[Digestion] Digestion Digest, Vol 34, Issue 8

[Paul Harris]

G'day Edward,

Have a look at the following - 
http://wastewaterbacteria.blogspot.com.au/2011/07/how-do-bacteria-lower-cod-and-bod.html

Basically it is a biological process (there are also thermal/chemical 
processes that yield carbon monoxide, hydrogen and methane from organic 
matter) that has several stages. Firstly extra-cellular enzymes break 
complex molecules (proteins, carbohydrates and starches) into smaller, 
soluble molecules that can enter the micro-organisms (this stage is 
known as "hydrolysis"). The next stage is "acidogenesis", where the 
products of hydrolysis are further broken down to short chain fatty 
acids, giving off CO2, hydrogen and possibly some methane. This is 
followed by "acetogenesis" where the fatty acids are reduced to acetic 
acid, again producing CO2 and some methane and hydrogen. Finally 
"methanogenesis" produces methane and CO2 from acetic acid (which is 
where the bulk of the methane is produced). There is another pathway 
where CO2 is reduced to produce methane and water, which uses up some of 
the CO2 from the other processes. Each stage is symbiotic, as the 
"waste" from one stage will inhibit that stage if it builds up too much 
but the waste is also the input to the next stage, which must keep the 
level low so the second stage is not also inhibited by high substrate 
levels. It's like us - too much food (or not enough!) makes us sick and 
if our waste accumulates instead of being disposed of we would get very 
sick as well!

Hope this helps,
Happy digesting,
HOOROO

On 24/06/2013 1:49 PM, Edward Silalahi (Medan) wrote:
> Dear sir,
> I meant how the chemical process or biological process can convert COD
> to be Bio gas detail? At least from theory
>
> Best Regards ++
>
>   
>
> Edward Silalahi
>
> Dy Head Mill and Engineering
>
> Asian Agri Group
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> MT Hariyono street no 1A Medan 20231
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> Email:Edward_Silalahi at asianagri.com
>
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