给排水专业英语.docx

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1、Unit20SludgeutilizationanddisposalRawsludgefromactivatedsludgetreatmentplantshasbeenapplieddirectlyontoagriculturallandparticularlyintheUnitedKingdom.Thispracticeisconsideredunsatisfactorybecauseofthepresenceofpathogensinthesludgeinhighnumbers.Therehasbeennothoro

2、ughstudy,however,whichhasshownthatthereisanincreaseintheriskofacquiringillnessesassociatedwithpathogensintherawsludgewhenproperhandlingprocedureandnon-entrytothelandfollowingapplicationisobserved.Reuseofcompostedsludgeasasoilconditionerinagricultureandhorticultur

3、ereturnscarbonnitrogen,phosphorusandelementsessentialforplantgrowthbacktothesoil.Lesschemicalfertilizersarerequiredandtheorganiccarbonhelpstoimprovesoilaeration,waterpercolationandrootgrowth.Thenitrogenandphosphorusarealsoreleasedgraduallyforplantuptakecomparedto

4、themoresolublechemicalfertilizers.Thepotentialofleachingofthenutrientstogroundorsurfacewaterbyrainfallrun-offismuchreduced.Pathogensandheavymetalscan,however,limitthereuseofsludge.Pathogensshouldbereducedtolevelsthatdonotposehealthhazardstoworkershandlingthesludg

5、e,potentialhealthhazardsfromthespreadingofhelmintheggsandfromhorticulturalproducecontaminatedbypathogens.Compostingofthesludgetoattainatemperatureof55℃fortwoweeksfollowedbywindrowmaturationproducescompostthatmeetstheseconditions.Stabilizedsludge,whichhasbeendewat

6、eredanddriedonsandbedstoattainalowmoisturecontent,canmeetthesameconditions.Heavymetalsandtoxicchemicalaredifficulttoremovefromsludge.Preventingthesechemicalsfromenteringthewastewaterorsludgebetheaimofwastewatermanagementforsludgeintendedforreuseinageicultureorhor

7、ticultur.Reusemaystillbepossibleforpurposessuchasminesiterehabilitation,highwaylandscapingorforlandfillcover.Sludgethathasbeenconditionedforreuseiscalled„biosolids‟.Conversionofsludge,whichisheavilycontaminatedbyheavymetalsortoxicchemicals,tooilistechnicallyfeasi

8、ble(Enersludgeprocess).Afull-scalepantisoperatinginPerth,WesternAustralia(Bridleetal.,2000).Theconversionisbyapyrolysisprocess,heatingdriedsludgetoahightempera