得利满手册AEROBICBIOLOGICALPROCESSES

1、11AEROBICBIOLOGICALPROCESSES1.ACTIVATEDSLUDGE1.1INSTALLATIONLOADINGANDOPERATIONALCHARACTERISTICSThepurificationefficiencyofanactivatedsludgeplantdependsontwofactorssimultaneously:-fixing,byadsorptionandoxidation,ofthepollutingelementsbythebacterialmass(orbiologicalfloc),-effectiveseparationofthisflocfromthepurifiedinterstitialwater.Intheactivatedsludgereactor,bacterialmassisaccumulatedduetosludgerecycling;sludgeagethusincreaseswiththeavailablebiomassquantityandhasasomewhatslowingeffectonthebact。

2、erialactivity;however,inthedevelopmentphase(seepage297)whichisthephaseofmostofthebacterialflora,thiseffectisnotpredominantand,generallyspeaking,thequantityofpollutionretainedisallthegreaterbecausethebacterialmassisconsiderable.Forcontinuousremovalofthesolublecarbonaceouspollution,thepurificationefficiencyisgreaterthelowertheF/Mratio(seepage296)andthegreaterthesludgeage.Thismightnotbethesameforconcomitantnitrificationorphosphateremoval.Purificationprocessesbyactivatedsludgearethusclassifiedinfami。

3、lies.However,itiscustomarytorelatetheseprocessesnotonlywithF/MratiobutalsowithBODloading.Therearetworeasonsforthis:-therequirementsofclarification-usuallycarriedoutbysettling-makeitnecessarynottoexceedmaximumconcentrationsofSS(g.l-1)oftheactivatedsludgeliquor.ForthelimitsofF/MratiotherearethuscorrespondinglimitsofloadinginBOD5orCOD(kg/m3.d)calculatedonthevolumeofthebiologicalreactor,-aminimumretentiontimeinthebiologicalreactorisnecessarytofacilitatetheChap.11:Aerobicbiologicalprocessesphenomenao。

4、fadsorptionandtodampentheeffectofpeaks,particularlycommoninmunicipaleffluents.Table76summarizestheusualclassificationbyloadingleveloftheprocessesofremovalofcarbonaceouspollutionbyactivatedsludge.Thestatedefficienciesassumethecaseofproperseparationofalltheelementsthatcanbesettledfromtheactivatedsludgeliquor.Table76.Classificationofprocessesusingactivatedsludge.F/MBODloadingSludgeageBOD5removalTypekgBOD5/kg(Cv)indaysefficiencyponSS.dkgBODs/m3.dMWWLowloadingF/M0.15Cv0.4010to30?90%Nitrificationpossi。

5、bleF/M0.07(extendedaeration)Mediumloading0.15F/M0.40.5Cv1.54to10?~80to90%NitrificationpossibleatelevatedtemperaturesHighloading1.2F/M0.41.5Cv31.5to4?80%Veryhighloadings(F/M1.2)aresometimesusedinaninitialroughingstagewherethepollutionisbasicallyremovedbyadsorptionandretainingofparticlesinthebiologicalfloc.Withconcentratedindustrialwastes,purificationefficienciesaregreaterthanthoseindicatedabove.ItiscustomarytocomparetheF/Mratiotothemassofaeratedsludgepresent0.5intheaerationtankalone,becauseitisus。

6、uallyinthisreactorthatmostoftheactivatedsludgeisfoundandthatthemediumisaerobic.However,incertainprocesses,thevolumeofsludgepresentintheclarifiermaybeofthesameorderofmagnitudeasorevengreaterthanthatoftheaeratedsludge.TheprecedingclassificationmustthenbemodifiedFigure363characterizesthedevelopmentofpurificationaccordingtotheF/Mratio.1.Activatedsludge1.2.POSSIBLEARRANGEMENTSOFACTIVATEDSLUDGETANKSIndependentoftheloadingcriteria(andsludgeage),thehydraulicarrangementofthebiologicalreactorandtherelatio。

7、nsbetweenreactorandclarifiermakeitpossibletodistinguishvarioussystemsofactivatedsludgetreatment.1.2.1.PlugflowtankThewastetobetreatedandtherecycledsludgeentermoreorlessatthesamepointattheheadofthetankwhichisarrangedinsuchawayastoformalongchannel(Figure364).Thesubstrateconcentrationsandtheoxygendemandsoftheactivatedsludgeliquorvarythroughoutitsflowpath.Thisiswhytheinstalledoxygenationpowernormallydecreasesfromupstreamtodownstream(taperedaeration)Thistypeoftankistheoldest.Itisusedparticularlyinthe。

8、caseofnitrificationandisespeciallysuitedtolarge.plants.Usuallysizedforconsiderableretentiontimes(5to6hataverageflow),itissometimesusedonahighratebasiswithretentiontimesof1to2handliquorconcentrationsofSSof1to2g.l-1(aprocesscalledmodifiedaeration).Foranyreactionthatisnotzero,theplugflowreactormakesitpossibletoachievethebestpurificationefficiency.However,aperfecthydraulicdesignisimpossibleandwouldleadtoexcessivelycostlyconstruction.Alongitudinaldispersionfactorisunavoidable(seepage288).1.2.2.Comple。

9、telymixedtankTheaimistoobtainacompletelyhomogeneousreactorpresenting,atallpoints,identicalconcentrationsofmicroorganisms,dissolvedoxygenandresidualsubstrate(Figure365).Theraweffluentisimmediatelydispersedinthereactor,andtheinterstitialliquidrepresentsthetreatedeffluent.Nevertheless,thetheoreticalconceptsofcompletemixingarerarelyfullyadheredtoinpractice,particularlywithlargeunits.Theyareonlyachievedpracticallyincertainpackageunits(Oxyrapid).Theadvantageofcompletemixingistolimitoverloadsduetopollu。

10、tionpeaks(daily,forexample).Chap.11:Aerobicbiologicalprocesses1.2.3.ClosedloopbasinsThistechnique(Figure366)issimilartothatofthecompletelymixedone.However,therelativelygreatlengthoftheloop,andtheverylocalizedarrangementoftheaerators,leadtoquiteconsiderablevariationsinthedissolvedoxygencontentthroughoutthebasin.Whentheaeratorsusedareofthehorizontaltype,thereactorisoftencalledanoxidationditch°.Iftheyareoftheverticaltype,itisoftencalledCarrousel.Itisalwayspossibletoconnectseveralbasins。