Effect of Domestic Water-Purifiers on Fluoridated Water

Objective: Activated carbon filters and hollow fiber film filters are used as domestic water purifiers. Further fluoride ion (F^-) supplements were suggested, as F^- absorption by the filters was reported. Therefore F^- adsorption by the filters was examined in this research with determining F^- concentrations in both water and filters. Material and Methods: A water purifier equipped with the activated carbon filters, the hollow fiber film filters (PF-CB-S and KIF227, Organo, Tokyo) and water pump (MDG-M2S100N, Iwaki, Tokyo) was developed to standardize the conditions of the experiments. The sample solutions were made of the mixture of distilled water or tap water with NaF at various F^- concentrations (0.1-10 mg/L). Each solution was examined at before and after each filter. The solution was passed through the filters at constant flow rate. F^- concentration was determined with using F^- electrode. Also, F^- concentrations absorbed into the filters were determined with both phyrohydrolysis method and flow-injection analysis. Results: F^- adsorption was not found in the hollow fiber film filter at any F^- concentration. When the solution of 0.8mgF/L was examined with using the activated carbon filter, F^- adsorption was found till 210 L passing through the filter. Similar results were found at other concentration. However, when the NaF solutions made of tap water were examined, F^- adsorption was disappeared after 8L passing through the filter. F^- concentrations in the activated carbon filters were found to be 230ppm or less, whereas F^- was not found in the fresh filters. Conclusions: The hollow fiber film filter did not absorb F^-. The activated carbon filter absorbed F^- in purified water and reduced its concentrations, but its effects on F^- concentrations in tap water were very limited and very quickly disappeared. Hence, further F^- supplement is not required, even if these domestic filters were utilized.