Biogas systems the way forward for Kenya?

Kenyacurrently has 1.9 per cent forest cover, which is well below the 10 per cent minimum recommended by the UN. 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 US$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 US$19,753 (KSh 1.6 million), and the 124 cu m plant for Meru prison cost about US$42,000 (KSh 3.4 million)

The institutional systems are built entirely by Sky Link technicians, including sourcing materials and construction. As far as possible, materials are sourced and manufactured locally, including quarry stones, clean river sand, cement, bricks, ballast, steel bars and timber. In the case of the domestic biogas plant, the customer is told what materials to buy and how to dig the pit. Sky Link makes the measurements and marks the pit outline, and the householder can work at their own pace. A technician then comes in to install the system.

So far, approximately 200 domestic biogas systems have been installed, benefiting some 1,200 people (assuming an average household size of six). It has also installed institutional biogas systems in five schools and orphanages, benefiting about 2,500 students and one in Meru Prison, improving sanitation for 1,500 prisoners and staff. The company is currently providing consultancy services for the installation of a second prison system.

Biogas plants cut greenhouse gas emissions, by reducing the use of unsustainable fuel-wood and (particularly for the larger plants) reducing methane emissions from poorly-managed sewage disposal. Based on typical measurements on biogas systems from elsewhere, a SkyLink domestic system probably saves about 3.5 tonnes/year of unsustainable wood or 5 tonnes/year CO2, and a school system about 10 tonnes/year wood and 15 tonnes/year CO2. From estimates made by SkyLink, the prison saves about 22 tonnes/year wood and 33 tonnes/year CO2.

Owners of biogas systems have a better quality of life because less time and money is spent collecting or buying firewood. Mary Waringa Nguku, a farmer said “I was really suffering from a shortage of firewood. The only alternative was LPG, and that was becoming expensive. Then I saw the biogas at my brother’s place, and thought I must have it. It’s so fast to cook with, compared to firewood, and you don’t have to stay in the kitchen the whole time, feeding the fire. You can leave a pot simmering and just get on other things.”

Indoor air pollution from cooking with fuel-wood is greatly reduced, so cooks enjoy a healthier and cleaner environment.

Children who would previously have spent time collecting wood can now attend school more regularly. The slurry, used as a fertiliser, increases crop yield and food security for families.

Alain Charles Publishing, University House, 11-13 Lower Grosvenor Place, London, SW1W 0EX, UK
T: +44 20 7834 7676, F: +44 20 7973 0076, W:

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