Comparison between laboratory

ResearchArticle

Received:10July2009

Revised:5August2009

Accepted:15August2009

PublishedonlineinWileyInterscience:12January2010

(http://wendang.chazidian.com)DOI10.1002/jctb.2327

Comparisonbetweenlaboratoryandpilotbiotrickling?ltrationofairemissionsfrompaintingandwood?nishing

FeliuSempere,VicenteMart´?nez-Soria,Josep-ManuelPenya-roja,

´?MartaIzquierdo,JordiPalauandCarmenGabaldon

Abstract

BACKGROUND:Paintingandwood?nishingisoneindustrialsectoraffectedbytheEuropeanUnionenvironmentalregulations

onvolatileorganiccompound(VOC)airemissions.Thepaintingprocesstypicallyresultsinhigh?owrateswithlowVOCconcentrations,sobiotrickling?ltrationcouldbeaneconomicalalternativeforcontrollingairemissions.Thisstudyanalysestheoperationofapilotunitinstalledinafurniturefacility,andcomparesitsperformancewiththeremovalef?ciencyobtainedinthelaboratoryusingasyntheticfeedcomposedofn-butylacetate,tolueneandm-xylenetosimulateindustrialairemissions.RESULTS:Laboratorystudiesshowedthat?uctuatingandoscillatingVOCfeedingadverselyaffectedtheperformanceofthebioreactorincomparisonwithstationaryfeeding.Theoperationofthepilotplantat35sofemptybedresidencetime(EBRT)remainedwithinthelegallimits.Theinstallationofanactivatedcarbonpre?lterimprovedconsiderablytheremovalef?ciency,withemissionskeptbelow40mgCm?3workingat24sofEBRT.

CONCLUSION:Biotrickling?http://wendang.chazidian.comboratorystudycanprovidevaluabledataforthescale-up.c2010SocietyofChemicalIndustry??

Keywords:biotrickling?lter;n-butylacetate;m-xylene;pilotunit;toluene;volatileorganiccompounds

INTRODUCTION

Theabatementofvolatileorganiccompounds(VOCs)fromairemissionsasafactorinprotectingtheenvironmentandpublichealthhasbeenemerginginEuropeanUnionenvironmentalpolicyoverthepastdecade.FurnituremanufacturingisoneoftheindustriesmostaffectedbytheenvironmentallegislationonVOCairemissionsintotheatmospheresincemostwood-coatingpaintscontainVOCsolvents.Inthiscontext,newSpanishrestrictionsonVOCconcentrationinexhaustairwereestablishedinOctober2007.1Thepollutantcompositionofexhaustgasesfromspraypaintboothsdiffersdependingontheapplication.Typicalcompo-sitionsinvolveamixtureofsolvents,includingbothhydrophobic(e.g.tolueneandxylenes)andhydrophilic(e.g.n-butylacetateandmethylpropylketone)components.2Thepaintingprocesstypi-callyresultsinhigh?owrateswithVOCemissionscharacterisedby?uctuating,discontinuousandlowconcentrationmixturesoforganiccompounds.Intheseconditions,biotreatmentsarepotentialalternativestoconventionalphysicochemicalprocessesowingtotheirloweroperationalcostsandthelackofsecondarypollutantproduction.Vapour-phasebiotreatmentshavebeenclassi?edasbestavailabletechnologies(BATs)forthereductionofthesepollutantsfromwastegasesinthechemicalsector.3

Amongbiotreatments,thebiotrickling?lter(BTF)isanemergenttechnologythatpresentsseveraladditionaladvantages:itoffersasmallersize,lowercapitalexpenditureandhigherremovalratesthanconventionalbio?lters.TheBTFusesawell-speci?edinert

packingmaterialandinvolvesaliquidphasetricklingthroughthebed.Thebio?lmisdevelopedonthepackingsurface,andtheliquidphaseprovidesnutrientstothebio?lmandallowsforpHcontrol,yieldingamorestableoperationthanbio?lters.Thesecharacteristics,alongwithalargerair/liquidinterfacialarea,canleadtohigherremovalratesthanthoseobtainedwithconventionalbio?lters.4

