Which pair of initial DO and final DO would yield the valid BOD example?

• A. 8.25 and 7.74
• B. 8.28 and 0.74
• C. 7.95 and 6.94
• D. 7.25 and 5.25

Answer: (A)

Biochemical Oxygen Demand (BOD) is found by subtracting the final dissolved oxygen (DO) from the initial DO after incubation. A valid example shows a real, positive drop in DO—not zero or negative—and the final DO remains above zero so oxygen isn’t completely exhausted. Here, initial DO is 8.25 mg/L and final DO is 7.74 mg/L, so the DO drop is 0.51 mg/L. That’s a plausible BOD5 value and keeps the final DO above zero, which fits a typical demonstration of how BOD is calculated. The other pairs would imply larger, less representative drops or more extreme final DO values that aren’t the standard example used for illustrating this concept.