• obtain supporting data to provide a basis for advising users on the optimum operational
requirements, and potential users on what conditions they should fulfil before investing in the
technology.
•
Gas metres were installed in five households to monitor gas production and utilization for periods
ranging from 88 to 279 days. The results showed that:
• Out of the five plants studied, only four were operational and only two of them were actually
beneficial to the users. Therefore users whose plants were operational had:
- three to five cows so they produced adequate dung to fill the plant
- maintained an interest in the operation of the plant
- integrated their working routine on the farm with the activities relating to the plant
therefore helping to ease feeding of the biogas plants on a daily basis.
• In households where the users were not benefiting:
- the biogas plants were not directly connected to the zero-grazing unit, creating
difficulty in feeding the plant and transporting the sludge to the farms
- the zero-grazing unit was only used as a night boma (shed) for the cows, hence only
small amounts of cow dung were collected
- conditions necessary for successful operation of a plant were not initially fulfilled
during the planning stages. The number of animals was not adequate so they could not
supply the required amount of dung - water was not adequately supplied.
The study concluded that the following factors are critical if a biogas plant is to operate successfully:
a) Before construction takes place conditions for successful operation of the plant must be met
b) The farmer must own at least three zero-grazed cows
c) There must be a reliable supply of water
d) There should be a well-managed farm system into which the biogas plant is integrated
e) The size of the plant constructed should provide enough gas to meet the cooking and lighting
requirements of the users
f) The plant owner must be interested in the operation and maintenance of the system.
Chapter Four
WHAT IS BIOGAS?
Biogas is produced by bacteria that break down organic matter in the absence of air. The process is
referred to as anaerobic digestion and takes place in a closed tank called a digester. Biogas plants are
sealed containers built specifically to create the anaerobic conditions necessary for digestion and
controlled production of gas.
Biogas is a mixture of methane (CHJ and carbon dioxide (C02), It is a high grade fuel used for cooking
and lighting. The digested residue or sludge is a good quality fertilizer.
Most common biogas plants must be fed daily with feed material or slurry to ensure continuous gas
production. The slurry is a mixture of organic material and water, usually in equal proportions. Many
types of organic materials such as coffee husks, sisal waste and animal dung can be used.
Products of biogas plants
Biogas
The digestion of organic matter in the biogas plant forms methane commonly referred to as biogas. This
is a combustible gas that bums with a hot blue flame. Biogas is neither poisonous nor as flammable as
other gases used for cooking or lighting. In Kenya, biogas is mainly used for cooking and lighting.
It is also used, to a limited extent, to run refrigerators, and diesel and petrol engines.