Methane and Nutrient cycling in Septic Leach Field Systems...Methane and Nutrient cycling in Septic Leach Field Systems This report was prepared for the New York State Water Resources

MethaneandNutrientcyclinginSepticLeachFieldSystemsCristinaFernandez-Baca,CivilandEnvironmentalEngineering,email:[email protected]

AbstractOnsitesepticsystemstreatapproximately25%ofU.S.domesticwastewater.Despitetheirprevalenceandcontinueduseinnewbuilding,fewstudieshaveattemptedtocharacterizesepticsystems’airandwaterqualityimpacts.Understandingsepticsystems’effectivenessisvitaltomanagingtheminawaythatpromotesbothairandwaterquality.Systemsthatareimproperlysitedand/ormanagedcancausegroundandsurfacewatercontaminationaswellasincreasedgreenhousegas(GHG)emissionsascomparedtowell-managedsystems.ToexaminemicrobialpopulationsandpotentialGHGandnutrientcyclingwithinleachfieldsoilsystems,weconstructedtwoleachfieldsoilcolumnsinthelab.Reactorsweresubjectedtoeitherfloodedconditions(ColumnA)orwell-maintainedconditions(ColumnB)andcomparedin:(1)measuredatmosphericmethane(CH4)fluxes;(2)measuredCH4depthprofile,(3)distributionandactivityofkeyorganismsinvolvedinCH4cycling;(4)measuredchemicaloxygendemand(COD)andnutrienttreatment(N,P).Overall,thecolumnsperformedmoresimilarlyinnutrientremovalthaninCH4cyclingwithfloodedconditionssignificantlyincreasingCH4fluxesandoverallCH4production.CODremovalwasvariableandisnegativelyimpactedbyfloodingwhilenutrientremovalappearstobeunaffectedbyfloodedconditions.ThreeSummaryPointsofInterest• Methane emissions from flooded septic leach field soils are significantly higher when compared to well-

maintained systems. Overall, flooded systems create more methane that is not consumed by microbialcommunities.

• Nutrient (nitrogenandphosphorus) removal is not affectedby flooding, howeverCOD removal is variable anddoesappeartobenegativelyaffectedbylong-termflooding.

• Abundance of microbial populations involved in methane cycling were affected by flooding. With methaneproducingorganismsmoreabundantinfloodedconditions.

KeywordsGreenhousegases,septicsystems,biomarkers,COD(chemicaloxygendemand)

NEW YORK STATE WATER RESOURCES INSTITUTE

Department of Biological and Environmental Engineering 230 Riley-Robb Hall, Cornell University Tel: (607) 254-7163 Ithaca, NY 14853-5701 Fax: (607) 255-4449 http://wri.cals.cornell.edu Email: [email protected]

MethaneandNutrientcyclinginSepticLeachFieldSystems

ThisreportwaspreparedfortheNewYorkStateWaterResourcesInstitute(WRI)andtheHudsonRiverEstuaryprogramoftheNewYorkStateDepartmentofEnvironmentalConservation,withsupportfromtheNYSEnvironmentalProtectionFund

