Biochemical Oxygen Demand (BOD) is a key indicator of the process performance of wastewater treatment plant. The plant is said to be efficient when BOD:

Correct option is B

Decreases

• Definition: Biochemical Oxygen Demand (BOD) is a measure of the amount of dissolved oxygen (DO) that microorganisms consume while decomposing organic matter in water.
• Significance: It indicates the level of organic pollution in water.
• Wastewater Treatment: The goal of wastewater treatment is to reduce the BOD of the water before it's released into the environment.

Analyzing the Question

The question asks: "Biochemical Oxygen Demand (BOD) is a key indicator of the process performance of a wastewater treatment plant. The plant is said to be efficient when BOD..."

• Efficiency and BOD: A highly efficient treatment plant will effectively remove organic matter from the wastewater. This removal process results in a significant reduction of the BOD.

Evaluating the Options

1. Increases/बढ़ती है: This is incorrect. If BOD increases after treatment, it means the plant is not removing organic matter effectively.

2. Decreases/घटती है: This is correct. A decrease in BOD indicates that the plant has successfully removed organic matter, making it more efficient.

3. Remains unchanged/अपरिवर्तित रहती है: This is incorrect. If the BOD remains the same, the treatment plant has had no impact on the organic pollution.

4. Increases for first 36 hours/पहले 36 घंटों में बढ़ती है: This option is misleading and generally incorrect. While there might be some fluctuations in BOD during the initial stages of treatment, a well-functioning plant ultimately reduces BOD over time.