The half-saturation constant (kinetic constant) of the Monod model which governs the reactions in the activated sludge system is 90 mg COD L-1. The concentration of Chemical Oxygen Demand (COD) in the effluent from this system is 25 mg L-1. The growth rate of the organisms in this case is 0.9 days-1. The activated sludge tank has a volume of 50 m3 and the flow rate through it is 500 m3 day-1. The organism concentration is measured as MLVSS (mixed liquor volatile suspended solids) and they are being produced at a rate of 150 mg MLVSS L hour at steady state. For this problem assume that the death rate in the process is zero (kd = 0.0) -1 -1

(a) What is the maximum specific growth rate of the organisms (day-1)
(b) What is the concentration of MLVSS in the activated sludge (mg L-1)
(c) What is the sludge wastage rate (kg day-1)?
(d) If the yield coefficient (mass suspended solids produced/mass substrate removed) of the system is
0.8, what is the concentration of COD (mg L-1) in the influent?