TheremovalofVOCsfrompaintapplicationsusingbio?ltersandBTFsislimitedintheliterature,5especiallyforpilot/full-scaleunits.Thescarceavailabledatashow,ingeneral,suitableperformancefortheremovalofVOCemissions.6–8

Industrialemissionspresentvariableanddiscontinuousconcen-trationsthatcanhindertheperformanceof?eld-scaleBTFs.Ithasbeenshownthatbioreactorsgivebetteryieldsunderstationaryconditions.9However,limitationsandproblemsof?eld-scaleBTFsundercyclicanddiscontinuousoperationhavebeenreported.10Inaddition,severalresearchershavestudiedtheuseofactivatedcarbon?ltersprecedingabiologicalreactortobufferthesudden

?

Correspondenceto:CarmenGabald´on,DepartmentofChemicalEngineering,UniversitatdeVal`encia,Dr.Moliner,50,46100Burjassot,Spain.E-mail:carmen.gabaldon@uv.es

DepartmentofChemicalEngineering,UniversitatdeVal`encia,Dr.Moliner,50,46100Burjassot,Spain

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variationsinconcentration,spikesandunstableloadsofVOCsinordertoenhancethereliabilityoftheBTF.11–14

ThemainobjectiveofthisstudywastoprovidedatarelatedtotheremovalofVOCsinairemissionsfromwoodcoatingandpaintingapplicationsbyusingBTFs.Thisworkinvolvesstudiesatbothlaboratoryandpilot-plantscales.Forthispurpose,aclosedboothoperatedtoautomaticallypaintpiecesinafurniturefacilitylocatedinVillarreal,Spain,wasselectedasrepresentativeoftheemissionsofthisindustrialsector.Alaboratorystudywasperformedusingasyntheticfeedcomposedofn-butylacetate,tolueneandm-xylene,whichsimulatedthesetypesofindustrialairemissions.Twofeedregimesweretested:?rst,continuousandstationaryloading,followedbydiscontinuousandoscillatingloading.Thepilot-plantunitwasconnectedtotheindustrialfocusmentionedabove.Inthiscase,themainpurposewastoshowtherobustnessoftheprocessandestablishtheminimumEBRTallowingthemeetingofthelegalregulations.Atbothscales,anactivatedcarbon(AC)pre?lterwasusedtoevaluatethein?uenceofloadequalisationontheoverallremovalef?ciency.

http://wendang.chazidian.comyoutofthelaboratorybiotrickling?lter.

MATERIALSANDMETHODS

Theresearchwasdividedintotwoexperimentalphases:(1)laboratoryscalebyusingsyntheticfeed,and(2)operationofaTable1.AverageperformanceobtainedfromthelaboratoryBTFpilotunitconnectedtoanindustrialfocusofafurniturefacility.underintermittentloadingduringworkingperiods(6a.m.to10p.m)Parameter

StageIStageIIStageIIIFurniturefacility

Emptybedresidencetime(s)

301515Thefurniturefactory,GamadecorSA,islocatedinVillarreal,Averageinletconcentration(mgCm?3)220105157Spain.ThisfactorypresentsseveralfociwithVOCemissionsAverageeliminationcapacity(gCm?3h?1)13.811.415.6ofdifferentconcentrationranges.ThefocusselectedforthisAverageoutletconcentration(mgCm?3)1035792studywasaclosedbooth,operatedtoautomaticallypaintpiecesTotalremovalef?ciency(%)53.245.741.4offurniture,whichwasinexcessoftheregulatorylimit.Then-ButylacetateRE(%)>99>9992.7emissionswererestrictedtotheoperatinghoursofthefactoryTolueneRE(%)22.99.98.2(MondaytoFriday,7a.m.to10p.m.).Airstreamsamplesofthem-XyleneRE(%)

20.3

9.2

6.2

booth’semissionsweretakenfollowingtheproceduredescribedinthestandardEN-13649:http://wendang.chazidian.compoundswereidenti?edbygascromatography–massspectrometryandcompositionwasdeterminedusingagaschromatographequippedwithaFIDLlobregat,Spain).Thecompositionofthegasstreamswereperi-(7890model;AgilentTechnologies,Madrid,Spain).

