What is correct

Options

A. Methanobacterium is aerobic bacterium found in rumen of cattle
B. Biogas is pure methane
C. Activated sludge sediment is rich in aerobic bacteria
D. Biogas is produced by activity of aerobic bacteria on animal waste

Answer

To solve the question of identifying the correct statement from the given options, we will analyze each statement one by one.

### Step-by-Step Solution:

1. **Analyze the First Statement:**
- **Statement:** Methanobacterium is an aerobic bacterium found in the rumen of cattle.
- **Analysis:** Methanobacterium is actually an anaerobic bacterium, not aerobic. It is found in the rumen of cattle, but the classification as aerobic makes this statement incorrect.
- **Conclusion:** This statement is **incorrect**.

2. **Analyze the Second Statement:**
- **Statement:** Biogas is pure methane.
- **Analysis:** Biogas is produced under anaerobic conditions by various bacteria, and while methane is the major component of biogas, it is not pure methane. Biogas contains other gases as well.
- **Conclusion:** This statement is **incorrect**.

3. **Analyze the Third Statement:**
- **Statement:** Activated sludge segment is rich in aerobic bacteria.
- **Analysis:** Activated sludge is indeed a mixture that contains a high concentration of aerobic bacteria, which are essential for the treatment of wastewater.
- **Conclusion:** This statement is **correct**.

4. **Analyze the Fourth Statement:**
- **Statement:** Biogas is produced by the activity of aerobic bacteria on animal wastes.
- **Analysis:** Biogas is produced by anaerobic bacteria, not aerobic bacteria. This statement is therefore incorrect.
- **Conclusion:** This statement is **incorrect**.

### Final Conclusion:
After analyzing all the statements, the only correct statement is:
- **Option 3:** Activated sludge segment is rich in aerobic bacteria.