a guide to creating wetlands for:
                      DOMESTIC WASTEWATER
                       COAL MINE DRAINAGE

                    in the Mid-Atlantic Region

 Many penpl.. contributed to this Handbook. A,i In.«r:u.,u<:y Core Group provido.l the initial impetus for the Handbook, and inter orovid*H
 guidnnce and technical input during its preparation. The Core Group comprised:
 Carl DuPoldl. USDA - NRCS. Chester. PA
 Robert Edwards, Susquuhanna River Basin Commission.
  Harrisburg. PA
 Lainonle Garber. Chesapeake Bay Foundation. Harrisburg, PA
 Barry Isaacs. USDA - NRCS, Harrisburg. PA
 Jeffrey Lapp. EPA. Philadelphia, PA
 Timothy Murphy. USDA - NRCS. Harrisburg. PA
 Glenn Rider. Pennsylvania Department of Environmental
  Resources, Harrisburg. PA
                  Melanie Sayers. Pennsylvania Department of Agriculture. Harrisburg. PA
                  Fred Suffian. USDA - NRCS, Philadelphia, PA
                  Charles Takita. Susquehanna River Basin Commission. Harrisbura. PA
                  Harold Webster, Penn State University, DuBois. PA.
                           Wet'andS C011tributed fay Providing information and by reviewing and commenting on the Handbook. These
 Robert Bastian. EPA .Washington. DC
 William Boyd. USDA - NRCS. Lincoln. NE
 Robert Brooks, Penn State University.
  University Park. PA
 Donald Brown. EPA, Cincinnati. OH
 Dana Chapman. USDA - NRCS, Auburn. NY
 Tracy Davenport, USDA • NRCS. Annapolis
 Paul DuBowy, Texas A & M University.
  College Station. TX
 Michelle Girts. CH2M HILL. Portland. OR
 Robert Hedin, Hedin Environmental,
  Sewickley. PA
 William  Hellier, Pennsylvania Department of
  Environmental Resources, Hawk Run. PA
 Robert Kadlec. Wetland Management
  Services. Chelsea, MI
 Douglas Kepler, DamariscoUa, Clarion. PA
 Robert Kleinmann, US Bureau of Mines,
  Pittsburgh, PA
 Robert Knight, CH2M HILL, Gainesville. FL
 Fran Koch, Pennsylvania Department of
  Environmental Resources, Harrisburg. PA
 Eric McCleary, Damariscotta, Clarion, PA
 Gerald Moshiri, Center for Wetlands and
  Eco-Technology Application, Gulf Breeze,
 John Murtha, Pennsylvania Department of
  Environmental Resources, Harrisburg, PA
 Robert Myers. USDA - NRCS, Syracuse, NY
 Kurt Neumilfer, EPA, Annapolis, MD
 Richard Reaves, Purdue University, West
  Lafayette. IN
 William Sanville, EPA, Cincinnati, OH
 Dennis Sievers. University of Missouri,
  Columbia, MO
Earl Shaver, Delaware Department of
  Natural Resources and Environmental
  Control, Dover, DE
Daniel Seibert, USDA - NRCS, Somerset, PA
Jeffrey Skousen, West Virginia University,
  Morgantown, WV
Peter Slack. Pennsylvania Department of
  Environmental Resources, Harrisburg, PA'....
Dennis Verdi, USDA - NRCS, Amherst, MA\
Thomas Walski, Wilkes University, Wilkes-
  Barre, PA                   '*",
Robert Wengryznek, USDA - NRCS. Orono,
Alfred Whitehouse, Office of Surface
  Mining, Pittsburgh, PA
Christopher Zabawa,  EPA, Washington.^.
This document was prepared by Luise Davis for the USDA-Natural Resources Conservation Service and the US Environmental Protection
Agency-Region III. in cooperation with the Pennsylvania Department of Environmental Resources. Partial funding has been provided with
nonpoint source management program funds under Section 319 of the Federal Clean Water Act.
The findings, conclusions, and recommendations contained in the Handbook do not necessarily represent the policy of the USDA - NRCS,
EPA - Region HI. the Commonwealth of Pennsylvania, or any other state in the northeastern United States concerning the use of constructed
wetlands for the treatment and control of nonpoint sources of pollutants.  Each state agency should be consulted to determine specific
programs and restrictions in this regard.

                                           VOLUME 3
                                   TABLE OF CONTENTS
                              	•	3
          Contaminant Removal Processes	           	'.'
          Advantages and Limitations of Constructed Wetlands	
          Creating Effective Constructed Wetlands	  '	6
          Types of Constructed Wetlands	.""
          Wastewater Characteristics	..'."."...'	
               Water Quality	,	     _	
               Water Quantity	;         	""  •
          Prertreatment	    .....	
          Discharge Option	,	',	'""""	

 CHAPTERS.  PERFORMANCE EXPECTATIONS	]	                       u
          Introduction	;....        _	'	'""
          Biochemical Oxygen demand and Total Suspended Solids	   n
          _,   .                   •""	"	•	14

 CHAPTER 4. SURFACE FLOW WETLANDS	;	               17
          Wetland Design	      ;               	'	
               Configuration	.-.	                          	 _
               Water Depth	       '	
          Sizing	„	ZZZZZZZZZZZZZZZ	18
               Presumptive Method for BOO		18
               Field Test Method for BOD	'.	ZZ.1Z....Z....ZZ...	    20
               Presumptive Method for Nitrogen	.	21

          Introduction	.	                 	'	"•
          Wetland Design	\	_          '""",".	  23
               Darcy's Law.	          	23
               Media Types	.^Z.Z.ZZ	24
               Length-to-Width Ratio	",'	24
               Bed Slope	.......Z.......Z .  	   25
          Sizing	;	ZZZZZZZZZZZZZ.25
          Biochemical Oxygen Demand	  	'	25
               Total Suspended Solids	.ZZZ"	26
              Nitrogen	_                             26