IntroductionOn-sitesepticsystemscurrentlytreatwastewaterfromapproximately25%ofU.S.households(USEPA2013).Septicsystemsareapracticalandinexpensivemeansofdecentralizedwastewatertreatmentforruralandperi-urbanareas.Theyareabletoachievesimilartreatmentlevelsastheirlarger,centralized,andmoreenergy-intensivewastewatertreatmentplantcounterpartswhilestillmaintainingmanyofthesamepublichealthandenvironmentalbenefits(USEPA2012;USEPA2014).Despitethepopularityandnumerousadvantagesofthesedecentralizedsystems,thereisafundamentallackofinformationonhowtheyeffectthesurroundingenvironment.Inparticular,theirimpactonwaterqualityandpotentialgreenhousegas(GHG)emissionsispoorlyunderstood.Septicsystemsarepopularinpartduetotheirlowoperatingandmaintenancerequirements.However,becausethesesystemsrequiresuchinfrequentserviceandareinconspicuousbynature,failurescanariseandremainunnoticedandthusun-repaired.Inparticular,failedsepticsystemscausinggroundand/orsurfacewatercontaminationaredifficulttoidentifyanddiagnose.ConsequentlythenumberoffailingsepticsystemsintheU.S.isunknown.Complicatingtheissueisthefactthatthereisnostrictdefinitionastowhatconstitutesafailingsystem(USEPA2002).Currentlytherearenorequirementsforstatestocollectdataonsepticsystemfailures.Statesthatdocollectthisinformationcreatetheirowndefinitionoffailure,whichcanrangefrom“sewageback-up”to“surfaceand/orgroundwatercontamination”(USEPA,2002).Severalstudieshavelookedatthepotentialforsepticsystemstocontaminategroundwateranddrinkingwatersources,howevernonehavelookedathowfailingsystemscomparetofunctioningsystemsintermsofwaterqualityimpacts(Coggeretal.,1984;Katzetal.,2011).IntermsofGHGemissions,functioningsepticsystemshavebeenestimatedtorelease0.22tonneCO2-equivalents(CO2e)capita-1year-1totheenvironment(Diaz-Valbuenaetal.,2011).However,dataonGHGemissionsfromsepticsystemsremainssparsewithonlyahandfulofpapersaddressingthesubjectandofthosenostudyto-datehasaddressedthequestionofhowfailing,floodedsepticsystemscomparetowell-

maintainedsystems(Diaz-Valbuenaetal.,2011;Kinnicuttetal.,1910;Truhlaretal.,2016).Basedona2002EPAreport,thepercentageoffailedsystemscouldrangeanywherefrom0.5%to70%bystate(USEPA,2002).Ifthesesystemsarefailingattheupperendoftheestimatedrate,theircontributionstoGHGemissionsaswellastheireffectsonneighboringwaterbodiescouldbesignificant.Itisimportanttodeterminetheextenttowhichthelackofmanagementandregulationsonthesesystemscanimpactbothairandwaterquality.PreviousstudieshaveoverlookedtheimportanceofmicrobialcommunitiescontrollingGHGemissionsfromsepticsystemleachfieldsystems.Microorganismsinvolvedinmethaneproduction(methanogens)anddestruction(methanotrophs)canbestudiedusingfunctionalgenebiomarkersmcrAandpmoA,respectively,forquantificationandcharacterizationandhavepreviouslybeenfoundtocorrelatewithCH4emissionsfromsoils(Freitagetal.,2010;Leeetal.,2014).Inparticular,greatermethanefluxeshavebeenobservedinfloodedsoilswithcorrespondinghigherabundancesofmcrAgenecopiesandtranscripts(Maetal.,2012).Floodedsepticleachfieldsystemsareexpectedtodisplaythesamerelationshipandcouldhavesignificantlydifferentmicrobialpopulationsascomparedtowell-maintainedsystems. Thedemandforlow-cost,decentralizedwastewatertreatmentcouldriseasgrowthinthesuburbanareasofNewYork’sHudsonandMohawkValleyscontinues(Roberts,2006).Thus,itisbecomingincreasinglyimperativetodeterminetheimpactofthesesystemsontheenvironment,withparticularattentiontohowfailingsystemscontributetoairandwaterpollution.TheHudsonRiverEstuaryActionAgenda(NYSDEC,2010)includesgoalsforprotectingwaterqualityandreducingGHGemissions,septicsystemshavethepotentialtoimpactbothoftheseareasandthereisasignificantlackofinformationsurroundingthesesystemsthatneedstobeaddressed.ObjectivesThisprojectbuildsonpreviousyears’workinwhichwefoundsignificantGHGemissionsfromsepticsystemsrelativetothesurroundinglandscape,particularlyforfailingsystems,aswellastheubiquitouspresenceof



