Environmental Engineering Reference
In-Depth Information
required to remove many of the dissolved organic and inorganic substances.
Examples would include groundwater with excessive dissolved solids and
surface waters containing organic compounds from domestic or industrial
wastewaters or organics occurring naturally such as humic acid or prod-
ucts of algal blooms. Additional processes are available for removing these
contaminants.
Note:
These additional water treatment processes involve sophisticated
equipment and require highly skilled operators; therefore, they are quite
expensive (Peavy et al., 1985).
Additional water unit treatment processes may be used in addition to clar-
ification or applied separately, depending on the source and quality of the
raw water. Let's take a closer look at groundwater. The question is—does a
typical groundwater source require treatment beyond conventional means?
The answer is that groundwater does not normally require processing by the
unit treatment steps listed above, other than disinfection, because ground-
water is filtered naturally by the layers of soil from which it is withdrawn.
Disinfection is only applied (in many cases) as a precautionary step required
by law for public water systems. Groundwater is usually free of bacteria or
other microorganisms; however, that all groundwater comes into contact
with soil and rock is a cause for concern. With such contact, groundwater
may become contaminated by high levels of dissolved minerals that must
be removed.
Fluoridation
Fluoride, when added to drinking water supplies in small concentrations
(about 1.0 mg/L), can be beneficial. In some locations, common practice is to
mix a 4% solution of sodium fluoride and feed that into the flow of the water
system. The amount that is fed depends on the air temperature and on the
fluoride levels in the raw water. Experience has shown that drinking water
containing a proper amount of fluoride can reduce tooth decay by 65% in
children. Fluoride combines chemically with tooth enamel when permanent
teeth are forming, and the result is teeth that are harder, stronger, and more
resistant to decay. The USEPA sets the upper limits for fluoride in drinking
water supplies based on ambient temperatures; for example, people drink
more water in warmer climates, so fluoride concentrations should be lower
in these areas (Spellman, 1998).
