Why do we prefer to call secondary waste water treatment as biological treatment?

Explanation

### Step-by-Step Solution:

1. **Understanding Wastewater Treatment Phases**: Wastewater treatment consists of two main phases: primary treatment and secondary treatment. The primary phase focuses on the physical removal of solid waste, while the secondary phase involves biological processes.

2. **Primary Treatment**: In the primary treatment, suspended particles, grit, and larger solids are removed from the wastewater through physical methods such as filtration and sedimentation. This phase does not involve microorganisms.

3. **Introduction to Secondary Treatment**: After the primary treatment, the effluent (the treated wastewater) is subjected to secondary treatment. This is where biological processes come into play.

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