Kineticanalysisofpalmoilmillwastewatertreatment
byamodifiedanaerobicbaffledreactor
M.Faisala,∗,HajimeUnnob
a
DepartmentofChemicalEngineering,FacultyofEngineering,SyiahKualaUniversity,Darussalam,BandaAceh23111,Indonesia
bDepartmentofBioengineering,SchoolofBioscienceandBiotechnology,TokyoInstituteofTechnology,
4259Nagatsuta-cho,Midoriku,Yokohama226-8501,Japan
Received4September2000;accepted19March2001
Abstract
Amodifiedanaerobicbaffledbioreactor(MABR)wasstudiedundersteady-stateconditionsfortreatingpalmoilmillwastewater.Methanegasproductionwasintherangeof0.32–0.42l-CH4(g-COD)−1removal,whichcorrespondedtothemethanecontentof67.3–71.2%withintherangeofexaminedhydraulicretentiontime(HRT)of3–10days.TheremovalrangesofCODandgrease/oilwerefrom87.4to95.3%andfrom44.1to91.3%,respectively.Thetotalvolatilefattyacidproductionwas1450mgl−1atHRTof3daysandgraduallydecreasedto608mgl−1atHRTof10days.Basedontheexperimentaldata,akineticmodelwasdiscussed.Throughthemodelthebiokineticparameterswereevaluated,whichrepresentedthebehaviorofreactorverywell.©2001ElsevierScienceB.V.Allrightsreserved.
Keywords:Anaerobicbioreactor;Kineticmodel;Steady-state;Hydraulicretentiontime
1.Introduction
Anaerobictreatmentofwastewaterhasbeenconsideredtohaveanumberofadvantagesovertheconventionalaer-obicprocess.Itsavestheenergyneededforaeration,con-vertsorganicpollutantsintomethanegas,areadilyuse-ablefuel,needslownutrientrequirementandproduceslowbiomass.Thetechnologyinrecentyearshasbeenappliedtothetreatmentofmanyhigh-strengthindustrialwastewa-ters.Butitsapplicationisstilllimitedmostlytotreatmentofreadilybiodegradablewastewaterfromagricultureandfood/beverageindustries[1].
Takingintoconsiderationtheslowgrowthrateofmanyanaerobicmicroorganisms,particularlymethanogenics,themainobjectivesoftheefficientreactordesignmustbehighretentiontimeofbacterialcellswithverylittlelossofbacte-riafromthebioreactor.Thetechnologicalchallengetoim-provetheanaerobicdigestionliesinenhancingthebacterialactivitytogetherwithgoodmixingtoensureahighrateofcontactbetweenthecellsandtheirsubstrate.
Theanaerobicbaffledreactorwasdesignedprimarilyforwater-solublewaste[2].Inthisstudy,theoriginaldesignofBachmannetal.[2]wasmodifiedinordertoimprovetheefficiencyofthereactor.Thebaffledesignwasmodifiedin
Correspondingauthor.Fax:+62-651-52222.
E-mailaddress:ftunsyiah@aceh.wasantara.net.id(M.Faisal).
∗boththeheightofbioreactorandthevolumeofthecom-partments,whichenabledtoincreasetheabilityofentrap-pingmicrobe-richsmallparticlesinthereactor.Thebaffleswereangledat45◦tothehorizontalandmakingupcomeranddowncomerratioof4:1toreduceentrancevelocitiesontheupcomeranddirectincomingwastewatertocenterofthechambers.Aseriesofverticalbaffleswhichforcethewastewatertoflowunderandoverthemasitpassesfrominlettooutlet.Thewastewatercan,thereforecomeintoin-timatecontactwithalargeamountofactivebiomassasitpassesthroughbioreactor.Thisnewconfigurationhasbeenshownthatmodifiedanaerobicbaffledbioreactor(MABR)iscapableofholdingahighretentiontimeofcellsinbioreactorandprovingefficienttreatmentofpalmoilmillwastewater.Theanaerobicbaffledreactor(ABR)showedpromiseforindustrialwastewatertreatment,i.e.simpleandinexpensivetoconstruct,sincethereisnomovingpartormechanicalmixingdevice.Inaddition,ithasbeenshowntobestabletoshockloadingandcapableofachievinghighvolumetricrates[2–5].
