废水处理：过滤与电渗析

NJUST废水处理工艺设计及计算第11章6&8节NJUST211-6Surfacefiltration表面过滤NJUSTFiltrationMechanism(机理)SurfacefiltrationDepthfiltrationSurfacefiltration,arelativelynewtechnology,involvesasievingactionsimilartoakitchencolander.Surfacefiltrationisusedtoremovetheresidualsuspendedsolidsfromsecondaryeffluentsandstabilizationpondeffluents,andasanalternativetodepthfiltration.Depthfiltrationwasdevelopedoriginallyforthetreatmentofsurfacewaterforpotableusesandlateradaptedforwastewatertreatmentapplications.Depthfiltrationisusedintoachievesupplementalremovalofsuspendedsolids(includingparticulateBOD)fromwastewatereffluentsforthefollowingpurposes:(1)toallowmoreeffectivedisinfection;(2)asapretreatmentstepforsubsequenttreatmentstepssuchascarbonadsorption,membranefiltration,oradvancedoxidation;(3)toremovechemicallyprecipitatedphosphorus.Definition3NJUSTSurfacefiltrationisgaininginpopularitybecauseofthe(1)highqualityeffluentproduced,(2)smallerfootprint,(3)lowbackwashrates,(4)reducedmaintenancerequirements.Surfacefiltrationhasbeenusedinseveralapplicationsincluding:(1)asareplacementfordepthfiltrationtoremoveresidualsuspendedsolidsfromsecondaryeffluents,(2)fortheremovalofsuspendedsolidsandalgaefromstabilizationpondeffluents,(3)asapretreatmentoperationbeforemicrofiltrationorUVdisinfection.4NJUSTAvailableFiltrationTechnologiesTheCMF,marketedunderthetrademarkAquaDisk®byAqua-AerobicSystems,alsoconsistsofseveraldisksmountedverticallyinatank.Eachdiskiscomprisedofsixequalsegments.Operationally,waterflowsbygravityfromtheexteriorofthedisksthroughthefiltermediumtoaninternalcollectionsystem.Typically,twotypesoffilterclothareused:1.aneedlefeltclothmadeofpolyesteror2.syntheticpilefabriccloth.Avacuumsystemis.Vacuumsuctionheads,locatedoneithersideofthedisk,areusedtoremovetheaccumulatedsolidsbydrawingfiltratewaterfromthefiltrateheaderbackthroughtheclothmediawhilethediskisrotating.5NJUSTTheDCMF,marketedunderthetrademarkAquaDisk®byAqua-AerobicSystems,consistsofclothfilterelements,whichhaveadiamondshapedcrosssection.Thefilterelementsarecleanedbyavacuumsweepwhichmovesbackandforthalongthelengthofthefilter,whenapredeterminedincreaseinheadlosshasoccurred.Solidsthatsettletothebottomofthereactorbelowthefilterelementareremoved6periodicallybyavacuumheader.Usingadiamondshapeforthefilter,itispossibletoincreasetheclothfiltersurfaceareaperunitofaerialsurfacearea.Becausehighervolumesforfilteredwatercanbeproducedperunitarea,theDCFMisusedinnewinstallationsandasareplacementforexistingsandfilters.NJUSTFlowcapacity:Upto400l/sperfilter.Filteropening:10-100μm.Filtermediaiseasytochangethankstonewinnovativedesign.Movingbackwashsystemforbettercleaning,minimalwateruseandlesswearonfiltermedia.Thewatertobetreatedflowsbygravityintothefiltersegmentsfromthecentredrum.Solidscatchontheinsideofthefilterpanelsmountedonthetwosidesofthediscsegments.Asthesolidscatchontheinsideofthefiltermediaimpedingtheflowofwaterthroughthedisc,thewaterlevelinsidethediscsbegintorise,triggeringalevelsensortostartthedisctorotateandabackwashcyclebegins.Highpressurerinsewaterbacksthesolidsoffthefiltermediaandintothesolidscollectiontrough.Typicallythebackwashrequires1-2%ofthetotalflowandfilteredwaterisused.7NJUSTTheUltrascreen®developedbyNovaWatertechnologiesthatconsistsoftwocontinu-ouslyrotatingcircularscreensofwovenstainlesssteelmesh.Theliquidtobefilteredisintroducedbetweenthetwoscreensatrightanglestothescreens.Thefilteredeffluentthatflowsthroughthescreenflowsoutandisdirectedtoacollectionchamberbelowthescreen.Unlikeotherdisktypescreens,thedischargefromthescreenisbygravityasthereisnowateronthedischargesideofthescreen.High-pressurewaterjetsareusedtocleantheaccumulatedsolidsfromthescreens.8NJUSTAsthenameimpliesthedrumfilterisintheshapeofadrum.Theliquidtobefilteredisintroducedontheinsideofthedrumandflowsoutthoughttheperipheryofthedrum,throughafilterclothofpolyesterorpolypropyleneorstainlesssteel,asthedrumrotatesslowly.Whenthewaterlevelwithinthedrumrisestospecifiedlevel,abackwashcycleisinitiatedtoremovetheaccumulatedsolids.Ahighpressurewatersprayisusedtodislodgeandremovetheaccumulatedsolidsasthedrumrotates.Thesolidsremovedfromthedrumarecollectedinacollectiontroughontheinsideofthedrum.Drumfiltercanbeinstalledinconcrete,stainlesssteel,orfiberglasstankage.Therangeofporeopeningsforthefilterclothrangefrom10mmto1mm,dependingontheapplication.9NJUSTDevelopedbyM2Renewables,theinclinedscreenisusedforthefiltrationofuntreatedwastewater.Asthemovingscreenrotates,solidsareaccumulatedonthescreen.Whenthescreenexitsthewaterpool,theaccumulatedsolidsarepartiallydewateredbytheforceofgravity.Theaccumulatedsolidsareremovedfromthescreenasitpassesovertheupperroller.High-pressurewaterjetscanalsobeused.AsnotedinChap.5,thefactthatthescreenalterstheparticlesizedistributionofthesolidstobetreatedandhasarelativelysmallfootprintissignificantrelativetoconventionalprimaryclarification.10NJUST11NJUSTDescriptionoftheSurfaceFiltrationProcessThekeyfeaturesofsurfacefiltersare(1)thefilterconfiguration,(2)thefiltermedium,(3)themethodusedtointroducetheliq