Identify the True or False statements about the sewage treatment plants.
I. The water is less polluted if BOD is high.
II. Flocs are formed by anaerobic bacteria with fungal filaments in mesh-like structures.
III. Activated sludge acts like an inoculum in activated sludge digesters.
IV. In activated sludge digesters, gases like methane, hydrogen sulphide and carbon dioxide are formed.

Options

A. I - False , II - True , III - True , IV - True ,
B. I - True , II - False , III - True , IV - True
C. I - False , II - False , III - False , IV - True
D. I - True , II - False , III - False , IV - False

Answer

To determine the truthfulness of the statements regarding sewage treatment plants, we will analyze each statement one by one.

### Step-by-Step Solution:

1. **Statement I: "The water is less polluted if BOD is high."**
- **Analysis:** BOD stands for Biological Oxygen Demand. A high BOD indicates a high concentration of organic matter in the water, which means that more oxygen is being consumed by bacteria to decompose this organic matter. Therefore, a high BOD signifies that the water is more polluted, not less.
- **Conclusion:** This statement is **False**.

2. **Statement II: "Flocs are formed by anaerobic bacteria with fungal filaments in mesh-like structures."**
- **Analysis:** Flocs are actually formed by aerobic bacteria along with fungal filaments, creating a mesh-like structure. Anaerobic bacteria do not form flocs in the same way. Flocs are involved in the aeration process where aerobic bacteria help in the breakdown of organic matter.
- **Conclusion:** This statement is **False**.

3. **Statement III: "Activated sludge acts like an inoculum in activated sludge digesters."**
- **Analysis:** Activated sludge is indeed used as an inoculum in the aeration tank to promote the growth of aerobic bacteria. However, the statement incorrectly refers to the activated sludge digesters. The major part of activated sludge is returned to the aeration tank, not the digester. Thus, while it acts like an inoculum, it does so in the aeration tank, not in the digester.
- **Conclusion:** This statement is **False**.

4. **Statement IV: "In activated sludge digesters, gases like methane, hydrogen sulphide, and carbon dioxide are formed."**
- **Analysis:** In activated sludge digesters, anaerobic bacteria break down the organic matter, producing gases such as methane, hydrogen sulfide, and carbon dioxide as by-products of this digestion process. This statement accurately describes the process.
- **Conclusion:** This statement is **True**.

### Final Summary:
- Statement I: **False**
- Statement II: **False**
- Statement III: **False**
- Statement IV: **True**

Thus, the correct option is that only Statement IV is true.