Select the correct statement regarding sewage treatment plant and biogas:

Options

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

Answer

To solve the question regarding the correct statement about sewage treatment plants and biogas, let's analyze each statement step by step.

### Step-by-Step Solution:

1. **Evaluate the First Statement:**
- The statement claims that "activated sludge sediment in settling tanks of sewage treatment plants is a rich source for aerobic bacteria."
- **Analysis:** Activated sludge is indeed a mixture of microorganisms, including aerobic bacteria, which play a crucial role in the breakdown of organic matter in sewage treatment. Therefore, this statement is correct.

2. **Evaluate the Second Statement:**
- The statement claims that "biogas is produced by the activity of aerobic bacteria on animal waste."
- **Analysis:** Biogas production occurs in anaerobic conditions, meaning it is produced in the absence of oxygen. The bacteria involved in this process are primarily anaerobic, not aerobic. Therefore, this statement is incorrect.

3. **Evaluate the Third Statement:**
- The statement claims that "methanobacterium is an aerobic bacterium which is found in cattle's rumen."
- **Analysis:** Methanobacterium is actually an anaerobic bacterium that helps in the production of methane in the rumen of cattle. Thus, this statement is also incorrect.

4. **Evaluate the Fourth Statement:**
- The statement claims that "biogas is commonly called gobergas and it is pure methane."
- **Analysis:** Biogas is a mixture of gases, primarily methane, carbon dioxide, and small amounts of other gases. It is not pure methane. Therefore, this statement is incorrect.

### Conclusion:
After evaluating all the statements, the only correct statement is the first one regarding the activated sludge in sewage treatment plants.

### Final Answer:
**The correct statement is:**
- Activated sludge sediment in settling tanks of sewage treatment plants is a rich source for aerobic bacteria.

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