污水处理工业废水回用中英文对照外文翻译文献.docx

污水处理工业废水回用中英文对照外文翻译文献.docx

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污水处理工业废水回用中英文对照外文翻译文献

Catalyticstrategiesforindustrialwaterre-use

Abstract

Theuseofcatalyticprocessesinpollutionabatementandresourcerecoveryiswidespreadandofsignificanteconomicimportance[R.J.Farrauto,C.H.Bartholomew,FundamentalsofIndustrialCatalyticProcesses,BlackieAcademicandProfessional,1997.].Forwaterrecoveryandre-usechemo-catalysisisonlyjuststartingtomakeanimpactalthoughbio-catalysisiswellestablished[J.N.Horan,BiologicalWastewaterTreatmentSystems;TheoryandOperation,Chichester,Wiley,1990.].Thispaperwilldiscusssomeoftheprinciplesbehinddevelopingchemo-catalyticprocessesforwaterre-use.Withinthiscontextoxidativecatalyticchemistryhasmanyopportunitiestounderpinthedevelopmentofsuccessfulprocessesandmanyemergingtechnologiesbasedonthischemistrycanbeconsidered.

Keywords:

CODremoval;Catalyticoxidation;Industrialwatertreatment1.Introduction

Industrialwaterre-useinEuropehasnotyetstartedonthelargescale.However,withpotentiallongtermchangesinEuropeanweatherandtheneedformorewaterabstractionfromboreholesandrivers,theavailabilityofwateratlowpriceswillbecomeincreasinglyrare.Aswaterpricesrisetherewillcomeapointwhentechnologiesthatexistnow（orarebeingdeveloped）willmakewaterrecycleandre-useaviablecommercialoperation.Asthatfutureapproaches,itisworthstatingthemostimportantfactaboutwastewaterimprovement–avoiditcompletelyifatallpossible!

Itisbesttoconsiderwaternotasanaturallyavailablecheapsolventbutrather,difficulttopurify,easilycontaminatedmaterialthatifallowedintotheenvironmentwillpermeateallpartsofthebiosphere.Apollutantisjustamaterialinthewrongplaceandthereforedesignyourprocesstokeepthematerialwhereitshouldbe–containedandsafe.Avoidanceandthenminimisationarethetwofirststepsinlookingatanypollutantremovalproblem.Ofcourseavoidancemaynotbeanoptiononanexistingplantwhereanychangesmayhavelargeconsequencesforplantitemsifmajorflowsheetrevisionwererequired.Alsoavoidancemaymeansimplytransferringtheissuefromtheaqueousphasetothegasphase.Thereareadvantagesanddisadvantagestobothwaterandgaspollutantabatement.However,itmustberememberedthatgasphaseorganicpollutantremoval（VOCcombustionetc.,）ismuchmoreadvancedthantheequivalentwaterCODremovalandthereforeworthconsideration[1].Becausetheseaspectscannotbeover-emphasised，athirdstepwouldbetovisitthefirsttwostepsagain.Clean-upisexpensive,recycleandre-useevenifyouhaveacosteffectiveprocessisstillmorecapitalequipmentthatwillloweryourreturnonassetsandmaketheprocesslessfinanciallyattractive.Atpresentthebesttechnologyforwaterrecycleismembranebased.Thisistheonlytechnologythatwillproduceasufficientlycleanpermeateforchemicalprocessuse.However,thetechnologycannotbeusedinisolationandinmany（all）caseswillrequirefiltrationupstreamandatechniqueforhandlingthedownstreamretentatecontainingthepollutants.Thus,hybridtechnologiesarerequiredthattogethercanhandletheallaspectsofthewaterimprovementprocess[6,7,8].

Hencethegeneralrulesforwastewaterimprovementare:

1.Avoidifpossible,considerallpossiblewaystominimise.

2.Keepcontaminatedstreamsseparate.

3.Treateachstreamatsourceformaximumconcentrationandminimumflow.

4.Measureandidentifycontaminantsovercompleteprocesscycle.Lookforpeaks,whichwillprovecostlytomanageandattempttoruntheprocessasclosetotypicalvaluesaspossible.Thispaperwillconsidertheindustriesthatareaffectedbywastewaterissuesandthetechnologiesthatareavailabletodisposeoftheretentatewhichwillcontainthepollutantsfromthewastewatereffluent.Thepaperwilldescribesomeoftheproblemstobeovercomeandhowthetechnologiessolvetheseproblemstovaryingdegrees.Itwillalsodiscusshowthecostdrivershouldinfluencedevelopersoffuturetechnologies.

2.Theindustries

TheprocessindustriesthathaveasignificantwastewatereffluentareshowninFig.1.Theseprocessindustriescanbeinvolvedinwastewatertreatmentinmanyareasandsomeillustrationsofthisareoutlinedbelow.

Fig.1.Processindustrieswithwastewaterissues.

2.1.Refineries

Theprocessofbringingoiltotherefinerywilloftenproducecontaminatedwater.Oilpipelinesfromoffshorerigsarecleanedwithwater;oilshipsballastwithwaterandtheresultcanbesignificantwaterimprovementissues.

2.2.Chemicals

Thesynthesisofintermediateandspecialitychemicalsofteninvolvetheuseofawaterwashsteptoremoveimpuritiesorwashoutresidualflammablesolventsbeforedrying.

