Florida Wastewater Practice Test

Which of the following would you not typically use a grab sample on?

1. BOD

2. pH

3. Temperature

4. Chlorine residuals

The correct answer is: BOD

A grab sample is a method of collection where a single sample is taken at one specific point in time, which can represent the wastewater at that moment. This is suitable for parameters that do not show significant variation over short periods or can be understood in a one-time snapshot. BOD (Biochemical Oxygen Demand), however, is typically monitored over a standardized time period (usually five days) to accurately determine the amount of oxygen consumed by microorganisms in the sample. This means that a single grab sample would not adequately reflect the BOD of a wastewater stream, as the sample taken may not capture the potential variations that occur over time. In contrast, parameters like pH, temperature, and chlorine residual can be effectively measured with grab samples because their values can be fairly representative of the conditions at that moment. Thus, BOD is the parameter for which a grab sample would not typically be employed.