                                     LIST OF TABLES
 Table 1.  Removal mechanisms in constructed wetlands
 Table 2. Advantages and limitations of constructed wetland treatoent'of [[[ 5
        domestic wastewater ....................................
 Table 3. Guidelines for creating constructed wetlands ................. • ........ ............................................... ' ............... 5
 Table 4. Summary of agricultural constructed wetland operationaTdata .............................. ' .............................. 6
 Table 5. Design summary for surface flow wetlarids ........              [[[ •  n
 Table 6. Design summary for subsurface flow wetlands  ............................................... " ..................... ' ............  17
                                               [[[  23

                                    LIST OF FIGURES

                                          CHAPTER 1
     This volume focuses on the use of con-
  structed wetlands to treat agricultural wastewa-
  ter. It is to be used in combination with
  Volume 1: General Considerations, which pro-
  vides information on wetland hydrology, soils
  and vegetation, and  on the design, construction.
  operation, and maintenance of constructed
  wetland systems.
     Constructed wetlands can provide an inex-
  pensive and easily operated means of removing
  organic matter, particulates, nutrients, and
  bacteria from agricultural wastewater. Agricul-
  tural wastewaters suitable for wetland treatment-
  include milkhouse wastewaters, runoff from
  concentrated livestock areas, and effluents from
  settling tanks and manure treatment lagoons.
     Interest in using constructed wetlands to
  treat agricultural wastewaters has been
  prompted by the success of constructed wet-
  lands in removing organic matter, particulates,
 and nutrients from municipal wastewaters.
 However, the use-of constructed wetlands in
 agriculture is a fairly recent development  and
 the number of systems that have been installed"
 is still small. While the data show  that properly
 designed wetlands can be effective  in treating
 agricultural wastewater,.much is not yet under-
 stood and many of the relationships between
 design and  performance have not been clearly
 established. The use  of constructed wetlands in
 agriculture  will be modified and refined as more
 systems are  installed and monitoring data are
 gathered over longer periods of time.  The guid-
 ance presented here should be considered as
 today's "state of the art" and will likely be modi-
 fied as our understanding of these systems grows.
    As with  other agricultural waste management
 practices, constructed wetlands are one compo-
 nent of an overall agricultural waste management
system (AWMS). This Handbook discusses the
contributions that constructed wetlands can  make
to an AWMS, the performance that can reasonably
be expected, and the factors that are important in
the design of effective constructed wetlands. Step-
by-step procedures in  designing constructed wet-
lands are given.
    This volume incorporates the guidance pre-
sented in the Soil Conservation Service (SCS, now
the Natural Resources  Conservation Service) 'con-
structed Wetlands for Agricultural Wastewater
Treatment Technical Requirements (1991), which is
an important reference for those interested in usin°
constructed wetlands in agriculture.            °


                                          CHAPTER 2

    The most important removal mechanisms in
agricultural constructed wetlands are physical
sedimentation and filtration, and biological assimila-
tion, breakdown, and transformation (table I).
The suspended solids that remain in the effluent
from pretreatment unit are removed in the wetland
by sedimentation and filtration. These physical
processes also remove a significant portion of other
wastewater constituents,such as biochemical
                    oxygen demand (BOD), nutrients, and pathooenc
                    (Brix 1993). Soluble organic compounds are° for
                    the most part, degraded by microbes, especially
                    bacteria, that are attached to the surfaces of pla'nts
                    litter, and the substrate.

                     OF CONSTRUCTED WETLANDS
                       Constructed wetland treatment of agricultural
                   wastewater offers a number of advantages (table 2),
                         Table 1. Removal mechanisms in constructed wetlands
                                          (after Brix 1993).
      Wastewater ConstihiPnf
    Biochemical oxygen demand
   Suspended solids
 Microbial degradation (aerobic and anaerobic)
 Sedimentation (accumulation of organic matter/slud°e
   sediment surfaces)
                                by microbial nitrification and
Plant uptake
Volatilization of ammonia
Soil sorption (adsorption-precipitation reactions with aluminum
  iron, calcium, and clay minerals in the soil)          "«««n.
Plant uptake
Natural die-off
                 Table\2. Advantages and limitations of constructed wetland treatment.
   • are capable of providing a high level of
   • can reduce or eliminate odors
   • are inexpensive to operate
   • are largely self-maintaining
                are affected by season and weather, which may
                reduce treatment reliability
                are sensitive to high ammonia levels
                may hold potential for mosquitoes and other insect
    are able to handle variable wastewater loadings  * require a continuous supply of water
   • reduce the amount of area needed for land
               require dedicated, single land use
              • may be more expensive to construct than other
               treatment options

including odor control and simplicity of opera-
tion.  Constructed wetland treatment is con-
strained by a number of limitations, including
variability in treatment effectiveness and the
sensitivity of wetland plants to high ammonia
concentrations. The advantages and limitations
of a constructed wetland as an alternative to
other treatment options must'be understood and
weighed before deciding to install a constructed
    Suggestions for creating an effective con-
structed wetland are given in table 3. Since the
objective of using a constructed wetland is to
simplify the handling of wastewater, the system
should be made as easy as possible to operate
while ensuring reliable treatment. Building a
    slightly larger system may be more expensive to
    construct but may be less costly and more
    reliable to operate than a smaller system. At-
    tention to several factors will help to ensure
    successful wetland treatment:

    • Adequate pretreatment. Pollutant loads in
     agricultural wastewaters often greatly exceed
     the ability of a wetland to treat or assimilate
     them.  A wetland can be severely damaged by
     a wastewater that is too concentrated, for
     instance, one that contains high levels of
     ammonia.  Pretreatment to lower pollutant
     loads is essential to avoid overloading the

    • Adequate retention time.  A wetland treats
     wastewater through a number of biological
     (largely microbial). physical, and chemical
     processes.  The water must remain in the
     wetland long enough for biological and
     chemical transformations to take place and for
                          Table 3. Guidelines for creating constructed wetlands.

   Know what you are dealing with
   Size the wetland generously

   Wetlands must have water

   Give the plants a chance

   Don't overload the wetland

   Don't kill the wetland

   Effluent disposal must be addressed

   Keep an eye on what is happening

   Get interdisciplinary help
Sample the wastewater
Know what pretreatment will accomplish

Too small a wetland cannot perform well

Know the water budget
Provide a supplemental source of clean water

Allow time for establishment
Avoid shock loading
Keep ammonia levels to 100 mg/L or less

Application rates must not exceed treatment rates  -

Keep raw milk out of the wetland
Keep herbicides out of the wetland

Use other recognized practices

Monitoring is important

Environmental engineer
Water quality specialist.
Plant materials specialist/biologist/extension agent
State agencies
                         VOLUME 3: AnRinn.TttPAi WASTCWATFB

 sedimentation and deposition to occur.  The
 wetland must be built large enough to pro-
 vide the necessary retention time.

