An engineer has determined that the flow patterns in a continuous flow reactor at a water treatment plant can be reasonably represented by a CFSTR with a 15-min hydraulic detention time, followed (in series) by a PFR with a 5-min detention time. This interpretation is based on the results of a step input tracer test. Hypochlorous acid (HOCl) is being dosed steadily into the influent; by convention, the disinfectant dose and the concentration of disinfectant remaining at any time thereafter are represented as Cl2". In these units, the dose is 8 mg Cl2/L. When the influent is chlorinated in a separate, batch test, 1.5 mg/L Cl2 is consumed before the first data point is analyzed, which is at t = 30 s. For the next 30 min, the Cl2 concentration in solution decays approximately according to the rate expres- sion: rcl, = -0.02 – 0.15cc1, 0.5, where rcle is in mg Cl2/(L min) and ccl, is in mg Cl2/L.
(A) Sketch the effluent tracer curve that you think led the engineer to infer the CFSTR-PFR reactor arrangement.
(B) Suggest a reason for the rapid disappearance of the first 1.5 mg Cl/L in the batch test.
(C) What is the value of T10 that would be used to compute the CT product for this system?
D() What is the value of C that would be used to compute the CT product for this system?
(E) The plant owners are considering installing a baffle that would convert the CFSTR portion of the system into two equal-sized CFSTRs in series. Would such a change increase, decrease, or have no effect on the values of C and T that would be used to compute the CT product? Explain your reasoning in a few sentences.