Science of Water : Concepts and Applications

Water Treatment Calculations 343
Now calculate percent strength:
Example 10.34
chemical (lb)
% Strength
100
water (lb) chemical
(lb)
0.625 lb chemical
100
(15 gal8.34 lbgal) 0.625
lb
0.625 lb chemical
100
125.7 lb solution
0.5%
Problem:
If 90 g (1 g = 0.0022 lb) of dry polymer are dissolved in 6 gal of water, what percent strength is the
solution?
Solution:
First, convert grams chemical into pounds chemical. Since 1 g = 0.0022 lb, 90 g is 90 times 0.0022 lb:
Now calculate percent strength of the solution:
(90 g polymer)(0.0022 lbg) 0.198 lb polymer
lb polymer
% Strength
100
lb water lb polymer
4%
0.198 lb polymer
100
(6 gal)(8.34 lbgal) 0.198 lb
DETERMINING PERCENT STRENGTH OF LIQUID SOLUTIONS
When using liquid chemicals to make up solutions (e.g., liquid polymer), a different calculation is
required, as shown below:
Example 10.35
Problem:
liquid polymer (% strength)
Liquid polymer, lb
100
polymer solid,
lb
polymer solution (% strength)
100
A 12% liquid polymer is to be used in making up a polymer solution. How many pounds of liquid polymer
should be mixed with water to produce 120 lb of a 0.5% polymer solution?
(10.31)