Sewage water is purified by

Options

A. Microorganisms
B. light
C. Fishes
D. Aquatic plants.

Answer

**Step-by-Step Solution:**

1. **Understanding Sewage Water**: Sewage water is a mixture of waste products, including organic matter and domestic waste released by humans. It contains pollutants that need to be treated before being released into the environment.

2. **Sewage Treatment Process**: The purification of sewage water involves several treatment stages:
- **Primary Treatment**: This involves the physical removal of large solids through filtration.
- **Secondary Treatment**: This stage focuses on biological processes where microorganisms play a crucial role. Here, the organic matter is broken down by bacteria, which can be aerobic (requiring oxygen) or anaerobic (not requiring oxygen).
- **Tertiary Treatment**: This is the final stage that further cleans the water, often involving additional filtration and disinfection processes.

3. **Role of Microorganisms**: In the secondary treatment, microorganisms are added to the sewage. These microorganisms metabolize or degrade the organic matter present in the sewage, effectively purifying the water. This process is essential for reducing the Biological Oxygen Demand (BOD) of the water, making it cleaner and safer for discharge.

4. **Conclusion**: The correct answer to the question "Sewage water is purified by" is **microorganisms**. They are vital in breaking down the organic pollutants in sewage during the treatment process.

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