During which stage of sewage treatment microbes are not used?

Options

A. Primary treatment
B. Secondary treatment
C. Tertiary treatment
D. Both a and c

Answer

### Step-by-Step Solution:

1. **Understanding Sewage Treatment**:
- Sewage treatment involves the process of removing contaminants from wastewater, which includes both solid and liquid waste from communities.

2. **Stages of Sewage Treatment**:
- There are three main stages of sewage treatment:
- **Primary Treatment**: This stage involves physical processes to remove large solids and grit from sewage.
- **Secondary Treatment**: This stage uses biological processes where microorganisms break down organic matter.
- **Tertiary Treatment**: This stage involves further purification processes, often including chemical treatments and filtration.

3. **Analyzing Each Stage**:
- **Primary Treatment**:
- Involves screening and grit removal. No microorganisms are used in this stage.
- **Secondary Treatment**:
- This stage actively uses microorganisms to decompose organic matter.
- **Tertiary Treatment**:
- Involves disinfection and further removal of contaminants, but does not utilize microorganisms.

4. **Conclusion**:
- The stages where microbes are not used are **Primary Treatment** and **Tertiary Treatment**. Therefore, the correct answer is **both A and C**.

### Final Answer:
The stages of sewage treatment during which microbes are not used are **Primary Treatment (A)** and **Tertiary Treatment (C)**. Thus, the answer is **both A and C**.

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