Question

Methanogenic bacteria are not found in
A)Rumen of cattle
B)Gobar gas plant
C)Waterlogged paddy field
D)Activated sludge

Answer 1

Methanogens are the bacteria which produce methane. They are found in an oxygen depleted environment like soil, sediments, intestine of other animals and humans. They are found in sediments and sewage treatment plants. They live on carbon dioxide gas. They release methane as their metabolic waste.

Complete answer:
To solve this question, we must know about the characteristics of methanogens.
The characteristics of methane producing organisms are:
1)They are strict methane producing organisms. They obtain energy by producing large quantities of methane.
2)They are strict anaerobes.
3)They decay organic matter.

The methanogens are found in:
1)Rumen of cattles- In the rumen of the cattle, methanogens play a wide role in digesting cellulose. They also initiate fermentation. These organisms ferment the feed and produce methane.
2)Gobar gas plant- Gobar gas is the mixture of methane and carbon dioxide. The anaerobic digestion of organic waste and cellulosic plant parts by methanogens produce methane, carbon dioxide and hydrogen. Thus, methanogens are used in gobar gas plants.
3)Water logged paddy field- Methanogens are found in water logged rice fields. Water logging provides a suitable environment for the methanogens to perform their metabolic activities and produce methane.
4)Activated sludge- It is a process of wastewater management in which the sewage and industrial waste is treated by using aeration and biological floc which is made of aerobic bacteria and protozoa. The aerobic conditions do not allow methanogens to survive.

Hence, the correct answer is option (D)

Note: Activated sludge is used for purposes like oxidizing carbon rich organic matter, oxidizing nitrogenous matter like ammonia, removing nitrogen and phosphorus. In this flocculation occurs due to clumping of the aerobic organisms.