During which stage of sewage treatment microbes are used

Options

A. Primary treatment
B. Secondary treatment
C. Tertiary treatment
D. All of these

Answer

To determine during which stage of sewage treatment microbes are used, we can analyze the three stages of sewage treatment: primary, secondary, and tertiary treatment.

### Step-by-Step Solution:

1. **Understanding Sewage Treatment Stages**:
- Sewage treatment consists of three main stages: primary, secondary, and tertiary treatment. Each stage has a specific function in the treatment process.

2. **Primary Treatment**:
- In this stage, the sewage undergoes physical processes such as screening and sedimentation. The main goal is to remove large solids and grit from the sewage. No microbes are involved in this stage.

3. **Secondary Treatment**:
- This stage is crucial as it involves biological processes. Here, decomposing microorganisms (microbes) are used to break down organic matter present in the sewage. This is the stage where microbial action is essential for treating the sewage effectively.

4. **Tertiary Treatment**:
- The final stage involves chemical processes to further purify the water. This may include filtration, disinfection, and nutrient removal. Microbes are not primarily used in this stage.

5. **Conclusion**:
- Based on the analysis of each stage, it is clear that microbes are specifically utilized during the secondary treatment of sewage.

### Final Answer:
The correct answer is **secondary treatment**.