Organic waste is a growing environmental problem and this coupled with the search for renewable domestic energy sources has sparked off interest in the west in the production of biogas or methane gas from such waste products.
Methane was discovered in the 18th century by Volta and has been produced on an organised basis from industrial and sewage sludges for more than 50 years. Denmark, a country comparable in agricultural and industrial development with Ireland is a world leader in the treatment of animal manures by bacterial digestion and hence the production of methane gas. Large scale plants are being used in the agricultural sector to a high degree of success.
Many believe that the time has come to put the production of Biogas into perspective, to show how and where it is used and to determine whether its production is viable as a supplement to existing power sources and a pollution control.
There are three natural sources of methane:
1. Is in the form of natural gas, similar to the gas being used in many Irish homes and is found trapped beneath the Earths crust.
2. Is from the decomposition of vegetation by bacteria in marsh ground. This methane can escape from beneath the mud and ignite causing the phenomenon sometimes known as Willo the Wisps.
3. Is from the stomachs of animals especially herbivores such as cattle and sheep. Food such as grass is broken down anaerobically (in the absence of oxygen) and Methane is produced.
In addition to methane, ethanol and hydrogen are both potentially useful as they can be obtained also from renewable sources like Biomass(trees, crops etc.)
The digestion process and production of methane has long been valued for its efficiency and cost effectiveness in the treatment of organic waste. In the 1840's, the city of Exeter England had its street lighting provided from methane gas produced from sewage. In developing countries where energy sources are more of a problem than in the west, work has been underway since the 19th century on smaller scale digestors for the production of Biogas. The Gobar Gas Institute was set up after the success of Biogas production and promotes the use of anaerobic digestion by families and villages, in the production of methane and fertilisers.
In China today there are reported to be over seven million small scale gas producing plants in operation saving millions in fuel costs for Chinese families.In addition to the gas produced, the remaining digested sewage sludge is a valuable organic fertiliser. The sludge retains a high nutrient value while the polluting organic content and the smell are reduced. This can be spread on the land in the same way raw manure is spread. Anaerobic digestion is also being recognised as an economic form of pollution control as the process can produce its own energy.
In a world where natural resources are rapidly depleting and where, for the first time in the history of the planet, more of the population are living in cities than rural areas, serious consideration of economic, social and environmental implications of Biogas should be made.