环境工程专业英语unit14Word文档下载推荐.docx
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环境工程专业英语unit14Word文档下载推荐.docx
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环境工程专业英语unit14@#@3BiologicalWastewaterTreatment@#@Applicationofmicrobialdegradationandremovalofundesirableconstituentsinindustrialandmunicipalwastesisnotanewconcept.Itiscommonlyusedprocessforgeneralwastewatertreatmentactivitiesandhasbeenformanyyears.Astheawarenessofchemicalcontaminationoftheenvironment,muchresearchonbiologicaldegradationoftoxicchemicalshasoccurred.Amongtherangeoftreatmenttechnologies,biologicaldegradationranksamongthemosteffective.Itsmanagementandapplicationisenhancedbythepotentialtoapplybiologicaltreatmentinsequencewithotherchemicalandthermalprocesses.@#@Activatedsludge@#@Theactivatedsludgeprocessisstypicaltypeofsuspendedgrowthbiologicaltreatmentsystemandprobablythemostwidelyusedbiologicalprocessforthetreatmentoforganicandindustrialwastewaters.However,itcanonlytreataqueousorganicwastestreamshavinglessthan1%suspendedsolidcontent,andcannottolerateshockloadingofconcentratedorganics.Therefore,thewastestreamenteringthisprocesswillusuallyhavepassedthroughapretreatmentprocesswhichincludesaclarifier(primaryclarifier)andanequalizationbasin.Theprimaryclarifierisusedforremovalofgrit,oilyandfattymaterialandgrosssolidmaterial,whiletheequalizationbasinisusedtodampenwastewaterflowvariationsandtoprovidemoreuniformorganicloadingtotheactivatedsludgesystem.@#@Activatedsludgeprocessareusedtotreatmunicipalandindustrialwastessincetheyareversatile,flexible,andcanbeusedtoproduceaneffluentofdesiredqualitybyvaryingprocessparameters.Theprocesswasso-namedbecauseitproducesanactivemassofmicroorganismscapableofaerobicallystabilizingawaste.Manyversionsofthebasicprocessexistbutallarefundamentallysimilar.@#@Thetermactivatedsludgeisappliedtoboththeprocessandtothebiologicalsolidsinthetreatmentunit.Themixedliquorsuspendedsolidsoractivatedsludgecontainsavarietyofheterotrophicmicroorganismssuchasbacteria,protozoa,fungi,andlargermicroorganisms.Thepredominanceofaparticularmicrobialspeciesdependsuponthewastethatistreatedandthewayinwhichtheprocessisoperated.@#@Theactivatedsludgeprocessiscurrentlythemostwidelyusedbiologicaltreatmentprocess.Thisispartlytheresultofthefactthatrecirculationofthebiomass,whichisanintegralpartoftheprocess,allowsmicroorganismstoadapttochangesinwastewatercompositionwitharelativelyshortacclimationtimeandalsoallowsagreaterdegreeofcontrolovertheacclimatedbacterialpopulation.@#@Anactivatedsludgesystemconsistsofanequalizationbasin,asettlingtank,anaerationbasin,aclarifier,andasludgerecycleline.Wastewaterishomogenizedinanequalizedbasintoreducevariationsinthefeed,whichmaycauseprocessupsetsofthemicroorganismsanddiminishtreatmentefficiency.Settleablesolidsarethenremovedinasettlingtank.@#@Next,wastewaterentersanaerationbasin,whereanaerobicbacterialpopulationismaintainedinsuspensionandoxygen,aswellasnutrients,areprovide.Thecontentsofthebasinarereferredtoasthemixedliquor.Oxygenissuppliedtotheaerationbasinbymechanicalordiffusedaeration,whichalsoaidsinkeepingthemicrobialpopulationinsuspension.Themixedliquoriscontinuouslydischargedfromtheaerationbasinintoaclarifier,wherethebiomassisseparatedfromthetreatedwastewater.Aportionofthebiomassisrecycledtotheaerationbasintomaintainanoptimumconcentrationofacclimatedmicroorganismsintheaerationbasin.Theremainderoftheseparatedbiomassisdischargedor“wasted”,Thebiomassmaybefurtherdewateredonsludgedryingbedsorbysludgefiltrationtodisposal.Theclarifiedeffluentisdischarged.@#@Therecycledbiomassisreferredtoasactivatedsludge.Theterm“activated”isusedbecausethebiomasscontainslivingandacclimatedmicroorganismsthatmetabolizeandassimilateorganicmaterialatahigherratewhenreturnedtotheaerationbasin.Thisoccursbecauseofthelowfood-to-microorganismratiointhesludgefromtheclarifier.@#@Forthetreatmentofindustrialwastewater,supplementalnutrientsourcesareoftenneededtoprovidesufficientnitrogenandphosphorus.Inmostcases,nitrogenisaddedasammoniaandphosphorusasphosphoricacid.AproperpHrange(6to8)andssufficientdissolvedoxygenconcentration(aminimumofIto2mg/L)mustalsobemaintainedintheaerationbasintosupportahealthyandactivesystem.@#@Theaerationbasinhydraulicretentiontime(HRT)andsludgeresidencetime(SRT)areimportantoperationalfactors.HRTisdefinedastheratioofthevolumeofaerationtanktotheinfluentliquidflowrate,andSRTisthetotalamountofsludgeinthesystemdividedbytherateofsludgeleavingthesystemaswaste.Suffic
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