METHANOGENS AND BIOGAS ucla genomics

Methanogens Methanogens are bacteria that produce methane gas They can be used as sources of biogas gas This would be a renewable source of energy © 2008 Paul Billiet ODWS

Ecology Methanogens require anaerobic conditions In the digestive systems of herbivores, marshes or lake bottoms. Many require warm conditions to work best. They are associated with a source of organic matter (e.g. plant remains or sewage) and with heterotrophic bacteria The heterotrophs break down this organic matter to release compounds such as ethanoic acid (aka acetic acid or vinegar) and hydrogen The ethanoate ions are a substrate for the methanogens © 2008 Paul Billiet ODWS

Classification Methanogens belong to the Archaea group of the Prokaryotes Examples Methanococcus jannaschii Methanobacterium thermoautotrophicum The prokaryote kingdom has been split into several further kingdoms (e.g. Archaea and Eubacteria) based on the genetics and biochemistry of microbes © 2008 Paul Billiet ODWS

CH3COO+ + H-  CH4 + CO2 +36 kJ mol-1 Biochemistry Methanogens are chemoautotrophs Methanogens use a number of different ways to produce methane Using ethanoate (acetate) that may be derived from the decomposition of cellulose: CH3COO+ + H-  CH4 + CO2 +36 kJ mol-1 Or using hydrogen and carbon dioxide produced by the decomposers: 4 H2 + CO2  CH4 + 2 H2O +130.4 kJ mol-1 © 2008 Paul Billiet ODWS

Biogas production From the decomposition of wastes in farming sewage treatment A bi-product of the cleaning up of waste water Biogas consists of about 40% CO2 and 60% CH4 BEA Dithmarschen © 2008 Paul Billiet ODWS

Requirements a fermenter, which is supplied with an innoculum of bacteria (methanogens and decomposers) anaerobic conditions an optimum temperature of 35°C an optimum pH of 6.5 to 8 This needs to be monitored as the decomposers produce acids and they work faster than the methanogens consume the acids organic waste (biomass) e.g. sewage, wood pulp © 2008 Paul Billiet ODWS

Methanogens and the greenhouse effect Half of the methane produced by methanogens is used up as an energy source by other bacteria Half is lost to the atmosphere (600 M tonnes y-1) where it acts as an important greenhouse gas As more land is converted to rice paddy fields and pasture for grazing animals more methane will be produced DAF Shiga Pref. © 2008 Paul Billiet ODWS

Warming up the brew As global warming progresses the permafrost with thaw in the regions covered by tundra Tundra contains extensive reserves of frozen peat As the peat warms and melts, it will provide a source of material for methanogens © 2008 Paul Billiet ODWS

The knock on effect The amount of methane release into the atmosphere will accelerate. This in turn will drive global warming even further Peatlands form 20-30% of organic C in N. Hemisphere UNEP © 2008 Paul Billiet ODWS