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BIODEGRADABILITYANDCHANGEOFPHYSICALCHARACTERISTICSOFPARTICLESDURINGANAEROBICDIGESTIONOFDOMESTICSEWAGEAbstract:Atthehigh-rateanaerobictreatmentofdomesticsewage,bothbiologicalandphysicalprocessesplayanimportantrole.Therefore,theanaerobicbiodegradabilityofraw,paper-filteredandmembrane-filteredsewageandblackwaterhasbeeninvestigatedinbatchexperiments.Additionally,theeffectofanaerobicdigestiononphysicalcharacteristics,likeparticlesize,surfacetensionandzeta-potential,ofthepresentparticlesisstudied.Thebiodegradabilityofdomesticsewageandblackwaterat308Cisalmostsimilar(71±74%).Moreover,ahighmethanogenesisofthecolloidalfractionindomesticsewage(86_3%)isachieved,showingthatthelowremovalofcolloidalparticlesincontinuoushigh-rateanaerobicreactorsisduetolowphysicalremovalratherthanbiodegradability.Thelowestbiodegradabilityisdemonstratedforthedissolvedfraction(62%).Theresultsshowthatafteranaerobicdigestiontheaverageradiusofparticleswithdiameter54.4and50.45mmincreasedfordomesticsewage,whileitdecreasedforblackwater.Partofthesurface-active\ncomponentsindomesticsewageisnotbiodegradedduringanaerobicbatchdigestion,asindicatedbythedevelopmentofthesurfacetension.Thenegativezeta-potentialofallparticleshardlychangesduringdigestion,showingthatcolloidalinteractionswerenotaffectedbyanaerobicdigestion.Keywords:anaerobictreatment,domesticsewage,blackwater,biodegradability,particlesize,surfactants,zeta-potentialINTRODUCTIONSeveralauthorshaveshownthatparticlesrepresentthemajorpart,upto85%,ofthetotalCOD(CODt)indomesticsewage(Levineetal.,1985;Zeemanetal.,1997).Theseparationofparticulateanddissolvedcompoundsindomesticsewageisusuallymadebyfiltrationthroughamembranefilterwithaporediameterofapproximately0.45mm(NielsenandHarremoes,1995).Theparticlesareoftenseparatedinasuspendedandacolloidalpart,withaparticlesizeofrespectivelylargerthan4.4mmandbetween0.45and54.4mm,althoughthesizerangefor\ncolloidalparticlesisnotinagreementwiththedefinitionasusedincolloidchemistry.Attreatmentunderanaerobicconditions,colloidalCOD(CODcol)fromdomesticsewageisremovedtoalowerdegreethanunderaerobicormicroaerophillicconditionsandrepresents60±80%ofthee.uentCODtofananaerobicreactor(Yodaetal.,1985;Wang,1994;Wangetal.,1995).TheremovalofCODcolinbatchrecirculationexperimentsatlongetentiontimes,indicateshoweverthatcolloidalarticlesarebiodegradable(LastandLettinga,992;Wang,1994).Sofarthishasneverbeenproven.Atthehigh-rateanaerobictreatmentofdomesticsewage,bothbiologicalandphysicalprocessesplayanimportantrole.Particlescanonlybeconvertedviahydrolysis,afterbeingphysicallyremovedbyadsorption,settlingorentrapmentinthesludgebed.Particlecharacterizationbasedonthebiologicalandphysicalaspectsarethereforeofthesameimportance.Thepresenceofsurfactantsindomesticsewage,whichareknowntoadsorbatbothsolid/liquidandliquid/airinterfaces,mayaffecttheanaerobicbiodegradabilityofparticles.Surfactantshavetheabilitytoemulsifypoorlysolublehydrophobiccompoundsinwater,thuspotentiallyimprovingthe\naccessibilityofthesesubstratestomicroorganisms(Rouseetal.,1994).Ontheotherhand,theemulsifyingeffectmightpreventthephysicalremovaloftheparticles.Moreoverinhibitionofanaerobicbiodegradationoforganiccompoundsinthepresenceofsurfactantshavealsobeenreported(WagenerandSchink,1987;Rouseetal.,1994).Boller(1993)mentionedthatthesurfactantconcentrationinZuÈrichCitywastewaterwas17±22mglÿ1andthenon-ionicandanionicsurfactantsrepresentthemainpart(91±94%).Linearalkylbenzenesulphonatesconstitutethemajoranionicsurfactantfractioninhouseholds(Holtetal.,1998)withaverageconcentrationsof4and3mgindomesticsewageinTheNetherlands(WaterandFeijtel,1995)andinUK(Holtetal.,1998),respectively.Atlowconcentrations,surfactantsarepresentasmonomers.Micellesareformedabovethecriticalmicelleconcentration(CMC).TheCMCofdodecylbenzenesulphonateamountsto264mglÿ1(MukerjeeandMysels,1971).Therefore,surfactantsindomesticsewageseemtobepresentasmonomers.Thesizeofparticlesindomesticsewageaffectsbothbiologicalandphysicalprocesses(Levineetal.,1985).Gravitationalanddragforcespredominateovercolloidalforces(vanderWaalsattractionandelectrostaticrepulsion)\nforlargerparticles,whilecolloidalforcesaremoreimportantforparticleslessthanafewmm(Gregory,1993).Thezeta-potential,whichrepresentsthepotentialonorjustoutsidetheSternlayer,isanimportantphysicalparameterforcolloidalparticleseparationbecauseelectrostaticinteractionsofcolloidalparticlesaremainlyrelatedtothezeta-potential.Thisresearchaimsforthedeterminationoftheanaerobicbiodegradabilityofthesuspended,colloidalanddissolvedfractionofdomesticsewageandblackwater.Moreover,thechangeinphysicalcharacteristics,likeparticlesize,zeta-potentialandsurfacetensionasaresultofbiodegradationisdetermined.MATERIALSANDMETHODSAnaerobicdigestionofdomesticsewageandblackwaterAnaerobicbatchdigestionhasbeencarriedoutinduplicateseriesofserumbottlesof120mleachateachtemperature.Toeachbottle100mlofwastewaterisadded.Thebiogascompositionintheheadspaceofeachbottleismonitoredintime.Foreachbottle,CODfractions,volatilefattyacids(VFA),andsurfacetensionweredetermined.Twoseriesofexperimentshavebeenperformed.Inthefirst\nrun,rawandpaper-filteredsewagewasdigestedat4,20and30Candbottlesweremonitoredafter8,15,23and43days.Theaimofthesecondrunwastoconfirmtheresultsofthefirstrunandtofindthemaximumconversionofwastewatertomethane(biodegradability).Thesecondrunwasperformedwithraw,paper-andmembrane-filtered(notinduplicate)sewageandblackwaterat20and30Candmonitoringwascarriedoutafter15,28and135days.Inthesecondrunalsotheaverageparticleradiusandzeta-potentialweremeasured.AnalysisCODwasanalysedusingthemicro-methodasdescribedbyJirkaandCarter(1975).RawsampleswereusedforCODt,4.4mmfoldedpaper-filtered(Schleicher&Schuell5951/2,Germany)samplesforCODpand0.45mmmembrane-filtered(Schleicher&SchuellME25,Germany)samplesfordissolvedCOD(CODdis).ThesuspendedCOD(CODss)andCODcolwerecalculatedbythedifferencesbetweenCODtandCODp,CODpandCODdis,respectively.IntheexperimentsitwasdiculttohaverepresentativesamplesforCODtduetotheformationoflarge¯ocsduringanaerobicdigestion.Therefore,onlyCODpandCODdisarepresented.VFAweredeterminedfrommembrane-filteredsamplesbygaschromatography.The\nchromatograph(HewlettPackard5890A,PaloAlto,USA)wasequippedwitha2m_2mm(innerdiameter)glasscolumn,packedwithSupelcoport(100±120mesh)coatedwith10%FluoradFC431.Operatingconditionswere:column,1308C;injectionport,2008C;¯ameionizationdetector,2808C.N2saturatedwithformicacidat208Cwasusedasacarriergas(30ml/min).ThebiogascompositionCH4,CO2,N2andO2wasdeterminedina100mlsampleusingFisonsInstrumentgaschromatographymodelGC8000series,equippedwithcolumnsconnectedinparallel(split1:1)±(1.5m_2mm)Te¯on,packedwithchromosorb108,(60±80mesh),anda(1.2m_2mm)stainlesssteel,packedwithmolecularsieve5A,(60±80mesh).Heliumwasusedascarriergas(45mlminÿ1).Theoven,detectorandinjectiontemperatureswere40,100and1108C,respectively.Allmeasurementswereperformedinduplicate.Anindicationofthepresenceofsurface-activecomponentscanbeobtainedbymeasuringthesurfacetensionwiththeWilhelmy-platemethod.Itislikelythatindomesticsewage,surfactantswillstronglycontributetotheloweringofthesurfacetensionoftheaqueoussolution.AftertheCMC,surfacetensionbecomesalmostindependentoftheoverallconcentration.However,oneshouldbeawarethatalsoother\nsurface-activecomponentscancontributetotheloweringofthesurfacetensionandthereforethequalitativeinterpretationcanbepresented.Inrun1,thesurfacetensionwasmeasuredfortheoriginalsampleswithoutfiltration.Theformationoflarge¯ocsduringrun1increasedthestandarddeviationsofthesurfacetensionmeasurements.Moreover,thesurfacetensionofwastewaterslightlyincreasesafterpaperfiltration(fromtheresultsofrun1).Therefore,thesurfacetensioninrun2wasmeasuredforallsamplesafterpaperandmembranefiltration.Thehydrodynamicparticleradiuswasdeterminedwithdynamiclightscattering.Measurementswerecarriedoutina2mlcylindricalquartzcellusinganALV5000systemwithaLexel150mWmultilineAr-laser.Particleswitharadiusbetween2.5nmand5mmcanbedetected.Themeasurementswereperformedforbothpaper-andmembrane-fiteredsamples.Foreachsample,theaverageparticleradiuswasmeasuredseventimesatanangleof90ElectrophoreticmobilitiesweredeterminedwithaMalvernZetasizerIII.Zeta-potentialswerecalculatedfromtheSmoluchowskiequation.Measurementswereperformedatconstantionicstrength(0.02MKCl)andsampleswerepaperfilteredto\nremovebigparticles.CalculationsThetotalCH4productionineachserumbottlewasthesummationoftheCH4intheheadspaceandthedissolvedCH4.ThedissolvedCH4wascalculatedaccordingtoHenry'slaw.Percentageofhydrolysis(H),acidification(A)andmethanogenesis(M)werecalculatedaccordingtoequations(1),(2)and(3)respectively.H,AandMofCODcolfordomesticsewageinrun2werecalculatedbysubtractingtheresultsofmembrane-filteredsewagefromtheresultsofpaper-filteredsewageandapplyingequations(1),(2)and(3),respectively.Similarly,H,AandMofCODssfordomesticsewageinrun2werecalculatedbysubtractingtheresultsofpaper-filteredsewagefromtheresultsofrawsewage.\nFig.1.ThecourseofthetotalCH4productionduringtheanaerobicbatchdigestionofrawsewage(}),paper-filteredsewage(&),membrane-fiteredsewage(n)andblackwater(*)inrun2attemperatureof20and30C.Fig.2.Thecourseofthesurfacetensionduringtheanaerobicbatchdigestionofraw(})andpaper-filtered(&)sewageinrun1attemperatureof4,20and30C.RESULTSANDDISCUSSIONBiodegradability\nTable1summarizesthecalculatedpercentagesofhydrolysis,acidificationandmethanogenesisforeachwastewatersampleafter43and135daysofdigestion,inruns1and2,respectively.Theresultsofrun1showthat43daysofbatchdigestionarenotsucientforcompleteanaerobicdigestionevenat30C.TheVFAconcentrationexceeds100mgCODÿ1latallappliedconditions.TheresultsofthetotalCH4productioninrun2(Fig.1)showthatthemaximumconversionofthedomesticsewagefractionsandblackwaterisachievedafterabout80daysat30C.Figure1theanaerobicdigestionhasacharacteristiclag-phaseperioddependingonthetemperatureandthesizeoftheparticles.At20Conlyrawsewagereachedthemaximumconversionafter135daysofdigestion.Themaximummethanogenesisforrawsewagewassimilarattemperaturesof20and30Cindicatingthatanaerobictreatmentisnotonlyapromisingtechniqueintropicalbutalsoinmoderateareas.Thebiodegradabilityofblackwater,rawsewageandpaper-filteredsewageat30Cisapproximatelythesame,viz,71±74%,whilethatofthemembranefilteredfractionwasrelativelylow(62%).Noreporteddataareavailabletocomparewiththepresentedresults.