Water Treatment Processes - Mathematics and Statistics for the Environment - page 656

23.7.5 C alCulating d ry h ypoChlorite F eed r ate
The most commonly used dry hypochlorite, calcium hypochlorite contains about 65 to 70% avail-
able chlorine, depending on the brand. Because hypochlorites are not 100% pure chorine, more lb/
day must be fed into the system to obtain the same amount of chlorine for disinfection. The equation
used to calculate the lb/day hypochlorite needed is Equation 23.90:

Chlorine (lb/day)
%Availablechlorine 100

Hypochlorite (lb/day)= (23.90)

■ EXAMPLE 23.112
Problem: A chlorine dosage of 110 lb/day is required to disinfect a flow of 1,550,000 gpd. If the
calcium hypochlorite to be used contains 65% available chlorine, how many lb/day hypochlorite
will be required for disinfection?

Solution: Because only 65% of the hypochlorite is chlorine, more than 110 lb of hypochlorite will
be required:

Chlorine (lb/day)
%Available c

110
65/100

110
065

Hypochlorite = = = = 169 lb/day

hlorine 100 .

■ EXAMPLE 23.113
Problem: A water flow of 900,000 gpd requires a chlorine dose of 3.1 mg/L. If calcium hypochlorite
(65% available chlorine) is to be used, how many lb/day of hypochlorite are required?

Solution: Calculate the lb/day chlorine required:

Chlorine = Chlorine (mg/L) × Flow (MGD) × 8.34 lb/gal

= 3.1 mg/L × 0.90 MGD × 8.34 lb/gal = 23 lb/day

Calculate the lb/day hypochlorite:

Chlorine (lb/day)
%Available c

23
65/100

23
065

Hypochlorite = = = = 35 lb/day

hlorine 100 .

■ EXAMPLE 23.114
Problem: A tank contains 550,000 gal of water and is to receive a chlorine dose of 2.0 mg/L. How
many pounds of calcium hypochlorite (65% available chlorine) will be required?

Solution:

Chlorine (mg/L) × × 34 lb/gal

%Availablechlorine 100

Volume (MG) 8.

Hypochlorite =

2.0 mg/L × 0.550 MG × 8.34 92

065

.
.

= = = 14.2 lb

65/100