外文翻译中文译文和致谢Word格式文档下载.docx

外文翻译中文译文和致谢Word格式文档下载.docx

《外文翻译中文译文和致谢Word格式文档下载.docx》由会员分享，可在线阅读，更多相关《外文翻译中文译文和致谢Word格式文档下载.docx（16页珍藏版）》请在冰豆网上搜索。

外文翻译中文译文和致谢@#@外文翻译@#@Coagulationandflocculation@#@14.1@#@Introduction@#@Coagulationandflocculationprovidethewatertreat-mentprocessbywhichfinelydividedsuspendedandcolloidalmatterinthewaterismadetoagglomerateandformflocs.Thisenablestheirremovalbysedi-mentation,dissolvedairflotationorfiltration.Colloidalparticles（colloids）aremidwayinsize1betweendissolvedsolidsandsuspendedmatter.Colloidsarekeptinsuspension（stabilised）byelectrostaticrepulsionandhydration.Electrostaticrepulsionoccursbecausecolloidsusuallyhaveasurfacechargeduetothepresenceofadoublelayerofionsaroundeachparticle.Thus,thecolloidhasanelectriccharge,mostlyanegativeone.Hydrationisthereactionofparticlesattheirsurfacewiththesurroundingwater.Theresultingparticle-wateragglomerateshaveaspecificgravity,whichdifferslittlefromthatofwateritself.@#@Thesubstancesthatfrequentlyaretoberemovedbycoagulationandflocculationarethosethatcauseturbidityandcolour.Surfacewatersintropicalcountriesoftenareturbidandcontaincolouringmaterial.Turbiditymayresultfromsoilerosion,algalgrowthoranimal/vegetabledebriscarriedbysurfacerun-off.Substancesleachedfromdecomposedorganicmatter,leaves,orsoilsuchaspeatmayimpartcolour.Bothturbidityandcolouraremostlypresentascolloidalparticles.@#@Theelectrostaticrepulsionbetweencolloidalparticleseffectivelycancelsouttheelectronicattractionforces（VanderWaals¡@#@¯@#@forces）thatwouldattachtheparticlestogether.Certainchemicals（calledcoagulatingagents,coagulants）havethecapacitytocompressthedoublelayerofionsaroundthecolloidalparticles.Theyreducetherangeoftheelectrostaticrepulsion,andthusenabletheparticlestoflocculate,i.e.toformflocs.Theseflocscangrowtoasufficientsizeandspecificweighttoallowtheirremovalbysettling,flotationorfiltration.@#@Generallywatertreatmentprocessesinvolvingtheuseofchemicalsarenotsosuitableforsmallcommunitywatersupplies.Theyshouldbeavoidedwheneverpossible.Chemicalcoagulationandflocculationshouldonlybeusedwhentheneededtreatmentresultcannotbeachievedwithanothertreatmentprocessusingnochemicals.Iftheturbidityandcolouroftherawwaterarenotmuchhigherthanispermissiblefordrinkingwater,itshouldbepossibletoavoidchemicalcoagulationinthetreatmentofthewater.Aprocesssuchasslowsandfiltrationormulti-stagefiltrationwouldservebothtoreducetheturbidityandcolourtoacceptablelevels,andtoimprovetheotherwaterqualitycharacteristics,inasingleunit.Aroughingfiltercanservetoreducetheturbidityloadontheslowsandfilter,ifnecessary.@#@.@#@14.2Coagulants@#@Alum（Al2（SO4）3.nH20）wheren=14,16,or18,dependsontheformofalumsupplied.Thismaybeinliquidsolution,brokencrystallinegranules2-5cmsize（kibbled）orcrystallineblocks.Itisbyfarthemostwidelyusedcoagulant.Ironsalts（e.g.ferricchloride（FeCl3）,orferricsulphate（Fe2（SO4）3.9H2O）canbeusedaswellandinsomeinstanceshaveadvantagesoveralum.AsignificantadvantageofironsaltsoveraluminiumisthebroaderpH2rangeforgoodcoagulation.Thus,inthetreatmentofsoftcolouredwaterswherecolourremovalisbestobtainedatlowpHs,ironsaltsmaybepreferredascoagulants.Iron@#@saltsshouldalsobeconsideredforcoagulationathighpHs,sinceferrichydroxideishighlyinsolubleincontrasttoaluminiumsalts,whichformsolublealuminateionsathighpHs.SodiumaluminateismostlyusedforcoagulationatmediumpHs.Syntheticorganicpolyelectrolyteshavebecomeavailableascoagulantsbutaregenerallynoteconomicalforsmallwatersupplysystems,noraretheyreadilyavailable.@#@Theuseofextractsfromthecrushedseedsofcertaintropicaltreesisdescribedindetailinthenextsection,14.3.@#@Coagulantssuchassolublealuminiumandironsaltsreactwiththealkalinityofthewater,andhydrolyseinit.Forexample,alumreactstoformaluminium-hydroxidefloc,Al（OH）3,agelatinousprecipitate.Therequiredalkalinitymaybenaturallypresentinthewaterorithastobeaddedthroughdosageoflime,Ca（0H）2orsodiumcarbonate,Na2CO3（alsocalledsodaash）.@#@Forgoodcoagulationtheoptimaldoseofcoagulantshouldbefedintothewaterandquicklyandproperlymixedwithit.Theoptimaldosewillvarydependinguponthenatureoftherawwateranditsoverallcomposition.Itisnotpossibletocomputetheoptimalcoagulantdoseforaparticularrawwater.Alaboratoryexperimentcalledthejartestisgenerallyusedfortheperiodicdeterminationoftheoptimaldose.@#@Thejartestmaybebrieflydescribedasfollows:

@#@Aseriesofsamplesofwaterareplacedonaspecialmultiplestirrerandthesamples,typically800mlin1-litrebeakers（orjars）,aredosedwitharangeofcoagulant,e.g.10,2