[Digestion] The biology of biogas production

[Gasan Osojnik]

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> wrote:

> Re: The biology of biogas production
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.bioenergylists.org/pipermail/digestion_lists.bioenergylists.org/attachments/20110323/52ef9fd4/attachment.html>