Why is it important to maintain a temperature of 20 degrees Celsius during BOD testing?

Maintaining a temperature of 20 degrees Celsius during BOD (Biochemical Oxygen Demand) testing is crucial to ensure accurate measurements of oxygen depletion. This temperature is standardized because it represents a common condition under which microbial processes occur. At this specific temperature, microbial activity is consistent and predictable, allowing for reliable comparisons of BOD levels across different water samples.

When the temperature is controlled at 20 degrees Celsius, the metabolic rates of the bacteria, which are responsible for consuming oxygen during the decomposition of organic materials, remain stable. Variations in temperature can lead to variations in microbial activity, potentially skewing the results. Therefore, consistency in temperature helps to provide a valid measure of the biological activity occurring in the sample over a specified period, which is fundamental for assessing the impact of wastewater on the environment.

The other options relate to aspects of microbial growth or chemical processes but do not directly address the primary goal of the BOD test, which is to measure the oxygen depletion caused by biotic processes at a controlled and standard temperature.