Unit 29SewagetreatmentText Sewageiscreatedbyresidences,institutions,andcommercialandindustrialestablishments①.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.Text Asrainfallrunsoverthesurfaceofroofsandtheground,itmaypickupvariouscontaminantsincludingsoilparticlesandothersediment,heavymetals,organiccompounds,animalwaste,andoilandgrease.Somejurisdictionsrequirestormwatertoreceivesomeleveloftreatmentbeforebeingdischargeddirectlyintowaterways.Examplesoftreatmentprocessesusedforstormwaterincludesedimentationbasins,wetlands,buriedconcretevaultswithvariouskindsoffilters,andvortexseparators(toremovecoarsesolids)②.Processoverview Sewagecanbetreatedclosetowhereitiscreated(inseptictanks,biofiltersoraerobictreatmentsystems),orcollectedandtransportedviaanetworkofpipesandpumpstationstoamunicipaltreatmentplant(seesewerageandpipesandinfrastructure).Sewagecollectionandtreatmentistypicallysubjecttolocal,stateandfederalregulationsandstandards.Industrialsourcesofwastewateroftenrequirespecializedtreatmentprocesses(seeIndustrialwastewatertreatment). Conventionalsewagetreatmentmayinvolvethreestages,calledprimary,secondaryandtertiarytreatment.TextPrimarytreatmentconsistsoftemporarilyholdingthesewageinaquiescentbasinwhereheavysolidscansettletothebottomwhileoil,greaseandlightersolidsfloattothesurface.Thesettledandfloatingmaterialsareremovedandtheremainingliquidmaybedischargedorsubjectedtosecondarytreatment.Secondarytreatmentremovesdissolvedandsuspendedbiologicalmatter.Secondarytreatmentistypicallyperformedbyindigenous,water-bornemicro-organismsinamanagedhabitat.Secondarytreatmentmayrequireaseparationprocesstoremovethemicro-organismsfromthetreatedwaterpriortodischargeortertiarytreatment.Tertiarytreatmentissometimesdefinedasanythingmorethanprimaryandsecondarytreatment.Treatedwaterissometimesdisinfectedchemicallyorphysically(forexamplebylagoonsandmicrofiltration)priortodischargeintoastream,river,bay,lagoonorwetland,oritcanbeusedfortheirrigationofagolfcourse,greenwayorpark.Ifitissufficientlyclean,itcanalsobeusedforgroundwaterrechargeoragriculturalpurposes③.Pre-treatment Pre-treatmentremovesmaterialsthatcanbeeasilycollectedfromtherawwastewaterbeforetheydamageorclogthepumpsandskimmersofprimarytreatmentclarifiers(trash,treelimbs,leaves,etc).TextScreening Theinfluentsewagewaterisstrainedtoremovealllargeobjectscarriedinthesewagestream.Thisismostcommonlydonewithanautomatedmechanicallyrakedbarscreeninmodernplantsservinglargepopulations,whilstinsmallerorlessmodernplantsamanuallycleanedscreenmaybeused.Therakingactionofamechanicalbarscreenistypicallypacedaccordingtotheaccumulationonthebarscreensand/orflowrate.Thesolidsarecollectedandlaterdisposedinalandfillorincinerated.Gritremoval Pre-treatmentmayincludeasandorgritchannelorchamberwherethevelocityoftheincomingwastewateriscarefullycontrolledtoallowsand,gritandstonestosettle.Primarytreatment Intheprimarysedimentationstage,sewageflowsthroughlargetanks,commonlycalled"primaryclarifiers"or"primarysedimentationtanks".TextThetanksarelargeenoughthatsludgecansettleandfloatingmaterialsuchasgreaseandoilscanrisetothesurfaceandbeskimmedoff.Themainpurposeoftheprimarysedimentationstageistoproducebothagenerallyhomogeneousliquidcapableofbeingtreatedbiologicallyandasludgethatcanbeseparatelytreatedorprocessed.Primarysettlingtanksareusuallyequippedwithmechanicallydrivenscrapersthatcontinuallydrivethecollectedsludgetowardsahopperinthebaseofthetankfromwhereitcanbepumpedtofurthersludgetreatmentstages④.Greaseandoilfromthefloatingmaterialcansometimesberecoveredforsaponification.Secondarytreatment