Describes how biogas is generated from activated sludge. List the components of biogas.

Explanation

### Step-by-Step Solution

1. **Understanding Activated Sludge**:
- Activated sludge is a key component of sewage treatment plants (STPs). It consists of a mixture of microorganisms, primarily bacteria and fungi, that help in breaking down organic matter in sewage.

2. **Process of Sewage Treatment**:
- The sewage treatment process involves two main stages: primary treatment and secondary treatment.
- **Primary Treatment**: This stage involves the physical separation of large particles from the sewage through manual or mechanical filtration. This helps in removing solid waste and plastics.
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