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发布时间：2023-12-04 21:08:45
ReducingtheHeavyMetalContentofSewageSludgebyAdvancedSludgeTreatmentMethodsABSTRACTWaste-activatedsludge(WASprocessesarekeytechnologiestotreatwastewater:theireffluentscanmeetstringentdischargestandards,thusensuringaminimumresidualimpactontheaquaticenvironment.Thepresenceofheavymetalsintheexcesssludgeposes,however,seriousproblems,andconsiderablyhampersthefinaldisposalalternatives,especiallyintheagriculturaluse(soilimprovement/amendment.ThisarticlestudiestheeffectofthermalhydrolysisandFenton’speroxidationontheheavymetalcontentofthedewateredsludge.AcidthermalhydrolysisreducestheheavymetalcontentinthefiltercakeexceptforCu,Hg,andPb.AlkalinethermalhydrolysisreleasesCu,Pb,andCr.Fenton’speroxidationtransfersCd,Cu,andNifromthefiltercakeintothefiltrate.Landapplicationoftheresidualcakecanhencebereconsidered.INTRODUCTIONWASTE-ACTIVATEDSLUDGE(WASprocessesarekeytechnologiestotreatwastewater:theireffluentscanmeetstringentdischargestandards,thusensuringaminimumresidualimpactontheaquaticenvironment.Throughtheirmicrobialactivity,thesebiologicalprocessesproducehugeamountsofWAS,nowcommonlycalledbiosolids.ThisexcesssludgeisaninevitabledrawbackinherenttotheWASprocess.IncreasingamountsofWAShavetobedealtwithdueto(1thehigherwastewatercollectionrates,(2thereliabilityandefficiencyofwastewater
treatmentplants,and(3thewidespreadapplicationofdenitrificationanddephosphatation.Thepresenceofheavymetalsintheexcesssludgeposes,however,seriousproblems,sincetheyareamongthemostimportantfactorsinassessingthefinaldisposalalternativesofthesludge,forexample,theywillaccumulateintheflyashintheeventofincineration,canbereleasedthroughleachinginlandfills,ormaypreventlandapplication.Manycountrieshaveimposedlegalrestrictionsconcerningtheheavymetalcontent,whenusingthesludgeforlandapplication(e.g.,agriculturaluseasfertilizerorsoilamendment,sincehighconcentrationsinthesludgemayresultinheavymetalaccumulationincultivatedsoils.IntheEuropeanUnion,themaximumacceptableconcentrationsarefixedbytheDirective86/278/EECoftheEuropeanCommission(CommissionoftheEuropeanCommunities,1986.Mostcountriesapply,however,amorestringentlegislation.InFlanders,thestandardsaredescribedinVLAREA(FlemishGovernment,1997.BothEuropeanandFlemishlegalstandards,aswellastheaverageconcentrationsofheavymetalsinmunicipalsewagesludgeinFlanders(Aquafin,2004,arepresentedinTable1.SomemetalspresentintheWASdonotcomplywiththeselegalstandards,thusnecessitatingtheapplicationoflesssustainableandmoreexpensivedisposalroutes.Heavymetalsinsludgecannotberemovedbycommonsludgetreatmentmethodssuchasaerobicoranaerobicdigestion.Someadvancedsludgetreatmentprocesses(ASTwererecentlyconfirmedashavingthepotentialtoenhancethedewaterabilityofthesludge.Themostpromisingtechniquesincludeacidandalkalinethermalhydrolysis(Neyensand
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