[Stoves] Dung as fertilizer and fuel

[jason marshall]

---------- Forwarded message ----------
From: jason marshall <jdmarshall at gmail.com>
Date: Sep 29, 2006 7:38 AM
Subject: Re: [Stoves] Dung as fertilizer and fuel
To: adkarve <adkarve at pn2.vsnl.net.in>


That can't be entirely true, can it?

I mean, we know that if you put cow dung and water in a closed
container, you continue to get methane for some time, yes?  I will
grant you that cow dung may be very poor food for bacteria.

I can see what you mean about other means of innoculating the
bioreactor.  As I said before, I suspect that, as you say, most of the
value of the dung is from this standpoint.  What I know of intentional
microbial action I learned from homebrewing, and that tells me that
your primary goal is ensuring that whatever you consider to be 'good'
microbes overwhelm and outnumber what you consider to be 'bad'
microbes, at all times.  To me, that means that if you want to keep
any long-running system operating robustly, it should have a routine
and possibly frequent reintroduction of a concentrated source of your
'good' bacteria.  If you're adding new dung every day (especially if
you avoid dung from sick cows), that would most definitely accomplish
this.  If you source it from the other sources you mention, it
wouldn't necessarily be a one-time application.

Your comment about wasted energy I thought to be the most interesting.
  Once the methane production potential of the dung has been exhausted
(and with it, the primary threat from dung for greenhouse gas
production), is the rest truly wasted?  If you apply bioreactor output
to your fields, don't the yields increase not just from the minerals
in the dung, but also from the remaining energy?  I know, for
instance, that the dregs from beer production (dead yeast, and
suspeded particles from the original ingredients, which have settled
out of solution) have been shown to cause vigorous plant growth.  The
situation is not completely analogous, but I suspect there are some
similarities. Yeast are eventually killed by their own effluent
(alcohol) before they can completely consume the sugars, and we know
that plants can and do absorb and use complex molecules from the soil,
including sugars.  The dead microbes in the 'compost' will be broken
down by the microbes in the soil, releasing some of that pent up
energy back into the food chain.  That part of the chain at least is
similar.

Certainly, if I had a steady supply of non-food grade starch, or fine
cellulose (rice husks, sawdust), I would incorporate them into my
bioreactor without hesitation.  But am I really better off burning the
dung, and sending all of those minerals up into the air?  Isn't
precisely that use of animal dung one of the primary causes of topsoil
exhaustion in Ethiopia?

-Jason

On 9/27/06, adkarve <adkarve at pn2.vsnl.net.in> wrote:
> Dear Mr. Marshall,
> the methanogenic bacteria cannot digest lignin, but they can easily digest
> cellulose, starch, sugar, fat or protein. Any of these substances would
> yield methane if fed to methanogenic bacteria. Dung is not the food of the
> methanogenic bacteria at all. They are only thrown out of the body along
> with dung. Therefore dung is required only as a source of bacteria. However,
> one can equally well use water from the septic tank of a latrine, or slurry
> from an existing biogas plant. Once the bacteria have established themselves
> in the biogas plant, one can operate the plant entirely without dung. In
> fact that is how all our clients operate their own domestic biogas plants.
> The number installed by us has, in the meanwhile, reached 900.
> Yours
> A.D.Karve
> ----- Original Message -----
> From: jason marshall <jdmarshall at gmail.com>
> To: Stoves <stoves at listserv.repp.org>
> Sent: Wednesday, September 27, 2006 11:35 AM
> Subject: Re: [Stoves] Dung as fertilizer and fuel
>
>
> > I remember reading at some point about a research project to determine
> > if mixing cow manure with waste cellulose could increase methane
> > production.  Unfortunately I'm unable to find a citation now.  It
> > would have been sometime in the last few years.
> >
> > All I can recall now was that yes, it did improve output, but I can't
> > tell you what sort of cellulose source they used (sawdust? straw?
> > wastepaper?), nor the ratio (1:1 seems to ring a bell, but I don't
> > know if that's by volume or by mass).
> >
> > The theory went that the manure provides the microbial action, but
> > most of the energy comes from the 'new' material.
> >
> > I wonder, for instance, what would happen if one put manure and
> > bagasse in a digester.
> >
> > -Jason
> >
> > On 8/29/06, adkarve <adkarve at pn2.vsnl.net.in> wrote:
> > > The sugar industry in India uses bagasse containing about 50% moisture
> as
> > > fuel, to produce steam for generating electricity. Dry dung cakes,
> > > especially those that contain straw and dry leaves as additives, have
> > > definitely a higher calorific value than bagasse with 50% moisture. The
> > > western part of Maharashtra State in India, has a well established sugar
> > > industry as well as a well established dairy industry. The dung
> available
> > > with the dairies can be mechanically briquetted, after squeezing the
> water
> > > out of the dung by means of a filter press. This process would yield the
> so
> > > called dung tea, that can go back to the field. Briquettes made from the
> > > dung solids can be burned in the boilers of the sugar factory to
> generate
> > > electricity or sold to anybody who may want to use them as fuel. Making
> > > biogas from dung is a wasteful process. One gets only 25 per cent of the
> > > original calorific value, if the dung is converted into methane.
> > > Yours
> > > A.D.Karve
> > >
> > >
> > >
> > > _______________________________________________
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> > > http://listserv.repp.org/mailman/listinfo/stoves_listserv.repp.org
> > >
> >
> >
> > --
> > - Jason
> >
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>
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--
- Jason


-- 
- Jason