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Studies on bio-oxidation of coal mine gas by a biofiiter

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Studies on bio-oxidation of coal mine gas by a biofiiter

    Studies on bio-oxidation of coal mine gas by

    a biofiiter

    JOURNALOFCOALSCIENCE&ENGINEERING

    (CHINA)DOI10.1007/s124040100407x

    PP367374Vo1.16No.4Dec.2010

    StudiesOilbiooxidationofcoalminegasbyabiofiiter

    YUHaixia',MINHangIL0Zhenmei

    (I?HangzhouEnvironmentalMonitoringCenterStation,Hangzhou310007,China;2.CollegeofLifeScience,Zhejiang

    University,Hangzhou310058,China)

    

    TheEditorialOfficeofJournalofCoalScienceandEngineeringfChina)andSpringer-VcrlagBerlinHeidelberg2010

    AbstractAnewbiofiltertechnologywasusedtocontroIthemethaneconcentrationjnthe coalmine.TheresultsjndicatethatthebiofilterachievesasteadymethaneremovaIca

    pacityof1470mg/(L?h)after30daysstartup.Morethan90%ofthemethanecanbere

    movedwithanemptybedretentiontime(EBRT)of5.6minwhentheinletconcentrationof methane(IMC)isIowerthan70mg/L(10%,V/V)andabout80%whenIMCisat105mg/L (15%,.ThebiofilterisstillareliablemethodtocontroImethaneconcentrationasan auxiliarymeanstoboostcoalmineproductionsafetytogetherwithaggrandizedventilation anddrainagetechnologies.eventhoughtheremovaIefficiencyofmethaneisnotvery satisfactorywithahighIMC(>10%)orashortEBRT(<3.8min).

    Keywordsbiofilter,biooxidation,coalminegas,methane,methanotroph

    Coa1minegasdisastersareconsideredtobethe

    biggesthazardinthesafeproductionofcoalmines

    andthecontrolofwhichhasalwaysbeenadifficult

    problemtosolveintheworld'scoalindustry.Tillnow-

    thereisnoperfectmethodtoeliminatecoalminegas disastersdrastically.Seventytoeightyseverecoal mineaccidents,eachofwhichresultsinthedeathof morethanl0people.arereportedbytheState AdministrationofWlorkSaf_etVofChinaeveryve andatotaleconomiclossofmorethanRMB750nil

    lionisbroughtaboutaswel1(Hu.2006).

    Atpresent,themosteffectivemethodsofgas controlarethecombinedapplicationofseamgas drainageaheadoftheminingoperationandthecircu

    lationofsufficientventilationairquantitiesthrough theworkingplacesofthemine(Lama.1995;Bobrov, 1995;Styles,1995;Zhang,1995).However,thereex- istsomeshortcomingsofthesemethods,suchashigh exhaustionandexpenditureandpotentialglobal wanningcausedbymethanebeingdrainedout.Itis Received:23July2010

    Tel:86571.87985823,E-mail:yuhx46@126.corn wellknownthatmethaneisestimatedtocontribute about26timesthatofcarbondioxide(molevs.mole) toclimatechange(RichardandThomas.1996;Khali 2000).Astheheadingfaceproceedsandtheexploita

    tionintensityincreases,thesetwomethodscannot controlthegasaccumulationeffectivelybecausethe poweroftheequipmentcannotmeetthedemand(Guo etal2003).

