Page 170 - Facility Piping Systems Handbook for Industrial, Commercial, and Healthcare Facilities

WATER TREATMENT AND PURIFICATION

4.6 CHAPTER FOUR

responsible for most of the scaling deposited on pipe walls and boilers. Generally accepted prac-
tice limits the term hardness to include only calcium and magnesium. Often, water is character-
ized in general terms by the amount of hardness, expressed in mg/L as CaCO , as follows:
3
Soft 0 to 75 mg/L as CaCO 3
Moderate 76 to 150 mg/L as CaCO 3
Hard 151 to 300 mg/L as CaCO 3
Very hard Over 300 mg/L as CaCO 3

Trace Elements
Trace elements are present in very small quantities and are only considered problems if
the amount is above an accepted level for the purpose for which the water is to be used.
Examples are lead, cadmium, copper, barium, silver, lithium, zinc, chromium, mercury,
arsenic, and selenium.

DISSOLVED GASES

The most common dissolved gases in natural raw water are oxygen, carbon dioxide, nitro-
gen, and hydrogen sulfide. In addition, water obtained from a potable water supply usually
has chlorine and fluorides present, added for public health. Of increasing concern is the
presence of radon gas in many water supplies obtained from wells.
Oxygen is the basic factor in the corrosion process and must be present for the corrosion
of metals. Removal or reduction reduces the corrosiveness of the water.
For chlorine, no pretreatment is usually necessary for feedwater containing less
than 1 ppm. When more than 1 ppm of chlorine is present, an activated carbon filter is
recommended.

WATER ANALYSIS AND
IMPURITY MEASUREMENT

GENERAL

Analyzing a water sample is the process of finding the quantity of various impurities pres-
ent. In order to accomplish this, the quantities must be presented in a logical and under-
standable manner to allow for easy and practical interpretation. It is of utmost importance
that the initial analysis of incoming water be accurate and contain a worst-case scenario
and that the desired output quality be established prior to the selection of any treatment
system.
The most accurate analysis of a water sample is done by laboratories specializing in
this type of work. Sterile containers must be used and several samples must be taken over
a period of time to ensure that peak readings and average values will be obtained. There
are also many field tests that are not as accurate as laboratory tests but give an accuracy
acceptable to the user.

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