What is this Action Sheet about?
Action Sheet 66
This Action Sheet is about biogas. If you live in an area where livestock are kept, and there is sufficient water supply, then a household biogas system - which takes waste and makes energy could help meet your household’s needs.
What are the benefits of biogas? G Biogas systems make clean energy for household use. After an initial investment in the system, there is no need to spend money on fuel and no more smoke from wood or charcoal G Cooking on biogas is quicker and easier than cooking with firewood G Biogas systems kill the bacteria in livestock manure. A farm with a biogas system is a cleaner and safer place. G Biogas systems produce excellent safe fertilizers for use on the farm G Biogas systems can help in the fight against global warming by allowing us to burn methane from organic waste, instead of letting it escape into the atmosphere where it adds to the greenhouse effect. It also helps by letting us leave more trees standing!
What is biogas and what is it used for? Biogas is a mixture of methane and carbon dioxide, produced by the breakdown of organic waste by bacteria without oxygen (anaerobic digestion). If you’ve ever seen bubbles rising from a swampy marshy area, that’s naturally produced methane. Like the gas in liquid petroleum gas canisters, methane can be burnt for cooking or lighting the house. It can also be used to power combustion engines to drive a motor or generate electricity.
Mrs Agnes Saidi Shabani cooking on biogas produced on the farm in Tanzania (Image: PACE)
A biogas light on the Mr Katakwa’s farm, Tanzania (Image: PACE)
What biogas can do:
1m3 1m3 1m3 1m3 of of of of biogas biogas biogas biogas can can can can give as much light as a 60-100 Watt bulb for 6 hours cook 3 meals for a family of 5 - 6 replace 0.7 kg of petrol generate1.25 kilowatt hours of electricity
Biogas bubbles (Image: PACE)
How do you make biogas? Biogas is made by fermenting organic waste in a biogas digester. The size of a digester can vary from a small household system to a large commercial plant of several thousand cubic metres. Farmers like Mr Anthony Paulo Katakwa in Tanzania use cow dung to feed their biogas digesters.
Mr Anthony Paulo Katakwa collecting dung…
….to feed his biogas digester
He adds water …
… and gives it a stir (Images: PACE)
Two simple biogas digester designs have been developed; the Chinese fixed dome digester and the Indian floating cover biogas digester (shown in Figures 1& 2). The digestion process is the same in both digesters but the gas collection method is different in each. In the floating cover type, the water sealed cover of the digester rises as gas is produced and acts as a storage chamber, whereas the fixed dome type has a lower gas storage capacity and requires good sealing if gas leakage is to be prevented. Both have been designed for use with animal waste or dung. The waste is fed into the digester via the inlet pipe and undergoes digestion in the digestion chamber. The temperature of the process is quite important because methane-producing bacteria do their work best at temperatures between 30 – 40oC or 50 – 60oC. It takes from 2 to 8 weeks to digest a load of waste, depending on the temperature. The left-over slurry is removed at the outlet for use as a fertilizer. If you are looking into building a biogas system you will need to decide on the size of the digester. This will depend on how much biogas you need to meet your daily cooking (and lighting) requirements, the availability and amount of livestock manure and water (water, number of cows, goats or other livestock), and the materials available on site (bricks, etc) for construction of the digester. A regular supply of water is essential for operation of biogas plants. Rainwater harvesting could help with this (see Action Sheets 13–15).
Loose cover Gas outlet pipe Removable...
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