\nLabor (192 man-hours)\\n3,209\\nMaterials\\n350\\nTotal\\n11,591\\nTable 7-12. Annual O M Costs for Constructed Wetlands\\nLocation\\nDesign Flow\\n(m 3 /d)\\nTreatment Area\\n(hectares)\\nCost\\n($/ha-yr)\\nOuray, CO (FWS)\\n1375\\n0.89\\n3370\\nGustine, CA (FWS)\\n3785\\n9.71\\n2025\\nTen Stones, VT (VSB)\\n25\\n0.05\\n4045\\nCarville, LA (VSB)\\n565\\n0.26\\n2510\\n\u00e2\u0080\u00991997$\\nrats can cause physical damage and leakage in the berms\\nand can destroy, as well as some insects, the plant cover in\\nthe wetland cells. If routine visual observations indicate\\ndamage, a more intense O M effort will be necessary for\\nrepair and animal or insect control.\\nActive mosquito control may be an issue in California\\nand in the southwestern and southeastern states, and the\\nFWS system O M costs will increase accordingly. None\\nof the systems listed in Table 7-12 were making special\\nefforts for either animal or mosquito control. On a long\u00c2\u00ac\\nterm basis, it will be necessary to remove accumulated\\nsediment from the wetland cells when it begins to interfere\\nwith the hydraulic performance of the system. A ramp for\\nthis purpose should be included in the design and con\u00c2\u00ac\\nstruction of each wetland cell.\\n7.4 References\\nCampbell, C.S. and M.H. Ogden. 1999. Constructed wet\u00c2\u00ac\\nlands in the sustainable landscape. New York, NY: John\\nWiley and Sons.\\nCrites, R.W. and M.H. Ogden. 1998. Costs of constructed\\nwetlands systems. Presented to WEFTEC, WEF 71st\\nAnnual Conference, Orlando, FL.\\nGearheart., R.A., B.A. Finney, M. Lang, and J. Anderson.\\n1998. A comparison of system planning, design, and\\nsizing methodologies for free water surface constructed\\nwetlands. In: 6th International Conference on Wetland\\nSystems for Water Pollution Control. IAWQ.\\nMiddlebrooks, E.J., C.H. Middlebrooks, J.H. Reynolds, G.Z.\\nWatters, S.C. Reed, and D.B. George. 1982. Waste-\\nwater stabilization lagoon design, performance, and\\nupgrading. New York, NY: Macmillan Publishing Co.\\n127", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0143.jp2"}, "144": {"fulltext": "Chapter 8\\nCase Studies\\nIn 1997, a series of site visits to constructed treatment\\nwetlands was performed for the U.S. EPA to compile back\u00c2\u00ac\\nground information and assess performance of free water\\nsurface (FWS) and vegetated submerged bed (VSB) wet\u00c2\u00ac\\nlands. Edited versions of these site visit reports are pre\u00c2\u00ac\\nsented in this chapter to enrich the reader\u00e2\u0080\u0099s understand\u00c2\u00ac\\ning with insight gained from actual construction and op\u00c2\u00ac\\neration of treatment wetland systems. Most quantifying\\nterms are expressed in English units. Conversion factors\\nare as follows:\\n1 acre 0.405 ha\\n1 mgd 3,780 m 3 /d\\n1 ft 0.3 m\\n1 gal/day-ft 2 4 cm/d 0.004 m 3 /m 2 -d\\n1 in 2.54 cm\\n1 lb 0.454 kg\\n8.1 Free Water Surface (FWS) Constructed\\nWetlands\\n8.1.1 Areata, California\\n8.1.1.1 Background\\nAreata is located on the northern coast of California about\\n240 miles north of San Francisco. The population of Areata\\nis about 15,000. The major local industries are logging,\\nwood products, fishing, and Humbolt State University. The\\nFWS constructed wetland located in Areata is one of the\\nmost famous in the United States.\\nThe community was originally served, starting in 1949,\\nwith a primary treatment plant that discharged undisinfected\\neffluent to Areata Bay. In 1957, oxidation ponds were con\u00c2\u00ac\\nstructed, and chlorine disinfection was added in 1966. In\\n1974, the State of California prohibited discharge to bays\\nand estuaries unless \u00e2\u0080\u009cenhancement\u00e2\u0080\u009d could be proven, and\\nthe construction of a regional treatment plant was recom\u00c2\u00ac\\nmended. In response, the City of Areata formed a Task\\nForce of interested participants, and this group began re\u00c2\u00ac\\nsearch on lower-cost alternative treatment processes us\u00c2\u00ac\\ning natural systems. From 1979 to 1982, research con\u00c2\u00ac\\nducted at pilot-scale wetland units confirmed their capabil\u00c2\u00ac\\nity to meet the proposed discharge limits. In 1983, the city\\nwas authorized by the state to proceed with development,\\ndesign, and construction of a full-scale wetland system.\\nConstruction was completed in 1986, and the system has\\nbeen in continuous service since that time.\\nThe wetland system proposed by the city was unique in\\nthat it included densely vegetated cells dedicated for treat\u00c2\u00ac\\nment followed by \u00e2\u0080\u009cenhancement\u00e2\u0080\u009d marsh cells with a large\\npercentage of open water for final polishing and habitat\\nand recreational benefits. This combined system has been\\nsuccessful since start-up and has become the model for\\nmany wetland systems elsewhere.\\nTwo NPDES permits are required for system operation:\\none for discharge to the enhancement wetlands for pro\u00c2\u00ac\\ntection of public access and one for discharge to the bay.\\nThe NPDES limits for both discharges are BOD 30 mg/L\\nand TSS 30 mg/L, pH 6.5 to 9.5, and fecal coliforms of 200\\nCFU/100 mL. Since public access is allowed to the en\u00c2\u00ac\\nhancement marshes, the state required disinfection prior\\nto transfer of the pond/treatment marsh effluent. The state\\nthen required final disinfection/dechlorination prior to final\\ndischarge to Areata Bay. The effluent from the final en\u00c2\u00ac\\nhancement marsh is pumped back to the treatment plant\\nfor this final disinfection step.\\nThe basic system design for the treatment and enhance\u00c2\u00ac\\nment marshes was prepared by Dr. Robert Gearheart and\\nhis colleagues at Humbolt State University. The design was\\nbased on experience with the pilot wetland system that\\nwas studied from 1979 through 1982.\\nThe pilot wetland system included 12 parallel wetland\\ncells, each 20 ft wide and 200 ft long (L:W 10:1), with a\\nmaximum possible depth of 4 ft. These were operated at\\nvariable hydraulic loadings, variable water depths, and\\nvariable initial plant types during the initial phase of the\\nstudy. Hardstem bulrush (Scirpus validus) was used as\\nthe sole type of vegetation on all cells. The inlet structure\\nfor each cell was a 60\u00c2\u00b0 V-notch weir, and the outlet used\\nan adjustable 90\u00c2\u00b0 V-notch weir, permitting control of the\\nwater depth. Heavy clay soils were used for construction\\nof these cells, so a liner was not necessary and seepage\\nwas minimal. The second phase of the pilot study focused\\non the influence of open water zones, plant harvesting,\\nand kinetics optimization for BOD, TSS, and nutrient re-\\n128", "height": "4267", "width": "3142", "jp2-path": "constructedwetla00nati_0144.jp2"}, "145": {"fulltext": "moval. Some of the cells, for example, were subdivided\\ninto smaller compartments with baffles and weirs along\\nthe flow path. The results from these pilot studies not only\\nprovided the basis for full-scale system design but have\\ncontributed significantly to the state-of-the-art for design\\nof all wetland systems.\\nThe full-scale treatment wetlands, with a design flow of\\n2.9 mgd, utilize three cells operated in parallel. Cells 1\\nand 2 have surface areas of about 2.75 acres each (L\\n600 ft, W 200 ft), and cell 3 is about 2.0 acres (L 510 ft,\\nW 170 ft). The original design water depth was 2 ft, but\\nat the time of the 1997 site visit for this report they were\\nbeing operated with a 4-ft depth. Hardstem bulrush was\\nagain used as the only plant species on these treatment\\nmarshes. Clumps of plant shoots and rhizomes were hand\\nplanted on about 1-m centers. Since nutrient removal is\\nnot a requirement for the full-scale system, the treatment\\nmarshes could be designed for a relatively short detention\\ntime primarily for removal of BOD and TSS. The HDT in\\nthese three cells is 1.9 d at design flow and a 2-ft water\\ndepth. These treatment marshes were designed to pro\u00c2\u00ac\\nduce an effluent meeting the NPDES limits for BOD and\\nTSS (30/30 mg/L) on an average basis. These wetland\\ncells utilized the bottom area of former lagoon cells. A sche\u00c2\u00ac\\nmatic diagram of the operating system is shown in Figure\\n8 1\\nThe final \u00e2\u0080\u009cenhancement\u00e2\u0080\u009d marshes were intended to pro\u00c2\u00ac\\nvide for further effluent polishing and to provide significant\\nhabitat and recreational benefits for the community. These\\nthree cells are operated in series at an average depth of\\n2.0 ft and have a total area of about 31 acres. Retention\\ntime is about 9 d at average flow rates. The first cell (Allen\\nMarsh), completed in 1981, was constructed on former log\\nstorage area and contains about 50% open water. The\\nsecond cell (Gearheart Marsh), completed in 1981, was\\nconstructed on former pasture land and contains about\\n80% open water. The third cell (Hauser Marsh) was con\u00c2\u00ac\\nstructed in a former borrow pit and contains about 60%\\nopen water. These 31 acres of constructed freshwater (ef\u00c2\u00ac\\nfluent) marshes have been supplemented with an addi\u00c2\u00ac\\ntional 70 acres of salt water marshes, freshwater wetlands,\\nbrackish ponds, and estuaries to form the Areata Marsh\\nand Wildlife Sanctuary, all of which has been developed\\nwith trails, an interpretive center, and other recreational\\nfeatures. The shallow water zones in these marshes con\u00c2\u00ac\\ntain a variety of emergent vegetation. The deeper zones\\ncontain submerged plants (Sago pondweed) that provide\\nfood sources for ducks and other birds and release oxy\u00c2\u00ac\\ngen to the water to further enhance treatment.\\nThe construction costs for the entire system, including\\nmodifications to the primary treatment plant, disinfection/\\ndechlorination, pumping stations, and so forth were\\n$5,300,000 (1985$). Construction costs for the treatment\\nwetlands are only estimated to be about $225,000, or\\n$30,000 per acre, or $78 per 1000 gpd of design capacity\\n(including removal of sludge from this site, which was pre\u00c2\u00ac\\nviously a sedimentation pond for an aerated lagoon). This\\ndoes not include pumping costs to transfer final effluent\\nback to the chlorination contact basin, disinfection facili-\\nFigure 8-1. Schematic diagram of wetland system at Areata, CA\\n129", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0145.jp2"}, "146": {"fulltext": "ties, or the pumping and piping costs to reach the enhance\u00c2\u00ac\\nment marshes. Land costs also are not included since the\\ntreatment wetlands were located on city-owned property.\\n8.1.1.2 Financial Arrangements\\nConstruction costs for the Areata system were funded\\nby a state/federal construction grant program with a grant\\nfor 85% of the project costs. O M costs for the system are\\npaid with a surcharge on the consumer\u00e2\u0080\u0099s water bills.\\n8.1.1.3 Construction and Start-up Procedures\\nThree of the final cells in the existing treatment pond\\nwere selected for the treatment wetlands. This allowed the\\nuse of city-owned land at no cost, a gravity flow connec\u00c2\u00ac\\ntion from the ponds, and clay soils that eliminated the need\\nfor liners and minimized the earthwork requirements. The\\nlagoon cells were drained and dried, local fill was placed\\nto the desired grade, and the wetland bottoms were graded\\nlevel. Shallow drainage channels were excavated to per\u00c2\u00ac\\nmit draining of the cell if desired. Construction of inlet and\\noutlet structures completed the construction activities. Each\\ncell has only one inlet and outlet structure. The wetland\\neffluent was collected from the bottom of the wetland in\\neach of these structures. The inlet structure has an adjust\u00c2\u00ac\\nable weir so the flow to the three cells can be balanced.\\nThe outlet weir is not adjustable and was originally de\u00c2\u00ac\\nsigned to maintain a 2-ft water depth in the cell. Prior to\\nthe 1997 site visit, timber sections had been bolted to the\\ntop perimeter of the outlet box. This raised the water level\\nin the bed and converted this box to a four-sided overflow\\nweir. This allowed wetland effluent to be decanted from\\nthe top of the wetland rather than off the bottom. The new\\n4-ft water depth was intended to suppress undesirable plant\\nspecies that had started to spread in the wetland.\\nThe treatment wetland cells were hand planted with\\nhardstem bulrush with clumps of shoots and rhizome ma\u00c2\u00ac\\nterial planted on about 1-m centers. These plants were\\nobtained from the pilot wetland channels. The wetland cells\\nwere flooded to a very shallow depth with tap water for\\nabout three months to encourage new plant development\\nand growth. Wastewater was not applied at full depth until\\nthe new plants were 3- to 4-ft tall and construction of the\\nrest of the system was complete (that is, effluent pump\\nstation and other features).\\nThe enhancement marshes were constructed on avail\u00c2\u00ac\\nable waterfront land but at some distance from the basic\\ntreatment system, so a pumping station and transmission\\npiping were required. These enhancement wetlands were\\nalso sited on clay soils, so extensive soils and geotechnical\\ninvestigations were not necessary. The grading for these\\nwetlands was more complex than the treatment wetlands\\nbecause berms did not previously exist, and it was de\u00c2\u00ac\\nsired to produce a wetland with different water depths and\\nwith several nesting islands in each cell. Each of these\\ncells also contains a single inlet and a single outlet struc\u00c2\u00ac\\nture. The final effluent comes through a highly vegetated\\nzone of emergent macrophytes with no open water. The\\nfinal cell is followed by a pumping station to return effluent\\nto the treatment plant for final disinfection and discharge.\\nThe entire treatment system is operated and maintained\\nby three operators who work five days per week and are\\non call on weekends. The only wetland-related O M task\\nis adjustment of the inlet weirs to ensure that flow is prop\u00c2\u00ac\\nerly balanced and to visually observe the status of the treat\u00c2\u00ac\\nment wetlands; this might require 20 minutes per day. With\\na total O M effort of 87 hours per year at an assumed rate\\nof $30/hr for operator costs, the O M costs for the treat\u00c2\u00ac\\nment wetlands alone would be $2,600 per year. The O M\\ncosts for the pumping and the double chlorination would\\nadd significantly to that, but these are unique to the Areata\\nsystem and not generic to all wetland systems. Harvesting\\nor other special vegetation-management activities are not\\npracticed at this site.\\n8.1.1.4 Performance History\\nPerformance data were collected for a two-year period\\nduring the Phase 1 pilot testing program. This program\\nvaried the flow rate and water depth in each of the two\\ncells to compare BOD removal performance at different\\ndetention times and loading rates that would represent the\\npotential range for full-scale application at Areata. These\\ndata are summarized in Table 8-1. The BOD and TSS in\\nthe pond effluent varied considerably during this period,\\nand not all of the cells were uniformly vegetated. Seasonal\\nvariations in performance were observed, but Table 8-1\\npresents only the average effluent characteristics for each\\nof the cells over the entire study period. It is apparent from\\nthe data that the wetlands were able to produce excellent\\neffluent quality over the full range of loadings and deten\u00c2\u00ac\\ntion times used.\\nThe long-term average performance of the Areata sys\u00c2\u00ac\\ntem is summarized in Table 8-2. It is clear that both the\\ntreatment and enhancement marshes provide significant\\ntreatment for BOD and TSS. The long- term removals fol\u00c2\u00ac\\nlow the pilot project results. Most of the nitrogen is removed\\nduring the final stage in the enhancement marshes. This\\nis because of the long hydraulic detention time (HRT 9\\nd), the availability of oxygen and nitrifying organisms in\\nTable 8-1. Summary of Results, Phase 1 Pilot Testing, Areata, CA\\n(cells 1-4 had received two different hydraulic loading rates for one\\nyear each-the higher loading occurred the first year)\\nItem\\nHRT\\nHLR\\nB0D 5\\nTSS\\nFECAL COLI\\n(Actual)\\ngal/ft 2 -d\\nmg/L\\nmg/L\\nCFU/100 ml\\nInfluent\\n26\\n37\\n3183\\nEffluent:\\nCell 1\\n2.1/10.7\\n5.89/1.22\\n11\\n6.8\\n317\\nCell 2\\n1.5/17\\n5.89/0.5\\n14.1\\n4.3\\n272\\nCell 3\\n2.7/29\\n4.66/0.5\\n13.3\\n4.7\\n419\\nCell 4\\n1.5/15\\n5.39/0.5\\n12.7\\n5.6\\n549\\nCell 5\\n3.7\\n2.94\\n14.0\\n4.3\\n493\\nCell 6\\n5.2\\n2.4\\n10.7\\n4.0\\n345\\nCell 7\\n5.2\\n4.4\\n13.3\\n7.3\\n785\\nCell 8\\n5.2\\n2.4\\n15.3\\n7.2\\n713\\nCell 9\\n6.6\\n1.71\\n11.9\\n9.4\\n318\\nCell 10\\n3.8\\n1.71\\n12.6\\n4.9\\n367\\nCell 11\\n7.6\\n1.47\\n9.4\\n5.7\\n288\\nCell 12\\n5.5\\n1.47\\n9.0\\n4.3\\n421\\n130", "height": "4267", "width": "3142", "jp2-path": "constructedwetla00nati_0146.jp2"}, "147": {"fulltext": "Table 8-2. Long-Term Average Performance, Areata WWTP\\nLocation\\nBOD\\nTSS\\nTN\\nmg/L\\nmg/L\\nmg/L\\nRaw Influent\\n174\\n214\\n40\\nPrimary Effluent\\n102\\n70\\n40\\nPond Effluent\\n53\\n58\\n40\\nTreatment Wetlands\\n28\\n21\\n30\\nEnhancement Marshes\\n3.3\\n3\\n3\\nthe open water zones, and anoxic conditions for denitrifi\u00c2\u00ac\\ncation in the areas with emergent vegetation.