85. 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?
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

Detailed Explanation:

When analyzing water quality, especially in wastewater from industrial sources, the BOD:COD ratio is a critical parameter. Here’s what each term means:

• BOD (Biochemical Oxygen Demand) measures the amount of oxygen required by microorganisms to break down biodegradable organic matter.

• COD (Chemical Oxygen Demand) represents the total oxygen required to chemically oxidize both biodegradable and non-biodegradable organic compounds.

A high BOD:COD ratio (closer to 1) indicates that most of the organic material is biodegradable and can be broken down by microbial populations. Conversely, a low BOD:COD ratio (less than 0.3) suggests that a significant portion of organic compounds is not biodegradable.

What Does a Low BOD:COD Ratio Mean?

A BOD:COD ratio < 0.3 typically points to the presence of complex, recalcitrant organic compounds, which are not easily degradable by standard microbial communities. This is commonly observed in industrial wastewaters containing:

• Synthetic chemicals

• Heavy hydrocarbons

• Dyes and solvents

• Toxic by-products

These substances resist microbial decomposition, resulting in a low BOD despite a high COD.

Correct Answer:

A. There are numerous carbon-based compounds in the sample which are not utilizable by the microbial population.