Question

BOD values (in ppm) for clean water (A) and polluted water (B) are expected respectively as :

• A. \( A>15, B>47 \)
• B. \( A<5, B>17 \)
• C. \( A>50, B<27 \)
• D. \( A>25, B<17 \)

Hint:

Higher BOD indicates lower dissolved oxygen levels and higher levels of organic pollution. Remember: Clean \(<5 \), Polluted \(>17 \).

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Biochemical Oxygen Demand (BOD) is a measure of the amount of dissolved oxygen needed by aerobic biological organisms to break down organic material present in a given water sample at a certain temperature over a specific time period.
It is a widely used indicator of the organic quality of water.
Step 2: Detailed Explanation:
1. Clean Water: High-quality water has a very low concentration of organic waste. Consequently, the microorganisms require very little oxygen to decompose the matter. For clean water, the BOD value is typically less than 5 ppm.
2. Polluted Water: Highly polluted water contains significant amounts of organic matter (from sewage, industrial waste, etc.). Microorganisms consume a large amount of dissolved oxygen to decompose this waste. Water is considered highly polluted if its BOD value is 17 ppm or higher.
Step 3: Final Answer:
Based on the standard environmental chemistry criteria, clean water (A) has \( \text{BOD}<5 \) ppm and polluted water (B) has \( \text{BOD}>17 \) ppm.