During sewage treatment , which group of microbes are used to reduce BOD of sewage water

Options

A. Autotrophic , aerobic
B. Heterotropic , anaerobic
C. Heterotropic , aerobic.
D. Heterotropic and autotropic both

Answer

To solve the question regarding which group of microbes are used to reduce the Biochemical Oxygen Demand (BOD) of sewage water during sewage treatment, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding BOD**:
- BOD stands for Biochemical Oxygen Demand, which is a measure of the amount of oxygen that microorganisms will consume while decomposing organic matter in water. The higher the BOD, the more polluted the water is.

2. **Sewage Treatment Process**:
- Sewage treatment typically involves multiple stages: primary, secondary, and sometimes tertiary treatment. The question specifically pertains to the secondary treatment phase.

3. **Role of Microbes in Sewage Treatment**:
- During the secondary treatment of sewage, microorganisms play a crucial role in breaking down organic matter. This is primarily where the reduction of BOD occurs.

4. **Types of Microbes**:
- There are different types of microbes involved in sewage treatment:
- **Aerobic bacteria**: These require oxygen to survive and are effective in breaking down organic matter in the presence of oxygen.
- **Anaerobic bacteria**: These do not require oxygen and are used in certain treatment processes but are not primarily responsible for reducing BOD in the secondary treatment.
- **Heterotrophic bacteria**: These consume organic compounds as their energy and carbon source. They are crucial in the breakdown of organic waste.
- **Autotrophic bacteria**: These can produce their own food from inorganic substances but are not primarily responsible for BOD reduction in sewage treatment.

5. **Conclusion**:
- The microbes that are primarily used to reduce BOD during sewage treatment are **heterotrophic aerobic bacteria**. They utilize oxygen to decompose organic matter, thereby reducing the BOD of the sewage water.

### Final Answer:
**Heterotrophic aerobic bacteria** are used to reduce the BOD of sewage water during sewage treatment.