Science of Water : Concepts and Applications

386 The Science of Water: Concepts and Applications
The strengths of one form of chlorine over the others for a given water system depends on the
amount of water to be treated, confi guration of the water system, the local availability of the chemicals,
and the skill of the operator.
One of the major advantages of using chlorine is the effective residual that it produces. A residual
indicates that disinfection is completed, and the system has an acceptable bacteriological quality.
Maintaining a residual in the distribution system helps prevent regrowth of those microorganisms
that were injured but not killed during the initial disinfection stage.
DETERMINING CHLORINE DOSAGE (FEED RATE)
The expressions milligrams per liter (mg/L) and pounds per day (lb/day) are most often used to
describe the amount of chlorine added or required. Equation 10.88 can be used to calculate either
mg/L or lb/day chlorine dosage.
Example 10.103
Chlorine feed rate, lbday (Cl, mgL)(flow, MGD)(8.34 lbgal) (10.88)
Problem:
Determine the chlorinator setting (lb/day) needed to treat a fl ow of 4 MGD with a chlorine dose of
5 mg/L.
Solution:
Example 10.104
Chlorine, lbday (chlorine, mgL)(flow, MGD)(8.34 lbgal) ( 5 mgL)(4MGD)(8.34 lbgal) 167 lb day
Problem:
A pipeline 12 in. in diameter and 1400 ft long is to be treated with a chlorine dose of 48 mg/L. How
many pounds of chlorine will this require?
Solution:
Determine the volume, in gallons, of the pipeline.
2 3
Volume, gal (0.785) ( D )(length, ft)(7.48 galft )
3
(0.785)( 1 ft)(1 ft)(1400 ft)(7.48 galft )
8221 gal