I purchased a homesteading book back in the '70s that had plans for
a single-family, 4-cow anaerobic digester (batch method, not flow-through).
It would produce enough methane for normal (if there is such a thing)
heating and cooking (in a mid-midwest environment). I also have a book
somewhere (purchased at the same time) by a South African hog farmer (3000
hogs) who constucted several large flow-through anaerobic digesters which
provided enough energy to power the entire farm's energy requirements (he
connected an old modified deisel engine/generator to the gas collector).
The moral of the story I got is that it IS economically feasible for
small-scale (on-farm) use. Drawbacks to usage of self-generated methane
from digesters is a) H2S (hydrogen sulphide) which can be removed by passing
the gas through a slurry of iron filings or steel wool, and b) CO2, which an
be precipitated out through a solution of Calcium Oxide. Neither problem is
insurmountable or terribly expensive.
The solids (sludge) have a higher N content as insoluable organic
nitrogen than aerobically produced compost (which produces high soluable
For what it's worth...
Improved State Mottos - Ohio:
Don't Judge Us by Cleveland
From: David Drexler [mailto:email@example.com]
Sent: Saturday, May 13, 2000 1:24 PM
To: Sanet Message
Subject: Anaerobics feasibility?
While researching for a large source of organic fertilizer I ran
across a company offering an anaerobic digester. They claimed any
organic type material could be used as input. My interest was caught
by the use of chicken litter, steer waste and piggy effluent. They
claimed an output of methane, CO2, and a dry bagable soil amendment with
a high N content. They claimed the sale of methane, CO2, and fertilizer
is an economical venture for the construction of the digester.
My question to this list is there enough "energy" in animal waste or
municipal waste for that matter, to justify such a plant operation?
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