污水处理设计-毕业论文英文翻译

污水处理设计—毕业论文英文翻译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-activecomponentsindomesticsewageisnotbiodegradedduringanaerobicbatchdigestion,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,althoughthesizerangeforcolloidalparticlesisnotinagreementwiththedefinitionasusedincolloidchemistry.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,thuspotentiallyimprovingtheaccessibilityofthesesubstratestomicroorganisms(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)forlargerparticles,whilecolloidalforcesaremoreimportantforparticleslessthanafewmm(Gregory,1993).Thezeta-potential,whichrepresentsthepotentialonorjustoutsidetheSternlayer,isanimportantphysicalparameterforcolloidalparticleseparationbecauseelectrostaticinteractionsofcolloidalparticlesaremainlyrelatedtothezeta-potential.Thisresearchaimsforthedeterminationoftheanaerobicbiodegradabilityofthesuspended,colloidalanddissolvedfractionofdomesticsewageandblackwater.Moreover,thechangeinphysicalcharacteristics,likeparticlesize,zeta-potentialandsurfacetensionasaresultofbiodegradationisdetermined.MATERIALSANDMETHODSAnaerobicdigestionofdomesticsewageandblackwaterAnaerobicbatchdigestionhasbeencarriedoutinduplicateseriesofserumbottlesof120mleachateachtemperature.Toeachbottle100mlofwastewaterisadded.Thebiogascompositionintheheadspaceofeachbottleismonitoredintime.Foreachbottle,CODfractions,volatilefattyacids(VFA),andsurfacetensionweredetermined.Twoseriesofexperimentshavebeenperformed.Inthefirstrun,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.Intheexperimentsitwasdi?culttohaverepresentativesamplesforCODtduetotheformationoflarge?ocsduringanaerobicdigestion.Therefore,onlyCODpandCODdisarepresented.VFAweredeterminedfrommembrane-filteredsamplesbygaschromatography.Thechromatograph(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,oneshouldbeawarethatalsoothersurface-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)andsampleswerepaperfilteredtoremovebigparticles.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.Fig.1.ThecourseofthetotalCH4productionduringtheanaerobicbatchdigestionofrawsewage(}),paper-filteredsewage(&),membrane-fiteredsewage(n)andblackwater(*)inrun2attemperatureof20and30C.Fig.2.Thecourseofthesurfacetensionduringtheanaerobicbatchdigestionofraw(})andpaper-filtered(&)sewageinrun1attemperatureof4,20and30C.RESULTSANDDISCUSSIONBiodegradabilityTable1summarizesthecalculatedpercentagesofhydrolysis,acidificationandmethanogenesisforeachwastewatersampleafter43and135daysofdigestion,inruns1and2,respectively.Theresultsofrun1showthat43daysofbatchdigestionarenotsucientforcompleteanaerobicdigestionevenat30C.TheVFAconcentrationexceeds100mgCODÿ1latallappliedconditions.TheresultsofthetotalCH4productioninrun2(Fig.1)showthatthemaximumconversionofthedomesticsewagefractionsandblackwaterisachievedafterabout80daysat30C.Figure1theanaerobicdigestionhasacharacteristiclag-phaseperioddependingonthetemperatureandthesizeoftheparticles.At20Conlyrawsewagereachedthemaximumconversionafter135daysofdigestion.Themaximummethanogenesisforrawsewagewassimilarattemperaturesof20and30Cindicatingthatanaerobictreatmentisnotonlyapromisingtechniqueintropicalbutalsoinmoderateareas.Thebiodegradabilityofblackwater,rawsewageandpaper-filteredsewageat30Cisapproximatelythesame,viz,71?74%,whilethatofthemembranefilteredfractionwasrelativelylow(62%).Noreporteddataareavailabletocomparewiththepresentedresults.Table2presentsthemaximumhydrolysis,acidificationandmethanogenesisoftheCODssandCODcolfractionofdomesticsewageat30C.ThemaximumhydrolysisforCODssandCODcolissimilar,whilethemaximumacidificationandmethanogenesisarehigherforCODcolascomparedtoCODss.Hydrolysisofsuspendedparticlesseemstoproducemorenon-degradableCODdisthanhydrolysisofcolloidalparticles.LastandLettinga(1992)reportedalowermaximumremovalofCODdisof54%duringbatchrecirculationofpre-settledsewageofthesameoriginasusedintheherepresentedexperiments.Thislowerbiodegradabilitymightbeduetotheproductionofnon-degradableCODdisfromthehydrolysisofparticlespresentinpre-settledsewage.SurfacetensionFig.2.Thecourseofthesurfacetensionduringtheanaerobicbatchdigestionofraw(})andpaper-filtered(&)sewageinrun1attemperatureof4,20and30C.Thesurfacetensionisameasureforthepresenceofsurface-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).Astheinitialsurfacetensionofthemembrane-filteredsewagewasstilllowerthanthatofwater,somesurfactantswereremaining,evenafter135daysbatchdigestion(Fig.3).Thesurfactants,remainingafterdigestion,arehoweverremovedbyarepeatedmembranefiltrationpriortomeasurement(Fig.3),whichindicatesthattheyaremainlyadsorbedtoparticlesproducedduringthedigestionprocess.Fig.3.Thecourseofthesurfacetensionduringtheanaerobicbatchdigestionofrawsewage(}),paper-filteredsewage(&),member-filteredsewage(n)andblackwater(*)inrun2attemperatureof20and30C.AverageradiusFigure4showsthattheaverageinitialradiusofparticlesafterpaperormembrane-fitrationofblackwaterismuchhigherascomparedtothatofdomesticsewage.Althoughtherawsewagewaspaper-filteredwithadiameterof4.4mm,theaverageradiusoftheparticlesinpaper-filteredsewagewasonly188nm.Therefore,alargequantityofverysmallparticlesispresentindomesticsewage.Thelatterisconfirmedbythelowaverageradiusof68nmoftheparticlesinmembrane-filteredsewage.Aperiodof135daysbatchdigestionofraw,paper-andmembrane-filteredsewagefollowedbypaperormembranefiltrationresultedinanincreaseoftheaverageradiusatboth20and30C.Itiswellknownthathydrolysiscausesadecreaseinthewastewatersubstrateparticles,whileremainingsubstrateisovergrownwithbiomass(Sandersetal.,2000),whichcanresultinanincreaseintheaverageradiusoftheparticles.Theanaerobicdigestionofmembrane-filteredsewageproducescolloidalparticles.After135daysofbatchdigestionat20and308C,theCODcolconcentrationinthemembrane-filteredsamplesamountedto,respectively,38and20mglÿ1.MethanogenesisofCODdismightthereforeaffecttheremovalofCODcolinacontinuousanaerobicreactortreatingdomesticsewage.Batchdigestionofblackwaterfor15?28daysfollowedbyeitherpaperormembranefiltrationdecreasedtheaverageradiusoftheparticlesatboth20and308C.However,after135daysbatchdigestion,italmostremainedunchangedforsamplesafterpaperfiltrationandincreasedforsamplesaftermembranefitration.Therefore,inthefirst15?28days,thehydrolysiswashigherthantheentrapmentofparticlestotheproducedbiomass.Fig.4.Thecourseoftheaverageradiusduringtheanaerobicbatchdigestionofrawsewage(}),paper-filteredsewage(&),membrane-filteredsewage(n)andblackwater(*)inrun2attemperatureof20and30C.ZetapotentialTable3showstheassessedvaluesofthezeta-potentialinrun2.Anaerobicbatchdigestionforaperiodof135days,ledtoonlyaslightdecreaseinthenegativezeta-potentialforallwastewatersamples.Thus,duringanaerobicdigestion,thenumberofnegativegroupsperunitarearemainsalmostconstantandelectrostaticrepulsionbetweenthecolloidalparticlesdoesnotchangesignificantly.GeneraldiscussionThehighbiodegradabilityofdomesticsewageandblackwaterrevealsthepotentialofanaerobictreatment.Moreover,ahighmethanogenesisofthecolloidalfractionindomesticsewage(86_3%)isachieved,showingthatthelowremovalofCODcolincontinuoushigh-rateanaerobicreactorsisduetolowphysicalremovalratherthanbiodegradability.Thedevelopmentofthesurfacetensionduringbatchdigestionindicatesalimitedbiodegradabilityofthepresentsurfactants.Animportantpartofthesurfactantsinsewageisformedbydetergents,whicharereportedtohavealowanaerobicbiodegradability.Thepresentresultsalsoshowthatpartofthesurfactantsisnotbiodegradedduringanaerobicbatchdigestion.Moreover,itisdemonstratedthatsurfactantsarepartlyconnectedtoparticles,bothsuspendedandcolloidal.Thelattercouldaffectthestabilityandtherefore,lowremovalofcolloidalparticlesindomesticsewage.Thoughcolloidalparticleswerehydrolysedtoahighdegree,theaverageparticlesizeincreasedduetogrowthofbiomass.Incontinuoushigh-ratesystems,thelattercannotbeexpected,asbiodegradationcanonlytakeplaceafterphysicalremovalbythesludgebed.Thezeta-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-filteredsewageandblackwaterbeforeandafteranaerobicbatchdigestioninrun2attemperaturesof20and308C.StandarddeviationsarepresentedinparenthesesCONCLUSIONS*Theanaerobicbiodegradabilityofdomesticsewageandblackwaterat308Cisalmostsimilar*Themaximumconversiontomethaneat30Cwasthehighest(86%)forthecolloidalfractionindomesticsewagefollowedbythesuspendedfraction(78%),whilethemaximumconversionofthedissolvedfractionwasthelowest(62%).*Afteranaerobicbatchdigestion,theaverageradiusoftheparticleswithdiameter54.4and50.45mmindomesticsewageincreased,whiletheaverageradiusoftheseparticlesinblackwaterdecreased.*Partofthesurface-activecomponentsindomesticsewagewasnotbiodegradedduringanaerobicbatchdigestion,asindicatedbythedevelopmentofthesurfacetension.*Thenegativezeta-potentialofallparticleshardlychangeduringdigestion,showingthatcolloidalinteractionswerenotaffectedbyanaerobicdigestion.ortreatmentinahigh-loadedanaerobicreactorREFERENCESBollerM.(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-automatedanalysisofsurfaceandwastewatersforchemicaloxygendemand.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.SandersW.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/CESIOEnvironmentalsurfactantmonitoringprogram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