度给排水专业英文文献翻译.docx

度给排水专业英文文献翻译.docx

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度给排水专业英文文献翻译

Sewagetreatment

Abstract

Sewagetreatment,ordomesticwastewatertreatment,istheprocessofremovingcontaminantsfromwastewaterandhouseholdsewage,bothrunoff（effluents）anddomestic.Itincludesphysical,chemical,andbiologicalprocessestoremovephysical,chemicalandbiologicalcontaminants.Itsobjectiveistoproduceawastestream（ortreatedeffluent）andasolidwasteorsludgesuitablefordischargeorreusebackintotheenvironment.Thismaterialisofteninadvertentlycontaminatedwithmanytoxicorganicandinorganiccompounds.

Keywords:

Sewagetreatment,fixed-filmandsuspended-growth,Activatedsludge

Originsofsewage

Sewageiscreatedbyresidences,institutions,andcommercialandindustrialestablishments.Rawinfluent（sewage）includeshouseholdwasteliquidfromtoilets,baths,showers,kitchens,sinks,andsoforththatisdisposedofviasewers.Inmanyareas,sewagealsoincludesliquidwastefromindustryandcommerce.Theseparationanddrainingofhouseholdwasteintogreywaterandblackwaterisbecomingmorecommoninthedevelopedworld,withgreywaterbeingpermittedtobeusedforwateringplantsorrecycledforflushingtoilets.Alotofsewagealsoincludessomesurfacewaterfromroofsorhard-standingareas.Municipalwastewaterthereforeincludesresidential,commercial,andindustrialliquidwastedischarges,andmayincludestormwaterrunoff.Sewagesystemscapableofhandlingstormwaterareknownascombinedsystemsorcombinedsewers.Suchsystemsareusuallyavoidedsincetheycomplicateandtherebyreducetheefficiencyofsewagetreatmentplantsowingtotheirseasonality.Thevariabilityinflowalsoleadstooftenlargerthannecessary,andsubsequentlymoreexpensive,treatmentfacilities.Inaddition,heavystormsthatcontributemoreflowsthanthetreatmentplantcanhandlemayoverwhelmthesewagetreatmentsystem,causingaspilloroverflow.Itispreferabletohaveaseparatestormdrainsystemforstormwaterinareasthataredevelopedwithsewersystems.

Asrainfallrunsoverthesurfaceofroofsandtheground,itmaypickupvariouscontaminantsincludingsoilparticlesandothersediment,heavymetals,organiccompounds,animalwaste,andoilandgrease.Somejurisdictionsrequirestormwatertoreceivesomeleveloftreatmentbeforebeingdischargeddirectlyintowaterways.Examplesoftreatmentprocessesusedforstormwaterincludesedimentationbasins,wetlands,buriedconcretevaultswithvariouskindsoffilters,andvortexseparators（toremovecoarsesolids）.

Processoverview

Sewagecanbetreatedclosetowhereitiscreated（inseptictanks,biofiltersoraerobictreatmentsystems）,orcollectedandtransportedviaanetworkofpipesandpumpstationstoamunicipaltreatmentplant（seesewerageandpipesandinfrastructure）.Sewagecollectionandtreatmentistypicallysubjecttolocal,stateandfederalregulationsandstandards.Industrialsourcesofwastewateroftenrequirespecializedtreatmentprocesses（seeIndustrialwastewatertreatment）.

Conventionalsewagetreatmentmayinvolvethreestages,calledprimary,secondaryandtertiarytreatment.Primarytreatmentconsistsoftemporarilyholdingthesewageinaquiescentbasinwhereheavysolidscansettletothebottomwhileoil,greaseandlightersolidsfloattothesurface.Thesettledandfloatingmaterialsareremovedandtheremainingliquidmaybedischargedorsubjectedtosecondarytreatment.Secondarytreatmentremovesdissolvedandsuspendedbiologicalmatter.Secondarytreatmentistypicallyperformedbyindigenous,water-bornemicro-organismsinamanagedhabitat.Secondarytreatmentmayrequireaseparationprocesstoremovethemicro-organismsfromthetreatedwaterpriortodischargeortertiarytreatment.Tertiarytreatmentissometimesdefinedasanythingmorethanprimaryandsecondarytreatment.Treatedwaterissometimesdisinfectedchemicallyorphysically（forexamplebylagoonsandmicrofiltration）priortodischargeintoastream,river,bay,lagoonorwetland,oritcanbeusedfortheirrigationofagolfcourse,greenwayorpark.Ifitissufficientlyclean,itcanalsobeusedforgroundwaterrechargeoragriculturalpurposes.

Pre-treatment

Pre-treatmentremovesmaterialsthatcanbeeasilycollectedfromtherawwastewaterbeforetheydamageorclogthepumpsandskimmersofprimarytreatmentclarifiers（trash,treelimbs,leaves,etc）.

Screening

Theinfluentsewagewaterisstrainedtoremovealllargeobjectscarriedinthesewagestream.Thisismostcommonlydonewithanautomatedmechanicallyrakedbarscreeninmodernplantsservinglargepopulations,whilstinsmallerorlessmodernplantsamanuallycleanedscreenmaybeused.Therakingactionofamechanicalbarscreenistypicallypacedaccordingtotheaccumulationonthebarscreensand/orflowrate.Thesolidsarecollectedandlaterdisposedinalandfillorincinerated.