\\n8.1.1.5 Lessons Learned\\nThe treatment wetlands (7.5 acres), with nominal HRTs\\nof three days, met weekly limits of 30 mg/L BOD and TSS\\n90% of the time. The enhancement wetlands (28 acres),\\nwith a nominal HRT of 11 days, met weekly limits of less\\nthan 5 mg/L BOD/TSS 90% of the time. Performance of\\nboth wetlands results primarily from proper operation and\\nappropriate design that involves a combination of emer\u00c2\u00ac\\ngent vegetation and open water zones. TSS levels are\\nhigher in cell effluents where outlets are located in open\\nwater zones.\\nWetland habitat values and opportunities for research\\nand environmental education provided by the enhance\u00c2\u00ac\\nment marshes were optimized to gain state approval for a\\nnear-shore discharge to Areata Bay. Optimizing ancillary\\nbenefits appears also to have complemented treatment\\ncapabilities.\\nNitrogen leaving the treatment wetlands in the ammonia\\nform is nitrified in the open water zones in the enhance\u00c2\u00ac\\nment marshes, where deeper open water zones with sub\u00c2\u00ac\\nmerged stands of Sago pond weed (Potemogeton\\npectinatus) produce oxygen, and plant surfaces become\\nthe substrate for attached- growth nitrifying organisms. This\\nplant also offers important habitat values since it is a ma\u00c2\u00ac\\njor food source for many duck species. Long total deten\u00c2\u00ac\\ntion times (~9 d) and alternating open and vegetated zones\\nresulted in excellent nitrogen-removal performance.\\nDuckweed that grows on the open water surfaces is pre\u00c2\u00ac\\nvented from becoming a permanent duckweed mat by suf\u00c2\u00ac\\nficient wind action. In vegetated areas, duckweed does\\nmat, and it impedes reaeration.\\nDenitrification takes place in the fully vegetated anoxic\\nzones in the enhancement marshes.\\nMost of the fecal coliforms in the effluent are from birds\\nand other wildlife in the marshes and not from wastewater\\nsources.\\nPilot-scale marshes produced better treatment than the\\nfull-scale treatment wetlands, possibly due in part to the\\ndifferent configurations of the two systems and the possi\u00c2\u00ac\\nbility for short-circuiting in the larger full-scale cells. A 3:1\\naspect ratio for the full-scale cells is acceptable as long as\\nthe influent is uniformly distributed over the full width of\\nthe cell and the effluent collected in a comparable man\u00c2\u00ac\\nner.\\nShort-circuiting probably occurs in the treatment cells,\\nbut this could be corrected by replacing the single-point\\ninlet and outlet structures with perforated pipe manifolds\\nextending the full width of the cell.\\n8.1.2 West Jackson County, Mississippi\\n8.1.2.1 Background\\nThe West Jackson County (WJC) wastewater treatment\\nsystem is owned and operated by the Mississippi Gulf\\nCoast Regional Wastewater Authority. It is one of several\\ntreatment systems serving communities within the\\nAuthority\u00e2\u0080\u0099s boundaries. The system is located near Ocean\\nSprings, MS, on the north side of 1-10, about 20 miles east\\nof Biloxi, Mississippi.\\nThe original WJC system included a 75-acre, multiple\u00c2\u00ac\\ncell facultative lagoon for preliminary treatment followed\\nby 415 acres of slow-rate (SR) land treatment fields (grow\u00c2\u00ac\\ning hay). The land treatment site was underdrained, and a\\nportion of that recovered water was to be used to supple\u00c2\u00ac\\nment dry-weather flow into marshes in the Mississippi San\u00c2\u00ac\\ndhill Crane National Wildlife Refuge. This system com\u00c2\u00ac\\nmenced operation in October 1987 with a design flow rate\\nof 2.6 mgd and a 56 d HRT. Problems developed soon\\nafter start-up since the clay soils at the land treatment site\\nproved not to be as permeable as originally expected. Af\u00c2\u00ac\\nter extensive investigations and discussions, the design\\nconsultant agreed to design and construct a supplemental\\nfree water surface wetland to treat the excess flow.\\nThree parallel wetland units were constructed with a to\u00c2\u00ac\\ntal area of 56 acres to treat a design flow of 1.6 mgd. The\\ndischarge from this new wetland was to Castapia Bayou,\\nwith NPDES permit limits for BOD at 10 mg/L, TSS at 30\\nmg/L, NH 4 -N at 2 mg/L, DO at 6 mg/L, pH at 6.0 to 8.5, and\\nfecal coliforms at 2200/100 mL. Phase 1 of this new wet\u00c2\u00ac\\nland was placed in operation in 1990 and Phase 2 in 1991.\\nFigure 8-2 is a schematic diagram of the 56-acre wetland.\\nDetailed costs are not available for the Phase 1 and 2\\nwetlands since they were funded privately by the design\\nconsultant as part of the agreement with the Wastewater\\nAuthority. Costs for Phase 3 (2.4 mgd) are available.\\nThe Phase 1 wetland had two cells in series totaling 22\\nacres. The Phase 2 wetland (set 2) had three cells totaling\\n21.5 acres and another (set 3) which had two cells with a\\ntotal area of 12.5 acres. Local soils were all clays, so a\\nliner for these wetlands was not required. Bottoms of all\\nwetland cells were constructed with an average slope of\\n0.19% in the flow direction. At the end of each cell, mul\u00c2\u00ac\\ntiple weir boxes were used as outlet structures with ad\u00c2\u00ac\\njustable weir plates, allowing a maximum water depth in\\nthe outlet zone of up to 2 ft. At the mean depth of 0.75 ft,\\nthe design hydraulic residence times in the three wetlands\\nwere 12.5 d in Phase 1,10.1 d in Phase 2-2, and 10.7 d in\\n131", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0147.jp2"}, "148": {"fulltext": "Post Aeration\\nPhase 2\\nCell\\nArea-Acres\\n(hectares)\\n1A\\n12\\n(4.8)\\nIB\\n10\\n(4.0)\\n2A\\n10\\n(4.0)\\n2B\\n8\\n(3.2)\\n2C\\n4\\n(1-6)\\n3A\\n9\\n(3.6)\\n3B\\n3\\n(1.2)\\n4\\nFigure 8-2. Schematic diagram of Phase 1 and 2 wetland systems at West Jackson County, MS\\nPhase 2-3. The inlets to all three sets of cells used a 12-\\ninch perforated PVC pipe manifold. The elevation of the\\nPhase 1 wetland was slightly higher than the lagoon, so it\\nwas necessary to pump lagoon effluent to this wetland.\\nThe Phase 2 wetlands were at a lower elevation, and gravity\\nwas used as the motive force.\\nA unique feature of this wetland system was the incor\u00c2\u00ac\\nporation of \u00e2\u0080\u009cdeep zones\u00e2\u0080\u009d in each wetland cell. These con\u00c2\u00ac\\nsisted of trenches excavated perpendicular to the flow di\u00c2\u00ac\\nrection, with the bottom of the trench excavated about 5 ft\\nbelow the general wetland bottom surface. This provided\\na water depth of about 6 ft in these \u00e2\u0080\u009cdeep zones,\u00e2\u0080\u009d which\\nwas sufficient to prevent colonization by the emergent\\nwetland plants. These trenches are about 20 ft wide at the\\nbottom and about 40 ft wide at the top. The purpose of\\nthese \u00e2\u0080\u009cdeep zones\u00e2\u0080\u009d was to redistribute the flow across the\\nwidth of the cell to minimize short-circuiting and to provide\\nan open water surface for atmospheric reaeration to sup\u00c2\u00ac\\nply the oxygen necessary for ammonia removal. The po\u00c2\u00ac\\ntential open water provided by these zones was only about\\n10% of the surface area in each wetland cell. The water\\nsurface in these zones also quickly became colonized by\\nduckweed (Lemna spp.).\\nIn larger open water bodies, duckweed is very suscep\u00c2\u00ac\\ntible to wind action; as a result, the water surface can re\u00c2\u00ac\\nmain available for atmospheric reaeration. At this location,\\nwith the relatively narrow \u00e2\u0080\u009cdeep zones\u00e2\u0080\u009d and the protection\\nprovided by the adjacent emergent vegetation in the shal\u00c2\u00ac\\nlow portions of the marsh, wind was not sufficient to move\\nthe duckweed mat, and oxygen transfer from the atmo\u00c2\u00ac\\nsphere did not develop.\\nBecause there was insufficient oxygen in the system to\\ncontinuously support nitrification reactions, there were sea\u00c2\u00ac\\nsonal violations (particularly in late summer and early fall)\\nof the ammonia limits commencing in 1992. Corrective\\naction for this problem considered an external vertical-flow\\nfilter bed for nitrification and submerged tubing aeration in\\nthe \u00e2\u0080\u009cdeep zones\u00e2\u0080\u009d to provide the necessary oxygen. The\\nlatter was selected as the lower-cost alternative and was\\ninstalled in 1993. Problems again developed because nu\u00c2\u00ac\\ntria (an animal similar to a muskrat), which occupy the\\nwetland in large numbers, were attracted to the air bubbles\\nand destroyed the aeration tubing by gnawing on it. In sub\u00c2\u00ac\\nsequent discussions with the State of Mississippi, it was\\ndecided that the ammonia limit would not be enforced until\\nthe Castapia Bayou began to exhibit oxygen stress, so the\\naeration tubing was not replaced.\\nThe population is increasing rapidly in the communities\\nserved by this system, and by 1996 the average flow into\\nthese wetland units had reached 2.2 mgd. The Wastewa-", "height": "4267", "width": "3142", "jp2-path": "constructedwetla00nati_0148.jp2"}, "149": {"fulltext": "ter Authority then authorized an upgrade and expansion of\\nthe facility for a design flow of 5 mgd (1 mgd to land treat\u00c2\u00ac\\nment, 4 mgd to wetlands). The design was completed in\\n1996 and construction began in August 1997. The expan\u00c2\u00ac\\nsion included modifications to the lagoon (providing aera\u00c2\u00ac\\ntion and baffles), 50 acres of additional wetland area, a\\nplastic-media trickling filter bed for nitrification, UV disin\u00c2\u00ac\\nfection, and additional post-treatment aeration to ensure\\nadequate DO in the final effluent. The expanded wetland\\nsystem is shown in Figure 8-3. The trickling filter compo\u00c2\u00ac\\nnent has been designed but will not be constructed until\\nthe State of Mississippi decides it will be necessary. Re\u00c2\u00ac\\ncent data, shown in Figure 8-3, indicate that the open wa\u00c2\u00ac\\nter zones appear to be functioning well. A UV disinfection\\nsystem was added to the system because the NPDES\\npermit limits for fecal conforms have been modified to 200/\\n100 mL in the summer and 2000/100 mL in the winter.\\nAdditional features of the existing Phase 1 and Phase 2\\nwetlands include post-treatment aeration to satisfy the\\nNPDES discharge limit for dissolved oxygen (6 mg/L).\\nMultiple outlet structures with adjustable weirs are used\\nfor cell-to-cell transfer and for final discharges from the\\nwetlands. A miniature \u00e2\u0080\u009cdeep zone\u00e2\u0080\u009d was excavated around\\neach of these structures to prevent the growth of emer\u00c2\u00ac\\ngent vegetation in the immediate vicinity, as done for a\\nFWS system at Fort Deposit, AL. Published design mod\u00c2\u00ac\\nels were not used in this case, and effluent quality (Figure\\n8-3) is excellent.\\n8.1.2.2 Financial Arrangements\\nThe initial lagoon/land treatment system was funded\\nunder a federal/state construction grant program in exist\u00c2\u00ac\\nence at the time. The Phase 1 and 2 wetlands were funded\\ndirectly by the design consultant. The Phase 3 expansion\\nwas funded through a revolving loan fund as administered\\nby the State of Mississippi. Total costs for the entire Phase\\n3 project are estimated to be $2,758,000 (1997$). This\\nincludes lagoon modifications, UV disinfection, the nitrifi\u00c2\u00ac\\ncation trickling filter, and post-aeration. The costs for just\\nthe 50 acres of wetland expansion are estimated to be\\nabout $700,000, or $14,000 per acre, or $250 per 1000\\ngallons of design flow capacity. Land costs for this project\\nare not included in this estimate since the land already\\nbelonged to the Wastewater Authority. The O M costs are\\nfunded by a surcharge on each consumer\u00e2\u0080\u0099s water bill within\\nthe Authority\u00e2\u0080\u0099s service area.\\n8.1.2.3 Construction and Start-up Procedures\\nThe site for the original lagoon and land treatment site\\nwas selected for its proximity to the Mississippi Sandhill\\nCrane National Wildlife Refuge, where the treated effluent\\ncould be utilized in refuge marshes. The sites for the Phase\\nFigure 8-3. Schematic diagram of Phase 3 wetland expansion at West Jackson County, MS\\n133", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0149.jp2"}, "150": {"fulltext": "1 and 2 wetlands were selected to take advantage of avail\u00c2\u00ac\\nable land already owned by the Wastewater Authority and\\nfor proximity to Castapia Bayou for the system discharge\\npoint. As shown in Figure 8-3, the Phase 3 wetlands were\\nthen located to utilize the remaining land available on this\\nsite.\\nThe site investigation for the wetlands included a\\ngeotechnical investigation which indicated that ground\\nwater impacts or intrusion would be minimized by underly\u00c2\u00ac\\ning clay subsoil. Borings and test pits verified the pres\u00c2\u00ac\\nence of these clay soils throughout the proposed wetland\\narea. Wetland sites originally were covered with scrub pine\\nand related ground cover, so clearing and grubbing of the\\nsite was the first construction task. This was followed by\\nexcavation to grade with typical highway construction\\nequipment and construction of both the external and inter\u00c2\u00ac\\nnal berms with spoil material from the excavations. A liner\\nwas not necessary due to the low permeability of clay soils,\\nbut geotextiles were used adjacent to the inlet and outlet\\nstructures to prevent erosion. The multiple concrete outlet\\nand transfer structures were cast in place.\\nThe bulrush {Scirpus spp.) and cattails (Typha spp.) se\u00c2\u00ac\\nlected as the vegetation for this wetland system were ob\u00c2\u00ac\\ntained locally by cleaning drainage ditches within the\\nAuthority\u00e2\u0080\u0099s jurisdictional area. The plants were brought to\\nthe site and separated, and shoots were cut to about 1 ft in\\nlength and planted by hand in individually augured holes.\\nThe plants were placed on about 1 -m centers. At that den\u00c2\u00ac\\nsity, it would require about 227,000 plants to cover the origi\u00c2\u00ac\\nnal 56-acre wetland site. Observations at the time showed\\nthat two laborers could prepare and plant about 1,200\\nplants per day. At that rate it would require about 54 man\u00c2\u00ac\\nhours per acre to vegetate a wetland bed using this tech\u00c2\u00ac\\nnique.\\nAs soon as a zone was planted, it was flooded with a\\nvery shallow depth of stream water to encourage plant\\ngrowth. Lagoon effluent at the design depth was not ap\u00c2\u00ac\\nplied for at least 30 days after planting was completed. A\\npattern was adopted for Phase 1, on which alternating\\nbands of bulrush and cattails were planted. This was aban\u00c2\u00ac\\ndoned for Phase 2, so whichever species was available\\non a given day was planted; as a result, cattails were the\\ndominant species in Phase 2.\\n8.1.2.4 Performance History\\nAt the original 1.6-mgd wetland design flow rate, the\\nflow was split between the three wetland units: 0.6 mgd to\\nPhase 1,0.65 mgd to Phase 2-2, and 0.35 mgd to Phase\\n2-3. During the period 1992 to 1995, the average effluent\\ncharacteristics from the facultative lagoon were BOD 31\\nmg/L, TSS 33 mg/L, TKN 12.9 mg/L, and NH 4 -N 4.4 mg/L. Dur\u00c2\u00ac\\ning this same period, the combined final effluent from the wet\u00c2\u00ac\\nland units met all NPDES limits on an annual average basis:\\nBOD 7.5 mg/L, TSS 4.6 mg/L, and NH 4 -N 1.85 mg/L. On a\\nmonthly basis, there were excursions; the BOD exceeded\\npermit limits eight times (18%) and ammonia exceeded lim\u00c2\u00ac\\nits 11 times (25%). The BOD violations were randomly dis\u00c2\u00ac\\ntributed throughout the period and generally reflected\\nhigher-than-normal loading. A more specific pattern was\\nshown by the ammonia, with the violations occurring in\\nlate summer and early fall. By 1996 the flow rate to the\\nwetlands had increased to 2.35 mgd (47% higher than the\\noriginal 1.6 mgd design), and the excursions for both BOD\\nand NH 4 -N were more frequent. Table 8-3 summarizes per\u00c2\u00ac\\nformance data for the period January 1996 through July\\n1997. It would appear from the data in this table that BOD\\nremoval is slightly better in the warmer months, indicating\\nsome dependence.\\n8.1.2.5 Lessons Learned\\nThe inlet zone was submerged with a significant depth\\nof water, so the overland flow mode with very shallow sheet\\nflow did not develop. Ammonia removal provided by the\\nshallow sheet flow of water and the continuous availability\\nof oxygen intended for the system did not take place, even\\nwith the weirs at their lowest setting.