Sodium hypochlorite (NaOCl, available at a strength of 14%) is used as a disinfectant at a water treatment plant that processes 25 mgd of water. When added to water, sodium hypochlorite undergoes the reactions shown below. The facility would like to achieve an initial hypochlorite dose of 4.5 mg/L OCl- and will disinfect the water pH = 7.0. The disinfection chamber will have a L:W:D ratio of 60:1:1.

Reaction #1: NaOCl --> Na+ + OCl- no pKa...reaction proceeds to completion

Reaction #2: HOCl <--> H+ + OCl- pKa = 7.6

a. Based on Reaction #1, how much NaOCl (in gal/min) will be required to achieve the target dose?

b. If the facility would like to maintain a 2-week supply of sodium hypochlorite, what storage volume is required (in 1,000 gallons)?

c. What percentage of the chlorine added will exist as OCl- at a pH = 7.0?

d. The facility would like to have a detention time of 1.2 hours for the disinfection process with a total of 5 passes (i.e., the reactor has a serpentine path with the length of each pass being 1/5 the total travel length). Calculate the reactor dimensions (in feet) and draw a plan- view schematic of the tank.