odicallydeterminedusingagaschromatographequippedwithaFIDdetector.Suspendedsolids,solublechemicaloxygendemand(COD),andnitrateconcentrationintherecirculationsolutionwereLaboratorybiotrickling?lter

periodicallymeasured.ThesolubleCODvaluesThelayoutofthelaboratoryunitispresentedinFig.1.TheBTF?1measuredinthewastewaterpurgewerelowerthan250mgL,whichrepresentedwascomposedofthreecylindricalmodulesofPlexiglaswithalessthan2%oftheweeklyinletloadfedtothesystemforalldata.totalbedlengthof

120cmandaninternaldiameterof14.4cm.Inconsequence,theorganiccarboninthepurgewasconsideredTheBTFwasrandomly?lledwithoneinchofnominaldiameternegligibleforevaluationoftheBTFperformanceintermsofinletFlexiring?polypropylenerings(Koch-GlitschB.V.B.A.,Wijnegem,load(IL),eliminationcapacity(EC)andremovalef?ciency(RE).Belgium),with92%voidfraction.Theset-upofthebioreactorwasAfterinoculationwithpre-acclimatedactivatedsludge,theex-completedwitharecirculationtank(effectivevolumeof10L).perimentalplanstartedundercontinuousandstationaryloading.Contaminatedairwitha2:1:1weightmixtureofn-butylacetate,Sixexperiments,eachwithadurationof2weeks,wereperformedtolueneandm-xylene,respectively,wasintroducedthroughthewithbottomofthecolumn.Therecirculationsolutionwasfedina3VOCconcentrationsvaryingfrom160mgCm?3to350mgCm?atcounter-current?owwithrespecttoair?owandwaspartially3gasEBRTbetween60and15s(correspondingto11–72gCm?h?1ofIL).Discontinuousandoscillatingloading(16hrenewed(50–100%oftotalvolume)everyweek.Abufferednu-day?1,7daysweek?1)wasthenappliedtosimulateindustrialtrientsolutioncontainingpotassiumnitratefertiliser(21.6gL?1),patternemissions.ThreesetsofexperimentalconditionswereNa3PO4·12H2O(7.36gL?1),andCa,Fe,Zn,Co,Mn,Mo,NiandtestedinwhichEBRTvariedfrom15to30sandaverageinletVOCBattracedoseswasused.The?owrateofthenutrientsolutionconcentrationduringworkingwasadjustedtokeepnitrogenconcentrationabove10mgL?13hoursvariedfrom120to240mgCm?3(ILfrom29to41gCm?h?1),withpeakstwotothreetimesintherecirculationsolution.ThetotalconcentrationofVOCswasgreaterthanthebaselineVOCconcentration(seeTable1).Air?owmeasuredusingatotalhydrocarbonanalyserequippedwitharatewaskeptconstantduringnightclosures.Inaddition,thein?u-FIDdetector(NiraMercury901model;Spirax-Sarco,SantTelisede

enceontheperformanceofa0.825LACpre?lterwasevaluated.

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http://wendang.chazidian.comyoutofthepilotunitofbiotrickling?lter(VOCUS?).

TheACselectedwastheextrudedACNoritRB3,withadiameter

of3mmand1100m2g?1ofBETsurfacearea(OMYAClariana,S.L.,EspluguesdeLlobregat,Spain).TheACwascrushedandsievedto0.75–2.0mmbeforeitsuseasapre?lterinthelaboratorystudy.Pilotunit

Thepilotplant(VOCUS?)wasprovidedbyPureAirSolutionsb.v.(Heerenveen,TheNetherlands).ThelayoutispresentedinFig.2.Thebioreactorvessel,apolyethylenecylinderwithacone-shapedbottomandaneffectivepackedvolumeof750L,wasrandomly?lledwithtwoinchesofnominaldiameterFlexiring?polypropylenerings(Koch-GlitschB.V.B.A.),with93%voidfraction.Apreviouslyacclimatedactivatedsludgetopaintsolventswasusedtoinoculatethesystem.Thebioreactorwasoperatedinthecounter-currentmode.VOC-pollutedairfromthefactorywasblownintothebottomofthecolumn,andrecirculatedwaterwassprinkledontopofthe?ltermedia.Thetrickledwaterwascollectedinarecirculationtankof400L.Anutrientsolution(pH7.0)containingbetween20and100gKNO3L?1andbetween7and30gNa3PO4·12H2OL?1alongwithtraceelementswasdosedtokeepnitrogenconcentrationabove10mgL?1intherecirculationsolution.Inletandoutlettemperature,inletandoutletVOCconcentration,conductivity,pHandpressuredropbetweenthegasinletandoutletofthemediabedwerecontinuouslymonitoredviamodemcommunication.ANiraMercurytotalhydrocarbonanalyserwasusedtocheckandcalibratethetwophotoionisationdetectors(PIDs)thatcontinuouslymonitoredtheinletandoutletVOCconcentration.