Despitetheadvantagesofferedbyanaerobicbaffledbiore-actor,onlyafewstudieshavebeenconductedfromtheview-pointoftheeffectonhydraulicretentiontime(HRT)understeady-stateconditionandscarcekineticanalysishasbeenreportedforsubstrateutilizationandmethaneproductioninthebioreactor.Thus,inthisstudythemodifiedanaerobicbaffledreactorperformanceundersteady-stateconditionwas
1369-703X/01/$–seefrontmatter©2001ElsevierScienceB.V.Allrightsreserved.PII:S1369-703X(01)00122-X
26M.Faisal,H.Unno/BiochemicalEngineeringJournal9(2001)25–31
NomenclatureAbiokineticparameter(KskY/Kh)Bspecificmethaneyield
(l-CH4(g-COD)−1removal)
B0maximumspecificmethaneyield(l-CH4
(g-COD)−1removalatinfiniteretentiontime)Fvolumetricsubstrateremovalrate(gl−1perday)khydrolyzedsubstrate−1transportratecoefficient(lg−1s)
Khsubstratehydrolysisratecoefficient(s−1)Kshalfsaturationconstantforhydrolyzedsubstrate(gl−1)Rrefractorycoefficient
Sbiodegradablesubstrateconcentrationintheeffluent(gl−1)
Shconcentrationofhydrolyzedsubstrate(gl−1)Suintracellularconcentration−1ofhydrolyzedsubstrate(gl)
S0influentbiodegradablesubstrateconcentration(gl−1)
Srrefractorysubstrateconcentrationintheinfluent(gl−1)
Stototalsubstrateconcentrationintheinfluent(gl−1)Sttotalsubstrateconcentration1intheeffluent(gl−1)Xconcentrationofcell(gl−)Y
cellyieldcoefficient(gg−1)
Greeklettersµµspecificgrowthrateoforganism(perday)mmaximumspecificgrowthrateof
organism(perday)θcmeancellretentiontime(day)investigated,andalsoakineticmodelwasproposedwiththeevaluationofmodelparameters.
2.Kineticmodel
Ithasbeengenerallyassumedthatthegrowthofmixedculturesincomplexwastewaterwouldbesimilartothegrowthofpureculture.Here,theMonodequation,whichhasbeenusedsuccessfullyinstudyingthekineticsofpurebacterialcultureutilizingsimplesubstrates,wasassumedindescribingtheanaerobicandaerobictreatmentofthecom-plexwastewater.
Digestionofcomplexorganicwastesinvolvesthehydrol-ysisofpolymericcompoundsandonlythesolubilizedcom-poundsmaybeconsideredasthegrowthlimitingsubstratesintermsoftheMonodrelationship.Itisnecessarytotakeintoaccountthehydrolysisprocessinmodelbuildingfordigestionofcomplexand/orwater-insolublewastewater.Inthepresentpaper,akineticmodelforsubstrateuti-lizationandmethaneproductioninanaerobicdigestionof
complexpalmoilmillwastewaterinamodifiedanaerobicbaffledbioreactorisdiscussedbyassumingrttotakeplaceinthreestages:(1)extracellularhydrolysisofcomplexwastew-aterintosolublesubstrates;(2)transportofthesolubilizedsubstratesintocells;and(3)utilizationofthesolublesub-stratesforcellgrowthandproductformation.
Stage1.Hydrolysis,afirststepsolubilizationofsolidand/oroil/grease,isassumedtobeafirstorderreactionwithrespecttotheconcentrationofhydrolyzablesubstrateS(mass/volume)asdSh
dt
=Kh(S−Sh)(1)
whereShistheconcentrationofhydrolyzedsubstrate(mass/volume)−1andKhisthehydrolysisratecoefficient(s).
Stage2.Internalization/transportofhydrolyzedsubstrateintothecellisconsideredtobeproportionaltothedifferenceinconcentrationsofthehydrolyzedsubstrateoutsideandinsidethecellsandtotheconcentrationoftheactivecellbiomassX(mass/volume).Itisassumedthathydrolyzedsubstrateenteringintothecellsismetabolizedfastcomparedwiththetransmembranetransferrate,sothatitsintracellularconcentrationSuisnegligiblysmall[6].Whentheuptakeofhydrolyzedsubstrateisnotratelimitingwithrespecttohydrolysis,thefollowingrelationshipcanbewrittenas−
dSh
dt
=k(Sh−Su)X=kShX(2)
where−1kisthehydrolyzedsubstratetransportratecoefficient(s).
