# DBT JRF 2022 — Question 143

Exam: DBT JRF 2022 · Section: B · Topic: Environmental Biotechnology › Water Quality - BOD & COD · Difficulty: Medium

## Question

In a water sample collected from an industrial cluster, the ratio of BOD:COD is found to be less than 0.3. Which one of the following may be presumed from this initial data?

## Options

- **A.** There are numerous carbon-based compounds in the sample which are not utilizable by the microbial population.
- **B.** The microbial population efficiently utilizes all the organic compounds present in the sample.
- **C.** The water sample may contain carbohydrates that promote microbial growth.
- **D.** The sample contains lipids and fatty acids which require less oxygen for breakdown.

## Answer

Option A

## Explanation

BOD:COD ratio < 0.3 — non-biodegradable organic compounds: BOD (Biochemical Oxygen Demand): O₂ consumed by microorganisms in 5 days at 20°C; measures BIODEGRADABLE organic content. COD (Chemical Oxygen Demand): O₂ required to chemically oxidise ALL organic matter (including non-biodegradable compounds); total organic content. Interpretation of BOD:COD ratio: • Ratio = 1.0: all organic matter is biodegradable. • Ratio = 0.5–0.6: typical domestic sewage (Mediumly biodegradable). • Ratio < 0.3: LARGE fraction of organic matter is NOT biodegradable by microorganisms. • This implies the presence of RECALCITRANT or TOXIC compounds (heavy metals, chlorinated organics, phenols, dyes) that resist microbial breakdown. Practical implication: Low BOD:COD ratio industrial effluents cannot be treated by conventional biological treatment (activated sludge) alone; advanced treatment (ozonation, coagulation, AOP) required. Answer: BOD:COD < 0.3 indicates most organic compounds are NOT biodegradable (recalcitrant/non-utilizable by microbes).

Source: https://mypyqbuddy.com/questions/in-a-water-sample-collected-from-an-industrial-6a104cd5920734408bc0c79e