PhosphorousRequirementsinaPostDenitrification

PhosphorousRequirementsinaPostDenitrificationMBBRataCombinedLimitOfTechnologyNitrogenandPhosphorousPlantMarijaPeric1*,DilliNeupane1,BeverleyStinson1,EdwardLocke1,SalilKharkar2,NicholasPassarelli2,MartinSultan2,GeorgeShih2,SudhirMurthy2,WalterBailey2,JohnCarr2,RoubenDerMinassian21AECOMWater,14504GreenviewDrive,Suite400,Laurel,MD,20708(*[e-mail])2DCWASA,5000OverlookAvenueSW,WashingtonDC,20032ABSTRACTAMovingBedBiofilmReactor(MBBR)postdenitrificationpilotwasimplementedattheBluePlainsAdvancedWastewaterTreatmentPlant(AWTP).Theobjectivewastoassesstheimpactofphosphorus(P)onthedenitrificationprocessandcomplianceriskrelatedtotheeffluenttotalphosphoruslimitof0.18mg/L.TheMBBRPrequirementswereassessedduringbothwarm(22°C)andcold(13°C)operatingconditions.Plimitationimpactswerenotobservedduringsteadystatewarmtemperatureoperations,evenafterfourweeksbutwereobservedimmediately(withinaday)asthetemperaturedecreased,asdemonstratedbyelevatedeffluentNOx-N(especiallynitrite)concentrations,andremainedpoorforthe2weekcoldtestperiod.ThepilottrainoperatingwithsufficientPcontinuedtoperformwellduringevenasthetemperaturesdecrease,averaging91%NOx-Nremoval.NOx-Neffluentconcentrationsduringthewarmperiodwere0.4mg/L(92%NOx-Nremoval)inP-unlimitedand0.6mg/L(86%NOx-Nremoval)intheP-limitedtrain.SignificantperformancedegradationwasobservedintheP-limitedtrainduringthecoldperiod,withanaverageeffluentNOx-Nof4.5mg/L,whilethetrainoperatingwithsufficientPdidnotdemonstrateasignificantdegradationinperformance(averageeffluentNOx-N=0.7mg/L).ThefindingsofthisstudyimplythatP-limitedeffectsbecomeapparentasthewastewatertemperaturesbegintodecreasebutduringperiodswherethetemperatureandloadingsarequitestableandthebiomassiswellestablished,Plimitationsarenotapparent.TheimplicationsforfullscaleoperationsarethatsupplementalPmayberequiredassignificantchangesintemperatureorloadingoccurtosupportincreasedbiomassgrowth.However,duringstableoperationtheprocessdoesnotdemonstratePlimitationseveniftheeffluentOPconcentrationsarealmostnon-detect.KEYWORDS:Postdenitrification,Phosphoruslimitation,Movingbedbiofilmreactor(MBBR),LimitofTechnology(LOT),ENRINTRODUCTIONDCWaterandSewerAuthority’s(DCWASA)BluePlainsAWTPisa370MGDplantthatservesapopulationofmorethan2,000,000peopleintheWashington,D.C.metropolitandistrict.TheexistingwastewatertreatmentprocessesattheBluePlainsAWTPconsistsofpreliminaryandprimarytreatment,secondaryhighrateactivatedsludgetreatment,nitrification/denitrificationactivatedsludgetreatment,effluentfiltration,chlorination/dechlorinationandpostaeration.237NutrientRemoval2009Copyright©2009WaterEnvironmentFederation.AllRightsReserved.Figure1-ArialviewofBluePlainsAWTPDCWASAcurrentlyoperatesitsBluePlainsAWTPtomeetaneffluentTNlimitof7.5mg/LandTPlimitof0.18mg/L.Anewpermitisanticipatedthatwillrequireadditionaldenitrification.Theplantinvestigatedvariousalternativestomeetalimitoftechnology(LOT)futuretotalnitrogen(TN)designgoalof3mg/Lwhilesustainingthecurrentverystringenttotalphosphorous(TP)limitof0.18mg/L.OneofthealternativeprocessapproachesunderconsiderationinvolvesaninnovativeMovingBedBiofilmReactor(MBBR)technologyasadenitrificationpolishingstepdownstreamoftheexistingnitrification/denitrification(N/DN)activatedsludgesystem.TounderstandtheapplicabilityofMBBRtechnologyattheBluePlainsAWTPanditsabilitytoreliablyandcost-effectivelyperformtocomplywiththestringenteffluentTNrequirements,apilotplanwasundertakenbetweenDecember2007andJuly2008.ObjectiveTheoverallgoalofthepilotingprogramwastodetermineifthepostdenitrificationMBBRprocessisabletoreliablyandcosteffectivelymeettheLOTeffluentqualitygoalsoverarangeofoperatingconditions.Itisanticipatedthatlowsolublephosphorusconcentrationsmayaffectthedenitrificationratebyinhibitingtherapidgrowthofheterotrophicmicroorganismsinresponsetoincreasingnitrate(NO3-N)andnitrite(NO2-N)loads.Hence,itwasprudenttoassesstheimpactofupstreamchemicalphosphorus(P)removalsonthedenitrificationMBBRprocessandtoevaluatetheabilitytotightlycontrolphosphorusadditiontoenhancedenitrificationperformancewithoutsignificantlyelevatingtheriskofnon-compliancewiththeLOTeffluentphosphoruslimits.MBBRTechnologyTheMBBRtechnologyisarobust,attached-growth,biologicalwastewatertreatmentprocess.ItisarelativelynewtechnologyintheUnitedStates,appliedmainlytothenitrificationprocess,238NutrientRemoval2009Copyright©2009WaterEnvironmentFederation.AllRightsReserved.althoughthetechnologyitselfhasbeenprovenforbothnitrificationanddenitrificationinEuropeoverthepast20years.InanMBBRprocess,biomassgrowthisprimarilysupportedonthebiofilmcarrierandnotinsuspensionasinaconventionalactivatedsludgeprocess.Clarifiersandreturnactivatedsludgesystemsarenotrequired,whichmakesitverysimpleandcosteffectiveprocesstooperate.Thecarriersarekeptwithinthereactorbyanoutletsievearrangement.Thebiofilmisprotectedwithinplasticcarriers,whicharedesignedwithahighinternalsurfacearearelativetotheirvolume.Ingeneral,biofilmprocessestendtobemoreresilienttoprocesschangessuchaswastewatertemperature,flowsandloads,thansuspendedgrowth