\\n\u00e2\u0080\u009cDeep zones\u00e2\u0080\u009d in each cell were intended to provide ad\u00c2\u00ac\\nditional oxygen to support nitrification reactions, but this\\nbenefit was not realized when duckweed mats formed over\\nthe surface of the deep zones. A single large \u00e2\u0080\u009cdeep water\u00e2\u0080\u009d\\nzone in each cell, instead of multiple narrow trenches,\\nshould have allowed sufficient duckweed movement to\\nsustain atmospheric reaeration.\\nThe Phase 3 design provides both a perforated mani\u00c2\u00ac\\nfold and an open ditch \u00e2\u0080\u009cdeep zone\u00e2\u0080\u009d in the inlet area of the\\ncells to promote proper lateral distribution of the influent\\nand increased volume to capture incoming TSS.\\nBulrush plants had been almost completely removed by\\nmuskrats and nutria using these plants for food and nest\u00c2\u00ac\\ning material, but damage to cattails was minor. Damaged\\nTable 8-3. Wetland Water Quality, West Jackson Co., MS\\nDate\\nbod 5\\nIn\\nmg/L\\nOut\\nTSS, mg/L\\nIn Out\\nNl-L-\\n4\\nIn\\n-N mg/L\\nOut\\n1996\\nJan\\n36\\n10\\n28\\n12\\n7\\n4\\nFeb\\n32\\n13\\n21\\n10\\n12\\n4\\nMar\\n36\\n12\\n24\\n14\\n9\\n6\\nApr\\n30\\n14\\n18\\n6\\n9\\n6\\nMay\\n32\\n8\\n32\\n5\\n10\\n4\\nJun\\n38\\n6\\n38\\n3\\n18\\n4\\nJul\\n36\\n3\\n42\\n5\\n6\\n3\\nAug\\n37\\n9\\n60\\n12\\n12\\n2\\nSep\\n32\\n8\\n40\\n13\\n2\\n2\\nOct\\n34\\n8\\n90\\n7\\n2\\n1\\nNov\\n34\\n8\\n41\\n5\\n2\\n1\\nDec\\n20\\n10\\n17\\n3\\n1\\n1\\n1997\\nJan\\n33\\n13\\n18\\n5\\n1\\n1\\nFeb\\n23\\n9\\n17\\n6\\n2\\n2\\nMar\\n43\\n10\\n24\\n5\\n16\\n8\\nApr\\n41\\n9\\n23\\n4\\n9\\n6\\nMay\\n28\\n4\\n24\\n2\\n9\\n7\\nJun\\n47\\n6\\n23\\n2\\n1\\n2\\nJul\\n42\\n4\\n43\\n3\\n3\\n2\\n134", "height": "4267", "width": "3142", "jp2-path": "constructedwetla00nati_0150.jp2"}, "151": {"fulltext": "sections in Phase 1 were planned to be temporarily drained\\nand replanted with cattails. In the new Phase 3 addition,\\ncattails were proposed as the only plant in the bottoms,\\nand a variety of attractive flowering wetland species were\\nplanned for the inside perimeter of the new cells.\\nThe system supports large numbers of birds and other\\nwildlife, even though special measures to enhance habitat\\nvalues were not taken in Phases 2 and 3.\\nBirds and other wildlife in the wetlands appear to have a\\nsignificant impact on effluent fecal conforms from the sys\u00c2\u00ac\\ntem, with the final wetland effluent often higher than la\u00c2\u00ac\\ngoon effluent entering the wetland.\\n8.1.3 Gustine, California\\n8.1.3.1 Background\\nGustine is an agricultural community located in the Cen\u00c2\u00ac\\ntral Valley of California on the east side of 1-5 and about 60\\nmiles south of Stockton. There are several milk-process\u00c2\u00ac\\ning industries in the community that impose high organic\\nloadings on the municipal wastewater treatment system.\\nThe original treatment system consisted of an oxidation\\npond with 14 cells operated in series (HRT 56 d, aver\u00c2\u00ac\\nage pond depth 4 ft), with final discharge without disin\u00c2\u00ac\\nfection to a small stream. Approximately one-third of the 1\\nmgd design flow originates from domestic and commer\u00c2\u00ac\\ncial sources; the remaining two-thirds come from dairy prod\u00c2\u00ac\\nuct industries. This combination produces a high-strength\\nwastewater with an average BOD of about 1200 mg/L and\\nTSS of 450 mg/L, and these characteristics resulted in fre\u00c2\u00ac\\nquent violations of the 30 BOD/30 TSS NPDES discharge\\nlimits for the original lagoon system.\\nIn 1981, a Facility Plan for the city was funded under the\\nClean Water Act. This plan considered a number of alter\u00c2\u00ac\\nnatives for upgrading the existing treatment system. The\\nmost cost-effective alternative was assumed to be a facul\u00c2\u00ac\\ntative lagoon followed by a constructed free water surface\\n(FWS) wetland for final polishing to consistently meet the\\nNPDES discharge limits. Since design criteria for FWS\\nwetlands were not well established in 1981, a pilot test to\\ndevelop final design criteria was recommended.\\nA pilot study was approved and was conducted from\\nDecember 1982 to October 1983. The pilot system modi\u00c2\u00ac\\nfied an existing ditch that already contained a stand of cat\u00c2\u00ac\\ntails. The pilot cell was 39 ft wide and 900 ft long. Partially\\ntreated water was taken from various intermediate pond\\ncells. The influent to the pilot wetland averaged 180 mg/L\\nBOD and 118 mg/L TSS. At the operational water depth of\\n6 in, the HRT in the wetland averaged 2.5 d. The BOD and\\nTSS in the wetland effluent stabilized at 30 mg/L after the\\nstart-up period. Just prior to the pilot testing, one of the\\ndairy industries closed and was not expected to reopen.\\nThis resulted in lower-strength wastewaters than had been\\npreviously experienced, and these were expected to pre\u00c2\u00ac\\nvail in the future. The pilot results were used as the basis\\nfor the design and sizing of the full-scale wetland compo\u00c2\u00ac\\nnent. Construction of the system commenced in March\\n1986 and was completed in October 1987.\\nThree of the 14 existing lagoon cells (plus some addi\u00c2\u00ac\\ntional adjacent land) were selected as the site for the new\\nwetland component. This area was converted to 24 wet\u00c2\u00ac\\nland cells operating in parallel. Each cell had a net area of\\nabout 1 acre and was 38 ft wide and 1107 ft long (L:W\\n29:1), similar to the size and the configuration of the pilot\\nwetland unit. Internal berms constructed to separate the\\nwetland cells were 10 ft wide and 2 ft deep. An exterior\\nlevee 6.5 ft high was constructed around the entire wet\u00c2\u00ac\\nland area to provide protection from the hundred-year flood,\\nas required by the State of California. Influent flow from\\nthe lagoon passes through a distribution box where V-notch\\nweirs divide the flow into six equal parts. Each part of the\\nflow is then piped to a group of four cells. Gated aluminum\\npipe is used to distribute flow across the width of each cell.\\nIn order to provide flexibility for high-strength flows, a simple\\nstep-feed arrangement was designed. Pipe manifolds were\\nlocated at the inlet to each cell and at the one-third point\\nalong the flow path. Each manifold was valved so the op\u00c2\u00ac\\nerator could vary the amount of flow applied to each and\\nthereby avoid an overloaded inlet zone. An adjustable out\u00c2\u00ac\\nlet weir at the end of each cell allows a water depth rang\u00c2\u00ac\\ning from 4 to 18 in. These weirs discharge to a common\\nsewer, and the effluent is then pumped to the chlorine dis\u00c2\u00ac\\ninfection/dechlorination system. At the design flow of 1 mgd,\\nthe design projected an average HRT at higher loading of\\nabout seven days, which could be varied from 4 d in the\\nsummer to 11 d in the winter, depending on the number of\\ncells in operation and on the water depth used. This op\u00c2\u00ac\\nerational flexibility allowed for each cell to be taken out of\\nservice each summer for vegetation management or other\\nO M, if required. The system is schematically depicted in\\nFigure 8-4.\\nAt the time this system was designed, the capability to\\neffectively remove algae in FWS wetland systems was not\\nclearly established. This issue was a concern since very\\nhigh concentrations of algae were known to develop dur\u00c2\u00ac\\ning the summer months in some of the lagoon cells at\\nGustine. In order to provide the operator some control over\\nthis situation, the new design incorporated separate outlet\\nstructures in each of the last seven cells of the remaining\\n11-cell (in series) lagoon system. In this way, the operator\\ncould visually observe which cell(s) had the least amount\\nof algae present and select those for discharge to the wet\u00c2\u00ac\\nland.\\nSoon after the 1987 system start-up, the milk-process\u00c2\u00ac\\ning industry in Gustine that had been closed for several\\nyears was reopened and full-scale operations commenced.\\nThis imposed a higher than expected organic load on the\\ntreatment system; as a result, the lagoon/wetland system\\ncould not consistently meet the 30/30 (BOD/TSS) NPDES\\ndischarge limits, especially during the winter months. Fol\u00c2\u00ac\\nlowing consent decree discussions with the U.S. EPA, the\\nCity of Gustine evaluated the performance of the system\\nand recommended action that would bring the system into\\ncompliance. The major system modification resulting from\\nthis study was the addition of floating aerators to most of\\nthe lagoon cells in order to reduce the organic loading.\\n135", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0151.jp2"}, "152": {"fulltext": "a) Overall System Plan\\nb) Typical Wetland Cell Plan\\nFigure 8-4. Schematic diagrams of the wetland system at Gustine, CA\\nThe shallow 4-ft depth of the lagoon cells is not desirable\\nfor efficient aeration but was too expensive to modify. As\u00c2\u00ac\\npirator aeration equipment was selected for this project\\nbecause of the shallow water depth. This equipment was\\ninstalled in 1992, and the lagoon has performed accept\u00c2\u00ac\\nably since.\\n8.1.3.2 Financial Arrangements\\nFederal and state funding for the facility plan, the pilot\\nstudy, and the design and construction of the wetland sys\u00c2\u00ac\\ntem was provided under the Clean Water Act Construction\\nGrant Program administered in the early 1980s. The total\\nconstruction cost for this wetland system was $882,000\\n(August 1985$). This includes the cost of the multiple-pond\\noutlet structures and related piping and the 6.5 ft levee\\naround the perimeter of the wetland area. On an area ba\u00c2\u00ac\\nsis (24 acres of treatment area), the cost would be $36,750\\nper acre. On a design flow basis (1 mgd system), the cost\\nwould be $882 per 1000 gpd of treatment capacity. Land\\ncosts are not included since the area was already owned\\nby the city. The gross area utilized was about 36 acres for\\nthe wetlands, levees, and disinfection facilities.\\nFor this facility, O M costs are funded by a surcharge\\non the consumer\u00e2\u0080\u0099s water bill. The City of Gustine budgeted\\n$433,275 in 1996 for operation and maintenance of the\\nwastewater treatment and sewerage systems in the com\u00c2\u00ac\\nmunity. Based on a 1 -mgd design flow, the unit costs would\\nbe $1.19 per 1000 gallons treated. The O M costs for just\\nthe wetland component are minimal and might represent\\nless than 10% of the total (e.g., $0.12/1000 gpd).\\n8.1.3.3 Construction and Start-up Procedures\\nThere were no soils or geotechnical or ground water in\u00c2\u00ac\\nvestigations at this site prior to or during construction. The\\nlocal soils were clays and the existing lagoons are unlined,\\nand it could therefore be assumed that the wetland cells\\nwould not require lining. The site lay within the flood plain\\nof a small local stream, and the State of California did re\u00c2\u00ac\\nquire a 6.5-ft high levee to protect the new wetland system\\nfrom the hundred-year flood.\\nConstruction commenced with the draining and drying\\nof the three existing lagoon cells and clearing and grub\u00c2\u00ac\\nbing of the adjacent land required to complete the system.\\n136", "height": "4267", "width": "3142", "jp2-path": "constructedwetla00nati_0152.jp2"}, "153": {"fulltext": "The entire wetland area was excavated to grade, with a\\nflat bottom, and then the interior berms were placed as\\nfill. Construction of the inlet and outlet structures and\\nthe related piping completed the physical aspects of the\\nwetland system.\\nCattails (Typha latifolia) and tristar bulrush (Scirpus\\ncalifornicus) were selected for use on this wetland\\nproject. The specifications required that 18 of the cells\\nwould be planted with cattail rhizomes on 3-ft centers,\\nand the remaining six cells would be planted with bul\u00c2\u00ac\\nrush rhizomes on 1.5-ft centers. During the first plant\u00c2\u00ac\\ning attempt in September 1986, rhizomes of both plant\\nspecies were obtained at local natural stands and spread\\non the wetland surfaces and disked into the soil. Water\\nwas not available for irrigation and very few plants\\nemerged the following spring. The second planting at\u00c2\u00ac\\ntempt occurred in June 1987 and consisted of mechani\u00c2\u00ac\\ncal planting of cattail seedlings obtained at a nursery.\\nThe bed was then flooded with high-BOD pond effluent.\\nAlmost all of the plants died in a short time. It is be\u00c2\u00ac\\nlieved this was due to heat stress (the air temperatures\\nwere 100%F) and the high oxygen demand from the\\npoorly treated water used to irrigate. The contractor also\\nseeded the wetland area by broadcasting mixed bul\u00c2\u00ac\\nrush seed (hardstem and tristar). Some live cattail plants\\nwere also transplanted to the wetland beds from local\\ndrainage ditches. These more mature plants survived,\\nwhereas the small seedlings did not. By the fall of 1987,\\na few of the cells were almost completely covered with\\nbulrush plants, but the majority contained random stands\\nof bulrush and isolated patches of cattails.\\nAs a result of these planting problems, the system\\nstarted up in 1987 with insufficient plant cover to pro\u00c2\u00ac\\nvide the necessary substrate for treatment and an or\u00c2\u00ac\\nganic loading that was more than double the design load.\\nIn the spring of 1988, about half of the cells had moder\u00c2\u00ac\\nately dense growth over about 75% of the cell area. The\\nother half of the system contained only random patches\\nof bulrush and cattails. This situation improved slowly\\nduring subsequent years; at the time of the 1989-1990\\nwetland evaluation, the wetland cells were still not com\u00c2\u00ac\\npletely covered with vegetation.\\nThe hardstem and tristar bulrush gradually spread and\\nbecame the dominant species on the system. The wet\u00c2\u00ac\\nland could be considered to be completely vegetated\\nsince early 1993. However, during the 1997 site visit for\\nthis report, patches of sparse vegetation and some open\\nwater areas were still observed on some cells. As the\\ndensity of the vegetation increased, it began to create\\nhydraulic problems for operation of the system. Flow\\nthrough these FWS wetlands is thought to be governed\\nby Manning\u00e2\u0080\u0099s equation. The frictional resistance to flow\\nthrough a wetland bed is significantly higher than in a\\nnormal grassed drainage channel since the vegetation\\n(and litter) exists throughout the full depth of the water\\ncolumn. This resistance obviously increases and the\\nlength of the flow path increases. A system with a high\\naspect ratio (29:1 at Gustine) has the potential to de\u00c2\u00ac\\nvelop a high enough resistance to force the water level\\nat the inlet to increase very significantly in order to pro\u00c2\u00ac\\nvide the necessary hydraulic gradient. This occurred at\\nGustine, and the water level at the inlets overtopped the\\nshallow berms. The operator had two options to solve this\\nproblem: increase the height of the berms or reduce the\\nresistance to flow. He chose the latter course and got per\u00c2\u00ac\\nmission to burn the vegetation in late fall after senescence.\\nThis immediately solved the hydraulic problem, and burn\u00c2\u00ac\\ning has become an annual occurrence at Gustine.\\nThere were no special start-up procedures used at this\\nsystem, and pond effluents at the full rate were applied to\\nall of the wetland cells regardless of vegetation coverage\\nin the fall of 1987. However, until corrective action was\\ntaken in 1992 to reduce the organic loading in the ponds,\\nthe system frequently did not meet the NPDES discharge\\nlimits.\\n8.1.3.4 Performance History\\nAs described in the previous section, this system did not\\nconsistently meet the NPDES limits at start-up and for sev\u00c2\u00ac\\neral years thereafter. The problem was due to a higher\\nthan expected organic load (particularly in the winter\\nmonths) and the lack of significant vegetation coverage\\non most of the wetland cells. The vegetation and litter in\\nthese FWS systems serve as the means for enhanced floc\u00c2\u00ac\\nculation and sedimentation that actually perform the treat\u00c2\u00ac\\nment. The importance of this vegetation and litter can be\\nseen by comparing the data in Table 8-4. These are per\u00c2\u00ac\\nformance results obtained during the 1989-1990 winter in\\nthe special evaluation study, when several cells in the\\nGustine wetlands were isolated and a careful performance\\nevaluation was conducted over a one-year period. One\\ncell (#6D in their set) was almost completely vegetated\\nwith bulrush; the other cell (#2A in their set) listed in Table\\n8-4 was sparsely vegetated with some bulrush and cat\u00c2\u00ac\\ntails. The influent BOD was slightly different for the two\\ncells because different source ponds were in use, but dur\u00c2\u00ac\\ning the period of concern the influent values were in the\\nsame range. The HRT during this period was about 10 d\\nfor both cells.