Secondarytreatmentisdesignedtosubstantiallydegradethebiologicalcontentofthesewagewhicharederivedfromhumanwaste,foodwaste,soapsanddetergent.Themajorityofmunicipalplantstreatthesettledsewageliquorusingaerobicbiologicalprocesses.Forthistobeeffective,thebiotarequirebothoxygenandasubstrateonwhichtolive.TextThereareanumberofwaysinwhichthisisdone.Inallthesemethods,thebacteriaandprotozoaconsumebiodegradablesolubleorganiccontaminants(e.g.sugars,fats,organicshort-chaincarbonmolecules,etc.)andbindmuchofthelesssolublefractionsintofloc.Secondarytreatmentsystemsareclassifiedasfixed-filmandsuspended-growth⑤. Fixed-filmORattachedgrowthsystemtreatmentprocessincludingtricklingfilterandrotatingbiologicalcontactorswherethebiomassgrowsonmediaandthesewagepassesoveritssurface. Insuspended-growthsystems,suchasactivatedsludge,thebiomassiswellmixedwiththesewageandcanbeoperatedinasmallerspacethanfixed-filmsystemsthattreatthesameamountofwater.However,fixed-filmsystemsaremoreabletocopewithdrasticchangesintheamountofbiologicalmaterialandcanprovidehigherremovalratesfororganicmaterialandsuspendedsolidsthansuspendedgrowthsystems. Roughingfiltersareintendedtotreatparticularlystrongorvariableorganicloads,typicallyindustrial,toallowthemtothenbetreatedbyconventionalsecondarytreatmentprocesses.Characteristicsincludetypicallytall,circularfiltersfilledwithopensyntheticfiltermediatowhichwastewaterisappliedatarelativelyhighrate.TextTheyaredesignedtoallowhighhydraulicloadingandahighflow-throughofair.Onlargerinstallations,airisforcedthroughthemediausingblowers.Theresultantwastewaterisusuallywithinthenormalrangeforconventionaltreatmentprocesses.Activatedsludge Ingeneral,activatedsludgeplantsencompassavarietyofmechanismsandprocessesthatusedissolvedoxygentopromotethegrowthofbiologicalflocthatsubstantiallyremovesorganicmaterial. Theprocesstrapsparticulatematerialandcan,underidealconditions,convertammoniatonitriteandnitrateandultimatelytonitrogengas,(seealsodenitrification).Surface-aeratedbasins Mostbiologicaloxidationprocessesfortreatingindustrialwastewatershaveincommontheuseofoxygen(orair)andmicrobialaction.TextSurface-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.TextFilterbeds(oxidizingbeds) Inolderplantsandplantsreceivingmorevariableloads,tricklingfilterbedsareusedwherethesettledsewageliquorisspreadontothesurfaceofadeepbedmadeupofcoke(carbonizedcoal),limestonechipsorspeciallyfabricatedplasticmedia.Suchmediamusthavehighsurfaceareastosupportthebiofilmsthatform.Theliquorisdistributedthroughperforatedrotatingarmsradiatingfromacentralpivot.Thedistributedliquortricklesthroughthisbedandiscollectedindrainsatthebase.Thesedrainsalsoprovideasourceofairwhichpercolatesupthroughthebed,keepingitaerobic.Biologicalfilmsofbacteria,protozoaandfungiformonthemedia’ssurfacesandeatorotherwisereducetheorganiccontent.Thisbiofilmisgrazedbyinsectlarvaeandwormswhichhelpmaintainanoptimalthickness.Overloadingofbedsincreasesthethicknessofthefilmleadingtocloggingofthefiltermediaandpondingonthesurface.TextBiologicalaeratedfilters BiologicalAerated(orAnoxic)Filter(BAF)orBiofilterscombinefiltrationwithbiologicalcarbonreduction,nitrificationordenitrification.BAFusuallyincludesareactorfilledwithafiltermedia.Themediaiseitherinsuspensionorsupportedbyagravellayeratthefootofthefilter.Thedualpurposeofthismediaistosupporthighlyactivebiomassthatisattachedtoitandtofiltersuspendedsolids.Carbonreductionandammoniaconversionoccursinaerobicmodeandsometimeachievedinasinglereactorwhilenitrateconversionoccursinanoxicmode.BAFisoperatedeitherinupflowordownflowconfigurationdependingondesignspecifiedbymanufacturer.Membranebioreactors Membranebioreactors(MBR)combineactivatedsludgetreatmentwithamembraneliquid-solidseparationprocess.Themembranecomponentuseslowpressuremicrofiltrationorultrafiltrationmembranesandeliminatestheneedforclarificationandtertiaryfiltration.TextThemembranesaretypicallyimmersedintheaerationtank;however,someapplicationsutilizeaseparatemembranetank.OneofthekeybenefitsofanMBRsystemisthatiteffectivelyovercomesthelimitationsassociatedwithpoorsettlingofsludgeinconventionalactivatedsludge(CAS)processes.Thetechnologypermitsbioreactoroperationwithconsiderablyhighermixedliquorsuspendedsolids(MLSS)concentrationthanCASsystems,whicharelimitedbysludgesettling.TheprocessistypicallyoperatedatMLSSintherangeof8,000–12,000