\nTable2presentsthemaximumhydrolysis,acidificationandmethanogenesisoftheCODssandCODcolfractionofdomesticsewageat30C.ThemaximumhydrolysisforCODssandCODcolissimilar,whilethemaximumacidificationandmethanogenesisarehigherforCODcolascomparedtoCODss.Hydrolysisofsuspendedparticlesseemstoproducemorenon-degradableCODdisthanhydrolysisofcolloidalparticles.LastandLettinga(1992)reportedalowermaximumremovalofCODdisof54%duringbatchrecirculationofpre-settledsewageofthesameoriginasusedintheherepresentedexperiments.Thislowerbiodegradabilitymightbeduetotheproductionofnon-degradableCODdisfromthehydrolysisofparticlespresentinpre-settledsewage.SurfacetensionFig.2.Thecourseofthesurfacetensionduringtheanaerobicbatchdigestionofraw(})andpaper-filtered(&)sewageinrun1attemperatureof4,20and30C.\nThesurfacetensionisameasureforthepresenceofsurface-activecompounds,suchasdetergents.Thedevelopmentofthesurfacetensionintimeduringbothruns1and2,wasalmostsimilarfortemperaturesof20and308C(Figs2and3).Themaximumsurfacetensionwashowevermuchlowerat48Cascomparedtothatattemperaturesof20and308C.Aplateauvalueonthesurfacetensionisobtainedbetween15and25days.Thisperiodismuchshorterthanthecharacteristicanaerobicdigestiontime.Itseemsthatasmallamountofhighlysurface-activecomponentsarerapidlydecreased.Degradationofthedetergentsseemmuchslowerleadingtoamaximumsurfacetensionmuchlowerthanthatofwater.Theinitialsurfacetensionofpaper-filteredblackwaterwashigherthanthatforpaper-filtereddomesticsewage(Fig.3),probablyduetothefactthathardlyanydetergentsareaddedtoblackwater.After135daysbatchdigestionat20and30Cthemaximumsurfacetensionofblackwateralmostreachedthatofwater.Partofthesurfactantswasretainedduringfiltrationasshownbythehigherinitialsurfacetensionofpaper-filteredascomparedtorawsewage(Fig.2),whilethatofmembrane-®lteredsewageishigherthanthatofpaper-filteredsewage(Fig.3).Astheinitialsurfacetension\nofthemembrane-filteredsewagewasstilllowerthanthatofwater,somesurfactantswereremaining,evenafter135daysbatchdigestion(Fig.3).Thesurfactants,remainingafterdigestion,arehoweverremovedbyarepeatedmembranefiltrationpriortomeasurement(Fig.3),whichindicatesthattheyaremainlyadsorbedtoparticlesproducedduringthedigestionprocess.Fig.3.Thecourseofthesurfacetensionduringtheanaerobicbatchdigestionofrawsewage(}),paper-filteredsewage(&),member-filteredsewage(n)andblackwater(*)inrun2attemperatureof20and30C.