Thepilotplantwasoperatedduring6monthsatEBRTsbetween10and40s.Airandwater?owalongwithnutrientdoseweremaintainedduringnightsandweekends,eventhoughtheboothwasnotrunning.TrickledwatersamplesweretakenonceaweektomeasurethesolubleCOD,suspendedsolidsandnitrogenandphosphoruscontent.Between50and100%ofthevolumeoftherecycledwaterwasdrainedandfreshwaterwasaddedtoreplaceitonceaweek;solubleCODvalueswerelowerthan500mgL?1(<3%oftheinletVOCwaspurgedwiththeliquidphase).Inthelast80days,a10L?lterofextrudedAC(NoritRB3)wasinstalledprecedingthe

bioreactor.

Figure3.TypicalpatternofVOCemissionsfromtheautomaticclosedbooth.Thediscontinuouslinecorrespondswiththelegallimit.

RESULTSANDDISCUSSION

Focuscharacterisation

Thefocusfromtheclosedboothwasconstitutedbytwochimneys,paintapplicationanddrying,bothconnectedtothepilotplant.Thecompoundsdetectedinmajorproportionsinweightweretoluene(20–50%),n-butylacetate(20–60%)andxylenes(5–20%);othercompoundspresentedwithproportionslessthan10%werei-butylacetate,ethylbenzeneandmethoxy-propylacetate.MostofthesecompoundshavebeenpreviouslyreportedasrepresentativesofVOCsinpaints.6TheVOCemissionwasuneven,withhighlevelemissionepisodes(>600–700mgCm?3)andanaverageconcentrationofVOCsofbetween140and200mgCm?3duringtheoperatinghoursofthefactory,inexcessSpanishregulatorylimits(averageVOCconcentration:dailybasis<75mgCm?3,hourlybasis<110mgCm?3).AtypicaldailyemissionpatternisshowninFig.3.

LaboratorystudyContinuousloading

TheBTFwasoperatedundercontinuousloadingexperimentsover3months;ILandEBRTvariedfrom11to72gCm?3h?1and60

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(b)

Figure4.(a)Eliminationcapacityversusinletload,and(b)removal

ef?ciencyversusinletVOCconcentrationatseveralEBRTsforthelaboratory

BTFundercontinuousloading.

to15s,respectively.TheECversusILisplottedinFig.4aandRE

versusinletVOCconcentrationisplottedinFig.4bfordifferent

EBRTs.EvenforthelowerappliedILnocompleteremovalwas

obtainedbecauseofthelowremoval3oftolueneandm-xylene.AmaximumECof32.5gCm?

1h?1with44.8%REwasachievedFigure5.Pollutantconcentrationpro?lesalongthelengthofthe

workingat72.4gCm?3h?ofILandat15sofEBRT(VOCinletlaboratoryBTFundercontinuousloading:(a)n-butylacetate;(b)toluene;concentrationof302mgCm?3).REincreasedwithEBRT:ataVOC(c)m-xylene.

inletconcentrationofaround170mgCm?3,REincreasedfrom53

to78%intherangeof15to60sofEBRT.Atthatconcentration,

theBTFwasabletomeettheregulatorylimits(dailybasis)evenforaromaticdegradingbacteriainthe?rstsectionwherethen-butylthelowerEBRT(ILof39.6gCm?3h?1).REwasadverselyaffectedacetateislargelypresent.Otherstudiespreviouslyreportedawheninletconcentrationwasduplicated,showingthatBTFwassimilarphenomenon.16,17Aromaticcompoundsalsopresentanotcompetitiveenoughtomeetthelegallimits.Inthiscase,REslowerdegradationrate;sotheBTFwasnotabletoremovethemincreasedslightly,from45to55%,whenEBRTincreasedfrom15inthepartofthebedwheren-butylacetatewasabsent.to60s.ResultsfromCO2monitoringindicatedaproductionof

