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epa/625/1-88/022 september 1988 design manual constructed wetlands and aquatic plant systems for municipal wastewater treatment u.s environmental protection agency office of research and development center for environmental research information cincinnati oh 45268

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notice this document has been reviewed in accordance with the u.s environmental protection agency s peer and administrative review policies and approved for publication mention of trade names or commercial products does not constitute endorsement or recommendation for use this document is not intended to be a guidance or support document for a specific regulatory program guidance documents are available from epa and must be consulted to address specific regulatory issues ii

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contents chapter 1 aquatic treatment systems page 1 1 1 1 2 2 3 4 4 4 4 5 5 5 6 7 9 9 9 10 10 10 10 11 11 11 12 15 15 15 15 15 15 15 16 16 16 18 19 1.1 introduction 1.1.1 scope 1.1.2 potential uses of natural systems 1.2 classification 1.2.1 natural wetlands 1.2.2 constructed wetlands 1.2.3 aquatic plant systems 1.3 natural wetlands 1.4 constructed wetlands 1.4.1 free water surface systems fws 1.4.2 subsurface flow systems sfs 1.5 aquatic plant systems 1.5.1 floating plant systems 1.5.2 submerged plant systems 1.6 references 2 environmental and public health considerations 2.1 2.2 2.3 2.4 introduction nitrogen phosphorus pathogens 2.4.1 parasites 2.4.2 bacteria 2.4.3 viruses 2.5 metals 2.6 trace organics 2.6 references design of constructed wetlands 3.1 types of constructed wetlands 3.1.1 free water surface systems with emergent plants 3.1.2 subsurface flow systems with emergent plants 3.2 site selection 3.2.1 topography 3.2.2 soil permeability for free water surface systems 3.2.3 hydrological factors 3.2.4 water rights considerations 3.3 performance expectations 3.3.1 bod5 removal in fws wetlands 3.3.2 bod5 removal in sfs wetlands 3 iii

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contents continued chapter page 4 design of aquatic plant systems 47

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figures number 1-1 3-1 3-2 3-3 3-4 3-5 3-6 3-7 3-8 3-9 3-10 3-11 3-12 3-13 3-14 3-15 4-1 4-2 4-3 4-4 4-5 4-6 4-7 4-8 4-9 4-10 4-11 4-12 4-13 4-14 4-15 4-16 page 3 16 18 20 20 23 28 31 32 35 35 37 37 40 42 43 50 50 51 56 57 63 64 65 66 66 common aquatic plants general design schemes for denitrification pilot-scale constructed wetland gravel planted trench with brush sensitivity of ce/co ratio to av sensitivity of ce/co ratio to temperature regression curve of tkn vs detention time in the effluent of an alternating typa/open-water/gravel system arcata ca pilot marsh system arcata ca wastewater treatment facilities flow diagram arcata ca intermediate fws system bod performance data for emmitsburg md sfs tss performance data for emmitsburg md sfs bod5 performance data for gustine ca pilot marsh system ss performance data for gustine ca pilot marsh system gustine ca marsh system flow schematic fabius coal facility site plan fabius coal facility impoundment 1 wetlands morphology of the hyacinth plant suitable areas for hyacinth systems morphology of and potential growth areas for duckweed plants evolution of flow pattern through san diego ca water hyacinth treatment ponds evolution of pond 3 flow and aeration system configurations at san diego,ca site plan for san diego ca aquaculture pilot plant schematic diagram of primary and secondary facilities san diego ca aquaculture pilot plant schematic of hyacinth pond step-feed system with recycle san diego ca bod5 performance data for san diego ca pond #3 with 200 percent recycle ss performance data for san diego ca pond #3 with 200 percent recycle lnfluent and effluent bod ss and do for step-feed hyacinth pond san diego ca definition sketch for the analysis of a hyacinth pond with step-feed and recycle analysis of performance data for hyacith pond 3 san diego ca with step-feed and recycle hornsby bend tx hyacinth facility basin configuration hornsby bend tx hyacinth facility pond and roof section iron bridge fl hyacinth facility basin configuration 68 70 70 72 72 76 vi

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contents continued chapter 4.5 performance expectations 4.5.1 design equations 4.5.2 nitrogen removal 4.6 sample design problems 4.6.1 sample problem no 1 4.6.2 sample problem no 2 4.7casestudies 4.7.1 san diego california 4.7.2 austin texas 4.7.3 orlando florida 4.7.4 summary 4.8 references appendixa appendixb page 56 56 56 58 58 59 61 61 69 74 77 78 81 83 v

