A municipal wastewater (Q0 = 104 m3 d-1, S0 = 500 mg L-1 COD, Xe = 0 mg L-1) is to be treated by an activated sludge process. The aerobic reactor is completely mixed. For a bacterial concentration of X = 2 g L-1 MLSS, an effluent COD concentration of S = 25 mg L-1 COD of dissolved biodegradable substances should be reached.


YX/s = 0.43 g MLSS/g COD Fmax = 7.2 d-1 KS = 100 mg L-1 COD kd = 0.24 d-1

1. Calculate the sludge age tRX and the critical sludge age tRXC.

2. Calculate the reactor volume V.

3. What is the mass flow rate of the surplus sludge which must be removed daily?

4. What is the critical mass flow rate?

5. Calculate the mass of bacteria which will be reduced by bacterial decay daily.

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