Environmental Engineering Reference
In-Depth Information
free chlorine residual (hypochlorous acid). Both sodium and cal-
cium hypochlorite form hydroxides in water that raise the pH.
This, consequently, favors the hypochlorite ion form of the free
chlorine residual. At a pH of 10, all of the free available chlorine
residual is in the hypochlorite ion form. This greatly reduces the
disinfection effectiveness.
Ops
Tip
High concentrations of calcium and sodium hypochlorite
raise the pH. This lowers the effectiveness of disinfection,
so pH adjustment may be necessary.
The three chemicals commonly used for disinfection of pipe-
lines and storage facilities are: liquid chlorine, sodium hypochlo-
rite, and calcium hypochlorite. Some of the more important
properties and concerns of these chemicals are discussed in the
following sections.
Liquid Chlorine
Chlorine (ANSI/AWWA B301) is a liquefied gas under pres-
sure and is normally packaged in steel cylinders, usually 100 lb,
150 lb, or 1 ton (45.4 kg, 68.0 kg, or 907.2 kg). It is also available
in bulk tankers or rail cars.
At room temperature, about 80 percent of the volume of a cyl-
inder is liquid chlorine. Liquid chlorine will change to gas very
rapidly when removed from the pressurized cylinder and exposed
to atmospheric conditions. One part of liquid chlorine will expand
459 times when it changes to a gas.
Chlorine is a hazardous substance. For detailed safety infor-
mation, refer to publications of the Chlorine Institute, Washing-
ton D.C., and OSHA and DOT regulations that apply to chlorine
handling and transportation. Safety precautions and special
training are required to comply with all applicable regulations
and to ensure safe handling and use. Chlorine use requires:
Appropriate gas-flow chlorinators and ejectors to provide
a controlled high-concentration solution feed.
Direct supervision of trained personnel who are equipped
to handle any emergency.
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