As distribution operators, there are times when storage tanks have to be disinfected. By rule, it has to be chlorinated at 50 ppm for 24 hours with a residual of 25 ppm. You may be asked to calculate the amount of chlorine necessary to disinfect. The following is an example of such a scenario.
A tank measures 20 feet, 6 inches in diameter by 80 feet, 6 inches tall, and you are preparing to disinfect it. How many pounds of chlorine are required to disinfect this tank to return to service?
.785 x 20.5 x 20.5 x 80.5 = 26,556.65 ft3
26,556.65 ft3 x 7.48 = 198,643.73 gal
Flow = .199 MGD
Lbs = Flow x mg/L x 8.34
Lbs = .199 MGD x 50 ppm x 8.34
Lbs = 82.98