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tables number 1-1 1-2 1-3 1-4 1-5 2-1 2-2 3-1 3-2 3-3 3-4 3-5 3-6 3-7 3-8 3-9 3-10 3-11 3-12 3-13 3-14 3-15 3-16 3-17 3-18 3-19 4-1 4-2 4-3 4-4 4-5 4-6 4-7 4-8 4-9 4-10 4-11 4-12 4-13 page functions of aquatic plants in aquatic treatment systems percent removal for several pollutants from secondary effluent in natural wetlands summary of nutrient removal from natural wetlands summary of nutrient removal from constructed wetlands summary of wastewater treatment performance of aquatic plant systems 2 4 5 5 6 pollutants and pathways of concern 9 trace organic removal in pilot-scale hyacinth basins 12 removal mechanisms in wetlands for the contaminants in wastewater performance of pilot-scale constructed wetland systems predicted vs actual ce/co values for constructed wetlands media characteristics for subsurface flow systems emergent aquatic plants for wastewater treatment city of arcata ca wastewater discharge requirements arcata ca pilot marsh system hydraulic loading ratios and detention times experimental vegetation and compartments for marsh cells arcata ca average annual bod5 concentration mg/l arcata ca arcata ca marsh and wildlife sanctuary wastewater treatment plant performance arcata ca marsh and wildlife sanctuary project expenditures performance of the emmitsburg md sfs determination of nitrification component in bod5 test gustine ca bod5 and ss removal efficiencies as a function of detention time gustine ca design criteria for constructed wetland at gustine ca initial operating schedule of the gustine ca marsh system capital costs for gustine ca marsh project fabius coal preparation facility marsh system performance constructed wetlands case studies summary history of use of floating aquatic treatment systems performance of existing duckweed systems composition of duckweeds grown in wastewater types of water hyacinth systems design criteria for water hyacinth systems design criteria for effluent polishing with duckweed treatment systems recommended sludge cleanout frequency for water hyacinth ponds nitrogen removal water hyacinth tertiary treatment design criteria for modified plug-flow water hyacinth ponds for expanded san diego ca aquatic treatment facility performance data hornsby bend tx hyacinth facility iron bridge fl water hyacinth system performance summary iron bridge fl water hyacinth system monitoring aquatic plant systems case studies summary 17 17 19 21 26 27 29 29 30 33 33 35 38 38 39 41 41 45 45 48 52 52 53 53 54 54 58 67 73 78 79 80 vii

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acknowledgments many individuals contributed to the preparation and review of this manual contract administration was provided by the u.s environmental protection agency epa center for environmental research information ceri cincinnati ohio authors ronald w crites project manager nolte and assocoiates sacramento california daniel c gunther nolte and associates andrew p kruzic nolte and associates jeffrey d pelz nolte and associates george tchobanoglous university of california davis california in-house review contributers and reviewers james f kreissl epa-risk reduction engineering laboratory cincinnati ohio sherwood c reed u.s army corps of engineers hanover new hampshire reviewers lowell l leach epa-robert s kerr environmental research laboratory ada oklahoma john meagher epa-office of wetlands protection washington dc william sipple epa-office of wetlands protection washington dc technical direction/coordination denis j lussier epa-ceri cincinnati ohio james e smith jr epa-ceri cincinnati ohio viii

