Biogas as a rural energy source
Composition
Biogas contains 55-75 percent methane, plus hydrogen, carbon
dioxide, and hydrogen sulphide. The percentage of inflammable methane gas
depends on the raw material used to make the biogas.
Biogas is a mixture of gases produced by the chemical
decomposition of organic material such as animal dung. Consider installing a
biogas plant. Animal dung, human waste, and waste plant material can be
converted to clean, cheap fuel for cooking and lighting. And, the byproduct is
good fertilizer. Biogas plants, also known as digesters or Gobar gas plants, can
be installed to meet the needs of individual families on very small sites (3 m x
2 m), or for groups of several families.
Benefits of biogas plants
Raw materials
- Animal wastes, such as dung of cows, elephants, horses, goats,
poultry, and pigs
- Plant wastes, such as husks, straw, dry leaves, weeds,
vegetable skins
- Human excrete
- Industrial and domestic wastes, such as
billow dust, pulp mill effluent, fruit and vegetable wastes
How it works
The main parts of a biogas plant are the digester, mixing pit,
inlet and outlet pipes, outlet tank, gas holder, and gas pipe.
1 Organic material and water are mixed thoroughly in a mixing
pit.
2 The mixture flows through the inlet pipe into the digester
tank.
3 As the organic material decomposes (in the absence of oxygen),
biogas is produced.
4 Gas collects in the gas holder. This gas can be used for fuel.
5 Decomposed material in the digester becomes light. It passes
through the outlet pipe to the outlet tank. The material is good quality manure,
rich in nitrogen and phosphorus.
Diagram of biogas plant (not to
scale), showing the main features.
Size
The size of your biogas plant should depend on your family's
fuel requirements, and the availability of dung and other organic material. The
table below will help determine the right size biogas plant for your homestead.
|
Capacity of plant (gas production per day in
m3) |
Daily requirement of dung (kg) |
Approximate number of cattle required for |
Cooking for num ber of persons |
|
1 |
25 |
2-3 |
3-4 |
|
2 |
50 |
4-5 |
5-8 |
|
3 |
75 |
6-7 |
8-12 |
|
4 |
100 |
8-9 |
12-16 |
Community-size biogas plants are also available which can serve
the needs of several families.
Site selection
- Install the biogas plant on an elevated, open, and dry site
which is exposed to sunshine most of the day.
- It should be near the kitchen and the animal sheds.
- The groundwater level should be at least two metres below the
surface.
- The biogas plant must be at least 15 metres away from drinking
water wells and hand pumps.
- Where the sanitary latrine is linked to the biogas plant, the
water seal of the latrine must be at least 30 centimeters above the upper level
of the biogas plant's slurry outlet pipe.
Cost of installation
The cost of installation depends on the type and size of plant
installed. The table below shows the approximate cost of installation of various
models at various capacities (assuming a 40-day retention period):
|
Capacity of plant (m') |
KVIC1 model |
Deenbandhu model |
Pragati model |
|
1 |
8,000 |
5,500 |
6,500 |
|
2 |
11,000 |
6,500 |
9,000 |
|
3 |
14,000 |
8,000 |
11,500 |
|
4 |
16,500 |
9,500 |
13,000 |
1 Khadi and Village Industries
Corporation
The national government provides facilities for promotion,
construction, service, and repair of biogas plants. Substantial subsidies are
also available through the National Programme on Biogas Development. As well,
both commercial and cooperative banks provide credit, without land mortgage, for
installation of family-size biogas plants. Repayment periods range between 5 and
7 years.
Installation
Biogas plants are installed by self-employed workers specially
trained in the construction, installation, maintenance, and repair of biogas
plants.
For more information contact the block development office in
your area.
Contributor: Mr. S. K.
Jagwani