    Methane(CH4),asthemaincomponentofcoal minegas,posesadistinctexplosionhazardwhenits concentrationliesintherangeof5%~15%finthe

    presenceofoxygen(Windholzeta1..1983;Johnsonet

    a1..1998;Wleieta1..2002).Reducingthemethane concentrationinthemineisthekeyfactortoavoid coalminegasdisasters.Themethanotrophscanoxy

    genateCH4intoC0,andwaterandacquirethecarbon andenergyneededintheprocessofgrowththrough theMethanemonoxygenase(MMO)system(Murrell, 2000a;Murrell,2000b).Themicrobialtechnologyto treattheminegaswhichtakesthemethanotrophsto oxygenatemethaneintoCO2andwaterinthecoal minehasalreadyreceivedwideattention,andhasbe

    llf1

    comeanimportantresearchfield.Therehavebeen somerelativelysuccessfulworksandapplicationsin India(Thakureta1.,1983),Australia(Ke,2005), canada(ChakravortyandForrester,1985),America (Ke,2005;Songeta1.,2001)andRussia(Ivanoveta1., l98l:ChernyshenkoandMalashenko,1986),inwhich researcherssprayedthebacterialagentorinjectedthe bacteria1suspensionmadeofthemethan0tr0Dhsinto thecoa1mine.resultinginevidentdecreaseofmethane contentafteraperiodoftime,However,certainprob

    emsalsoexistedwiththemethodsofsprayingorin

    iection.Forexample,theactivityofthemethano. trophswaslowerinthecoalminebecauseoflackof nutrition.anditwasnoteasytocontroIandinspectme situation0fmethanotroDhs.Theapplicationofa bioreactorintreatingwastegashasahistoryofmore than50years,andthetechnologiesarequitemature andwidelyusedjnmanycountries.Whereas.rela

tivelylittleinformationhasbeenobtainedintheap

    plicationofmethanebiofiltrationincoalmines(Wei. 2002;Hu,2006).Comparedwiththesprayandinjec

    tionmethods.theapplicationofmethanebiofiltration hasmorebenefitsasfollows:itissimpleandsafe: (itiseasytoinspectandcontrolthemethanotrophs; (3)thecostismuchlower.

    Thispaperreportsonthetechnologyandthefea

    sibilityofacontinuousbiofilterutilizingthemeth

    ane.oxidizingbacterialmixturetoremovemethane fromcoalmineatmospheres.Thebiofilmgrowing processandmedegradationratesofmethaneinthe rangeofexplosionunderdifferentconditionswere investigatedafterthebiofilmformed.Theabilityof thebiofiltertowithstandimpactwasalsoappraised. {t21ialsill12|hods

    1.1Reactordescription

    Becauseofthe1owwatersolubilityofmethane, theeffectofutilizingabioreactortodealwithmethane isworsethanthehighsolubilitygases(Murrelland McDonald,2000).Inthiswork,amulti.1ayerreactor wasdesignedandmethanewasremovedgraduallyin thewholereactor.Theexperimentalreactorconsisted ofthFeePVCsections(Fig.11eachwithaninnerdi

    ameterof6cmandaheightOf25cm.Eachsection wasseparatedbyaPVCsieve1ocatedatthebottom, waspackedto5cmfromthetop,formingaplenumto makethegasflowredistribute.

    Thedimensionofthereactorisillustratedin

    able1.Gassamplingsiteswerelocatedineachofthe plenums.Gaswasfedfromthetopofthecolumnand outthroughventilationpipesatthebottom.Airand methanewerecontrolledthroughindividualflowme

    ters,mixedandprehumidifiedbc:foreenteringthe biofilterthroughasingleinlet.Athirdmeterwasused tocontrolthetotalgasflow.Liquidmediumwasrecy

    cledthroughthereservoirbyaperistalticpumptothe topofthebiofilter,afterwhichthemediumtrickled throughthepackedbed.

    Fig.1Schematicdiagramoftheexperimentalbiofilter l--Compressedmethane;2AIrpump;3Gasflowmeters;4Mixing

    chamber;5--Biofiltercolumn;6--Sampleports;7Waterdistributor; 8--Nutrientreservoir;9--Peristalticpump;10--Liquidflowmeters;I.II

