Studyofmunicipalwastewatertreatmentwithoystershell

StudyofmunicipalwastewatertreatmentwithoystershellasbiologicalaeratedfiltermediumYao-XingLiu,TongOuYang⁎,Dong-XingYuan,Xiao-YunWuStateKeyLaboratoryofMarineEnvironmentalScience,EnvironmentalScienceResearchCenter,XiamenUniversity,Xiamen361005,ChinaabstractarticleinfoArticlehistory:Received1September2009Receivedinrevisedform25November2009Accepted1December2009Availableonline8January2010Keywords:BiologicalaeratedfilterOystershellMunicipalwastewaterpHTotalphosphorusOystershellandplasticballwereappliedasthemediaofbiologicalaeratedfilters(BAF)totreatmunicipalwastewaterintwolabscaleupflowBAFs.TheresultsindicatedthatoystershellBAFandplasticballBAFhadaveragechemicaloxygendemand(COD)removalsof85.1%and80.0%,whenhydraulicretentiontime(HRT)waslongerthan4h,and65.7%and68%withHRTof2h,respectively.Intermsofremovingammonianitrogen(NH3-N),oystershellBAFandplasticballBAFhadaverageremovalsof98.1%and93.7%forHRTlongerthan4h,and47.2%and65.1%forHRTof2h,respectively.Totalphosphorus(TP)removalsofoystershellBAFwereincreasedto79.9%and90.6%asthepHincreasedto9and10,respectively,whilenoimprovementwasobservedforplasticballBAF.TheeffluentpHofoystershellBAFwashigherandbufferedcomparedwiththatoftheinfluent,mainlyduetotheCaCO3releasedfromtheshell.TheoystershellmayalsobethemainreasontosupporttheBAFahigherNH3-NremovalefficiencywhenHRTwaslongerthan4h,comparedwithplasticballBAF.CrownCopyright©2009PublishedbyElsevierB.V.Allrightsreserved.1.IntroductionBiologicalaeratedfilter(BAF)isanovel,flexibleandeffectivebioreactorthatprovidesasmallfootprintprocessatvariousstagesofwastewatertreatment[1].BAFwasfirstdevelopedinEuropeandthenwidelyappliedallovertheworldasawastewatertreatmentsystemduetoitsadvantagescomparedtoothersystems[2].StenselandReiber[3]foundthatthelandrequiredforaBAFsystemwasapproximatelyonlyonefifthofthatneededforplasticmediumtricklingfiltersandonetenthofthatneededforactivatedsludgeplants.BAFtechnologyisbasedontheprincipleofbiofiltrationthroughasubmergedgranularmediumthatservestwopurposes:biologicalconversionoforganicmatterbythebiomassattachedontothelargesupportmediumsurfaceandphysicalremovalofsuspendedparticlesbymediumfiltration.Asapromisingtechnologyforthedecentralisatedwastewatertreatment,BAFremovesorganicmatter,solidsandNH3-Ninonereactorunit.Itcanbeutilizedatbothsecondaryandtertiarystagesofwastewatertreatment,wastewaterreclamationengineeringandpretreatmentprocessofnewlydevel-opedmembranetechniques,particularlywhenlowlandusageisrequiredinurbanareas[4].ForemostBAFs,asdefinedbyStephenson[5],containagranularmediumthatprovidesalargesurfaceareaperunitvolumeforbiofilmdevelopment.Theinitialpurposeoftheseprocesseswastoobtaincarbonoxidationandsolidfiltration[6].Inrecentyears,severaltechnologiesusingBAFhavebeendevelopedtotreatwastewaterfromslaughterhouses,pulp,millindustries[7,8],andrefractorywastewatersuchastextileandoilfieldwastewater[6,9].Inaddition,someBAFcombinationtechniqueshavebeenstudiedtotreatformalinwaste-waterandremovenitrogenfromlowcarbon-to-nitrogenwastewater[10,11].Severalmodelstudieshavebeencarriedouttoimprovetheperformanceandtheoreticalknowledge[12,13].MediumselectionisimportantforBAFtoachieveeffluentqualityrequirements.Themediaplayakeyroleinmaintainingahighamountofactivebiomassandavarietyofmicrobicpopulations.Themostfrequentlystudiedbiofilmsupportmediaincludeclay-,schist-orplastic-basedonesofvarioustypes,suchaspolyethylene,polystyrene,andpolyesterene[14].Oystershellsarewasteproductfrommaricultureandcauseamajordisposalproblemincoastalregions,e.g.southeastChina.Shellfish-farmingisalargepartoftheregionaleconomy,sincethecustomoftakingshellfishasamajorpartofthedietcreatesalargemarketofmarineproducts.Alargeamountofoystershellisproducedeveryyear.Shellfishfarmshavefacedtotheproblemofdisposingoystershellwaste.Oystershellwastedumpedintocoastalwaterorreclaimedlandproducesapotentsmellanddisservessurroundingenvironments.Someofthewasteoystershellsareusedaslimestoneinfertilizersandchickenfeed,buttheusagesarelimited.Thewasteoystershellsleadtosevereproblemofsolidwastepollution.Thus,recyclehasarisenasanimminentissueinmaricultureareas.Theidealsolutionistoconvertthewasteoystershellstoaproductthatisbothbeneficialandeconomicallyviable.Desalination254(2010)149–153⁎Correspondingauthor.Fax:[phone].E-mailaddress:[e-mail](T.O.Yang).0011-9164/$–seefrontmatter.CrownCopyright©2009PublishedbyElsevierB.V.Allrightsreserved.doi:10.1016/j.desal.2009.12.003ContentslistsavailableatScienceDirectDesalinationjournalhomepage:[15].TheshellssupplysufficientalkalinitytoenhancethedecreasingpHcausedbynitrificationinBAF.Oystershellisalsogoodforremovingphosphorusfromwastewaterbyproducingcalciumphosphateprecip-itation.Moreover,itshighroughnesssurfacemakesthemicroorganismsg