keyfunctionalbiomarkergenesinvolvedinGHGcycling(Truhlaretal.,2016;Fernandez-Baca,unpublished).Wefurtherwantedtocharacterizethemicrobialcommunitiespopulatingtheseleachfieldsystemsandexaminetheimpactoffailingsystems,specificallyfloodedsystems,onbothairandwaterquality.Theobjectiveofthisprojectwastocomparetwosepticleachfieldsystemsinfourcategories:(1)measuredatmosphericmethane(CH4)fluxes;(2)measuredCH4depthprofile,(3)distributionandactivityofkeyorganismsinvolvedinCH4cycling;(4)measuredchemicaloxygendemand(COD)andnutrienttreatment(N,P).Thisresearchwillaidingainingabetterunderstandingofhowsepticsystemsimpactwaterqualityandcontributetoclimatechange.Thisworkwillemphasizetheimportanceofeffectivelymanagingthesesystemstoreduceairandwaterpollution.Results&DiscussionOperationTwocolumnswereoperatedunderdifferentconditions(Figure1).ColumnAwasoperatedunderpermanently‘Flooded’conditionswhileColumnBwasoperatedunder‘Well-Maintained’conditionsuntilAugust10,2016.FromAugust10th,2016untilFebruary19th,2017,ColumnBwasoperatedunderfloodedconditions.AfterFebruary19thColumnBwasrevertedbackto‘Well-Maintained’conditions.

Figure 1. Schematic of soil column operation and setup. Column B has been operated under both ‘well-maintained’ and ‘flooded’ regimes.

MethaneDepthProfileandFluxesColumnAhadgreaterCH4productioninthesoilprofilecomparedtoColumnB(Figure2)priortofloodingofColumnB.MethaneconcentrationsinColumnAwerehighestnearthewastewaterinlet(Ports2and3),

whereconditionsareanaerobic.ColumnBshowednomethaneproductionatanydepthbeforeflooding.

Figure 2. Methane depth profile for (A) Column A and (B) Column B. Soil column schematic indicates location of port number with relation to soil column depth.

CH4fluxesforColumnAweresignificantlyhigherthanColumnB(p<0.05)priortofloodingofB.NetemissionsforColumnBwereonaverage0gCH4/day.

Figure 3. CH4 fluxes from Column A and B prior to flooding of B showed significant differences in CH4 emissions.

Uponflooding,ColumnBbegantodisplayincreasedCH4porewaterconcentrationswithcorrespondingincreasesinsurfaceCH4fluxes(Figures4and5).Withtime,ColumnB’sCH4depthprofilebegantoresemblethatofColumnA.

Figure 4. Pore water CH4 concentrations with depth for (A) Column A and (B) Column B after flooding Column B. Methane concentrations in Column B increased to levels comparable to Column A.

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AfterprolongedfloodingofColumnB,therewasnosignificantdifferencebetweenemissionsfromColumnAandColumnB(Figure5).

Figure 5. Methane fluxes from Column A and B when both were operated in flooded conditions. Fluxes from Column B increased during this time.

AfterreturningColumnBtonormal,‘well-maintained’operation,theporewaterCH4concentrationsbegantodecreaseonceagaintopre-floodedlevels.ColumnAcontinuedtoproduceCH4neartheinlet.

Figure 6. Pore water CH4 concentrations for (A) Column A and (B) Column B after returning Column B to 'well-maintained conditions. Column A remained flooded and producing CH4 while Column B had a decrease in CH4 production.

GeneabundancesGenecopiesofpmoAandmcrAwerefoundinbothsystems(FigureXXX).DNAanalysisofsoilsshowedColumnAhadhigherabundanceofmcrAcomparedtoColumnBimmediatelyafterfloodingColumnB,howeverunderprolongedfloodedconditionstheabundanceofmcrAgenecopiesinColumnCincreasedrelativetoColumnA.Bothcolumnshada‘peak’inmcrAgeneabundancenearestPorts2and3,wheretheinfluentwastewaterisdosed.

PmoAhadgreatergenecopylevelsinsurfacesoilsthanmcrAinbothcolumns.Surprisingly,bothcolumnsshowedgreaterabundanceofpmoA(aswellasmcrA)

belowthesoilsurfacenearthewastewaterinlet–likelyreflectinganicheformethanotrophsclosetothesubsurfacesourceofmethane.

Figure 7. Gene abundances for mcrA and pmoA from two soil sample dates. Abundance of mcrA increases in Column B with sustained flooding. PmoA is found throughout the column.

ColumnBhadgreaterCODremovalonaverage(>90%)comparedtoA(30-65%)beforeflooding(Figure8).

