环境工程专业英语 课件 U3L3 Advanced Wastewater Treatment

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AdvancedWastewaterTreatment

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Secondarytreatmentcanremovebetween85and95percentoftheBODandTSSinrawsanitarysewage.Generally,thisleaves30mg/LorlessofBODandTSSinthesecondaryeffluent.Butsometimesthislevelofsewagetreatmentisnotsufficienttoprotecttheaquaticenvironment.Forexample,periodiclowflowratesinatroutstreammaynotprovidetheamountofdilutionoftheeffluentthatisneededtomaintainthenecessaryDOlevelsfortroutsurvival.AdvancedWastewaterTreatment

Secondarytreatment

Anotherlimitationofsecondarytreatmentisthatitdoesnotsignificantlyreducetheeffluentconcentrationsofnitrogenandphosphorusinthesewage.Nitrogenandphosphorusareimportantplantnutrients.Iftheyaredischargedintoalake,algalbloomsandacceleratedlakeagingoreutrophicationmaybetheresult.AdvancedWastewaterTreatment

Secondarytreatment

Also,thenitrogeninthesewageeffluentmaybepresentmostlyintheformofammoniacompounds.Thesecompoundsaretoxictofishiftheconcentrationsarehighenough.Yetanotherproblemwiththeammoniaisthatitexertsanitrogenousoxygendemandinthereceivingwater,asitisconvertedtonitrates.Thisprocessiscallednitrification.AdvancedWastewaterTreatment

Secondarytreatment

Whenpollutantremovalgreaterthanthatprovidedbysecondarytreatmentisrequired,eitherfurtherreducetheBODorTSSconcentrationsintheeffluentortoremoveplantnutrients.Additionaloradvancedtreatmentstepsarerequired.Thisisalsocalledtertiarytreatment,becauseanyoftheadditionalprocessesfollowtheprimaryandsecondaryprocessesinsequence.AdvancedWastewaterTreatment

SecondarytreatmentTertiarytreatment

Tertiarytreatmentofsewagecanremovemorethan99percentofthepollutantsfromrawsewageandcanproduceaneffluentofalmostdrinkingwaterquality.Butthecostoftertiarytreatment,foroperationandmaintenanceaswellasforconstruction,isveryhigh,sometimesdoublingthecostofsecondarytreatment.Thebenefit-to-costratioisnotalwaysbigenoughtojustifytheadditionalexpense.Nevertheless,applicationofsomeformoftertiarytreatmentisnotuncommon.AdvancedWastewaterTreatment

Tertiarytreatment

TheremovalofadditionalBODandTSSfromsecondaryeffluentsissometimesreferredtoaseffluentpolishing.Itismostoftenaccomplishedusingagranular-mediafilter,muchlikethefiltersusedtopurifydrinkingwater.Sincethesuspendedsolidsconsistmostlyoforganiccompounds,filtrationremovesBODaswellasTSS.AdvancedWastewaterTreatment

Tertiarytreatment

EffluentPolishingGenerally,mixed-mediafiltersareusedtoachievein-depthfiltrationoftheeffluent.Becauseoftheorganicandbiodegradablenatureofthesuspendedsolidsinthesecondaryeffluent,tertiaryfiltersmustbebackwashedfrequently.Otherwise,decompositionwouldcausesepticoranaerobicconditionstodevelopinthefilterbed.Inadditiontotheconventionalbackwashcycle,anauxiliarysurfaceair-washisusedtothoroughlyscourandcleanthefilterbed.Filtrationmaybedonebygravityinanopentankorbypressureinclosedpressurevessels.AdvancedWastewaterTreatment

Tertiarytreatment

EffluentPolishingThefilteredwatermaybestoredinanadjacenttankandusedforbackwashwaterwhentheheadlossthroughtheautomatic-backwashtertiaryfilterreachesapredeterminedlevel.Somefiltermanufacturersmountthebackwashstoragetankdirectlyabovethefilter,formingasingleself-contained.AdvancedWastewaterTreatment

