Assessment of Constructed Wetlands for Mass Removal - USDA ARS

Assessment of Constructed Wetlands for Mass Removal of Nitrogen from Swine Wastewater A.A. Szogil,P.G.Hunt, F.J. Humenik2,S.W. Broome3,andJ.M. Rice2

Abstract Disposalof wastewatergeneratedby confmedswineproductionunits is a problemwhenland is limited. Improperlysizedor managedwastetreatmentsystemscancauseodor and water pollution problems.Our objectivewasto comparethe massremovalof nitrogen from swine wastewaterby the currenttechnologythatusesanaerobiclagoontreatmentwith alternativetechnologiesusing constructedwetlands,overlandflow, andmediafilter. Lagoonsare a commoncomponentof nutrient managementsystemsbecausethey canreducenitrogenin wastewaterup to 80%. However, residual ammonia-Nconcentrationsin the lagooneffluentarevery high. Whenland is limited, constructed wetlandscanbe a viable componentof a systemfor safe disposalof lagooneffluents.Nitrogen removalefficienciesmore than 80%were obtainedfor wetlandsplantedto two mixtures of rush/bulrushand cattail/bur-reedplants with N applicationratesup to 15 kg/ha-day.Two critical aspectsof the wetland systemare plant toleranceto ammonia-Nand nitrification-denitrificationrates to transformammoniainto N2.Becauselevels of ammonia-Ntoleratedby plantswere unknown,the lagooneffluentwas diluted with freshwater. A microcosmsstudyshowedthatwetlandplants grew vigorously with ammonia-Nconcentrationlevels up to 240 mg/L. Sincenitrification seemsto be the limiting factorto treathigh ammonialoads,aerationof the wastewatermay enhancetreatment.When lagoonwastewaspretreatedby overlandflow, the N removalefficiencywas 59% for a N application rate of 50 kg/ha-day.Arnmonia-N in the effluentwasreducedto levels that canbe efficiently treated by constructedwetlands.In the media filter treatment,up to 32% of the influent TKN was transformedinto nitrate-Nwhenwastewaterwasrecycled four times. Either overlandflow or media filter offeredthe opportunityto eliminatethe dilution of lagooneffluentsprior to wetlandtreatment. By sequencingnitrification and denitrificationprocesses,advancedwastewatertreatmentlevelscould be achieved.Sucha systemcould offer a saferalternativeto anaerobiclagoons.

Introduction Disposal of livestock wastes has become an important environmental problem in the U.S. due to the fast growth of confIned animal production. This is particularly true with modem swine production, which generates large amounts of liquid manure. In North Carolina, many counties are producing more manure-nitrogen than currently grown crops can utilize (Barker and Zublena, 1995). This can result in overloaded land applications causing water pollution problems. Therefore, proper manure management is necessary to prevent this situation. Liquid manure from hog operations typically is stored and treated in anaerobic lagoons prior to land application. However, treatment of animal wastes before terminal application is necessary when land is limited. Thus, constructed wetlands have received considerable attention as a pretreatment method for wastewater renovation that could reduce land requirements and prevent over-application

(Hammer, 1989, and Hunt, et al., 1995b).

Constructed wetland systems are capable of removing nitrogen by nitrification, denitrification, volatilization of ammonia, and plant uptake. Since anaerobic lagoon effluents are rich

I USDA-ARS Coastal Plains Soil, Water, and Plant Research Center, Florence, SC. 2 North Carolina State University, Biological and Agricultural Engineering Dept., Raleigh, NC. J North Carolina State University, Soil Science Dept., Raleigh, NC.

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Proceedings: Second National Workshopon Constructed Wetlandsfor Animal Waste Management Fort Worth, Texas, 15-18 May, 1996

in ammonia-N(NH3-N), the ratesof nitrification and denitrificationto convertexcessNH3-Ninto N2 are critical to the efficiency of thesesystems.Of thesetwo processes,ammonianitrification is the most limiting factor in wetlands.Also, the toleranceof wetlandplantsto high NH3-Nlevelsis critical for a successfulwetlandtreatment.An aerobicpretreatmentto convert NH3-Nto nitrate-N suchas overlandflow (Hunt and Lee, 1976;Overcashet al., 1976)or media filter (U.S. EPA, 1971)before wetlandtreatmentcould improve nitrogenremovalby wetlands. Currently, dischargeof animalwastewaterto surfacewatersis not allowed.Thus,mass reductionof nutrientsis the goal for constructedwetlandtreatment.In this paper,we comparethe massremoval of nitrogen from swine wastewaterby the presenttechnologyusinganaerobiclagoons with constructedwetlands,overlandflow, andmedia filter technologies.