\\nThis FWS wetland system has had problems in meeting\\nits NPDES discharge limits since start-up. During the pe\u00c2\u00ac\\nriod 1987 to 1992, the problem was believed to be an or\u00c2\u00ac\\nganic overload on both the lagoon pretreatment and on\\nthe wetland component in this system as evidenced by\\nthe data in Table 8-4. The system design expected a BOD\\nconcentration of 150 mg/L entering the wetland, but the\\nactual average wetland influent BOD during this initial pe\u00c2\u00ac\\nriod was close to 300 mg/L, with weekly excursions up to\\n630 mg/L during the winter months. This problem was com\u00c2\u00ac\\npounded by the immature vegetative growth in the wet\u00c2\u00ac\\nland cells that significantly reduced the flocculation/sedi\u00c2\u00ac\\nmentation treatment potential. The organic loading prob\u00c2\u00ac\\nlem was corrected by the addition of aeration capacity to\\nthe lagoon component, and the plant density has gradu\u00c2\u00ac\\nally increased on the wetland cells.\\n137", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0153.jp2"}, "154": {"fulltext": "Table 8-4. Performance Results in Mature Vegetated vs Immature Vegetated FWS Cells, Gustine, CA\\nFull Vegetation Partial Vegetation\\nBOD 5 mg/L TSS, mg/L BOD 5 mg/L TSS, mg/L\\nMonth Temp In Out In Out In Out In Out\\n1989-90 \u00c2\u00b0F*\\nNov\\n50\\n54\\n8\\n72\\n13\\n49\\n20\\n80\\n24\\nDec\\n43\\n154\\n17\\n103\\n6\\n150\\n66\\n104\\n42\\nJan\\n44\\n525\\n35\\n116\\n24\\n515\\n153\\n113\\n71\\nFeb\\n45\\n483\\n29\\n79\\n19\\n478\\n123\\n86\\n49\\nMar\\n56\\n215\\n16\\n100\\n17\\n185\\n21\\n94\\n20\\nAvg\\n286\\n21\\n94\\n16\\n275\\n77\\n95\\n41\\nAverage water temperature in the marsh cells\\nTable 8-5 presents current wetland effluent BOD and TSS\\nvalues for 1996-1997. Ammonia (NH3) and Kjedahl nitro\u00c2\u00ac\\ngen (TKN) values also were measured during the first half\\nof 1996 and are shown in Table 8-5. Wetland influent char\u00c2\u00ac\\nacteristics were not measured during this period, but the\\nnew aerators in the lagoon cells were operating continu\u00c2\u00ac\\nously, so it can be assumed that the organic loading on\\nthe wetland probably does not exceed the original design\\nexpectations. During 1996 the average daily flow into the\\ntreatment system was 1.02 mgd, which is essentially equal\\nto the design capacity, so the system is not overloaded\\nhydraulically. It is clear from these data that this wetland\\nsystem is still having difficulty meeting the NPDES dis\u00c2\u00ac\\ncharge limits. The effluent BOD exceeded 30 mg/L twice\\nduring 1996 and once during the first half of 1997; the ef\u00c2\u00ac\\nfluent TSS met the 30 mg/L limit three times during 1996\\n(25% of the time) and three times during the first half of\\n1997 (50% of the time).\\n8.1.3.5 Lessons Learned\\nPoor performance evident in the 1996-1997 data may\\nnot have been caused by an organic overload, since the\\neffluent BOD had been significantly below the discharge\\nlimit most of the time, and the few BOD excursions were\\nrelatively small and occurred mostly during the warm\\nmonths. Birds and other wildlife may be a contributing fac\u00c2\u00ac\\ntor. Detritus and similar natural organic materials may also\\nbe a source for the excess TSS.\\nPlant litter allowed to accumulate in the cells may im\u00c2\u00ac\\nprove water quality. With the litter burned each year, sol\u00c2\u00ac\\nids entrapment must depend on living plants. Also, the\\ntristar bulrush that dominates many of the wetland cells\\nhas narrow stalks and no leaves, so the plants\u00e2\u0080\u0099 surface\\narea beneath the water surface is minimal, further reduc\u00c2\u00ac\\ning entrapment of solids. However, plant litter in the chan\u00c2\u00ac\\nnels caused hydraulic failure when resistance to flow in\u00c2\u00ac\\ncreased and the cells overflowed their banks at the entry\\nzone, owing to the excessive L:W ratio.\\nThe hydraulic problem was corrected in 1995 when three\\ninterior berms in each set of four cells were removed and\\nsome of the surplus material was used to increase the\\nheight of the remaining berms. This action reduced the\\nsystem to six larger cells, changed the aspect ratio from\\n26:1 to 5.5:1, and increased water depth near the entry\\nzone. Removing the three interior berms also opened up\\nan additional 30,000 ft 2 in each of the remaining cells to\\nserve as part of the wetland.\\nThe initial selection of long, narrow wetland channels\\nwas consistent with wetland design experience available\\nin 1983-1984, but experience has since shown that proper\\ntreatment can be achieved in FWS wetlands with aspect\\nratios as low as 2:1 to 3:1 as long as the system is prop\u00c2\u00ac\\nerly constructed and the inlet and outlet structures allow\\nfor uniform flow through the system.\\nSeparate outlet structures at seven of the 11 lagoon cells\\nallow the operator to select the lagoon cell(s) with the least\\nalgae for discharge to the wetland. This technique has been\\nvery effective at algae removal as long as sufficient plants\\nand litter are present in the wetland, and as long as veloc\u00c2\u00ac\\nity of flow in large open water zones is sufficient to prevent\\nredevelopment and discharge of algae to the FWS sys\u00c2\u00ac\\ntem.\\nToxicity discharge limits imposed by the State of Califor\u00c2\u00ac\\nnia for un-ionized ammonia could not be met by the exist\u00c2\u00ac\\ning pond-wetland system in the present mode of opera\u00c2\u00ac\\ntion. The existing point discharge is planned to be aban\u00c2\u00ac\\ndoned and the effluent from the wetland component to be\\nused for irrigation in a slow-rate land-treatment system.\\n8.1.4 Ouray, Colorado\\n8.1.4.1 Background\\nOuray is located in southwestern Colorado, about 60\\nmiles north of Durango, on State Route 50. Its population\\nis about 2,500 in summer and about 900 in winter. The\\ntown is at an elevation of 7,580 ft in a mountain valley and\\nexperiences severe winter conditions.\\nThe free water surface (FWS) wetland at Ouray receives\\ninfluent from a two-cell aerated lagoon and provides sec\u00c2\u00ac\\nondary treatment prior to chlorine disinfection/dechlorina\u00c2\u00ac\\ntion and final discharge to the Uncompahgre River. The\\nNPDES monthly average discharge limits are BOD 5 30 mg/\\nL, TSS 30 mg/L, and fecal coliforms 6000 CFU/100 mL.\\nThe wetland was designed for an expected winter water\\ntemperature of 3\u00c2\u00b0C and a summer water temperature of\\n20\u00c2\u00b0C, with a 25% safety factor on sizing for BOD removal,\\nbased on existing design equations.\\n138", "height": "4267", "width": "3142", "jp2-path": "constructedwetla00nati_0154.jp2"}, "155": {"fulltext": "Table 8-5.\\nMonth\\nWetland Effluent Characteristics, Gustine, CA\\nTemp. \u00c2\u00b0F BOD 5 mg/L\\nTSS, mg/L\\nNH 4 -N mg/L\\nTKN, mg/L\\n1996\\nJAN\\n48\\n21\\n20\\n13\\n15\\nFEB\\n54\\n20\\n22\\n16\\n18\\nMAR\\n55\\n16\\n24\\n11\\n16\\nAPR\\n61\\n30\\n45\\n4\\n7\\nMAY\\n64\\n29\\n57\\n3\\n9\\nJUN\\n72\\n18\\n41\\n2\\n7\\nJUL\\n75\\n22\\n36\\n7\\n15\\nAUG\\n70\\n47\\n71\\nSEP\\n63\\n32\\n39\\nOCT\\n59\\n26\\n43\\nNOV\\n52\\n28\\n42\\nDEC\\n48\\n24\\n50\\n1997\\nJAN\\n48\\n25\\n26\\nFEB\\n50\\n22\\n27\\nMAR\\n54\\n27\\n38\\nAPR\\n61\\n24\\n34\\nMAY\\n66\\n22\\n26\\nJUN\\n70\\n31\\n34\\nThe design flow for the 2.2-acre wetland system is 0.250\\nmgd in winter and 0.363 mgd in summer. As shown in Fig\u00c2\u00ac\\nure 8-5, the wetland includes two parallel trains with three\\ncells each. The two trains operate in parallel, and one can\\nbe taken out of service during the summer months for\\nmaintenance if required. The curved configuration of these\\nwetland cells was selected in part because of the confined\\nsite and in part for aesthetic reasons. The water depth in\\nthe cells is adjustable via the outlet from a minimum of 8 in\\nto a maximum of 18 in. This water level is increased to the\\nmaximum depth prior to the onset of winter to provide the\\nmaximum possible detention time during the low tempera\u00c2\u00ac\\nture periods and to provide additional depth for ice forma\u00c2\u00ac\\ntion on the water surface during the winter months.\\nA perforated manifold is used for both inlet and final out\u00c2\u00ac\\nlet structures for the two sets of cells. Internal transfer from\\ncell to cell is accomplished with two parallel pipes through\\neach internal berm. The wetland cells are lined with 30-mil\\nHDPE membrane liners to prevent seepage since the lo\u00c2\u00ac\\ncal soils are sandy clay loams. The detention time in the\\nsystem depends on water depth and on the presence of\\nwinter ice. At minimum water depth the HRT is 2.2 d; at\\nmaximum water depth without ice, the HRT is 3.8 d. Lo\u00c2\u00ac\\ncally obtained cattails (Typha spp.) and bulrush (Scirpus\\nspp.) were planted in the wetland cells. The vegetation is\\ncontinuous, and there are no intended open water zones.\\nThe wetland was designed in 1992, constructed during\\nthe spring and summer of 1993, planted in October 1993,\\nand placed in partial operation in November 1993. It has\\nbeen in continuous operation since that time.\\nThe construction costs for the entire system, including\\naerated lagoons, chlorine disinfection/dechlorination equip\u00c2\u00ac\\nment, and miscellaneous features was $816,530 (1993$).\\nConstruction costs for just the treatment wetlands is esti\u00c2\u00ac\\nmated to be about $108,500 or $49,300 per acre, or $300\\nper 1000 gpd of design capacity.\\n8.1.4.2 Financial Arrangements\\nThe construction costs for the Ouray system were funded\\nby a state revolving-loan fund as administered by the State\\nof Colorado in 1993. O M costs for the system are funded\\nwith a surcharge on the consumer\u00e2\u0080\u0099s water bills. The total\\nmonthly O M cost for the entire system at Ouray is $2,625;\\nmost of this is related to power costs, sludge removal from\\nthe aerated lagoon, and laboratory testing for NPDES\\nmonitoring. The average O M costs for the wetland com\u00c2\u00ac\\nponent is estimated to be about $200 per month for minor\\nmaintenance tasks.\\n8.1.4.3 Construction and Start-up Procedures\\nA geotechnical investigation was undertaken at the site\\nfor the new wetlands to determine underlying soil proper\u00c2\u00ac\\nties and ground water conditions. Soil borings to several\\nfeet below the final wetland grade revealed the presence\\nof sandy clay loams with sand and gravel inclusions, with\\nan unconfined ground water aquifer at greater depth. These\\nsoils were typical of the local flood plain and were consid\u00c2\u00ac\\nered too permeable, so a membrane liner was selected\\nfor the wetland.\\nClearing and grubbing was the first construction activity\\nat the new wetland site. This was followed by grading, berm\\nconstruction, and liner placement. Prior to liner placement,\\nthe subgrade was leveled and compacted to 90% of Proc\u00c2\u00ac\\ntor density to preserve the intended grade during subse\u00c2\u00ac\\nquent construction activities. After the liner was placed,\\n1.5 ft of local sandy clay loam was placed in the wetland\\nbottom to serve as the rooting medium for the wetland\\nvegetation. The curved configuration of the wetland cells\\nincreased construction costs somewhat, but the site was\\n139", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0155.jp2"}, "156": {"fulltext": "To Discharge\\nFigure 8-5. Schematic diagram of the wetland system at Ouray, CO\\ntoo confined to permit construction of a typical rectangular\\nsystem with straight sides.\\nTreatment wetland cells were hand planted by correc\u00c2\u00ac\\ntional facility inmates with locally obtained bulrush and\\ncattail plants. The vegetation was planted on about 18-in\\ncenters; at this density about 43,000 plants were required.\\nThe bed was flooded with about 8-in of water and main\u00c2\u00ac\\ntained in that condition until sufficient new plant growth\\nwas observed. Some wastewater was applied during the\\nremainder of the 1993 winter, but full-scale operation did\\nnot commence until the spring of 1994.\\nThis system experiences subfreezing air temperatures\\nfor extended periods each winter. An ice cover at least 6-\\nin thick persists for at least six months.\\nThe inlet and outlet devices for each set of cells are 8-in,\\nperforated, Schedule 80 PVC pipe. These pipes were laid\\nin a 2-ft-wide, 18-in-deep trench extending the full width of\\nthe cell. The trench bottom and sides are protected with 2-\\nto 4-in riprap. One end of each manifold has a 90% elbow\\nand a capped riser extending above the water surface to\\nserve as a cleanout if required. The effluent manifolds con\u00c2\u00ac\\nnect to a concrete outlet structure that contains adjustable\\noutlet riser pipes for controlling the water level in the cells.\\nThere are no special O M requirements for these wet\u00c2\u00ac\\nland units, including harvesting or other plant management\\nprocedures. Raising and lowering the wetland water lev\u00c2\u00ac\\nels on a seasonal basis and sampling for NPDES compli\u00c2\u00ac\\nance are about the only O M tasks required. There have\\nbeen no problems with muskrats or other animals damag\u00c2\u00ac\\nFrom Lagoon\\ning the plants as has occurred at several other wetland\\nsystems. The wetland tasks listed in the O M manual in\u00c2\u00ac\\nclude weekly cleaning of effluent debris screens, weekly\\nchecking of berms for erosion or muskrat damage, clean\u00c2\u00ac\\ning influent and effluent manifolds as required, and occa\u00c2\u00ac\\nsional muskrat control. Mosquitoes have not been a prob\u00c2\u00ac\\nlem at this site.\\n8.1.4.4 Performance History\\nIt is typical for most small systems, including the Ouray\\nsystem, to monitor only for NPDES limits, and for that rea\u00c2\u00ac\\nson to sample only the untreated (raw) wastewater and\\nthe final effluent. As a result, the actual influent to the wet\u00c2\u00ac\\nland component is not known. Data from the Ouray sys\u00c2\u00ac\\ntem for the 1995-1996 period is shown in Table 8-6.\\nBased on limited data, the aerated lagoon at Ouray is\\nestimated to remove about 54% of influent BOD 5 and 65%\\nof influent TSS. On that basis, with the average wetland\\ninfluent in 1995 at 58 mg/L BOD 5 and 63 mg/LTSS, the\\nwetland achieved an average removal of 83% BOD 5 and\\n90% TSS. In 1996, the average wetland removal percent\u00c2\u00ac\\nages were 88% for BOD 5 and 91 for TSS. Wetland aver\u00c2\u00ac\\nage effluent fecal coliform concentrations during 1995 and\\n1996 were 570 CFU/100 mL and 1300 CFU/100 mL, re\u00c2\u00ac\\nspectively. All of the monthly values were well below the\\nNPDES limit of 6000 CFU/100 mL, so it was not neces\u00c2\u00ac\\nsary to operate the disinfection/dechlorination equipment\\ninstalled at the site.\\n8.1.4.5 Lessons Learned\\nThe Ouray system incorporated many improvements\\nlearned from earlier FWS systems, including perforated\\n140", "height": "4267", "width": "3142", "jp2-path": "constructedwetla00nati_0156.jp2"}, "157": {"fulltext": "Table 8-6. BOD TSS Removal for Ouray, CO\\nDate\\nBOD In,\\nmg/L*\\nBOD Out,\\nmg/L\u00e2\u0080\u009c\\nTSS In,\\nmg/L*\\nTSS Out,\\nmg/L\\n1995\\nJan\\n84\\n5\\n124\\n11\\nFeb\\n78\\n8\\n122\\n8\\nMar\\n84\\n7\\n216\\n10\\nApr\\n132\\n9\\n182\\n5\\nMay\\n66\\n8\\n152\\n11\\nJun\\n174\\n15\\n196\\n4\\nJul\\n180\\n14\\n170\\n5\\nAug\\n216\\n10\\n316\\n5\\nSep\\n204\\n18\\n296\\n4\\nOct\\n132\\n16\\n144\\n6\\nNov\\n96\\n6\\n146\\n5\\nDec\\n78\\n3\\n98\\n4\\nAverage\\n127\\n10\\n180\\n6\\n1996\\nJan\\n90\\n4\\n176\\n4\\nFeb\\n92\\n6\\n154\\n6\\nMar\\n95\\n2\\n184\\n2\\nApr\\n60\\n5\\n178\\n2\\nMay\\n78\\n13\\n68\\n11\\nJun\\n96\\n11\\n109\\n6\\nJul\\n162\\n7\\n334\\n9\\nAug\\n168\\n11\\n226\\n5\\nSep\\n120\\n5\\n102\\n4\\nOct\\n126\\n8\\n127\\n5\\nNov\\n108\\n3\\n121\\n3\\nDec\\n78\\n2\\n160\\n4\\nAverage\\n106\\n6\\n162\\n5\\n\u00e2\u0080\u0098Untreated wastewater\\n\u00e2\u0080\u009cFinal system (wetland) effluent\\nmanifolds extending the full width of the wetland cells\\nfor inlets and outlets, cleanouts on the ends of these\\nmanifolds, and a simple adjustable outlet structure for\\ncontrol of the water level in the wetland cells.\\nThe adjustable outlet structure for water-level control\\nwas essential for the water level to be raised during\\nthe winter months to accommodate expected ice for\u00c2\u00ac\\nmation.\\nLarge-sized riprap (4- to 6-in size) as a permanent slop\u00c2\u00ac\\ning cover for both the influent and effluent manifolds\\nexcludes clogging debris and prevents algae devel\u00c2\u00ac\\nopment. This technique precludes periodic cleaning\\nof a screen over the effluent manifold that would have\\nbeen installed to prevent accumulation of debris.\\nBats and dragonflies contribute to mosquito control dur\u00c2\u00ac\\ning the warm summer months, so mosquitoes and simi\u00c2\u00ac\\nlar insect vectors have not been a health problem at\\nthis system.\\nOdors occasionally noticed at the inlet end of the wet\u00c2\u00ac\\nland cells are caused by accumulation of TSS and al\u00c2\u00ac\\ngae carried over from the final aerated lagoon cell\\nbecause the settling zone in this final lagoon cell is too\\nsmall to be completely effective.