Process
Organic materials such as dung and agricultural waste can easily be treated in biogas plants to produce energy (biogas) and fertiliser (slurry). Biogas is generated if organic materials are allowed to rot in closed, airless tanks at suitable temperatures (20-40¡C). This is ideal for Equatorial areas. The process is called “anaerobic digestion”. Bacteria converts the organic matter into combustible biogas (methane, carbon dioxide) and fertiliser (ammonia).
Utilisation
Biogas can be used like any other combustible gas, it can be burnt in stoves, lamps and motors, or be used to produce electrical power and pump water. Biogas is somewhat lighter than air, and has an ignition temperature of approximately 700¡C (diesel oil 350¡C; petrol and propane about 500¡C). The temperature of a biogas flame is 870¡C. One cubic metre of biogas generates 5500 kcal of energy, corresponding to the thermal power of 0.6 litres of diesel fuel.
The byproduct of this process is the fermentation slurry, which contains a lot of ammonia nitrogen. This is practically odourless and can be used as a very efficient fertiliser. When the fermentation slurry is used as fertiliser for a period of years, the soil structure is improved and the proportion of organic materials in the soil increases, enabling it to store more water.
Advantages
By relatively simple means, biogas can be utilised as a source of energy in integrated farming. In addition, the use of biogas has a number of advantages, providing a solution to energy demands which is both ecological as well as economical.
The environment is being destroyed by the demand for firewood and charcoal. To avoid catastrophe, it has to be protected, and one way of doing this is to use biogas.
One major problem for people who are economically or geographically disadvantaged is to get electricity or fossil fuels for cooking and lighting. At the moment, biogas seems to be the most logical source of cheap energy.
In the developing countries, women spend many hours collecting firewood. This is a big burden on them, and their time could be used more productively.
Cooking with firewood produces a lot of smoke, which is bad for the health of the women, who tend the kitchen fire. The smoke pollutes the air, and can cause problems with lungs, eyes etc. The flame from burning biogas does not need tending