Direction: An activated sludge system (sketched below) is operating at equilibrium with the following information. Waste water related data: flow rate = 500 m³/hour, influent BOD = 150 mg/l, effluent BOD = 10 mg/l. Aeration tank related data: hydraulic retention time = 8 hours, mean-cell-residence time = 240 hours, volume = 4000 m³, mixed liquor suspended solids = 2000 mg/l. 
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The food-to-biomass (F/M) ratio (in kg BOD per kg biomass per day) for the aeration tank is
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- 0.015
- 0.210
- 0.225
- 0.240
Correct Option: C
| = | |||
| m | V × MLSS |
| = | ||
| 4000 × 200 |
= 9.375 × 10–3 per hour
= 0.225 per day.
