METHANOGENS
AND BIOGAS
ucla genomics
Methanogens
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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
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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
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
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© 2008 Paul Billiet ODWS
Biogas production
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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
© 2008 Paul Billiet ODWS
BEA Dithmarschen
Requirements
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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
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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
© 2008 Paul Billiet ODWS
DAF Shiga Pref.
Warming up the brew
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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
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The amount of
methane release into
the atmosphere will
accelerate.
This in turn will drive
global warming even
further
Peatlands form 2030% of organic C in
N. Hemisphere
© 2008 Paul Billiet ODWS
UNEP