- Energy & Power
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- Buyers' Guide
How biogas may be part of the solution to inadequate forest cover
The population of Kenya, especially the rural community, continue to rely on wood for fuel despite its increasing cost. SkyLink Innovators is focused on tackling this problem by spreading the use of biogas as a source of fuel for cooking, heating and electricity; they have recently picked up a 2010 Ashden Award for it's innovative work.
The domestic biogas systems have a cylindrical, domed digester vessel built from brick. Biogas, which collects under the dome, is taken through a pipe to the kitchen. The cattle dung is mixed with water in an inlet tank and flows under gravity into the digester. Bacteria decompose the slurry under anaerobic (oxygen-free) conditions, and the biogas produced pushes the digested slurry into an outlet tank. The system is built in an underground pit which is re-filled with soil, so that only the inlet and outlet tanks, and the dome with the biogas pipe through it, are visible when the system is completed.
The larger sewage-treatment plants use a series of digesters, with an aerobic gravel filter as the final stage. These increase biogas production and kill pathogens in the output material, so that the liquid effluent can be used on crops.
Sky Link installs 12 to 16 cu m size domestic systems which are designed to use mainly animal dung. Such a system requires the household to have between about three and eight cows. The gas is used mostly for cooking but can also be used to generate electricity. The cost is about $1,850 (KSh 150,000).
Sky Link also installs larger systems for institutions, ranging in size from about 30 cu m for schools to 124 cu m in Meru prison. These can also process animal dung, but the main purpose of the larger ones is to manage human sewage from latrines. A typical school system costs about $19,753 (KSh1.6mn), and the 124 cu m plant for Meru prison cost about $42,000 (KSh3.4mn)