 Supplemental water. If a constructed wet-
 land is to remain healthy, it must remain
 relatively wet.  Wetlands are generally
 .tolerant of fluctuating flows, but they cannot
 withstand complete drying.  For this reason,
 either a slow release of wastewater must be
 assured or a supplemental source of water
 must be provided. Supplemental water can
 be used to dilute the wastewater to accept-
 able levels and also to  assure that the wet-
 land stays wet. Enough water should be
 supplied to the wetland to maintain a slow
 flow of water, since stagnant water can lead
 to problems with odors and mosquitoes.
 Proper management. Constructed wetlands
 are "high management, low maintenance"
 systems.  They must be actively managed  if
 they are to perform well. "Management"
 means watching the wetland for signs of
 stress or disease and adjusting water levels
 or input streams accordingly. While wet-
 lands are low maintenance systems, they are
 not maintenance-free.  For instance, the
 pretreatment unit must be cleaned periodi-
 cally to keep excessive solids from entering
 the wetland, and valves and piping must be
 checked to detect and correct blockages or
   Most wetlands used in agriculture are
surface flow (SF) wetlands.  The advantages of
SF wetlands are that their design and construc-
tion are straightforward. Operation and main-
tenance are simple.  Because the water surface
is unconstrained, SF wetlands are able to
accept wide variations in flow. SF wetlands
can provide excellent removal of 5-day bio-
chemical oxygen demand (BOD5) and total
suspended solids (TSS). Good removal of ammo-
nia and total nitrogen has been achieved at some
wetlands.  SF wetlands are discussed in Chapter 4.
   In subsurface flow (SSF) wetlands, the water
level must.r.emain below the surface of the sub-
strate if the wetland is to perform well. The
design and construction of SSF wetlands are
therefore more complicated than for SF wetlands
and SSF wetlands must be managed and moni-
tored much more closely. There have been prob-
lems with  unintended surface flow and apparent
plugging.  Because of the hydraulic constraints
imposed by the media, SSF wetlands are best
suited to relatively uniform flows. Their use in
agriculture has thus been limited.  SSF wetlands
may be appropriate for field drain discharges and
research on such systems is being conducted.
   SSF systems are discussed in Chapter 5.

    To design the wetland correctly, an accurate
assessment of contaminant loadings is needed
(loading = contaminant concentration x waste-
water volume). To calculate loadings, data are
needed on the average water quality, the maximum
concentrations, and the largest and smallest
volumes that may occur.  Loadings may vary
throughout the year as the volumes of water
change in response to climatic factors, such as
rainfall and evaporation.  Maximum concentra-
tions will probably occur in the late summer and
fall, when water losses due to evapotranspiration'
are greatest. The highest flows can be expected
during the wet season, but pollutant concentra-
tions may be lower at this time because of dilu-
tion. The design should be based on the highest
pollutant loadings.

    The characteristics of agricultural wastewater'
vary, depending on the specifics of the agricultural
operation, and should be determined by laboratory
analysis before the wetland is designed. The Soil

        Conservation Service (SCS. nou- the Natural
        Resources Conservation Service) recommends the
        following analyses for agricultural wastewater
        (SCS 1991):

           5-day biochemical oxygen demand (BOD )
           total solids (TS)      "                 3
           total Kjeldahl nitrogen (TKN)
           nitrate nitrogen (NO3-N)
           ammonia nitrogen (NH3 + NH^-N)
           total phosphorus (TP).
           The design of the wetland is usually based on
        the removal of BOD (usually measured as 5-day
        biochemical oxygen demand, BODS) or nitrogen
        (measured as total Kjeldahl nitrogen or nitrate
        nitrogen).  Concentrations of ammonia (NH3 +
        NH4-N, un-ionized ammonia + the ammonium ion)
        should be evaluated because of the toxicity of
        ammonia to \vetland plants.
           Additional analyses may be  needed. For
        instance, if high salinities could occur, chloride
        concentrations should be measured to determine
        the salinities that the vegetation will be exposed
        to; salinities in the brackish range will suggest that
        salt-tolerant vegetation should be planted. The
        likelihood of toxic compounds, and high or low
        pHs that could affect the biological components
        of the wetland should be considered.
           An accurate estimate of the volume of waste-
       water is needed, including the expected average,
       maximum, and minimum wastewater flows,  An
       accurate figure for the volume of water to be
       treated must be determined: too small  a wetland
       will perform poorly; a large wetland may require
       supplemental water to maintain the wetland
       during the dry season. The maximum  expected
       flow must be determined. If the maximum ex-
       pected flow is larger than the capacity  of the
       wetland, a bypass will be required. The minimum
       expected flow should be calculated to  determine
       the volume of supplemental clean water that may
       be needed.

     Raw agricultural wastewaters are character-
 ized by very high concentrations of BODS,
 nutrients, and total and dissolved solids.3 To
 avoid overloading \vetland removal capabili-
 ties, raw wastewaters must be pretreated to
 lower the concentrations of these contami-
 nants.  Pretreatment is also necessary to lower
 nutrient and organic loads (particularly ammo-
 nia) to avoid damaging the wetland vegetation.
 Pretreatment to lo\ver total organic loading
 also helps to control mosquito populations
 (Wieder et al. 1989). Pretreatment can be made
 through settling tanks and basins, flotation
 tanks, filters, or mechanical separators, either
 singly or in combination. The Agricultural
 Waste Management Field Handbook (SCS
 1992) discusses various pretreatment options.
     In the northeastern United States, percent
 removals in BODsby settling tanks are gener-
 ally around 70%. To protect the vegetation,
 SCS (1991) suggests a target concentration of
 100 mg/L ammonia for the effluent from the
 pretreatment unit. However, Reaves et al.
 (1995) found that while concentrations of
 200 -.300 mg/L ammonia damaged the growth
 of young cattail shoots in a wetland used to
 treat swine effluent, mature cattails did not
 seem to be affected. Reaves et al, (1995)
 theorize that the ammonia may be present as
 the non-toxic ammonium ion (NH/) rather
 than the toxic ammonia ion (NH3).
    Pretreatment must remove solids.  Most
 settleable, floating, and non-biodegradable
 solids, such as plastics and grease, must be
 removed before the water enters the wetland  or
 the wetland will eventually clog.  Pretreatment
 to remove solids also avoids potential clogging
 of pipelines, gates, and valves.  Since bacteria"
 and viruses adsorb on solids, pretreatment to
 decrease solids also decreases the numbers of
bacteria and viruses (Ives 1988).  SCS (1991)
suggests 1,5 00 mg/L total solids or less as a
target concentration for the effluent from the
pretreatment unit.
                                 VOLUME 3- Anorr-MtTtiD»t U/»