Figure 8. COD removal was variable. Column B pre-flood had consistently higher COD removals than Column A but this difference was less prominent after both columns were flooded.

Bothcolumnshad>90%phosphorus(P)andammonium(NH4

+)removalsuggestingnutrientremovalwasunaffectedbyflooding(Figures9and10).Nitrate/nitritewereproducedatlowlevels(0.3-2mg-N/L)inthecolumns’porewaterandwerereducedtobelowdetectionineffluent.Thisindicatesthatanyproductionofnitrateandnitritewaslowinthesesystemsandlikelynotcontributingtogroundwatercontamination.

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Figure 9. NH4 removal in both columns was consistent.

Figure 10. P removal from both columns was >90% and was unaffected by flooding.

FutureshiftsinDNAgenecopieswithtimewillbedetermined.AsColumnBrevertsbacktoa‘well-maintained’systemweexpecttoseeadecreaseinmcrAgeneabundance.Wearefurthercharacterizingthemicrobialcommunityusinghigh-throughputsequencingofoursoilsamples.ThisadditionaldatasetwillinformthegroupsofmethanogensandmethanotrophsresponsibleforthemajorityofCH4cyclingandwillshedlightonthecommunityshiftswithsoildepthandmoisture.UnderstandinghowthepresenceandabundanceofbiomarkergenesarerelatedtoCH4cyclingcanelucidatewhatcontrolsCH4emissionsfromthesesystemsandinformfuturesepticsystemsdesignsforbetterGHGmitigationstrategies. Overall,thetwocolumnsperformedmoresimilarlyinnutrientremovalthaninCH4cyclingunderboth‘flooded’and‘well-maintained’conditions.Althougheffectivenutrientremovals(NandP)wereachievedbybothfloodedandnon-floodedleachfieldsoils,CODremovalwasvariableanddidappeartobeimpactedbyflooding.Methanewasshowntobesignificantlyhigherinfloodedsystemsboththroughout

thesoilprofileandinemissionsfromthesoilsurface.TheseresultsshowthatmanagementoffailingsepticsystemsisvitalforminimizingairandwaterpollutioninNewYorkstate.PolicyImplicationsThis researchshowsthat failingsystemscannegativelyimpact air quality and potentially also impair waterquality.Policiesshouldfocusonenforcingmaintenanceofsepticsystems.MethodsFluxmeasurementsweredonefollowingamodifiedfieldfluxchambermethodfromMolodovskyaetal.(2011).Briefly,5mLgassamplesaretakenthroughaseptaatthetopofthecapevery10minutesfor30minutesandinjectedintopre-sealed9mLvial.ThestoredgassampleisanalyzedviaGC-FIDonthesameday.Alinearregressionwasfittothedatatoestimatefluxfromsoilsurface.Thecalculatedfluxwasscaledbyatypicalleachfieldareaadomestichousehold.Porewatersampleswereanalyzedforammonium,nitrate,nitrite,PandCODaswellasdissolvedmethane.Nutrientconcentrationsweredeterminedusingpublishedcolorimetricassaysammonium(BowerandHolm-Hansen,1980),nitrate/nitrite(Mirandaetal.,2001),phosphorus(APHA,2005)modifiedforamicroplatereader.CODmeasurementsweredoneusingaCHEMetricskit(Cat.No.K-7365).Dissolvedmethanewasmeasuredbyinjecting5mLofporewaterintoapre-sealed9mLvial,shakingfor5minutesandsamplingtheheadspaceforGC-FIDanalysis.Dissolvedmethaneconcentrationswereback-calculatedusingHenry’sConstantformethanepartitioninginwater.Soilsweresampledperiodicallybydrillingthroughthecolumnandsubsamplingsoil.DNAextractionsweredoneusingtheMoBioRNAPowerSoilextractionkit(MoBio Laboratories,Carlsbad,CA).Allreactionswererunintriplicateusingatotalreactionvolumeof25µL.Eachreactionwascomprisedof2XiQSYBRGreenSupermix(Bio-Rad,US),17.5pmolofprimer,and3uLoftemplateDNA(withconcentrationsof10ng/uL).ThermalcyclingwasconductedonaniCyclerIQ(Bio-Rad).QuantificationanalysiswascarriedoutusingCtvaluesfromtheiCyclerIQsoftware.Meltcurveanalyseswereconductedonallproductstoensurespecificity.