Tertiarytreatment

EffluentPolishingAnotherprocess,calledmicrostraining,alsofindsapplicationasatertiarystepinwastewatertreatmentforsuspendedsolidsreduction.Themicrostrainers,alsocalledmicroscreen,arecomposedofspeciallywovensteelwireclothmountedaroundtheperimeterofalargerevolvingdrum.Thesteelwireclothactsasafinescreen,withopeningsassmallas20micrometers(μm，ormillionthsofameter).AdvancedWastewaterTreatment

Tertiarytreatment

EffluentPolishingTherotatingdrumispartiallysubemergedinthesecondaryeffluent,whichmustflowintothedrumandthenoutwardthroughthemicroscreen.Asthedrumrotates,capturedsolidsarecarriedtothetop,whereahigh-velocitywatersprayflushesthemintoahoppermountedonthehollowaxleofthedrumAdvancedWastewaterTreatment

Tertiarytreatment

EffluentPolishingPhosphorusisoneoftheplantnutrientsthatcontributestotheeutrophicationoflakes.Rawsewagecontainsabout10mg/Lphosphorus,fromhouseholddetergentsaswellasfromsanitarywastes.Thephosphorusinwastewaterisprimarilyintheformoforganicphosphorusandasphosphates,PO43-,compounds.Onlyabout30percentofthisphosphorusisremovedbythebacteriainaconventionalsecondarysewagetreatmentplant,leavingabout7mg/Lofphosphorusintheeffluent.AdvancedWastewaterTreatment

Tertiarytreatment

PhosphorusRemovalWhenstreamoreffluentstandardsrequirelowerphosphorusconcentrations,atertiarytreatmentprocessmustbeaddedtothetreatmentplant.Thisusuallyinvolvesflocculationandcoagulation.Theorganicphosphoruscompoundsareentrappedinthecoagulantflocsthatareformedandsettleoutinaclarifier.AdvancedWastewaterTreatment

Tertiarytreatment

PhosphorusRemovalOnechemicalfrequentlyusedinthisprocessisaluminumsulfate,Al2(S04)3.Thisiscalledalum,thesamecoagulantchemicalusedtopurifydrinkingwater.Thealuminumionsinthealumreactwiththephosphateionsinthesewagetoformtheinsolubleprecipitatecalledaluminumphosphate.Otherchemicalsthatmaybeusedtoprecipitatethephosphorusincludeferricchloride,FeCl3,andlime,CaO.AdvancedWastewaterTreatment

Tertiarytreatment

PhosphorusRemovalAddingthecoagulantdownstreamofthesecondaryprocessesprovidesthegreatestoverallreliabilityforphosphorusreduction.Itnotonlyremovesabout90percentofthephosphorus,butinremovesadditionalTSSandservestopolishtheeffluentaswell.Butwhenappliedinthismanner,asathirdortertiarytreatmentstep,additionalflocculationandsettlingtanksmustbebuilt.Insomecases,evenfiltersmayhavetobeaddedtoremovethenonsettleablefloc.AdvancedWastewaterTreatment

Tertiarytreatment

PhosphorusRemovalToavoidtheneedforconstructionofadditionaltanksandfilters,inmostplantsrequiringphosphorusremovalthecoagulantisaddedtothewastewateratsomepointintheconventionalprocess.Forexample,alummaybeaddedjustbeforetheprimarysettlingtanks.Theresultingcombinationofprimaryandchemicalsludgeisremovedfromtheprimaryclarifiers.AdvancedWastewaterTreatment

Tertiarytreatment

PhosphorusRemovalOr,inactivatedsludgeplants,thecoagulantmaybeaddeddirectlyintotheaerationtanks.Inthiscase,theprecipitationandflocculationreactionsoccuralongwiththebiochemicalreactions.Sometimes,thecoagulantmaybeaddedtothewastewaterjustbeforethesecondaryorfinalclarifiers.Regardlessofthepointintheprocessatwhichcoagulantisadded,thetotalvolumeandweightofsludgerequiringdisposalincreasesignificantly.AdvancedWastewaterTreatment

