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WaterPractice™•Vol.1•No.5©2007WaterEnvironmentFederation•doi:10.2175/193317707X256937APilot-ScaleComparisonofIFASandMBBRtoAchieveVeryLowTotalNitrogenConcentrationsTerryL.Johnson1*,AndrewShaw1,HeatherPhillips1,NancyChoi1,ThomasLauro2,RalphButler3,LeahRadko31Black&VeatchCorporation,KansasCity,Missouri64114.2WestchesterCountyDepartmentofEnvironmentalFacilities.3WestchesterCountyDepartmentofPublicWorks.*Towhomcorrespondenceshouldbeaddressed:johnsontl@bv.com.ABSTRACTInnorthernEurope,theMovingBedBiofilmReactor(MBBR)process,whichusesequipmentalmostidenticaltothatusedfortheIntegratedFixed-filmActivatedSludge(IFAS)processbuthasonlyanattached-growthbiomass,hasproventobeagoodnutrientremovalchoiceforfacilitiesthattreatlow-strengthwasteandoperateatlowtemperatures.PilottestingofbothprocesseswascarriedoutattheMamaroneckwastewatertreatmentplantinWestchesterCounty,NewYork,whereconditionsaresimilartothoseencounteredinnorthernEurope.TheprogramwasintendedtotesttheabilityofbothMBBRandIFAStomeetafuturetotalnitrogeneffluentlimitofapproximately4mg/L.Theloadingtothepilotunitwaspushedtoitsmaximumduringthelowestwintertemperature,enablingthetwoprocessestobeassessedundermaximumstressconditions.Resultsfromthepilottestingconfirmedthateitherprocesswouldbecapableofachievingthetargettotalnitrogenconcentration.KEYWORDS:IFAS,MBBR,lownitrogeneffluentplant,limitsoftechnology.INTRODUCTIONProcessdescription.IntegratedFixed-filmActivatedSludge(IFAS)technologyisgainingincreasingacceptanceinmanyfacilitiesinNorthAmericaasanoptionforupgradingactivatedsludgeplantstoadvancednutrientcontrol(Johnsonetal.,2006).TheIFASprocesscombinesfixed-filmandsuspendedactivatedsludgeprocessesinthesamebasinbyaddingmediatotheaerationbasinsofanactivatedsludgeprocess.Thiscombinationmakesitpossibletoattainnitrifyingsludgeagesinaconsiderablysmallerbasinthanrequiredforacomparableactivatedsludgenitrificationprocess.Themediaprovidessurfaceareaforgrowthofmicrobesand,incombinationwiththeMLSS,givestheprocessabiomasssufficientforthedesirednitrification.TheresultisanequivalentMLSSconcentrationofmorethan6,000mg/L.Theattachedgrowth,however,doesnotimposeexcessivesolidsloadingsonthefinalclarifiersbecausethegrowthremainsintheaerationbasin.ThemainfeaturesofatypicalIFASsystemarethemedia(Figure1);meansofretainingthemediainthebasins,suchascylindricalsieves(Figure2);andmodificationstotheaerationsystemtoprovideeffectivemixingofmedia,controlofbiomassgrowth,andoxygenfortreatment.InnorthernEurope,theMovingBedBiofilmReactor(MBBR)processhasproventobeagoodmethodofnutrientremovalforlow-strengthwastewatersatlowoperatingtemperatures.Forexample,theLillehammertreatmentplantinNorwayusesprimarytreatmentfollowedbyMBBRtosuccessfullytreatwastewaterwithaninfluentstrengthofjust210mg/LCOD,100mg/LTSS,and26mg/LTKNattemperaturesaslowas3ºC(Rustenetal.,1995).TheequipmentusedforMBBRandIFASisnearlyidentical.Bothincorporatemediaonwhichbiomasscangrow;however,theMBBRprocesshasnoreturnsludgelineandthereforenosignificantsuspended-growthbiomasspopulation.Consequently,itreliessolelyontheattached-growthbiomasstoprovidetreatment.Johnsonetal.WaterPractice™•Vol.1•No.5©2007WaterEnvironmentFederation•doi:10.2175/193317707X2569372Figure1.ExampleIFASMediafromPilotTesting.Figure2.CylindricalSieve.MamaroneckWWTPTheMamaroneck,NewYork,wastewatertreatmentplantisoneoffourfacilitiesownedbyWestchesterCounty.LocatedinthedowntownsectionoftheVillageofMamaroneck,itservestheMamaroneckSewerDistrict.Itsoriginalfacilities,includingtheadministrationbuildingthatisnowanhistoriclandmark,wereconstructedinthe1930s.Sincethentheplanthasundergoneseveralexpansions.Themostrecentexpansion,whichaddedsecondarytreatment,wascompletedinthe1980sandbroughtthe2-acresiteto“build-out,”leavingnoroomforadditionalfacilities.TheplantsiteisborderedonthenorthandwestbyBostonPostRoad,ontheeastbytheOrientalYachtClub,andonthesouthbyHarborIslandPark.Treatmentcurrentlyconsistsofscreening,gritremoval,primarysedimentation,theactivatedsludgeprocess,anddisinfectionwithsodiumhypochlorite.ThroughitsStatePollutantDischargeEliminationSystem(SPDES),theNewYorkStateDepartmentofEnvironmentalConservation(NYSDEC)hasimposedWasteLoadAllocation(WLA)limitsfornitrogenonthefourWestchesterCountywastewatertreatmentplantsthatdischargetotheLongIslandSound.TheincreasinglystringentWLAlimitsfornitrogenwillbephasedinoverthe10-yearperiodfrom2004to2014,andtheMamaroneckplantisfacinganultimatetotalnitrogenlimitofapproximately4mg/Lcalculatedona12-monthrollingaveragebasis,auniquelylowlimitforthisclimateintheUnitedStates.Theveryweakwastewater(primaryeffluentCOD124mg/L,TSS44mg/L,andTKN18mg/L)meansthatinordertomeetthelownitrogenlimits,carbonwillhavetobeaddedtotheprocesstosupportbiologicaldenitrification.AnumberofupgradeoptionsarebeingconsideredtoenabletheplanttomeetitsnewAPilot-ScaleComparisonofIFASandMBBRtoAchieve…WaterPractice™•Vol.1•No.5©2007WaterEnvironmentFederation•doi:10.2175/193317707X2569373permitrequirements.AninitialevaluationindicatedthatnitrificationanddenitrificationcouldbeachievedusingtheIFASprocess.Thelo