PilotTestingofMBBRandIFASTreatmentProcesses

PILOTTESTINGOFMBBRANDIFASTREATMENTPROCESSESFORNITRIFICATIONANDDENITRIFICATIONATTHEMAMARONECKWWTPNancyChoi*,HeatherPhillips*,Dr.TerryL.Johnson*,RalphButler**,ThomasLauro****Black&VeatchCorporation489FifthAvenue12thFloorNewYork,NewYork10017**WestchesterCountyDepartmentofPublicWorks***WestchesterCountyDepartmentofEnvironmentalFacilitiesABSTRACTTheMamaroneckWWTPisoneoffourWWTPsinWestchesterCountythattheNewYorkStateDepartmentofEnvironmentalConservation(NYSDEC),throughitsStatePollutionDischargeEliminationSystem(SPDES),imposedWasteLoadAllocation(WLA)limitsfornitrogenbecauseofitsdischargeintotheLongIslandSound.ThefocusofthisPilotStudywasintendedtotesttheabilityofbothMovingBedBiofilmReactor(MBBR)processandIntegratedFixed-filmActivatedSludge(IFAS)processformeetingfutureloweffluenttotalnitrogenlimitsofapproximately4mg/L.Thesetwoprocessesareworthwhileforthissitebecause(1)averyhighleveloftreatmentcanbeachievedwithinasmallareawhichisattractivesincespaceisquitelimitedattheWWTPsiteand(2)theprocessesarewell-suitedforretrofitinstallationintotheexistingaerationtanks.TheMBBRoptionrequiredatertiarydenitrificationstage,whereastheIFASoptionrequiredtoachievecompletenitrificationanddenitrificationintheexistingpilottankagewithatotalhydraulicretentiontimeofonlythreehours.Inordertoprovideadequatedenitrificationinsuchalimitedvolume,IFASmediawasaddedtothepost-denitrificationstagewiththethoughtthatitwouldfacilitatethegrowthofslowergrowingmethanolotrophic(methanol-loving)bacteriaonthemedia,enhancingdenitrificationandpreventingtheirwashout.Thisapproachprovedsuccessful,effectivelydoublingthedenitrificationratefrom14to28mg/L/hr.Nitrificationratesandbiomassgrowthonthemediaweremeasuredthroughthetestperiod.Theloadingtothepilotwaspushedtoitsmaximumduringthecoldestwintertemperatureenablingthetwoprocessestobeassessedunderthemoststressedconditions.ResultsfromthepilottestingconfirmedthateitherIFASortheMBBRwouldbecapableofachievingthetargettotalnitrogenconcentration.KEYWORDSIFAS,MBBR,LowEffluentNitrogen,PilotPlant,Nitrification,Denitrification229WEFTEC®.07Copyright2007WaterEnvironmentFederation.AllRightsReserved©INTRODUCTIONIFASandMBBRTechnologiesIntegratedFixed-filmActivatedSludge(IFAS)technologyisgainingincreasingacceptanceasanoptionforupgradingactivatedsludgeplantstoadvancednutrientcontrolinmanyfacilitiesinNorthAmerica(Johnsonetal.,2006).TheIFASprocessisacombinationoffixed-filmandsuspendedactivatedsludgeprocessesinthesamebasinbyaddingmediatotheaerationbasinsofanactivatedsludgeprocesswhichmakesitpossibletoattainnitrifyingsludgeagesinaconsiderablysmallerbasinthanrequiredforacomparablesingle-stageactivatedsludgenitrificationprocess.Themediaprovidessurfaceareaforthegrowthofmicrobesand,incombinationwiththeMLSS,thedesirednitrification.TheresultisanequivalentMLSSconcentrationupwardsof6,000mg/L.Theattachedgrowth,however,doesnotimposeexcessivesolidsloadingsonthefinalclarifiers,sincethegrowthremainsintheaerationbasin.ThemainfeaturesofatypicalIFASsystemarethemedia(Figure1);somemeansofretainingthemediainthebasins,suchascylindricalsieves(Figure2);andmodificationstotheaerationsystemtoprovidegoodmediamixing,tocontrolbiomassgrowth,andtoprovideoxygenfortreatment.Figure1.ExampleofIFASMediaFigure2.CylindricalSieveInnorthernEurope,theMovingBedBio-Reactor(MBBR)processhasproventobeagoodmethodofnutrientremovalforlow-strengthwastewatersandlowoperatingtemperatures.Forexample,theLillehammertreatmentplantusesprimarytreatmentfollowedbyMBBRtosuccessfullytreatwastewaterwithaninfluentstrengthofjust210mg/LCOD,100mg/LTSS,and26mg/LTKNattemperaturesaslowas3ºC(Rustenetal.,1995).TheequipmentusedforbothMBBRandIFASisnearlyidenticalwithbothincorporatingmediaonwhichbiomasscangrow,buttheMBBRprocesshasnoreturnsludgelineand,therefore,nosignificantsuspendedgrowthbiomasspopulation.TheMBBRprocess,consequently,reliessolelyontheattached-growthbiomasstoprovidetreatment.230WEFTEC®.07Copyright2007WaterEnvironmentFederation.AllRightsReserved©MamaroneckWWTPTheMamaroneck,NewYork,WastewaterTreatmentPlantisoneoffourfacilitiesownedbyWestchesterCounty,thatdischargesintotheLongIslandSound.LocatedinthedowntownsectionoftheVillageofMamaroneck,itservestheMamaroneckSewerDistrict.Itsoriginalfacilities,includingtheadministrationbuildingwhichisnowanhistoriclandmark(Figure3),wereconstructedinthe1930s.Sincethentheplanthasundergoneseveralexpansions;themostrecentofthese,whichaddedsecondarytreatment,wascompletedinthe1980s,broughtthe2-acresiteto“build-out,”leavingnoroomforadditionalfacilities.TheplantsiteisborderedonthenorthandwestbyBostonPostRoad,ontheeastbytheOrientalYachtClub,andonthesouthbyHarborIslandPark.Treatmentcurrentlyconsistsofscreening,gritremoval,primarysedimentation,theactivatedsludgeprocess,anddisinfectionwithsodiumhypochlorite.Figure3.MamaroneckWWTPHistoricAdministrationBuildingThroughitsStatePollutantDischargeEliminationSystem(SPDES),theNewYorkStateDepartmentofEnvironmentalConservation(NYSDEC)hasimposedWasteLoadAllocation(WLA)limitsfornitrogenonthefourWestchesterCountyWWTPsthatdischargetotheLongIslandSo