Chemical Storage and Feeding Systems - Public Water Systems - page 822

TABLE 24-2. Recommended Optimal Fluoride Level

Recommended Control Range

Annual Average
of Maximum
Daily Air
Temperature*
(F)

Recommended Fluoride
Concentrations

Community
Systems School Systems

Community
(ppm)

School†
(ppm)

0.1
Below

0.5
Above

20%
Low

20%
High

High40.0-53.7
53.8-58.3
58.4-63.8
63.9-70.6
70.7-79.2
79.3-90.5

1.2
1.1
1.0
0.9
0.8
0.7

5.4
5.0
4.5
4.1
3.6
3.2

1.1 - 1.7 4.3 - 6.5

1.0 - 1.6 4.0 - 6.0

0.9 - 1.5 3.6 - 5.4

0.8 - 1.4 3.3 - 4.9

0.7 - 1.3 2.9 - 4.3

0.6 - 1.2 2.6 - 3.8

Source: Reference 2.
* Based on temperature data obtained for a minimum of five years.
† Based on 4.5 times the optimum fluoride level for communities.

larger quantities of water. Fluospar and calcium fluoride are the commercial fluoride
compounds usually used in water treatment. Sodium silicofluoride is the most com-
monly used compound for fluoridation of municipal water supplies, whereas sodium
fluoride is used less frequently because of higher costs. Ammonium silicofluoride and
hydrofluosilicic acid also can be used for fluoridation. More detail is presented in
Chapter 20.

Fluoride Reduction Because fluoride compounds are present in natural environ-
ments (13th rank among the elements), a raw-water supply may contain too much
fluoride. Excess fluoride concentrations may cause blackening or mottling of teeth.
Several chemicals can be used for fluoride reduction, including commercially produced
products such as fluorex and fluo-carbon, as well as magnesium oxide and activated
alumina. The defluoridation process is discussed in Chapter 20.

pH Adjustment There may be several points in the water treatment process where
the pH must be adjusted. Several acids and bases can be used, depending on the final
pH desired. Those typically used are listed in Table 24-1.

Iron and Manganese Removal Iron and manganese concentrations above 0.3
mg / L total should be removed from water. Although not harmful to health, they cause
staining and taste problems. These constituents are removed through oxidation, by
settling and filtration, using chlorine, chlorine dioxide, ozone, or potassium perman-
ganate. Small amounts (below 1 mg / L) can be sequestered by sodium hexametaphos-
phate. More detail is presented in Chapter 14.

Corrosion Control At the completion of the water treatment process and prior to
entering the distribution system, the water must not be corrosive. Corrosive water will
cause costly problems in the distribution and storage systems as well as for the indi-
vidual consumer. Lime, soda ash, sodium hydroxide, sodium hexametaphosphate, and
sodium tripolyphosphate are all used to minimize the corrosive property of waters.