Theeffectofdifferentcarbonsourcesonrespiratorydeni

JOURNALOFFERMENTATIONANDBIOENGINEERINGVol.82,No.3,277-285.1996TheEffectofDifferentCarbonSourcesonRespiratoryDenitrificationinBiologicalWastewaterTreatmentNATUSCKAM.LEE’*ANDTHOMASWELANDER’,*DepartmentofBiotechnology,CenterforChemistryandChemicalEngineering,LundUniversity,P.O.Box124,S-22100Lund,landAnoxAB,IdeonResearchPark,S-22370Lund,2SwedenReceived12December1995/Accepted30June1996Therespiratorydenitrificationactivityofactivatedsludgebacteriawithdiierentcarbonsources(aceticacid,crudesyrup,hydrolyzedstarch,methanol-withandwithoutasmallamountofyeastextract)wasstudiedinlong-termcontinuouscultivationsandbatchtests.Massbalancecalculationsshowedthatthemainproductinlong-termcultivationswithallcarbonsourceswasmolecularnitrogen.However,thetypeofcarbonsourcehadasignificantinfluenceonthedenitrificationrate,denitrificationyield,sludgeyieldandthecompositionofthemicroflora.Withacetateandmethanolhigherdenitrificationyields,lowersludgeyieldsandmoretrue(endproductN&denitrifyingbacteriawereobtainedthanwithcrudesyrupandhydrolyzedstarch.Furthermore,withacetateahighergrowthrateandahigherdenitrificationratewasobtainedthanwithmethanol.[Keywords:biologicalwastewatertreatment,nitrogenremoval,respiratorydenitrification,aceticacid,hydrolyzedstarch,methanol]Respiratorydenitrificationisoneofthemainmicro-biologicalprocessesfornutrientremovalinbiologicalwastewatertreatment.Precededbyammonificationandnitrification,whichreduceorganicnitrogenintooxidizedinorganicnitrogencompoundssuchasnitrate,denitrifi-cationisthelaststepinthenitrogencyclewherethenitrateistransformedthroughseveralintermediaryproducts(NO*-,NO,N20)tomolecularnitrogen.Itisananaerobicprocesswheretheoxidizednitrogencom-poundservesasanelectronacceptor,whiletheelectrondonormaybeofeitherinorganicororganicnature(1).Inmunicipalwastewatertreatment,therespiratorydenitrificationreliesuponacarbonsourceasanelectrondonor.However,theconcentrationofavailablecarbonsourceinthewastewatermaynotalwaysbesufficient,sothatanexternalcarbonsourcemaybeneeded(2).Someofthemainrequirementsforasuitableexternalcarbonsource,apartfromlowcosts,areanontoxic/nondan-gerousnature,alowsludgeyieldandtheabilitytostimu-lateacompletedenitrificationwithouttheneedforad-aptationofthemicroflora,sothatenvironmentallydetrimental,intermediaryproductssuchasnitriteandnitrogenousoxidescanbeavoided.Severalexternalcarbonsourceshavebeentestedandfoundtohavevariouseffectsontherespiratorydenitrificationintermsofthedenitrificationrate,thedenitrificationyieldandthesludgeproduction(3).However,thesestudieshavemostlybeenperformedonunadaptedwastewateroractivatedsludgeinbatchreac-torsforkineticdeterminations,whereasonlyafewhavepaidattentiontothelong-terminfluenceofacarbonsourceonthedenitrifyingmicroflora(4-6).Someofthesestudieshavefocusedontheeffectofmethanolandhaveshownthatappendagedbacteria,mainlyHyphomicrobium,seemtobefavoured(7,8).Inothermicrobiologicalinvestigationsindifferenttypesofdenitrificationsystemswithexternalcarbonsources,in-cludingmethanol,bothHyphomicrobiumaswellasotherbacterialgenerahavebeenobserved(9-13;Dr.*Correspondingauthor.HildeLemmer,personalcommunication,BavarianStateAgency,D-8000Munich22,Germany).Theaimofthisstudywastodeterminethedenitrifica-tionactivityofbacteriaselectivelyenrichedfromactivat-edsludgewithdifferentcarbonsources.Bothlong-termcultivationsinchemostatsaswellasbatchtestswereper-formedinordertodeterminethedenitrificationrate,thedenitrificationyield,thesludgeyieldandthemicrobialcomposition.Fourcarbonsourceswereselected:acetateandmethanol,whicharecommonlyusedeitherinfullscaleorinlaboratoryscale(3),andtwocarbohydrateproducts,crudesyrupandhydrolyzedstarch,whichhavebeenusedtosomeextentasexternalcarbonsources.MATERIALSANDMETHODSChemicalsAllchemicalswereofproanalysisquali-ty,exceptforcrudesyrupandhydrolyzedstarch.Crudesyrup,abyproductfromsugarrefining,contains800gsucrose/land50-lOOg/lunspecifiedorganicmatter,andtheCODcontentis9OOg/l.Hydrolyzedstarchconsistsof60%lower(mono-,di-,tri-saccharides)and40%highersugarcompounds,andtheCODcontentis860g/l.AnalysesNitrate,nitriteandammoniumwereanalysedaccordingto(14).ChemicalOxygenDemand(COD)wasmeasuredasdescribedin(15).Aceticacidandmethanolweremeasuredbythegaschromatograph-icmethodasdescribedin(16).Starchandsucrose/D-glucose/DfructosewereanalysedenzymaticallybykitsfromBoehringerMannheim,no.207748andno.716260,respectively.TotalSuspendedSolids(TSS)weredeterminedaccordingto(17),using0.45pmmembranefilters(Schleicher&Schuell).Nitrogengas,dinitrogenoxide,nitrogenoxideandcarbondioxidewereanalysedbygaschromatographyasdescribedin(18).Theoxi-dation-reductionpotential(ORP)wasmonitoredinthereactorsthroughouttheexperimentasdescribedin(19).Microscopicexaminationsbymeansofphasecontrastandinterferencemicroscopy(NikonOptiphot-2)ofthe277278LEEANDWELANDERJ.FERMENT.BIOENG..microflorainthechemostatswerecarriedoutthrough-outtheexperiment.ChemostatexperimentsTheeffectofasolecarbonsourceonthedenitrificationactivitywasstudiedinfour5OOmlchemostatsoperatedinparallelonthesamebasicsterilemedium,butwithdif