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 are a type of microorganisms that produce methane as a metabolic byproduct in anoxic (absence of oxygen) conditions. They are classified as anaerobic bacteria.

2. **Analyzing the Options**:
- **Option A: Rumen of Cattle**: The rumen is an anaerobic environment where methanogenic bacteria thrive, as it is part of the digestive system of ruminants.
- **Option B: Cow Dung Gas Plant**: These plants utilize anaerobic digestion, which is conducive for methanogenic bacteria to produce biogas (methane).
- **Option C: Bottom of Waterlogged Paddy Field**: Waterlogged conditions create an anaerobic environment that supports methanogenic bacteria.
- **Option D: Activated Sludge**: Activated sludge processes involve aeration, which introduces oxygen into the environment, making it unsuitable for anaerobic bacteria like methanogens.

3. **Identifying the Correct Answer**:
Since methanogenic bacteria require anaerobic conditions to thrive, they will not be found in environments where oxygen is present. Therefore, the correct answer is **Option D: Activated Sludge**.

### Final Answer:
Methanogenic bacteria are not found in **Activated Sludge**.

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