环境科学与工程毕业设计英文文章

Anaerobicpondstreatmentofstarchwastewater:casestudyinThailandB.K.Rajbhandari,A.P.Annachhatre*EnvironmentalEngineeringandManagement,AsianInstituteofTechnology,P.O.Box4,KlongLuang,Pathumthani12120,ThailandReceivedinrevisedform20January2004;accepted26January2004Availableonline12March2004AbstractAnaerobicpondsareparticularlyeffectiveintreatinghigh-strengthwastewatercontainingbiodegradablesolidsastheyachievethedualpurposeofparticulatesettlementandorganicremoval.Performanceofananaerobicpondsystemfortreatmentofstarchwastewatercontaininghighorganiccarbon,biodegradablestarchparticulatematterandcyanidewasassessedundertropicalclimateconditions.Approximately5000m3/dofwastewaterfromstarchindustrywastreatedinaseriesofanaerobicpondswithatotalareaof7.39hafollowedbyfacultativepondswithanareaof29.11ha.OverallCODandTSSremovalofover90%andCNremovalof51%wasobserved.Activebiomassobtainedfromtheanaerobicpondssedimentsandbulkliquidlayerexhibitedspecificmethano-genicactivityof20.7and11.3mlCH4/gVSSd,respectively.Thecyanidedegradabilityofsludgeatinitialcyanideconcentrationof10and20mg/lweredeterminedtobe0.43and0.84mgCN
/gVSSd,respectively.Aseparatesettlingcolumnexperimentwithstarchwastewaterrevealedthatasettlingtimeofapproximately120minissufficienttoremove90–95%oftheinfluentTSS.
2004ElsevierLtd.Allrightsreserved.Keywords:Anaerobicpond;Cyanidedegradability;Organiccarbon;Settlingcharacteristics;Specificmethanogenicactivity;Starchfactorywastewater1.IntroductionAnaerobicponds(APs)arepopularlyemployedfortreatmentoforganicwastewateremanatingfromvarietyofindustriessuchasfood,pulpandpaper,sugaranddistillery.Anaerobicpondsareparticularlyeffectiveintreatinghigh-strengthwastewaterscontainingbiodegrad-abletotalsuspendedsolids(TSS).Insuchcasestheliquidlayerinanaerobicpondsactasasettlingbasinforthesuspendedsolidswhiletheanaerobicbiodegradationprimarilytakesplaceinpondsediments(Toprak,1994).Anaerobicreactionstakingplaceinthesedimentincludesolubilizationofbiodegradableparticulatematterfol-lowedbyacidogenesis,acetogenesisandmethanogenesis(Parker,1979;Pescod,1996).Thereactionsoccurringinthebulkliquidareoftennegligibleascomparedtothoseinthepondsediments.Thus,anaerobicpondsachieveadualpurposeofsedimentationofparticulatematteraswellasanaerobicconversionoforganics.However,anaerobicpondoperationalsohasmanyintrinsicprob-lemssuchashighlandrequirementsandemissionofobnoxiousandgreenhousegasessuchashydrogensulfide(H2S),carbondioxide(CO2)andmethane(CH4)(Parker,1979;Pescod,1996;Toprak,1997;Paingetal.,2003).Inspiteoftheseproblems,anaerobicpondsarepopularparticularlywhereverlandisabundant(Arthur,1983).Wastewatercomingfromstarchfactoriesisonesuchtypeofwastewater,whichistreatedextensivelyinanaerobicponds.Starchisoftenproducedinmanypartsoftheworldfromtapioca.Tapiocarootscontain20–25%starch.Thestarchextractionprocessessentiallyinvolvespre-processingofroots,followedbystarchextraction,separationanddrying.Theprocessgenerates20–60m3/tonofwastewaterwithalowpHintherange3.8–5.2(EconomicandSocialCommissionforAsiaandThePacific,1982).Thewastewaterishighlyorganicinnaturewithchemicaloxygendemand(COD)upto25,000mg/l(BengtssonandTreit,1994).ThewastewaterconsistsofhighTSScomprisingstarchgranulesintherange3000–15,000mg/l,whicharehighlybiodegradablebynature.Tapiocastarchwastewateralsohashighcyanidecontentupto10–15mg/l,whichishighlytoxic*Correspondingauthor.Tel./fax:[phone].E-mailaddress:[e-mail](A.P.Annachhatre).0960-8524/$-seefrontmatter
2004ElsevierLtd.Allrightsreserved.doi:10.1016/j.biortech.2004.01.017BioresourceTechnology95(2004)135–143toaquaticlifeatconcentrationsofcyanideaslowas0.3mg/lhavebeenreportedascauseforamassivefishkill(BengtssonandTreit,1994).Problemsrelatedtowaterpollutionarereportedtobeserious.Theacidicnatureofwastewatercanharmaquaticorganismsandreducetheself-purificationcapacityofthereceivingstream.Suspendedsolidspresentinthewastewatercansettleonthestreambedandspoilfishbreedingareasinthestream.Sincethesesolidsareprimarilyorganicinnature,theydecomposeeasilyandthusdeoxygenatethewater.Similarly,highbiochemicaloxygendemand(BOD)ofthewastewateralsocancauserapiddepletionofoxygencontentinthereceivingwaterbodyandpromotethegrowthofnui-sanceorganisms.Waterpollutioncausedbytapiocastarchproductionhasbeenreportedasaseriousprob-leminmanyAsiancountries,particularlyinThailand(Kiravanich,1977)andinIndia(Padmajaetal.,1990).Tapiocaalsocontainsboundcyanideasanaturalde-fensemechanism.Duringthestarchmanufacturingprocess,boundcyanideintheformoflinamarinandlotaustralinfromtapiocarootsishydrolyzedbytheenzymelinamarasewithdecompositiontohydrogencyanide(HCN),whichfindsitswayintothewastewater.Cyanidecontainingstarchwastewatercanbeeffectivelydetoxifiedinanaerobicprocesses(AnnachhatreandAmornkaew,2000).Upflowanaerobicsludgeblanket(UASB)processesareeffectiveintreatingstarchwaste-water(AnnachhatreandAmatya,2000),particularly,inremovingcyanide(AnnachhatreandAmornkaew,2001).Adaptationbymethanogenstocyanideconcen-trationsof5–30mg/lhasbeenreportedinliterature(Fedoraketal.,1986;Harperetal.,1983).Thus,intreatingt