Biogas consists mainly of
methane
(about 60% to 80%) and carbon dioxide
(about 20% to 40%) with some other gases, such as
hydrogen sulfide, ammonia, and water vapour, in trace amounts.
Biogas is highly flammable and is produced through
the anaerobic (without oxygen) decomposition of organic materials from
plants and animals. It is similar in most
respect to Natural gas (obtained
from fossil fuel) used for heating and cooking at homes and industries.
Biogas, just like natural gas consists mainly of methane, which is
the gas that gives both gases their burning strength.
Raw biogas, however, has much lower strength than natural gas
because its methane content is lower than that of natural gas. Natural gas
has between 90 to 99 % methane content where most raw biogas will have
about 60 to 80% methane. To make biogas compete with natural gas, the
impurities (gases such as CO2, H2S etc) should be removed. CO2 removal is termed biogas upgrade while the removal of H2S and
other gases is often termed biogas cleaning.
Therefore, after undergoing some purification,
biogas can be used just the
same way we use natural
gas to produce heating and
cooking at homes and offices.
Biogas is obtainable or through biogas digesters. The
naturally occurring sources of biogas are:
Wetlands
(e.g. swamps and marshes),
Sewage sludge and
Solid waste dumps or landfill sites.
Various techniques are being
developed for the abstraction of biogas from these sources.
Biogas is also produced,
artificially, using
biogas generators/digesters.
Biogas digesters
are large air-tight tanks used to simulate the natural processes
that produce biogas,
by allowing the digestion of organic matters from plants and animals under
anaerobic conditions.
The processes are as follows:
Plant materials and animal wastes (feedstock) are
shredded and placed inside the biogas
digester.
Water is added and the tank is closed
and properly sealed to allow no air into the tank.
After several days, biogas begins to form at the top of
the tank due to the activities of some bacteria usually termed
“methanogenic” bacteria (i.e. methane forming bacteria).
The biogas that is formed is piped into a storage
location where it can be used as needed.
As the production of biogas in the generator slows down,
old feeds of organic matters are taken out and new feeds of organic
matters and water added to the generator.
The old feeds can be dried and used as soil manure or
fertilizer.
Food processing (by-products of meat
processing, potato, dairy, cheese whey, sugar beet, pea hulls, and
vegetables); and
Energy crops cut as silage (wheat, barley,
clover, alfalfa, ryegrass, turnips and corn).
Unlike natural gas,
biogas is renewable; it can be replaced in a life time. It is
environmentally friendly; it reduces greenhouse gases. Methane gas from
Swamps, Landfill sites and Sewage Treatment sites, that could have
been released directly to the atmosphere are redirected for power
production. In cases where plants are planted to provide feedstock to
Biogas generators or digesters, the plants serve as sinks to reduce the
amount of carbon dioxide released to the atmosphere.
