The polluting strength sewage is usually characterized by its:

Options

A. BOD
B. Ozone content
C. Nitrogen content
D. Eutrophication

Answer

To determine the polluting strength of sewage, we need to identify the correct characteristic that represents it. The options provided are BOD (Biological Oxygen Demand), ozone content, nitrogen content, and eutrophication.

### Step-by-Step Solution:

1. **Understanding Polluting Strength**: The polluting strength of sewage refers to the degree to which it can cause harm to the environment, particularly to water bodies. This is often measured by specific parameters.

2. **Identifying the Options**:
- **BOD (Biological Oxygen Demand)**: This measures the amount of dissolved oxygen required by bacteria to decompose organic matter in water.
- **Ozone Content**: Refers to the concentration of ozone in the atmosphere, which is not directly related to sewage pollution.
- **Nitrogen Content**: While nitrogen can contribute to water pollution, it does not specifically measure the polluting strength of sewage.
- **Eutrophication**: This is a process where water bodies become enriched with nutrients, leading to excessive growth of algae, but it is not a direct measure of sewage pollution.

3. **Analyzing BOD**: The BOD test is crucial for assessing the organic pollution level in water. High BOD values indicate a high level of organic pollutants, such as sewage, which require more oxygen for decomposition.

4. **Comparative Values**: Raw sewage typically has a BOD of 40 to 150 mg/L, while treated sewage or drinking water has a BOD of less than 0.5 mg/L. This stark difference highlights the polluting strength of untreated sewage.

5. **Conclusion**: Based on the analysis, the characteristic that best represents the polluting strength of sewage is **BOD (Biological Oxygen Demand)**.

### Final Answer:
The polluting strength of sewage is usually characterized by its **BOD (Biological Oxygen Demand)**.

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