给水排水专业英语课件(李田)9

1Unit9Sedimentation2考试12周随堂考试可以携带词典，课本3Newwordsandexpressionspotableadj.可饮用的，potablewaterClarificationn.澄清，净化clarifiern.澄清池，澄清器开.apparatusn.器械,设备,仪器prechlorinationn.预氯化inletn.进口turbulentadj.紊流的，湍流的Turbulencen.紊流，紊乱perimetern.周长圆周weirn.堰，溢流堰layoutn.规划,设计,(书刊等)编排,版面,(工厂的)布局图rectangularadj.矩形的，成直角的4NewwordsandexpressionsInclinedtuben.斜管effluentadj.流出的n.流出物,出水Sphericaln.球形的球的depositn.沉淀物堆积物；储蓄存款Reinforcedconcreten.钢筋混凝土controversialn.争论的争议的Innovationn.改革创新inclinationadj.倾斜,弯曲,倾度,倾向,爱好hexagonaladj.六角形的六边形的backwashn.v.反洗反冲洗modulen.模数，模块，组件5Sedimentationorclarificationistheremovalofparticulatematter,chemicalfloc,andprecipitatesfromsuspensionthroughgravitysettling.Thismakeswaterclarificationavitallyimportantstepinthetreatmentofsurfacewatersforpotablesupplyandinmostcasesthemainfactorindeterminingtheoverallcostoftreatment.Poordesignofthesedimentationbasinwillresultinreducedtreatmentefficiencythatmaysubsequentlyupsetotheroperations.6Surfacewatercontaininghighturbiditymayrequiresedimentationpriortochemicaltreatment.Presedimentationbasinsareconstructedinexcavatedgroundoroutofsteelorconcrete.Steelandconcretetanksareoftenequippedwithacontinuousmechanicalsludgeremovalapparatus.7Theminimumrecommendeddetentiontimeforpresedimentationis3h,althoughatmanytimesoftheyear,thismaynotbeadequatetoremovefinesuspensions.Chemicalfeedequipmentmaybeprovidedaheadofpresedimentationtoprovideprechlorinationorpartialcoagulationforperiodswhenwateristooturbidtoclarifybyplainsedimentation.8Settlingbasinsareusuallyprovidedforchemicalcoagulationorsoftening.Thesebasinsmaybeconstructedofconcreteorsteelinawidevarietyofshapesandflowmechanisms.Tominimizetheeffectsofshort-circuitingandturbulentflow,careistakenintheeffectivehydraulicdesignofinletandoutletstructuresinalltanks.9Inletstructuresareexpectedto:(1)uniformlydistributeflowoverthecrosssectionofthesettlingzone;(2)initiateparallelorradialflow;(3)minimizelarge-scaleturbulence;and(4)precludeexcessivevelocitiesnearthesludgezone.Flowthroughasedimentationbasinentersatthetopofthebasin.Insomecircularbasins,theflowmayenteracentralflocculatingchamberofthebasin,effluentflowsverticallyoutoverperimeterweirs.断面，截面10Inrectangulartankswaterflowshorizontallytoanendweirfordischarge.Anefficientlydesignedverticaltankismorestablethanahorizontalone.Theratingofaverticaltankasrelatedtothebulksettlingvelocityisusually3.3to9.8ft/h(1to3m/h).11Recentdevelopmentshavebeenmadewiththeimplementationoftubesettlinginthedesignofhorizontal-flowsettlingtanks,whicharesaidtoovercomesomeofthepreviousdifficultiesandenablehigherratesofsedimentation.Upflowsolidscontactclarifiers,andhorizontal-flowbasinsmayincreasetheirvolumetriccapacity50to150percentormorewiththeintroductionofinclinedtubesintotheirbasins.Similarorimprovedeffluentqualityisobservedinthesemodifiedprocesses.12Effluentqualityforanysedimentationprocessisdependentuponpreviouswaterquality,coagulantsadded,mixing,flocculation,andfiltration.Withtheexceptionofpresedimentation,sedimentationprocessesareusuallyprecededbycoagulationandfollowedbyfiltration.Therefore,typicalremovalsofregulatedcontaminantsbysedimentationandfiltrationarereportedaccordingtocoagulantsusedinconjunctionwiththeseprocessesforremovalofaspecificcontaminant.13Basically,thetheoryofsedimentationisthetheoryoftheeffectofgravityonparticlessuspendedinaliquidoflesserdensity.Undertheinfluenceofgravity,anyparticlehavingadensitygreaterthan1.0willsettleinwateratanacceleratingvelocityuntiltheresistanceoftheliquidequalstheeffectiveweightoftheparticle.Thereafter,thesettlingvelocitywillbeessentiallyconstantandwilldependuponthesize,shape,anddensityoftheparticle,aswellasthedensityandviscosityofthewater.14Formosttheoreticalandpracticalcomputationsofsettlingvelocitiesinsedimentationbasins,theshapeoftheparticlesisassumedtobespherical.Settlingvelocitiesofparticlesofothershapescanbeanalyzedinrelationtospheres.Paragraphfive:4-515NumberofBasinsProbablythemostimportantconsiderationsintheselectionofthenumberofsedimentationbasinsare:(1)theeffectupontheproductionofwaterifonebasinisremovedfromservice;and(2)thelargestsizewhichcanbeexpectedtoproducesatisfactoryresults.16Plantlayoutandsiteconditionsalsomayinfluencethenumberofbasins.Foranysupplywhichrequirescoagulationandfiltrationfortheproductionofsafewater,aminimumoftwobasinsshouldbeprovided.Thegreaterthenumberavailable,thelesswillbetheeffectuponvelocityanddetentionperiodintheremainingbasinsshouldonebeoutofserviceforcleaning,repairs,oranyotherreason.17SizeandShapeofBasinsThemostcommonformsofsedimentationbasinsarecircular,square,orrectangular.Theselectionoftheparticularformorshapeforagivenplantdependsuponareaavailable,conformitywithadjacentstructures,andthetheoriesandexperienceofthedesignengineer.18Themajorityofsedimentationbasinsnowinusearerectangularinshapeandofreinforcedconcreteconstruction.Circularbasinsofeitherconcreteorsteelhavebeenusedwidelyforbothcoagulationandsoftening.19Mostsedimentationbasinsareprovidedwithslopingbottomstofacilita