\\nIce cover and snow accumulation have provided ac\u00c2\u00ac\\nceptable thermal protection for the FWS system, and\\nthe system has not needed alteration during the win\u00c2\u00ac\\nter months. In response to State of Colorado concerns\\nthat FWS wetlands would not sustain acceptable per\u00c2\u00ac\\nformance during low-temperature winter months, the\\nlagoon aeration system had been designed to allow\\nlonger operational periods during winter months to\\nprovide additional treatment so the wetland cells could\\nhave been bypassed during winter months, if neces\u00c2\u00ac\\nsary.\\nChlorination/dechlorination equipment included in the\\noriginal design at the insistence of the State of Colo\u00c2\u00ac\\nrado has not been used, as the wetland effluent has\\nbeen consistently below permit limits.\\n8.2 Vegetated Submerged Bed (VSB)\\nSystems\\n8.2.1 Village of Minoa, New York\\n8.2.1.1 Background\\nThe Village of Minoa is a small residential community of\\napproximately 3,700 in central New York state east of Syra\u00c2\u00ac\\ncuse. The average daily flow to the wastewater treatment\\nplant in 1993 was approximately 0.35 mgd, but peak flows\\nas high as 1.6 mgd had been recorded. Efforts between\\n1990 and 1993 to abate the high rates of infiltration and\\ninflow were unsuccessful, and the Village of Minoa was\\nforced into a consent order with the New York State De\u00c2\u00ac\\npartment of Environmental Conservation (NYSDEC) to\\ncorrect discharge violations.\\nIn 1994 the village decided to use a VSB constructed\\nwetland system to treat primary effluent to secondary ef\u00c2\u00ac\\nfluent standards, with an ultimate oxygen demand limit that\\nrequired at least partial nitrification. The VSB system also\\nwould be used during wet weather conditions to treat\\n640,000 gpd of wet weather flow. The dry weather capac\u00c2\u00ac\\nity of the VSB system was to be 160,000 gpd, but the ac\u00c2\u00ac\\ntual constructed size of the system was smaller than the\\noriginal design, reducing the design capacity to approxi\u00c2\u00ac\\nmately 130,000 gpd. The treatment goal also was changed\\nfrom a BOD 5 concentration of less than 30 mg/L and par\u00c2\u00ac\\ntial nitrification to BOD 5 alone.\\nTwo New York state agencies and the U.S. EPA pro\u00c2\u00ac\\nvided grant funds to the village for incorporation of several\\nspecial features in the VSB system and for a research and\\ntechnology transfer study of the system by researchers at\\nClarkson University, Potsdam, NY.\\nThe VSB system consists of three cells that can be op\u00c2\u00ac\\nerated in parallel, combined parallel and series, or series\\nmodes. Cells 1 and 2 are approximately the same size\\n(0.17 ha or 0.42 acres). Cell 3 is significantly smaller and\\nis irregularly shaped (0.1 ha or 0.25 acres) (Figure 8-6). At\\nthe inlet end, the media depth is 0.5 m and the bottom\\nsurface has a slope of 1%, resulting in a bed depth of ap\u00c2\u00ac\\nproximately 0.9 m at the outlet end and an average depth\\nof 0.76 m. The upper 7.6 cm of the beds consist of 0.6 mm\\npea gravel, which allowed for the establishment of wet-\\n141", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0157.jp2"}, "158": {"fulltext": "a) Period One Continuous Flow in Parallel\\n0.17 ha 0.175 ha 0.10 ha\\nP Phragmites\\nS Scirpus\\nN No Plants\\nb) Period Two Fill and Drain Flow in Series\\nc) Period Three Combination Sequence (fill and draw [1 and 2] to continuous 3)\\nFigure 8-6. Schematic of Minoa, NY, VSB system\\nland plants. The larger treatment media have an effective\\nsize of approximately 1.9 cm and a measured porosity of\\n0.39. The cells are lined with a 60-mil HDPE liner.\\nEach cell is divided in half longitudinally by an extension\\nof the liner to the top of the media. Three of the half cells\\nwere planted with Phragmites, two of the half cells were\\nplanted with Scirpus, and the final half cell was left\\nunplanted. This planting scheme allowed for performance\\ncomparisons of planted versus unplanted cells and Scirpus\\nversus Phragmites. The system is depicted in Figure 8-6.\\nIn addition to the multicell design and multiple opera\u00c2\u00ac\\ntional modes, the VSB system at Minoa incorporated sev\u00c2\u00ac\\neral other special features, including trilevel observation\\nwell clusters within each half cell, specially designed inlet\\nweirs, thermistors beneath one of the cell liners and at\\nvarious levels within the cell, a dual-level effluent with\u00c2\u00ac\\ndrawal, and an adjustable water-level control.\\nThe specific goals of the research/technology transfer\\nefforts were the following:\\n1. Establish optimum hydraulic, organic, and solids\\napplication rates necessary to achieve Village of\\nMinoa NPDES permit limitations.\\n1\\n2. Conduct testing to determine the impact of wet-event\\npeak-day hydraulic impacts on treatment perfor\u00c2\u00ac\\nmance. One of the project objectives was to evalu-\\n142", "height": "4267", "width": "3142", "jp2-path": "constructedwetla00nati_0158.jp2"}, "159": {"fulltext": "ate the performance of the system under the maxi\u00c2\u00ac\\nmum hydraulic design condition of 640,000 gpd.\\n3. Conduct tracer dispersion testing to measure actual\\nbed HRT and \u00e2\u0080\u009cin-place\u00e2\u0080\u009d hydraulic conductivities, to\\nevaluate impacts due to clogging, and to determine\\nthe extent of short-circuiting.\\n4. Correlate ambient and wastewater temperature data\\nwith observed removal efficiency for BOD, UOD (Ul\u00c2\u00ac\\ntimate Oxygen Demand), and ammonia nitrogen.\\n5. Evaluate the effect of plants (vs. no plants) and spe\u00c2\u00ac\\ncific plants (Scirpus vs. Phragmites) on treatment\\nperformance.\\n6. Evaluate the effect of vegetative harvesting on nu\u00c2\u00ac\\ntrient removal efficiency.\\n7. Provide data for calibrating an existing VSB heat-\\nloss model that predicts the substrate temperature\\nat various locations in the system.\\n8. Evaluate effects of series- versus parallel-flow con\u00c2\u00ac\\nfigurations on treatment performance.\\n9. Conduct a detailed energy audit to establish the\\nenergy benefits of this system in comparison with a\\nconventional treatment approach.\\nConstruction costs for the system are summarized in\\nTable 8-7. It should be noted that (1) the work at Minoa\\nwas completed under adverse weather conditions and a\\ntight construction schedule because of the consent order\\nrequirements, and (2) costs reflect all of the special fea\u00c2\u00ac\\ntures incorporated in the system for research.\\n8.2.1.2 Financial Arrangements\\nThe costs of the Minoa wetland system associated with\\nthe research aspects of the project were funded by the\\nU.S. EPA and the two State of New York agencies. The\\nremaining capital costs of the project were funded with a\\nstate revolving-fund loan under the innovative and alter\u00c2\u00ac\\nnative system program.\\n8.2.1.3 Construction and Start-up Procedures\\nAs noted previously, the work at Minoa was completed\\nunder adverse weather conditions and a tight construction\\nschedule because of the consent order requirements. Dur\u00c2\u00ac\\ning the establishment of the wetland plants throughout most\\nTable 8-7. Village of Minoa VSB Construction Costs (Fall, 1994)\\nSitework\\n$135,500\\n60 Mil HDPE Liner\\n82,500\\nWetland Media\\n104,500\\nWetland Plants\\n29,000\\nPiping Distribution\\n179,000\\nMiscellaneous\\n25,500\\nTotal\\n$568,000\\nof 1995, the wetland cells received only secondary efflu\u00c2\u00ac\\nent from the existing trickling filter.\\n8.2.1.4 Performance History\\nThe performance of the Minoa VSB system in treating\\nprimary effluent can be divided into three periods. During\\nthe first period of January 1996 to March 1997, the system\\nwas operated as a conventional VSB system, with the three\\ncells in parallel. From April 1997 to March 1998, the three\\ncells were operated in series and in a sequential fill-and-\\ndrain mode. From March 1998 to the writing of this manual,\\nthe system has been operated in a different fill-and-drain\\nmode. Two cells, cells 1 and 2, operate in parallel but in\\nalternating fill-and-drain mode, similar to sequencing batch\\nreactors. The third cell, cell 3, operates in series-flow, but\\nwith a constant water level, following the other two cells.\\nConventional Parallel Operation\\nThe BOD t removal performance of the Minoa VSB sys\u00c2\u00ac\\ntem in the conventional mode was very poor when com\u00c2\u00ac\\npared with the original design expectations. The three cells\\nwere operated in parallel flow, but with different HRTs. The\\nperformance of the Minoa system in BOD 5 removal during\\nthe first 10 months of conventional operation is summa\u00c2\u00ac\\nrized in several of the figures (identified as CU) in Chapter\\n5 and can be compared with two other systems. The false\\nperformance expectations for the system were based on a\\ndesign equation developed with limited data, mostly from\\nVSB systems treating lagoon and pond effluents. The equa\u00c2\u00ac\\ntion assumed that BOD 5 removal performance is depen\u00c2\u00ac\\ndent on temperature. Pollutant removal was not found to\\nvary significantly with temperature at Minoa.\\nThe performance of the Minoa VSB system in TSS, TKN,\\nand total phosphorus removal during this period was simi\u00c2\u00ac\\nlar to the performance of other VSB systems treating sep\u00c2\u00ac\\ntic tank effluents (see Chapter 5 figures). TSS and BOD\\nremoval were reasonably good, whereas TKN and total\\nphosphorus removal was quite poor.\\nTracer study results from Minoa were also very similar\\nto tracer study results from other VSB systems. After one\\nyear of operation, a significant fraction of the wastewater\\nflowed under the shallow root zone of the system. Also\\nobserved were substantial dead volumes and typical\\namounts of dispersion within the media.\\nComparing the treatment performance of planted and\\nunplanted half cells, the Clarkson researchers found that\\nthe unplanted half-cell performance was equal to the\\nplanted cells for all pollutants measured. They also found\\nthat the Phragmites cells removed more COD, TKN, and\\ntotal phosphorus than the cells planted with Scirpus.\\nSeries-Flow, Sequential Fill-and-Drain Operation\\nThe three cells of the Minoa VSB system were operated\\nin series-flow, sequential fill-and-drain operation for approxi\u00c2\u00ac\\nmately 12 months. The operation during this time made\\nuse of the dual effluent piping to achieve the fill-and-drain\\n143", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0159.jp2"}, "160": {"fulltext": "operation, even though the flow through all three cells was\\ncontinuous. The water surface in a cell was controlled by\\nopening and closing the bottom drain line valve. When the\\ndrain valve was closed, effluent from a cell flowed through\\nthe upper effluent piping.\\nA typical cycle started with wastewater flowing through\\na filled cell 1. The drain valve in cell 1 was opened\\nwhile drain valves in the other cells 2 and 3 were\\nclosed. Twenty-four hours later, the drain valve in\\ncell 1 was closed and the drain valve in cell 2 was\\nopened. After 24 hours in this configuration, the drain\\nvalve in cell 2 was closed and the drain valve in cell\\n3 was opened. It should be noted that this mode of\\noperation was possible at Minoa because of the sig\u00c2\u00ac\\nnificant drop in elevation from cell 1 to Cell 3. At a\\nflow rate of 130,000 gpd, the draining of cells 1 and\\n2 from their upper levels would take four to five hours,\\nwhile cell 3 required only three hours. In filling, cells\\n1 and 2 would require 24 hours, while cell 3 required\\n12 hours.\\nThe performance in BOD 5 removal during the sequen\u00c2\u00ac\\ntial fill-and-drain operation was significantly better than\\nduring the previous period of conventional operation. Ef\u00c2\u00ac\\nfluent BOD 5 averaged less than 15 mg/L while the system\\nwas treating a much higher flow, and performance improved\\nduring the latter months of the period. TSS removal was\\nalso good, but TKN and total phosphorus removal did not\\nimprove significantly. One of the most important improve\u00c2\u00ac\\nments in the operation of the Minoa system during this\\nperiod was the reduction in the hydrogen sulfide odors that\\nhad plagued the system during the period of conventional\\noperation.\\nAlternating Parallel Fill-and-Drain/Series-Flow Operation\\nOperation since March 1997 has had cells 1 and 2 oper\u00c2\u00ac\\nating in an alternating fill-and-drain mode followed by cell\\n3 operating in a constant-saturated mode. The pollutant\\nremoval performance for BOD 5 and TSS has remained\\nquite good, and there has been a significant increase in\\nnitrogen removal performance.\\n8.2.1.5 Lessons Learned\\nFill-and-drain operation can significantly increase the\\nBOD and nitrogen removal performance of conven\u00c2\u00ac\\ntional VSB systems.\\nBOD 5 removal is not temperature dependent in con\u00c2\u00ac\\nventional VSB systems.\\nBecause of the potential for severe odor problems, con\u00c2\u00ac\\nventional VSB systems must be designed to have lower\\norganic loading rates when sited near households.\\n8.2.2 Mesquite, Nevada\\n8.2.2.1 Background\\nMesquite, Nevada, is located on 1-15 near the Nevada-\\nArizona border, about 112 miles east of Las Vegas. The\\noriginal treatment system for the community included\\ncoarse screening and aerated facultative ponds followed\\nby storage ponds and land application on 62 acres of al\u00c2\u00ac\\nfalfa fields. The State of Nevada required an effluent with\\nBOD at 30 mg/L and TSS at 90 mg/L prior to land applica\u00c2\u00ac\\ntion. The effluent at the Mesquite facility often exceeded\\nthese limits, so an upgrade was required.\\nA 1989 facility plan for the upgraded facility recom\u00c2\u00ac\\nmended an increase in total treatment capacity to 1.2 mgd,\\nadditional aerated lagoons with lagoon effluent to either\\noverland flow terraces or a VSB, and either of these fol\u00c2\u00ac\\nlowed by rapid infiltration basins. The VSB concept was\\nselected for this system because a free water surface\\n(FWS) wetland would have required a larger land area,\\nmight not have been as effective for algae removal, and\\nwould have been more susceptible to mosquito problems.\\nThe design flow to the VSB was 400,000 gpd, with the\\nremainder routed from the lagoon to the overland flow\\nslopes. The existing facultative pond contained multiple\\ncells, and three of these were selected for conversion to\\nVSBs. The total VSB area was 4.7 acres.\\nThe modified aerated lagoons were expected to produce\\nan effluent with about 70 mg/L, and the VSB wetlands were\\ndesigned to produce an effluent with 30 mg/L BOD 5 in the\\ncoldest month, which was January. The design model used\\nfor BOD 5 removal is temperature dependent, so the sys\u00c2\u00ac\\ntem was sized to produce the target effluent value during\\nthe coldest month. There were no NPDES discharge lim\u00c2\u00ac\\nits for the VSBs since they were designed to discharge to\\nrapid infiltration basins and not to a receiving stream.\\nA schematic plan is shown in Figure 8-7 for one of the\\nthree similarly configured VSB units. Each of the three\\nparallel units contained four parallel cells as shown on the\\nfigure. The flow path in each of the four cells averaged 50\\nft, and the cell width averaged 380 ft. This configuration\\nproduces an average aspect ratio (L:W) of 0.13:1. This\\nvery low aspect ratio was selected following observation\\nof surface flooding and related problems with VSB sys\u00c2\u00ac\\ntems in Louisiana, Mississippi, and Oklahoma that had\\naspect ratios of 10:1 or more and no provision for the nec\u00c2\u00ac\\nessary hydraulic gradient to overcome the frictional resis\u00c2\u00ac\\ntance of a very long flow path. In addition to the short flow\\npath distance provided at Mesquite, a bottom slope of 1%\\nwas provided for the cell bottoms.\\n8.2.2.2 Financial Arrangements\\nFunding for construction of this new system was pro\u00c2\u00ac\\nvided by a combination of municipal bonds and the State\\nof Nevada\u00e2\u0080\u0099s revolving-loan fund. The total construction\\ncosts for the VSB component at Mesquite was $515,000\\n(1990$), or $109,600 per acre, or $1,287 per 1000 gallons\\nof treatment capacity. The area cost is less than the\\n$178,000/acre (1990$) at the comparable VSB system in\\nMandeville, Louisiana (see Mandeville case study), and\\nthe difference is probably due to the higher cost of rock\\nand gravel in Louisiana. Land and liner costs for the Mes\u00c2\u00ac\\nquite project were zero because existing lagoon cells were\\n144", "height": "4267", "width": "3142", "jp2-path": "constructedwetla00nati_0160.jp2"}, "161": {"fulltext": "380 ft\\nFigure 8-7. Schematic diagram of typical VSB (one of three) at Mesquite, NV\\nconverted to VSB units. The O M costs are funded di\u00c2\u00ac\\nrectly by a sewer charge for each connected user; a single\u00c2\u00ac\\nfamily connection would pay approximately $8.63 per\\nmonth for this service.