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ConfirmationofproductsbySangersequencingshowedamplificationoftargetedgenes.StudentTrainingTwoundergraduatestudentsweretrainedduringthecourseofthisproject.BothwereJuniorsinEnvironmentalEngineeringandcontributeddirectlytothedatasummarizedhere.Additionalfinalreportsrelatedtowaterresourceresearchareavailableathttp://wri.cals.cornell.edu/news/research-reportsReferences APHA(2005)Standardmethodsfortheexaminationofwaterandwastewater,21stedn.AmericanPublicHealthAssociation,Washington,DC

Bower,C.E.,&Holm-Hansen,T.(1980).ASalicylate–HypochloriteMethodforDeterminingAmmoniainSeawater.CanadianJournalofFisheriesandAquaticSciences,37(5),794–798.

Cogger,C.G.,&Carlile,B.L.(1984).FieldPerformanceofConventionalandAlternativeSepticSystemsinWetSoils1.JournalofEnvironmentQuality,13(1),137.

Diaz-Valbuena,L.R.,H.L.Leverenz,C.D.Cappa,G.Tchobanoglous,W.R.Horwath,J.L.Darby.2011.Methane,carbondioxide,andnitrousoxideemissionsfromSepticTankSystems.EnvironmentalScience&Technology45(7):2741-2747.

Fernandez-Baca,C.,Pollard,J.,Richardson,R.

(2017).Methaneandnutrientcycling:activeprocessesinleachfieldsoilsystems.Manuscriptinpreparation.

Freitag,T.E.,Toet,S.,Ineson,P.,&Prosser,J.I.(2010).Linksbetweenmethanefluxandtranscriptionalactivitiesofmethanogensandmethaneoxidizersinablanketpeatbog.FEMSMicrobiologyEcology,73(1),157–65.

Katz,B.G.,Eberts,S.M.,&Kauffman,L.J.(2011).UsingCl/Brratiosandotherindicatorstoassesspotentialimpactsongroundwaterqualityfromsepticsystems:AreviewandexamplesfromprincipalaquifersintheUnitedStates.JournalofHydrology,397(3-4),151–166.

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Lee,H.J.,Kim,S.Y.,Kim,P.J.,Madsen,E.L.,&Jeon,C.O.(2014).Methaneemissionanddynamicsofmethanotrophicandmethanogeniccommunitiesinafloodedricefieldecosystem.FEMSMicrobiologyEcology,88(1),195–212.

Ma,K.,Conrad,R.,&Lu,Y.(2012).ResponsesofmethanogenmcrAgenesandtheirtranscriptstoanalternatedry/wetcycleofpaddyfieldsoil.AppliedandEnvironmentalMicrobiology,78(2),445–54.

Miranda,K.M.,Espey,M.G.,&Wink,D.A.(2001).Arapid,simplespectrophotometricmethodforsimultaneousdetectionofnitrateandnitrite.NitricOxide :BiologyandChemistry/OfficialJournaloftheNitricOxideSociety,5(1),62–71.

Molodovskaya,M.,Warland,J.,Richards,B.K.,Öberg,G.,& Steenhuis,T.S.(2011).NitrousOxidefromHeterogeneousAgriculturalLandscapes:SourceContributionAnalysisbyEddyCovarianceandChambers.SoilScienceSocietyofAmericaJournal,75(5),1829.

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Truhlar,A.M.,Rahm,B.G.,Brooks,R.A.,Nadeau,S.A.,Makarsky,E.T.,&Walter,M.T.(2016).GreenhouseGasEmissionsfromSepticSystemsinNewYorkState.JournalofEnvironmentQuality,45(4),1153.



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BeGreenandSustainable.USEPA.<http://water.epa.gov/infrastructure/septic/upload/MOU-Green-Paper-081712-v2.pdf.>

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Documents

Methane and Nutrient cycling in Septic Leach Field Systems...Methane and Nutrient cycling in Septic Leach Field Systems This report was prepared for the New York State Water Resources