Methanogenic bacteria are not found in :
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) – Activated sludge .
Methanogenic bacteria are anaerobic microorganisms that produce methane during the decomposition of organic matter.
They are typically found in:
- Gobar gas plants (anaerobic digesters)
- Rumen of cattle (helps in digestion of cellulose)
- Anaerobic sludge (during the anaerobic phase of sewage treatment)
Activated sludge is part of the aerobic phase of sewage treatment, where aerobic bacteria are active — methanogens cannot survive in this oxygen-rich environment.