Page 201 - Facility Piping Systems Handbook for Industrial, Commercial, and Healthcare Facilities

WATER TREATMENT AND PURIFICATION

WATER TREATMENT AND PURIFICATION 4.37

FIGURE 4.15 Principle of corona-discharge ozone generator.

1. Feed gas treatment. The gas reaching the generator must have all particles larger than
0.3 μm and 95 percent of particles larger than 0.1 μm removed. In addition, aerosols,
moisture, and hydrocarbons must be removed, as required by the manufacturer. This
purification is usually supplied as part of a package.
2. Ozone generator. The three basic types of generators are the Lowther plate unit, Otto
plate unit, and tube units. They differ only in the manner they are cooled. Ozone gen-
erators use large amounts of electrical power, generally between 15 and 26 kWh per
kilogram of O .
3
3. Water-ozone contact mechanism. Ozone and water at a pH of 7.5 or less are mixed in
direct contact with one another by the use of static or mechanical mixers, injectors, or
columns that optimize the dissolution of the gas.
4. Destruction unit. Depending on the generator, ozone concentrations can vary from 100
to 3000 ppm. Because high concentrations are harmful to humans and metals, the ozone
should not be allowed to escape to the atmosphere without being treated to a level below
0.1 ppm. Destruction can be accomplished by catalytic, thermal, or activated carbon.
Thermal units operate at a temperature of 300°C and generally require a 3- to 5-min
contact time to be effective.
The mechanism for ozone oxidation is through the generation of hydroxyl radicals. The
gas is directly injected into the water stream. Problems with this method include incomplete
oxidation of organic compounds and slow operation. Action is enhanced with the applica-
tion of UV radiation at 185 nm.

WATER TREATMENT

This section will describe the various methods and equipment used to treat water for various
purposes.

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