SidebySidePilotScaleComparisonofIFASandMBBR

Side-by-SidePilot-ScaleComparisonofIFASandMBBRProcessesOperatedatVaryingDOConditionsNicholasLandes1*,ChristopheDesmottes1,andSunilMehta11DegremontNorthAmericanResearchandDevelopmentCenter,Richmond,Virginia*Email:[e-mail]dyconductedaside-by-sideevaluationofsingle-stageIFASandMBBRprocessesforconcomitantcarbonoxidationandnitrificationofaprimaryeffluent.BothprocesseswerecomparedasafunctionofDO,temperature,andpollutantloadingrate.Ofparticularinterest,thestudysoughttoidentifythelowestresidualDOconcentrationthatsupportedeffectivenitrificationinthepresenceoforganiccarbon.Throughoutthestudy,medianpercentammoniumremovalwas90%and70%forIFASandMBBRprocesses,respectively.Forbothpilots,ammoniumremovalratesincreasedwithincreasingDO;however,astheammoniumloadingratewasdecreased,thedependenceofnitrificationratesonresidualDOwasdampened.AsresidualDOconcentrationsdecreased,theIFASreactorevidencedimprovedperformancewhencomparedtotheMBBR.KEYWORDS:IFAS,MBBR,suspendedcarrierreactor,nitrification,oxygenlimitationINTRODUCTIONMoving-bedbiofilmreactors(MBBR)andintegratedfixed-filmactivatedsludge(IFAS)processeshaveemergedastwoofthemostpromisingoptionsforhigh-ratenutrientremoval.Inparticular,theversatilityandadaptabilityofbothprocessesallowsengineerstoretrofitawidevarietyofexistingorabandonedtankgeometries(activatedsludgebasins,clarifiers,etc…)toserveasanIFASorMBBR(WaterEnvironmentFederation,2010).Otheradvantagesinclude:smallfootprintrequirementduetothehighlyconcentratedpopulationofactivebacteria(WEF,2010),protectedsurfacescapableofsustainingslowgrowingorganismssuchasnitrifiers(WEF,2010),consistentperformancethroughouttemperaturevariationsascausedbyself-regulatingmetabolicmechanisms(Bjornbergetal.,2010;Salvettietal.,2006;Strickeretal.,2009),protectionfromtoxiccontaminantsonaccountofthebacterialpopulationslocatedwithinbiofilmcommunities(Kimetal.,2010a),andimprovedeffluentsolidsproperties(loweffluentTSSforMBBRandlowSVIforIFAS)whencomparedtoconventionalactivatedsludge(CAS)(DiTrapanietal.,2010;Kimetal.,2010b).5178WEFTEC2011Copyright©2011WaterEnvironmentFederation.AllRightsReserved.Despitetheseadvantages,MBBRandIFASaresubjecttoconsiderableaerationcosts,oftentimesmorecostlythanCASprocesses(Strickeretal.,2009;Rossoetal.,2011).InordertobettermanagetheaerationburdenimpartedtoMBBRandIFASconfigurations,ithasbeenpostulatedthattheresidualdissolvedoxygen(DO)concentrationcanbeminimizedasafunctionofnutrientloadinginordertoreduceaerationcostswithoutdeleteriouslyimpactingeffluentwaterquality.ExtensiveworkhasbeenconductedregardingtheeffectsofDOonnitrificationperformanceinmoving-bedbiofilmprocesses.Theimportanceofoxygenmasstransferlimitationshasbeenexaminedusingtechniquesthatincluderegressionanalysis(Hemetal.,1994),oxygenmicrosensors(Masicetal.,2010),andlab-scalebatchtesting(Thomas,2009).Ingeneral,itisviewedthatnitrificationratesincreaselinearlywithincreasingresidualDO(WEF,2010).Withthisassumptioninmind,GapesandKeller(2009)conductedrespirometricexperimentsonmoving-bedbiofilmcarrierssourcedfromalab-scalenitrifyingreactoranddemonstratedthatoxygenuptakeratesandnitrificationratesincreaseduptoaDOconcentrationof20g/m3.Infact,paststudieshaveappliedpureoxygentopromotenitrificationratesupto10g-N/m2-dwithresidualDOconcentrationsashighas35g/m3(Bonomoetal.,2000;Salvettietal.,2006).Despitethewealthofinformationontheimpactsofoxygen,studieshavenotbeenconductedinordertocomparethedifferencesinoxygenlimitationforMBBRandIFASsystems.WhileseveralstudieshaveelucidatedthekeyadvantagesaffordedbytheIFASprocesswhencomparedinside-by-sidestudieswithCASsystems(vandenAkkeretal.,2010;Kimetal.,2010;Strickeretal.,2009;DiTrapanietal.,2010),onlyonesuchstudyhascomparedtheperformanceofIFASandMBBRprocessesinaside-by-sidefashion(Johnsonetal.,2007).ThestudybyJohnsonetal.(2007)wasconductedwithaweak-strengthprimaryeffluent(COD=124g/m3,TKN=18g-N/m3,TSS=44g/m3)thatwasfedtoIFASandMBBRprocesstrains,bothofwhichhadthreereactorsinseries.LowlevelsofeffluentammoniawerereportedforbothIFAS(averageNH3=1.1g-N/m3)andMBBR(averageNH3=0.6g-N/m3)configurations;however,theeffectofresidualDOconcentrationsontheseprocesseswasnotexplicitlyinvestigated.Thecurrentstudyconductedaside-by-sideevaluationofsingle-stageIFASandMBBRprocessesforconcomitantcarbonoxidationandnitrificationofanormal-strengthprimaryeffluent(COD=270g/m3,TKN=33g-N/m3,TSS=120g/m3).TheobjectivesofthestudyweretoassessandcomparetheperformanceofbothprocessesasafunctionofDO,temperature,andpollutantloadingrate.Inparticular,thestudysoughttoidentifythelowestresidualDOconcentrationthatsupportedeffectivenitrificationinthepresenceoforganiccarbon.MATERIALSANDMETHODSPilotTrailerSetupandOperationPilottestingwasconductedonsiteatthe75MGDHenricoCountyWaterReclamationFacility(WRF)inRichmond,Virginia.Thestudywasperformedinapilottrailerequippedwithtwo1.89m3(500gal)tanksthatwereoperatedinparallelwhereinonetankwasoperatedinanMBBRmodewithoutareturnactivatedsludge(RAS)linewhiletheothertankwasoperatedinaIFASconfigurationwithaRASline(