\nAverageradiusFigure4showsthattheaverageinitialradiusofparticlesafterpaperormembrane-fitrationofblackwaterismuchhigherascomparedtothatofdomesticsewage.Althoughtherawsewagewaspaper-filteredwithadiameterof4.4mm,theaverageradiusoftheparticlesinpaper-filteredsewagewasonly188nm.Therefore,alargequantityofverysmallparticlesispresentindomesticsewage.Thelatterisconfirmedbythelowaverageradiusof68nmoftheparticlesinmembrane-filteredsewage.Aperiodof135daysbatchdigestionofraw,paper-and\nmembrane-filteredsewagefollowedbypaperormembranefiltrationresultedinanincreaseoftheaverageradiusatboth20and30C.Itiswellknownthathydrolysiscausesadecreaseinthewastewatersubstrateparticles,whileremainingsubstrateisovergrownwithbiomass(Sandersetal.,2000),whichcanresultinanincreaseintheaverageradiusoftheparticles.Theanaerobicdigestionofmembrane-filteredsewageproducescolloidalparticles.After135daysofbatchdigestionat20and308C,theCODcolconcentrationinthemembrane-filteredsamplesamountedto,respectively,38and20mglÿ1.MethanogenesisofCODdismightthereforeaffecttheremovalofCODcolinacontinuousanaerobicreactortreatingdomesticsewage.Batchdigestionofblackwaterfor15±28daysfollowedbyeitherpaperormembranefiltrationdecreasedtheaverageradiusoftheparticlesatboth20and308C.However,after135daysbatchdigestion,italmostremainedunchangedforsamplesafterpaperfiltrationandincreasedforsamplesaftermembranefitration.Therefore,inthefirst15±28days,thehydrolysiswashigherthantheentrapmentofparticlestotheproducedbiomass.\nFig.4.Thecourseoftheaverageradiusduringtheanaerobicbatchdigestionofrawsewage(}),paper-filteredsewage(&),membrane-filteredsewage(n)andblackwater(*)inrun2attemperatureof20and30C.ZetapotentialTable3showstheassessedvaluesofthezeta-potentialinrun2.Anaerobicbatchdigestionforaperiodof135days,ledtoonlyaslightdecreaseinthenegativezeta-potentialforallwastewatersamples.Thus,duringanaerobicdigestion,thenumberofnegativegroupsperunitarearemainsalmostconstantandelectrostaticrepulsionbetweenthecolloidalparticles\ndoesnotchangesignificantly.GeneraldiscussionThehighbiodegradabilityofdomesticsewageandblackwaterrevealsthepotentialofanaerobictreatment.Moreover,ahighmethanogenesisofthecolloidalfractionindomesticsewage(86_3%)isachieved,showingthatthelowremovalofCODcolincontinuoushigh-rateanaerobicreactorsisduetolowphysicalremovalratherthanbiodegradability.Thedevelopmentofthesurfacetensionduringbatchdigestionindicatesalimitedbiodegradabilityofthepresentsurfactants.Animportantpartofthesurfactantsinsewageisformedbydetergents,whicharereportedtohavealowanaerobicbiodegradability.Thepresentresultsalsoshowthatpartofthesurfactantsisnotbiodegradedduringanaerobicbatchdigestion.Moreover,itisdemonstratedthatsurfactantsarepartlyconnectedtoparticles,bothsuspendedandcolloidal.Thelattercouldaffectthestabilityandtherefore,lowremovalofcolloidalparticlesindomesticsewage.Thoughcolloidalparticleswerehydrolysedtoahighdegree,theaverageparticlesizeincreasedduetogrowthofbiomass.Incontinuoushigh-ratesystems,thelattercannotbeexpected,asbiodegradationcanonlytakeplaceafterphysicalremovalbythesludgebed.The\nzeta-potentialofallparticlesisnegativeandhardlychangesduringdigestion,showingthatcolloidalinteractionswerenotaffectedduetoanaerobicdigestion.Astheanaerobicbiomassalsohasanegativecharge(Morganetal.,1990),colloidalremovalincontinuousanaerobicsystemstreatingdomesticsewagecanbeexpectedtoremainlow,independentoftheappliedconditions.ImprovementofthecolloidalfractionandtherewithconversiontoCH4gas,couldbeimposedbyadditionofcoagulants,fordestabilisationofthecolloids.Bypre-removaloftheSSinafirstanaerobicstep,thecostsoftheuseofcoagulantsinthesecondstepcouldbereduced.AshydrolysisofsuspendedparticlesproducesmoreinertdissolvedCODthanhydrolysisofcolloidalparticles,theintroductionofafirsthigh-loadedanaerobicstepfortheremovalofSScouldmoreoverimprovethedissolvede.uentquality.ThelatterisalsoshownbyElmitwallietal.