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1、SewagetreatmentTheobjectiveofsewagetreatmentistoGproduceadisposableeffluentwithoutcausingharmortroubletothecommunitiesandpreventpollution•⑴Sewagetreatment,ordomesticwastewatertreatment,istheprocessofremovingcontaminantsfromwastewaterandhouseholdsewag
2、e,bothrunoff(effluents)anddomestic・1(includesphysical,chemical,andbiologicalprocessestoremovephysical,chemicalandbiologicalcontaminants.Itsobjectiveistoproduceawastestream(ortreatedeffluent)andasolidwasteorsludgesuitablefordischargeorreusebackintothe
3、environment.Thismaterialisofteninadvertentlycontaminatedwithmanytoxicorganicandinorganiccompounds.OriginsofsewageSewageiscreatedbyresidences,institutions,andcommercialandindustrialestablishments.Rawinfluent(sewage)includeshouseholdwasteliquidfromtoil
4、ets,baths,showers,kitchens,sinks,andsoforththatisdisposedofviasewers・Inmanyareas,sewagealsoineludesliquidwastefromindustryandcommerce・Theseparationanddrainingofhouseholdwasteintogreywaterandblackwaterisbecomingmorecommoninthedevelopedworld,withgreywa
5、terbeingpermittedtobeusedforwateringplantsorrecycledforflushingtoilets.Alotofsewagealsoincludessomesurfacewaterfromroofsorhard-standingareas.Municipalwastewaterthereforeincludesresidential,commercial,andindustrialliquidwastedischarges,andmayineludest
6、ormwaterrunoff.Sewagesystemscapableofhandlingstormwaterareknownascombinedsystemsorcombinedsewers・Suchsystemsareusuallyavoidedsincetheycomplicateandtherebyreducetheefficiencyofsewagetreatmentplantsowingtotheirseasonality.Thevariabilityinflowalsoleadst
7、ooftenlargerthannecessary,andsubsequentlymoreexpensive,treatmentfacilities.Inaddition,heavystormsthatcontributemoreflowsthanthetreatmentplantcanhandlemayoverwhelmthesewagetreatmentsystem,causingaspilloroverflow.Itispreferabletohaveaseparatestormdrain
8、systemforstormwaterinareasthataredevelopedwithsewersystems.Asrainfallrunsoverthesurfaceofroofsandtheground,itmaypickupvariouscontaminantsincludingsoilparticlesandothersediment,heavymetals,organiccompounds,animalwaste,andoilandgrease.Somejurisdictions
