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

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

Biochemistry Methanogens are chemoautotrophs Methanogens use a number of different ways

to produce methaneUsing 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