Eqs.(1)and(2)giveSh=
KhSkX+K(3)
h
Stage3.Cellgrowthonhydrolyzed(assimilable)substrateisassumedtofollowaMonodtypekineticsexpressedasµ=
µmShKs+S(4)
h
whereKsisthehalf-saturationconstantwithrespecttohy-drolyzedsubstrate(mass/volume).UponsubstitutionofthevalueofShfromEq.(3),Eq.(4)becomesµµm=S(KskX/K(5)
h)+Ks+SAmaterialbalanceoncellconcentrationinMABRcanbeexpressedas
Q0X−QXe+VRµXR−VRkdXR=
VRdXdt
(6)
whereXRandXeare,respectively,concentrationofmicroor-ganisminbioreactorandineffluent,VRandQarevolumeofbioreactorandwastewaterflowrate,respectively.Understeady-stateconditionsofcontinuousdigestioninMABR
M.Faisal,H.Unno/BiochemicalEngineeringJournal9(2001)25–3127
(dX/dt=0)andtheassumptionthatconcentrationofmi-croorganisminthewater,X0=0,andiftheendogenousmetabolismordeathrateisnegligiblecomparedwiththegrowthrate(kdµ),thenµ=
QXe
1VRXR=θc
(7)
VolumetricsubstrateremovalrateF(mass/volume/time)
maybeexpressedasF=
S0−Sθc
(8)
whereS0istheinfluenthydrolyzable(biodegradable)sub-strateconcentration(mass/volume),Sthehydrolyzablesub-strateconcentration(mass/volume)intheeffluentandθcisthemeancellretentiontime.
Undertheconditionofactivemicrobialreaction,main-tenanceenergyandmicrobialdecayareconsideredsmall,sothatthebiomassyieldcoefficientY(cellmass/substratemass)isassumedconstant[6].X=Y(S0−S)
(9)
ByuseofEq.(9),Eq.(5)canberearrangedasµm
µ=AS0−SKsS+S+1(10)whereA=KskY/Kh.
2.1.Incorporationofrefractorycoefficient
Inthecaseofcomplexorganicsubstrates,whicharegen-erallyexpressedasCOD,apartofthesubstrateisusuallyrefractorytobiodegradation.TherefractorycoefficientRisdefinedasSr/Sto,whereSrandStoarerespectivelythere-fractoryandtotalCODconcentrationintheinfluentfeed.WhenStdenotestheeffluenttotalCOD,thefollowingex-pressionscanbewrittenasS0=Sto(1−R)(11)S=St−RSto
(12)ByuseEqs.(6),(11)and(12),Eq.(10)canberearrangedintoEq.(13).
StSto=(1−R)A+(Ks/Sto)µmθc+A−1+R(13)
Eq.(13)showstherelationshipbetweentheinfluentandeffluentconcentrationsoftotalCODintermsofmicrobialandsubstratecharacteristics.2.2.Methaneproductionkinetics
FollowingthederivationofChenandHashimoto[7],letBandB0bethespecificmethaneyieldinlitersatSTPpergramofCODremovedanditsmaximumatinfiniteretentiontime,
respectively,thebiodegradableCODinthebioreactorwill
beproportionaltoB0−BandalsoB0willbeproportionaltothebiodegradableCODloading[7].ThenthefollowingrelationshipcanbewrittenasS0−SS=B
B0−B(14)
InsertingEq.(14)intoEq.(10)resultsasµmµ=ABKsB0−B+S+1(15)ByuseofEqs.(6)and(12),Eq.(15)isrearrangedtogive
B
B0=1−A+(Ks/(1−R)Sto)µmθc+A−1(16)
Eq.(16)representstherelationshipbetweenthemethaneproductionrate,B,andtheinfluentsubstrateconcentrationtobetreated,Sto,whichshowsthatatconstantinfluentsub-strateconcentration,allthebiodegradablesubstratechangedintobiogasasB/B0approachesunityastheretentiontimeofactivemethanogen,θc,approachesinfinite.However,itshouldbecarefultonotethatthisequationisbasedontheassumptionthatconstantfractionofthebiodegradablesub-strateistobeconvertedintomethanegas.3.Materialsandmethods3.1.Wastewaterpreparation
ThepalmoilmillwastewaterwasobtainedfromP.T.PerkebunanNusantaraI,Aceh,Indonesia.Thecharacteris-ticsofthepalmoilmillwastewaterusedintheexperimentisshowninTable1.