mg/L,whileCASareoperatedintherangeof2,000–3,000

mg/L.TheelevatedbiomassconcentrationintheMBRprocessallowsforveryeffectiveremovalofbothsolubleandparticulatebiodegradablematerialsathigherloadingrates.ThusincreasedSludgeRetentionTimes(SRTs)—usuallyexceeding15days—ensurecompletenitrificationeveninextremelycoldweather. ThecostofbuildingandoperatinganMBRisusuallyhigherthanconventionalwastewatertreatment.Membranefilterscanbeblindedwithgreaseorabradedbysuspendedgritandlackaclarifier'sflexibilitytopasspeakflows.TextThetechnologyhasbecomeincreasinglypopularforreliablypretreatedwastestreamsandhasgainedwideracceptancewhereinfiltrationandinflowhavebeencontrolled,however,andthelife-cyclecostshavebeensteadilydecreasing.ThesmallfootprintofMBRsystems,andthehighqualityeffluentproduced,makethemparticularlyusefulforwaterreuseapplications. ThereareMBRplantsbeingbuiltthroughouttheworld,includingNorthLibrty,Iowa,Georgia,andCanada.Secondarysedimentation Thefinalstepinthesecondarytreatmentstageistosettleoutthebiologicalflocorfiltermaterialandproducesewagewatercontainingverylowlevelsoforganicmaterialandsuspendedmatter.RotatingbiologicalcontactorsText Rotatingbiologicalcontactors(RBCs)aremechanicalsecondarytreatmentsystems,whicharerobustandcapableofwithstandingsurgesinorganicload.RBCswerefirstinstalledinGermanyin1960andhavesincebeendevelopedandrefinedintoareliableoperatingunit.Therotatingdiskssupportthegrowthofbacteriaandmicro-organismspresentinthesewage,whichbreakdownandstabiliseorganicpollutants.Tobesuccessful,micro-organismsneedbothoxygentoliveandfoodtogrow.Oxygenisobtainedfromtheatmosphereasthedisksrotate.Asthemicro-organismsgrow,theybuilduponthemediauntiltheyaresloughedoffduetoshearforcesprovidedbytherotatingdiscsinthesewage.EffluentfromtheRBCisthenpassedthroughfinalclarifierswherethemicro-organismsinsuspensionsettleasasludge.Thesludgeiswithdrawnfromtheclarifierforfurthertreatment. Afunctionallysimilarbiologicalfilteringsystemhasbecomepopularaspartofhomeaquariumfiltrationandpurification.Theaquariumwaterisdrawnupoutofthetankandthencascadedoverafreelyspinningcorrugatedfiber-meshwheelbeforepassingthroughamediafilterandbackintotheaquarium.TextThespinningmeshwheeldevelopsabiofilmcoatingofmicroorganismsthatfeedonthesuspendedwastesintheaquariumwaterandarealsoexposedtotheatmosphereasthewheelrotates.Thisisespeciallygoodatremovingwasteureaandammoniaurinatedintotheaquariumwaterbythefishandotheranimals.sewage n.污水；下水道；污物residence n.住宅，住處；居住institution n.公共機(jī)構(gòu)；制度；建立；（社 會(huì)或宗教等）習(xí)俗sink n.水槽；洗滌槽；污水坑sewer n.下水道；陰溝；污水管municipal adj.市政的，市的；地方自治的discharge vi.排放；卸貨；流出stormwater n.雨水；暴雨水overwhelm vt.壓倒；淹沒(méi)；受打擊spill