Tertiarytreatment

PhosphorusRemovalTheeffluentfromaconventionalactivatedsludgeplantcontainsmostlytheammonianitrogenform,NH4+.Effluentsfromatricklingfilterorrotatingbiodiscmaycontainmoreofthenitrateform,NO3-.Thisisbecausethenitrifyingbacteria,thosemicrobesthatconvertammoniatonitrate,haveachancetogrowandmultiplyonsomeofthesurfacesinthetricklingfilterorbiodiscunits.Theydonotsurviveinamixed-growthaerationtank,wheretheyarecrowdedoutbyfaster-growingbacteriathatconsumecarbonaceousorganics.AdvancedWastewaterTreatment

Tertiarytreatment

NitrogenRemovalNitrogencanexistinwastewaterintheformoforganicnitrogen,ammonia,ornitratecompounds.Nitrogenintheformofammoniacanbetoxictofish,anditexertsanoxygendemandinreceivingwatersasitisconvertedtonitrate.Nitratenitrogenisoneofthemajornutrientsthatcausesalgalbloomsandeutrophication.Forthesereasons,itissometimesnecessarytoremovethenitrogenfromthesewageeffluentbeforedischarge.Thisisparticularlyimportantifitisdischargeddirectlyintoalake.AdvancedWastewaterTreatment

Tertiarytreatment

NitrogenRemovalOneofthemethodsusedtoremovenitrogeniscalledbiologicalnitrification-denitrification.Itconsistsoftwobasicsteps.First,thesecondaryeffluentisintroducedintoanotheraerationtank,tricklingfilter,orbiodisc.SincemostofthecarbonaceousBODhasalreadybeenremoved,themicroorganismsthatwillnowthriveinthistertiarysteparethenitrifyingbacteria,NitrosomonasandNitrobacter.AdvancedWastewaterTreatment

Tertiarytreatment

NitrogenRemovalInthisfirststep,callednitrification,theammonianitrogenisconvertedtonitratenitrogen,producinganitrifiedeffluent.Atthispoint,thenitrogenhasnotactuallybeenremoved,butonlyconvertedtoaformthatisnottoxictofishandthatdoesnotcauseanadditionaloxygendemand.Asecondbiologicaltreatmentstepisnecessarytoactuallyremovethenitrogenfromthewastewater.Thisiscalleddenitrification.Itisanaerobicprocessinwhichtheorganicchemicalmethanolisaddedtothenitrifiedeffluenttoserveasasourceofcarbon.AdvancedWastewaterTreatment

Tertiarytreatment

NitrogenRemovalThedenitrifyingbacteriaPseudomonasandothergroupsusethecarbonfromthemethanolandtheoxygenfromthenitratesintheirmetabolicprocesses.Oneproductofthisbiochemicalreactionismolecularnitrogen,N2,whichescapesintotheatmosphereasagas.AdvancedWastewaterTreatment

Tertiarytreatment

NitrogenRemovalFirst,thepHofthewastewaterisraisedinordertoconverttheammoniumions,NH4+,toammoniagas,NH3.Second,thewastewateriscascadeddownthroughatalltower;thiscausesturbulenceandcontactwithairallowingtheammoniatoescapeasagas.Largevolumesofairarecirculatedthroughthetowertocarrythegasoutofthesystem.AdvancedWastewaterTreatment

Tertiarytreatment

NitrogenRemovalAnothermethodfornitrogenremovaliscalledammoniastripping.Itisaphysical-chemicalratherthanabiologicalprocess,consistingoftwobasicsteps.Thecombinationofammoniastrippingwithphosphorusremovalusinglimeasacoagulantisadvantageous,sincethelimecanalsoservetoraisethepHofwastewater.Ammoniastrippingislessexpensivethanbiologicalnitrification-denitrification,butitdoesnotworkveryefficientlyundercoldweatherconditions.AdvancedWastewaterTreatment