Thewastewaterwasstoredat4◦Cuntilrequired.Thisstoragehadnoobservableeffectonthecomposition.ThepHwasneveradjustedandnochemicalswereaddedtothewastewater.3.2.Bioreactor
ThebioreactorwasmadeofglassasshowninFig.1.Thereactordesignwasrectangularboxwithinternalverti-calbafflesalternatelyhangingandstanding.Thesebaffles
Table1
CharacteristicofpalmoilmillwastewaterusedinexperimentParametersAveragevalue(mgl−1)COD16000TOC
4000Greaseandoil410Phosphor38.3NH396TKN179BOD58700
pH
4.8
28M.Faisal,H.Unno/BiochemicalEngineeringJournal9(2001)25–31
Fig.1.Experimentalset-up.
dividedthebioreactorintofivecompartments.Thebafflesspacingwasdeterminedbykeepingthecompartmentsonequalsizeandmakingtheupcomeranddowncomerratioof4:1.Thereactorhasasizeof50cminlength,16.5cmwidthand38.5cminheight,havingatotaleffectivevolumeof20l.Thedownflowandtheupflowchamberswere2and8cmwide,respectively.Thelowerportionsofthebaffleswerebent5cmabovethereactorbottomat45◦angleinor-dertoroutetheflowtothecenteroftheupflowchamberstoachievebettermixingofmicroorganismsandsubstrate.Peristalticpumpswereusedtofeedthebioreactorandtorecyclethemixedliquor.3.3.Reactoroperation
Afterthestart-upstagehadbeencompleted,thesteady-stateoperationwasconducted.Theseedingandac-climatizationofanaerobicmixedcultureandstart-upbiore-actordatawerepresentedelsewhere[8,11].Thesteady-stateperformancewasevaluatedunderhydraulicretentiontimeof3–10days(organicloadingrateof1.60–5.33g-COD(lday)−1.Therecycleratio(recycleflowrate/feedflowrate)wasmaintainedat30,whichvalueenablestoassumethemicrobialreactioncanberepresentedbyanaveragesub-strateconcentrationinthereactor.Atgivenloadingrate,thebioreactorwascontinuouslyoperateduntilsteady-stateconditionwasachieved,wheneffluentCOD,VSSandgasproductionrateinbioreactorbecameconstant.Thensam-pleswerecollectedandsubjectedtotheanalysisofthefollowingparameters,i.e.feedandeffluentCOD,effluenttotalalkalinity;effluenttotalvolatilefattyacid,effluent
suspendedsolidsandvolatilesuspendedsolids,reactorpH,gasproductionandcompositionweremeasuredaccordingtostandardmethods[9].
3.4.Estimationofthekineticparameters
Fortheestimationofkineticparametersµm,Ks,A,B0andR,thenon-linearleast-quaresmethodwasusedbymin-imizingthecombinedsumoferrorsquaresforresponsesofSt/StoandBthroughthebestcriterion[6].Eq.(13)wasusedtopredictthevaluesofStandEq.(16)wasusedforcalculatingvaluesofB.4.Resultsanddiscussion
Thesteady-stateperformanceofMABRattheHRTof3,5,6,7and10daysareshowninTable2.AsshowninFig.2,effluentCOD,volatilefattyacid(VFA)andgrease/oildecreasedasthehydraulicretentiontimeincreased.Effi-cienciesofCODremovalandgrease/oilremovalwereintherangeof77.3–95.3%and44.2–91.3%atHRTof3–10days,respectively.TheMABRperformancewasworthattheshortestHRTof3days.4.1.VolatilefattyacidandpH
Fig.3showsthatVFAconcentrationwasfairlyhighatHRTof3daysandgraduallydecreasedatlongerHRTop-eration.LowlevelconcentrationofVFAatthelongerHRTcanbeattributedtoloworganicloadingrate.Inaddition,
M.Faisal,H.Unno/BiochemicalEngineeringJournal9(2001)25–31
Table2
Bioreactorperformanceonsteady-stateconditionEffluentparameters
Hydraulicretentiontime(days)3
COD(mgl−1)TOC(mgl−1)
Volatilefattyacid(mgl−1)Alkalinity(mgl−1)pH
VSS(mgl−1)
Greaseandoil(mgl−1)
Biogasproductionrate(lperday)
BiogascompositionCH4(vol.%)CO2(vol.%)
Methanegasrate(lperday)
Methanegasyield(l-CH4(g-COD)−1removal)VSSinbioreactor(mgl−1)SRT(days)
36301110143017507.0257020042.169.130.927.40.33035900189
52010899145025406.9014702293468.032.023.10.41336400124
6161080713901790
6.90140019328.770.229.820.10.42035500152
7136060612501910
6.96104011721.867.332.714.60.35033900229
8133028710501940
7.1091310018.869.121.913.00.35512300107
10
29
7541636082070
7.2027035.612.271.228.98.710.326460239
Fig.2.EffluentCOD,VFA,grease/oilremovalefficiencyundersteady-stateconditiononvarioushydraulicretentiontimes(brokenlineshowstheeffluentCODcalculatedbyEq.(13)).
