Select the correct statement from the following:
- Methanobacterium is an aerobic bacterium found in rumen of cattle
- Activated sludge-sediment in settlement tanks of sewage treatment plant is a rich source of aerobic bacteria
- Biogas, commonly called gobar gas, is pure methane
- Biogas is produced by the activity of aerobic bacteria on animal waste
Answer
(2) Activated sludge-sediment in settlement tanks of sewage treatment plant is a rich source of aerobic bacteria
Solution
As per NCERT, in secondary treatment the effluent is aerated so that aerobic microbes grow into flocs; in the settling tank these bacterial flocs sediment as activated sludge. A small part of it is pumped back into the aeration tank as inoculum. Activated sludge is a rich source of aerobic bacteria; (2) is correct.
(1) Incorrect: Methanobacterium is an anaerobic methanogen found in the rumen of cattle.
(3) Incorrect: biogas is predominantly methane, along with CO2 and H2; it is not pure methane.
(4) Incorrect: biogas is produced by anaerobic methanogens acting on cellulosic material such as cattle dung.
Answer: (2)