Select the correct statement from the following

Options

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

Answer

To solve the question of selecting the correct statement, we will analyze each of the provided statements based on the information from the video transcript.

### Step-by-Step Solution:

1. **Analyze the first statement:**
- **Statement:** Methanobacterium are aerobic bacteria found in the rumen of cattle.
- **Analysis:** The video states that Methanobacterium are anaerobic bacteria, not aerobic. Therefore, this statement is incorrect.

2. **Analyze the second statement:**
- **Statement:** Biogas, commonly called gober gas, is pure methane.
- **Analysis:** The video clarifies that biogas is primarily composed of methane, but it also contains carbon dioxide and hydrogen sulfide (H2S). Thus, this statement is also incorrect.

3. **Analyze the third statement:**
- **Statement:** Activated sludge sediment settling tanks of the sewage treatment plant is a rich source of aerobic bacteria.
- **Analysis:** The video explains that after primary treatment, sewage is moved to aeration tanks where aerobic bacteria grow. The mass formed, which includes bacteria and fungal filaments, is called floc, and this is part of the activated sludge process. Therefore, this statement is correct.

4. **Analyze the fourth statement:**
- **Statement:** Biogas is produced by the activity of aerobic bacteria.
- **Analysis:** The video states that Methanobacterium, which are anaerobic bacteria, are involved in biogas production. Therefore, this statement is incorrect.

### Conclusion:
The correct statement is the third one: "Activated sludge sediment settling tanks of the sewage treatment plant is a rich source of aerobic bacteria."