(1999a).TheremovalofSSfromdomesticsewagepriortomethanogenesiscanbeachievedbyeithersettlingBiodegradabilityandchangeofphysicalcharacteristicsTable3.Zeta-potentialatconstantionicstrength(0.02MKCl)forrawandpaper-filteredsewageandblackwaterbeforeandafteranaerobicbatchdigestioninrun2attemperaturesof20\nand308C.StandarddeviationsarepresentedinparenthesesCONCLUSIONS*Theanaerobicbiodegradabilityofdomesticsewageandblackwaterat308Cisalmostsimilar*Themaximumconversiontomethaneat30Cwasthehighest(86%)forthecolloidalfractionindomesticsewagefollowedbythesuspendedfraction(78%),whilethemaximumconversionofthedissolvedfractionwasthelowest(62%).*Afteranaerobicbatchdigestion,theaverageradiusoftheparticleswithdiameter54.4and50.45mmindomesticsewageincreased,whiletheaverageradiusoftheseparticlesinblackwaterdecreased.*Partofthesurface-activecomponentsindomesticsewagewasnotbiodegradedduringanaerobicbatchdigestion,asindicatedbythedevelopmentofthesurfacetension.*Thenegativezeta-potentialofallparticleshardlychangeduringdigestion,showingthatcolloidalinteractionswerenotaffectedbyanaerobicdigestion.ortreatmentinahigh-loadedanaerobicreactor\nREFERENCESBollerM.(1993)Removaloforganicmatterbyphysicochemicalmechanismsinwastewatertreatmentplants.WaterSci.Technol.27(11),167±183.ElmitwalliT.A.,ZandvoortM.,ZeemanG.andLettingaG.(1999a)Lowtemperaturetreatmentofdomesticsewageinup¯owanaerobicsludgeblanketandanaerobichybridreactors.WaterSci.Technol.39(5),177±185.ElmitwalliT.A.,SklyarV.,ZeemanG.andLettingaG.(1999b).Lowtemperaturepre-treatmentofdomesticsewageinanaerobichybridandanaerobicfilterreactor.Proc.4th.IAWQConferenceonBio®lmReactors.17±20October1999,NewYork,USA.GregoryJ.(1993)Theroleofcolloidinteractionsinsolid-liquidseparation.WaterSci.Technol.27(10),1±17.HoltM.S.,FoxK.K.,BurfordM.,DanielM.andBucklandH.(1998)UKmonitoringstudyontheremovaloflinearalkylbenzenesulphonateintricklingfiltertypesewagetreatmentplants.ContributiontoGREAT-ERprojectsNo.2.TheSci.ofthetotalEnviron.210/211,255±269.JirkaA.andCarterM.J.(1975)Microsemi-automated\nanalysisofsurfaceandwastewatersforchemicaloxygendemand.AnalyticalChem.47,1397±1401.LastA.R.M.,vanderandLettingaG.(1992)Anaerobictreatmentofdomesticsewageundermoderateclimatic(Dutch)conditionsusingup¯owreactorsatincreasedsuperficialvelocities.WaterSci.Technol.25(7),LevineA.D.,TchobanaglousG.andAsanoT.(1985)Characterizationofthesizedistributionofcontaminantsinwastewater:treatmentandreuseimplications.J.WaterPollut.ControlFed.57(7),805±816.NielsenP.H.andHarremoesP.(1995)Solids:Reportofthediscussionsession.WaterSci.Technol.32(8),MorganJ.W.,ForsterC.F.andEvisonL.(1990)Acomparativestudyofthenatureofbiopolymersextractedfromanaerobicandactivatedsludge.WaterRes.24(6),743±750.MukerjeeP.andMyselsK.J.(1971)Criticalmicelleconcentrationofaqueoussurfactantsystems.NationalStandardReferenceDataSystem.USDepartmentofCommerce,Washington.RouseJ.D.,SabatiniD.A.,Su¯itaJ.M.andHarwellJ.H.(1994)In¯uenceofsurfactantsonmicrobialdegradationoforganiccompounds.CriticalRev.inEnviron.Sci.Technol.24(4),325±370.\nSandersW.T.M.,ZeemanG.andLettingaG.(2000)Anaerobichydrolysiskineticsofparticulatesubstrate.WaterSci.Technol.41(3),17±24.WagenerS.andSchinkB.