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Because fluoride is so effective inreducing dental caries, many USwater suppliers add the chemicalduring the treatment process, withthe result that some 62% of the Americanpopulation currently receives fluoridatedwater. But few utilities may be aware that thepoint at which fluoride is added can have adeleterious effect on the treatment process,particularly with respect to removal of particlesand natural organic matter.Generally, fluoride is added after thesource water has passed through a plant'sphysicochemical process train and shortlybefore the water enters a clearwell or finishedwater reservoir. When added this way, fluorideis likely to have no influence on thetreatment processes occurring upstream.However, a review of data compiled for theInformation Collection Rule found thatmany utilities add fluoride near the beginningof the treatment process.Results from bench- and pilot-scale studiesinvolving conventional water treatmentfound that under conditions typical fortreatment plants practicing enhanced coagulation,application of fluoride to the rawwater significantly reduced removal of totalorganic carbon, decreased clarifier performanceand increased filtered turbiditybreakthrough, shortened filter run times, ledto a tenfold increase in finished water aluminumconcentration, and resulted in a lossof up to 40% of the applied fluoride dosebecause of sorption to flocs. Given thesefindings, utilities that practice prefluoridationmay need to assess whether fluorideaddition is exerting a negative influence ontreatment performance and finished waterquality. Includes 28 references, figures.

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Edition: Vol. 94 - No. 2 Published: 02/01/2002 Number of Pages: 10File Size: 1 file , 480 KB