Biogas usage
Practical Action
The following table gives the information about the amount of waste that is needed and the
output.
The capacity of a
digester
(square meter)
1
2
3
4
Raw material (cow
dun) Kg (per day)
25
50
75
100
Sri Lankan biogas digester
For cooking
(number of people)
3-4
4-7
7-10
10-12
The number of lamps
that can be burnt
2
3
6
8
This is a novel method identified by the Sri Lanka National Engineering and Research
Institute. It also won the silver medal at the International New Developers contest held in
Geneva, Switzerland, 1996. As shown in the picture the cylinder is made using brick and
cement. The cambers used to collect the biogas are made of low-cost 45 gallon barrels, which
can be bought from a normal market. As shown in the picture these barrels are kept
separately and connected with air pipes.
The raw material (hay, grass, seaweed, waste from the markets etc) is added and waste is
collected by removing the cap on the top.
Connecting pipe
Water
Manhole
Connecting pipe
Dome
Concrete ring
G.I Pipe
Gas release pipe
Gas collecting
chambers
Manometer
Water
Digester
Brick base and walls
Concrete ring
Concrete bottom
The special advantages of the Sri Lankan bio-digester
When filled, biogas can be obtained for about 5-6 months.
Therefore there is no need to add the raw material daily
The main raw material is hay, which is abundant in Sri Lanka and is commonly burnt.
Additionally, waste vegetables from markets (market waste), aquatic plants and other
grass can be used. Even some factory waste can be used.
The remaining waste is organic manure full of nitrogen.
This is an environmentally friendly method of generating energy and helps in the process
of recycling waste that is otherwise a threat to the environment.
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