环境生物技术--3--4

环境生物技术沈阳大学07环境工程2009-9-gying3ActivatedSludgeProcess•3.1.1Single-stageprocess•Fig.Flowdiagramofanactivatedsludgeplant.3ActivatedSludgeProcess•3.1.1Single-stageprocess•Anactivatedsludgeplantischaracterizedbyfourelements:•Anaerationtankequippedwithappropriateaerationequipment,inwhichthebiomassismixedwithwastewaterandsuppliedwithoxygen.•Afinalclarifier,inwhichthebiomassisremovedfromthetreatedwastewaterbysettlingorothermeans.•Continuouscollectionofreturnsludgeandpumpingitbackintotheaerationtank.•Withdrawalofexcesssludgetomaintaintheappropriateconcentrationofmixedliquor.3.1.2Two-stageprocess•Thetwo-stageprocesshasseveraladvantages.Harmfulsubstancescanberemovedinthefirststage,whichisimportantforthetreatmentofindustrialwastewater;andinthelow-loadsecondstage,duetothehighsludgeagemicroorganismscanbemaintainedthatareabletoremoveslowlybiodegradableorganicsortooxidizeammonia.Furthermore,bulkingsludgeisonlyrarelyobservedineitherstage.•Thedisadvantagesarethatabouttwiceasmanyclarifiersareneededasintheone-stageprocessandthatnitrogenremoval,aswellasenhancedbiologicalphosphateremoval,maybeinhibitedowingtomissingorganics,whichareremovedinthefirststage.•3.1.3Singlesludgecarbon,nitrogen,andphosphorousremoval•Intheearly1960sthreedifferentmethodsfornitrogenremovalweredemonstrated:•post-denitrification;•pre-anoxiczonedenitrification;•simultaneousdenitrification;•Todaymostnewerplantsarebuiltwithmeansforenhancedbiologicalphosphateremovaland/orequipmentforsimultaneousprecipitation.•3.1.4Sequencingbatchreactor(SBR)process•Becauseofthedevelopmentofreliableautomaticprocesscontrolandaerationsystems,theSBRprocesstodayisaperfectalternativetotheconventionalactivatedsludgeprocess.Thereactorisusuallyequippedwithanaerationsystem,amixingdevice,adecantertowithdrawtreatedwastewater,anexcesssludgeremovaldevice,andtheprocesscontrolsystem.Wastewatertreatmentisperformedbyatimeseriesofprocessphases(fill,react,settle,decant).Asintheconventionalactivatedsludgeprocess,theSBRprocessiscapableofcarbon,nitrogen,andphosphorousremoval.Itisusedforbothindustrialandmunicipalwastewater.•3.1.5Specialdevelopments•3.1.5.1Pureoxygen-activatedsludgeprocess•3.1.5.2Attachedgrowthmaterialinactivatedsludgeaerationtanks•3.1.5.3High-ratereactors•3.1.5.4Membraneseparationofmixedliquor•3.2Technologicalandmicrobiologicalaspects•3.2.1Wastewatercharacteristics•Wastewatertobetreatedcancontainorganiccarbonpredominantlyasasinglesolublesubstance(e.g.,analcohol),asamixtureofsolublesubstances,orasamixtureofsolidsandnumeroussolubleorganicsubstances.Manyindustrialwastewatersaremixturesofsolubleorganicsubstances,butsomemaycontainmainlyoneorganicsubstance.Municipalwastewaterandwastewaterfrommostfoodprocessingindustriesisalwaysamixtureofsolubleandparticulateorganicmatter.•Microbialdegradationoforganiccarbonrequirescertainamountsofnitrogen,phosphorous,calcium,sodium,magnesium,iron,andotheressentialtraceelementstogrowbiomass.Inindustrialwastewatertreatmentplants,missingelementshavetobeadded.Sincedomesticwastewatercontainsallthenecessaryelementsinexcess,itisadvantageoustotreatspecialindustrialwastewatertogetherwithmunicipalwastewater.•Theconcentrationoforganicmatterinwastewaterismeasuredasthebiochemicaloxygendemand(BOD5,orBOD20,incubationperiodof5or20d,nitrificationinhibited),chemicaloxygendemand(COD),ortotalorganiccarbon(TOC).•3.2.6Environmentalfactors•3.2.6.1Dissolvedoxygen•Thedissolvedoxygenconcentration(DO),thepH,andtoxicsubstancesinthewastewaterareconsideredasenvironmentalfactorsthatmayinhibitthebiologicalreactions.•3.2.6.2AlkalinityandpH•3.2.6.3ToxicsubstancesThanks!3.3设备结构3.3PlantConfigurations3.3.1TypicalTanksformixingandaerationMixingtanksfordenitrificationcanbesquare,rectangular,orcircularandhavemixersinthecenterorpropellers（螺旋桨）(Fig.3.12).Rectangulartankscanbevisualizedasaseriesofsquaretanks.Inclosed-loop,tankseitherpropellersorverticalshaft（轴）impellers（推动器）maintainthecirculatingflow.Fine-bubblediffused-airaeration(曝气)systemscanbeinstalledinalmostanytypeoftank.Tanksforverticalshaftsurfaceaeratorsareeithersquareorrectangularinwhichthelengthisamultipleofthewidth(Fig.3.13).Tanksforcyclic（循环）aerationarepreferably（更好的，更可取的）circularorofclosedlooptype.Aerationequipmentaswellasappropriatemixersmustbeinstalled.Mixingcanalsobeperformedbyrotatingbridgesonwhichdiffusersaremounted.(Fig.3.14).Sincetheaerationisswitchedoffcyclically（循环的）,onlynon-cloggingaerationsystems,e.g.,membranediffusersforfinebubbleaerationareappropriate.Simultaneousnitrificationanddenitrificationinpracticeisperformedmainlyinclosed-looptanksequippedwithhorizontal-axis（水平的，轴）surfaceaerators,e.g.,mammoth（巨大的）rotors（旋翼）orverticalshaftsurfaceaerators,asinthecarousel（转盘）process.Simultaneousdenitrificationcanalsobeperformedwithairdiffusersarrangedin‘fields’inclosed-looptanks.3.3.2CarbonremovalprocessesInindustrializedcountriestoday,removalofbothcarbonandnitrogenisincreasinglyrequired;however,indevelopingcountriesandforpretreatmentofindustrialandtradewastewater,removaloforganiccarbononlyisimportant.Indesigning,provisionsshouldbemadef