污水处理的英文文献中英文翻译Word下载.docx
《污水处理的英文文献中英文翻译Word下载.docx》由会员分享,可在线阅读,更多相关《污水处理的英文文献中英文翻译Word下载.docx(25页珍藏版)》请在冰点文库上搜索。
Keywords:
A2Oreactor;
MBR;
Nutrientremoval;
TMP
1.Introduction
Excesssludgereductionandnutrientsremovalarethetwoimportantproblemsassociatedwithwastewatertreatmentplant.MBRprocesshasbeenknownasaprocesswithrelativelyhighdecayrateandlesssludgeproductionduetomuchlongersludgeageinthereactor(Wen
etal.,2004).SludgeproductioninMBRisreducedby28-68%,dependingonthesludgeageused(Xiaetal.,
2008).However,minimizingthesludgeproductionbyincreasingsludgeageislimitedduetothepotentialadverseeffectofhighMLSSconcentrationsonmembrane(Yoonetal.,2004).ThisproblemcanbesolvedbyintroducingsludgedisintegrationtechniqueinMBR(Youngetal.,2007).Sludgedisintegrationtechniqueshavebeenreportedtoenhancethebiodegradabilityofexcesssludge(VlyssidesandKarlis,2004).Inoverall,thebasisforsludgereductionprocessesiseffectivecombinationofthemethodsforsludgedisintegrationandbiodegradationoftreatedsludge.Advancesinsludgedisintegrationtechniquesofferafewpromisingoptionsincludingultrasound(Guoetal.,2008),pulsepower(Choietal.,2006),ozone(Weemaesetal.,2000),thermal(Kimetal.,2003),alkaline(Lietal.,2008)acid(Kimetal.,2003)andthermochemical
(VlyssidesandKarlis,2004).Amongthevariousdisintegrationtechniques,thermochemicalwasreportedtobesimpleandcosteffective(WeemaesandVerstraete,1998).Inthermal-chemicalhydrolysis,alkalisodiumhydroxidewasfoundtobethemosteffectiveagentininducingcelllysis(Rockeretal.,1999).
Conventionally,thenutrientremovalwascarriedoutinanA2Oprocess.Ithasadvantageofachieving,nutrientremovalalongwithorganiccompoundoxidationinasinglesludgeconfigurationusinglinkedreactorsinseries(Tchobanoglousetal.,2003).Thephosphoroesremovalhappensbysubjectingphosphorousaccumulatingorganisms(PAO)bacteriaunderaerobicandanaerobicconditions(AkinandUgurlu,2004).TheseoperatingproceduresenhancepredominancePAO,whichareabletouptakephosphorousinexcess.Duringthesludgepretreatmentprocessestheboundphosphorouswassolubilisedanditincreasesthephosphorous
concentrationintheeffluentstream(Nishimura,2001).So,itisnecessarytoremovethesolubilisedphosphorusbeforeitentersintomainstream.Besides,thereisagrowingdemandforthesustainablephosphorousresourcesintheindustrializedworld.Inmanydevelopedcountries,researchesarecurrentlyunderwaytorecoverthephosphoroesboundinthesludge'
sofenhancedbiologicalphosphorusremovalsystem(EBPR).Thereleasedphosphorouscanberecoveredinusableproductsusingcalciumsaltsprecipitationmethod.Keepingthisfactinmind,inthepresentstudy,anewadvancedwastewatertreatmentprocessisdevelopedbyintegratingthreeprocesses,whichare:
(a)thermochemicalpretreatmentinMBRforexcesssludgereduction(b)A2Oprocessforbiologicalnutrientremoval(c)Precoverythroughcalciumsaltprecipitation.Theexperimentaldataobtainedwerethenusedtoevaluatetheperformanceofthisintegratedsystem.
2.Methods
2.1.Wastewater
Thesyntheticdomesticwastewaterwasusedastheexperimentalinfluent.Itwasbasicallycomposedofamixedcarbonsource,macronutrients(NandP),analkalinitycontrol(NaHCO3)andamicroelementsolution.Thecompositioncontained(/L)210mgglucose,200mgNH4C1,220mgNaHCO3,22一34mgKH2PO4,microelementsolution(0.19mgMnCl24H20,0.0018mgZnCl22H2O,
0.022mgCuCl22H2O,5.6mgMgSO47H2O,0.88mgFeCl36H2O,
1.3mgCaCl2·
2H2O).Thesyntheticwastewaterwaspreparedthreetimesaweekwithconcentrationsof210±
1.5mg/Lchemicaloxygendemand(COD),40±
1mg/Ltotalnitrogen(TN)and5.5mg/Ltotal
phosphorus(TP).