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chapter 1 aquatic treatment system 1 .1 introduction the trend over the past 70 years in the construction of water pollution control facilities for metropolitan areas has been toward concrete and steel alternatives with the advent of higher energy prices and higher labor costs these systems have become significant cost items for the communities that operate them for small communities in particular this cost represents a higher percentage of the budget than historically allocated to water pollution control processes that use relatively more land and are lower in energy use and labor costs are therefore becoming attractive alternatives for these communities the high cost of some conventional treatment processes has produced economic pressures and has caused engineers to search for creative costeffective and environmentally sound ways to control water pollution one technical approach is to construct artificial ecosystems as a functional part of wastewater treatment wastewater has been treated and reused successfully as a water and nutrient resource in agriculture silviculture aquaculture golf course and green belt irrigation the conceptual change that has allowed these innovative processes is to approach wastewater treatment as water pollution control with the production of useful resources water and plant nutrients rather than as a liability the interest in aquatic wastewater treatment systems can be attributed to three basic factors 1 recognition of the natural treatment functions of aquatic plant systems and wetlands particularly as nutrient sinks and buffering zones 2 in the case of wetlands emerging or renewed application of aesthetic wildlife and other incidental environmental benefits associated with the preservation and enhancement of wetlands 3 rapidly escalating costs of construction and operation associated with conventional treatment facilities 7.7.7 scope application of wastewater to wetlands and aquatic pond systems must be free of unreasonable risks to public health pathogenic organisms may be present in both wastewaters and sludges and their control is one of the fundamental reasons for waste management public health considerations of aquatic plant systems and constructed wetlands are discussed in chapter 2 the portion of this manual concerning constructed wetlands chapter 3 focuses on studies of pilotand full-scale systems that have published results the general case in favor of constructed wetland systems is tied to the fact that they can operate in cold as well as warm climates the discussion of aquatic plant systems chapter 4 concentrates on the results with water hyacinth systems operated in the warm southern regions of the united states a few duckweed systems have been tried either alone or in conjunction with hyacinths the projects discussed in this manual reflect this geographical distribution of project sites and of the plant species that have been studied extensively a list of existing constructed wetlands and aquatic plant systems is presented in appendix a 7.7.2 potential uses of natural systems where natural wetlands are located conveniently to municipalities the major cost of implementing a discharge system is for pumping treatment plant effluent to the site once there further wastewater treatment occurs by the application of natural processes in some cases the wetland alternative can be the least cost advanced wastewater treatment and disposal alternative in locations where poorly drained land that is unsuitable for land application is available wetlands can often be constructed inexpensively with minimal diking in considering the application of wastewaters to wetlands the relationship between hydrology and ecosystem characteristics needs to be recognized factors such as source of water velocity flow rate renewal rate and frequency of inundation have a major bearing on the chemical and physical properties of the wetland substrate these properties in turn 1

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influence the character and health of the ecosystem as reflected by species composition and richness primary productivity organic deposition and flux and nutrient cycling 1 in general water movement through wetlands tends to have a positive impact on the ecosystem 2 rather than wasting water upland swamps appear to save water and thus promote increased regional production indirectly 3 1 physical entrapment of pollutants through sorption in the surface soils and organic litter 2 utilization and transformation of elements by microorganisms 3 low energy and low maintenance requirements to attain consistent treatment levels wetlands are comparatively shallow typically less than 0.6 m 2 ft bodies of slow-moving water in which dense stands of water tolerant plants such as cattails bulrushes or reeds are grown in manmade systems these bodies are artificially created and are typically long narrow trenches or channels 8 three major systems involving wastewater and wetlands can be observed in the united states 9 1 disposal of treated effluent into natural wetlands 2 use of effluents or partially treated wastewater for enhancement restoration or creation of wetlands 3 use of constructed wetlands for wastewater treatment these three categories provide some degree of wastewater treatment either directly or indirectly in the united states however there are some constraints on the use of natural wetlands as functional components of wastewater treatment systems almost all natural wetlands are waters of the united states and as such a permit is required for any discharge the water quality requirements for this discharge are specified by the applicable federal state and/or local agencies and typically are at least equal to secondary effluent standards 1o on the other hand constructed wetlands designed and built for the express purpose of treating municipal wastewater are not waters of the united states there are three categories of aquatic treatment systems considered in this manual 1 natural wetlands 2 constructed wetlands 3 aquatic plant systems 1.2 classification in aquatic systems wastewater is treated principally by means of bacterial metabolism and physical sedimentation as is the case in conventional activated sludge and trickling filter systems the aquatic plants themselves bring about little actual treatment of the wastewater 4 their function is generally to support components of the aquatic environment that improve the wastewater treatment capability and/or reliability of that environment 5 some specific functions of aquatic plants in aquatic treatment systems are summarized in table 1-1 the morphology of some typical aquatic plants is shown schematically in figure 1-1 table 1-1 functions of aquatic plants in aquatic treatment systems 8 plant parts roots and/or stems in the water column function 1 surfaces on which bacteria grow 2 media for filtration and adsorption of solids 1 attenuate sunlight and thus can prevent the growth of algae 2 reduce the effects of wind on the water i.e the transfer of gases between the atmosphere and water 3 important in the transfer of gases to and from the submerged parts of plant stems and/or leaves at or above the water surface wetlands are those areas that are inundated or saturated by surface or ground water at a frequency and duration sufficient to maintain saturated conditions these can be either preexisting natural wetlands e.g marshes swamps bogs cypress domes and strands etc or constructed wetland systems constructed systems can range from creation of a marsh in a natural setting where one did not permanently exist before to intensive construction involving earth moving grading impermeable barriers or erection of containers such as tanks or trenches the vegetation that is introduced or emerges from these constructed systems will generally be similar to that found in the natural wetlands 6 there are three basic functions of wetlands that make them potentially attractive for wastewater treatment 7 7.2.1 natural wetlands while the interest in wetlands for wastewater treatment is fairly recent the term wetlands is also a relatively new expression encompassing what for years have simply been referred to as marshes swamps or bogs the difference in these wetlands is related to a large extent to the vegetation which dominates the area grasses or forbs are generally 2

