Methanogenic bacteria are not found in

Options

A. rumen of cattle
B. gobar gas plant
C. bottom of water-logged paddy fields
D. activated sludge

Explanation

**Step-by-Step Solution:**

1. **Understanding Methanogenic Bacteria:**
- Methanogenic bacteria, also known as methanogens, are microorganisms that produce methane as a metabolic by-product. They are strictly anaerobic, meaning they thrive in environments devoid of oxygen.

2. **Analyzing the Options:**
- The question provides four options regarding where methanogenic bacteria might not be found. We will evaluate each option one by one.

3. **Option A: Rumen of Cattle**
- Methanogens are present in the rumen of cattle. They act as symbionts, aiding in the digestion of cellulose from the plant material that cattle consume. Therefore, this option is incorrect regarding the question.

4. **Option B: Gober Gas Plant**
- Gober gas plants utilize methanogenic bacteria to convert organic waste into methane. These bacteria thrive in anaerobic conditions, making this option also incorrect.

5. **Option C: Bottom of Waterlogged Fields**
- Waterlogged paddy fields provide anaerobic conditions suitable for methanogens. They are commonly found in such environments, where they contribute to methane production. Thus, this option is also incorrect.

6. **Option D: Activated Sludge**
- Activated sludge processes involve aerobic microorganisms that require oxygen to thrive. Since methanogenic bacteria are strict anaerobes, they are not found in activated sludge. Therefore, this is the correct answer to the question.

7. **Final Answer:**
- Methanogenic bacteria are not found in activated sludge. The correct answer is option D.

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