2.3.Petrochemicals

Ethyleneplantsneedtoremoveacidgases（CO2,H2S）formedinthemanufactureprocess.Thissituationcanbeexacerbatedbytheneedtoaddsulphurcompoundsbeforethepyrolysisstagetoimprovetheprocessselectivity.Causticscrubbingistheusualmethodandthisproducesasignificantwatereffluentdisposalproblem.

2.4.Pharmaceuticalsandagrochemicals

Theseindustriescanhavewaterwashstepsinsynthesisbutinadditiontheyareoftenformulatedwithwater-basedsurfactantsorwettingagents.

2.5.Foodsandbeverages

ClearlyusewaterinprocessingandCODandBODissueswillbetheendresult.

2.6.Pulpandpaper

Thisindustryusesverylargequantitiesofwaterforprocessing–aqueousperoxideandenzymesforbleachinginadditiontothestandardKrafttypeprocessingofthepulp.Itisimportanttorealisehowmuchhumansocietycontributestocontaminatedwaterandaninvestigationoftheflowratesthroughmunicipaltreatmentplantssoonshowsthesignificanceofnon-processindustryderivedwastewater.

3.Thetechnologies

ThetechnologiesforrecalcitrantCODandtoxicpollutantsinaqueouseffluentareshowninFig.2.Theseexamplesoftechnologies[2,6,8]availableorindevelopmentcanbecategorisedaccordingtothegeneralprincipleunderlyingthemechanismofaction.Ifinadditiontheadsorption（absorption）processesareignoredforthiscatalysisdiscussionthenthecategoriesare:

1.Biocatalysis

2.Air/oxygenbasedcatalytic（ornon-catalytic）.

3.Chemicaloxidation

1.Withoutcatalysisusingchemicaloxidants

2.Withcatalysisusingeitherthegenerationof_OHoractiveoxygentransfer.BiocatalysisisanexcellenttechnologyforMunicipalwastewatertreatmentprovidingaverycost-effectiveroutefortheremovaloforganicsfromwater.Itiscapableofmuchdevelopmentviatheuseofdifferenttypesofbacteriatoincreasetheoverallflexibilityofthetechnology.Oneissueremains–whattodowithalltheactivatedsludgeevenaftermassreductionbyde-watering.Thequantitiesinvolvedmeanthatthisisnotaneasyproblemtosolveandre-useasafertilizercanonlyusesomuch.Thesludgecanbetoxicviaabsorptionofheavymetals,recalcitranttoxicCOD.Inthiscaseincinerationandsafedisposaloftheashtoacceptablelandfillmayberequired.Airbasedoxidation[6,7]isveryattractivebecauseprovidingpurergradesofoxygenarenotrequirediftheoxidantisfree.Unfortunately,itisonlyslightlysolubleinwater,ratherunreactiveatlowtemperaturesand,therefore,needsheatandpressuretodeliverreasonableratesofreaction.Theseplantsbecomecapitalintensiveaspressures（from_10to100bar）areused.Therefore,althoughtherunningcostsmaybelowtheinitialcapitaloutlayontheplanthasaverysignificanteffectonthecostsoftheprocess.Catalysisimprovestheratesofreactionandhencelowersthetemperatureandpressurebutisnotabletoavoidthemandhencedoesnotofferacompletesolution.ThecatalystsusedaregenerallyGroupVIIImetalssuchascobaltorcopper.Theleachingofthesemetalsintotheaqueousphaseisadifficultythatinhibitsthegeneraluseofheterogeneouscatalysts[7].Chemicaloxidationwithcheapoxidantshasbeenwellpractisedonintegratedchemicalplants.Theusualexampleiswastesodiumhypochloritegeneratedinchlor-alkaliunitsthatcanbeutilisedtooxidiseCODstreamsfromotherplantswithinthecomplex.Hydrogenperoxide,chlorinedioxide,potassiumpermanganateareallpossibleoxidantsinthistypeofprocess.Thechoiceisprimarilydeterminedbywhichisthecheapestatthepointofuse.Asecondaryconsiderationishoweffectiveistheoxidant.Possiblythemostresearchedcatalyticareaisthegenerationanduseof_OHasaveryactiveoxidant（advancedoxidationprocesses）[8].Thereareavarietyofwaysofdoingthisbutthemostusualiswithphotonsandaphotocatalyst.ThephotocatalystisnormallyTiO2butothermaterialswithasuitablebandgapcanbeused[9,10].Theprocessescanbeveryactivehowevertheengineeringdifficultiesofgettinglight,acatalystandtheeffluentefficientlycontactedisnoteasy.Infactthepoorefficiencyoflightusagebythecatalyst（eitherthroughcontactingproblemsorinherenttothecatalyst）makethisprocessonlysuitableforlightfromsolarsources.PhotonsderivedfromelectricalpowerthatcomesfromfossilfuelsarenotacceptablebecausethecarbondioxideemissionthisimpliesfaroutweighsandCODabatement.Hydroelectricpower（andnuclearpower）arepossiblesourcesbutthebasicinefficiencyisnotbeingavoided.HydrogenperoxideandozonehavebeenusedwithphotocatalysisbuttheycanbeusedseparatelyortogetherwithcatalyststoeffectCODoxidation.Forozonethereistheproblemofthemanufacturingroute,coronadischarge,whichisacapitalintensiveprocessoftenlimitsitsapplicationandbetterroutetoozonewouldbeveryuseful.Itisimportanttonoteatthispoint