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figure l-l common aquatic plants cattail bulrush water hyacinth submerged duck dominant in marshes trees and shrubs characterize swamps and sedge/peat vegetation occurs in various bogs natural wetlands are effective as wastewater treatment processes for a number of reasons natural wetlands support a large and diverse population of bacteria which grow on the submerged roots and stems of aquatic plants and are of particular importance in the removal of bod5 from wastewater in addition the quiescent water conditions of a wetland are conducive to the sedimentation of wastewater solids other aspects of wetlands that facilitate wastewater treatment are the adsorption/filtration potential of the aquatic plants roots and stems the ion exchange/adsorption capacity of wetlands natural sediments and the mitigating effect that the plants themselves have on climatic forces such as wind sunlight and temperature 9 natural wetland systems are typically characterized by emergent aquatic vegetation such as cattails typha rushes scirpus and reeds phragmites they can also contain some of the floating and submerged plant species discussed in chapter 4 as well as phreatophytes plants whose roots extend to the ground-water table or the saturated soil area immediately above it 10 most states except florida and a few others considering special wetland standards make no distinction between the wetland and the adjacent surface waters and apply the same requirements to both under these conditions economics will not favor the utilization of natural wetlands as a major component in a wastewater treatment process as the basic treatment must be provided prior to discharge to the wetland special situations may arise in which natural wetlands may provide further effluent polishing or if the wetland is isolated from other surface waters more basic treatment the use of treated effluent for enhancement restoration or creation of wetlands can be a very desirable and environmentally compatible activity 10 7.2.2 constructed wetlands studies in the united states have focused on peatlands bogs cypress domes and strands as well as cattails reeds rushes and related plants in wetland settings 6 constructed wetlands are either free water surface systems fws with shallow water depths or subsurface flow systems sfs with water flowing laterally through the sand or gravel a constructed wetland involving bulrushes in gravel filled trenches was developed at the max planck institute in west germany this patented process has seen limited application to date in the united states 3

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the constructed wetlands at santee california was operated in a similar fashion 1.2.3 aquatic plant systems aquatic plant systems are shallow ponds with floating or submerged aquatic plants the most thoroughly studied systems are those which use water hyacinth or duckweed these systems include two types based on the dominant plant types the first type uses floating plants and is distinguished by the ability of these plants to derive their carbon-dioxide and oxygen needs from the atmosphere directly the plants receive their mineral nutrients from the water the second type of system consists of submerged plants and is distinguished by the ability of these plants to absorb oxygen carbon-dioxide and minerals from the water column submerged plants are relatively easily inhibited by high turbidity in the water because their photosynthetic parts are below the water 1.3 natural wetlands examples of pollutant removal in natural wetlands receiving treated wastewater are presented in table 1-2 the values for percent removal show quite a range for treatment this summary table is included to indicate the general finding for natural wetlands systems i.e that levels of removal for bod5 and ss can be high but are not consistently high nutrient removals from several specific natural wetlands projects are presented in table 1-3 11 table 1-2 pollutant bod5 suspended solids nitrogen phosphorus controlled to eliminate the negative aspects of natural wetlands the removal efficiency of typical pollutants are reported in table 1-4 bacteria attached to plant stems and the humic deposits are the major factor for bod5 removal with respect to phosphorus removal the contact opportunities with the soil are limited in most natural wetland systems an exception might be peat bogs and release of phosphorus has been observed during the winter in some cases the surface area for constructed marshes ranges from 24.6 to 39.6 m2/m3 of applied wastewater per day 23-37 ac/mgd 6 the major costs and energy requirements for constructed wetlands are associated with preapplication treatment pumping and transmission to the site distribution at the site minor earthwork and land costs in addition a constructed system may require the installation of a barrier layer to limit percolation to groundwater and additional containment structures in case of flooding 6 possible constraints to the use of constructed wetlands for wastewater treatment include the following geographical limitations of plant species as well as the potential that a newly introduced plant species will become a nuisance or an agricultural competitor constructed wetlands that discharge to surface water require 4 to 10 times more land area than a conventional wastewater treatment facility zerodischarge constructed wetlands require 10 to 100 times the area of conventional wastewater treatment plants an example of a zero-discharge system is the incline village wetlands enhancement facility near carson city nevada plant biomass harvesting is constrained by high plant moisture content and wetland configuration some types of constructed wetlands may provide breeding grounds for disease producing organisms and insects and may generate odors if not properly managed constructed wetlands however offer the engineer greater hydraulic control for general use and are not restricted by many of the environmental concerns and user conflicts associated with natural wetlands unlike natural wetlands which are confined by availability and proximity to the wastewater source constructed wetlands can be built anywhere including lands with limited alternative uses they also offer greater flexibility scope for design and management options and thus may provide superior performance and reliability 1 1.4.1 free water surface systems fws these systems typically consist of basins or channels with some sort of subsurface barrier to percent removal for several pollutants from secondary effluent in natural wetlands 6 removal percent 70-96 60-90 40-90 seasonal current experience with wetland systems is generally limited to the further treatment of secondary effluents 6 factors to be considered are potential disruption of the existing wildlife habitat and ecosystems in a natural wetland loss of water via evapotranspiration for all wetlands in arid climates the potential for increased breeding of mosquitos or flies and the development of odor the major benefits that can be realized from use of wetlands include preservation of open space wildlife habitat enhancement increased recreation potential streamflow stabilization and augmentation in addition to wastewater treatment 6 1.4 constructed wetlands constructed wetlands have the positive characteristics of a natural wetland and can also be 4

