AWWA JAW56403

Because fluoride is so effective in reducing dental caries, many US water suppliers add the chemical during the treatment process, with the result that some 62% of the American population currently receives fluoridated water. But few utilities may be aware that the point at which fluoride is added can have a deleterious effect on the treatment process, particularly with respect to removal of particles and natural organic matter. Generally, fluoride is added after the source water has passed through a plant's physicochemical process train and shortly before the water enters a clearwell or finished water reservoir. When added this way, fluoride is likely to have no influence on the treatment processes occurring upstream. However, a review of data compiled for the Information Collection Rule found that many utilities add fluoride near the beginning of the treatment process. Results from bench- and pilot-scale studies involving conventional water treatment found that under conditions typical for treatment plants practicing enhanced coagulation, application of fluoride to the raw water significantly reduced removal of total organic carbon, decreased clarifier performance and increased filtered turbidity breakthrough, shortened filter run times, led to a tenfold increase in finished water aluminum concentration, and resulted in a loss of up to 40% of the applied fluoride dose because of sorption to flocs. Given these findings, utilities that practice prefluoridation may need to assess whether fluoride addition is exerting a negative influence on treatment performance and finished water quality. Includes 28 references, figures.