Biologicalphosphorusandnitrogenremovalinasequencin

BIOLOGICALPHOSPHORUSANDNITOGENREMOVALINASQUENCHINGBATCHMOVINGBEDBIOFILMREACTORH.Helness*andH.Ødegaard***SINTEFCivilandEnvironmentalEngineering,N-7034Trondheim-NorwayE-mail:[e-mail]**FacultyofCivilandEnvironmentalEngineering,NorwegianUniversityofScienceandTechnology(NTNU),N-7034Trondheim,NorwayE-mail:[e-mail]phorusandnitrogenremovalinbiofilmprocesseshaveapotentialadvantagecomparedtoactivatedsludgeprocesses,becauseoflessvulnerabilitywithrespecttosludgelossandbecausebiofilmprocesses,ingeneral,aremorecompactwithasmallerfootprint.However,withbiologicalphosphorusremovalabiofilmprocessdiffersfromanactivatedsludgeprocessbecausegreatercaremustbetakentoavoidcompetitionfromnon-phosphorusaccumulatingheterotrophicbacteria.Anotherdifferenceisthatinabiofilmprocess,nitrificationwillalwaysoccurunderconditionsfavourableforbio-P.Experimentshavebeencarriedout,demonstratingthatbiologicalphosphorusandnitrogenremovalcanbeachievedinamovingbedbiofilmreactoroperatedasaSBR,withsimultaneousnitrification,phosphorusuptakeanddenitrificationintheaerobicphase.KEYWORDSBiofilm;biologicalphosphorusremoval;nitrogenremoval;movingbed;sequencingbatchreactor;wastewaterINTRODUCTIONBiologicalphosphorusandnitrogenremovalinbiofilmprocesseshaveapotentialadvantagecomparedtoactivatedsludgeprocesses,becauseoflessvulnerabilitywithrespecttosludgelossandbecausebiofilmprocesses,ingeneral,aremorecompactwithasmallerfootprint.Mostoftheresearchonbio-Phasbeenconductedwithactivatedsludgesystems.However,therearereportsofbio-Pinlaboratoryorpilotscalebiofilmprocesseswerefixedbedfiltershavebeenoperatedinasequencingbatchmodeorasacontinuosprocesswithseveralfiltersinseries(Gonzales-MartinesandWilderer,1991,GoncalvesandRogalla,1992,Goncalveset.al.1994,Kerrn-Jespersenet.al.1994,Morgenroth,1998).ShinandParkreportedbio-Pinalaboratoryscalesequencingbatchreactor(SBR)withaporousbiomasscarrier(ShinandPark,1991).Simultaneousnitrificationanddenitrificationcanbeachievedunderaerobicconditionsinthebulkwaterphase,inaprocesswithathickbiofilm.Oxygenwillonlypenetratetoacertaindepthinthebiofilmgivinganouteraerobiclayer,werenitrificationoccurs.Thedeeperlayerswillbeanoxicwithdenitrifyingbacteriautilisingthenitrateproducedbythenitrifyersintheouterlayer.Biologicalphosphorusremovalwithsimultaneousnitrification-denitrificationandphosphateuptakeintheaerobicphasehasbeenreportedinbiofilmsystemsbyseveralauthors(Garzón-ZúñigaandGonzález-Martínez,1996,Castilloet.al.1998,HelnessandØdegaard,1998andPastorelliet.al.1998).Inthisworkwehaveusedasequencingbatchmovingbedbiofilmreactor(SBMBBR)withaplasticbiofilmcarriersuspendedinthewastewater.Inthispaperwepresentresults,fromanongoingexperimentalprogram,withrespecttocombinedbiologicalphosphateandnitrogenremoval.BIO-PINAMOVINGBEDBIOFILMPROCESSInamovingbedbiofilmprocessthesolidsretentiontimeisgovernedbysloughingofbiomass.Atsteadystatewithaconstantbiomassconcentration,thesolidsretentiontime(SRT)willcorrelatewiththeloadingrateoftheprocess.Inasequencingbatchreactorusedforbio-P,onemaydefineseveralloadingratesreferringtotheanaerobicphase,theaerobicphaseandthetotalcycle.Toavoidcompetitionfromnon-phosphateaccumulatingaerobicheterotrophs,allinfluentCODshouldbetakenupbyphosphateaccumulatingorganisms(PAO)intheanaerobicphase.ThisimpliesthatevenatthemaximumanaerobicCOD-loadingrate,onemayhavealowtotalCOD-loadingrateontheprocess.Basedonthebiochemicalmodelforbio-PdevelopedbySmolders(Smolderset.al.1994a,band1995)andlaterformulatedfordenitrifyingphosphateuptakebyKuba(Kubaet.al.1996a),onemaythereforeexpectthephosphateuptaketobecontrolledbytheavailabilityofpoly-β-hydroxy-alkanoates(PHA)intheaerobicphase.DuetothelowtotalCOD-loadingrate,onewillalsogetnitrificationinsuchaprocess.Inordertoensurecompletenitrification,theaerobicphasemustbelongenoughtoallowthis.Onehas,therefore,asituationwithpotentiallyconflictinginterests,imposingcertainlimitingfactorsontheprocess.IngeneraltheratioofCODtophosphateintheinfluentmustbehighenoughforremovalofallphosphate.Inaprocesswithdenitrifyingphosphateuptakebydenitrifyingphosphate-accumulatingbacteria(DPB),theremustalsobesufficientammoniumavailablefordenitrification.Giventhesecriteriafortheinfluentquality,theSBR-cyclemustbetuned.OnonehandtheanaerobicCOD-loadingrateshouldbekeptlowenoughtoavoidcompetitionfromnon-phosphateaccumulatingaerobicheterotrophs,andontheotherhandthetotalCOD-loadingrateshouldbehighenoughtogivesufficientPHAforphosphateuptakeandanetgrowthofbiomass.OnestrategyforachievingthiscouldbetooperatewitharelativelyshorttotalcyclelengthinordertohaveahighenoughtotalCOD-loadingrateandusearelativelylonganaerobicphasetominimisethecompetitionfromaerobicheterotrophs.However,onemustatthesametimekeeptheaerobicammoniumloadlowenoughtoachievecompletenitrification.Theminimumlengthoftheaerobicphasemaythereforebecontrolledbythenitrification.METHODSThestudieswerecarriedoutinalaboratoryscaleSBR(10lwatervolume,53%fillingofKaldnesK1biofilmmedia)withaconstructedwastewater.Adescriptionofthelaboratoryapp