    Ill--Sectionsofbiofilter

    Table1DimensionofthebiofiItercolumn

    1.2Methanotrophiemixtureandmineralsalt medium

    Anemcientmethanotrophsystemwasgained

    fromthericefieldsoilatHuajiachicampus,Zhejiang Universityasenrichedsourceafterdomesticationwith methaneandoptimizationofthemedium.Theopti

    mizedmediumwascomposedof(g/L):MgSO4.7H20, 0.5;KNO3,l;Na2HPO4'12H20,0.36;KH2PO4,0.28; CaCI,?6H,O,0.1:NH4Cl,0.25andlmLtraceele. mentssolution.Thetraceelementsolutioncontained (g/L):disodiumEDTA0.5,FeSO4.7H2O,0_4; CuSO4?5H20.0.06;pHisadjustedat6.2-6.4. 1.3BiOfiltersupportcarrier

    Thereactorwaspackedwithceramicpellets

whichwerebroadlyutilizedasthecoveringorsup

    portingmaterialsofcatalystinthereactorsandthe carrierinthecolumns.Itsbasiccharacteristicsare showninTable2.

    :!:CS1bioo~idaliont)fCO~I]minebyabiol'il/cl?369 Table2Thecharactersofceramicpellets

    1.4Startupofthebiofilter

    Thebacterialsuspensionwascirculatedcontinu

    ouslyinthebiofilterfor10daysafteritwasstartedup. Whenanevidentbiofilmcouldbeobservedeasily, intermittentcirculationofthemediumwithliquidflow rate(LFR)of25mL,/minwasconductedforonehour withtheintervalofl2hours.ThegasflowratefGFR1 was30~90L/h,theinletconcentrationofmethane (IMC)wasvariedintherangeof0-140mg/L,andthe environmentaltemperaturewassetat30?.which

    wasoptimalforthegrowthofmethanotrophs. 2Analyticalmethods

    Gassampleswerecollectedfromthebiofilterus

    ing1mLgastightsamplingsyringesequippedwith butylrubberstopperstopreventgasfromleakingout. Samplesweredetectedusinga7890Gaschromato

    graph(TechcompLTD,Shanghai,China1equipped withaPorapakOcolumn(2mx2mm)andaflame

    ionizationdetector(FID).Nitrogenwasusedascarrier gaswiththeflowrateof25mL/min,theflowratesof H2andairwere60-70mL/rainand600-700mL/min. respectively.Thecolumntemperaturewassetat120.C. thedetectorandoventemperatureat120.Cand60.C.

respectively.

    3ReSUIts

    3.1Operationofthebiofilter

    Theoperationofthebiofilterwasstudiedunder differentemptybedretentiontimes(EBRT1wimthe control0fIMCafterthestartuD.Theoutletconcentra

    tionofmethane(OMC)wasmeasuredatintervals,and theoperationresultofthebiofilterafterthestartuDis

    showninFig.2.

    AsFig.2(a)shows,themethaneoxidationcapac

    ityofthebiofilterwasfairlylowwithinthefirst5days afterthestartup,buttheremovaleciencyofmeth.

    anejncreasedgraduallyfromthe6thday,andsome milk.whitebiofilmcouldbeseenonthecarrieratthat time.Onthe12thday,themethaneremova1efficiency appearedtohaveasignificantenhancement.Mcan. while,theEBRTwasreducedfrom5.6minto3.8min. andtheOMCwasonly2.58mg/LwhentheIMCwas l8.28mg/L.Fig.2fbdemonstratesthatmethane eliminationloadingwentuptogetherwithinletload

    ingincreasingatthestartofoperationofthebiofilter butkeptaconstantlevelatabout1470mg/Lhafter the30thday.Thisindicatedthatthebiofilteroperation hadbeenatasteadystate,andpossessedastable eliminationcapacityofmethane.Themorphological characteristicsofthesupportcarrierandthebiofilm areshowninFig.3andFig.4.

