Select the statement that correctly relates to biogas and sewage treatment process.

Options

A. Activated sludge sediment in settlement tanks of the sewage treatment plants 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's
D. Biogas, commonly called gobar gas is pure methane.

Answer

To solve the question regarding which statement correctly relates to biogas and the sewage treatment process, we will analyze each statement one by one.

### Step-by-Step Solution:

1. **Evaluate Statement 1**:
- 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 are crucial for the breakdown of organic matter in sewage treatment. This statement is correct.

2. **Evaluate Statement 2**:
- 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 by anaerobic bacteria, not aerobic bacteria. Therefore, this statement is incorrect.

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

4. **Evaluate Statement 4**:
- The statement claims that "biogas is commonly called gobergas and it is pure methane."
- **Analysis**: Biogas is a mixture of gases, primarily methane, but also includes carbon dioxide, hydrogen, nitrogen, and hydrogen sulfide. Therefore, stating that it is "pure methane" is incorrect.

5. **Conclusion**:
- After evaluating all statements, the only correct statement is Statement 1, which accurately describes the role of activated sludge in sewage treatment.

### Final Answer:
The correct statement that relates to biogas and sewage treatment process is **Statement 1**: "Activated sludge sediment in settling tanks of sewage treatment plants is a rich source for aerobic bacteria."

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