04/06/2015 [Digestion]BiogasCOD/CH4yield

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[Digestion]BiogasCOD/CH4yieldGasanOsojnikgasan.osojnikatgmail.comMonFeb1422:32:04PST2011

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Dearall,

IthinkthediscussedparametersregardingtheCOD/CH4yieldhavetobefurtherclarified.

Thereferencevalue0.35m3methane/kgofCODisatheoreticalvalueeveryonecancalculate,andisusedforengineeringpurposesinthedesigning&optimizationstageofthebiogasplant.AsMarcusalreadyexplained,itiscalculatedonthebasisofCOD*of*methane,therefore:

CH4+2xO2>CO2+2xH2O

m(CH4)=16gm(2xO2)=64gCOD(CH4)=16gCH4/64gO2=4gCOD

As1moleofgas=22,4dm3@stp,

(CH4)=16g/22,4dm3=0,71g/dm3

And1gofCH4occupies@stp

V(CH4)=22,4/16g=1,4dm3CH4

Tosummarize,1gofCH4is4gofCODandoccupies1,4dm3CH4@stp,

therefore,per1gofCOD

Y=1,4dm3CH4/4gCOD=0,35m3CH4/kgCOD

Anaerobicdegradationof1kgCODofsubstrate(whichis"transfered"totheCODofmethane)thereforetheoreticallyyields0,35m3ofmethane.Asexpected,thisvaluesarestronglyundermatchedinrealoperatingconditions.

ThevaluementionedbyMel,derivedfromexperimentalconditions,ismostlikelycoincidental,meaningthattheoperatingconditionsinthatparticularcase(0,35m3CH4/4kgCOD)meaning,thattheYi=(0,35/1)/(0,35/4)=25%oftheoreticalyield,orcanbederivedfrominappropriateinterpretationofthetheoreticalvalues,as1000molofCH4doindeedcorrespondto4kgofCOD(4gCOD/moleofCH4).

BRfromSI,Gasan

>>ThanksMarcusforyourresponsetomyquery:>>>>>>>All,>>>>>>Doyouknowof(have)awayto"translate"BODand/orCODtomethane>>>potential?ItwouldofcoursehavetobeintermsofBOD/CODremoved>>>givingrisetosomuchmethane.>>>>>>Mel>>>>>>HiMel,>>>>>>ifyouconsidertheremovedCODiscompletelytransferredtoCH4inthe>>>Biogas(CO2=0COD)youcancalculate:>>>>>>1gCODremoved>0,25gCH4>>>Or1gCODremoved>0,35LCH4(273K,1013mbar).>>>>>>Ifyouwanttoestimatemoreexactlyyoumayconsiderthatsomefothe>>>removedCODflowsintoH2andmicrobialbiomass.>>>>>>Markus>>>>Yourcalculation,however,isatoddswiththestatementinGradyetal.

04/06/2015 [Digestion]BiogasCOD/CH4yield

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>>1999,page600in"BiologicalWastewaterTreatment2ndedition"Marcel>>Dekker.Thestatementisthat4kgCODremovedgenerates0.35m3of>>methane(0.35LCH4/4gCODremoved).Alsothatfigureornearaboutsis>>foundinotherdocuments.Apparentlyitwasderivedfromtheoretical>>calculation(notunderstoodbyme)andalsofromseriousobservationof>>realsystems.Ifrepetition=validity,thhanthfigureisusable.>>>>Perhapsotherscanweighinonthetheoreticalend,orreportother>>"sightingsofthetranslation.>>>>Mel>nextpartAnHTMLattachmentwasscrubbed...URL:

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