Tertiarytreatment

NitrogenRemovalTheapplicationofsecondaryeffluentontothelandsurfacecanprovideaneffectivealternativetotheexpensiveandcomplicatedadvancedtreatmentmethodspreviouslydiscussed.Ahigh-qualitypolishedeffluentcanbeobtainedbythenaturalprocessesthatoccurastheeffluentflowsoverthevegetatedgroundsurfaceandpercolatesthroughthesoil.AdvancedWastewaterTreatment

Tertiarytreatment

LandTreatmentofWastewater成都活水公园Anadditionalbenefitoflandtreatmentisthatitcanprovidethemoistureandnutrientsneededforvegetationgrowth,anditcanhelptorechargegroundwateraquifers.Ineffect,landtreatmentofwastewaterallowsadirectrecyclingofwaterandnutrientsforbeneficialuse:thesewagebecomesavaluablenaturalresourcethatisnotsimplydisposedof.Butrelativelylargelandareasareneededforthislandoftreatment.Andsoiltypesaswellasclimatearecriticalfactorsincontrollingthefeasibilityanddesignofalandtreatmentprocess.AdvancedWastewaterTreatment

Tertiarytreatment

LandTreatmentofWastewaterIntheslowratesystem,alsocalledirrigation,vegetationisthecriticalcomponentforthewastewatertreatmentprocess.Althoughthebasicobjectiveiswastewatertreatmentanddisposal,anothergoalistoobtainaneconomicbenefitfromtheuseofthewaterandnutrientstoproducemarketablecrops(thatis,cornorgrain)foranimalfeed.Anotherobjectivemightbetoconservepotablewaterbyusingsecondaryeffluenttoirrigatelawnsandotherlandscapedareas.AdvancedWastewaterTreatment

Tertiarytreatment

LandTreatmentofWastewaterTherearethreebasictypesormodesoflandtreatment:slowrate,rapidinfiltration,andoverlandflow.Therapidinfiltrationorinfiltration-percolationmodeoflandtreatmenthasasbasicobjectivestorechargegroundwateraquifersandtoprovideadvancedtreatmentofwastewater.Mostofthesecondaryeffluentpercolatestothegroundwater:verylittleofitisabsorbedbyvegetation.ThefilteringandadsorptionactionofthesoilremovesmostoftheBOD,TSS,andphosphorusfromtheeffluent,butnitrogenremovalisrelativelypoor.Soilsmustbehighlypermeablefortherapidinfiltrationmethodtoworkproperly.Usually,thewastewaterisappliedinlargepondscalledrechargebasins.AdvancedWastewaterTreatment

Tertiarytreatment

LandTreatmentofWastewaterTherearethreebasictypesormodesoflandtreatment:slowrate,rapidinfiltration,andoverlandflow.Inanoverlandflowsystem,wastewaterissprayedonaslopedterraceandallowedtoflowacrossthevegetatedsurfacetoarunoffcollectionditch.Purificationisaccomplishedbyphysical,chemicalandbiologicalprocessesasthewastewaterflowsinathinfilmdowntherelativelypermeablesurface.OverlandflowcanbeusedtoachieveremovalefficienciesforBODandnitrogencomparabletoothermethodsoftertiarytreatment,butphosphorusremovalissomewhatlimited.Thewatercollectedintheditchisusuallydischargedtoanearbybodyofsurfacewater.AdvancedWastewaterTreatment

Tertiarytreatment

LandTreatmentofWastewaterTherearethreebasictypesormodesoflandtreatment:slowrate,rapidinfiltration,andoverlandflow.DiscussionEutrophicationremainsamajorproblemforEurope’sseasdespitesomeprogressEutrophicationinChina英语翻译的减译

语法需要引起的减译1.冠词的减译

英语中有冠词，而汉语中没有这类词语。(2)Iftheyaredischargedintoalake,algalbloomsandacceleratedlakeagingoreutrophicationmaybetheresult.译文：如果它们被排放到湖中，可能会导致藻类大量繁殖，加速湖泊老化或富营养化。(减译了不定冠词a)

此外，有些情况下，冠词也需要译出。如不定冠词表示数量、表示每一、表示同一、固定搭配，定冠词表示特指、重复等情况下，不能减译。

(4)Suchmodelshaveanumberofspecialfeatures,ofwhichperhapsthemostimportantarecompletedynamicfreedomandtheabsenceofwindtunnelsupportandwall.

