Biogas: In the anaerobic condition (absence of oxygen), the decomposition of waste in the form of cow dung, sewage, fruits and vegetable peels takes place. As a result, the formation of biogas takes place. The main constituent of biogas is methane. Biogas is made from:

i. First, to form a slurry, cow dung is aggregated with equal volumes of water.

ii. Then the formed slurry is decomposed by the microorganisms present in the form of waste.

iii. Then after decomposition, biogas is produced.

The two advantages of using the biogas are:

i. It has high calorific value.

ii. It is eco-friendly hence more preferable.