Class 12 NEET Biology Microbes in Human Welfare

Methanobacterium are anaerobic organisms.
Biogas refers to a mixture of different gases produced by the breakdown of organic matter in the absence of oxygen.
Activated sludge-sediment in settlement tanks of sewage treatment plant is a rich source of aerobic bacteria.
Biogas can be produced by anaerobic digestion with anaerobic bacteria.
Thus, the correct answer is option (D), 'Activated sludge-sediment in settlement tanks of sewage treatment plant is a rich source of aerobic bacteria'.