A completely mixed activated process is to be used to treat wastewater flow of 500 m³/hr having soluble BOD₅ of 250 mg/L. If the concentration of soluble BOD₅ escaping treatment is 10 mg/L, the treatment efficiency will be
- A82%
- B86%
- C92%
- D96%Correct
Solution
Concept
BOD removal efficiency
Formula
E = (S₀ − S) / S₀ × 100
Step-by-step solution
1. E = (250 − 10) / 250 = 0.96 = 96%.
Explanation
The treatment efficiency is the fraction of influent BOD that is removed.
Why the other options are wrong
82, 86 and 92% do not equal 240/250.
Shortcut
E = (S₀ − S)/S₀.
Common mistake
Dividing by the effluent BOD.
Correct answer: D) 96%