\\n8.2.2.3 Construction and Start-up Procedures\\nConstruction of the new system components was com\u00c2\u00ac\\npleted in late 1990 and start-up occurred in April 1991.\\nThe original lagoon cells were lined with asphaltic con\u00c2\u00ac\\ncrete. These were prepared for the new VSB units by drain\u00c2\u00ac\\ning and drying, and then placement and compaction of lo\u00c2\u00ac\\ncal clay soil backfill to a depth of about 2 ft. This backfill\\nwas then graded to provide the desired 1% slope for the\\nbottom. This 2-ft of compacted soil also ensured the im\u00c2\u00ac\\npermeability of the bottoms. The effluent manifolds were\\nplaced and leveled on the bottom prior to gravel bed con\u00c2\u00ac\\nstruction. Gravel for the bed was transported from the lo\u00c2\u00ac\\ncal pit, dumped in the wetland cell, and spread with a small\\nbulldozer. Trenches for the coarse inlet zone rock were\\nexcavated and backfilled after placement of the entire 32-\\nin-deep gravel layer. The 2-in layer of fine gravel/coarse\\nsand was then placed on the surface of the bed, with the\\nexception of the inlet and outlet zones. Posts were then\\ndriven into the gravel layer for support of the distribution\\nmanifold pipes. Construction of external piping, outlet struc\u00c2\u00ac\\ntures, and pumping stations then completed the work.\\nFlow distribution to the three VSB units utilized orifice\\nplates to split the flow, and 8-in perforated pipe manifolds\\nwere used in each cell for both distribution and effluent\\ncollection, as shown in Figure 8-7. The influent pipes were\\nelevated slightly above the bed surface, and the effluent\\nmanifolds were at the bottom of the bed. The main VSB\\nbed consisted of a 32-in depth of washed river gravel rang\u00c2\u00ac\\ning in size from 0.4 in to 1.0 in obtained at a local gravel\\npit. An inlet zone underneath each inlet pipe contains 2-in\\nto 4-in rock to ensure rapid infiltration and distribution. This\\nzone is about 3 ft wide at the top and extends the full\\ndepth of the bed. The gravel in the main bed was then\\ncovered with about a 2-in layer of fine gravel/coarse sand\\nmixture to aid in the germination and growth of the veg\u00c2\u00ac\\netation.\\nThere were no soils or geotechnical investigations at\\nthis site since existing lined lagoon cells were to be used\\nfor the new VSBs. The only geotechnical activity involved\\nwith this project was to find a suitable source for the rock\\nand gravel required. The layer of fine gravel/coarse sand\\nwas chosen because the intended method of planting was\\nhydroseeding. A layer of fine gravel/coarse sand mixture\\nwas placed on top of the gravel in the VSB cells to serve\\nas a growth substrate for the intended hydroseeding. The\\nfirst bed was hydroseeded in July 1991 at a rate of 25 lb/\\nacre of seed mixed with 2500 Ib/acre of mulch fiber. Sprin\u00c2\u00ac\\nklers were then used to periodically flood the surface of\\nthe bed to encourage germination and growth. By Sep\u00c2\u00ac\\ntember 1991, only 20% germination could be observed.\\nAlkali bulrush (Scirpus robustus) was selected as the sole\\nvegetation type for all of the VSB cells. Again hydroseeding\\nwas attempted but proved not to be successful. Planting\\nby hand with locally available plant materials (from ditches,\\netc.) was successfully completed during the second year\\nof system operation. In 1997, the VSB cells were com\u00c2\u00ac\\npletely covered with healthy vegetation. There is no har-\\n145", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0161.jp2"}, "162": {"fulltext": "vesting or other vegetation- management procedures at\\nthis site.\\nWater-level control in two of the three VSB units is pro\u00c2\u00ac\\nvided by overflow weirs in the outlet structures. In the third\\nunit, water-level control depends on float-switch settings\\nfor the discharge pump. In addition, the piping and distri\u00c2\u00ac\\nbution and collection system were designed to operate with\\na continuous 0.4 mgd recycle flow (100% of forward flow).\\nAs of August 1997, an additional plant expansion was\\nunderway at the Mesquite system. The city is growing rap\u00c2\u00ac\\nidly as a retirement/recreational community and a number\\nof golf courses are under construction or planned. To pro\u00c2\u00ac\\nvide irrigation water for these golf courses, the wastewa\u00c2\u00ac\\nter plant expansion is including an oxidation ditch with ni\u00c2\u00ac\\ntrification/denitrification capability and UV disinfection to\\nmeet the necessary bacterial limits for golf course irriga\u00c2\u00ac\\ntion. The VSB/overland flow/rapid-infiltration units at Mes\u00c2\u00ac\\nquite will remain in stand-by use and will be operational\\nduring high-flow winter months.\\n8.2.2.4 Performance History\\nThe inlet orifice plates were provided to split the influent\\nflow proportionally to the surface area of each VSB unit\\nsince there were slight variations in the size of the three\\nunits. Table 8-8 presents average VSB performance data\\nduring the period June 1992 through May 1993. Data are\\nnot available on the performance of individual units or cells\\nwithin a unit.\\nAlthough the system met its effluent BOD target on an\\nannual average basis, there were monthly variations, as\\nshown in Table 8-9. However, these excursions had mini\u00c2\u00ac\\nmal impact on the rapid-infiltration system.\\nThese 1992-1993 performance results were achieved\\nwithout recycling VSB effluent. However, at the time of the\\n1997 site visit, recycle at 400,000 gpd was practiced con\u00c2\u00ac\\ntinuously and produced essentially the same performance\\nresults shown in the tables. Recycle was only considered\\nto be essential in the very hot and dry summer months in\\norder to keep the plants on the beds alive and functional.\\nIn the general case, algae forms in the lagoon and is\\nseparated in the VSB, and the decomposition of the algae\\nreleases additional ammonia and organics. As a result,\\nthe effluent ammonia and organics are elevated due to\\ninternal loading during the warmest periods. Removal dur\u00c2\u00ac\\ning the warmer months of the year is believed to be offset\\nTable 8-8. Summary Performance, Mesquite, Nevada, VSB Compo\u00c2\u00ac\\nnent, June 1992-May 1993\\nParameter\\nInfluent, mg/L\\nEffluent, mg/L\\nRemoval\\nbod 5\\n64\\n29\\n55\\nTSS\\n57\\n13\\n77\\nnh 4 -n\\n16\\n10\\n38\\nTKN\\n29\\n16\\n46\\nTP\\n7.4\\n6.2\\n16\\nTable 8-9. Effluent Characteristics, Mesquite, NV, VSB Component,\\nJune 1992-May 1993\\nMonth\\nTemp.\\n\u00c2\u00b0C\\nBOD\\nmg/L\\nTSS\\nmg/L\\nnh 4 -n\\nmg/L\\nTKN\\nmg/L\\nTP\\nmg/L\\n1992\\nJun\\n21.6\\n32\\n6\\n3.3\\n6.7\\n5.0\\nJul\\n26.7\\n24\\n6\\n4.3\\n6.4\\n5.3\\nAug\\n27.1\\n26\\n6\\n4.5\\n7.6\\n4.8\\nSep\\n23.6\\n22\\n5\\n4.1\\n6.8\\n5.5\\nOct\\n19.1\\n37\\n5\\n3.3\\n5.6\\n6.1\\nNov\\n13.5\\n32\\n22\\n5.3\\n8.6\\n5.8\\nDec\\n7.5\\n27\\n16\\n15.7\\n22.3\\n4.7\\n1993\\nJan\\n8.1\\n24\\n14\\n19.8\\n29.7\\n6.1\\nFeb\\n12.7\\n24\\n18\\n21.9\\n29.9\\n8.0\\nMar\\n13.9\\n23\\n16\\n22.1\\n29.9\\n9.2\\nApr\\n16.2\\n49\\n17\\n12.4\\n23.6\\n7.1\\nMay\\n20.3\\n27\\n21\\n6.0\\n9.5\\n7.0\\nby plant uptake during the growing season. Subsequent\\ndata would be very useful to help identify the annual cycle\\nover several years.\\n8.2.2.5 Lessons Learned\\nThe wetland configuration and cross section shown in\\nFigure 8-7 were designed to maximize the available\\narea in the former lagoon cell, while at the same time\\nminimizing the aspect ratio.\\nSurface overflows are due to improper hydraulic de\u00c2\u00ac\\nsign rather than clogging.\\nSubdividing each VSB into four separate cells with the\\nright slope in each cell to ensure proper flows required\\nvery careful grading of subgrade soils that significantly\\nincreased the cost and complexity of construction.\\nSubdividing each unit into two cells by applying influ\u00c2\u00ac\\nent along the centerline and collecting effluent along\\nthe two sides would have produced an aspect ratio of\\n0.26:1.\\nConverting each former lagoon cell to a single wet\u00c2\u00ac\\nland bed, with application along one long side and ef\u00c2\u00ac\\nfluent collection along the opposite side, would have\\nproduced an aspect ratio of 0.5:1, with a level subgrade\\nand the water level and hydraulic gradient controlled\\nby an adjustable outlet.\\nContinuously flooding the bed with a few inches of wa\u00c2\u00ac\\nter after hydroseeding, rather than intermittently wet\u00c2\u00ac\\nting it, may have improved germination, as would plant\u00c2\u00ac\\ning in a more moderate season in the desert climate.\\nHand planting of shoots or rhizomes in the gravel of a\\nVSB system is preferred. Potted shoots and rhizome\\nmaterial for a wide variety of plant species are com\u00c2\u00ac\\nmercially available.\\nAn effluent recycle feature permitting 100% recycle is\\nnot typical at most VSB systems and was not neces\u00c2\u00ac\\nsary for water quality purposes.\\n146", "height": "4267", "width": "3142", "jp2-path": "constructedwetla00nati_0162.jp2"}, "163": {"fulltext": "Routine maintenance requirements at this system are\\nminimal and consist of periodic pump inspections and\\nmonthly cleaning of orifices in the influent distribution\\nmanifolds.\\n8.2.3 Mandeville, Louisiana\\n8.2.3.1 Background\\nMandeville, Louisiana, is located on the northern shore\\nof Lake Pontchartrain at the end of the causeway bridge\\nfrom New Orleans. The 1997 population of Mandeville was\\nabout 10,000, and the suburban residential community was\\nexpanding rapidly. A vegetative submerged bed (VSB) was\\nselected as a component in the new wastewater treatment\\nfacilities at the recommendation of the State of Louisiana\\nand the U.S. EPA Region VI. The system was constructed\\nduring 1989 and placed in operation in February 1990, with\\na design flow of 1.5 mgd. The system discharges to Bayou\\nChinchuba, which drains to Lake Pontchartrain. The\\nNPDES limits are BOD 5 10 mg/L, TSS 15 mg/L, NH3/NH4\\n5 mg/L, fecal coliform 200/100 mL, and a maximum pH of\\n9.\\nThe new system was constructed at the site of the\\ncommunity\u00e2\u0080\u0099s original three-cell facultative lagoon, and one\\nof the original cells was retained for temporary treatment\\nand later abandoned at the completion of the new system.\\nA second original cell was deepened and converted to a\\npartial-mix aerated lagoon with three cells operated in se\u00c2\u00ac\\nries and submerged perforated tubing in the first two cells.\\nThe hydraulic residence time (HRT) in this new lagoon was\\nabout 15 days at design flow. The third original lagoon cell\\nwas converted to a three-cell VSB gravel bed. The VSB\\ncells operate in parallel. Other new elements in the sys\u00c2\u00ac\\ntem included a headworks containing a bar screen and\\ngrit chamber, final disinfection with UV, and an effluent\\npumping station. All of these major system components\\nare shown in Figure 8-8.\\nAt the time this system was designed, sizing criteria were\\n5 acres per mgd of design flow, a one- to two- day HRT in\\nthe VSB, and an aspect ratio (L:W) of at least 10:1 to en\u00c2\u00ac\\nsure plug flow conditions. These criteria assumed that the\\nVSB influent would contain about 30 mg/L of BOD 5 and\\nTSS following treatment in the aerated lagoon. All of these\\ncriteria were applied at Mandeville except the 10:1 aspect\\nratio, which could not be used due to the preexisting con\u00c2\u00ac\\nfiguration of the facultative lagoon cell. The average as\u00c2\u00ac\\npect ratio of the three VSBs is about 2.5:1.\\nThe three VSBs are separated by low internal earthen\\nberms that provide about 1.5 ft of freeboard above the\\ngravel surface in the bed. The external berms are the pre\u00c2\u00ac\\nexisting dikes of the former facultative lagoon. The bottom\\nsurface area is 6 acres. The VSB bed is composed of a\\n1.5-ft depth of crushed limestone rock (2- to 4-in size) over-\\nlain by 6 in of granite gravel (0.5- to 1-in size). The surface\\nlayer of gravel was considered necessary as a rooting\\nFigure 8-8. Schematic of VSB system at Mandeville, LA\\n147", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0163.jp2"}, "164": {"fulltext": "medium for the vegetation. Softstem bulrush (Scirpus\\nvalidus) was selected as the sole vegetation type, and nurs\u00c2\u00ac\\nery-grown shoots were planted on about 4-ft centers. An\\nannual harvest of these plants was recommended by the\\ndesigners and was practiced for several years after start\u00c2\u00ac\\nup.\\nA 20-in PVC pipe conveys lagoon effluent to the VSB.\\nThis pipe connects to a PVC manifold extending the full\\nwidth of the three cells. At three equidistant points in each\\ncell, the manifold discharges to a 10-in outlet pipe that is\\nvalved and extends 25 ft into the bed. These outlet pipes\\nare at the surface of the bed, and they each end in a 90\u00c2\u00b0\\n\u00e2\u0080\u009cdown\u00e2\u0080\u009d elbow that penetrates into the rock layer. These\\nnine gate valves were intended for flow control so that a\\ncell could be taken out of service and/or flow could be ad\u00c2\u00ac\\njusted as required to produce a relatively uniform distribu\u00c2\u00ac\\ntion of flow.\\nThe effluent manifold for cells 1 and 3 is 21-in PVC and\\n24-in PVC for cell 2. These manifold pipes were buried\\nwith the top of the pipe flush with the top of the coarse rock\\nlayer. Four-in-diameter holes were drilled on 8-in centers\\nat the top center of these manifold pipes. These manifolds\\nconnect to the UV disinfection chamber, which then dis\u00c2\u00ac\\ncharges to the sump of the discharge pump. The top of the\\ngravel layer was graded level, as was the bottom of the\\nbed, and no adjustment was possible in the water level in\\nthe bed, nor was it possible to drain the cells.\\nA special feature in all three wetland cells is the inclu\u00c2\u00ac\\nsion of buried 6-in perforated PVC pipes. Two of these\\nopen-ended pipes are buried in each cell, about 6 in above\\nthe bed bottom in the coarse rock media. Their apparent\\npurpose is redistribution of subsurface flow in case the entry\\nzone of the bed becomes clogged with solids. Each pipe\\nis 100 ft in length and is laid parallel to the flow direction;\\nthe two pipes in each bed are located about 35 ft on each\\nside of the longitudinal bed centerline.\\nThe construction costs for the entire system, including\\nthe aerated lagoons, was about $3,000,000 (1990$). The\\ncost for the VSB cells was about $590,000 (1990$), with\\nabout 70% of that for procurement and placement of the\\nrock media and gravel layer. The materials used at\\nMandeville were barged from Arkansas, since rock and\\ngravel are not readily available in this part of Louisiana.\\nOther VSB projects in the vicinity have used rock and gravel\\nbarged from Mexico. The VSBs are not lined since the\\nsubsoils are clay and sandy clay. Since the exterior dikes\\nfor the former lagoon were utilized, construction costs were\\nminimal (except for the cost of rock and gravel). Land costs\\nwere zero since the preexisting lagoon was municipally\\nowned. The construction costs for this VSB were about\\n$590 (1990$) per 1000 gallons of design flow, or $105,400\\nper acre of treatment area for the 5.6-acre system.\\n8.2.3.2 Financial Arrangements\\nThe construction costs for the Mandeville system were\\nfunded privately through bonds issued by the City of\\nMandeville. No grant or funding support was provided by\\nthe State of Louisiana or the U.S. EPA. The apparent rea\u00c2\u00ac\\nson was the relatively low position of the city on the grant\\npriority list. The city, faced with the choice of curtailing com\u00c2\u00ac\\nmunity growth or funding a new system itself, chose the\\nlatter option. The O M costs for the system have been\\nobtained as a surcharge on the consumer\u00e2\u0080\u0099s water bill.\\n8.2.3.3 Construction and Start-up Procedures\\nConstruction activities commenced with draining of the\\nexisting facultative lagoon. The bottom was allowed to dry,\\nand then accumulated sludge was removed and disposed\\nof. The bottom was then leveled in preparation for backfill\u00c2\u00ac\\ning with gravel. The concrete structures containing the UV\\ndisinfection components and the effluent pump station were\\nalso constructed at this time. The low interior earthen berms\\nwere then constructed to divide the lagoon cell into three\\nparallel units. These interior berms permit foot traffic only.\\nThe rock and gravel were hauled by truck from the barge\\ndock on Lake Pontchartrain to the site, dumped into the\\nbed, and spread with small bulldozers. The entire coarse\\nrock layer was placed and leveled before any gravel was\\nplaced as the top layer. The inlet and outlet manifolds were\\nthen installed and connected and rock backfilled around\\nthem (the top gravel layer was not placed in these inlet\\nand outlet zones). The bed was then filled with water (with\\neffluent from the temporary lagoon) to the top of the coarse\\nrock. The bulrush shoots, obtained from a nursery in Mis\u00c2\u00ac\\nsissippi, were planted by hand on 4-ft centers, with their\\nroots in contact with the water at the top of the coarse\\ngravel. About 15,000 plants were planted in the three cells.