When calculating dosages for sodium hypo, especially in the process design you may want to take into account possible degradation of the hypochlorite over time.
I agree with paulrau, but would include that the chlorine demand of the water should be considered if you required 40ppm of free chlorine for disinfection purposes.
I agree with the others regarding "chlorine demand" of the solution to be disinfected and to be aware of "degradation" of the chlorine prior to use as advised in the link.
I am a little slow on the uptake, but if the flow rate is 300 gpm then that would be 18000 gal/hour. That would seem to come out to 0.018 gal = 1/1,000,000 of 18,000 gal. If the desire dose was 40 ppm, then that would require 40 x 0.018 gal/hr or 0.72 gal / hr cl2. If the sodium hypochlorite is a 12.5% solution, then the 0.72 gal/hr chlorine would have to be divided by the 0.125 solution leaving a feed rate for the sodium hypochlorite of 5.76 gal/hr. What am I missing here? Are you factoring in the s.g. of sodium hypochlorite? If so I find that somewhat curious as I was always told that because commerical strength hypo is based on 1% figured at one pound of chlorine per 10 gallons of water which would balance out the s.g. Is this incorrect?