1.74gofCO2pergofCremoved(regressioncoef?cient=0.96).Intermittentloading

AssumingthatorganicandinorganiccarbonlosseswiththepurgeTheexperimentcontinuedbyusingadiscontinuousloadforwerenegligible,abiomassyieldof0.53(expressedintermsof16hoursperday(6a.m.to10p.m.,7daysweek?1).Acyclicfeedcarboncontent)wasobtained.Darlingtonreportedacarbonyieldincludingvariablestepswasplannedasanapproximationtotheof0.55fortheaerobicmicrobialgrowthonhydrocarbons.15dynamicemissionsfoundintheindustrialfocus.Eightdailycycles,TheeliminationofeachindividualcomponentisshowninFig.5eachwithdurationof2h,wereapplied,witheachcyclecomposingwherethepollutantconcentrationpro?lesalongthelengthofoffourstepsof30min,withpeakstwoorthreetimesgreaterthantheBTFhavebeenplottedforthethreehigherILs.FromtheVOCthebaselineconcentration.ThreestagesofvaryingEBRTorILwereconcentrationpro?ledata,acompleteremovalofn-butylacetateapplied.Eachstagewasappliedforaminimumof2weeks.Atypicalwasobservedinthe?rsttwo-thirdsofthecolumn,whereasnopatternofemissionsisshowninFig.6aforstageIII.Theaveragedegradationofthearomaticcompoundswasobservedinthe?rstperformanceresultsaresummarisedinTable1.The?uctuationinthirdofthecolumn.n-ButylacetateisahydrophilicandeasilyVOCconcentrationalongwiththenightlyshutdownsadverselybiodegradablecompound,henceitcouldinhibitthegrowth

ofaffectedtheperformanceofthebioreactor,especiallybecauseofJChemTechnolBiotechnol2010;85:364–370??http://wendang.chazidian.com/jctb

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improvementintheinstantaneousemissionwasmainlydueto

effectiveloadequalisationbytheACratherthananappreciableincreaseintheremovalcapacityoftheBTF.

Achangeinthelastexperiment(con?gurationACpre?lter+BTF,stageIII)wasperformed.Thesystemwasexposedtoamixture1:1weighttolueneandm-xyleneinordertoevaluatethein?uenceofn-butylacetateontheremovalofthearomaticpollutants.EBRTandILwerekeptconstant,buttheinletconcentrationsofbotharomaticcompoundswereduplicated.ThesystemachievedanaverageREof26%,withsimilarvaluesforbotharomaticcompounds.Thethree-foldincreaseinREcomparedwiththevaluesobtainedintheexperimentsperformedwithahighconcentrationofn-butylacetateindicatesthatthehydrophilicpollutantinterfereswiththedegradationofthesecompounds.Pilotunitoperation