     Fats are a particular problem since they float
 on the surface of the water, causing a scum that
 blocks gas transport and rapidly depletes dis-
 solved oxygen.  Raw milk can suffocate a wetland
 and must be kept out of the wetland.
     An organic filter (a bed of chipped mixed
 wood bark) is being tested as a means of reducing
 odors and ammonia concentrations at a veal
 operation (Murphy et al. 1993). The effluent from
 the settling tanks passes through the filter by
 subsurface flow before .entering the wetland. The
 bed has completely eliminated odors; ammonia
 removals have been variable.
     In addition to pretreatment, dilution may be
 necessary for som.e wastewaters. The wetland
 system can be designed to recycle the wetland
 effluent for use in diluting the effluent from the
 pretreatment unit.
     There are several options for the wetland
 • storage for later land application
 • discharge to an infiltration area
 • recycle through the wetland.
     Where possible, the effluent should be re-
 cycled. Recyling the treated effluent from the
 wetland is an efficient way to dilute influent BOD
 and suspended solids.  Recycling decreases the
. potential for odors and may possibly increase
 dissolved oxygen concentrations, which in turn
 may enhance nitrification.  Recycling is also an
 efficient way to maintain adequate flows during
 low-flow periods.
     The disadvantages  of recycling are the in-
 creased construction costs and increased operation
 (pumping) costs.  Also, recyling may slowly
 increase salinities as evapotranspiration removes
 water from the system.


                             PERFORMANCE EXPECTATIONS

    Data on agricultural systems are limited, both
in the number of systems that have been built and
in the length of time the systems have been operat-
ing.  However, a number of constructed wetland
systems are being used to treat domestic wastewa-
ters, which contain a array of contaminants similar
to those in agricultural wastewater.  Information
from domestic systems is thus useful in assessing
the potential of constructed wetlands to .treat
agricultural wastewater.
                              BIOCHEMICAL OXYGEN
                                DEMAND AND TOTAL
                                 SUSPENDED SOLIDS

                           Wetlands provide a number of mechanisms for
                       removing BOD5 and TSS, and constructed wet-
                       lands are,extremely efficient at removing these
                       contaminants.  At seven agricultural systems that
                       have recently begun operating, removals range
                       from about 60% to more than 90% (table 4).  In a
                       survey of 324 municipal, industrial, stormwater,
                       and other constructed wetlands, Knight et al.
                 Table 4. Summary of agricultural constructed wetland operational data
                BODs (mg/L)
                In Out   %.
   TSS (mg/L)
   In  Out
               NH3-N (mg/L)
               In  Out  %.




Field drain





                     13   65
                      9   75
                     11   70

                    375   68
                    339   81
                    397   62

                    138   61

                      6   91

                     28   38
                     20   56
                     24   47
                    230   83
                    190   88
 44   68
 56   49
 47   62
281   65
151   89
558   42









0.4  93
0.3  95
1.2  84
 68  70
110  51
 90  SO
 29  54
3.5  94
 23  76
  3  97
  2  98
 36  68
 41  63
                                                   0.3   0.3
                           In  Out
654  201  56
476  215  57
890  275  36
 92   38  57
 70    6  91
104   41  61
104    6  94
104    5  95
                  295  <95   68
                  320   64   80
                   23   21    6
                                   In   Qui
 3.3   76
 3.8   74
 5.7   60
 24   58
 22   78
 23   49
  S   66
 6.2   76
 30   55
 23   65
 15   77
 18   36
 16   41
 <4 >80
  5   80
0.02    0
   %: percent removal                                                                .
   a   surface flow, milkhouse wash water + runoff + rainfall, Mississippi, 2 years of data (Cooper et al. 1993)
   b   surface flow, bam washwater + yard runoff, Indiana, 1 year of data (arcsine means) (Reaves et al. 1994)
   c   surface flow, milking parlor washwater + yard runoff + rainfall, Oregon, 6 months of data (Skarda et al. 1994)
   d   surface flow, effluent diluted with stormwater pond effluent. Alabama, 1 year of data (Hammer et al. 1993)
   e   surface flow, lagoon effluent, flow rates of 2610 gpd/1094 gpd/540 gpd (lines 1-3). Alabama. 3 months of data
       (McCaskey et al. 1994)                     or  _    or
   f   surface flow, lagoon effluent, marsh-pond-marsh system, Mississippi, 16 months of data (Cathcart, Hammer.
       and Triyono 1994).                                            .
   g   subsurface flow, dilute chicken manure, Czechoslovakia, 1 year of data (Vymazal 1993]
   h   subsurface flow, cropland tile drain effluent, Pennsylvania, 4 years of data (Taylor et al. in preparation)

^ „!_•
s "°!
- m r 	 . .
™ 1M 	 	
•i 4-... _
i .ua
J .1 'L

.; 1

i 4- ' .
\" *'•• 1
. i >
1 !
i . •• i
1 •
g ' . " " '" - •"
BOD, Mass Loading Rate (kg/ha/d)
Figure 1. BOD, mass loading and removal rates in
wetland treatment systems
(from Knight et al. 1993).
 (1993) found that BOD, mass removal efficiencies
 were generally 70% or more at mass loading rates
 up to 250 Ib/ac/day (280 kg/ha/day),  which is
 considerably higher than the 65 Ib/ac/day recom-
 mended by SCS (1992) as the maximum BOD,
 loading rate for agricultural wetlands. A linear
 regression of the 324 data records used to examine
 the predictability of BOD, outflow concentration as
 a function of BOD, inflow concentration and
 hydraulic loading produced the following (figure 1)
 (Knight et al. 1993):
     BODOUT = 0.097*HLR + 0.192*BODIN
                 Rz'= 0.72
     BODOUT = BOD, outflow concentration, mg/L
       BODIN = BOD, inflow concentration, mg/L
         HLR = hydraulic loading rate, cm/day.