(1987)Anaerobicdegradationofnonionicandanionicsurfactantsinenrichmentculturesandfixed-bedreactors.WaterRes.21(5),615±622.WangK.(1994)Integratedanaerobicandaerobictreatmentofsewage.Ph.D.Thesis,WageningenUniversity,TheNetherlands.WangK.,ZeemanG.andLettingaG.(1995)Alterationinsewagecharacteristicsuponaging.WaterSci.Technol.31(7),191±200.WatersJ.andFeijtelT.C.J.(1995)AIS/CESIOEnvironmentalsurfactantmonitoringprogramme:outcomeoffivenationalpilotstudiesonLAS.Chemosphere30,1939±1956.YodaM.,HattoriM.andMiyajiY.(1985)Treatmentofmunicipalwastewaterbyanaerobic¯uidizedbed:behaviouroforganicsuspendedsolidsinanaerobictreatmentofsewage.Proc.Seminar/Workshop:AnaerobicTreatmentofSewage,Amherst,Mass.,USA,161±197.ZeemanG.,SandersW.T.M.,WangK.Y.andLettingaG.(1997)Anaerobictreatmentofcomplexwastewaterandwasteactivated\nsludge.Applicationofup¯owanaerobicsolidremoval(UASR)reactorfortheremovalandprehydrolysisofsuspendedCOD.WaterSci.Technol.35(10),121±128.用生物降解法与厌氧颗粒的物理变化特性来降解污水摘要：在高速率厌氧处理生活污水时，生物和物理进程发挥了重要作用。因此，研究小组调查了大量实验中被厌氧生物降解的原材料---过滤纸和过滤膜处理后的生活污水，对厌氧消化影响的物理特性如粒径、表面张力等，进行了研究。生活污水的生物降解性能和污水在摄氏30度时几乎71%-74%是相似。此外,高产甲烷的胶体颗粒在国内86%的污水里,已经证明了低去除胶体在连续高速厌氧反应器是由于低物理切除而非生物降解性。最低的生物降解性,提出了被解散的分数为所有胶体颗粒总数的62%。结果表明,经过厌氧消化的粒子的平均半径在0.45毫米到4.4毫米增加的同时,对生活污水的降解却在减少。部分生活污水的表面活性物质在厌氧消化过程中是不经过生物降解的,这就表明了污水表面张力的特性。所有的粒子在负面泽塔-潜在里几乎没有变化,表明在消化胶体均没有受到厌氧消化的相互作用。\n关键词:厌氧处理，生活污水，生物降解性，颗粒大小，表面活性剂，简介：多位学者表明：在国内污水中，粒子代表的主要部分里，总化学需氧量就高达85%。微粒和溶解的化合物,通常是通过孔径大约为0.45毫米的过滤膜来过滤的。然而，这种微粒通常是分离粒径大于4.4毫米或在0.45到4.4毫米之间与胶体悬浮部分,却不符合国际胶体化学所用的大小范围。厌氧条件下,生活污水里胶体的化学需氧量的含量远比在需氧或微需氧的条件下要低。经过对去除化学需氧量的再循环的实验研究发现,溶胶是可生物降解的,但这从来没有被证实过。在高速厌氧处理生活污水的过程中,非生物和物理过程起着重要的作用。粒子只能被转换为原料经水解后,被吸附、沉降或残留在污泥床上。因此，基于粒子的表征，其生物和物理方面是同样重要。众所周知，生活污水在表面活性剂的作用下,是被吸附在两个固体/液体和液体/空气界面,是有可能会影响厌氧生物降解性能的颗粒。表面活性剂在水中可溶性的疏水化合物里的乳化能力较差,从而可能改善微生物基质的可溶性。另一方面,乳化这一现象可以避免物理法去除粒子。而且，厌氧生物降解会抑制有机化合物在表面活性剂的存在也已被报道。保罗在1993年提到，\n苏黎世富裕的城市废水表面活性剂浓度约为17到21，其中非离子型和阴离子的表面活性是最主要的部分。线性烷基苯磺酸盐是主要构成阴离子表面活性剂的物质，在荷兰，污水的平均浓度约是3或4。在低浓度时、表面活性剂通常以单体存在。以上便形成了聚集体的临界胶束浓度(CMC)。十二烷基苯磺酸钠的临界胶束浓度为264毫克。因此,在国内污水中，表面活性剂似乎呈现为单体。在生活污水中，颗粒的大小也会影响生物和物理过程，其中重力和阻力的力量占主导地位。胶体力如范德华吸引力和静电斥力对粒子的静电作用较大。泽塔-潜在，主要体现了潜在的或仅仅是表层的,且由于静电作用的胶体粒子与泽塔-潜在有一定的相关性，是胶体粒子分离后的一个重要的物理参数。本研究的目的是确定生活污水中厌氧生物降解性的悬浮物、胶体和溶解的一部分。材料与方法在不同温度下，对生活污水的厌氧消化反应进行试验。首先，在每一份容器中加入血清瓶120毫升，再补充100毫升的废水，对每个含有沼气成分的瓶子采用时间监测。然后对每个瓶子里的化学需氧量分数，挥发性脂肪酸（挥发性脂肪酸）和表面张力进行了测定。该实验分为两部分。在首次运行时，在20°C和30°C的温度下对瓶子里的污水原材料和纸过滤分别在8，15，23和43天后进行监测。第二个实验\n目的是为了确认第一次运行的结果,并找出可生物降解废水中甲烷的最大的转变。第二次运行是在20°C和30°C时，污水原料中过滤纸和过滤膜分别在15，28和135天后进行监测（不重复）。第二轮运行结果证明，粒子的平均半径和zeta电势发生了变化。分析：实例表明，可以通过实验来测量颗粒的表面张力。但是同时也发现在处理生活污水时，很可能在表面活性剂的作用下降低的水溶液的表面张力。在测完临界胶束浓度后，表面张力的整体几乎是独立的浓度。然而，人们应该意识到，还有其他表面活性成分可以促进表面张力降低，因此，对以上结论提出了定性解释。在首次运行时，表面张力的样品测定是原始无过滤的。此外，从首次运行的结果可以发现，废水的表面张力在过滤纸后会增加。因此，在第二次运行时，对所有样品的表面张力进行纸和膜过滤的测量。确定颗粒半径与动态光散射。使用ALV5000、150mW的折线测量2毫升的圆柱石英细胞。粒子半径在2.5到5毫米之间,能被检测出来。每个样本,在90°的角度下对粒子的平均半径进行七次测定。分别测定了电泳迁移率与玛韦恩激光粒度仪，泽塔-电位的计算方程。在离子强度（0.02MKCl）恒定不变时，样品测量的数据表示，过滤纸可以消除大颗粒物质。计算\n利用甲烷生产总量是每个血清瓶甲烷的总和这一特点，利用亨利定律计算甲烷的产量。分别根据方程(1)、(2)、(3)计算(H)的百分比,水解酸化(A)和产甲烷(M)。生物降解性和物理特征的变化　生活污水的化学需氧量中的A、M和H,分别应用方程(1)、(2)、(3),计算纸过滤和膜过滤污水的结果减去例2的结果。同样,化学需氧中的H,和M为通过计算所得的国内污水未经处理的结果。结果与讨论表1分别总结了每个污水样品在43天和135天之后,运行1和2计算的水解百分比、酸化和产甲烷量。1的运行结果表明,在30°C时运行43天是不完全厌氧消化,在所有应用环境的微生物里化学需氧量浓度超过100。总甲烷的结果在运行2（图1）表明，生活污水在30°C，约80天达到最大转换分数。