A waste stream is to be treated by holding it for some time in a surge tank prior to discharging it into a river. The waste stream has a dissolved toxic species A, which is unstable and undergoes a first-order chemical reaction. The purpose of the surge tank is to allow enough residence time for some decomposition of A to occur in order to reduce the concentration of the pollutant. Derive an expression for the exit concentration as a function of time and the final steady-state concentration in the system. Assume that the tank is well stirred and use the backmixed assumption. The problem is sketched in Fig. 2.2.