METHANOGENS AND BIOGAS

MethanogensMethanogens are bacteria that produce methane gas They can be used as sources of biogas gasThis would be a renewable source of energy

2008 Paul Billiet ODWS

EcologyMethanogens 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 bacteriaThe heterotrophs break down this organic matter to release compounds such as ethanoic acid (aka acetic acid or vinegar) and hydrogenThe ethanoate ions are a substrate for the methanogens

2008 Paul Billiet ODWS

ClassificationMethanogens belong to the Archaea group of the ProkaryotesExamples Methanococcus jannaschiiMethanobacterium 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

BiochemistryMethanogens are chemoautotrophsMethanogens 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-1Or 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 productionFrom the decomposition of wastes in farming sewage treatmentA bi-product of the cleaning up of waste waterBiogas consists of about 40% CO2 and 60% CH4

2008 Paul Billiet ODWS

Requirementsa fermenter, which is supplied with an innoculum of bacteria (methanogens and decomposers)anaerobic conditionsan optimum temperature of 35Can optimum pH of 6.5 to 8This needs to be monitored as the decomposers produce acids and they work faster than the methanogens consume the acidsorganic waste (biomass) e.g. sewage, wood pulp

2008 Paul Billiet ODWS

Methanogens and the greenhouse effectHalf of the methane produced by methanogens is used up as an energy source by other bacteriaHalf is lost to the atmosphere (600 M tonnes y-1) where it acts as an important greenhouse gasAs more land is converted to rice paddy fields and pasture for grazing animals more methane will be produced

2008 Paul Billiet ODWS

Warming up the brewAs global warming progresses the permafrost with thaw in the regions covered by tundraTundra 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 effectThe amount of methane release into the atmosphere will accelerate. This in turn will drive global warming even furtherPeatlands form 20-30% of organic C in N. Hemisphere

2008 Paul Billiet ODWS