What is the key difference between primary and secondary sewage treatment?

Explanation

### Step-by-Step Solution:

1. **Definition of Primary Sewage Treatment**:
- Primary sewage treatment involves the initial process of treating sewage to remove large and small particles. This is done primarily through physical or mechanical methods.

2. **Methods Used in Primary Treatment**:
- The main methods used in primary sewage treatment are filtration and sedimentation. These processes help in separating solid waste from the liquid sewage.

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