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BiosorptioncharacteristicsofextracellularpolymericsubstanceEPSproducedbyRhizobiumradiobacterforremovalofCuIIandMnIIionsformaqueoussolutionsLiLiWanga,b,FangMaa,b,ShanShanFenga,b,DeZhiSunb,c,BingYua,b,JieXinga,baStateKeyLaboratoryofUrbanWaterResourceandEnvironment,Harbin,150090,ChinabDepartmentofMunicipalandEnvironmentalEngineering,HarbinInstituteofTechnologycCollegeofEnvironmentalScienceandEngineering,BeijingForestryUniversity,Beijing100083,Chinaemailliilive163.comAbstractThispaperdealswiththeextracellularpolymericsubstanceEPSofRhizobiumradiobacterF2usedasanovelbiosorbenttoremoveCuIIandMnIIionsfromaqueoussolutions.TheCuIIandMnIIionsbiosorptioncharacteristicsoftheEPSwereexaminedasafunctionofinitialpH,contacttimeandEPSconcentration.TheproperpHoftheaqueoussolutionwasfoundtobe6.0forboththebiosorptionofCuIIandMnII.BiosorptionequilibriumtimesofCuIIandMnIIwereachievedin1.0h.ThemaximumbiosorptioncapacitiesunderoptimumconditionsofCuIIandMnIIontheEPSweredeterminedtobe45.30±1.62mg/gand28.86±1.28mg/g,respectively.ThefitnessofthebiosorptiondataforLangmuirandFreundlichisothermmodelswasinvestigated.ItwasfoundthatbiosorptionofCuIIandMnIIionsontotheEPSwerebettersuitabletoLangmuirthanFreundlichisothermmodel.CompetitivebiosorptionofMnIIandCuIIionswasalsoinvestigatedtodeterminetheselectivityofthebioflocculant.KeywordsbiosorptionextracellularpolymericsubstanceEPSCuIIMnIIcompetitivebiosorptionI.INTRODUCTIONHEADING1Waterandwastewaterscontaminatedbyheavymetalshaveresultedinadverseimpactonpublichealthandeconomy1,andexposuretoheavymetalsevenattracelevelsisbelievedtobeariskforhumanbeings2.Inthepastdecadesvariousprocesseshavebeendevelopedtotreatsuchwatersincludingchemicalprecipitation,ionexchange,adsorptionandreverseosmosis3.However,thesemethodsaresometimesrestrictedbecauseoftechnicaland/oreconomicalconstraints4.Biosorptionisconsideredasanalternativeprocessfortheremovalofheavymetals,metalloidspecies,compoundsandparticlesfromaqueoussolutionbybiologicalmaterials5.Comparedwithconventionalmethodsfortheremovaloftoxicmetalsfromwastewater,thebiosorptionprocessofferspotentialadvantagessuchaslowoperatingcost,minimizationofthevolumeofchemicaland/orbiologicalsludgetobedisposedof,andhighefficiencyindetoxifyingverydiluteeffluents6.ThispaperwascarriedouttoinvestigatetheEPSproducedbycultureofRhizobiumradiobacterF2asabiosorbentfortheremovalofMnIIandCuIIfromaqueoussolutions.TheoptimumbiosorptionconditionsweredeterminedsuchasinitialpH,contacttimeanddosageoftheEPS.Thesuitablebiosorptionisothermwasputforwardbasedonthebiosorptiondata.Inaddition,thebiosorptionperformanceoftheEPSinbinarymetalsolutionsystemswasalsoexamined.Thechoiceofmetalswasmaderegardingtheirindustrialuseandpotentialpollutionimpact.Cuisnotacutelytoxictohumansbutitsextensiveuseandincreasinglevelsintheenvironmentmaycauseserioushealthproblems7.MnremovalisoneoftheproblemsinusinggroundwatersinceMnisacommonelementingroundwater.ElevatedlevelsofMnindrinkingwaterareconsideredundesirable.Whenwaterisexposedtoair,MnIIisoxidizedtoMnIV.TheMnIVprecipitatecanstainhouseholdutensilsandclothesandmayimpartametallic,bitter,astringentormedicinaltastetothewater8.II.METHODSA.MicroorganismsStrainF2wasoriginallyscreenedfromsoilbyStateKeyLaboratoryofUrbanWaterResourceandEnvironmentSKLUWREandidentifiedasRhizobiumradiobacter.B.PreparationoftheEPSofF2Thecompositionofproductionmediumwasasfollowsperliter10gglucose,5gK2HPO4,2gKH2PO4,0.5gpeptone,0.5gurea,0.2gMgSO47H2O,and0.2gNaCl.CorrelativedetailsweredescribedinapreviouspaperbyZhuetal.9.National863programSQ2009AA06XK14824129781424447138/10/25.00©2010IEEEThefermentationbrothwascentrifugedat16,000gfor20mintoremovecells.Twovolumesof4℃coldethanolwereaddedtothesupernatantandstoredat4℃for24h.Theprecipitatewasobtainedbycentrifugationat10,000gfor5minandwashedseveraltimeswithethanol.Thentheprecipitatewaslyophilizedandthecrudecompoundbioflocculantwasobtained.C.BiosorptionexperimentsMnIIandCuIIsolutionswerepreparedfrom1000mg/lstocksolutionsofCuIIandMnIIobtainedbydissolvingCuSO45H2OandMnSO4H2Oindoubledistilledwater,respectively.ThelyophilizedEPSwasdissolvedindoubledistilledwastogivea2g/lsolution.Theadsorptionstudieswerecarriedoutin250mlErlenmeyerflasks.Inthefirstgroupofexperiments,biosorptionofmanganeseIIandcopperIIfromaqueoussolutionscontainingasinglemetalionwasinvestigated.TheeffectofpHonthebiosorptionofcopperIIandmanganeseIIontheEPSwasinvestigatedinthepHrangeof2.07.0.100mlofsolutionscontaining100mg/lmanganeseIIand100mg/lCopperIIionswerepreparedusingthestocksolutions,respectively.TheinitialpHofeachmetalsolutionwasadjustedtotherequiredpHvalue.Then3mloftheEPSsolutionwasaddedtotheeachmetalsolutionandthemixturewasshakenonanorbitalshakerat125r/minand25℃±0.1for2h.Similarly,metalsolutionswith100mg/lmetalionswereusedtoinvestigatethepropercontacttimerangingfrom0.5to3hwithatimeintervalof0.5h.Inthelatterexperiments,thedosageoftheEPSvariedfrom1to5mlusingsolutionscontaining100mg/lmetalions.Theircontentswerecentrifugedat3600gfor5minandthesupernatantwasanalyzedforresidualmetalionconcentration.Inthesecondgroupofexperiments,competitivebiosorptionofMnIIandCuIIionsfromsolutionscontainingthesetwometalswasinvestigated.Themedium100mlcontaining100mg/lofeachmetalionwasincubatedwith3mloftheEPSsolutionat25℃±0.1.Afterbiosorption,supernatantwasseparatedfromtheEPSbycentrifugationasdescribedabove.D.AnalyticalproceduresTheconcentrationsofremainedMnIIandCuIIionsinthesupernatantweredeterminedbyICPAESOptima5300DV,PE,USAwithworkingwavelengthsforCuIIandMnIIat327.393.3nmand257.610nm,respectively.TheamountofadsorbedmetalionsonpergramoftheEPSwasobtainedbyusingthegeneralequationMVeCiCeq/⋅−1whereqeistheamountofmetalionsadsorbedontheEPSmg/gCiistheinitialmetalionconcentrationinsolutionmg/lCeistheequilibriummetalionconcentrationinsolutionmg/lVisthevolumeofthesolutionlMistheamountoftheEPSusedinthereactionmixtureg.Alltheexperimentswerecarriedoutintriplicateandthearithmeticalmeanvalueswereusedincalculations.Allthechemicalsusedinthisstudywereofanalyticalgrade.III.RESULTSANDDISCUSSIONA.EffectofpHonbiosorptioncapacityHydrogenionconcentrationisconsideredasoneofthemostimportantparametersthatinfluencetheadsorptionbehaviourofmetalionsinaqueoussolutions10.TheeffectofinitialpHonthebiosorptionofCuIIandMnIIionsontotheEPSwereevaluatedwithinthepHrangeof2.07.0at100mg/linitialmetalionconcentrations,respectivelyFig.1.StudiesbeyondpH7werenotattemptedbecauseprecipitationwouldbelikelyinthepresenceofhigherconcentrationofhydroxylionsinthebiosorptionmedium.FromFig.1,itwasobservedthatboththeadsorptionofCuIIandMnIIwerehighlypHdependentandincreasedwiththeincreaseofpHoftheaqueoussolutionuptopH6.ThebiosorptionofmetalionsreachedthemaximumatpH6anddecreasedthereafter.ThispHdependencyofbiosorptioncapacitycouldbeexplainedbythefunctionalgroupsinvolvedinmetaluptakeandmetalchemistry.BecauseofthecompetitionofhighprotonconcentrationatlowpHconditions,heavymetalswerepartiallyreleasedtoaqueousphase11.WhenthepHincreases,themetalionsthencompetemoreeffectivelyforavailablebindingsites,whichincreasesbiosorption12.B.EffectofcontacttimeonbiosorptioncapacityTheeffectofthecontacttimeonthebiosorptionofCuIIandMnIIontheEPSwasdepictedinFig.2.InthecaseofCuIIbiosorptionontotheEPS,thebiosorptionprocessreachedequilibriumat1.0handabiosorptioncapacityof42.07±1.22mg/gwasachieved.ThemaximumbiosorptionofMnoccurredat1.0h.AfterthisequilibriumperiodtheamountofadsorbedmetalionsdidnotchangesignificantlywithanincreaseincontacttimeforbothCuIIandMnII.ThussubsequentbiosorptionexperimentswereperformedusingtheoptimumpHandcontacttimerequiredtoreachequilibriumofeachmetalion.Thisrapiduptakeofmealsmaybeanimportantparameterforapracticalapplicationofbiosorptioninindustrialwastewatertreatment.23456701020304050copperIImanganseseIIqemg/gpHFig.1.EffectofpHontheCuIIandMnIIbiosorptionontheEPS.0.51.01.52.02.53.001020304050copperIImanganeseIIqemg/gTimehFig.2.EffectofcontacttimeontheCuIIandMnIIbiosorptionontheEPSC.EffectoftheEPSdosageonbiosorptioncapacityThenumberofavailablesitesandexchangingionsforadsorptiondependsupontheamountofadsorbentinthebiosorptionprocess.TheeffectofadsorbentconcentrationonthemetalremovalefficiencywaspresentedinFig.3.ItwasfoundthattheCuuptakeofpergramEPSreacheditsmaximumattheEPSdoseof10mginto100mlsolutionofmetals.Similarlyinthecaseoflead,thebiosorptioncapacitywasfoundtoincreasewithincreaseinEPSdosageupto30mg.However,thebiosorptioncapacitydecreasewithincreasingdosageathighEPSconcentrationandthismaybebecausethatanincreaseinpolysaccharideconcentrationleadstointerferencebetweenbindingsites.Thedecreaseofspecificuptakemightbeattributedtometalconcentrationshortageinsolution13.ThebiosorptioncapacitiesoftheEPSreached45.30±1.62mg/gforCuIIionsand28.86±1.28mg/gforMnIIionsthesearecomparablewiththevaluesreportedinpreviousstudies.ThebiosorptioncapacitiesofGeobacillustoebiisub.sp.decanicusweredeterminedas41.5and23.2mg/gbiosorbentforCuIIandMnII14.ThemaximumbiosorptionvaluesofCuIIontheAspergillusflavusfungalbiomasswasfoundtobe13.46±0.99mg/g3.102030405001020304050copperIImanganneseIIqemg/gDosageoftheEPSmgFig.3.EffectofEPSdosageontheCuIIandMnIIbiosorptionontheEPSTABLEI.ISOTHERMPARAMETERSFORCUIIANDMNIIBIOSORPTIONMetalsLangmuirparametersFreundlichparametersQ0mg/gb1/mgR2nKfR2CuII51.2300.1560.9894.83920.4170.882MnII28.1691.3080.9908.13318.0480.513D.BiosorptionisothermsLangmuirandFreundlichmodelsarethemostwidelyusedmodelsinthecaseoftheadsorptionofmetalions.TheseisothermequationsareasfollowsFreundlichneCFKeq/12eCnFKeqlog/1loglog3Langmuir1/0ebCebCQeq401011QebCQeq510203040500.00.51.01.52.0copperIImanganeseIICe/qeg/lCemg/lFig.4.LangmuirisothermsforbiosorptionofCuIIandMnII.1.52.02.53.03.54.04.53.03.23.43.63.84.0copperIImanganeseIIlnqelnCeFig.5.FreundlichisothermsforbiosorptionofCuIIandMnII.01020304050binarymetalmixturesinglemetalionqemg/gcopperIImanganeseIIFig.6.BiosorptionofCuIIandMnIIontheEPSinbinarymetalionmixtureIntheaboveequations,KFandnareFreundlichconstants,whichaffecttheadsorptionprocess,suchasadsorptioncapacityandintensityofadsorption,respectively.Q0mg/gandbareLangmuirconstantsrelatedtomonolayeradsorptioncapacityandenergyofadsorptionrespectively.Thevaluesoftheconstantsaswellasthecorrespondingregressioncoefficients,whichwereobtainedbyfittingtheexperimentaldataatpH6andacontacttimeof1.0h,werelistedinTable1.Figs.4and5indicatedtheLangmuirandFreundlichisothermsforbiosorptionofCuIIandMnIIontotheEPS,respectively.WithregardtothevaluesofregressioncoefficientsR2giveninTable1,itwasnotedthattheLangmuirisothermmodelexhibitedbetterfitnesstothebiosorptiondataofbothCuIIandMnIIontotheEPSthantheFreundlichisothermmodel,whichcouldalsobeconfirmedfromFigs.4and5.Langmuirmodelsuggestsmonolayersorptiononahomogeneoussurfacewithoutinteractionbetweenadsorbedmolecules.Inaddition,themodelassumesuniformenergiesofsorptionontothesurfaceandnotransmigrationofthesorbate15.Therefore,biosorptionprocessinthisstudymaybeinterpretedasmonolayeradsorption.E.BiosorptionfrombinarymetalsolutionSimultaneousbiosorptionofCuIIandMnIIionsbytheEPSwasstudiedusinganaqueoussolutioncontaining100mg/lofeachmetalion.Thebiosorptioncapacitieswere36.26±1.52mg/gforCuIIand16.23±1.09mg/gforMnII,whichwerelowerthanthatofnoncompetitiveconditionsFig.6.Theorderofthebiosorptioncapacityforcompetitiveconditionswasasfollowsbasedonmg/gaccumulationCuIIMnII,whichwasinagreementwiththatinthenoncompetitiveconditions.IV.CONCLUSIONSResultspresentedinthispaperindicatedthatthebiosorptionprocessofCuIIandMnIIontotheEPSproducedformRhizobiumradiobacterF2wasdependentonexperimentalconditionssuchaspH,contacttimeanddosageoftheEPS.TheequilibriumdatawereappliedtotheLangmuirandFreundlichisothermmodelsanditwasfoundthattheLangmuirisothermdescribedthebiosorptionofCuIIandMnIIionsontotheEPSverywell.Inthecaseofabinarymetalmixture,thebiosorptioncapacityoftheEPSdecreasedforeachmetalion,CuIIionswerefoundtobeadsorbedmoreeffectivelythanMnIIionsontotheEPSinbothsingleandbinarymetalsolutions.ThepresentdatasuggestthatEPSproducedformRhizobiumradiobacterF2maybeusedasefficientbiosorbentfortheremovalofCuIIandMnIIionsfromaqueoussolution.ACKNOWLEDGMENTTheauthorswishtoexpresstheirgratitudetotheStateKeyLaboratoryofUrbanWaterResourceandEnvironmentSKLUWREandtheNational863programSQ2009AA06XK1482412forfinancialsupport.REFERENCES1J.O.Nriagu,J.M.Pacyna,Quantitativeassessmentofworldwidecontaminationofair,waterandsoilsbytracemetals,Nature,vol.333,pp.134139,1988.2X.Bosch,CadmiumcutstwowaysTheheavymetalmutatesDNA,andthenpreventscellsfromrepairingthedamage,Science,vol.609,pp.11,2003.3T.Akar,S.Tunali,BiosorptioncharacteristicsofAspergillusflavusbiomassforremovalofPbIIandCuIIionsfromanaqueoussolution,BioresourceTechnology,vol.97,pp.17801787,2006.4F.Pagnanelli,M.Trifoni,F.Beolchini,A.Esposito,L.Toro,F.Vegli,Equilibriumbiosorptionstudiesinsingleandmultimetalsystems,ProcessBiochemistry,vol.37,pp.115124,2001.5A.Artola,M.D.Balaguer,M.Rigola,Heavymetalbindingtoanaerobicsludge,WaterResearch,vol.31,pp.9971004,1997.6D.Kratochvil,B.Volesky,Advancesinthebiosorptionofheavymetals,TrendsinBiotechnology,vol.16,pp.291300,1998.7A.Sánchez,A.Ballester,M.L.Blázquez,F.González,J.Muňoz,A.Hammaini,BiosorptionofCuandzincbyCymodoceanodosa,FEMSMicrobiologyReviews,vol.23,pp.527536,1999.8Z.Teng,J.Y.Huang,K.Fujita,S.Takizawa,Mnremovalbyhollowfibermicrofiltermembraneseparationfordrinkingwater,Desalination,vol.139,pp.411418,2001.9Y.B.Zhu,F.Ma,D.P.Li,Researchonfermentativeperformanceofcompoundbioflocculantproducingbacteria,ChinaWaterWastewater,vol.24,pp.7073,2008inChinese.10S.M.Nomanbhay,K.Palanisamy,Removalofheavymetalsfromindustrialwastewaterusingchitosancoatedoilpalmshellcharcoal,ElectronicJournalofBiotechnology,vol.8,pp.4353,2004.11M.Ajmal,R.A.K.Rao,R.Ahmad,J.Ahmad,AdsorptionstudiesonCitrusreticulatefruitpeeloforangeremovalandrecoveryofNiIIfromelectroplatingwastewater,JournalofHazardousMaterials,vol.B79,pp.117–131,2000.12A.Kapoor,T.Viraraghavan,D.R.Cullimore,RemovalofheavymetalsusingthefungusAspergillusniger,BioresourceTechnology,vol.70,pp.95104,1999.13E.Fourest,J.C.Roux,HeavymetalbiosorptionbyfungalmycelialbyproductmechanismandinfluenceofpH,AppliedMicrobiologyBiotechnology,vol.37,pp.399403,1992.14S.Özdemir,E.Kilinc,A.Poli,B.Nicolaus,K.Güven,BiosorptionofCd,Cu,Ni,MnandZnfromaqueoussolutionsbythermophilicbacteria,Geobacillustoebiisub.sp.decanicusandGeobacillusthermoleovoranssub.sp.stromboliensisEquilibrium,kineticandthermodynamicstudies,ChemicalEngineeringJournal,vol.152,pp.195206,2009.15R.Vimala,N.Das,BiosorptionofcadmiumIIandleadIIfromaqueoussolutionsusingmushroomsAcomparativestudy,JournalofHazardousMaterials,vol.168,pp.376382,2009.
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