n.溢出，濺出；溢出量；摔下；小塞子overflow

n.充滿，洋溢；泛濫；超值；溢值sediment

n.沉積；沉淀物sedimentationbasin

澄清池；沉淀池grease

n.油脂；賄賂jurisdictions

n.司法權(quán)，審判權(quán)，管轄權(quán)；權(quán)限，

權(quán)力wetland

n.濕地；沼澤地；塘地filter

n.濾波器；過(guò)濾器；篩選；濾光器vortex

n.渦流；漩渦；旋風(fēng)septictank化糞池biofiltern.生物濾池NewWordsandPhrasesaerobic adj.需氧的；好氧的quiescent adj.靜止的；不活動(dòng)的；沉寂的indigenous adj.本土的；土著的；國(guó)產(chǎn)的；固 有的disinfect vt.將…消毒lagoon n.瀉湖；環(huán)礁湖；咸水湖whilst conj.同時(shí)；時(shí)時(shí)，有時(shí)；當(dāng)…的 時(shí)候landfill n.垃圾填埋地；垃圾堆grit n.粗砂，砂礫sludge n.污泥；泥狀雪；沉淀物detergent

n.清潔劑；去垢劑soluble

adj.可溶的，可溶解的；可解決的activatedsludge

活性污泥denitrification

n.脫氮；反硝化作用ammonia

n.氨nitrite

n.亞硝酸鹽nitrate

n.硝酸鹽surface-aeratedbasin

表面曝氣池filterbed

濾床；濾水池biologicalaeratedfilter

曝氣生物濾池membranebioreactor

膜生物反應(yīng)器rotatingbiologicalcontactor生物轉(zhuǎn)盤(pán)NewWordsandPhrasesNotes（1）Sewageiscreatedbyresidences,institutions,andcommercialandindustrialestablishments. 污水是由居民住宅，機(jī)關(guān)機(jī)構(gòu)，商業(yè)和工業(yè)活動(dòng)產(chǎn)生的。（2）Examplesoftreatmentprocessesusedforstormwaterincludesedimentationbasins,wetlands,buriedconcretevaultswithvariouskindsoffilters,andvortexseparators(toremovecoarsesolids). 例如以下對(duì)雨水進(jìn)行的處理：盆地沉淀處理，濕地過(guò)濾處理，混凝土地窖過(guò)濾處理，和旋渦分離器（去除粗固體）。（3）Ifitissufficientlyclean,itcanalsobeusedforgroundwaterrechargeoragriculturalpurposes. 如果它足夠清潔，也可以用于地下水回灌或農(nóng)業(yè)用途。（4）Themainpurposeoftheprimarysedimentationstageistoproducebothagenerallyhomogeneousliquidcapableofbeingtreatedbiologicallyandasludgethatcanbeseparatelytreatedorprocessed.Primarysettlingtanksareusuallyequippedwithmechanicallydrivenscrapersthatcontinuallydrivethecollectedsludgetowardsahopperinthebaseofthetankfromwhere