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PinkMonkey Online Study Guide-Biology
9.4 Methane
As stated earlier in this chapter, the common raw materials used for the production of methane are biomass products such as human and animal wastes, agricultural, industrial and domestic residues. Cattle dung is the most common material used in most biogas plants.
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Stage
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Process
involved
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Group
of bacteria involved
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1
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Solubilization
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Hydrolytic
fermentor bacteria
(mostly
anaerobic).
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2
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Acetogenesis
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Hydrogen
- producing acetogenic
bacteria
(facultative anaerobic)
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3
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Methanogenesis
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Methanogens(
i.e. methane
producing
anaerobic bacteria)
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Micro-organisms involved : Conversion of the biomass
into biogas (methane) is a process called anaerobic digestion. It
is completed in three stages. Breakdown of the biomass as each stage
is done by a different group of bacteria as shown in the above table.
Gobar gas plant (Figure 9.2) : As the biogas (gobar
gas) production is an anaerobic process, it is carried out in an air tight,
closed cylindrical concrete tank called a digester. In countries
like India, domestic gobar gas plants use single digester tanks (Fig.
9.2). The tank has a concrete inlet basin on one side for feeding fresh
cattle dung (gobar). There is a concrete outlet on the outer side
for removing the digested sludge. The top of the tank serves as the gas
tank. It has an outlet pipe for the gobar gas/ biogas.
Figure 9.2 Domestic Gobar gas plant (Diagrammatic)
Process : Fresh cattle dung is fed into the digester
tank through the inlet and allowed to remain there. After about 50 days,
a sufficient amount of gobar gas is accumulated in the gas tank. It is
conducted through the outlet pipe and used for domestic purposes. The
digested sludge (digested biomass) is removed from the tank and is used
as fertilizer. The tank is again filled with fresh dung and the process
is repeated.
Uses
(1) Gobar gas is mainly used for cooking and lighting in rural areas.
(2) Also used in internal combustion engines to power water pumps and electric generators.
(3) Used as a fuel in the fuel type refrigerators.
There are certain advantages in using methane (gobar gas) as
a source of energy :
i. Methane is very insoluble, hence it separates
very readily from the fermentor system.
ii. It can be very easily collected, pressurized
or liquified for storage.
iii. It is readily combustible.
Other advantages are :
(a) Sludge is used as fertilizer.
(b) It serves as a pollution free method for the disposal
of human and animal wastes in rural areas.
(c) The anaerobic process involved also eliminates
pathogenic bacteria from the biomass.
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