Materials and Methods Anaerobic Lagoon A single-stagelagoonsystemwas usedto treatthe wastegeneratedby a pig nurseryin Duplin County,N.C. The productionunit had a capacityof2600 pigs with an averageweightof 13 kg (28Ibs). The wastewas conveyedout of the pig houseby a flushing system.The systemused siphon-flushtanksactivatedfour timesa day. Thus,the lagoonwastewaterrecirculatedat a rate of about2100 L/I000 kg live massper day.The lagoonhad a total 4100-m3liquid volume with a top surfaceareaof 2400m2. ConstructedWetlands Four, 3.6-x33.5-m,wetlandcells were constructedadjacentto the anaerobiclagoonin 1992. They were divided into parallel setsof two end-on-endconnectedcells. In 1992,wetland system1 wasplanted with a mixture of rush (Juncuseffusus)andbulrushes(Scirpusamericanus,Scirpus cyperinusand Scirpus validus)andwetland system2 wasplantedto bur-reed(Sparganium americanum)and cattails (Typhalatifolia and Typhaangustifolia).Wastewaterapplicationto the cells startedwith low total nitrogenloadingrates.A more detaileddescriptioncanbe found in Hunt et al. (1994). In the fIrst year, lagoonwastewaterwas diluted with freshwaterand appliedat a total N rate of 0.3 g/m2-day(3 kg/ha-day).The N loadingrate was increasedto 0.8 g/m2-dayor 8 kg/ha-day during the secondyear, and to 1.5 g/m2-dayor15 kg ha-1day-l in the third year. Although dilution is not practical on actualwastetreatmentsystems,it wasnecessarybecauseof unknowntolerancelevels of wetlandplantsto NH3-N. Wetlandplantstoleranceto NH3-Nwas investigatedin a wetlandmicrocosm.The wetland microcosmconsistedof eighteen0.5-x2-mcells.Half of the cells were plantedto a mixture of commonrush (Joeffusus)and softstemrush(Sovalidus)and the otherhalf was usedas a control (no plants).The soil depthwas 18 cm andthe flooding depthwas 10 cm. The experimentaldesignwas a 2x3 factorial with plantsandno plantstreatedwith freshwater,half strengthand full strength wastewater.The retentiontime was 2 weeks.The cells were dosedthreetimes daily with a total of 7.IUday. Full-strengthlagooneffluenthad NH3-Nconcentrationsof 400 to 480 mgiL. The loading rate was about3.0 g TN/m2-day(30 kg/ha-day)for the full strengthtreatment.Above groundbiomass andnumberof stemswere measuredfor both plant speciesin orderto assesstheir toleranceto NH3-N loads.

AerobicTreatments Two aerobictreatmentunits thatconsistedof overlandflow andonemedia filter were constructednextto the anaerobiclagoonin summer1995.The overlandflow systemconsistedof a 4x20-m plot with 2% slope.The sidesand bottomof the overlandflow plot were lined with a plastic Proceedings:SecondNational Workshopon ConstructedWetlandsfor Animal WasteManagement Fort Worth, Texas,15-/8 May, 1996

