Direction: A completely mixed activated sludge process is used to treat a wastewater flow of 1 million litres per day (1 MLD) having a BOD5 of 200 mg/l. The biomass concentration in the aeration tank is 2000 mg/l and the concentration of the net biomass leaving the system is 50 mg/l. The aeration tank has a volume of 200 m³.
-
What is the average time for which the biomass stays in the system?
-
- 5 h
- 8 h
- 2 days
- 8 days
Correct Option: D
The time spend by biomass in system is called sludge age (Qc).
| Qc = | ||
| Mass of biomass leaving the system |
| = | = 8 days | |
| 50 × 106 |
