08-11-2012, 10:50 AM
Biogas Technology
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What is this Action Sheet about?
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?
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
Cooking on biogas is quicker and easier than cooking with firewood
Biogas systems kill the bacteria in livestock manure. A farm with a biogas system is a cleaner
and safer place.
Biogas systems produce excellent safe fertilizers for use on the farm
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.
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.
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.