Question

Select the correct statement from the following

• A. biogas is produced by the activity of aerobic bacteria on animal waste
• B. Methanobacterium is an aerobic bacterium found in rumen of cattle
• C. biogas, commonly called gobar gas, is pure methane
• D. activated sludge-sediment in settlement tanks of sewage treatment plant is a rich source of aerobic bacteria.

Answer 1

Answer: (D)

In activated sludge system (secondary sewage treatment), the primary effluent is taken to aeration tank. A large number of aerobic heterotrophic microbes grow in aeration tank. They form floes, which digest a lot of organic matter. As the BOD of waste water is reduced sufficiently, it is passed into setting tank where bacterial floes are allowed to undergo sedimentation. The sediment of the settling tank is called activated sludge which is a rich source of aerobic bacteria. It is further processed in anaerobic sludge digester. Biogas commonly called gobar gas is produced by anaerobic breakdown of biomass with the help of methanogenic bacteria. Biogas is made up of methane (50-70%), CO₂ (30-40%) with traces of nitrogen, hydrogen sulphide and hydrogen. Methanobacterium is an anaerobic methanogenic bacteria which is found in rumen of cattle and helpful in the breakdown of cellulose.