Which of the following statements about biogas production and methanogens is correct?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Biogas is a mixture of gases mainly containing CH4, CO2 and H2, and is produced by methanogenic bacteria.
Biogas is a mixture of gases, mostly methane, made by microbes. It is produced by methanogens, bacteria that grow anaerobically (without oxygen) on cellulosic material and give out a large amount of methane along with CO2 and H2. These bacteria live in the rumen of cattle, so cattle dung (gobar) is rich in them.
Option (1) Biogas is a mixture of gases mainly containing CH4, CO2 and H2, and is produced by methanogenic bacteria. — Correct. This brings both points together: biogas is a mixture of gases with methane, CO2 and H2, and the bacteria that make it are the methanogens, such as Methanobacterium.
Option (2) Biogas is produced by aerobic bacteria that break down cellulosic material. — Incorrect. The bacteria that break down cellulosic material to make biogas grow anaerobically, not aerobically. In a biogas plant the slurry of dung is kept under a cover, away from air.
Option (3) Methanogens are aerobic bacteria found in the dung of cattle. — Incorrect. Methanogens are indeed found in the dung of cattle, but they are anaerobic bacteria. They grow in the rumen and in the anaerobic sludge of sewage plants, where there is little oxygen.
Option (4) Biogas, commonly called gobar gas, consists mainly of carbon dioxide. — Incorrect. Biogas is commonly called gobar gas, but it contains predominantly methane, not carbon dioxide. CO2 is present only along with the methane.
NCERT Extract:
Microbes in Production of Biogas – “Biogas is a mixture of gases (containing predominantly methane) produced by the microbial activity and which may be used as fuel. … However, certain bacteria, which grow anaerobically on cellulosic material, produce large amount of methane along with CO2 and H2. These bacteria are collectively called methanogens, and one such common bacterium is Methanobacterium. These bacteria are commonly found in the anaerobic sludge during sewage treatment. These bacteria are also present in the rumen (a part of stomach) of cattle.”