    While average annual removal rates were
 usually high, rates sometimes varied considerably
 on  a monthly or seasonal basis (Knight et al. 1993).
    In wetlands, BOD is produced within the
 system by the decomposition of algae and fallen
 plant litter.  As a result, wetland systems do not
 completely remove BOD and a residual BOD of
 5 to 7 mg/L is often present in wetland effluent
 (EPA 1993). This internal production of BOD
decreases removal efficiencies at very low inflow
                                                         TSS is removed primarily by sedimentation and
                                                      Miration, and removal is enhanced as the density of
                                                      surfaces within the wetland increases. Cooper et al
                                                      (1993) found that TSS removals increased as plant
                                                      litter accumulated.
                                                         To maximize the removal of BOD5 and TSS, the
                                                      growth of plants (particularly underground tissues)
                                                      and the accumulation of litter should be encouraged.
                                                      Plants and plant litter provide organic carbon and
                                                      attachment sites for microbial growth, and promote
                                                      filtration and sedimentation. Because of the impor-
                                                      tance of microbial  processes in removing BOD ,
                                                      adequate residence time must be provided. The SCS
                                                      (1991) recommends a hydraulic residence time of at
                                                      least 12 days.
    In contrast to the simplicity of BOD and TSS
 removal, the chemistry of nitrogen removal is com-
 plex (figure 2). Nitrogen occurs in a number of
 forms, including organic and inorganic compounds,
 and nitrogen gas. In wetlands, the important forms
 include nitrogen gas (N2j, nitrate (NO/), nitrite (NO/)',
 ammonia (NH3), and ammonium (NH/).
  . In wetlands, the removal of nitrogen involves a
 series of reactions (Mitsch and Gosselink 1986).
 Decomposition and mineralization processes .convert
 a significant part of organic nitrogen to ammonia.
 Ammonia is oxidized to nitrate by nitrifying bacteria
 in aerobic zones (nitrification) and nitrates are
 converted to nitrogen gas by denitrifying bacteria in
 anoxic zones (denitrification); the gas is released to
 the atmosphere.  The sequence is:
    organic nitrogen  -> ammonia    aerobic or anaerobic
                   nitrogen     reaction
    ammonia nitrogen -> nitrate      aerobic reaction
    nitrate nitrogen  -> nitrogen gas  anaerobic reaction,
                              requires a carbon source
                              as food for the bacteria

    Since nitrification is an aerobic process, rates are
controlled by the availability of dissolved oxygen to

.--»"""       ,„.,„,,„»"—

                            * and 95% W"   °80 to/ac/day. «*a

              f^W^^ M—UMli°ni
                               Residence ^j^. The system

                                 deep and the v    ^ surface to pro   °0b\em

                                 turbulence of t^    ^ correct thvsp_

^WaisT* tho^rt co; Tab/e <;• HO ,.
   ,-f' ph°sPnorUs is a h-
    l      *  1
            f°rins- It has

            ' ^



                                        CHAPTER 4
                             SURFACE FLOW WETLANDS
    Guidelines to designing a SF constructed
wetland are given in table 5.  The design assumes
that the wastewater has been pretreated to reduce.
BOP5 by 70%, TSS to less than 1,500 mg/L, and
ammonia to less than 100 mg/L.
    The configuration should take advantage of the
natural topography of the site to minimize excava-
tion and grading costs. The configuration should
allow water to move through the wetland by
gravity.  The wetland should not be placed where
excess solids could be washed into the wetland;
for instance, sites next to solids;settling pads
should be avoided. While treatment wetlands are
often designed as rectangles, wetlands can be built
as semi-circular or irregular shapes to fit the
                          topography of the site. Using curved shapes also
                          eliminates right-angled corners, which tend to be
                          "dead water" areas. If a shape other than a rect-
                          angle is used, the widest portion should be located
                          at the inlet end to facilitate equal flow distribu-
                              For large wetlands, dividing the, wetland into
                          side-by-side cells should be considered. Dividing
                          a wide wetland into parallel cells lessens the
                          likelihood of preferential flow paths and short-
                          circuiting and promotes the contact of the waste-
                          water with the surfaces in the wetland.  It also
                          facilitates maintenance since one set of cells can
                          be taken out of operation temporarily.
                              If the removal of nitrogen and ammonia is-a
                          major objective, including a deeper (2-3 ft) open
                          water pond in the middle of a longer wetland cell
                          should be considered to increase nitrification and


   Bottom slopes

   Water depth


Table 5. Design summary for surface flow wetlands.

             Reduction of BOD5 by 70%
             Reduction of solids to <1,5 00 mg/L
             Reduction of ammonia to <100 mg/L
             Fit the wetland to the site
             Divide large wetlands into side-by-side cells

             3y gravuy, as much as possible
             Side-to-side elevations: level
             Inlet to outlet slopes: almost flat (0.5 -1.0%)
              3 - 8 inches, depending on the plants selected
              18 inches maximum
              Complete coverage is more important than the species used
              Use at least two or three different species

              Wetland must be sealed to limit infiltration and exfiltration
              Water table must be below or excluded from the wetland