\n图1中的厌氧消化有一个特点：厌氧消化的周期取决于温度和粒子的大小。在未经处理的污水里，只有在20°C时，且经过135天后才能达到最高的转换消化。这不仅需要较好的技术，而且在温和的热带地区，污水原材料的最大产甲烷量在20°C和30°C的温度下属于厌氧处理。图1、未经处理的污水厌氧消化过程期间，在温度为20和30°C时，运行纸过滤、膜过滤处理污水，测得实验中总甲烷的产生量。　所得数据，可比较未经处理的污水和纸过滤的污水中的生物降解性在30°C时约有71%到74％是相同的，即该过滤膜处理的分数相对较低。提交结果表2给出生活污水中的一部分在30°C时CODss和CODcol的\n最大水解、酸化和产甲烷量。其中，CODss和CODcol的最大水解是相似的,而CODss最大时的酸化比产甲烷的CODcol高。悬浮颗粒物的水解产生更多的未降解的COD水解胶体。最后,Lettinga在1992年的报道中解决了在同一源的污水循环较低期间时的实验最高清除54%的CODdis。这可能是由于污水中可生物降解的CODdis水解而成的降解粒子决定的。表2。计算最大水解，生活污水中阳离子和甲烷在30°C时的CODss和CODcol。表面张力表面张力是衡量是否存在表面活性的化合物。在计划时间内同时运行1和2，在温度为20°C和30°C时表面张力几乎相似（图2和3）。然而在4°C时的最大的表面张力相比在20°C和30°C的表面张力要低得多。得到表面张力的一个稳定的价值是在15到25天之间。这段时间厌氧消化的特性时间大为缩短,有少量的高度表面张力能力\n都正在迅速下降，且退化速度较慢的化合物导致其最大表面张力远远要高。图2。在20°C和30°C温度时，污水原材料中纸和膜过滤的厌氧消化过程中的表面张力。图3。在20°C和30°C温度时，未经处理的污水，仅通过纸过滤厌氧消化过程后的表面张力。\n最初未经处理的污水表面张力明显高于过滤纸处理后污水的表面张力(图3)。在20°C和30°C的条件下，135天厌氧消化后，污水的表面张力几乎达到了最大值。未经处理的污水表面活性剂相比纸过滤后所表现出的初始表面张力要高（图2），而过滤膜污水的污水表面活性剂比过滤纸的污水表面活性剂污水要高（图3）。重复膜过滤前所测量的消化后的表面活性剂（图3），表明它们主要吸附在消化产生的粒子过程中。平均半径\n图4表示，污水经过纸过滤或膜过滤后颗粒的平均半径较一般污水要高得多。未经处理的直径为440毫米的污水经过过滤纸作用后其颗粒的平均半径只有188纳米。因此，大量非常小的颗粒存在于生活污水中。后者则确认经过过滤膜处理的污水的平均半径是低于直径为68nm的微粒。在20°C和30°C温度时，污水原材料在厌氧消化135天中的一段时间经过纸过滤和膜过滤后导致的颗粒的平均半径都增加。众所周知,水解导致废水基质粒子的减少,从而导致粒子的平均半径的增加。采用厌氧消化过滤膜产生的胶体，在20°C和30°C温度，135天的间歇消化后,化学需氧量的样品中的颗粒分别是20毫克,38毫克。因此,在厌氧反应器连续处理生活污水时CODdis会影响去除CODcol。图4、在20°C和30°C温度时，未经处理的污水，厌氧消化后仅通过过滤纸和过滤膜过程的平均半径。\n表3.在20°C和30°C温度时，泽塔潜力在离子强度（0.02MKCl）恒定不变时，污水原料进过和过滤纸厌氧后的数据。标准差列于括号泽塔潜在\n表3表示的是运行2后的泽塔潜在评估值。厌氧消化135天,只是导致所有在负面的泽塔潜在的污水样品略有减少。因此,在厌氧消化中，一定数量的阴性离子的单位面积和胶体颗粒之间的静电斥力几乎是恒定的，变化不明显的。一般讨论生活污水的生物降解性能揭示了厌氧治疗的高潜力。此外,国内污水里高产甲烷的胶体颗粒,在连续高速厌氧反应器里实现了对CODcol的低去除，是低物理切除而非生物降解性。表面张力的发展预示着一种有限批量的消化过程中表面活性剂生物降解性的前景。,目前的结果表明,部分的表面活性剂在厌氧消化时并不降解。此外,结果也表明,表面活性剂是连接到粒子和胶体两部分的。后者可能会影响稳定,因此,生活污水胶体的去除率较低。虽然胶体颗粒在一定程度下，其平均粒径是增加的。但在连续高速反应时,污泥床在发生生物降解时只能是因为经过了物理切除。所有的粒子的泽塔潜在是负面的、难以消化的,且在显示期间厌氧消化胶体间的相互作用不受影响。厌氧生物也有一个负电荷,因此胶体去除污水厌氧系统可以保持在一个较低的水平,具有独立的应用条件。由于水解产生更多的悬浮颗粒的比水解惰性溶解胶体,引进的一个厌氧悬浮颗粒能溶解而且提高质量。固体悬浮颗粒的去除之前从生活污水产甲烷,才能实现沉降结论\n*生活污水采用厌氧生物降解性能后在30°C时几乎是相似的*生活污水经过处理后，胶体颗粒的甲烷产量在30°C时最大,悬浮分数是78%,而最大转变的溶解分数是最低(62%)。*生活污水厌氧消化后,颗粒的平均半径在0.45毫米到54.4毫米之间。*部分生活污水并不是生物厌氧消化过程中,这表明生活污水的表面张力的前景。*泽塔潜力的负面期间几乎所有的粒子没有变化。这表明,在厌氧反应器处理后，胶体相互作用会出现的消化现象。致谢参考文献：博勒M.（1993）污水处理厂去除有机物的物理化学机制的研究，水科技技术，27（11），167±183。elmitwalliT.A.，赞德福特M.，塞曼G.和LettingaG.（1999a）低温生活污水处理中厌氧污泥床反应器研究，水科技技术，39（5），177±185。elmitwalli，sklyar，塞曼G.和LettingaG（1999）混合厌氧反应器处理生活污水的温度控制过程，水科技技术，39（5），177±185。格雷戈瑞J.（1993）固液分离胶体的相互作用，水科技技术，27（10），1±17。\n丹尼尔M.andbucklandH（1998）英国对滴滤式污水处理厂的直链烷基苯磺酸盐去除监测研究，210/211，255±269。jirkaA.和卡特M.J.（1975）微半自动分析和废水化学需氧量的研究，分析化学，47，1401，1397±。A.M.，Vander和LettingaG.（1992）温和的气候中生活污水在厌氧处理的条件下，利用反应器增加流速，水科技技术，257。Levine公元，tchobanaglousG.和浅野T（1985）废水中污染物的粒度分布特性及处理和再利用的影响，J.水污染，57（7），805±816。尼尔森普华和哈里莫斯P（1995）固体的讨论会议的报告，水科技技术，328。摩根J.W.，福斯特C.F.和伊文森L.（1990）厌氧活性污泥中提取的生物聚合物的性质比较研究，水资源24（6），743±750。慕克吉P.MyselsK.J.（1971）表面活性剂水溶液体系。美国商务部，华盛顿。劳斯J.D.，萨巴蒂尼D.A.，ITAJ.M.和哈维尔祝建华（1994）表面活性剂对有机化合物的微生物降解的影响，SCI技术，24（4），325±370。桑德斯W.T.M.，塞曼G.和LettingaG.（2000）颗粒基质的厌氧水解反应动力学，水科技技术，41（3），17±24。瓦格纳和施林克B（1987）阳离子、阴离子表面活性剂在富集培养和固定床厌氧反应器降解的研究，水资源21（5），615±622。王凯（1994）综合污水的厌氧好氧处理，博士论文，瓦格宁根大学，荷兰。\n王凯，塞曼G.和LettingaG.（1995）污水特征的改变，水科技技术，31（7），191±200。feijtelT.C.J.J.（1995）表面活性剂的AIS/Cesio环境监测计划。光化层±1956。尤达M.（1985）厌氧流化床处理城市污水中的悬浮物，有机污水厌氧处理的研究，161±197。塞曼G.，桑德斯W.（1997）厌氧处理复杂的废水和污泥，水科技技术，35（10），121±128。