译文:这些模型具有一系列的特点，其中最重要的特点是具有完全的动力自由度，没有风洞支架干扰和洞壁干扰。Translation

英语翻译的减译

语法需要引起的减译2.介词的减译

大量使用介词是英语的特点之一，它和冠词的使用频率一样高。虽然介词不能单独作为句子成分存在，但它可以表示名词或代词等与句中其他词的关系。汉语里面介词较少，而且用法也没有英语介词使用那么复杂。在翻译时，要么将介词转译为汉语里面的其他成分，要么省略不译。

(5)Thedifferencebetweenthetwomachinesconsistsinpower.

译文：这两台机器的区别在于功率不同。(减译介词“between”)Translation

英语翻译的减译

语法需要引起的减译3.连词的减译

英语属于形合语言，其句式的构成需要连词的连接作用，常用于表示前后词语的逻辑关系和语法关系。相对而言，汉语中连词用得不多。一般来说，英语中的连词可以分为并列连词和从属连词两种，后者包括时间连词、地点连词、原因连词、条件连词、程度与结果连词，它们在句子中只是起到连接作用而不具有句子成分的功能用来表达句子的逻辑关系。汉语则将时间、逻辑关系暗含在句子中，不需要使用连词。

(10)Thevolumeofagivenweightofgasvariesdirectlytheabsolutetemperatureprovidedthepressuredoesnotchange.

译文：压力不变，一定重量的气体的体积与绝对温度成正比。（减译条件连词“provided”，同时句子的顺序也有变化）Translation

英语翻译的减译

语法需要引起的减译4.引导词there的减译

英语中，以there（也作副词）这个引导词引导的句子随处可见，可以与系动词以及其他部分不及物动词，如seem，appear，exist，happen，stand，remain等连用，构成与汉语不同的一种“某地存在/有……”句式。在这种句式中“there”已经失去了原有的意义，翻译的时候也大可不必强行翻译出来。

(11)Therearethreebasictypesormodesoflandtreatment:slowrate,rapidinfiltration,andoverlandflow.译文：土地处理有三种基本类型或方式：慢渗、快渗和地表漫流。（减译引导词there）Translation

英语翻译的减译

语法需要引起的减译5.引导词it的减译

“it”除了做人称代词、指示代词和无人称代词之外，还可以用作引导词。此外，“it”不仅可以作形式主语，还可以起强调作用，改变句子的结构，还可以作形式宾语。例如:

(13)Itismostoftenaccomplishedusingagranular-mediafilter,muchlikethefiltersusedtopurifydrinkingwater.译文：颗粒介质过滤器是最常用的，如用于净化饮用水的过滤器。（减译形式主语“it”）

Translation

英语翻译的减译

意义需要进行的减译1.名词的减译由于英语句法结构而不得不添加的名词或某种特殊结构中的名词，考虑到汉语表达时，不必翻译出来，而句子的意思也不会受损。

(1)Theproblemofalternativefuelsofvehicleisoneproblemweshallapproach.

译文：车辆的代用燃料是我们将要着手处理的一个问题。（减译名词“problem”）Translation

英语翻译的减译

意义需要进行的减译2.动词的减译

一般来说，英语的句式比较固定，由“主语+谓语+宾语+……”构成，而汉语则可以使用意合的词语（包括其他词性的词，如名词、形容词、介词短语等）替代谓语动词。所以，将某些动词（包括行为动词和系动词，如be/become/get等）省略不译也是常见的。如：

(4)Thisdioxideproducesabouttentimesmoreradiantpowerthanthatone.

译文：这只二极管的耗散功率比那只高9