microbes in production oF biogas
Biogas is a methane rich fuel gas produced by anaerobic breakdown
or digestion of biomass with the help of methanogenic bacteria
or methanogens Methanobacterium is a common methanogenic
bacteria.
Biogas is made up of methane (50-70%), carbon dioxide (30-40%)
with traces of nitrogen, hydrogen sulphide and hydrogen. 50% of
the combustible energy present in the organic waste can be changed
into methane gas. The energy released from biogas depends upon the
proportion of methane present in it. The calorific value of biogas is
23-28 MJ/m^3.
As the biogas production is an anaerobic process, it is carried out in an
air tight, closed cylindrical concrete tank called a digester. The tank
has a concrete inlet basin on one side for feeding fresh cattle dung.
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 biogas.
Biogas generation is a three-stage anaerobic digestion of animal and other organic wastes. The latter consist of lignin, cellulose,
hemicellulose, lipids and proteins. Lignin cannot be broken down under anaerobic conditions.
Cellulose digestion is slower than that of other substances. In the first stage of anaerobic digestion (solubilisation), facultative
anaerobic decomposer microbes bring about enzymatic breakdown of complex organic compounds into simpler and soluble
compounds often called ‘monomers’. For this, the decomposer microbes secrete cellulases, proteases and lipases (cellulolytic,
proteolytic and lipolytic enzymes).
In the second stage (acidogenesis), the simple soluble compounds
of microbial digestion or monomers are acted upon by fermentation
causing microbes. The latter change the monomers into organic acids.
Organic acids, especially acetic acid, are acted upon by methanogenic
bacteria in the third or final stage (methanogenesis). The methane
bacteria convert organic acids as well as carbon dioxide into methane.
The biogas thus formed is stored in tanks for supply.
The technology of biogas production was developed in India by
collaboration of Indian Agriculture Research Institute (IARI) and
Khadi and Village Industries Commission (KVIC).
advantages of biogas
Using organic wastes first for biogas generation has following
advantages over their direct use as fuel or fertiliser:
(i) It provides both energy and manure.
(ii) Biogas has wider applications than the direct burning of organic wastes.
(iii) The energy value of biogas is lower than that of organic matter but due to more efficient handling, the net energy output is
roughly equal to the output in direct burning of organic wastes.
(iv) Minimises the chances of spread of faecal pathogens.
(v) The fertiliser value of the manure produced in biogas plants is similar to that of manure formed directly from organic wastes.
(vi) Biogas use does not add to pollution.
microbes as biocontrol agents
The natural method of pest and pathogen control involving use of viruses, bacteria and other insects (which are their natural
predators and pests) is called biocontrol or biological control.
For example, Lady bird beetle (beetle with red and black markings) feeds on aphids while dragonflies prey upon mosquitoes. Free
living fungus Trichoderma exerts biocontrol over several plant pathogens.
An example of microbial biocontrol agent that can be introduced in order to control butterfly caterpillars is the bacteria Bacillus