    The design should plan for 3 to 8 inches c:
 surface xvater, with a maximum of 18 inches.
 Deeper water may be advisable in winter to accom-
 modate the slower reaction rates during cold
 weather and to guard against freezing.  The \vet-
 land may have to be divided lengthwise into a
 series of cells to prevent the water in any of the
 cells from being deeper than desired. Each ceil
 will then discharge to a downstream cell of the
 same width. The maximum length of each cell is
 based on the slope of the bottom of the cell (which
 should not exceed 0.5 to 1.0%) and the water
 depth suitable for the wetland vegetation (which
 is generally 18 inches or less).  The number and
 length of the subdivisions \vill  depend  on the
 length of the cells and the slope of the bottom.
    The bottom of the cells should be flat from
 side to side to assure an even distribution of water
 across the cells and to prevent channeling.
    Procedures for sizing SF wetlands for the
removal of BOD5. TSS, and nitrogen are still
preliminary. It has been widely presumed that
simple first order chemical reaction rates apply for
pollutant removal and that constructed wetlands
roughly follow plug flow in their internal hydrol-
ogy. However, several recent studies have shown
that the movement of water thrtiugh constructed
wetlands is considerably more complex than that
described by standard flow equations (Kadlec et al.
1993, Kadlec 1994). The flow through a wetland is
related to the morphology of the cell, the pattern of
vegetation density, and the balance between
evapotranspiration and precipitation. Constructed
wetlands exhibit mixing characteristics intermedi-
ate between plug flow and well-mixed, flows are
typically in the transition zone between laminar
and turbulent, and hydrologic conditions change
continuously with changes in the weather and the
seasons. Factors such as obstructions to flow, the
development of channeling, recirculation patterns,
 and the presence of stagnant areas cause further
 deviations from calculated theoretical flows.
 Contact times are not often as great as the theoreti-
 cal residence time calculated from the wetland
 empty volume and the volumetric flow rate. As
 a final complicating factor, the chemistry of
 wetlands is complex, involving interrelated
 biological reactions and mass transfers. These
 factors and the lack of good information on factors
 such as reaction rate constants have probably led
 to many systems being underdesigned.
    Agricultural wetland systems are usually sized
 to remove the necessary amount of BOD5. The
 SCS (1992) uses two methods to determine the size
 of a constructed wetland for a specific site: the
 presumptive method and the field test method.
    The presumptive method is used when the
 pretreatment system has not yet been installed and
 the concentration of BOD, in the pretreatment unit
 can only be estimated. The presumptive method
 first calculates a surface area and then determines
 the resulting hydraulic residence time, adjusting
 the size as necessary to achieve the required
 residence times.
    The field test method uses known, measured
 BOD5 concentrations in the effluent from the
 pretreatment unit to calculate hydraulic residence
 times, from which the required surface area is then
    Removal efficiencies for TSS are similar to
 those for BODS and design for BOD5 removal
should achieve similar TSS removal.
    For wetlands designed to remove ammonia as
well as BOD5, the size of the wetland should be
based on the removal of the ammonia. Since
ammonia removal is a less efficient process than
BOD, removal, ammonia removal requires a larger
wetland area than does BOD5 removal.
   This method assumes that a certain amount of
BOD, is present in the wastewater and that a
certain amount is removed by the pretreatment
system. It then uses the remaining BOD, load with

a standard wetland areal loading rate to determine
the surface area needed for adequate treatment.
Determine the production of BOD. per day:
Livestock production of BOD5 is as follows:
                            production (Ib)
                 Average     ,1000 Ib animal
                weight Hbl  unit (AU1 per day
    Dairy cows       1300
    Beef cattle         750
    Swine            200
    Poultry - layers      4
    Poultry - broilers     2.2
BODS= BOD5/1000 Ib AU x number of
animals x average weight/1000 Ib
Add 10%  BOD5to account for that in waste
hay and feed:
Adjusted BOD3= BODsx 1.1
Determine BOD3 remaining after pretreatment.
if known.
A well-managed settling/flotation tank for
milkhouse wastewater will remove 70% of
BOP5. Use a removal factor of 0.30 (70%
BOD5 remaining in tank effluent = adjusted
If using an anaerobic lagoon, use a rate of 40%
rate (60% removal):
BODS remaining in lagoon effluent = adjusted
Determine the water surface area (SA) for the
constructed wetland:
SA = BOD3 loading / recommended areal BODS
loading rate
SCS recommends an areal BOD5 loading rate of
65 Ib BOD5 /ac/day. It is known that treatment,
and therefore areal loading rate, are affected by
climate but no research or field data are
 available that can be used to quantify the
 influence of different climate conditions.
A  standard value is therefore used.
Determine the overall dimensions. The
optimal length-to-width ratio has not yet been
determined. The SCS (1992) recommends a
ratio of 3:1  to 4:1. For a length-to-width ratio
       W = width of constructed wetland
       L= length = 3VV
 Then SA = 3W x VV = 3W*
Determine the hydraulic residence time (t) in
days. Data needed are average water depth
(D). porosity (P), and daily flow rate (Q).
        t = SAxD  xP/Q         (4.1)
where: t = hydraulic  residence time, days
      SA = surface area of constructed
            wetland, ft2 (length x width)
       D = average water depth in
            constructed wetland, ft
       Q = average daily flow rate. ftVday
        P = porosity, percent as a decimal.
    The Q value is the average flow in the bed,
 calculated  from flow through the bed plus
 gains and losses from precipitation and evapo-
 transpiration. Published values are usually
 available for precipitation .and evapotranspira-
 tion for local conditions. Large rainfall and
 snowmelt volumes can greatly affect Q and
 must be considered in  the design; some con-
 structed .wetlands have failed because high
 flows were not factored into the design.
    The porosity (P)  is  the ratio of the volume
 occupied by water to the volume occupied by
 plants and water combined. The following
 porosity values have been determined:
 cattails (Typha spp.) 0.95   (SCS 1992)
 bulrush            0.86
   (Scirpus yalidus]
                                                          (S. cyperinus]
                                                        common reed        0.98
                                                        rushes (Juncus spp.)  0.95
(Watson and
Hobson 1989)
(Watson and
Hobson 1989)
{Watson and
 Hobson 1989)
(Watson and
Hobson 1989).

     The volume occupied by underground plant
 structures (roots and rhizomes) increases over time
 (Reed 1993) and porosity gradually decreases. Tin;
 wetland should be designed conservatively to
 allow for the diminished porositv.
     The SCS recommends a hydraulic residence
 lime of at least 12 days since this residence time
 has been found empirically to provide adequate
 removal of BOD5.