2.2.A2O-MBR
TheworkingvolumeoftheA2O-MBRwas83.4L.Abafflewasplacedinsidethereactortodivideitintoanaerobic(8.4L)anoxic(25
L)andaerobicbasin(50L).Thesyntheticwastewaterwasfeedintothereactorataflowrateof8.4L/h(Q)usingafeedpump.Aliquidlevelsensor,plantedinaerobicbasinofA2O-MBRcontrolledtheflowofinfluent.TheHRTofanaerobic,anoxicandaerobicbasinswere1,3and6h,respectively.Inordertofacilitatenutrientremoval,thereactorwasprovidedwithtwointernalrecycle(1R).IRl(Q=1)connectsanoxicandanaerobicandIR2(Q=3)wasbetweenaerobicandanoxic.Anaerobicandanoxicbasinswereprovidedwithlowspeedmixertokeepthemixedliquidsuspendedsolids(MLSS)insuspension.Intheaerobiczone,diffuserswereusedtogenerateairbubblesforoxidationoforganicsandammonia.Dissolvedoxygen(DO)concentrationintheaerobicbasinwasmaintainedat3.5mg/1andwasmonitoredcontinuouslythroughonlineDOmeter.Thesolidliquidseparationhappensin
aerobicbasinwiththehelpoffiveflatsheetmembraneshavingaporesizeof0.23pm.Theareaofeachmembranewas0.1m2.Theywereconnectedtogetherbyacommontube.Aperistalticpump
wasconnectedinthecommontubetogeneratesuctionpressure.Inthecommontubeprovisionwasmadetoaccommodatepressuregaugetomeasuretransmembranepressure(TMP)duringsuction.Thesuctionpumpwasoperatedinsequenceoftiming,whichconsistsof10minswitchon,and2minswitchoff.
2.3.Thermochemicaldigestionofsludge
MixedliquorfromaerobicbasinofMBRwaswithdrawnattheratioof1.5%ofQ/dayandsubjectedtothermochemicaldigestion.ThermochemicaldigestionwascarriedoutatafixedpHof11(NaOH)
andtemperatureof75℃for3h.Afterthermochemicaldigestion
thesupernatantandsludgewereseparated.Thethermo-chemicallydigestedsludgewasamenabletofurtheranaerobicbio-degradation(VlyssidesandKarlis,2004),soitwassenttotheanaerobicbasinoftheMBR
2.4.Phosphorusrecovery
Limewasusedasaprecipitanttorecoverthephosphorousinthesupernatant.Aftertherecoveryofprecipitantthecontentwassentbacktoanoxictankasacarbonsourceandalkalinitysupelementfordenitrification.
2.5.Chemicalanalysis
COD,MLSS,TP,TNoftherawandtreatedwastewaterwereanalyzedfollowingmethodsdetailedin(APHA,2003).Theinfluentandeffluentammoniaconcentrationwasmeasuredusinganion-selectiveelectrode(TheretoOrion,Model:
95一12).Nitrateinthesamplewasanalyzedusingcadmiumreductionmethod(APHA,2003).
3.Resultsanddiscussion
Fig.1presentsdataofMLSSandyieldobservedduringtheoperationalperiodofthereactor.OneoftheadvantagesofMBRreactorwasitcanbeoperatedinhighMLSSconcentration.ThereactorwasseededwithEBPRsludgefromtheKiheung,sewagetreatmentplant,Korea.ThereactorwasstartupwiththeMLSSconcentrationof5700mg/L.Itstartstoincreasesteadilywithincreaseinperiodofreactoroperationandreachedavalueof8100mg/Londay38.Fromthenonwards,MLSSconcentrationwasmaintainedintherangeof7500mg/LbywithdrawingexcesssludgeproducedandcalledrunI.Theobservedyields(Yobs)forexperimentswithoutsludgedigestion(runI)andwithsludgedigestionwerecalculatedand
giveninFig.1.TheYobsforrunIwasfoundtobe0.12gMLSS/gCOD.Itwascomparativelylowerthanavalueof0.4gMLSS/gCODreportedfortheconventionalactivatedsludgeprocesses(Tchoba-noglousetal.,2003).ThedifferenceinobservedyieldofthesetwosystemsisattributedtotheirworkingMLSSconcentration.AthighMLSSconcentrationtheyieldobservedwasfoundtobelow(Visva-nathanetal.,2000).AsaresultofthatMBRgeneratedlesssludge.ThepresentlyusedMLSSranges(7.5一10.5g/L)areselectedonthebasisoftherecommendationbyRosenbergeretal.(2002).Intheirstudy,theyreportedthatthegeneraltrendofMLSSincreaseonfoulinginmunicipalapplicationsseemstoresultinnoimpactatmediumMLSSconcentrations(7一12g/L).
ItisevidentfromthedatathattheCODremovalefficiencyofA2Osystemremainsunaffectedbeforeandaftertheintroductionofsludgedigestionpractices.Atestanalysisshowedthatthedifferencesbetweentheperiodwithoutsludgedigestion(runI)andwithsludgedigestion(runIIandIII)arenotstatisticallysignificant.
However,ithasbeenreportedthat,inwastewatertreatmentprocessesincludingdisintegration-inducedsludgedegradation,theeffluentwaterqualityisslightlydetonatedduetothereleaseofnondegradablesubstancessuchassolublemicrobialproducts(Ya-suiandShibata,1994;
Salcaietal.,1997;
Yoonetal.,2004).Duringthestudyperiod,CODconcentrationintheaerobicbasinofMBRwasintherangeof18-38mg/Landcorrespondingorganicconcentrationintheeffluentwasvariedfrom4to12mg/L.Fromthisdataitcanbeconcludedthattheme