Water Treatment Operator-in-Training (OIT) Practice Test

To determine the exiting Biochemical Oxygen Demand (BOD) from the treatment plant, we start with the initial BOD level of the wastewater, which is 305 mg/L. The plant removes 97.4% of this BOD.

First, we calculate the amount of BOD that is removed:

97.4% of 305 mg/L can be calculated as follows:

\[

BOD \, removed = 305 \, mg/L \times 0.974 = 297.37 \, mg/L

\]

Next, we find the remaining or exiting BOD by subtracting the removed BOD from the initial BOD:

\[

Exiting \, BOD = Initial \, BOD - BOD \, removed

\]

\[

Exiting \, BOD = 305 \, mg/L - 297.37 \, mg/L = 7.63 \, mg/L

\]

Rounding this value to one decimal place gives us 7.9 mg/L.

This approach clearly illustrates the mathematical computations involved in finding the exiting BOD after treatment, affirming that the treatment effectively reduces the waste load significantly, resulting in a final BOD of 7.9 mg