Select the correct statement from the following

Options

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

Answer

To solve the question, we need to evaluate each of the provided statements regarding microbes and their role in human welfare, particularly in sewage treatment and biogas production.

### Step-by-Step Solution:

1. **Evaluate the First Statement**:
- The first statement claims that "activated sludge sediment in settling tanks of sewage treatment plant is a rich source of aerobic material."
- In sewage treatment, activated sludge is indeed rich in aerobic bacteria which help in the breakdown of organic matter in the presence of oxygen.
- **Conclusion**: This statement is correct.

2. **Evaluate the Second Statement**:
- The second statement states that "biogas is produced by the activity of aerobic bacteria on animal waste."
- Biogas production primarily occurs through anaerobic digestion, which involves anaerobic bacteria breaking down organic matter in the absence of oxygen.
- **Conclusion**: This statement is incorrect.

3. **Evaluate the Third Statement**:
- The third statement claims that "methanobacterium is an aerobic bacterium and found in the rumen of cattle."
- Methanobacterium is a type of methanogen, which is an anaerobic bacterium that produces methane during anaerobic digestion.
- **Conclusion**: This statement is incorrect.

4. **Evaluate the Fourth Statement**:
- The fourth statement states that "biogas is commonly called gobergas and is pure methane."
- While biogas is often referred to as gobergas, it is not pure methane; it typically contains about 50-70% methane along with other gases like carbon dioxide, hydrogen sulfide, and hydrogen.
- **Conclusion**: This statement is incorrect.

5. **Final Conclusion**:
- After evaluating all the statements, the only correct statement is the first one regarding activated sludge being a rich source of aerobic material.

### Final Answer:
The correct statement is: **"Activated sludge sediment in settling tanks of sewage treatment plant is a rich source of aerobic material."**

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