So where does that leave us?
Well, number one, we
obviously must get serious about population control and per capita consumption
of power and, number two, if we don't want to see brownouts and rationing of
the power we do use, we'd better start looking around for ecologically-sound alternative
sources of energy.
And there are alternatives.
One potent reservoir that's hardly been tapped is methane gas.
Hundreds of millions of
cubic feet of methane -- sometimes called "swamp" or bio-gas -- are
generated every year by the de- composition of organic material. It's a
near-twin of the natural gas that big utility companies pump out of the ground
and which so many of us use for heating our homes and for cooking. Instead of
being harnessed like natural gas, however, methane has traditionally been
considered as merely a dangerous nuisance that should be gotten rid of as fast
as possible. Only recently have a few thoughtful men begun to regard methane as
a potentially revolutionary source of controllable energy.
And with good reason.
Population pressure has practically eliminated India's forests, causing
desperate fuel shortages in most rural areas. As a result, up to three-quarters
of the country's annual billion tons of manure (India has two cows for
every person) is burned for cooking or heating. This creates enormous medical
problems -- the drying dung is a dangerous breeding place for flies and the
acrid smoke is responsible for widespread eye disease -- and deprives the
country's soil of vital organic nutrients contained in the manure.
dung gas is 55-65% methane, 30-35% carbon di- oxide, with some hydrogen,
nitrogen and other traces. Its heat value is about 600 B.T.U.'s per cubic
sample analyzed by the Gas Council Laboratory at Watson House
in England contained 68% methane, 31% carbon dioxide and 1%
nitrogen. It tested at 678 B.T.U.
compares with natural gas's 80% methane, which yields a B.T.U. value of
gas may be improved by filtering it through limewater (to remove carbon
dioxide), iron filings (to absorb corrosive hydrogen sulphide) and calcium
chloride (to extract water vapor).
dung slurry is composed of 1.8-2.4% nitrogen (N), 1.0-1.2/a phosphorus
(P2O5), 0.6-0.8% potassium (K2O) and from 50-75% organic humus.
one cubic foot of gas may be generated from one pound of cow manure at 75
F. This is enough gas to cook a day's meals for 4-6 people.
225 cubic feet of gas equals one gallon of gasoline. The manure produced
by one cow in one year can be converted to methane which is the equivalent
of over 50 gallons of gasoline.
engines require 18 cubic feet of methane per horse- power per hour. *Hindi
for "cow dung"
eleven-year-long research program has yielded designs for five standardized,
basic gobar plants that operate efficiently under widely varying conditions
with only minor modifications (see construction details of 100 cubic foot
digester that accompany this article)... and a treasure trove of specific,
field-tested principles for methane gas production.
There are two kinds of
organic decomposition: aerobic (requiring oxygen) and anaerobic (in the absence
of oxygen). Any kind of organic material -- animal or vegetable -- may be
broken down by either process, but the end-products will be quite different.
Aerobic fermentation produces carbon di- oxide, ammonia, small amounts of other
gases, considerable heat and a residue which can be used as fertilizer.
Anaerobic decomposition -- on the other hand -- creates combustible meth- ane,
carbon dioxide, hydrogen, traces of other gases, only a little heat and a
slurry which is superior in nitrogen content to the residue yielded by aerobic
takes place in two stages as certain micro-organisms feed on organic materials.
First, acid- producing bacteria break the complex organic molecules down into
simpler sugars, alcohol, glycerol and peptides. Then -- and only when these
substances have accumulated in sufficient quantities -- a second group of
bacteria converts some of the simpler molecules into methane. The
methane-releasing microorganisms are especially sensitive to environmental
the operation and common to all gobar plant designs' is an enclosed tank called
a digester. This is an airtight tank which may be filled with raw organic waste
and from which the final slurry and generated gas may be drawn. Differences in
the design of these tanks are based primarily on the material to be fed to the
generator, the cycle of fermentation desired and the temperatures under which
the plant will operate.
designed for the digestion of liquid or suspended- solid waste (such as cow
manure) are usually filled and emptied with pipes and pumps. Circulation
through the digester may also be achieved without pumps by allowing old slurry
to overflow the tank as fresh material is fed in by gravity. An advantage of
the gravity system is its ability to handle bits of chopped vegetable matter
which would clog pumps. This is quite desirable, since the vegetable waste
provides more carbon than the nitrogen-rich animal manure.
anaerobic digestion of animal wastes, such as cow manure, takes about fifty
days at moderately warm temperatures. Such matter -- if allowed to remain
undisturbed for the full period -- will produce more than a third of its total
gas the first week, another quarter the second week and the remainder during
the final six weeks.
consistent and rapid rate of gas production may be maintained by continuously
feeding small amounts of waste into the digester daily. The method has the
additional advantage of preserving a higher percentage of the nitrogen in the
slurry for effective fertilizer use.
continuous feeding system is used, care must be taken to insure that the plant
is large enough to accommodate all the waste material that will be fed through
in one fermentation cycle. A two-stage digester -- in which the first tank
produces the bulk of the methane (up to 80%) while the second finishes the
digestion at a more leisurely rate -- is often the answer.
collected inside an anaerobic digester tank in an inverted drum. The walls of
this upside down drum extend down into the slurry, forming a "cap"
which both seals in the gas and is free to rise and fall as more or less gas is
weight provides the pressure which forces the gas to its point of use through a
small valve in the top of the cap. Drums on larger plants must be
counter-weighted to keep them from exerting too much pressure on the slurry.
Care must also be taken to insure that such a cap is not counter-weighted to
less than atmospheric pressure, since this would allow air to travel backwards
through the exhaust line into the digester with two results: destruction of the
anaerobic conditions inside the tank and possible destruction of you by an
explosion of the methane-oxygen mixture.
of an inverted drum should never be less than three inches smaller than the
radius of the tank in which it floats, so that minimal slurry is exposed to the
air and maximum gas is captured.