49

liner after excavationto a 20-cmdepth,and filled with the samesandyloamtopsoil. Vegetation consistedof a mixture of fescue,coastalbermudagrass, andreed canarygrass.Lagoonliquid was applied with hydraulicrates of 2.5 to 3.0 cm/dayduring 8-hourperiods.Surfaceflow was collectedat the end of the plot by a troughandpassedthrougha 6-slot flow divisor and storedin a tank. Subsurfaceflow wascollectedby a subsurfacedrainroutedto a secondtank at the end of the plot. Inflow, surface,and subsurfaceflow were measuredwith mechanicalflow meterswhentankswere emptied.Hydraulic losseswere similar to the expectedevapotranspiration losses(0.5 to 0.8 cm/day). Nitrogenwas appliedat a rate of 5.4 g TN/m2-day(54 kg/ha-day).Three-daycompositesamples were obtainedwith automatedsamplersfor nutrientanalysis. The media filter was similar to a trickling filter. The unit consistedof a 1.6-mdiameterby 0.6-m tall tankfilled with marl gravel. Marl gravelwas usedinsteadof typical sandmediato avoid cloggingby suspendedsolids in the lagoonliquid. The distributionof the gravelparticleswas 85%in the 4.7- to 12.7-mmsize classand 14% in the 12.7-to 19-mmsize class,providing a pore spaceof 57%. The filtration unit was placedinside anothertank with slightly larger diameterto collectthe effluent for recirculation.The systemwas completedwith a secondtankused for storageof the treatedlagoonliquid. Lagoonwastewaterwas appliedas a fme sprayon the surfaceof the media filter. The hydraulic loadingrate was 1010Um3 reactorvolume/day(606 L/m2 reactorarea-day). Lagoonwastewaterwas appliedcontinuouslyandcirculatedfour times throughthe media filter during 6-hourperiod.The averageapplicationrate for TN was 330 g/m3-day(198 g/m2reactorareaday). The flow wasmeasuredwith a mechanicalflow meter,and grabsamplesfor wateranalysis were obtainedat the end of eachof the fITstand fourth recirculationcycles. WastewaterAnalyses Watersampleswerepackedin ice andtransportedto the laboratoryfor analysis.Total Kjeldahl Nitrogen(TKN), nitrate-N (NO2+NO3-N),and NH3-Nwere analyzedusing U.S. EPA methods351.2.350.1,and 353.1,respectively(Kopp andMcKee, 1983).Total suspendedsolids (TSS), chemicaloxygendemand(COD) and pH were analyzedusing EPA methods160.3,410.4, 150,1,respectively. Nitrogen MassBalance Massbalancesfor N were calculatedusing flow and nutrient concentrationdataon a threedaybasisfor the constructedwetlandsandthe overlandflow. The massbalancewas usedto estimate the specificreduction(expressedasmassreductionof nutrientper areaper day). The massremoval or treatmentefficiencywas calculatedasmassreductionof a nutrient in the effluentrelative to the nutrientmassinflow.

Results Anaerobic Lagoon Treatment The pig-houseeffluent (Table 1)was low in TS (0.18 %) andTSS,becauseof the large volume of lagoonwater(2100 L/1000 kg live massper day)used for flushingthe house,but still high in TKN concentration.The TKN componentsare NH3-Nfrom the lagoonwastewater,and inorganic N (NH3-N)andorganicN suppliedby freshmanure.We madetwo assumptionsto estimatethe total N inflow into the lagoon.First, we assumedthat 38% of the N in the freshwastewas in organic form (BarkerandZublena,1995).Second,we assumedthat N in the lagoonwastewaterused for flushing is 100%NH3-N.Underthesetwo assumptionswe estimateda total inflow of 16.8kg Niday into the lagoon.On a massbasis,we estimatedthat 83%ofN enteringthe lagoonwas lost in gaseousform, 13%remainedin the lagooneffluent, and 4% was in the settledsludge.Theseestimatesare consistent with averageN lossesfor swine operationsin North Carolina(Barkerand Zublena, 1995).Anaerobic lagoontreatmentis aneffective way to reducehigh TKN and COD levels in swineoperations.Most 50


