Fundamental Chemistry and Hydraulics - Mathematics and Statistics for the Environment - page 365

Note: Because neither type of hypochlorite is 100% pure chlorine, more lb/day must be fed into the
system to obtain the same amount of chlorine for disinfection. This is an important economi-
cal consideration for those facilities thinking about substituting hypochlorite for chlorine.
Some studies indicate that such a switch can increase overall operating costs by up to three
times the cost of using chlorine.

To calculate the lb/day hypochlorite required, a two-step calculation is necessary:

mg/L × MGD × 8.34 lb/gal = lb/day

Chlorine (lb/day)
%Available

×= 100 Hypochlori te (lb/day)

■ EXAMPLE 14.18
Problem: A total chlorine dosage of 10 mg/L is required to treat a particular wastewater. If the flow
is 1.4 MGD and the hypochlorite has 65% available chlorine, how many pounds per day of hypo-
chlorite will be required?

Solution:

1. Calculate the lb/day chlorine required using the mg/L to lb/day equation:

mg/L × MGD × 8.34 lb/gal = lb/day

10 mg/L × 1.4 MGD × 8.34 lb/gal = 117 lb/day

2. Calculate the lb/day hypochlorite required. Because only 65% of the hypochlorite is chlo-
rine, more than 117 lb/day will be required:

117 lb/day chlorine
65% availablechlorine

×100 = 180 lb/day hypochlorite

■ EXAMPLE 14.19
Problem: A wastewater flow of 840,000 gpd requires a chlorine dose of 20 mg/L. If sodium hypo-
chlorite (15% available chlorine) is to be used, how many pounds per day of sodium hypochlorite
are required? How many gallons per day of sodium hypochlorite is this?

Solution:

1. Calculate the lb/day chlorine required:

mg/L × MGD × 8.34 lb/gal = lb/day

20 mg/L × 0.84 MGD × 8.34 lb/gal = 140 lb/day chlorine

2. Calculate the lb/day sodium hypochlorite:

140 lb/day chlorine
15% availablechlorine

×100 = 933 lb/day hypochlorite