\\nStart-up of this system commenced immediately upon\\ncompletion of construction. In some systems of this type,\\nclean water is used to initially fill the bed, and the plant\\nshoots are allowed to grow for four to six weeks prior to\\nintroduction of wastewater. In this case, lagoon effluent\\nwas introduced during the planting stage, and daily flow\\nthrough the VSB commenced as soon as the aerated la\u00c2\u00ac\\ngoons were operational. There were no special start-up\\nprocedures used at this site. However, a unique mainte\u00c2\u00ac\\nnance procedure was adopted for several years, which\\nstarted with harvesting of weeds to encourage growth and\\nspread of the bulrush, which evolved into a complete an\u00c2\u00ac\\nnual harvest of all vegetation and the removal and dis\u00c2\u00ac\\nposal of the harvested material. That practice has now been\\nterminated.\\n8.2.3.4 Performance History\\nIn 1991, the Mandeville system was selected by the U.S.\\nEPA for a detailed eight-week performance evaluation. This\\neffort included independent flow metering of system influ\u00c2\u00ac\\nent, VSB influent and effluent, tracer studies to verify HRT,\\nand weekly composite sampling and testing for BOD (total\\nand soluble), COD (total and soluble), TSS, VSS, TKN,\\nNH 4 -N, N0 3 TP, DO, pH, and temperature. The study pe\u00c2\u00ac\\nriod commenced in mid-June 1991 and was completed by\\nlate September 1991. The average flow rate during this\\nperiod was 1.16 mgd, indicating that 77% of the system\\ndesign capacity was achieved in the second year of op-\\n148", "height": "4267", "width": "3142", "jp2-path": "constructedwetla00nati_0164.jp2"}, "165": {"fulltext": "eration. This is a reflection of the very rapid growth and\\nresidential construction in the community. A summary of\\nthe water quality performance data is given in Table 8-10.\\nThe tracer study, conducted only in cells 2 and 3 because\\nthe valves for cell 1 had been inadvertently closed, mea\u00c2\u00ac\\nsured a flow rate of 1.352 mgd, which indicated an actual\\nHRT of 17.8 hours. This compared favorably with the theo\u00c2\u00ac\\nretical HRT of 18 hours for the same flow rate, assuming a\\nporosity of 42% in the rock/gravel bed. At the time of the\\ntracer test, surface water was apparent on portions of the\\nwetland cells, but the majority of the flow was subsurface.\\nIf cell 1 had been operational during the test, it is believed\\nthat the actual HRT would have been close to the one-day\\ntheoretical HRT for the full system.\\nTable 8-11 presents a summary of system performance\\ndata collected in 1996 and 1997. The values shown are\\nthe averages for the month shown.\\nAs shown in Table 8-11, the current actual flow exceeds\\nthe original design rate of 1.5 mgd, but the system contin\u00c2\u00ac\\nues to meet the discharge limits for BOD and TSS but ex\u00c2\u00ac\\nceeds the ammonia limit on a seasonal basis (i.e., non-\\ncompliance in the colder months). The routine compliance\\nwith BOD 5 and TSS limits is in part due to the reliability of\\nthese systems for removal of these parameters, but is also\\nin part due to significant modifications to the system made\\nin 1992. The present system configuration, with the sur\u00c2\u00ac\\nface aerators, the subsurface aerators, and the baffle cur\u00c2\u00ac\\ntains as shown in Figure 8-8, has been in place since 1992.\\nThe lagoons as originally constructed had submerged,\\npartial-mix aeration tubing in the first and second aeration\\ncells, and there were no baffles in place. In effect, the first\\nbaffle in the first lagoon cell converts the entry zone into a\\ncomplete-mix aeration component. The purpose of these\\nmodifications was to obtain a more rapid removal of BOD 5\\nand more effective settling of TSS in the lagoons, and to\\nsubsequently permit more effective ammonia removal in\\nTable 8-10. Water Quality Performance, Mandeville LA Treatment\\nSystem, June/September 1991\\nParameter\\nSystem\\nInfluent\\nWetland\\nInfluent\\nWetland\\nEffluent\\nBOD (Total) mg/L\\n154\\n41\\n10\\nBOD (Soluble) mg/L\\nND\\n21\\n8\\nCOD (Total) mg/L\\n349\\n79\\n43\\nCOD (Soluble) mg/L\\nND\\n40\\n31\\nTSS mg/L\\n132\\n59\\n7\\nVSS mg/L\\nND\\n39\\n5\\nTKN mg/L\\nND\\n5\\n3\\nNH 4 -N mg/L\\nND\\n1.4\\n2.1\\nOrganic N mg/L\\nND\\n3.1\\n1.1\\nN0 3 -N mg/L\\nND\\n4\\n0.2\\nTN mg/L\\nND\\n9\\n3\\nTP mg/L\\nND\\n3\\n4\\nFecal Coliforms#/100ml\\nND\\nTNTC\\nTNTC 2\\nDO mg/L\\nND\\n2.4\\n1.8\\npH\\n6.9\\n6.9\\n7.0\\nTemperature \u00c2\u00b0C\\nND\\n31.8\\n30.5\\nND No data available.\\n2 TNTC Too numerous to count, sample taken prior to disinfection\\nthe lagoons and VSB component. This strategy has been\\nsuccessful for BOD 5 and TSS, but not for ammonia. The\\nlow ammonia values obtained in the EPA study during the\\n1991 summer are misleading. The records for the entire\\nyear show a seasonal trend in effluent concentrations that\\nare similar to those shown in Table 8-11 for 1996-1997. In\\n1991, the effluent ammonia concentration averaged 3.2\\nmg/L during the warm months (March-November) and 7.8\\nmg/L during the colder months (December-February). The\\nsystem met the ammonia limit by a significant margin dur\u00c2\u00ac\\ning that first year of operation.\\nThere are no significant seasonal trends in the ammo\u00c2\u00ac\\nnia concentration in the untreated wastewater, but there\\nare in the lagoon effluent, which indicates that these higher\\nwinter values are not treated effectively by the VSB. As a\\nresult, the system effluent exceeds the discharge limit. This\\ncondition suggests that the lagoon, as presently config\u00c2\u00ac\\nured, does not provide effective nitrification during the\\ncolder weather. That is a plausible hypothesis since the\\nnitrifier organisms are temperature sensitive and gener\u00c2\u00ac\\nally exist in relatively low numbers in these partial-mix aer\u00c2\u00ac\\nated lagoons with no sludge return.\\nThe city intends to increase the capacity of the system\\nto about 4 mgd to keep up with expected growth in the\\ncommunity. Discussions are underway regarding the fu\u00c2\u00ac\\nture system configuration to solve both the ammonia prob\u00c2\u00ac\\nlem and permit capacity expansion with maximum utiliza\u00c2\u00ac\\ntion of the existing facilities.\\n8.2.3.5 Lessons Learned\\nThe internal hydraulics of the wetland cells force all of\\nthe influent to enter the cell at three points, with a total\\ncross-sectional area of about 2 ft 2 which is inadequate\\nto receive a design flow of about 350 gpm and results\\nin surface flow in the inlet zone. A perforated inlet\\nmanifold that extended the full width of each cell should\\nhave prevented surface flow. At the effluent end of the\\ncells, surface flow was caused by outlet ports installed\\nat the same elevation as the rock surface.\\nA means of controlling water levels in the bed and al\u00c2\u00ac\\nlowing the bed to be drained for maintenance would\\nhave improved the system.\\nModifications to the system, including additional ori\u00c2\u00ac\\nfices drilled in the effluent manifold in the side and lower\\nquadrant, additional surface gravel placed in the area\\nof the manifold, and a new pipe installed to permit drain\u00c2\u00ac\\nage of the cells, resulted in a lowering of the water\\nlevel in the effluent zone of the wetland bed, so the\\ngravel surface in that area is generally dry.\\nSurface flow was experienced almost immediately in\\nthe inlet and outlet zones of this system and was not\\ncaused by clogging, as confirmed by EPA investiga\u00c2\u00ac\\ntions in 1991, but rather by lack of hydraulic gradient.\\nHydraulic gradient for a flat-bottomed system can be\\nprovided with a water-level control device at the efflu\u00c2\u00ac\\nent end of the cell.\\n149", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0165.jp2"}, "166": {"fulltext": "Table 8-11. Water Quality Performance, Mandeville, LA, Treatment System, 1996 -1997\\nDate\\nAvg. Flow\\nmgd\\nBOD\\nmg/L\\nRaw Wastewater\\nTSS\\nmg/L\\nnh 4 -n\\nmg/L\\nBOD\\nmg/L\\nWetland Influent\\nTSS\\nmg/L\\nnh 4 -n\\nmg/L\\nBOD\\nmg/L\\nWetland Effluent\\nTSS\\nmg/L\\nnh 4 -n\\nmg/L\\n1996\\nJan\\n1.57\\n133\\n115\\n14\\n15\\n8\\n14.3\\n5\\n2\\n11.9\\nFeb\\n1.60\\n156\\n120\\n15\\n14\\n8\\n14\\n6\\n2\\n12\\nMar\\n1.75\\n126\\n116\\n13\\n16\\n11\\n16\\n2\\n2\\n11\\nApr\\n1.26\\n145\\n148\\n14\\n11\\n8\\n12\\n4\\n1\\n8\\nMay\\n1.11\\n137\\n133\\n18\\n45\\n25\\n10\\n3\\n2\\n9\\nJun\\n1.72\\n138\\n132\\n18\\n27\\n18\\n1\\n2\\n2\\n0.5\\nJul\\n1.33\\n131\\n115\\n16\\n24\\n24\\n1\\n2\\n1\\n0.7\\nAug\\n1.71\\n64\\n70\\n20\\n30\\n48\\n7\\n10\\n7\\n5\\nSep\\n1.32\\n61\\n155\\n31\\n59\\n20\\n12\\n9\\n7\\n5\\nOct\\n1.69\\n86\\n137\\n21\\n43\\n18\\n14\\n7\\n4\\n5\\nNov\\n1.51\\n119\\n126\\n44\\n62\\n8\\n8\\n8\\n5\\n4\\nDec\\n1.57\\n116\\n122\\n37\\n43\\n11\\n28\\n6\\n2\\n19\\nAvg\\n1.51\\n118\\n124\\n22\\n32\\n17\\n11\\n5\\n3\\n8\\n1997\\nJan\\n1.85\\n89\\n111\\n20\\n70\\n14\\n12\\n7\\n4\\n7\\nFeb\\n2.31\\n63\\n94\\n24\\n62\\n23\\n44\\n10\\n6\\n20\\nMar\\n1.53\\n94\\n128\\n26\\n59\\n16\\n16\\n7\\n3\\n5\\nApr\\n1.44\\n97\\n98\\n22\\n52\\n20\\n10\\n6\\n4\\n4\\nMay\\n1.67\\n112\\n140\\n25\\n34\\n14\\n6\\n4\\n3\\n4\\nJun\\n1.64\\n93\\n167\\n28\\n57\\n10\\n12\\n4\\n3\\n4\\nJul\\n1.68\\n108\\n109\\n16\\n51\\n9\\n9\\n6\\n2\\n5\\nAvg\\n1.73\\n94\\n121\\n23\\n55\\n15\\n16\\n6\\n4\\n7\\nWeighted\\n1.59\\n109\\n123\\n22\\n40\\n16\\n13\\n5\\n3\\n8\\nAverage\\n1996/97\\n1991\\n1.16\\n154\\n132\\nND\\n41\\n59\\n1.4\\n10\\n7\\n2.1\\nBulrush planted in this system has attracted nutria and\\nmuskrat, which favor bulrush for food and nesting\\nmaterial. Nutria have eaten most of the bulrush plants\\nand bored through the interior berms, which causes\\nsignificant leakage between the cells. Small sacks filled\\nwith a mixture of cement and sand have corrected the\\nleakage problem of nutria boring through interior\\nberms.\\nThe minimal availability of oxygen in VSB wetland beds\\nmakes them ineffective for nitrification of ammonia, and\\nthe Mandeville system can meet ammonia discharge\\nlimits only when the aerated lagoon provides sufficient\\nammonia removal.\\n8.2.4 Sorrento, Louisiana\\n8.2.4.1 Background\\nSorrento, a small residential community in southeastern\\nLouisiana, is located about 50 miles southeast of Baton\\nRouge. Prior to construction of the aerated lagoon wet\u00c2\u00ac\\nland system, the community was served by on-site septic\\ntank systems. Many of these on-site systems were not func\u00c2\u00ac\\ntioning properly due to the difficult soil conditions in the\\narea. The new system was designed in 1990 and placed\\nin operation in late 1991. The lagoon component consists\\nof two 10-ft-deep aerated cells (first cell contains four 3-hp\\nfloating aerators, second cell contains four 2-hp floating\\naerators), followed by a 7-ft-deep settling pond. The two\\naerated cells were designed for 10 d HRT at the potential\\nultimate flow rate of 130,000 gpd. At the 1997 flow rate of\\n32,000 gpd, the HRT is about 40 d, and only a few of the\\naerators were operated.\\nThe VSB cell, with a bottom area of about 7800 ft 2 was\\ndesigned for a flow rate of 50,000 gpd with the intention of\\nadding a second parallel cell as the flow rate increases in\\nthe future. The design HRT in this bed at 50,000 gpd would\\nbe one day. The native soils are clays and silty clays, so\\nthe bottoms of the lagoon cells and the VSB cells are not\\nlined. However, a geotextile liner is used on the inner slope\\nof all berms to prevent erosion and weed growth; the outer\\nslope of these berms is grassed. The system discharges\\nto Bayou Conway, and the NPDES discharge limits are\\nBOD 5 20 mg/L, TSS 20 mg/L, pH 6-9, and fecal coliforms\\n200-400/100 mL. There are no ammonia limits for this sys\u00c2\u00ac\\ntem.\\nAs shown in Figure 8-9, the VSB cell is triangular in\\nshape, with the inlet zone about 60 ft wide and the flow\\npath to the outlet about 250 ft long. This shape was se\u00c2\u00ac\\nlected to minimize short-circuiting of flow. Previous designs\\nhad large aspect ratios (10:1 or greater) but insufficient\\nhydraulic gradient to overcome the frictional resistance,\\nresulting in surface flow on top of the bed. At Sorrento, the\\naverage aspect ratio is only 6:1, but all of the flow con\u00c2\u00ac\\nverges at the end of the triangular bed.\\n150", "height": "4267", "width": "3142", "jp2-path": "constructedwetla00nati_0166.jp2"}, "167": {"fulltext": "Aerators\\nInfluent\\nDischarge Chlorination\\nAerated Lagoons\\nVegetated Bed\\n60 X 250 ft\\nSettling Pond\\nFigure 8-9. Schematic of VSB system at Sorrento, LA\\nThe design engineer of the Sorrento system also incor\u00c2\u00ac\\nporated several features to ensure that an adequate hy\u00c2\u00ac\\ndraulic gradient would always be available based on les\u00c2\u00ac\\nsons learned from other systems. The bottom of the bed is\\nflat and level throughout its length, but the gravel depth is\\n3 ft at the inlet and 2.5 ft at the outlet, so the top surface of\\nthe gravel slopes to provide for 0.5 ft of headloss. In addi\u00c2\u00ac\\ntion, the single outlet structure contains an adjustable sluice\\ngate that allows a further increase in the available hydrau\u00c2\u00ac\\nlic gradient by adjusting the water level in the bed. The\\ninlet to the bed is an 8-in perforated pipe resting on the\\nbottom of the bed and extending the full width. The bed\\neffluent discharges to a concrete outlet box. There is also\\nan 8-in valved drain pipe at the outlet end of the bed to\\ndrain the cell completely, if necessary. A chlorine contact\\nchamber is provided for disinfection prior to final discharge.\\nTwo layers of aggregate are used in the Sorrento VSB.\\nThe top layer is a 6-in depth of washed, 0.75-in gravel.\\nThe main part of the bed is composed of crushed lime\u00c2\u00ac\\nstone imported from Mexico, ranging from 1.5 to 3 in in\\nsize. Since ammonia removal was not required and be\u00c2\u00ac\\ncause maintenance problems with vegetation were appar\u00c2\u00ac\\nent at other systems, it was decided not to plant vegeta\u00c2\u00ac\\ntion on the Sorrento VSB cell. At the time of the 1997 in\u00c2\u00ac\\nspection for this report, weeds were growing around the\\nfringes of the wetland bed, but the general bed surface\\nwas still free of vegetation.\\nThis wetland system was selected for use at Sorrento\\nbecause the facility planning evaluation showed it to be\\nthe most cost-effective process for meeting the NPDES\\ndischarge requirements. The total construction cost for the\\nentire system was about $233,400 (1991$), with an esti\u00c2\u00ac\\nmated $75,000 for the VSB component. The unit construc\u00c2\u00ac\\ntion cost for the VSB would then be about $1500 per 1000\\ngallons of design capacity (for the 50,000 gpd design flow).\\nOn an area basis, the capital costs would be about\\n$419,000 per acre for the 0.18-acre VSB.\\n8.2.4.2 Financial Arrangements\\nThe construction costs for the Sorrento system were\\nfunded with federal and state money provided under the\\nU.S. EPA Construction Grant Program that existed at that\\ntime. The O M costs for the system are supported by sewer\\nfees from the connected users.\\n8.2.4.3 Construction and Start-up Procedures\\nA site for the new lagoon/wetland system was identified\\non available land between the community and the final dis\u00c2\u00ac\\ncharge point to Bayou Conway. Geotechnical investiga\u00c2\u00ac\\ntions were undertaken to identify and characterize the in\\nsitu soils. These proved to be clays and silty clays that\\nwould provide adequate protection for ground water. There\\nalso was no identified risk of ground water intrusion or sur\u00c2\u00ac\\nface water flooding at this site.\\nThe site is relatively level, so the entire system was ex\u00c2\u00ac\\ncavated, with excess material used to construct the berms.\\nA 3-ft freeboard was provided for the lagoon cells and the\\nVSB component. The rock and gravel were hauled by truck\\nfrom a barge dock on the Mississippi River, dumped into\\nthe bed, and spread with a small bulldozer. The entire\\ncoarse rock layer was placed and leveled before any gravel\\nwas placed as the top layer. Inlet and outlet manifolds were\\nthen installed and connected and rock backfilled around\\n151", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0167.jp2"}, "168": {"fulltext": "them. The bed was then filled with effluent from the lagoon\\nto the top of the coarse rock. Since vegetation was not\\nused on this system, start-up was immediate.\\nRoutine maintenance procedures include servicing of the\\nlagoon aerators and the chlorine disinfection equipment;\\nthere are no routine maintenance requirements for the\\nwetland bed. There have been problems with nutria bur\u00c2\u00ac\\nrowing in the banks of the lagoon cells; however, since\\nthere is no vegetation and no exposed water in the wet\u00c2\u00ac\\nland cell, these animals have not been a problem at this\\nsite. Since maintenance has not been required for the\\nwetland cell, the O M cost for this component is zero.