of the nitrogenin this systemis lost in gaseousform. The residuallevels of ammoniain the lagoon are not a problemif enoughland is availablefor land application. ConstructedWetlands Constructedwetlandsshowedgreatpromiseby removingmore than 80% of the appliedN (Table2). Nitrogen removalefficiencywas similar in bothrush/bulrushesand bur-reed/cattailsplant systems.Initially, a loadingrate of 3 kg N/ha-daywas usedto evaluateif streamdischarge requirementscould be achieved.This low loadingrate was selectedto meetthe TennesseeValley Authority criteria for advancedwastewatertreatment(Hammer,1994).Becausestreamdischarge concentrationrequirementscould not consistentlybe achieved,the loadingrate was increasedto 8 kg N/ha-dayduringthe secondyearandto 15 kg N/ha-dayduringthe third year with the goal of maximumnitrogenmassreduction.At the highestapplicationrate and 300 applicationdays,wetlands couldhave anaverageannualremovalrate of 3700 kg N/ha. This high nitrogenremovalrate was likely dueto microbial conversionof excessnitrogenin the wastewaterto N gasvia nitrificationdenitrificationprocesses.In a relatedstudy,Hunt, et al. (l995a) showedthat thesewetlandshad prevalentanaerobicconditionsand werenitrate limited. Theseconditionsindicated that somedirect loss of ammoniavia volatilizationcould not be disregarded.Consequently,we investigated alternativenitrification treatmentsthatwould lower potentialloss of ammoniaand eliminatedilution with freshwaterprior to wetlandtreatment. Plant Toleranceto Ammonia In the wetlandmicrocosmunits, bothJuncuseffususand Scirpusvalidus grew vigorouslyin half and full strengthlagooneffluent (Table3). Above-groundbiomassvalues from the half strength treatmentwere in the samerangeas of thosemeasuredin the constructedwetland with rush/bulrush plants(system1) in May 1995(Szogi et al., 1996).Plantsin the full strengtheffluent died during an extremelydry period, but it was not apparentwhetherthis was due to the high concentrationof effluent or the dry conditions.Wetlandmicrocosmsunits with plantswere more effective than units with no plants in removingN from the lagooneffluent with an efficiency as high as 99% (Broome, 1996). Aerobic Pretreatment ofLagoon Effluents 1. Overlandflow Overlandflow hasseveralcharacteristicsthatmake it an attractivemethod for pretreatment of wastes.In overlandflow, nitrification occurswhena thin film of wateris in close contactwith the nitrifying populationat the soil surface.It alsooffers the advantageof partial denitrificationofNO3N in the underlyingsaturatedsoil layer (Hunt and Lee, 1976).High hydraulic rates in overlandflow systemsare not uncommon;Hegg and Turner (1983)reportedloadingratesas high as 2 cm/day.Our overlandflow systemhad an average2.7 cm/dayhydraulic loadingrate.This high hydraulic rate was necessaryto obtainmeasurablesurfaceflow at the end of the plot. Our results show thatthe overland flow systemwas effective in reducingthe concentrationofTSS, COD, TKN, and NH3-Nin boththe surfaceand subsurfaceeffluents(Table4). The increasein NO3-Nconcentrationin both effluentsis an indicationthat nitrification occurred.The pH of the effluentsdid not changewith respectto the lagoonwastewaterinflow, and probablysomeNH3-Nvolatilizationlossesoccurred. Overlandflow systemscanremovesignificantamountsof nitrogen. Humenik et al. (1975) obtained35% N removal from swine lagoonwastewatertreatedon 17-moverland flow plots with a 1.8-cm/dayhydraulicloading. With our system,a massloadingrate was applied at 5.4 g NH3-N/m2day (54 kgiha-day).At this high N loadingrate,a meanTN 3.2 gim2-day(32 kgiha-day)removalrate wasobtainedduringthe Augustto December1995period.The respectivetotal N removalefficiency was 59%. Proceedings:SecondNational Workshopon ConstructedWetlandsfor Animal WasteManagement Fort Worth,Texas,15-18May,1996

51

2. MediaFilter Sand filters have become popular for small waste generators especially where soil conditions are not suitable for subsurface disposal systems (Rubin et al., 1994). These recirculating sand filters provided excellent oxygen demand and suspendedsolids removal as well as high degree of nitrification (Hines and Favreau, 1975; Mote et al., 1991). The use of gravel to avoid clogging in our experimental unit also allowed for very good natural aeration of the applied lagoon wastewater, rapid vertical flow rates and some phosphorus sorption. Results in Table 5 show high removal of TSS with efficiencies of 50% to 71 % with one and four cycles, respectively. Results on COD showed no difference in efficiency (54%) with one or four cycles. Removal efficiencies were 11% and 22% for TN with one and four cycles, respectively. The NO)-N (mg/L) to TKN (mg/L) x 100 nitrification ratio (Loehr et al., 1973) was used to estimate the proportion ofTKN in the influent that was converted to NO)-N. With four cycles, a nitrification ratio of 24% was obtained with data from Table 5. A nitrification ratio of 32% was obtained with wastewater recycled four times during the August to December 1995 period. We concluded that this method might provide effluents with NH)-N levels that can be tolerated by wetland plants according to the results obtained in the microcosm study and eliminate the problem of dilution with fresh water prior to wetland treatment.

Summary The goal of the studied wetland systems was to maximize nitrogen removal to protect soil, air and water quality. Wetlands by themselves cannot remove sufficient amounts ofN to meet stream discharge requirements, but do show promise for high rates ofN removal. Since wetlands are nitrate .limited the mass removal rate can be increased by nitrifying the effluent prior to wetland application and at the same time eliminate dilution. By sequencing nitrification and denitrification processes, advanced wastewater treatment levels could be achieved. Such a system could offer a safer alternative to anaerobic lagoons.

