A comprehensive study on membrane fouling in submerged membr

Available online at http://doc.guandang.net

SeparationandPuri cationTechnology

59 (2008) 91–100

Acomprehensivestudyonmembranefoulinginsubmergedmembrane

bioreactorsoperatedunderdifferentaerationintensities

FangangMeng ,FenglinYang,BaoqiangShi,HanminZhang

KeyLaboratoryofIndustrialEcologyandEnvironmentalEngineering,MOE,SchoolofEnvironmentalandBiologicalScienceandTechnology,

DalianUniversityofTechnology,Dalian116024,PRChina

Received8December2006;receivedinrevisedform22May2007;accepted29May2007

Abstract

Inthispaper,membranefoulinginthreeparallelMBRsoperatedunderdifferentaerationintensities(150,400and800L/h)wasstudiedtohaveabetterunderstandingofthemembranefoulingmechanism.Theimpactofaerationonmembranefoulingwasinterpretedfromtwoaspects:evolutionofbiomasscharacteristicsandformationmechanismofthecakelayer.Theresultsshowedthateithersmallorlargeaerationintensityhadanegativein uenceonmembranepermeability.Thelargeaerationintensityresultedinaseverebreakupofsludge ocs,andpromotedthereleaseofcolloidsandsolutesfromthemicrobial ocstothebulksolution.Thesludgesupernatantwouldbecomeheterogeneousastheaerationintensityincreased.AstheMBRoperatedunderhighaerationintensityof800L/h,colloidsandsolutesbecamethemajorfoulants.Inaddition,thebacktransportmechanismofmembranefoulantsinthethreeMBRswasdifferentfromeachother.Aerationhadapositiveeffectoncakelayerremoval,butporeblockingbecamesevereasaerationintensityincreasedto800L/h.Themaincomponentsoforganicmattersinthemembranefoulantswereidenti edasproteins,polysaccharidematerialsandlipidsbytheFouriertransforminfraredspectroscopy(FTIR).© 2007 Published by Elsevier B.V.

Keywords:Membranebioreactor;Membranefouling;Aeration;Sludgecharacteristics;Cakelayer

1.Introduction

Membranebioreactorisabiologicalwastewatertreatmentprocessthatusesmembranetoreplacethegravitationalsettlingoftheconventionalactivatedsludgeprocessforthesolid–liquidseparationofsludgesuspension[1].MBRs,inwhichbiomassisstrictlyseparatedbyamembrane,offerseveraladvantagesovertheconventionalactivatedsludgeprocess,includingahigherbiomassconcentration,reducedfootprint,lowsludgeproduc-tionandbetterpermeatequality[2].AmajorobstaclefortheapplicationofMBRsistherapiddeclineofthepermeation uxasaresultofmembranefouling[3–8].

The rstgenerationofMBRswassidestreamorcross- owsystemswiththemembranemoduleplacesinarecirculationloopexternaltothebioreactor.Theuseofrecirculationloopsleadstoincreasedenergycosts.Inaddition,thehighshearstressesinthetubesandrecirculationpumpscancontributetothedestructionofbio ocsandthishasbeenlinkedtoaloss

Correspondingauthor.

E-mailaddress:fgmeng80@http://doc.guandang.net(F.Meng).

ofbiologicalactivity[9].Toovercometheselimits,thesub-mergedMBRsweredevelopedandpopularlyusedinwastewatertreatment[10].InasubmergedMBR,shearstressiscreatedbyaeration,whichnotonlyprovidesoxygentothebiomass,butalsomaintainsthesolidsinsuspensionandscoursthemembranesurfacetoalleviatemembranefouling.Thenormalprocessofaerationcanbeusedtogenerateashearstressonthemem-branesurfacewithoutrequiringarecirculationpump.But,ithasbeenfoundthatmorethan80%energyconsumptionwasforaeration[11].Uedaetal.[12,13]examinedtheeffectofaera-tiononcakeremovalandsuctionpressureusingapilot-scalesubmergedMBRandconcludedthataerationwasasigni -cantfactorgoverningthe ltrationconditions.Previousworks[14,15]alsoshowedthatthecake-removingef ciencyofaera-tiondidnotincreaseproportionallywiththeincreaseintheair owrateandthattheair owratehadanoptimumvaluefromthecake-removingpointofview.

Ahighaerationratecertainlycanreducesludgeattachmenttothemembrane,butitalsohassigni cantin uenceonthebiomasscharacteristics.Mostofthepreviousliteraturesfocusedoninvestigatingthein uenceofaerationintensitiesonmem-branepermeabilityandbiomasscharacteristics,butthereislittle

1383-5866/$–seefrontmatter© 2007 Published by Elsevier B.V.doi:10.1016/j.seppur.2007.05.040

92F.Mengetal./SeparationandPuri cationTechnology 59 (2008) 91–100

informationonhowtospecifytheimpactsofaerationintensityontheformationofmembranefoulants.Infact,thereshouldbeadirectrelationbetweenaerationintensitiesandtheformationofmembranefoulants.Theaerationintensityisexpectedtohaveaverycomplexin uenceonMBRperformance.

Inthispaper,threesubmergedMBRsunderdifferentaera-tionintensitieswereoperatedforabout50daystoinvestigatethein uencemechanismofaerationintensityonmembranefouling.Inthewholetests,themembranepermeate uxwasmeasuredtostudythemembranefoulingbehaviorunderdiffer-entaerationintensities.Thesludgeparticlesizedistributionsofsludgesuspensionandsludgesupernatant,solubleCOD,col-loidalCODandEPSwereanalyzedtocharacterizetheeffectofaerationintensitiesonbiomasscharacteristics.Thefoulinglayerformationmechanismwasexaminedtodescribethedepo-sition/adsorptionmechanismofmembranefoulants.Thefoulingcakelayeronthemembranesurfacewasanalyzedbasedonresistanceanalysis.Thedepositionofbiopolymersonthemem-branesurfacewascharacterizedbyFouriertransforminfraredspectroscopy(FTIR).2.Materialsandmethods2.1.OperationofMBRs

AsshowninFig.1,theexperimentalsystembasicallycon-sistedofthreeactivatedsludgebioreactor(MBR-A,MBR-BandMBR-C).Ineachbioreactoramembranemodulewassub-merged.Theeffectivevolumeofthebioreactorwas12L.EachMBRwasasubmergedhollow bermembranemodulemadeofpolyethylenethathadatotalareaof0.1m2andanormalporesizeof0.1 m(DAIKI,Japan).PriortotheMBRsoperation,thesludgewasacclimatizedbyotherMBRs.TheMLSSconcentra-tionofeachactivatedsludgesuspensionwasadjustedtoabout6000mg/Lwithwaterpriortothemembrane ltration.Thecom-positionofthefeedwaterwasasfollows:sucrose(300mg/L),urea(78mg/L)anddipotassiumhydrogenphosphate(38mg/L)wereusedasthemainfeedforactivatedsludge,andcalciumchloridewasappliedasmineral.SodiumbicarbonatewasusedasabuffertoadjustthemixedliquorpHtoabout7.0.Thetemper-atureofthemixedliquorwascontrolledat25.0 Cwithelectricheaters.Thehydraulicretentiontime(HRT)rangedfrom10to12h,thesludgeretention …… 此处隐藏：37117字，全部文档内容请下载后查看。喜欢就下载吧 ……