Question

Which of the following is true for a water sample with a BOD value of more than 50 ppm?

• A. The DO content would be less than 6 ppm
• B. The water is clean and potable
• C. Aquatic life will thrive
• D. The COD of the sample is 25 ppm

Hint:

Remember that high BOD values indicate water pollution, resulting in low dissolved oxygen (DO) content, which harms aquatic life and makes the water unsuitable for consumption.

Answer 1

The Correct Option is A

Step 1: Understand the concept of BOD (Biochemical Oxygen Demand)
BOD refers to the amount of oxygen required by bacteria and microorganisms to decompose the organic matter in a water sample. This process consumes oxygen, and the higher the BOD, the more oxygen is used in the decomposition process. A high BOD indicates the presence of a large amount of organic matter in the water, which is typically the result of pollution.

Step 2: The relationship between BOD and DO (Dissolved Oxygen)
Dissolved Oxygen (DO) is the amount of oxygen present in water. The more organic matter there is, the more oxygen is consumed by bacteria for decomposition, thus reducing the available oxygen for aquatic life. In a water sample with a high BOD value (greater than 50 ppm), the oxygen content (DO) will likely drop below 6 ppm, which makes the water unsuitable for most aquatic organisms to survive.

Step 3: Analyze the options

Option (1): The DO content would be less than 6 ppm
This statement is true because as the BOD value increases, the oxygen required for decomposition increases, leaving less oxygen available for other organisms. A BOD value of more than 50 ppm typically indicates a very low DO content.

Option (2): The water is clean and potable
This statement is false because a high BOD value indicates pollution. Water with such a high BOD value would be polluted and not suitable for drinking or as a clean water source.

Option (3): Aquatic life will thrive
This statement is false because high BOD values mean that the oxygen in the water is being consumed rapidly by bacteria, which depletes the oxygen needed for aquatic life to thrive. Hence, aquatic life would not thrive in water with such a high BOD.

Option (4): The COD of the sample is 25 ppm
This option is not directly relevant in this context because Chemical Oxygen Demand (COD) measures the oxygen needed to oxidize both organic and inorganic compounds, while BOD measures the oxygen required to biodegrade organic matter. These two values are not directly comparable without additional information.