What are 'flocs', formed during secondary treatment of sewage ?
OR
Write any two places where methanogens can be found.

Explanation

### Step-by-Step Solution

1. **Understanding Sewage Treatment**: The sewage treatment process consists of two main stages: primary treatment and secondary treatment.

2. **Primary Treatment**: In the primary treatment stage, large solid particles and suspended materials in the sewage are removed. This step primarily focuses on separating the solid waste from the liquid effluent.

3. **Secondary Treatment**: After primary treatment, the sewage moves to the secondary treatment stage, which is a biological treatment process.

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