Tennessee Wastewater Operator Practice Exam

What is the first step in analyzing a water sample for BOD?

1. Diluting the sample

2. Measuring the pH

3. Preparing the seed

4. Measuring the initial DO

The correct answer is: Measuring the initial DO

Measuring the initial dissolved oxygen (DO) is an essential first step in analyzing a water sample for biological oxygen demand (BOD). This measurement establishes a baseline level of oxygen present in the sample before any biological activity occurs. The BOD test evaluates the amount of oxygen that microorganisms will consume while decomposing organic matter in the sample over a specific incubation period, typically five days at a controlled temperature. By determining the initial DO, you can assess the decrease in oxygen levels caused by microbial activity after the sample has been incubated. The difference between the initial DO and the DO measured at the end of the incubation period gives you the BOD value, which reflects the organic matter's impact on the water's oxygen levels. While diluting the sample, measuring the pH, and preparing the seed are important processes in various methods of conducting BOD tests, those steps follow the initial DO measurement. They help ensure that the sample is in the proper condition for the test, but the initial measurement of DO is fundamental to quantifying the BOD accurately.