Thepilotplantwasconnectedtotheautomaticclosedboothafterapreviousstudyinanotherfocusattheselectedindustrialsite.18TheoperationstartedatEBRTof24s.Atransitoryperiodofabout3–4weekswithaprogressiveincreaseintheVOCremovalwasneededtoreachastableperformance.Figure7aandbshowstheresultsobtainedinatypicaldayofthestableperiod.Theperformanceofthesystemindicatedthattheregulatorylimit(hourlybasis)wasnotreachedwheninletemissionepisodeswithahighdurationandconcentrationoccurred.Theair?owratewasthenchangedcorrespondingtoEBRTsbetween40and10s.Figure7canddshowstheresultsobtainedinadayoperatedatEBRTof35s.Ascanbeseen,intheseconditionscompliancewiththelegallimit(hourlybasis)wasreachedfortheentiredaytimeperiod.Table2summarisestheaverageperformanceduringtheoperatinghoursofthefactoryfortypicaldaysatdifferentEBRTs.Theproductionofthefactorywasstableintermsofdailysolventemission,withsimilarinletVOCconcentrationsfordifferentdays.Foranaverageinletconcentrationofaround180mgCm?3,theREincreasedfrom49to70%asEBRTincreasedfrom10to35s;byonlyworkingat35swasitpossibletomeetthelegalregulations(dailybasis).AlthoughtheEBRTstestedarenotexactlythesameasthoseusedatlaboratoryscale,theRE–EBRTpairsmatchedwiththetrendobtainedatthelaboratoryscaleundercontinuousfeeding(Fig.4b).Indeed,theperformanceofthepilotunitwasslightlybetterthanthatobservedatlaboratoryscalewhenoscillatingandintermittentVOCemissionswereapplied,e.g.theREsobtainedinthepilotunitatEBRTsof10and24swere49and57%,respectively,whereasinthelaboratorystudyitwasonlypossibletoreachaREof41%at15sofEBRT(stageIII,inletVOCconc.?160mgCm?3).Theslightlybetterperformanceofthepilotunitthanthelaboratorystudyunderdiscontinuousfeedingcouldbeattributedto(1)thegreatervariabilityoftheorganiccompositionintheairemission(e.g.aromaticcompoundsproportionvariedbetween25and70%)thatcouldhavederivedinamorecomplexmicrobialecosystemand(2)theunevenpatternemissionwithhighpeaksofshortdurationfollowedbylow-concentrationvalleysthatcouldhaveallowedsomebufferingeffectofthesystemrelatedtoshort-termabsorptionandadsorptionphenomena.ThecomparisonbetweenthelaboratoryresultsandthoseobtainedhereinindicatesthatsimulatingtheoscillatingandintermittentVOCemissionsatthelaboratorycouldbeatimesavingtoolforobtainingvaluabledatatoestablishsafelimitsoftheoperationconditionsallowingthelegalrequirementstobemet.

Inordertoimprovesystemperformance,apassiveACsmoothingpre?lterwasinstalledattheinletstream,beforethebiotricklingreactor.Thiscon?gurationwastestedattheEBRTof

Figure6.MonitoringdataforthelaboratoryBTFunderstageIIIofintermittentloading:(a)withoutand(b)withanactivatedcarbonpre?lter.

thedecreaseintheremovalofthelessbiodegradablecompounds.ThiseffectwasobservedforthetwotestedEBRTs.Forexample,at15sofEBRT,theoverallREdecreasedfrom53to41%whenthecontinuousfeedingwaschangedtointermittentatanaverageinletVOCconcentrationof150mgCm?3(stageIII).TheREoftolueneandm-xylenedecreasedfromvaluesbelow10%,whereasundercontinuousfeedinga26.5%tolueneREand18.4%m-xyleneREwereobtained(Fig.5,dataofIL40gCm?3h?1,EBRT15s).Thedeteriorationoftheperformanceimpliesthatanaverageoutletconcentrationbelow75mgCm?3couldonlybereachedwheninletconcentrationduringworkinghourswaslowerthan105mgCm?3(stageII,ILof25gCm?3h?1andEBRTof15s).

Activatedcarbonpre?lter

InordertoevaluatethecapacityoftheACtobuffertheinletpeaksanditseffectonbioreactorperformance,anACpre?lterprecedingtheBTFwasinstalledandsequentiallyusedforatleast2weeksattheendofstagesItoIII.Intheseconditions,theACpre?lterachievedastableoperationwithreversibleadsorption/desorptioncyclesrelatedtotheworking/non-workingperiods.Adecreaseintheinstantaneousemissionwasobservedforallstages,sothesystemwasabletomeetthelegalregulations,evenatthemostsevereconditions(EBRTcarbon?pre?lter=0.6s).ExperimentaldataofthedailymonitoringofthebioreactorforstageIIIcanbeseeninFig.6.DataonthestandaloneBTFcon?gurationareplottedinFig.6a,whiledataontheACpre?lter+BTFareshowninFig.6b.Ascanbeseen,theACpre?ltertemporarilyaccumulatedduringperiodsofhighcontaminantloadingandthensubsequentlydesorbedcontaminantsduringintervalswhenconcentrationintheairwaslow,bufferingtheinletemissionintotheBTF.TheuseofanACpre?lterslightlyincreasedtheremovaloftolueneandm-xylene(9.3and7.3%RE,respectively),theoutletemissionwasmainlycomposedoftolueneandm-xylene.Therefore,the

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