[Digestion] Fwd: The biology of biogas production

Paul Harris paul.harris at adelaide.edu.au
Tue Jun 28 21:44:39 CDT 2011


G'day A.D. Karve et al,

 

This post from a while back prompted an interesting thought - if you are
right we may be able to acclimate a digester to using just CO2 as the carbon
source, so we could convert CO2 back to methane and solve both CO2 emissions
and "peak oil".

 

The quality ratio of CH4 to CO2 does vary a bit, sometimes being less than
50% methane and sometimes claims of over 90% methane, but David Fulford has
shown that sugar and starch give 50% methane so any improvement is due to
some methanogens using CO2 produced earlier in the sequence and H+ from
water and acids to make CH4 and H2O.

 

Happy digesting,

HOOROO

 

Mr. Paul Harris, Room 202 Charles Hawker Building, Faculty of Sciences, The
University of Adelaide, Waite Campus, PMB 1, Glen Osmond SA 5064 Ph    : +61
8 8303 7880      Fax   : +61 8 8303 4386
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From: digestion-bounces at lists.bioenergylists.org
[mailto:digestion-bounces at lists.bioenergylists.org] On Behalf Of Anand Karve
Sent: Thursday, 2 June 2011 12:50 PM
To: digestion at lists.bioenergylists.org
Subject: [Digestion] Fwd: The biology of biogas production

 

 

---------- Forwarded message ----------
From: Anand Karve <adkarve at gmail.com>
Date: 2011/6/2
Subject: Re: [Digestion] The biology of biogas production
To: Gasan Osojnik <gasan.osojnik at gmail.com>



Dear List,

 Irrespective of the substrate, design of the system or the temperature of
the reaction, the proportion of methane to carbon dioxide in the biogas
seems to be constant all over the world. Is there an equilibrium between
these two gases that keeps this proportion constant? Because in that case,
one might introduce carbon dioxide from outside into the biogas plant and
see if the organisms in the digester produce more methane to reach the
euilibrium constant. I shall be grateful to get your reaction on this. 

Yours

A.D.Karve  

2011/3/22 Gasan Osojnik <gasan.osojnik at gmail.com>

Hi Mohamed,

The general (though I am sure there will be other interpretations) mechanism
of biogas formation is 4-step and involves:
1. Hydrolysis (degradation of polymers)
2. Acidogenesis (the formation of volatile fatty acids - low molecular
carboxylic acids)
3. Acetogenesis (the formation of acetate, CO2 and H2)
4. Methanogenesis (from acetete -> CO2 and CH4 is formed, from CO2 and H2 ->
CH4 is formed, methanogenesis from acetate and CO2+H2 has to run
simultaneously for the proces to be stable) 

The last step is the reason why there will be always some CO2 in biogas.
Each of this steps is carried out by different groups of microorganisms.

So the initial biochemical sources of biogas are carbohydrates, proteins,
fats etc. In the long run, any substance that can be converted
intermediately either to dissolved CO2 and H2 or to acetate is appropriate
for biogas production.

BR from Slovenia, Gasan

 

Ilja Gasan OSOJNIK ČRNIVEC, L05 - Laboratory for Environmental Sciences and
Engineering 

 

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National Institute of Chemistry

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SI-1001 Ljubljana

 

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