A completely mixed activated sludge plant is designed to treat 10,000 m3/d of an industrial wastewater. The wastewater has a BOD5 of 1200 mg/L. Pilot plant data indicates that a reactor volume of 6090 m3 with an MLSS concentration of 5000 mg/L should produce 83% BOD5 removal. The value for Y is determined to be 0.7 kg/kg and the value of kd is found to be 0.03 d–1. Under ow solids concentra- tion is 12,000 mg/L. The ow diagram is similar to Figure 8.6.

Determine the mean cell residence time for the reactor.

Calculate the mass of solids wasted per day.

Calculate the volume of sludge wasted each day.
 

Primary effluent! Q, Xo, So Aeration tank V, X, S Sludge return | System Boundary QR Xw S Q+ QR X, S Secondary clarifier Sludge! underflow --- Sludge waste Qw Xw S Qw Xw S Effluent Qe Xe, S