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The Power of Biogas

Biogas is a generic term for the gas produced from the anaerobic digestion of biological material, ranging from cooking oils and crops to manure. Its composition is generally 60% methane and 40% carbon dioxide, though this mixture varies depending on the material used. The process of digestion eliminates all harmful pathogens, weed seeds and odors.

Methane is a highly potent fuel similar in composition to natural gas, which can be used to power an engine. In turn, the energy it generates can feed directly into the electrical grid. The process also creates heat energy, which can be used locally.

The Anaerobic Digestion Process

Used for decades in the treatment of sewage and animal wastes, anaerobic digestion is an efficient way to generate and capture the useful energy of many organic products, from bakery dough to manure.

The anaerobic digestion process can be divided into three steps:

1. Hydrolysis occurs as complex organic molecules are broken down into their constituent parts, including fatty acids, amino acids, and simple sugars.

2. Volatile acid fermentation converts the products of hydrolosis into organic acids through acidogenesis and acetogenesis.

3. Methanogenesis is the final stage, in which methane, analogous to natural gas, is formed, along with carbon dioxide and water.***

Methane: Fuelling the Benefits

The natural decomposition of manure releases a combination of carbon dioxide and methane into the atmosphere. The amount of methane produced by livestock such as cattle and sheep is substantial: in Australia (home to 120 million sheep and 28 million head of cattle) these animals constituted 12.3% of the country's greenhouse gas emissions in 2002*. In the US, livestock manure accounts for about 7% of methane released.

For more information on the environmental impacts of methane and the environmental and social benefits of biogas, click here.

* "Ewe, Too, Can Cut Greenhouse Gases." CBC website. February 2, 2005.
** "Air Emissions from Ammonia and Methane in Livestock Operations." Resources for the Future. 2006