Fromthosedata,itcanbeseenthatpHvaluesatdiffer-entHRTwerestableintherangeof6.90–7.02,althoughnochemicalswereaddedforadjustingpH.Thestabilityisconsideredtohavebeenachievedbythehighrecycleratioof30timesfeedflowrate.Byrecyclingtheeffluenttotheinfluent,thealkalinityintheeffluentwasrecovered.
BasedontheobservedlowconcentrationofremainedVFAandhighperformanceofMABR,itcanbeconcludedthatMABRisareactorsystemwhichcanmaintainactivemethanogensbykeepingtheVFAconcentrationlow,espe-ciallyatthelongerhydraulicretentiontime.Thisallowsforhighconversionoforganicmattertothefinalendproduct,methane,withoutsignificantaccumulationofintermediateproducts.
4.2.Biogasproduction
shortHRTpromotedtheaccumulationofintermediateprod-uctssuchasVFA.ThehigherconcentrationsofVFAattheshorterHRTarealsoreflectedinlowerCODremovalasshowninTable2andFig.2.TheVFAconcentrationatlow-estHRTwas1430mgl−1,whichdecreasedto608mgl−1atthelongestHRT.
Fig.4showsthatbiogasproductionwashigheratshortHRTthanatlongHRT,whichisconsideredtobeduetohighorganicloadingrate.Biogasproductionsteadilyde-creasedashydraulicretentiontimeincreased.AttheHRT
Fig.3.EffluentVFAconcentrationandpHundersteady-stateconditiononvarioushydraulicretentiontimes.Fig.4.Biogasproductionandmethanegasyieldundersteady-statecon-ditiononvarioushydraulicretentiontimes.
30M.Faisal,H.Unno/BiochemicalEngineeringJournal9(2001)25–31
of10days,thebiogasproductionwas12.2lperdaywhichincreasedto42.1lperdayathydraulicretentiontimeof3days.Althoughthebiogasproductiondecreasedwithin-creaseofHRT,methaneyieldwasalmostconstantofabout0.38l-CH4(g-COD)−1removed.
TheresidualVFAconcentrationintheMABRshowedthatthesystemsmaintainedactivemethanogensandthatveryhighpercentagesoftheorganicmatterswereconvertedintothefinalendproduct,methaneandcarbondioxides.Effluentvolatilesuspendedsolid(VSS)wasrangingfromabout210to1470mgl−1acrosstheoperationalrangeofHRTasshowninTable2.EffluentsolidswerefoundtoincreasewithdecreaseinHRT.ThehighVSSconcentrationinreactordemonstratesthatMABRiscapableofholdinghighsolidsinthereactorandprovidingefficienttreatmentofpalmoilmillwastewater.EvenattheshortestHRTof3daysthesystemcanachievehighperformanceasabove77.3%CODremoval.
