Science of Water : Concepts and Applications

Water Treatment Calculations 397
Example 10.121
total chemical in inventory, gal
Days’ supply in inventory
average use, gpd
Problem:
The pounds (lb) calcium hypochlorite used for each day during a week is given below. Based on these
data, what was the average lb/day hypochlorite chemical use during the week?
Solution:
Example 10.122
Monday—50 lb/day Friday—56 lb/day
Tuesday—55 lb/day Saturday—51 lb/day
Wednesday—51 lb/day Sunday—48 lb/day
Thursday—46 lb/day
Average use, lb/day
total chemical used, lb
number of days
357
7
51 lb/day average use
Problem:
The average calcium hypochlorite use at a plant is 40 lb/day. If the chemical inventory in stock is
1100 lb, how many days’ supply is this?
Solution:
CHLORINATION CHEMISTRY
total chemical in inventory, lb
Days’ supply in inventory
average
use, lbday 1100 lb in inventory
Days’ supply in inventory
40 lbday average use
27.5 days’ supply in inventory
(10.98)
As mentioned, chlorine is used in the form of free elemental chlorine or as hypochlorites. Temperature,
pH, and organic content in the water infl uence its chemical form in water. When chlorine gas is
dissolved in water, it rapidly hydrolyzes to hydrochloric acid (HCl) and hypochlorous acid (HOCl):
According to G.C. White (1972), the equilibrium constant is:
Cl2H2O↔ H ClHOCl (10.99)
KH
[H ][Cl ][HOCl]
[Cl ]
2(aq)
4.48104at 25° C
(10.100)