Secondary treatment in sewage treatment is
Physical
Chemical
Biological
None of these

Options

A. Physical
B. Chemical
C. Biological
D. None of these

Answer

**Step-by-Step Solution:**

1. **Understanding Sewage Treatment**: Sewage treatment refers to the processes used to remove contaminants from wastewater, which is often referred to as sewage. This sewage can come from domestic or industrial sources and contains various pollutants.

2. **Types of Sewage Treatment**: There are three main types of sewage treatment methods: primary, secondary, and tertiary. Each of these methods serves a different purpose in the treatment process.

3. **Primary Treatment**: This is the first step in sewage treatment and is primarily a physical process. It involves the removal of suspended and floating solids from the sewage.

4. **Secondary Treatment**: This step is crucial and involves biological processes. During secondary treatment, microorganisms, particularly aerobic bacteria, are used to break down organic matter in the sewage, making it less polluting.

5. **Tertiary Treatment**: This is the final stage of sewage treatment and typically involves chemical processes to further purify the water, removing any remaining contaminants.

6. **Conclusion**: Since secondary treatment relies on biological processes to treat sewage, we can conclude that the correct answer to the question is "Biological".

**Final Answer**: Secondary treatment in sewage treatment is Biological.

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