Science of Water : Concepts and Applications

Water Treatment Calculations 391
Solution:
Calculate the expected increase in chlorine residual:
The actual increase in residual is:
Increase, lbday (increase, mgL)(flow, MGD)(8.34 lbgal) 4lb/d
( x mg/L)(1.4 MGD)(8.34 lbgal) 4
x
(1.4 MGD) (8.34)
x 0.34 mgL
CALCULATING DRY HYPOCHLORITE FEED RATE
0.4 mgL- 0.3 mgL0.1 mgL The most commonly used dry hypochlorite, calcium hypochlorite, contains about 65–70%
available 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 hypochlorite, lb/day, needed can be found using
Equation 10.91.
Example 10.112
chlorine, lbday Hypochlorite (lbday)
% available chlorine100
Problem:
A chlorine dosage of 110 lb/day is required to disinfect a fl ow 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, lbday Hypochlorite (lbday)
% available chlorine
100
110 lbday
65100 110
65 .
169 lbday hypochlorite
(10.91)