废水处理：过滤与电渗析 38页

废水处理工艺设计及计算第11章6&8节n211-6Surfacefiltration表面过滤nFiltrationMechanism(机理)SurfacefiltrationDepthfiltrationSurfacefiltration,arelativelynewtechnology,involvesasievingactionsimilartoakitchencolander.Surfacefiltrationisusedtoremovetheresidualsuspendedsolidsfromsecondaryeffluentsandstabilizationpondeffluents,andasanalternativetodepthfiltration.Depthfiltrationwasdevelopedoriginallyforthetreatmentofsurfacewaterforpotableusesandlateradaptedforwastewatertreatmentapplications.Depthfiltrationisusedintoachievesupplementalremovalofsuspendedsolids(includingparticulateBOD)fromwastewatereffluentsforthefollowingpurposes:toallowmoreeffectivedisinfection;asapretreatmentstepforsubsequenttreatmentstepssuchascarbonadsorption,membranefiltration,oradvancedoxidation;toremovechemicallyprecipitatedphosphorus.Definition3nSurfacefiltrationisgaininginpopularitybecauseofthe(1)highqualityeffluentproduced,(2)smallerfootprint,(3)lowbackwashrates,(4)reducedmaintenancerequirements.Surfacefiltrationhasbeenusedinseveralapplicationsincluding:asareplacementfordepthfiltrationtoremoveresidualsuspendedsolidsfromsecondaryeffluents,fortheremovalofsuspendedsolidsandalgaefromstabilizationpondeffluents,asapretreatmentoperationbeforemicrofiltrationorUVdisinfection.4nAvailableFiltrationTechnologiesTheCMF,marketedunderthetrademarkAquaDisk®byAqua-AerobicSystems,alsoconsistsofseveraldisksmountedverticallyinatank.Eachdiskiscomprisedofsixequalsegments.Operationally,waterflowsbygravityfromtheexteriorofthedisksthroughthefiltermediumtoaninternalcollectionsystem.Typically,twotypesoffilterclothareused:aneedlefeltclothmadeofpolyesterorsyntheticpilefabriccloth.Avacuumsystemis.Vacuumsuctionheads,locatedoneithersideofthedisk,areusedtoremovetheaccumulatedsolidsbydrawingfiltratewaterfromthefiltrateheaderbackthroughtheclothmediawhilethediskisrotating.5nTheDCMF,marketedunderthetrademarkAquaDisk®byAqua-AerobicSystems,consistsofclothfilterelements,whichhaveadiamondshapedcrosssection.Thefilterelementsarecleanedbyavacuumsweepwhichmovesbackandforthalongthelengthofthefilter,whenapredeterminedincreaseinheadlosshasoccurred.Solidsthatsettletothebottomofthereactorbelowthefilterelementareremoved6periodicallybyavacuumheader.Usingadiamondshapeforthefilter,itispossibletoincreasetheclothfiltersurfaceareaperunitofaerialsurfacearea.Becausehighervolumesforfilteredwatercanbeproducedperunitarea,theDCFMisusedinnewinstallationsandasareplacementforexistingsandfilters.nFlowcapacity:Upto400l/sperfilter.Filteropening:10-100μm.Filtermediaiseasytochangethankstonewinnovativedesign.Movingbackwashsystemforbettercleaning,minimalwateruseandlesswearonfiltermedia.Thewatertobetreatedflowsbygravityintothefiltersegmentsfromthecentredrum.Solidscatchontheinsideofthefilterpanelsmountedonthetwosidesofthediscsegments.Asthesolidscatchontheinsideofthefiltermediaimpedingtheflowofwaterthroughthedisc,thewaterlevelinsidethediscsbegintorise,triggeringalevelsensortostartthedisctorotateandabackwashcyclebegins.Highpressurerinsewaterbacksthesolidsoffthefiltermediaandintothesolidscollectiontrough.Typicallythebackwashrequires1-2%ofthetotalflowandfilteredwaterisused.7nTheUltrascreen®developedbyNovaWatertechnologiesthatconsistsoftwocontinu-ouslyrotatingcircularscreensofwovenstainlesssteelmesh.Theliquidtobefilteredisintroducedbetweenthetwoscreensatrightanglestothescreens.Thefilteredeffluentthatflowsthroughthescreenflowsoutandisdirectedtoacollectionchamberbelowthescreen.Unlikeotherdisktypescreens,thedischargefromthescreenisbygravityasthereisnowateronthedischargesideofthescreen.High-pressurewaterjetsareusedtocleantheaccumulatedsolidsfromthescreens.8nAsthenameimpliesthedrumfilterisintheshapeofadrum.Theliquidtobefilteredisintroducedontheinsideofthedrumandflowsoutthoughttheperipheryofthedrum,throughafilterclothofpolyesterorpolypropyleneorstainlesssteel,asthedrumrotatesslowly.Whenthewaterlevelwithinthedrumrisestospecifiedlevel,abackwashcycleisinitiatedtoremovetheaccumulatedsolids.Ahighpressurewatersprayisusedtodislodgeandremovetheaccumulatedsolidsasthedrumrotates.Thesolidsremovedfromthedrumarecollectedinacollectiontroughontheinsideofthedrum.Drumfiltercanbeinstalledinconcrete,stainlesssteel,orfiberglasstankage.Therangeofporeopeningsforthefilterclothrangefrom10mmto1mm,dependingontheapplication.9nDevelopedbyM2Renewables,theinclinedscreenisusedforthefiltrationofuntreatedwastewater.Asthemovingscreenrotates,solidsareaccumulatedonthescreen.Whenthescreenexitsthewaterpool,theaccumulatedsolidsarepartiallydewateredbytheforceofgravity.Theaccumulatedsolidsareremovedfromthescreenasitpassesovertheupperroller.High-pressurewaterjetscanalsobeused.AsnotedinChap.5,thefactthatthescreenalterstheparticlesizedistributionofthesolidstobetreatedandhasarelativelysmallfootprintissignificantrelativetoconventionalprimaryclarification.10n11nDescriptionoftheSurfaceFiltrationProcessThekeyfeaturesofsurfacefiltersarethefilterconfiguration,thefiltermedium,themethodusedtointroducetheliquidtobefiltered,themethodusedtocleanthefilteringmedium,(5)theimpactoftheaccumulationofsolidshasonprocessperformance.12nFilterConfigurationsSurfacefiltersareavailableinavarietyofconfigurations.Themostcommontypeofsurfacefilteriscomprisedofaseriesofdisksattachedtoacentralshaft.Theindividualdisksaremadeupoftwofilteringsurfacesattachedtoametalsupportframe.Thedrumfilterforeffluentfiltrationisarelativelyrecentdevelopment,althoughdrumfiltersareusedinanumberoffilteringapplications.Operationofthedifferentsurfacefiltersdependsonhowtheliquidtobefilteredisappliedtothefilteringmediumandhowthefilteringmaterialiscleanedofaccumulatedmaterial.13nFilterMaterialsThefiltermaterialusedinsurfacefilterscanbecategorizedastwodimensionalandthreedimensional.Twodimensionalmediumsaretypicallymadeofsyntheticfabricsofdifferentweavesandwovenmetalfabrics(mostcommonlystainlesssteel).Themostcommonweaveforsyntheticmaterialsisknownasaplainweave,whichissimilartobroadcloth.Stainlesssteelweavescanincludeplainweave,twilledweave,andDutchweavewiremeshes.Threedimensionalfilteringmediumsincludepolyesterneedlefeltclothandsyntheticpilefabriccloth.14nFlowPathforLiquidtobeFilteredTheflowpathcanalsobeusedtoclassifysurfacefilters.Basically,twomethodsareusedtoapplytheliquidtobefilteredtothefilteringmedium.Inthefirst,theliquidentersthefeedtankandflowsfromtheoutsidethroughthefilterclothintoareceivingarea(out-in).Inthesecondmethod,theliquidtobefilteredisintroducedintotheannularvolumebetweenthetwofilteringsurfacesandflowsoutwardthroughthefilteringmediumintothecollectionvessel(in-out).Ineithercase,solidsaccumulateonthesurfaceinthedirectionofflow.Thedirectionofflowaffectsthemethodtobeusedfortheremovaloftheaccumulatedmaterial,thesubmergence(i.e.theactivefilterarea),andtheoveralldepthoftheunit.15nCleaningtheFilterMediumTwotypesofmethodsareusedtoremovetheaccumulatedmaterialremovedfromthefluid:vacuumremoval(真空去除)intermittentand/orcontinuoushigh-pressurespraywashing.