[Digestion] The biology of biogas production

[David Fulford]

Dear Gasan and listers,

This is the sort of information we need on the biogas wiki. Can you 
provide us with some basic references (books, academic articles) that we 
can use for this data, especially on item 2. This is the clearest 
statement I have read on the relative proportions of CH4/CO2 from 
various substrates.

Do you mean stochiometric, or is stechiometric another term that we need 
to learn?

Thanks

David F

On 23/03/2011 07:49, Gasan Osojnik wrote:
> Dear dr. Karve
>
> I do not wish to engage nor in a lengthy philosophical or 
> physiological debate, but I do have one or two points to make:
>
> 1. Methanogenic archaea do not degrade sugar or even complex 
> substances, they use either acetate or hydrogen + carbon dioxide to 
> survive. They are old an primitive organisms, that originate back to 
> the beginning of life, even before glucose was formed by other 
> organisms, therefore they can feast on very basic energy sources.  
> There are not any other "methanogens" in other branches of the 
> evolution tree.
> 2. The stechiometric ratio of methane/carbon dioxide fromation from 
> carbohydrates is CH4/CO2 = 50/50, from fats = 62.5/37.5 and from 
> proteins 71/29 (due to absorptive properties of the sediment), so the 
> number mentioned is presumably based on anaerobic microbial protein 
> degradation?
> 3. The chain of microorganisms is not only highly likely, but is 
> confirmed by the means of certified analytical techniques, such as the 
> techniques of molecular biology and can be even seen under the  
> electron microscope. The sole biochemistry and the termoenergetics of 
> the methane formation process from polymers reveal, that it is 
> impossible for the process to start and finish in only one type of 
> unicellular procaryotic microorganisms (or any other). We have 
> pictures of microorganisms of species that are literary "glued one 
> another" for better substrate / intermediate exchange, and this is no 
> exception but a necessity for their survival. Currently it is believed 
> that around 800 species are involved in the biogas formation community 
> (not all at the same time) but this number is increasing rapidly (e.g. 
> 2008 this number was around 400). Personally I believe this number to 
> be much greater, as methanogenic microbiota is found on very diverse 
> parts of the planet and is a common way of surviving in areas with no 
> / low oxygen concentrations.
> 4. The issue of  CO2 which has ben adressed needs some basic insight 
> in the process. The dissolved co2 that is produced intermediately in 
> the proceses of acetogenesis (some also in the  hydrolysis ans 
> acetogenesis) is, as said, a substrate for the production of methane, 
> and is taken up very rapidly  by the archaea. Therefore, you should 
> not look at the intermediate CO2 as a product but as a reactant. As 
> most of the biogas (at least up to 70%) is formed via acetate 
> decarboxylation to methane and CO2. The partial pressures of surplus 
> CO2 equilibrate in the headspace of the reactor and the liquid, so the 
> CO2 that you get in biogas is actualy mostly the product of 
> acetoclastic methanogenesis.
>
> BR, Gasan
>
>
> Dear Mr. Afilal,
> if you used any substance that is digested by humans,(sugar, starch,
> digestible protein or fat), it gets completely converted into biogas by
> the methanogens. 1 kg of any of these substances would yield about 1 kg
> biogas, containing the theoretically calculated proportion of roughly 
> 25 to
> 30% methane and 70 to 75% carbon dioxide. The presence of a chain of
> micro-organisms, with each one producing a product that serves as food for
> the next one in the chain is not believable. If it were really so, one 
> would
> get a much higher concentration of carbon dioxide in the resultant biogas,
> because the intermediate organisms produce only carbon dioxide and not
> methane.
> Yours
> A.D.Karve
>
>
>
> On 22 March 2011 20:00, <digestion-request at lists.bioenergylists.org 
> <mailto:digestion-request at lists.bioenergylists.org>> wrote:
>
>     Re: The biology of biogas production
>
>
>
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> for more information about digestion, see
> Beginner's Guide to Biogas
> http://www.adelaide.edu.au/biogas/
> and the Biogas Wiki http://biogas.wikispaces.com/
>

-- 

********************************************************************
Dr David Fulford CEnv MEI, 15, Brandon Ave, Woodley, Reading RG5 4PU
d.j.fulford at btinternet.com <mailto:d.j.fulford at btinternet.com>, Tel: 
+44(0)118 326 9779 Mob: +44(0)7746 806401
Kingdom Bioenergy Ltd, www.kingdombio.com <http://www.kingdombio.com>, 
davidf at kindombio.com <mailto:davidf at kindombio.com>

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