[Digestion] Digestion Digest, Vol 11, Issue 3

Thu May 3 12:14:28 CDT 2007

Eric--On a mass basis, every gram of COD that is digested to methane 
produces 0.25 grams of methane--that is just stoichiometry. In terms of 
volume, at STP. the equivalence is 0.35 L of methane per gram of COD that 
is degraded.

   As Warren indicates, the methane production depends on the feedstock 
because the fraction that is biodegradable and the extent of degradation 
are variable.  There are lab bioassays that can be used to estimate the 
biodegradation potential for a feedstock and, of course, there is a lot of 
information in the literature about the extent of degradation (COD 
reduction) for most of the common feedstocks.

 	John

John Ferguson,
Acting Chair and Professor
Department of Civil and Environmental Engineering
Box 352700
University of Washington
Seattle WA 98195-2700
phone: 206-543-5176
fax:   206-685-9185
jferg at u.washington.edu
http://www.ce.washington.edu

On Thu, 3 May 2007, digestion-request at listserv.repp.org wrote:

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> Today's Topics:
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>   1. Calculating Methane Generation (Eric Fitch)
>   2. Re: Calculating Methane Generation (Warren Weisman)
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>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Thu, 3 May 2007 10:58:47 -0400
> From: "Eric Fitch" <fitch at springstreetgarage.com>
> Subject: [Digestion] Calculating Methane Generation
> To: <digestion at listserv.repp.org>
> Message-ID: <011801c78d93$8db92ae0$6a0fa8c0 at Papelbon>
> Content-Type: text/plain;	charset="us-ascii"
>
> Dear AD Listers,
>
>
>
> Can anyone site a credible reference that explains how to calculate the
> methane output from a proposed digester with a known feedstock?  I am
> looking for a valid set of equations where inputs would be measurable
> properties like COD, TSS, VS, etc. and the output would be a normalized
> result, like mass of methane produced per mass of COD input.
>
>
>
> I have found conflicting references while searching the web that result in
> an order of magnitude variation.  Unfortunately this spread straddles the
> point of viability for this project.  In order to move forward I need more
> confidence in the expected methane output.
>
>
>
> Thank you in advance for your help.
>
>
>
> Sincerely,
>
> Eric Fitch
>
>
>
> ------------------------------
>
> Message: 2
> Date: Thu, 3 May 2007 09:12:58 -0700 (PDT)
> From: Warren Weisman <weiswar at yahoo.com>
> Subject: Re: [Digestion] Calculating Methane Generation
> To: digestion at listserv.repp.org
> Message-ID: <905951.5420.qm at web62401.mail.re1.yahoo.com>
> Content-Type: text/plain; charset=iso-8859-1
>
>
> Eric,
>
> You're asking the million dollar question, but the
> answer is methane production is a variable and no one
> has done a definitive work on it, yet. There's no way
> to predict it with great accuracy---which makes it so
> fun to work with!
>
> But you might find some use in METHANE GENERATION FROM
> HUMAN, ANIMAL AND AGRICULTURAL WASTES by the National
> Academy of Sciences. It predicts a methane
> production---separated from biogas---between 3.6-4.8
> cubic feet per pound of volatile solids over 15 days.
> but, of course there's things---like gas recirculation
> and better stirring---that can be done to improve gas
> production and of course, lots you can do to reduce
> it, too! The above mentioned book has exhaustive
> footnotes and references. Another helpful resource is
> A CHINESE BIOGAS MANUAL---which is the small digester
> standard at this time.
>
> Warren Weisman, USA
>
> --- Eric Fitch <fitch at springstreetgarage.com> wrote:
>
>> Dear AD Listers,
>>
>>
>>
>> Can anyone site a credible reference that explains
>> how to calculate the
>> methane output from a proposed digester with a known
>> feedstock?  I am
>> looking for a valid set of equations where inputs
>> would be measurable
>> properties like COD, TSS, VS, etc. and the output
>> would be a normalized
>> result, like mass of methane produced per mass of
>> COD input.
>>
>>
>>
>> I have found conflicting references while searching
>> the web that result in
>> an order of magnitude variation.  Unfortunately this
>> spread straddles the
>> point of viability for this project.  In order to
>> move forward I need more
>> confidence in the expected methane output.
>>
>>
>>
>> Thank you in advance for your help.
>>
>>
>>
>> Sincerely,
>>
>> Eric Fitch
>>
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> End of Digestion Digest, Vol 11, Issue 3
> ****************************************
>