Problem #3 (10 marks) (a) Prove that for a first order decay reaction (k= 2 days:') taking place in reactors of identical size at steady state, it does not matter if you use a CMFR followed by a PFR or a PFR followed by a CMFR (i.e. show that the final treated effluent concentration, in mg/L, is approx. the same in each scenario). Assume the volume of each reactor is 15 L and the reactors in series will be used to treat a wastewater containing 5 mg/L of contaminant "C" at a flowrate of 10 L/day. (b) Does this remain true if a second order decay reaction was taking place? If not, which sequence of reactors is more efficient (i.e. removes more of the contaminant)? Assume the same reactor volumes, flow rate and contaminant concentration as in part (a), and k2 = 2 Lmg'day!. You must show your derivation of the expression for a PFR with 2nd order decay