Select the correct statement regarding sewage and its treatment

Options

A. Sedimentation is preceeded by sequential filtration
B. BOD of waste water is inversely proportional to its pollution potential
C. Secondary treatment is a physico chemical process
D. Biological treatment is performed on primary effluent

Answer

To solve the question regarding sewage and its treatment, we will analyze each statement provided and determine which one is correct.

### Step-by-Step Solution:

1. **Understanding Sewage**:
- Sewage is a combination of human waste, industrial waste, and other substances that are discharged into the sewage system. It is important to treat sewage to prevent pollution and protect public health.

2. **Analyzing the Statements**:
- **Statement 1**: "Sedimentation is preceded by sequential filtration."
- This statement is incorrect. In sewage treatment, sedimentation usually occurs before filtration. Sedimentation allows heavier solids to settle at the bottom, while lighter materials can be removed later.

- **Statement 2**: "BOD of wastewater is inversely proportional to its pollutant potential."
- This statement is also incorrect. Biochemical Oxygen Demand (BOD) is a measure of the amount of oxygen that microorganisms will consume while decomposing organic matter in water. A higher BOD indicates a higher level of organic pollution, meaning they are directly proportional, not inversely.

- **Statement 3**: "Secondary treatment is a physiochemical process."
- This statement is incorrect. Secondary treatment primarily involves biological processes where microorganisms break down organic matter. It is not primarily a physiochemical process.

- **Statement 4**: "Biological treatment is used in secondary treatment."
- This statement is correct. Secondary treatment involves biological processes, typically using aerobic bacteria to decompose organic matter and reduce BOD in the wastewater.

3. **Conclusion**:
- After analyzing all the statements, the correct statement regarding sewage and its treatment is **Statement 4**: "Biological treatment is used in secondary treatment."

### Final Answer:
The correct statement regarding sewage and its treatment is: **"Biological treatment is used in secondary treatment."**

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