What type of reactor meets with the following conditions? 1) complete mixing; 2) continuous flow

A treatment plant treats water at an average daily flowrate of 2.7 m3/s. The water is chlorinated before it flows into a 15000 m3 reservoir. The water flowing into the reservoir has a chlorine concentration of 3 mg/L. Chlorine decays at a rate of 0.24 h-1. Assume the reservoir is well-mixed and the system is at steady-state condition. (a) Determine the chlorine concentration at the discharge point of the reservoir. (b) The treated water flows from the reservoir into a transmission main. The pipe carrying the water has a diameter of 2 m and flows full. In the transmission main, chlorine decays at a rate of 0.19 h-1. Determine the concentration of chlorine 2 km from the treatment plant.

Environmental Engineering: Water Treatment Please consider each of the following points: a. Determine the required residence time for each reactor of 3 equal volume CSTRs in series given a zero-order reaction with a reaction rate constant, k = -5 mg/L hr. The influent concentration is 125 mg/L and 95% conversion is required across the three-reactor system. What is the total reactor system residence time? b. Determine the required residence time for a single CSTR given the same conditions.  c. Determine the required residence time for a PFR given the same conditions. d. Why are all three residence time the same?

I need hand written solution only otherwise I will down vote