1.) Fluoridation
- The purpose of adding fluoride to the water is to help prevent tooth decay (cavities) in people consuming the water. It is applied in Philadelphia due to the Health Code issued by the Health Department. We have been dosing fluoride since 1952.
- Many chemicals can be used to add fluoride to drinking water. Our Water Department use hydrofluosilicic acid, which is a colorless, transparent, corrosive liquid that is produced as a by-product in the manufacturing of phosphate fertilizers.
We are not required to feed fluoride by the EPA or the State DEP. In fact, many communities object to the addition of fluoride to their water.
2.) Application Points
- At Baxter and Belmont, hydrofluosilicic acid is fed after the filters but before the clearwells.
- Due to poor post filtration mixing, at another of our plants the hydrofluosilicic acid is fed at the "E" Shaft. This results in applying 20% more chemical in order to achieve the desired concentration.
- The chemical is fed by an injector system at one plant, metering pumps at another and centrifugal pumps at the third, Feed outages are not critical, however, the chemical is fed continuously. The Health Department is notified when chemical feed is interrupted.
3. Concentration Guideline
- The desired fluoride concentration in the finished water is 1.0 mg/l.
- There is an Primary MCL of 4.0 mg/I. Too much fluoride can result in tooth discoloration (mottling of teeth).
- Chemists monitor fluoride concentration once per shift using an EPA approved ion-selective electrode technique (see photo above).
4.) Miscellaneous
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Safety precautions must be taken when working with hydrofluosilicic acid, since it is VERY corrosive. Fluoride can be used in tracer studies to determine detention times in basins and the distribution system...Operators need to monitor tank elevations for leaks.
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