    16O

    12O

    80

0

    5.6rain3.8min2.8min

    2610141822263034

    Time(d)

    (a)Relationshipoftheinletconcentration andtheoutletconcentratiOnofmethane 2610141822263O34

    Timefd1

    (b)Relationshipoftheinletloadingand theeliminationloadingofmethane volume

    Fig.2Operationcurvesofthebiofilter (a)Ceramicpellets

    (b)Maturedbiofilm

    Fig.3Comparisonofceramicpelletsandpelletswith

    maturedbiofiIm

    =}g0ull0Il0锚扫口0u0j

    兽【pguIIIn10>ug

1

    (a)Environmentalscanningelectron micrographofthecarrier

    (b)Environmentalscanningelectron micrographmicrobesonthesurlhce ofcarriertakenfrombiofilter

    Fig.4Comparisonofcarriersurfacebeforeandafter

    formationofbiofiilm

    AsindicatedinFig.3andFig.4.theivorywhite

    biofilmwithabout1mmthicknesscouldbeobserved onthecarriersurfaceaftertheformationofbiofilm

    whichwasmostlycomposedofrodandcoccibacteria. 3.2Therelationshipbetweenmethaneinletvol- nineloadingandmethaneremovalloading

    underdifferentEBRT

    Therelationshipbetweenmethaneinletvolume loadingandmethanevolumeremovalloadingunder dif.ferentEBRTafterthebioreactorwasstablewas studiedanddrawninFig.5.ThelinesinFig.5arethe aggregationofal1thepointsonwhichthevolumere

    movalefficiencywas100%.thatiswheretheinlet volumeloadingwasequaltotheremovalloading. Fig.5showsthatmethaneeliminationcapacitywent upalongwithmethaneiMetloadingincreasing.Al

    most100%removalrateofmethanewasachieved wheninletIoadingofmethanewasatalowIeve1. However,theenhancementofmethaneelimination capacitywouldbecomeslowatvariousEBRTwiththe inletloadingfurtherincreasing.andtheexperimental datadeflectedthe100%removalratelinegradually. Thisfactsuggestedthatthemethanotrophicbacteria couldnotoxidizeallmethaneenteringthebiofilterata higherinletloading.Fig.5alsoimpliesthatmethane eliminationefficiencywouldkeepastableleve1when theinletloadingofmethaneincreasedtosomedegree. ForthedifferentEBRT,themethaneeliminationeffi

    ciencydidnotchange,butremainednearly1470mg/ (L?h)methane,whichwasjusttheoptimalelimination capacityofthisbioreacton

    MethaneinletvolumeIoading(mg/(L.h))

    (a)EBRT=5.6min

Methaneinletvolumeloading(mg/(L.h11

(b)EBRT=3.8min

    Methaneinletvolumeloading(mg/(L?h,, (c)EBRT=2.8rain

    Fig.5Therelationshipbetweenmethaneinletvolume loadingandmethanevolumeremovalloading 3.3EflfectofEBRTandIMContheremovaleffi- ciencyofmethane

    ItcanbeseenclearlyinFig.6thatthereisasis- nificanteriectofEBRTontheremovalefficiencyof methane.ThemethaneremovalefnciencywentuD whenEBRTwasincreasedandIMCmaintaineda constant1eve1.Morethan90percentofmethane wouldbeoxidizedwhenEBRTis5.6rainandIMC lessthan70mg/L(10%,V/.Whereastheremoval rateofmethanedroppedsharplyafterEBRTwas shortenedto1.8min.andonly60%ofmethanere. movalratecouldbereachedeventhoughIMCwas ((q-/g一?Ip0

    >0舞【.l=0>0'I^

    ((1,g】嚣口lp鲁一

    一对0a|0IlInl0>.0

    一一q.一一,III一?ul.

    02吕声100口时g?

    Y1laixiaclallIHlies01]bic{_')\idationelcmincgasby.1biolihot'37 35mg/L(5%,.withthefurtherincreaseofIMC. theremovalemciencywoulddiminishdramatically. Thereasonmightbethatthesolubilityofmethanein waterislower,andtooshortEBIisdisadvantageous formethanotrophicbacteriainbiofilmtocontactand

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