What are methanogens? Describe the production of biogas with a labelled diagram of a biogas plant.

1. 1 · Define biogas and methanogens. Biogas is a microbial mixture of gases, mainly methane; methanogens such as Methanobacterium produce it by growing anaerobically on cellulosic material.
2. 2 · Source of methanogens. Anaerobic sludge of sewage plants and the rumen of cattle, where they digest cellulose; so dung (gobar) is rich in them.
3. 3 · Working of the plant.
   • Concrete tank 10 to 15 feet deep; dung slurry fed in.
   • Anaerobic digestion releases gas; floating cover rises.
   • Gas outlet supplies homes; spent slurry outlet gives fertiliser.
4. 4 · Draw the plant. [Diagram: inlet with slurry, digester tank, sludge, floating gas holder, gas outlet, spent slurry outlet]
5. 5 · Uses and Indian link. Cooking and lighting in villages; developed by IARI and KVIC.
6. 6 · Close in one line. So methanogens turn cattle dung into clean fuel and manure.

Scoring tip: Label the floating cover, gas outlet and spent slurry outlet. These three labels carry the diagram marks.