[Digestion] [work] Re: Digestion Digest, Vol 2, Issue 40

David david at h4c.org
Mon Oct 25 18:55:46 PDT 2010


On 10/25/2010 1:28 PM, Markus Schlattmann wrote:
> I still don't believe in those 540 m³ from 1000 kg dung....

A sensible analysis. Maybe the key to the conundrum is the statement:

> ...the biogas plant in Wardha... accepts 1000 kg cattle dung as a 
> one-time load and produces daily 3 cubic meter biogas continuously 
> over a period of 180 days...

It is well known that batch digestion does not produce the same amount 
of biogas every day. Obviously it takes some time for the ecology of 
the digester to get established (during which time, of course, gas 
production is low), and it is surely something approaching a law of 
biology that the more digestible components of the substrate will be 
used up first, and then some of the more recalcitrant materials will-- 
eventually-- be digested. The succession of these stages offers a 
well-known curve, which is either bell-shaped, if it plots daily 
production, or a long S (ogee) curve if we are plotting cumulative 

In sum, I have no doubt that biogas is produced, and that for a period 
of time production is good. Thus I would accept that the reported 
plants produce well for a time, but not that they produce the same 
amount every day, continuously for six months. But surely the 
statement as quoted has to do with genuine enthusiasm, and should not 
be taken as a rigorous mathematical description.

While my search turned up a number of references to the organization 
in Wardha in connection with biogas, none provided any reference to 
these batch digesters, unless they are very large clay pots, as one 
reference mentions. It would be salutary to have some literature on 
the subject, if any has been produced.

David William House
"The Complete Biogas Handbook" |www.completebiogas.com|
/Vahid Biogas/, an alternative energy consultancy |www.vahidbiogas.com

"Make no search for water.       But find thirst,
And water from the very ground will burst."
(Rumi, a Persian mystic poet, quoted in /Delight of Hearts/, p. 77)

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