An aeration tank has a volume of 0.80 MG (800,000 gallons) and operates at an MLSS concentration of 2,400 mg/L. The influent flow is 1.50 MGD with a BOD concentration of 180 mg/L. What is the Food-to-Microorganism (F/M) ratio?

Formula Used: F/M Ratio = [Influent BOD (lbs/day)] ÷ [Aeration Basin MLSS (lbs)]

Step-by-Step Mathematical Derivation:

1. Calculate Food (BOD lbs/day) = 1.50 MGD × 180 mg/L × 8.34 = 2,251.8 lbs BOD/day.
2. Calculate Microorganisms (Tank MLSS lbs) = 0.80 MG × 2,400 mg/L × 8.34 = 16,012.8 lbs MLSS.
3. F/M Ratio = 2,251.8 lbs ÷ 16,012.8 lbs = 0.14 lb BOD / lb MLSS.

⚠️ Common Exam Trap: Ensure both Food (numerator) and Microorganisms (denominator) are in pounds, which cancels out the 8.34 factor.