     The field test method uses data from samples
 collected in  the pretreatment unit to calculate
 hydraulic residence times via the following
     t = 2.7 (In C - In Ce + In F) / 1.1 '™>'. or    (4.2)
     t « (In C. - In Ce + In F) / 65K,.
     t = hydraulic residence time, days
    C( = constructed wetland influent BOD5
        concentration, mg/L
    Ce = desired constructed wetland effluent
        BODj concentration, mg/L
    In = natural logarithm
    F = fraction of BODS that is not removed as
        settleable solids near the head of the
        wetland, expressed as a decimal fraction,
        (soluble BODj/total BOD5)
    T = water temperature, °C
   Kj. = temperature-dependent reaction rate
        constant, days •'
    The values for C, and F are determined from
samples of the supernatant (the liquid above the
solid layer) in the pretreatment unit. A composite
sample (several samples combined) should be
collected within the unit. Ideally, samples should
be collected and analyzed during various seasonal
conditions. Because BOD. concentrations in these
systems can vary widely, and because an adequate
safety factor must be assured, the highest sample
value should be used to design the system.
    The temperature of the water (T) is controlled
by local climatic conditions. The lowest water
temperature under which the wetland will be
 expected to perform should be used for the design
 In constructed wetlands in the northern states, if
 the wetland does not freeze completely, the
 wetland will continue to function and water
 temperatures under the ice can be estimated as
 40°F (5"C)(Bovd 1991). However, at low tempera-
 tures, removal rates will be lower and the wetland
 will have to be larger to accommodate the slower
 rates. Alternatively, the  wastewater can be stored
 in the pretreatment unit  during the cold seasons.
 In this case, a higher value for water temperature
 can be used and the wetland made smaller, de-
 pending on BOD5load. wastewater volume, and
 local temperatures.
     The values to be used for F and K_ in design-
 ing constructed wetlands have not been con- °
 firmed. The value often used for F in domestic
 systems is about 0.52. This should be the lower
 limit for F unless research determines otherwise.
 If organic material is adequately removed by
 pretreatment. the value of F can be increased, but
 it should not be more than 0.90. For an agricul-
 tural waste treatment lagoon, the value ofF may-
 equal 0.90.  A value for K,. of 0.0057 (l.lpM)is~
 often used.  However, experimental data on the
 values to be used in designing constructed wet-
 lands have been difficult to obtain because of the .
 logistic and  economic difficulties in experiment-
 ing with wetlands on a scale large enough to be
 appropriate. The wetland should be sized gener-
 ously to accommodate these uncertainties.
    The hydraulic characteristics of the con-
 structed wetland should provide the required
 hydraulic residence time of at least,12 days. The
 hydraulic design is calculated using the average
 depth of water and average daily flow rate into the
wetland to find an arrangement that results in the
required hydraulic residence time:
        SA=t/(DxP/Q)                (4.3)
        SA = surface area, ft2 (length x width)
         t  = hydraulic residence time, days
         D = average water depth in the
             constructed wetland, ft
        P = porosity, percent as a decimal
         Q = average daily flow rate, ftVday.

   The presumptive method can be modified to
design wetlands for nitrogen removal. To treat
ammonia to concentrations in the wetland
effluent of less than 10 mg/L (the usual discharge
limit). Hammer (1992) recommends that influent
nitrogen not exceed 9 Ib/ac/day as TKN (10 kg/
ha/day). To size the constructed  wetland for
1.  Determine the production of  ammonia:
                               production (Ib)
                     Average    1000 Ib animal
                    weight fib)  unit fAU1 per dav
   Dairy cows         1300           1.6
   Beef cattle          750           1.4
   Swine              200           2.1
   Poultry - layers        4           3.7
   Poultry - broilers     2.2           5.1

 1.  Calculate the concentration of nitrogen (as
     TKN) per day:
     Assuming that TKN is 150% of ammonia:
     mg/L TKN = mg/L ammonia x 1.5
 2.  Calculate the daily load of TKN:
     TKN (Ib/day) = mg/L TKN x fWhr of influent
     x 680 (conversion factor)
 3.  Determine the surface area needed:
     Surface area (SA)(ac) = Ib/day TKN +
     9 Ib TKN ac/day.


                                        CHAPTER 5
                          SUBSURFACE FLOW WETLANDS

    The use of SSF wetlands in agriculture has
been limited because of the high probability that
they will be clogged by water containing more
than about 30 mg/L solids.
    The design information provided in this
chapter is a summary of the information in Subsur-
face Flow Constructed Wetlands for Wastewater
Treatment: A Technology Assessment (Reed 1993).
Reed based his recommendations on the perfor-
mance of 14 municipal, domestic, hospital, and
industrial systems that have provided detailed
data and that are thought to be representative of
constructed wetland systems in the United States.
Many of these systems are in the South and West,
and most have been operating for less than five
years.  Only a limited number of systems\in the
Northeast have provided operational data.
                                  WETLAND DESIGN

                            Guidelines to designing a SSF constructed
                        wetland are given in table 6. The design assumes
                        that the wastewater has been pretreated to reduce
                        BOD,by 70%, TSS to less than 1,500 mg/L, and
                        ammonia to less than 100 mg/L.
                        DARCY'S LAW
                            The intent of the SSF wetland treatment
                        concept is .to maintain the flow below the surface
                        of the media in the bed. The design of SSF wet-
                        lands has generally been based on Darcy's Law.
                        which describes the flow regime in a porous
                        medium.  However, many of the systems designed
                        with Darcy's Law have developed unintended
                        surface flow and may have been under-designed.



   Bottom slopes




Tables. Design summary for subsurface flow wetlands.

