Methanogenesis
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During the fourth and last stage of anaerobic degradation of organic matter, a group of methanogenic bacteria both reduce the carbon dioxide by hydrogen and decarboxylate acetate to form methane (CH4) (figure 2). The methanogenic bacteria are obligate anaerobes, able to utilize only certain determined substrates. They use organic substrate or specific carbon source such as acetate, H2 and formate. Some strains are autotrophic, using only CO2 or CO as carbon source. Generally, 70 - 80 % of the methane formed from the organic materials originates from acetate. The rest is mainly derived from H2 and CO2.
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