Question

All of the following statements are correct with respect to a biogas plant except

• A. It has a floating cover that keeps on rising as gas is produced.
• B. It consists of a $10$ – to $15$ – foot – deep tank in which biowastes are collected and a slurry of dung is fed.
• C. Spent slurry may be used as fertilizers.
• D. Main gases produced are methane, $\text{CO}$ , and nitrogen oxide.

Answer 1

Answer: (D)

Biogas is a mixture of gases (containing predominantly methane) produced by microbial activity and which may be used as fuel. The major components of biogas are methane (50-70%) which is highly inflammable other gases are carbon dioxide (30-40%) and a mixture of other gases H₂, H₂S etc. (10%).
Certain bacteria, which grow anaerobically on cellulosic material, produce a large amount of methane along with CO₂ and H₂. Such bacteria are collectively known as methanogens, and an example of a common methanogen is Methanobacterium.
These bacteria are commonly found in anaerobic sludge during sewage treatment. These bacteria are also present in the rumen of cattle where they help in the breakdown of cellulose and play an important role in the nutrition of cattle. Thus, the excreta (dung) of cattle can be used for the generation of biogas, because of which it is commonly called gobar gas.
The biogas plant consists of:
⦁ A concrete tank, 10-15 feet deep, in which bio-wastes are collected and a slurry of dung is fed.
⦁ A floating cover is placed over the slurry, which keeps on rising as the gas is produced in the tank due to microbial activity. It has an outlet, which is connected to a pipe to supply biogas to nearby houses.
⦁ The spent slurry is removed through an outlet and may be used as fertilizer.