A 1.0 × 106 gallon reactor is used in a sewage-treatment plant. The influent biochemical oxygen demand (BOD) concentration is 100 mg/L, the effluent BOD concentration is 25 mg/L, and the flow rate through the reactor is 500 gal/min.
(a) What is the first-order rate constant for decay of BOD in the reactor? Assume that the reactor can be modeled as a comply mixed flow reactor (CMFR). Report your answer in units of per hour.
(b) Assume that the reactor should be modeled as a plug flow reactor (PFR) with first-order decay, not as a CMFR. In that case, what must the first-order decay rate constant be within the PFR reactor?