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table 1-3 project summary of nutrient removal from natural wetlands percent reduction flow m3/d 757 379 946 2,309 1,136 -227 d wetland type marsh peatland swamp/marsh marsh peatland marsh cypress dome tdp a 13 95 98 47 88 nh 3 -n 71 58 n0 3 -n 51 99c 20 tnb brillion marsh wi houghton lake mi wildwood fl concord ma bellaire ml coots paradise town of dundas ontario canada whitney mobile park home park fl abcd 90 64 60-70 89 80 91 total dissolved phosphorus total nitrogen nitrate and nitrite may-november only table 1-4 summary of nutrient removal from constructed wetlands wetland type fws sfs fws sfs fws a bod5 mg/l lnfluent 56 effluent 10 30 4.6 13 ss mg/l lnfluent 111 57 57 43 30 140 effluent percent reduction bod 5 82 75 86 64 71 64 ss 93 90 92 28 73 86 project listowel ontario 12 santee ca 10 sidney australia 13 arcata ca emmitsburg md gustine ca a b flow m /d 17 240 11,350 132 3,785 3 hydraulic surface loading rate m3ha-d a 5.5 4.5 31 8.3 19 sfs b 118 33 36 62 150 907 1,543 412 18 24 free water surface system subsurface flow system prevent seepage soil or another suitable medium to support the emergent vegetation and water at a relatively shallow depth flowing through the unit the shallow water depth low flow velocity and presence of the plant stalks and litter regulate water flow and especially in long narrow channels minimize short circuiting results from listowel ontario are related in chapter 3 to theoretical results using mathematical modeling for bod5 removal the general result shown in chapter 3 is that equation 3-5 gives correct orderof-magnitude predictions of the system response for greater accuracy in predicting effluent bod5 levels for a fws system the coefficient of specific surface for microbial growth must be estimated this coefficient is related to the surface area of the vegetation stems and leaves in the water column predicted results are not extremely sensitive to this coefficient as shown in chapter 3 water temperature has a large influence on microbial activity and must be known rather accurately to predict the extent of bod5 degradation in the constructed wetland 1.4.2 subsurface flow systems sfs these systems are essentially horizontal trickling filters when they use rock media they have the added component of emergent plants with extensive root systems within the media systems using sand or soil media are also used soil media systems designated as the root-zone-method rzm were developed in west germany a theoretical basis for design of a sfs is shown in chapter 3 equation 3-7 unlike the fws system equation in which the specific surface area is important but not critical the media porosity is critical to predicting the required area for a given level of treatment media porosity has a direct mathematical relationship with the microbial degradation rate constant the general ability of the equations shown in chapter 3 to predict the extent of bod5 removal should be used in conjunction with pilot studies the mathematical and theoretical basis is not refined enough to allow engineering design of a treatment system from the equations alone 1.5 aquatic plant systems 1.51 floating plant systems the water hyacinth eichhornia crassipes has been studied extensively for use in improving the wastewater effluent from oxidation ponds and as the major component in an integrated advanced 5

