[Digestion] [work] Re: Digestion Digest, Vol 2, Issue 40
adkarve at gmail.com
Mon Oct 25 20:25:32 PDT 2010
Dr. Soham Pandya, the Director of Centre of Science for Villages, told us
that the biogas generating system being demonstrated at his Institute was
meant for using the dung of a single cow. One accumulates the dung for 6
months, and then loads all of it at once into the biogas digester, as a
one-time feedstock. An Indian cow would produce daily about 6 kg dung.
Therefore, accumulation of 180 days' produce explains the1000 kg that goes
into the digester all at once. The biogas emanating from the digester is
stored by him in a moving drum type gas holder, which floats on water. He
has made this arrangement firstly to be able to deliver the gas to an
electricity generator under a constant pressure, and secondly to know how
much gas is produced daily.
My own explanation of this phenomenon is as follows: I assume that some of
the micro-organisms in the alimentary canal of herbivorous animals have the
capacity to digest lignin. I also assume that normally their number is quite
low, but in a system, in which only lignin is left after a certain period of
time, the lignin decomposing organisms are the only ones that can survive
and multiply. Therefore, from this point onwards, it is the lignin that
keeps the biogas production going. The lignin digesting organisms must be
rather slow in digesting lignin, because it takes them about 4 to 5 months
to digest the lignin left in the system.
On Tue, Oct 26, 2010 at 9:55 AM, David <david at h4c.org> wrote:
> 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 production.
> 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
> 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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Dr. A.D. Karve
President, Appropriate Rural Technology Institute (ARTI)
*Please change my email address in your records to: adkarve at gmail.com *
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