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 is the initial stage of sewage treatment that primarily involves physical processes. It aims to remove large solids and suspended particles from wastewater.

2. **Processes Involved in Primary Treatment**:
- The primary treatment consists of two main processes:
- **Filtration**: This process filters out large particles and debris from the sewage.
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