Page 202 - Facility Piping Systems Handbook for Industrial, Commercial, and Healthcare Facilities

WATER TREATMENT AND PURIFICATION

4.38 CHAPTER FOUR

UTILITY WATER TREATMENT

Water from wells, rivers, lakes, and streams is commonly used for cooling and washing.
Clarifying and treating this water in order to meet the purity requirements of the proposed
end use requires good monitoring and quick reactions to raw and treated water fluctua-
tions. If the water is to be recirculated, the treatment methods are more stringent. If the
water is to be discharged into the environment, local codes must be followed regarding
allowable chemical amounts present in the wastewater in order to avoid the need for waste
treatment.

Initial Filtering
If the supply is from surface water, a coarse or fine screen is usually placed at the intake to
keep out fish and other large debris. Coarse screens are usually 1/2-in diameter bars with a
2
clear opening of 1 to 3 in. Fine screens could have openings of approximately 3/8-in , with
the water velocity through the screen limited to about 2 ft/s. If the quantity of water is small
enough, basket strainers can be used. In climates where freezing may occur, the inlet should
be placed far enough below the low water level to prevent freezing.

Clarification
After initial filtering, clarification is required to obtain water that meets the standards for
proposed use. The selection of the clarifier is based on the volume of water to be treated
and the final quality desired. If the volume of water is small and the raw water is not very
turbid, filters may be used.

Biological Control
In order to control microorganism fouling of the system, they must be destroyed, if pos-
sible, or at least inactivated (to keep them from reproducing) and then removed from the
water stream. This is usually accomplished by chlorination, filtration, UV radiation, ozone
generation, and special adsorbents.
Chlorination is the least costly and most common method. The action of chlorine
requires a contact time and the establishment of a residual chlorine amount. A range of 0.5
to 1.0 ppm is generally acceptable for typical water.

Water Softening
Water softening should be considered to reduce the hardness in the utility water system
when used for recirculated cooling purposes.

POTABLE WATER TREATMENT

Water used for human consumption or intended to be part of food products must be treated
to comply with the Safe Drinking Water Act (SDWA), local regulations, and also the
Surface Water Treatment Rule, which is a part of the SDWA. In addition, compliance with
regulation 10 CFR 141 is required. Substances that affect the quality of potable water are
classified in four major categories:

Downloaded from Digital Engineering Library @ McGraw-Hill (www.accessengineeringlibrary.com)
Copyright © 2009 The McGraw-Hill Companies. All rights reserved.
Any use is subject to the Terms of Use as given at the website.