Water Treatment Processes - Mathematics and Statistics for the Environment - page 657

■ EXAMPLE 23.115
Problem: A total of 40 lb of calcium hypochlorite (65% available chlorine) is used in a day. If the
flow rate treated is 1,100,000 gpd, what is the chlorine dosage in mg/L?

Solution : Calculate the lb/day chlorine dosage:

Chlorine (lb/day)
%Available c

Hypochlorite =

hlorine 100

x lb/day

0.65

40 lb/day =

06540 . ×= x

2 66lb/day = x

Then calculate mg/L chlorine using the mg/L to lb/day equation and filling in the known information:

26 lb/day chlorine = x mg/L chlorine × 1.10 MGD × 8.34 lb/gal

x = 26 lb/day/(1.10 MGD × 8.34 lb/gal) = 2.8 mg/L

■ EXAMPLE 23.116
Problem: A flow of 2,550,000 gpd is disinfected with calcium hypochlorite (65% available chlo-
rine). If 50 lb of hypochlorite are used in a 24-hr period, what is the mg/L chlorine dosage?

Solution: Calculate the lb/day chlorine dosage:

50 lb/day hypochlorite = ( x lb/day chlorine)/0.65

x = 32.5 lb/day chlorine

Calculate mg/L chlorine:

x mg/L chlorine × 2.55 MGD × 8.34 lb/gal = 32.5 lb/day

x = 1.5 mg/L chlorine

23.7.6 C alCulating h ypoChlorite s olution F eed r ate
Liquid hypochlorite (i.e., sodium hypochlorite) is supplied as a clear, greenish-yellow liquid in
strengths varying from 5.25 to 16% available chlorine. Often referred to as bleach , it is, in fact,
used for bleaching. Common household bleach is a solution of sodium hypochlorite containing
5.25% available chlorine. When calculating gallons per day (gpd) liquid hypochlorite, the lb/day
hypochlorite required must be converted to gpd hypochlorite. This conversion is accomplished
using Equation 23.91:

Hypochlorite (lb/day)
8.34 lb/gal

Hypochlorite (gpd) = (23.91)