Give the composition of biogas.(b) Enlist the benefits of biogas.

Answer:

(a) Composition of biogas (produced by anaerobic digestion of cattle dung and organic waste by methanogens such as Methanobacterium):

• Methane (CH₄): about 50 to 70%
• Carbon dioxide (CO₂): about 30 to 40%
• Small amounts of hydrogen sulphide (H₂S), hydrogen, nitrogen and water vapour.

(b) Benefits of biogas:

1. It is a cheap, renewable and eco-friendly fuel for cooking and lighting, especially in rural areas.
2. It burns with a blue flame without smoke and soot, so there is no indoor air pollution.
3. It saves firewood, so deforestation is reduced.
4. The slurry left after digestion is a good manure rich in nitrogen and phosphorus.
5. It helps in hygienic disposal of dung, sewage and organic waste.