Page 256 -

10.2 CHAPTER TEN

TABLE 10.1 Physical Constants for Common Disinfecting Agents

Solubility
in water at Heat of
Molecular 1 atm and Boiling Melting vaporization,
Name Symbol weight 25 ° C, g/L point, °C point, °C cal/g
Chlorine C12 70.91 7.29 -34.5 - 101 68.7
Ozone 03 48.00 0.006* - 112 - 192 54.0
Chlorine dioxide C102 67.45 8.0t 10.9 -59 96.6

• 190 03 by weight.
tAssumes equilibrium with 10% C102 gas phase.

tion. The first use of ozone for disinfection was at Nice, France, in 1910. Since that time,
disinfection has become an accepted water supply practice throughout the world. Chlori-
nation has been the dominant method employed, but ozonation has been widely used also.
There has also been increasing use of chlorine dioxide as a disinfectant in the United
States and Europe.
Some of the physical constants for the three most common disinfecting agents, chlo-
rine, ozone, and chlorine dioxide, are listed in Table 10.1. Note that all three normally
exist as gases, although chlorine dioxide liquefies at a temperature near 10 ° C. Chlorine
is available as a compressed liquid, but ozone and chlorine dioxide must be manufactured
on-site (ozone because it decomposes, chlorine dioxide because it is dangerous to store
in a concentrated compressed form). Chlorine can also be provided as one of the hypochlo-
rites available as a bulk liquid or generated on-site.
Oxidants are used in water treatment to accomplish a wide variety of treatment ob-
jectives besides disinfection, including mitigation of objectionable tastes and odors, re-
moval of color, removal of iron and manganese, and oxidation of organic chemicals.
Oxidation of contaminants in water by means of aeration is covered in detail in Chapter
5. Information on the chemicals used in water treatment is provided in Appendix A. In-
formation on chemical handling and chemical feed equipment is covered in Chapter 15.
For additional information on the theory and chemical reactions involved in oxidation
and disinfection, refer to the companion AWWA text Water Quality and Treatment.

REGULA TORY FRAMEWORK

A number of regulations have been promulgated by the U.S. Environmental Protection
Agency (USEPA) under the Safe Drinking Water Act (SDWA) that affect how or when
a water treatment system performs oxidation or disinfection. In addition to the require-
ments under the Primary and Secondary Regulations, several specific rules have a great
impact on oxidation and disinfection process and are described in the following sections.

Secondary Regulations

The National Secondary Drinking Water Standards apply to drinking water contaminants
that may adversely affect the aesthetic qualities of water, such as odor and appearance.
These qualities have no known adverse health effects, and thus secondary regulations are
not mandatory. However, the quantities listed in the Secondary Standards do seriously af-