You are designing a reactor that uses chlorine in a PFR or CMFR to destroy pathogens in water. A minimum contact time of 30 min is required to reduce the pathogen concentration from 100 pathogens/L to below 1 pathogen/L through a first-order decay process. You plan on treating water at a rate of 1,000 gal/min.
(a) What is the first-order decay rate constant (assume PFR)?
(b) What is the minimal size (in gallons) of the reactor required for a plug flow reactor?
(c) What size (in gallons) of CMFR would be required to reach the same outlet concentration?
(d) Which type of reactor would you select if your treatment objective stated that "no discharge can ever be greater than 1 pathogen/L?" Explain your reasoning.
(e) If the desired chlorine residual in the treated water after it leaves the reactor is 0.20 mg/L and the chlorine demand used during treatment is 0.15 mg/L, what must be the daily mass of chlorine added to the reactor (in grams)?