Gritremoval

Pre-treatmentmayincludeasandorgritchannelorchamberwherethevelocityoftheincomingwastewateriscarefullycontrolledtoallowsand,gritandstonestosettle.

Primarytreatment

Intheprimarysedimentationstage,sewageflowsthroughlargetanks,commonlycalled"primaryclarifiers"or"primarysedimentationtanks".Thetanksarelargeenoughthatsludgecansettleandfloatingmaterialsuchasgreaseandoilscanrisetothesurfaceandbeskimmedoff.Themainpurposeoftheprimarysedimentationstageistoproducebothagenerallyhomogeneousliquidcapableofbeingtreatedbiologicallyandasludgethatcanbeseparatelytreatedorprocessed.Primarysettlingtanksareusuallyequippedwithmechanicallydrivenscrapersthatcontinuallydrivethecollectedsludgetowardsahopperinthebaseofthetankfromwhereitcanbepumpedtofurthersludgetreatmentstages.Greaseandoilfromthefloatingmaterialcansometimesberecoveredforsaponification.

Secondarytreatment

Secondarytreatmentisdesignedtosubstantiallydegradethebiologicalcontentofthesewagewhicharederivedfromhumanwaste,foodwaste,soapsanddetergent.Themajorityofmunicipalplantstreatthesettledsewageliquorusingaerobicbiologicalprocesses.Forthistobeeffective,thebiotarequirebothoxygenandasubstrateonwhichtolive.Thereareanumberofwaysinwhichthisisdone.Inallthesemethods,thebacteriaandprotozoaconsumebiodegradablesolubleorganiccontaminants（e.g.sugars,fats,organicshort-chaincarbonmolecules,etc.）andbindmuchofthelesssolublefractionsintofloc.Secondarytreatmentsystemsareclassifiedas

fixed-filmandsuspended-growth

Fixed-filmORattachedgrowthsystemtreatmentprocessincludingtricklingfilterandrotatingbiologicalcontactorswherethebiomassgrowsonmediaandthesewagepassesoveritssurface.

Insuspended-growthsystems,suchasactivatedsludge,thebiomassiswellmixedwiththesewageandcanbeoperatedinasmallerspacethanfixed-filmsystemsthattreatthesameamountofwater.However,fixed-filmsystemsaremoreabletocopewithdrasticchangesintheamountofbiologicalmaterialandcanprovidehigherremovalratesfororganicmaterialandsuspendedsolidsthansuspendedgrowthsystems.

Roughingfiltersareintendedtotreatparticularlystrongorvariableorganicloads,typicallyindustrial,toallowthemtothenbetreatedbyconventionalsecondarytreatmentprocesses.Characteristicsincludetypicallytall,circularfiltersfilledwithopensyntheticfiltermediatowhichwastewaterisappliedatarelativelyhighrate.Theyaredesignedtoallowhighhydraulicloadingandahighflow-throughofair.Onlargerinstallations,airisforcedthroughthemediausingblowers.Theresultantwastewaterisusuallywithinthenormalrangeforconventionaltreatmentprocesses.

c:

\iknow\docshare\data\cur_work\Activated_Sludge_1.pngc:

\iknow\docshare\data\cur_work\Activated_Sludge_1.pngActivatedsludge

Mainarticle:

Activatedsludge

Ingeneral,activatedsludgeplantsencompassavarietyofmechanismsandprocessesthatusedissolvedoxygentopromotethegrowthofbiologicalflocthatsubstantiallyremovesorganicmaterial.

Theprocesstrapsparticulatematerialandcan,underidealconditions,convertammoniatonitriteandnitrateandultimatelytonitrogengas,（seealsodenitrification）.

Surface-aeratedbasins

Mostbiologicaloxidationprocessesfortreatingindustrialwastewatershaveincommontheuseofoxygen（orair）andmicrobialaction.Surface-aeratedbasinsachieve80to90%removalofBiochemicalOxygenDemandwithretentiontimesof1to10days.Thebasinsmayrangeindepthfrom1.5to5.0metresandusemotor-drivenaeratorsfloatingonthesurfaceofthewastewater.

Inanaeratedbasinsystem,theaeratorsprovidetwofunctions:

theytransferairintothebasinsrequiredbythebiologicaloxidationreactions,andtheyprovidethemixingrequiredfordispersingtheairandforcontactingthereactants（thatis,oxygen,wastewaterandmicrobes）.Typically,thefloatingsurfaceaeratorsareratedtodelivertheamountofairequivalentto1.8to2.7 kgO2/kW·h.However,theydonotprovideasgoodmixingasisnormallyachievedinactivatedsludgesystemsandthereforeaeratedbasinsdonotachievethesameperformancelevelasactivatedsludgeunits.

Biologicaloxidationprocessesaresensitivetotemperatureand,between0°Cand40°C,therateofbiologicalreactionsincreasewithtemperature.Mostsurfaceaeratedvesselsoperateatbetween4°Cand32°C.

Filterbeds（oxidizingbeds）

Mainarticle:

Tricklingfilter

Inolderplantsandplantsreceivingmorevariableloads,tricklingfilterbedsareusedwherethesettledsewageliquorisspreadontothesurfaceofadeepbedmadeupofcoke（carbonizedcoal）,limestonechipsorspeciallyfabricatedplas