Thesolidretentiontimes(SRT)werecalculatedbasedonEq.(8)usingaveragevaluesofVSSconcentrationinbiore-actorandeffluentVSS,theeffectivevolumeofbioreactorandwastewaterflowrate.SRTpresentedinTable2showsasimilartrendasthatoftheVSSwithahighSRToccurringunderhighVSSconditions.However,theoperationalSRTwasconsiderablybeyondtheminimumvaluerequiredforpreventingfailureduetowashoutofthemethanogensinaconventionalanaerobicreactor.Therefore,itissafelycon-cludedthatoneoftheimportantcharacteristicsofMABRisitsabilitytoretainhighlevelsofVSSinbioreactor.4.3.Biokineticparameters
Theexperimentaldataundersteady-statecondition(Table2)wereanalyzedandkineticparameterswereevalu-atedbythemethodmentionedin2.4.Thevaluesofkineticparametersandrefractorycoefficient(R)calculatedaccord-ingtothemodelequationsareshowninthefirstlineofTable3.Byusingtheseparameters,thespecificmethaneyield(B)andthesubstrateconcentrationintheeffluent(St)werecalculatedbyEqs.(16)and(13),respectively,whichareshownrespectivelyinFigs.4and2withbrokenlines.Themodelequationsrepresentedtheexperimentaldatawell,whichimpliesthereasonabilityofthemodelequations.Generallyspeaking,themodelparametersarespecifictotheconfigurationandoperationalmodeofthereactor,which
inturnsuggeststhenecessaryguidelinesforoperatingthereactorsystem.Therefractorycoefficientreflectsthedi-gestibleabilityofthesubstrateintheanaerobicdigestion.ThevaluesofRreportedbytheotherresearchersaresum-marizedinTable3togetherwiththepresentstudy.There-actorsusedinthereportsarenotnecessarilysimilartothepresentstudyinbothscaleandtype.However,thevalueRcanbecomparedinthelightofthedifferenceofmaterialstohavebeendigested.Refractorycoefficientinthisstudyismuchsmallerthanthatfordairymanureandcattlewaste,whileitishigherthanthatforaceticacidandpropionicacid.SmallerRvaluemeanshigherdigestibility,whichshowedthatthepalmoilmillwastewaterisappropriatesubstrateforanaerobicdigestiontoobtainmethanegas.TheRval-uesforaceticacidandpropionicacidwereinsignificant,becausetheseliquidorganicsubstratesareconsideredtobecompletelydigestible.
ThemeaningofthekineticparameterAismadeclearbymodifyingEq.(10)intoEq.(17).
µS(1/(1−A))S==µmA(S0−S)+Ks+S(AS0+Ks)/(1−A)+S(17)Intermsofmicrobialspecificgrowthrate,thevariablegroupA(S0−S)+Kscanbeseenasanapparenthalfsaturationsubstrateconcentration.Maximumattainablespecificgrowthratewillbeµm/(1+Ks/S0),sincethemaximumattainablesubstrateconcentrationisS0.ThekineticparameterA=KskY/Khisaparameterwhichreflectssolelythereactioncharacteristics,independenlyofthesubstrateconcentration.Fig.5showsagraphicalrepresentationofEq.(17)incaseofKs/S0=0.2.Smallvalueofparameter,A,correspondstoanextremelyhighhydrolysisrate,i.e.largeKh.Underthiscondition,thespe-cificgrowthratewillbemaximumforthegivensubstrateconcentrationirrespectivelyofthereactioncharacteristics.Whentheparameter,A,increasestounity,thespecificgrowthratebecomesaproportionalfunctionofsubstrateconcentration.Further,theparameterincreasesgreaterthanunity,wherethemicrobialsubstrateutilizationrateisacontrollingparameterforthegrowth,thedependencyofthespecificgrowthrateonthesubstrateconcentrationbecameconvex,andthephysicallyattainablemaximumspecificgrowthratewillbeµm/(1+Ks/S0).However,underthemoderatesubstrateconcentration,thespecificgrowthrate
Table3
KineticparametersandrefractorycoefficientsintheanaerobicdigestionofvariousfeedsFeed
PalmoilmillwastewaterDairymanureCattlewasteAceticacidPropionicacid
ab
Sto(gl−1)16.0(COD)82.2(VS)49.7(COD)1.145.52
A0.3290.7510.6400.0000.001
R0.1190.5850.4000.0000.000
µm(perday)0.3040.4500.2500.4400.274
Ks(gl−1)0.3130.2800.3000.3000.250
B0(lg−1)0.381a0.2230.370a0.332b0.37
ReferenceThiswork[6][10][6][6]
l-CH4(g-COD)−1removal.l-CH4g−1acidremoval.
M.Faisal,H.Unno/BiochemicalEngineeringJournal9(2001)25–3131
Fig.5.EffectofparameterAonthemicrobialspecificgrowthrate.
willbetoosmalltobeobservableifthehydrolysisrateisverysmall.