Acknowledgments This research has been funded by: N.C. Herrings Marsh Run Water Quality Demonstration Project, USDA Project No. 90-EWQD-1-9504; N.C. Goshen Swamp Hydrologic Unit Area Project, USDA Project No. 90-EHUA-l-0013; Evaluation of Alternative Constructed Wetland Systems for Swine Wastewater Treatment, USEPA Project No. CR 823808-01-0.

References Barker, J.C. and J.P. Zublena. 1995. Livestock manure nutrient assessment in North Carolina. p. 98106. In Proceedings of the Seventh International Symposium on Agricultural Wastes. Chicago, Ill. June 18-20, 1995. ASAE Pub. 7-95, St. Joseph, Mich. Broome, S.W. 1996. Constructed wetlands for wastewater treatment. p. 53-55. In Proceedings of Solutions: A Technical Conference on Water Quality. March 19-21, 1996. North Carolina State University, Raleigh, N.C. Kopp, J.F., and G.D. McKee. 1983. Methods for chemical analysis of water and wastes. U.S. EPA Report No. EP A-600/4- 79020. Environmental Monitoring and Support Lab., Office of Research and Development, U.S. Environmental Protection Agency, Cincinnati, Ohio. Hammer, D.A. 1989. Constructed wetlands for wastewater treatment: Municipal, agricultural.

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industrial, and

Lewis Publishers.

Proceedings:SecondNational Workshop on ConstroctedWetlandsfor Animal WasteManagement Fort Worth,Texas,15-18 May, 1996

Hammer,D.A. 1994.Guidelinesfor design,constructionand operationof constructedwetlandsfor wastewatertreatment.Guidelines,NPS, CommunityPartnerships,TennesseeValley Authority. Hegg,R.O., and A.K. Turner. 1983.Overlandflow as a methodof treatmentfor animalwastes-A review. Agricultural Wastes8:167-184. Hines,M., andR.E. Favreau.1975.Recirculatingsandfilter: analternativeto traditionalsewage absorptionsystems.p. 130-136.In Proceedingsof the NationalHome SewageDisposal Symposium.ASAE Pub.Proc.-175.St. Joseph,Mich. Humenik,F.J.,R.E. Sneed,M.R. Overcash,J.C. Barker, and G.D. Netherill. 1975.Total waste managementfor a large swine productionfacility. p. 68-71. In Proceedingsof the Third InternationalSymposiumon LivestockWastes.ASAE, St. Joseph,Mich. Hunt, P.G., and C.R. Lee. 1976.Land treatmentof wastewaterby overlandflow for improved water quality.p.151-160.In J. TourbierandR.W. Pierson,Jr. (eds.)Biological Control of Water Pollution. University of PennsylvaniaPress,Pa. Hunt, P.G.,A.A. Szogi,F.J. Humenik,J.M. Rice, andK.C. Stone.1994.Swine wastewatertreatment by constructedwetlandsin the southeastern United States.p. 144~154.In P.J. DuBowy and R.P.Reaves(eds.)ProceedingsConstructedWetlandsfor Animal WasteManagement Workshop.Dept. of Forestryand NaturalResources,PurdueUniversity, WestLafayette,Ind. Hunt, P.G.,T.A. Matheny,A.A. Szogi,andF.J. Humenik. 1995a.Denitrification in constructed wetlandsfor swine wastewatertreatment.p. 329. AgronomyAbstracts.ASA, Madison,Wis. Hunt, P.G.,W.O. Thorn,A.A. Szogi,andF.J. Humenik. 1995b.Stateof the art for animalwastewater treatmentin constructedwetlands.p. 53-65.In Proceedingsof the SeventhInternational Symposiumon Agricultural Wastes.Chicago,Ill. June 18-20,1995.ASAE Pub. 7-95, St. Joseph,Mich. Loehr,R.C., T.B.S. Prakasam,E.G. Srinath,andY.D. Joo. 1973.Developmentand demonstrationof nutrientremoval from animalwastes.Office of Researchand Monitoring. Environmental ProtectionAgency.U.S. GovernmentPrinting Office, Washington,D.C. Mote, C.R.,J.W. Kleene,and J.S. Allen. 1991.On-sitewastewaterrenovationutilizing a partially saturatedsandfilter for nitrogenremovaland lawn sprinkler for effluent discharge.p. 173181. In Proceedingsof SixthOn-SiteWastewatertreatmentConference.ASAE Pub. 10-91. St. Joseph,Mich. Overcash,M.R., D. M. Covil, G.W. Gilliam, P.W. Westerman,and F.J. Humenik. 1976.Overland flow pretreatmentof wastewater.WaterResourcesResearchInstitute of the University of North Carolina Report#76-117.Raleigh,N.C. Rubin, A.R., S. Greene,T. Sinclair, andA. Jantrania.1994.Performanceevaluationof drip disposal systemfor residentialtreatment.p. 467-474.In Proceedingsof the SeventhInternational Symposiumon Individual and Small CommunitySewageSystems.ASAE Publication18-94. St. Joseph,Mich. Szogi,A.A., P.G. Hunt, and F.J. Humenik. 1996.Abovegroundbiomassand nutrient accumulationin a constructedwetland for swine wastewatertreatment.In 4th Symposiumon Biogeochemistryof Wetlands.March4-6, 1996.New Orleans,La. Wetland Biogeochemistry Institute,LouisianaStateUniversity. BatonRouge,La. U.S. EPA. 1971.A literature searchand critical analysisof biological trickling filter studies.U.S. GovernmentPrinting Office. Washington,D.C.

