Biogas
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Direct answer
Biogas is a flammable mixture of gases, predominantly methane, produced when anaerobic bacteria called methanogens digest cellulosic material such as cattle dung. The same microbes that generate methane in the anaerobic sludge digesters of sewage plants also live in the rumen of cattle, which is why cow dung, or gobar, is rich in them and fuels the gobar gas plants of rural India. Biogas thus converts farm and animal waste into clean fuel and leaves spent slurry as manure.
What you must remember
- The producers: methanogens, anaerobic bacteria exemplified by Methanobacterium, which grow on cellulosic material and release large amounts of methane along with carbon dioxide and hydrogen.
- Natural homes: methanogens occur in the anaerobic sludge of sewage treatment and in the rumen, the specialised stomach chamber of cattle where they digest cellulose.
- The substrate: cattle excreta, popularly gobar, is naturally loaded with these bacteria and is the standard feed of village biogas plants.
- The plant: dung mixed with water forms a slurry that feeds an underground digester, where anaerobic fermentation over days yields the gas collected from the dome.
- The product: biogas is predominantly methane, with carbon dioxide and traces of other gases — a clean-burning fuel for cooking and lighting.
- By-product: the spent slurry is an excellent organic manure, so the plant returns nutrients to the field.
- Advantages: low-cost rural energy, disposal of animal waste, freedom from smoke pollution, and manure for agriculture.
Common confusion
Biogas is not the gas of the aeration tank — methanogens are strict anaerobes that act only in oxygen-free digesters or sludge chambers. Its main component is methane, not butane or LPG, and the microbes come with the dung itself rather than being added from outside. Also, cellulose, not protein or fat, is the feed these bacteria attack in the rumen and the digester alike.
Exam-focused takeaway
NEET-UG links Methanobacterium with methane production, locates methanogens in the rumen and in anaerobic sludge, and asks what gas dominates biogas. Statement items test that biogas generation is anaerobic, that gobar gas plants use cattle dung, and that the slurry left behind serves as manure. Match-the-following pairs the microbe with the gas and the animal chamber with cellulose digestion.
Frequently asked questions
Which microbes produce biogas?
Methanogens — anaerobic bacteria such as Methanobacterium that release methane while digesting cellulosic waste.
What is the main constituent of biogas?
Methane, accompanied by carbon dioxide and hydrogen in smaller amounts.
Why is cattle dung used in biogas plants?
Because cow dung, or gobar, is naturally rich in methanogens from the cattle rumen, making it an ideal anaerobic feed.
Where else do methanogens occur naturally?
In the anaerobic sludge of sewage treatment plants and in the rumen of cattle, where they help digest cellulose.
What remains after biogas is generated?
The spent slurry, a nutrient-rich residue used as organic manure in fields.