- 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 mechanical 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.

The common feedstock for biogas include:

• Livestock Manure (e.g. cow dungs, pig dungs/hog, poultry dungs etc),
• 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.

Related pages: Renewable Energy Resources, Biodiesel, Ethanol

External Biogas Links:

• Methane Digester for Biogas
• Construction of a Biodigester
• Small Scale Biodigester built in the Philipines by Gerry Baron