AnewMABRforlowenergytreatment

WaterTechnologies&SolutionstechnicalpaperFindacontactnearyoubyvisiting“ContactUs.”*TrademarkofSUEZ;mayberegisteredinoneormorecountries.©2017SUEZ.Allrightsreserved.TP1210EN.docxOct-15anewmembrane-aeratedbiofilmreactorforlowenergywastewatertreatment:pilotresultsPresentedatWEFTECConference,2015.Authors:PierreCôté1,JeffPeeters2,NicholasAdams2,YoungseckHong2,ZeboLong2,JohnIreland21COTEMembraneSeparationLtd,Hamilton,Ontario2SUEZWaterTechnologies&Solutions,Oakville,OntarioabstractAnewhybridmembrane-aeratedbiofilmreactor(MABR)technologythatenablesenergy-neutraltreatmentofmunicipalwastewaterisintroduced.Theprocess,whichremovesnitrogenusingconventionalnitrification-denitrification,wasdemonstratedatpilot-scale,treatingprimaryeffluent.ThenewMABRmembraneproductcanoperateinahighmixedliquorsuspendedsolids(MLSS)environment,makingitsuitableforuseinaconventionalactivatedsludgereactortoincreaseoxygentransferandnitrificationcapacity.Thepilotachievedremovalratesof91%forTSS,83%forCOD,95%forammonia,and66%fortotalinorganicnitrogen.MABRtechnologyhasthepo-tentialtotransferoxygenveryefficiently,atanaerationefficiencyof6kgO2/kWh.Keywords:Membrane-aeratedbiofilmreactor,integratedfixed-filmactivatedsludge,energy-neutralwastewatertreatment.introductionAbiologicalprocessthatenablesenergy-neutraltreatmentofmunicipalwastewaterwasintroducedbyPeetersetal(2014a).Theprocessisahybridmembrane-aeratedbiofilmreactor(MABR)thatremovesnitrogenusingtheconventionalnitrification-denitrificationpathway.AnMABRoffersallthebenefitsofbiofilmreactorswith,inaddition,theabilitytotransferoxygenveryefficientlyandatlowenergyinput.Oxygenistransferredwithoutbubblesthroughagas-transfermembrane,whichfavorstheestablishmentofanitrifyingbiofilm.InahybridMABRprocess,themembranesareimmersedinasuspend-edbiomassthatiskeptanoxicormicro-aerobicfordenitrification.ThenewMABRproductanditsperformancetreatingasyntheticammoniasolutionweredescribedbyAdamsetal(2014).Thispaperpresentstheresultsofa220daystudytreatingprimaryeffluentusingpilot-scalemodules.Page2TP1210EN.docxnewmembrane-aeratedbiofilmreactortechnologyThebuildingblockofthenewMABRmembraneisanunbreakable“cord”,whichisconstructedofdense-wall,oxygen-permeablehollowfibermembranesdistributedaroundthecircumferenceofayarnreinforcementcore(Figure1).Acordhasadiameterofabout1.1mmandisdesignedtobedeployedinamoduleapproximately2mlong.Figure1.CordstructureThenewMABRmodulehastwothin/elongatedheadersforairfeedandexhaustandcontainsthousandsofcords.Thecordsaregeometricallyspacedapartintheheadersandmountedwithslacktoallowfreeswaying.Modulesareassembledintocassettes(Figure2).Anairscouringsystematthebottomofthecassettehasbeenadaptedtomixwastewaterinsidethecordbundlesandcontrolbiofilmthickness.Figure2.NewMABRcassetteTP1210EN.docxPage3OxygentransferperformancewithanMABRisafunctionofthemembranecharacteristicsandoperationalpa-rametersthataresimilartofinebubbleaerationsystems.Becausethebiofilmsurfaceareachangeswiththebiofilmthickness(andthebiofilmthicknessisnotnormallyknown),performanceisexpressedonthebasisof“surfaceareaofcord”,usingacordoutsidediameterof1.1mm.InanMABR,itiseasytoperformanoxygenmassbalanceonthegassidebecausetheexhaustgasiscontainedandkeyvariables(flowandoxygenconcentration)canbemeasuredonacontinuousbasis(thiswouldbeanalo-goustomeasuringoxygentransferefficiencywiththeoff-gasmethodonacontinuousbasisinabubbleaerationsystem).Theprimaryparameterdeterminedfromexperimentaldataistheoxygenfluxthroughthemembranes:Equation1where:J=oxygenflux(gO2/d/m2)MO=oxygenmolecularweight(32g/mol)QPF,QPE=processgasfeedandexhaustspecificflowrates(Nm3/h/m2)Vm=standardgasvolumeatSTP(0.0224m3/mol)XF,XE=molarfractionofoxygeninfeedandexhaustgas(-)Theoxygentransferrate(OTR)isdirectlyproportionaltothesurfaceareaofmembranedeployed:Equation2whereOTR=oxygentransferrate(gO2/d)S=surfaceareaofcord(m2)Thereisasimplerelationshipbetweentheoxygenfluxandtheoxygentransferefficiency(OTE):Equation3whereallthetermshavebeenpreviouslydefined.Whendesigninganactivatedsludgeaerationsystem,thepowerinputforthebloweriscalculatedtwodifferentways–firsttomeettheoxygendemandandsecondtokeepthemixedliquorinsuspension–andthehigherofthetwovaluesdeterminestheblowersize.AsimilarsituationexistsforanMABR:thereisapowerinputcompo-nentrequiredforaerationtomeettheoxygendemandandasecondcomponenttoprovidemixingontheliquidsidetopromotesubstratepenetrationintothebiofilm(i.e.;renewtheboundarylayer).Mathematically,theaera-tionefficiencycanbeexpressedasfollows:Equation4Page4TP1210EN.docxwhere:AE=aerationefficiency(kgO2/kWh)f=mixingtimefraction(-)QM=specificmixinggasflowrateatSTP(Nm3/h/m2)WP,WM=adiabaticcompressionenergyfortheprocessandmixinggasblowers(Wh/molair)InEquation4,thetwotermsontherightsidehaveunitsofkWh/kgO2andrepresentthespecificenergytocausethereactantstomeetinthebiofilm:thefirsttermforoxygenandthesecondtermforthesubstrate.TheadiabaticcompressionenergyWinEquation4iscalculatedwith:Equation5where:e=blower/motorefficiencyfactor(0.65)k=ratioofspecificheatofairatco