What is the difference between chemical oxygen demand (COD) and biochemical oxygen demand (BOD)?

The distinction between chemical oxygen demand (COD) and biochemical oxygen demand (BOD) lies in the specific pollutants they measure and the scope of what they assess. COD quantifies the total amount of oxygen required to chemically oxidize all organic and inorganic matter in water, providing a broad picture of the water’s pollution load. This includes substances that can be oxidized by chemical reagents, comprehensively indicating the potential for water pollution.

In contrast, BOD focuses specifically on the quantity of oxygen that microorganisms will consume while decomposing organic matter over a set period, typically five days. This means BOD is a measure of the biodegradable portion of the pollution and gives insight into how much organic material is available for biological degradation in a water body.

In summary, option B is correct because it accurately describes COD as measuring all chemical oxygen needed for oxidizing pollutants, while BOD is concerned solely with the biodegradable portion of organic pollutants. The other options do not accurately capture the essential differences between the two measurements, leading to a misunderstanding of their respective roles in water quality assessment.