\\n8.2.4.4 Performance History\\nWater quality data are not available for untreated sew\u00c2\u00ac\\nage at Sorrento or for lagoon effluent entering the wetland\\nsystem. The 1997 flow is estimated to be in the range of\\n15,000 gpd. At that rate the HRT would be about 100 d in\\nthe lagoons and 4 d in the VSB component. With such a\\nlong HRT, lagoon effluent could be expected to have a\\nBOD b of less than 20 mg/L and a TSS in the same range\\n(except for algal bloom periods). With inputs at this level,\\nthe VSB with an HRT of 4 d could be expected to produce\\nbackground levels of BOD 5 and TSS, as confirmed in Table\\n8 12\\n8.2.4.5 Lessons Learned\\nThe triangular configuration of this VSB system causes\\nflow lines to converge at the end of the system in a\\nsingle outlet point, which is cost effective, but any such\\ndesign would need to evaluate weir loading rates per\\nunit length to avoid excessive velocity in the outlet zone\\nthat could cause resuspension of TSS and its associ\u00c2\u00ac\\nated contaminants.\\nThe sloping surface of the gravel (0.2% grade) pro\u00c2\u00ac\\nvides an additional 0.5 ft of potential head at the inlet\\nTable 8-12. VSB Effluent Water Quality, Sorrento, LA\\nDate\\nBOD, mg/L\\nTSS, mg/L\\nFecal Coli\\npH\\n2/23/94\\n6\\n5\\n0\\n7.2\\n3/31/94\\n6\\n4\\n0\\n7.2\\n5/18/94\\n6\\n2\\n20\\n7.5\\n7/28/94\\n6\\n4\\n100\\n7.4\\n8/10/94\\n6\\n4\\n0\\n7.2\\n9/26/94\\n6\\n4\\n6\\n7.8\\n12/30/94\\n6\\n4\\n180\\n7.6\\n1/12/95\\n6\\n4\\nTNTC\\n7.9\\n3/8/95\\n6\\n4\\n4200\\n7.9\\n4/28/95\\n6\\n4\\n666\\n7.1\\n6/16/95\\n6\\n11\\n0\\n7.8\\n7/12/95\\n6\\n4\\n0\\n7.5\\n8/10/95\\n6\\n4\\n0\\n7.3\\n9/13/95\\n6\\n4\\n0\\n7.5\\n10/11/95\\n6\\n4\\n0\\n7.4\\n11/8/95\\n6\\n4\\n0\\n7.5\\n12/13/95\\n6\\n4\\n53\\n7.4\\n1/24/96\\n6\\n4\\n350\\n7.4\\n2/14/96\\n6\\n4\\n3\\n7.5\\n3/13/96\\n6\\n4\\n6\\n7.0\\nNote: after chlorine disinfection, #/100 ml\\nto help ensure that the hydraulic gradient is sufficient\\nto avoid surface flow on the bed.\\nThe adjustable outlet gate provides additional water\\nlevel adjustment; however, the outlet gate cannot be\\nlowered completely, so an additional drain pipe for de\u00c2\u00ac\\nwatering the bed is necessary. A completely adjust\u00c2\u00ac\\nable outlet may have eliminated both the additional\\ngravel necessary to produce the sloping surface and\\nthe drain pipe for dewatering.\\nThe system is oversized for the current flow rate and\\norganic loading, so an additional VSB cell may not be\\nnecessary for the system to handle flow rate increases\\nanticipated in the future.\\nThe lack of plants in this system does not appear to\\naffect removal of BOD and TSS, as was observed in a\\n1992 EPA performance evaluation of a vegetated sys\u00c2\u00ac\\ntem and a temporarily nonvegetated system.\\nThe lack of plants in effect equates the VSB concept\\nto a horizontal-flow, coarse-media, contact filter.\\n8.3 Lessons Learned\\n8.3.1 Design\\nOrganic Loading\\nOrganic loadings in the range of 10 to 25 lbs BOD/acre/\\nday to FWS systems have been shown to effectively meet\\n30 mg/L BOD and TSS monthly effluent standards, with\\nno need after 15 years of operation to remove the settled\\nmaterial from a FWS system. For the majority of these\\nsystems, this range of organic loading results in six to eight\\ndays of theoretical hydraulic retention.\\nD ata Gaps\\nThe database for both VSB and FWS systems has a\\ncontinuing problem of not having enough quality-assured\\ndata to evaluate removal rates, seasonal differences, wa\u00c2\u00ac\\nter balances, and long-term treatment effectiveness. In\u00c2\u00ac\\nsufficient data have been collected on contaminant load\u00c2\u00ac\\nings (both flow and concentration), incremental data\\nthrough the system (multiple data collection points), and\\nwater column data (temperature, pH, and dissolved oxy\u00c2\u00ac\\ngen) at different locations.\\nInlet/Outlet Works\\nStudies comparing the placement of inlet/outlet (I/O)\\nworks as a function of cell geometry and outlet approach\\nconditions are lacking. As a result, there is not a complete\\nrational approach to the placement and design of inlet and\\noutlet works for these types of systems. For example, the\\ncriterion of weir overflow rate typically has been used to\\nplace outlet weirs and specify weir length in these low ap\u00c2\u00ac\\nproach-velocity systems. Included in the outlet design are\\nbathymetric and vegetative conditions of the outlet zone\\nof FWS wetlands. Large collection areas immediately up\u00c2\u00ac\\nstream from outlet works that have no emergent vegeta-\\n152", "height": "4267", "width": "3142", "jp2-path": "constructedwetla00nati_0168.jp2"}, "169": {"fulltext": "tion have resulted in poor effluent quality. Relatively shal\u00c2\u00ac\\nlow collection zones with emergent vegetation have shown\\nless variability of effluent quality, but more O/M require\u00c2\u00ac\\nments.\\nHeadloss\\nWhile headloss is a factor of concern in VSB systems, it\\nis not a major factor in FWS wetlands unless they have\\nextremely long and narrow flow reaches. Headloss is a\\nconsideration in FWS wetlands only when L:W ratios are\\ngreat (10:1 or greater) and are combined with high hy\u00c2\u00ac\\ndraulic loading rates in heavily vegetated cells. Proper\\nplacement of I/O works, sufficient berm height, and L:W\\nratios less than 10:1 minimize headloss effects in FWS\\nwetlands. Clean-water headloss through a VSB wetland\\nsystem is quickly modified as pore spaces are filled with\\nseparated solids and, to a lesser degree, rhizosphere de\u00c2\u00ac\\nvelopment. Under conditions of plugging by these mecha\u00c2\u00ac\\nnisms, the liquid level will eventually surface and an un\u00c2\u00ac\\ndersized, fully vegetated FWS wetland condition will be\u00c2\u00ac\\ngin to develop on the surface.\\nHy d r aulics\\nThe internal hydraulics of a VSB system are critical to\\ntreatment success. Systems constructed with high L:W\\nratios, flat bottoms, and with effluent manifold ports lo\u00c2\u00ac\\ncated at the top of the gravel produced surface flow at the\\neffluent ends of the cell. These types of systems also did\\nnot allow for water level control within the bed and cell\\ndrainage. Multiple-ported influent manifolds extending the\\nwidth of the inlet zone, coupled with similar effluent col\u00c2\u00ac\\nlection manifolds with adjustable weirs or rotating elbows,\\nwould allow for greater hydraulic contact in the basin and\\nmore operational flexibility. Sloping the surface of the\\ngravel bed based on the design flow headloss may also\\npermit increases in VSB hydraulic loading and duration of\\nservice prior to major inlet maintenance.\\nAspect Ratio\\nHigh aspect ratio FWS wetland cells can produce sig\u00c2\u00ac\\nnificant operational problems at high hydraulic loading\\nrates and/or with dense stands of emergent vegetation.\\nHeadloss effects are additive and are greatly aggravated\\nwith high length-to-width ratios in totally vegetated FWS\\nwetlands. Both types of systems with L:W ratios as high\\nas 30:1 have produced significant flooding at the influent\\nberms while dropping the effluent water elevation below\\nweir recovery levels. Parallel cells with lower L:W with\\nmultiple I/O works can control this effect. The only design\\nlimitation is that the HRT must be above some minimum\\nto assure removal of TSS and associated pollutants of\\nconcern.\\nIce Formation\\nIn colder climates where ice forms on standing water,\\nsufficient freeboard and outlet control is essential to allow\\nfor ice formation to cap the normal operating depth of the\\nfree surface water column. In most cases, this distance is\\nless than 1 ft. The ability to operate the wetland with the\\nwater column directly in contact with the ice, with no low\u00c2\u00ac\\nering of the water level once the ice forms, is another im\u00c2\u00ac\\nportant design feature. Lowering the water under these\\nconditions could allow for a secondary ice level, with a\\nliquid level constraint, to form under the primary level.\\n8.3.2 Mechanisms and Processes\\nOxvoen Transfer\\nOxygen transfer through the rhizosphere evidently is not\\na major contributor to contaminant oxidation in vegetated\\nsubmerged bed systems, based on both research and full-\\nscale studies. Oxygen demand associated with storage\\nproducts in roots and tubers is much greater than excess\\noxygen available at the root hairs and other plant parts. In\\nFWS wetlands, epiphytes can colonize on stems and\\nleaves preferentially depending on oxygen exuding from\\nthe gas transport plant structures.\\nNitrification-Denitrification in VSB Systems\\nCost-effectively sized VSB systems have not been shown\\nto significantly nitrify treated influent. It follows that VSBs\\nhave not been shown to be able to denitrify an influent,\\nwhich is predominantly ammonia. Early studies that sug\u00c2\u00ac\\ngested that significant amounts of nitrogen can be removed\\nin a VSB wetland system have not been duplicated in sub\u00c2\u00ac\\nsequent studies and full-scale evaluations.\\nPlant Coverage\\nCoverage by emergent plants in FWS wetlands should\\nnot be 100% because too much coverage by emergent\\nplants is negatively correlated with effluent quality. Plac\u00c2\u00ac\\ning open water (submergent aquatic macrophytes) between\\nareas of closed water (emergent macrophytes) is corre\u00c2\u00ac\\nlated with better effluent quality than a wetland that has\\n100% emergence. Submergent plants release oxygen to\\nthe water column, and these open water zones allow for\\nmore surface reaeration. Emergent plants also contribute\\nmore internal BOD loading upon decomposition.\\nGround Water Recharge\\nSiting and designing FWS wetlands with intentional dis\u00c2\u00ac\\ncharge to ground water is a legitimate application of this\\ntreatment technology. With proper design, FWS wetlands\\nfor ground water recharge can remove nitrate nitrogen\\n(through denitrification) and indicator organisms. Data col\u00c2\u00ac\\nlected at \u00e2\u0080\u009cleaky wetland sites,\u00e2\u0080\u009d such as in Jackson Bot\u00c2\u00ac\\ntom, Oregon, have demonstrated the effectiveness of these\\nprocesses in locations where soils are sufficiently porous.\\nPlant Litter\\nPlant litter is an essential component of a FWS con\u00c2\u00ac\\nstructed wetland. While this material contributes to flow\\nresistance, it more importantly seals surface areas in fully\\nvegetated zones to assure anoxic conditions.\\n153", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0169.jp2"}, "170": {"fulltext": "8.3.3 Vegetation\\nDevelopment of Treatment Effectiveness\\nThe full treatment potential of a FWS system may not be\\nrealized until there is both full coverage of plants (as de\u00c2\u00ac\\nsigned) and a layer of litter beginning to accumulate on\\nthe surface of the water. Depending on the type of plants,\\nplanting density, and time of planting, a minimum of two\\ngrowing seasons, or two to three years, may be needed.\\nThis may be important when negotiating discharge permit\\nrequirements.\\nAmmonia Nitrogen\\nIn VSB systems, plants are not critical to the removal of\\nBOD and TSS, as shown in several systems. Evidence\\nsuggests, however, that they are effective in removing\\nportions of the nitrogen and phosphorus due to uptake by\\nthe plants during the growing season. Most of these nutri\u00c2\u00ac\\nents are returned to the water column during the senes\u00c2\u00ac\\ncent period.\\nAeration\\nAttempts to aerate outlet zones of FWS systems with\\nsubmerged tubing have resulted in attracting animals such\\nas muskrats and nutria, which may damage the tubing.\\nShort-circuiting\\nVegetation predation by nutria and muskrats in FWS\\nwetlands can produce serious hydraulic short-circuiting.\\nVarying plant resistance as the wastewater moves through\\nthe wetland also can cause short-circuiting. Preferential\\nflow routes can develop in these systems, which have rela\u00c2\u00ac\\ntively low velocities.\\nSeeding and Germination\\nHydroseeding both VSB and FWS wetlands has only\\nbeen successful for cattails in some instances. Additional\\nstudies of this low-cost approach to planting are recom\u00c2\u00ac\\nmended. Seeding with 25 Ib/acre mixed with a mulch at\\n2500 Ib/acre have been used for VSB systems. Continu\u00c2\u00ac\\nous shallow-water inundation has consistently produced\\nhigher germination rates than have sprinklers.\\nPlant Toxicity\\nEmergent vegetation species, such as cattails and bul\u00c2\u00ac\\nrushes, are sensitive to deep anaerobic sludge banks. In\\nsituations with large volumes of carryover solids and mal\u00c2\u00ac\\nfunctioning activated sludge units, emergent vegetation in\\nthe inlet zone can die from sulfide toxicity in the rhizosphere.\\nWastewaters with high levels of suspended and settle-\\nable solids should be pretreated upstream from a wetland\\nsystem through use of a settling pond.\\n8.3.4 Treatment Effectiveness\\nNutrient Uptake\\nBoth FWS and VSB wetlands have been shown to be\\nunable to reduce levels of BOD, dissolved phosphorus,\\nand ammonia nitrogen below certain minimums. This is\\ndue to internal processes in a wetland, such as the solubi\u00c2\u00ac\\nlization of influent settleable/suspended solids and the lit\u00c2\u00ac\\nter layer of aquatic macrophytes. Depending on the cli\u00c2\u00ac\\nmate, pulses of dissolved carbon (both degradable and\\nnon-degradable), soluble reactive phosphorus, and am\u00c2\u00ac\\nmonia nitrogen are taken up by the plants, and they are\\nreleased during periods of active decomposition in the\\nwetland. Colder climatic conditions with early falls, long\\ncold winters, and warm springs will pulse these materials\\ninto the water column during the spring warm-up period.\\nNitrification\\nWithout operating in a fill-and-draw batch mode, it is not\\neconomically feasible to attain aerobic conditions in a VSB\\nsystem to convert ammonia to nitrate. A VSB is anaerobic\\nthroughout most of its depth, with little opportunity for nitri\u00c2\u00ac\\nfying bacteria populations to develop. Internally loaded\\nammonia from the decomposition of algal cells has also\\nbeen shown to be a factor when attempting to use a VSB\\nto meet ammonia standards.\\nSheet Flow for Nitrification\\nAttempts to operate a fully vegetated FWS wetland in a\\nshallow mode to simulate conditions of overland flow have\\nnot proven to be effective.\\nMeasurement of Treatment Effectiveness\\nMost of the FWS wetlands in the NADB are used to treat\\nhigh-quality influents producing low organic loading con\u00c2\u00ac\\nditions. In most of these cases, the internal load is more\\nsignificant than the influent load. In only a few cases with\\nhigh organic loading rates were the upper limits of treat\u00c2\u00ac\\nment effectiveness measured, such as Gustine, Califor\u00c2\u00ac\\nnia. While many viewed Gustine as a failure, it provided\\nwell-documented data on a wide range of BOD, TSS, ni\u00c2\u00ac\\ntrogen, and coliform fully vegetated zone loading condi\u00c2\u00ac\\ntions. These data showed that the upper instantaneous\\nBOD loadings of 150 to 200 Ibs/acre/day could still result\\nin less than 40 mg/L BOD in the effluent. Such loading\\nrates were based on a fully vegetated FWS system and a\\nspecific wastewater, so the utility of this information is lim\u00c2\u00ac\\nited. For example, if a wastewater had a soluble BOD load\u00c2\u00ac\\ning of this magnitude, it would not be prudent (or success\u00c2\u00ac\\nful) to use a single fully vegetated cell for treatment.\\n154", "height": "4267", "width": "3142", "jp2-path": "constructedwetla00nati_0170.jp2"}, "171": {"fulltext": "", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0171.jp2"}, "172": {"fulltext": "", "height": "4267", "width": "3142", "jp2-path": "constructedwetla00nati_0172.jp2"}, "173": {"fulltext": "", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0173.jp2"}, "174": {"fulltext": "United States\\nEnvironmental Protection Agency\\nNational Risk Management Research Laboratory\\nTechnology Transfer and Support Division\\nCincinnati, OH 45268\\nOfficial Business\\nPenalty for Private Use\\n$300\\nEPA/625/R-99/010\\nLIBRARY OF CONGRESS\\n0 007 123 825 8\\nPRESORTED STANDARD\\nPOSTAGE FEES PAID\\nEPA PERMIT NO. G-35", "height": "4267", "width": "3142", "jp2-path": "constructedwetla00nati_0174.jp2"}, "175": {"fulltext": "", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0175.jp2"}, "176": {"fulltext": "", "height": "4267", "width": "3142", "jp2-path": "constructedwetla00nati_0176.jp2"}, "177": {"fulltext": "nMC\\nv n v rm% w tmws\\n\u00c2\u00a3-Cr 1\\nV V rw 4\\nx\\nf, V *n\\nVa, a.\\niK.", "height": "4267", "width": "3150", "jp2-path": "constructedwetla00nati_0177.jp2"}, "178": {"fulltext": "", "height": "4267", "width": "3142", "jp2-path": "constructedwetla00nati_0178.jp2"}}