8 min readPathway sheet1-mark MCQ on methanogens, a 2 or 3-mark question on a biogas plant, sometimes with a labelled diagram; also a NEET favourite

Microbes in energy generation: biogas

Methanogens such as Methanobacterium break down cellulose without oxygen and release mainly methane. Cattle dung, rich in them, is used to make gobar gas.

BiogasA mixture of gases, mainly methane, with CO₂ and H₂, produced by microbes; used as fuel

MethanogensAnaerobic bacteria growing on cellulosic material, e.g. Methanobacterium

Where methanogens liveAnaerobic sludge of sewage plants and the rumen of cattle

Developed in India byIndian Agricultural Research Institute (IARI) and Khadi and Village Industries Commission (KVIC)

Methanogens and cattle

Some bacteria grow anaerobically (without oxygen) on cellulosic material and produce a large amount of methane, along with CO₂ and H₂. They are called methanogens; a common one is Methanobacterium. They live in the anaerobic sludge of sewage plants and in the rumen (a part of the stomach) of cattle. In the rumen they help break down cellulose, which is important for the cattle's nutrition. So cattle dung (gobar) is rich in methanogens and can be used to make biogas, called gobar gas.

How a biogas plant works

1
Bio-wastes and a slurry of dung (dung mixed with water) are fed into a concrete tank, about 10 to 15 feet deep.
2★
Methanogens in the slurry digest the organic matter anaerobically and release biogas.
3
A floating cover over the slurry keeps rising as gas collects under it.
4
A gas outlet with a pipe supplies biogas to nearby houses for cooking and lighting.
5
The spent slurry is removed through another outlet and used as fertiliser.

★ key step

How to draw a biogas plant

Draw a deep digester tank below ground level, with a line showing the soil surface.
On one side, draw a sloping inlet pipe from a small mixing tank; label dung + water (slurry).
Inside the tank, shade the lower part and label sludge; above it, label slurry being digested.
On top of the slurry, draw an inverted drum labelled floating gas holder (cover), with gas collected under it.
From the top of the cover, draw a pipe with a valve labelled gas outlet: biogas to homes.
On the other side, draw an outlet pipe to a pit labelled spent slurry (manure).

Why biogas suits rural India

Cattle dung is available in large quantities in villages, where cattle are used for many purposes.
Biogas burns with a clean, smokeless flame, unlike firewood or dung cakes, so kitchens stay healthier.
The spent slurry is a good organic manure for fields.
It is a renewable fuel and reduces the need to cut trees for firewood.

In real life

In many Indian villages, a gobar gas plant lets families cook on a smokeless flame instead of a smoky chulha. This protects women and children from smoke-related lung disease, and the spent slurry goes back to the fields as manure.

Exam angle

2 marks: “What are methanogens? Name one and state where it is found.” Anaerobic bacteria that grow on cellulosic material and produce large amounts of methane with CO₂ and H₂. Example: Methanobacterium; found in anaerobic sludge of sewage plants and in the rumen of cattle.

3 marks: “Describe the structure and working of a biogas plant. Why are such plants more common in rural areas?” Concrete tank 10 to 15 feet deep; dung slurry fed; methanogens produce gas anaerobically; floating cover rises; gas outlet to houses; spent slurry outlet for fertiliser. Rural areas have plenty of cattle dung.

Remember it

Gobar + Methanogens + No oxygen = Gas. IARI and KVIC brought it to Indian villages.