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wastewater treatment system the major characteristics of water hyacinths that make them an attractive biological support media for bacteria are their extensive root system and rapid growth rate the major characteristic that limits their widespread use is their temperature sensitivity i.e they are rapidly killed by winter frost conditions duckweed systems have been studied alone and as components of water hyacinths in polyculture systems the major advantage of duckweeds is their lower sensitivity to cold climates while their major disadvantages have been their shallow root systems and sensitivity to wind several projects which have provided valuable performance data for water hyacinth and duckweed systems are summarized in table 1-5 the orlando and san diego projects will be discussed in more detail in the case studies of chapter 4 1.5.2 submerged plant systems submerged plants are either suspended in the water column or rooted in the bottom sediments typically their photosynthetic parts are in the water column the potential for use of submerged plants for polishing of effluent seems at least theoretically an attractive option the tendency of these plants to be shaded out by algal growths and to be killed or severely harmed by anaerobic conditions limits their practical usefulness table 1-5 summary of wastewater treatment performance of aquatic plant systems bod5 mg/l ss mg/l lnfluent 3.8 120 47.7 effluent 3 20 11.5 percent reduction bod 5 37 91 85 ss 21 83 76 hydraulic surface loading rate m3 /ha-d 2,525 590 504 project orlando fl san diego ca nstl ms flow m /d 30,280 378 8 3 plant type water hyacinth water hyacinth duckweed and penny-wart w ater hyacinth duckweed water hyacinth lnfluent 4.9 160 35 effluent 3.1 15 5.3 austin tx n biloxi ms cedar lake disney world fl 1,700 49 30 42 30 200 12 15 26 40 155 50 9 12 14 73 50 87 78 92 72 140 700 300 6

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1.6 references when an ntis number is cited in a reference that reference is available from national technical information service 5285 port royal road springfield va 22161 703 487-4650 1 wile i g miller and s black design and use of artificial wetlands in ecological considerations in wetland treatment of municipal wastewaters van nostrand reinhold co ny pp 26-37 1985 hantzsche n n w e t andsystemsfor wastewater treatment engineering applications in ecological considerations in wet/and treatment of municipal wastewaters van nostrand reinhold co ny pp 7-25 1985 godfrey p.j e.r kaynor and s pelczarski ecological considerations in wet/and treatment of municipal wastewaters van nostrand reinhold co ny 1985 tchobanoglous g aquatic p/ant systems for wastewater treatment engineering considerations 1987 in aquatic plants for water treatment and resource recovery magnolia publishing inc orlando fl pp 27-48 1987 stowell r r ludwig j colt and g tchobanoglous toward the rational design of aquatic treatment systems presented at the american society of civil engineers spring convention portland or april 14-18 1980 reed s r bastian w jewell engineering assessment of aquaculture systems for wastewater treatment an overview in aquaculture systems for wastewater treatment seminar proceedings and engineering assessment u.s environmental protection agency epa 430/9-801006 ntis no pb 81156705 pp 1-12 1979 chan e t.a bursztynsky n.n hatzsche and y.j litwin 1981 the use of wetlands for water pollution control u.s epa grant no r806357 8 stowell r s weber g tchobanoglous b wilson and k townzen mosquito considerations in the design of wet/and systems for the treatment of wastewater department of civil engineering university of california davis california and vector biology control branch california state department of health services sacramento ca 1982 9 reed s.c and r.k bastian wetlands for wastewater treatment an engineering perspective in ecological considerations in wetlands treatment of municipal wastewaters van nostrand reinhold ny pp 444-450 1985 10 reed s.c e.j middlebrooks and r.w crites natural systems for waste management and treatment mcgraw-hill book co ny 1987 11 hyde h.c and r.s ross technology assessment of wetlands for municipal wastewater treatment municipal environmental research laboratory office of research and development u.s environmental protection agency epa600/2-841154 ntis no pb 85106896 1984 12 herskowitz j s black and w lewandowski listowel artrticial marsh treatment project in aquatic p/ants for water treatment and resource recovery proceedings of the conference on research and applications of aquatic plants for water treatment and resource recovery magnolia publishing inc orlando fl pp 247261 1987 13 bavor h.j d.j roser and s mckersie nutrient removal using shallow lagoon-so/id matrix macrophyte susyems in aquatic plants for water treatment and resource recovery proceedings of the conference on research and applications of aquatic plants for water treatment and resource recovery magnolia publishing inc orlando fl 1987 2 3 4 5 6 7.

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