（间歇和/或连续高压喷洗）Thevacuumremovalsystemisusedforsurfacefilterswheretheflowisfromtheoutsideinwhereasthehigh-pressurewaterspraynozzlesareusedwheretheflowisfromtheinsidetotheoutside.16nVacuumRemovalWhentheheadlossthroughtheCMFreachesapredeterminedsetpoint,thedisksarecleaned.Asthedisksrotate,solidsareremovedfrombothsidesofthediskbyliquidvacuumsuctionheads,locatedoneithersideofeachdisk,whichdrawsfilteredwaterfromthefiltrateheaderbackthroughtheclothmediawhilethediskisrotating.Thisreversalofflowremovesparticlesthathavebecomeentrappedonthesurfaceandwithintheclothmedium.Thediamondclothfilterisalsocleanedbyavacuumsweepwhichmovesbackandforthalongthelengthofthefilter.Solidsthatsettletothebottomofthereactorbelowthefilterelementareremovedperiodicallybyavacuumheader.17nHigh-PressureWaterSpraysInsurfacefilterswheretheflowisfrominsidetooutside,high-pressurewaterspraysareusedtoremovethematerialthataccumulatesontheinsideofthedisk.Mosthigh-pressurewaterspraywashsystemscanoperateineitheranintermittentorcontinuousbackwashmode.Intheintermittentmode,high-pressurebackwashsprayjetsareactivatedonlywhenheadlossthroughthefilterreachesapresetlevelortime.Onceactivated,washwaterissprayedthroughthefiltermaterialfromtheoutsideasthediskrotates.Theaccumulatedsolidsthataredislodgedfallintoacollectiontrough.Whenoperatinginacontinuousbackwashmode,theproductionoffilteredwaterandbackwashedoccursimultaneously.Thelocationandconfigurationofthehigh-pressurespraynozzlesandsolidscollectiontrougharemanufacturerspecific.18nImpactoftheAccumulationofSolidsonProcessPerformanceTheremovalofparticulatematterwithsurfacefiltersisillustratedschematicallyonFigforpartiallyandcompletelysubmergedsurfacefilters.Forpartiallysubmergedfilters[seeFig(a)],theaccumulationofsolidsonthefiltermediumoccursbetweenpoint1,wherethecleanfiltercomesincontactwiththefluidtobefiltered,andpoint2,wherethefilterleavesthefluid.Forthecompletelysubmergedfilter[seeFig(b)],theaccumulationofsolidsoccurswithtimeuntilthebackwashheadlossisreached,atwhichtimethefilteriscleaned.19nInbothcases,theaccumulatedmaterialonthesurfaceofthefilterbeginstoactasafilter.Thefilteringactionoftheaccumulatedmaterialisknownasauto-filtration.Auto-filtrationcanbeusedtoexplainwhymaterialofasmallersizethantheporesizeofthefiltermediumcanberemovedbysurfacefiltration.Forbothtypesofsurfacefilterswilldependonthemeshsizeofthefilteringmedium,thecharacteristicsofthewastewater,andthefiltrationrate.20nPerformanceofSurfaceFiltershydraulicloadingrateremovalofturbidityandtotalsuspendedsolidsvariabilityofturbidityandTSSremovalremovalofdifferentparticlesizesremovalofmicroorganismbackwashwaterrequirements21nHydraulicLoadingRateAswithdepthfilters,thereisaconsiderabledifferenceintheHLRsoverwhichsurfacefiltersoperate.TypicalHLRsforsurfacefiltersarereportedinTable.Forexample,whiletwosurfacefilterscanproduceafilteredeffluentwithturbidityof2NTUorlessfilteringthesameeffluent,theHLRscanvarybymorethatafactoroffourorfive.Aswithdepthfilters,theHLRandthebackwashwaterrequirementsforsurfacefilterswillimpactcostandthecarbonfootprintsignificantly.22n所选表面过滤器操作特征的比较23nRemovalofTurbidityandTotalSuspendedSolidsToevaluateperformancecapabilitiesofsurfacefiltration,aCMFpilotplantwastestedusingsecondaryeffluentfromanextendedaerationactivatedsludgeprocesswithasolidsretentiontimegreaterthan15d.TSS、浊度值（mg/L）24nTheperformanceoftheCMFascomparedtodepthfilters,alltestedwiththesameactivatedsludgeeffluent,isshownonFig.Asshown,theeffluentturbidityfromtheCMFremainedconstantoverarangeofinfluentturbidityvaluesthattestedupto30NTU.ThedegreeofremovalofTSSfromsettledactivatedsludgeeffluentwithsurfacefilters,aswithdepthfilters,willdependontheSRT（污泥停留时间）atwhichtheactivatedsludgeprocessisoperated.Similarresultshavebeenreportedforothersurfacefiltrationtechnologies.25nVariabilityinTurbidityandTotalSuspendedSolidsRemoval26nRemovalofDifferentParticleSizesIncomparativetestingwithagranularmediumfilter,thesurfacefilterconsistentlyoutperformedthegranularmediumfilterinrespecttoparticleremoval(seeFig).TheparticlesizereductionalsohadasignificantimpactontheinactivationoftotalcoliformbacteriawhenusedwithUVdisinfection.27nDesignConsiderationsPilotstudiesarerecommendedindevelopingdesignandoperatingparametersfornewinstallations.Usefuldatafordesignincludesthevariabilityofthecharacteristicsofthefeedwatertobetreatedtheamountofbackwashwaterrequiredfornormaloperation.ThebackwashwaterrequirementsareafunctionoftheTSSinthefeedwaterandthesolidsloadingonthefilters.IfthesecondarytreatmentsystemiseffectiveinTSSremoval,thevolumeofbackwashwatercanbereducedsubstantially.28n2911-8Electrodialysis电渗析nDefinition30Electrodialysis(ED)isanelectrochemicalseparationprocessinwhichmineralsaltsandotherionicspeciesaretransportedthroughion-selectivemembranesfromonesolutiontoanotherunderthedrivingforceofadirectcurrent(DC)electricpotential.AscomparedtoNFandRO,whichtransportpurewaterthroughthemembraneleavingthesaltsbehind,withEDsaltisgraduallystrippedfromsolutionleavingadilutesolutionbehindcontainingparticulatematterandneutralspeciesnotremovedbytheEDprocess.Thesalttransferredthroughthemembranethenformstheconcentrate.Atypicalflowdiagramemploying(流程图)electrodialysisforthecontrolofdissolvedsolidsisshownonFig.n31（阳极）（阴极）浓缩盐水Electrolysisstackscancontainasmanyas600cellpairs.Feedwater(filteredwastewater)ispumpedthroughthestackassembly.Typicalfluxratesarefrom35to45L/m2·h.Dissolvedsolidsremovalsvarywiththe(1)wastewatertemperature,(2)amountsofelectriccurrentpassed,(3)typeandamountofions,(4)permeability/selectivityofthemembrane,(5)foulingandscalingpotentialofthefeedwater,(6)feedwaterflowrates,and(7)numberandconfigurationofstages.DescriptionoftheElectrodialysisProcessnElectrodialysisReversal（反向电渗析）Intheearly1970s,theelectrodialysisreversal(EDR)processwasintroduced.AnEDRunitoperatesonthesameprincipleasEDtechnology,exceptthatboththeproductandconcentratechannelsareidenticalinconstruction(seeFig).32（阳极）（阳极）（阴极）（阴极）n电渗析的典型参数33(流量)(水回收率)(除盐消耗能量)(总溶解固体去除率)(电流效率)(膜电阻)(能量消耗)(电流密度)nPowerRequirementsforIonTransferThecurrentrequiredforEDcanbeestimatedusingFaraday’slawsofelectrolysis.BecauseoneFaradayofelectricitywillcauseonegramequivalentofasubstancetomigratefromoneelectrodetoanother,thenumberofgramequivalentsremovedperunittimeisgivenby:34n35IntheanalysisoftheEDprocess,ithasbeenfoundthatthecapacityofthemembranetopassanelectricalcurrentisrelatedtothecurrentdensity(CD)andthenormality(N)ofthefeedsolution.Currentdensityisdefinedasthecurrentinmilliamperesthatflowsthroughasquarecentimeterofmembraneperpendiculartothecurrentdirection.Normalitycorrespondstotheconcentrationofasolutionbasedonthenumberofgramequivalentweightsofasoluteperliterofsolution.Asolutioncontainingonegramofequivalentweightperliterisreferredtoasonenormal(1N).Therelationshipbetweencurrentdensityandthesolutionnormalityisknownasthecurrentdensitytonormality(CD/N)ratio.HighvaluesoftheCD/Nratioareindicativethatthereisinsufficientchargetocarrythecurrent.Whenhighratiosexist,alocalizeddeficiencyofionsmayoccuronthesurfaceofthemembrane,causingaconditioncalledpolarization.Polarizationshouldbeavoidedasitresultsinhighelectricalresistanceleadingtoexcessivepowerconsumption.Inpractice,CD/Nratioswillvaryfrom500to800whenthecurrentdensityisexpressedasmA/cm2.TheresistanceofanEDunitusedtotreataparticularwatermustbedeterminedexperimentally.Oncetheresistance,R,andthecurrentflow,i,areknown,thepowerrequiredcanbecomputedusingOhm’slawasfollows:nMembraneandElectrodeLifeMembranesforEDandEDRapplicationshavealifeofabout10yearsbeforetheyarereplaced.Effectiveandtimelycleaning-inplaceextendsthemembranelifeandimprovesproductqualityandpowerconsumption.Cationmembranestypicallylastlongerthananionmembranesbecauseanionmembranesareparticularlysusceptibletooxidationbychlorineandotherstrongoxidants(USBR,2003).WiththedevelopmentoftheEDRprocessandnewelectrodedesign,thelifeofanodeandcathodeelectrodesistypically2to3years.Anodelifeistypicallylessthancathodelife.Electrodescanbereconditioned(USBR,2003).36nElectrodialysisVersusReverseOsmosis37n38Thanks！