Question

The biochemical oxygen demand is computed by

• A. Dissolved oxygen / Dilution factor
• B. Dissolved oxygen + Dilution factor
• C. Dissolved oxygen – Dilution factor
• D. Dissolved oxygen \( \times \) Dilution factor

Hint:

BOD is a measure of organic pollution. The standard BOD test involves diluting the sample to ensure oxygen is not a limiting factor. The final BOD value is obtained by correcting the observed dissolved oxygen depletion in the diluted sample by the dilution factor, which accounts for the original concentration of the undiluted sample.

Answer 1

The Correct Option is D

In civil engineering, especially in environmental engineering, the Biochemical Oxygen Demand (BOD) is an important parameter used to measure the amount of oxygen required for the biochemical decomposition of organic material in water. It serves as an indicator of the degree of pollution in the water body.

Formula for Biochemical Oxygen Demand (BOD):

The biochemical oxygen demand is computed by the expression: 

\[ \text{BOD} = \text{Dissolved Oxygen} \times \text{Dilution Factor} \]

• Dissolved Oxygen (DO): This is the amount of oxygen gas that is dissolved in the water. It is a crucial parameter because sufficient dissolved oxygen is necessary for aquatic life.
• Dilution Factor: This accounts for any dilution that occurs when measuring the dissolved oxygen in the sample, which might be due to the addition of distilled water or other agents.

Thus, the calculation of BOD involves multiplying the measured dissolved oxygen by the dilution factor to adjust for conditions under which the sample has been tested.

Final Answer:

Dissolved oxygen \( \times \) Dilution factor