TheevaluatedvalueofA=0.329inthepresentstudywasclosetothatfordairymanureandcattlewaste.Thisresultsuggeststhatthedigestionprocessofsubstrateweresimilarinthesecases,probablydependedonthesolubiliza-tionprocessofsolidand/oroilysubstances.Thesevaluesarehigherthanthoseforthecasesofaceticacidandpropi-onicacidduetothattheseacidsarewatersolubleandeasilyassimilablesubstratesforanaerobicdigestion.Therefore,in-significantvalueofAimpliesthatthehydrolysissteppriortosubstratetransportintothecellsisnegligiblysmall.ThemaximumspecificmethaneyieldforpalmoilmillwastewaterofB0=0.381l(g-COD)−1removalissimilartothatforcattlewaste,showingthesamebiodegradability.While,thevaluesofB0fordairymanurecannotbecompareddirectlywiththeabovenumeralbecauseofthedifferenceintheunitasindicatedinthefootnoteofthetable.TheKsandµmvaluesobtainedinthepresentanalysisareclosetothereportedvaluesfordairymanure,cattlewaste,aceticacidandforpropionicacid,showingsimilaractivityformicrobialgrowth.5.Conclusion
Amodifiedanaerobicbaffledbioreactorisapplicabletotreatpalmoilmillwastewater.Understeady-statecon-ditionathydraulicretentiontimefrom3to10days,theorganicremovalefficiencyintherangeof77.3–95.3%was
achievedonatotalCODbasis,72.1–95.9%onTOCba-sisand44.2–91.3%ongrease/oilbasis.Methanegasyieldwasfrom0.32to0.42l-methane(g-COD)−1removed,bio-gasproductionratewas12.2–42.1lperdayandcontainedaround70%ofmethaneontheaverage.
Theproposedkineticequationsareapplicableforanaer-obictreatmentofpalmoilmillwastewaterbyamodifiedanaerobicbaffledreactor.Thekineticequationwellrepre-sentedtheexperimentalmethaneproduction.Thekineticparameterswerewelldiscussedintermsofwastewatercharacteristic.Acknowledgements
Theauthorswouldliketoexpresstheirthanksforthesup-portbytheProjectforHigherEducationDevelopmentSup-portinIndonesia(HEDS)organizedbyJapanInternationalCooperationAgency(JICA)andProjectManagementUnitofIndonesia(PMU).References
[1]H.Herbert,O.C.Chan,Toxicityofphenoltowardsanaerobic
biogranules,Wat.Res.31(9)(1997)2229–2242.
[2]A.Bachmann,V.L.Beard,P.L.McCarty,Performancecharacteristics
ofanaerobicbaffledreactor,Wat.Res.19(1)(1985)99–106.
[3]R.Boopathy,V.F.Larsen,E.Senior,Performanceofanaerobicbaffled
reactorintreatingdistillerywastewaterfromascotchwhiskyfactory,J.Biomass16(1988)133–143.
[4]A.Grobicki,D.C.Stuckey,Performanceoftheanaerobicbaffled
reactorundersteady-stateandshockloadingcondition,Biotechnol.Bioeng.37(1991)344–355.
[5]S.Nachaiyasit,D.C.Stuckey,Theeffectofshockloadsonthe
performanceofananaerobicbaffledreactor(ABR):stepandtransienthydraulicretentionshocksatconstantfeedstrength,Wat.Res.31(11)(1997)2747–2754.
[6]A.Barthakur,M.Bora,H.D.Sigh,Kineticmodelforsubstrate
utilizationoforganicfeeds,Biotechnol.Prog.7(4)(1991)369–376.[7]Y.R.Chen,A.G.Hasyimoto,Substrateutilizationkineticmodelfor
biologicaltreatmentprocess,Biotech.Bioeng.22(1980)2081–2095.[8]Faisal,H.Unno,Palmoilmillwastewatertreatmentbyamodified
anaerobicbaffledreactor,in:ProceedingsoftheRegionalSymposiumonChemicalEngineering,1998,pp.104–110.
[9]APHA,StandardMethodsfortheExaminationofWaterand
Wastewater,17thEdition,AmericanPublicHealthAssociation,Washington,DC,1989.
[10]A.G.Hasyimoto,L.Roman,U.S.Hruska,Methanefromcattlewaste:
effectsoftemperature,hydraulicretentiontime,andinfluentsubstrateconcentrationonkineticparameter,Biotech.Bioeng.26(1982)2039–2052.
[11]T.Setiadi,Faisal,Palmoilmilleffluenttreatmentbyanaerobic
baffledreactor,in:ProceedingsoftheAquatechAsia’94,1994.
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