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Vanotti, M.V., andP.G.Hunt. 1996.The use of polymersfor nitrogenremovalin swinewastewater: PAM andencapsulatednitrifier technologies.p. 116-120.In Proceedingsof Solutions:A TechnicalConferenceon Water Quality. March 19-21,1996.North CarolinaState University,Raleigh,N.C.

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Proceedings: Second National Workshopon Constructed Wetlands for Animal Waste Management Fort Worth, Texas, 15-18 May, 1996

Table1. Characteristic~'ofthepig-house effluent when entering the anaerobiclagoon. Datafrom Vanotti and Hunt (1996).

Constituent

Unit

Concentration

Total Solids

g L-1

1.83

SuspendedSolids

mgL-1

335

ChemicalOxygenDemand

mgL-1

1370

Total Kjeldahl Nitrogen

mgL-1

374

OrganicNitrogen

mgL-1

88

Ammonia Nitrogen

mgL-1

286

PH

8.1

Table2. Nitrogen loading ratesand massremoval efficienciesfor the constructedwetlands,Duplin Co.,N.C.

Nitrogen Loading ratet

System

Mass Removal +

%

Rush/bulrush

94

Cattails/bur-reed

94

Rush/bulrush

88

Cattails/bur-reed

86

Rush/bulrush

85

Cattails/bur-reed

81

3 kg ha-1 d-1

8 kg ha-1 d-1

15 kg ha-' dt Expressedas TN.

t % Mass Removal= % massreduction ofN (TN = NHrN + NOJ-N)in the effluent with respectto the nutrient massinflow.

Table3. Above ground ,biomassand stemdensity ofplants in a microcosmsstudytreated with fresh water and lagoon wastewaterat halfandjrull strength (means%one standard error, May 1995).Datafrom Broome (1996).

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Table4. Characteristics ofthe influent wastewaterand overlandflow effluent separatedin surface and subsurfaceflow (mean:i: one standarderror from August to December1995).

Constituent

Unit

Influent

Surface Effluent

Total Suspended Solids

gL-1

Wastewater 0.25

0.21

Subsurface Effluent 0.11


rngL-1

446 :f: 28

372 :i: 33

207 :f: 19


rng L-1

250::1: 12

128 % 16

78I8

Ammonia Nitrogen

rngL-1

198:j:: 5

110x6

73 :I: 5

Nitrate Nitrogen

rngL-1

0.2

24:f: 3

30 :f: 3

8.4

8.3

8.2

pH

Table5. Characteristics ofthe influent wastewaterand mediafilter treatedeffluent (mean:f: one standard error, August

16-23,1995).

Constituent

Unit

Influent Wastewater

Onecycle Effluent

Total Suspended Solids

gL-1

0.52 :!:0.11

0.26:i: 0.02

Effluentt 0.15:%:0.02


mgL-1

869 :f: 117

432:%:35

403 ::I:40


mgL-1

327:i: 16

257:I: 14

180::1:9

Ammonia Nitrogen

mgLO1

236:i: 19

182:i: 14

147:i: 7

Nitrate Nitrogen

mgLO1

6::1:2

40:f: 5

80 :J:4

8.6

8.5

8.4

PH

Four cycles

t The lagoon wastewaterwaspassedoncethrough the mediafilter (one cycle)and then re-circulatedthree more times (four cycles).

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