             Reduction of BODS by 70%
             Reduction of solids to <1,5 00 mg/L
             Reduction of ammonia to <100 mg/L
             Fit the wetland to the site
             Divide large wetlands into side-by-side cells

             By gravity, as much as possible
             Subsurface flow design based on Darcy's Law

             Side-to-side elevations: level
             Inlet to outlet slopes: almost flat (0.5 -1.0%)

             Surface manifold with adjustable outlets

             Perforated subsurface manifold connected to adjustable outlet

             Complete coverage is more important than the species used
             Use at least two or three  different species        ;

             Medium(a) must be clean
             Wetland must be sealed to limit infiltration and exfiltration
             Water table must be below or excluded from the wetland

    Darcy's Law assumes laminar flow, a constant
 and uniform flow (Q). and lack of short-circuiting.
 conditions that do not exist in constructed wet- °.
 lands (see Volume I).  Darcy's Law is thought to
 provide a reasonable approximation of the°hydrau-
 lic conditions in an SSF bed if small to moderate
 size gravel (
lie gradient will help to maintain near-laminar
flow in the bed and validate the use of Darcy's Law
in the design of the system. Since this approach
ensures a relatively wide entry zone, it will also
result in low organic loading on the cross-sectional
area and thereby lessen concerns over clogging.
    The bottom of the cell can be flat or
slightly sloping from top to bottom.  The top
surface of the medium should be level regardless
of the slope,of the bottom.  A level surface
facilitates plant management and minimizes
surface flow problems.  Once surface flow
develops on a downward sloping surface, flow
may not penetrate the medium even though the
true water level within the medium is well
below the surface.

    SSF systems are generally designed for BOD5
 removal. In SSF systems, the physical removal
 of BOD5 is believed to occur rapidly through
 settling and entrapment of particulate matter in
 the void spaces in the gravel or rock media
 (Reed 1993).
    Most of the existing systems in the United
 States and Europe have been designed as at-
 tached growth biological reactors using the same
 equations as those used for SF wetlands (equa-
 tions 4.1 - 4.3).  The plug flow model is pres-
 ently in general use and seems to provide a
 general approximation of performance.  It is
 believed that the plug flow rate constant for SSF
 wetlands is higher than for facultative lagoons or
 SF wetlands because the surface area available
 on the media in SSF wetlands is much higher
 than in the other two cases.  This  surface area
 supports the attached growth microorganisms
that are believed to provide most of the treat-
ment responses in the system.  At an apparent
organic loading of 98 Ib/ac/day (110 kg/ha/day).
the rate constant for the SSF wetland (1.104 d'1)
is about an order of magnitude higher than that
for facultative lagoons, and about double the
value often used for SF wetlands.
   The "t". or hydraulic residence time factor in
equation 4.1 can be defined as:
        t  =  nLWd/Q
       n  =  porosity (% as a decimal)
       L  =  length of bed (ft.'m)
       W  =  width of bed (ft, m)
       d  =  average water depth (ft, m)
       Q  =  average flow rate through bed
             (ftVday, mVday).
    The Q value in equation 5.2 is the average
 flow in the bed [(Q,0 + Q.J/2]'. calculated from
 flow through the bed plus gains and losses from
 precipitation and evapotranspiration. This is
 the same value used in Darcy's Law for hydrau-
 lic design.
    The "d"  value in the equation is the average
 depth of  liquid in the bed.  If- the design hydrau-
 lic gradient  is  limited to 10% of the potential
 available, as recommended above, then the
 average depth of water in the bed will be equal
 to 95% of the total depth of the treatment media
 in the bed.
     Since the term LVV in equation 5.1 is equal to
 the surface area of the bed, rearrangement of    •
 terms permits the calculation of the surface area
 (A ) required to achieve the necessary level of
 BOD, removal:
       A, = LxW = Qln(C./C0)/-kTdn    (5.3)
       Af = bed surface area (ft2)
       other terms as defined previously.
     The depth of the media selected will depend
 on the design intentions for the system. If the
 vegetation is intended as a major source of oxygen
 for nitrification in the system, then the depth of

the bed should not exceed the potential root
penetration depth for the plant species chosen.
This will ensure the availability of some oxygen
throughout the bed profile but may require man-
agement practices which assure root penetration to
these depths.
   The design and sizing of the SSF bed for BODS
removal is an iterative process:
1. Determine the media type, vegetation, and
   depth of bed to be used.
2. By field or laboratory testing, determine the
   porosity (n) and "effective" hydraulic conduc-
   tivity (kj of the media to be used.
3. Use equation 5.3 to determine the required
   surface area of the bed for the desired levels of
   BOD5 removal.
4. Depending on site topography, select a pre-
   liminary length-to-width ratio; 0.4:1 up to 3:1
   are generally acceptable.
5.  Determine bed length (L)'and width (W) for
   the previously assumed length-to-width ratio,
   and the results of step 2.
6.  Using Darcy's Law (equation 5.1) with the
   previously recommended limits (ks 
plants can provie o               ^ ^
plants can provide oxy en       ^^

Pe.  The ^^^^e ?or denitrification. i
  ould then be ava,  able t     ri{ication include
   the substrate.


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ac, acre
cfs, cubic foot per second
cfs. cubic fool per second
cm, centimeter
cm/sec, centimeter per second
°F. degree Fahrenheit
ft, foot
ft2, square foot
ft3, cubic foot
ft/mi, foot per mile
fps, foot per second
g/m2/day. gram per square meter per day
gal, gallon
gal, gallon
gpm, gallon per minute
ha, hectare
kg, kilogram
kg/ha/day, kilogram per hectare per day
kg/m2, kilogram per square meter
L, liter
L, lite*
Ib, pound
Ib/ac, pound per acre
m, meter
m2, square meter
m3, cubic meter
m3, cubic meter
nvVha/day, cubic meter per hectare per day
mm, millimeter
mi, mile
2.8317 x 10'2
3.28 X 10"2
9.29 x 10'2
2.83 x 10'2
3.785 x 10'3
6.308 x 10'2
3. 531 x lO'2
3.94 x 10'2
ha, hectare
gpm, gallon per minute
m3/s, cubic meter per second
fps, foot per second
°C, degree Celsius
m, meter
m2- square meter
m3. cubic meter
m/km, meter per kilometer
m/min, meter per minute
Ib/ac/day, pound per acre per day
L, liter
m3, cubic meter
L/s, liter per second
ac, acre
cm, centimeter
Ib, pound
Ib/ac/day, pound per acre per day
Ib/ft2, pound per square foot
ft3, cubic foot
gal, gallon
kg, kilogram
kg/ha, kilogram per hectare
ft. foot
ft2, square foot
yd3, cubic yard
gallon, gal
gallon per day per acre, gpd/ac
kilometer, km