The use of electrodialysis with mono-anion permselective membranes for defluoridation

Abstract

Water contamination by fluoride is a common problem present in many regions of the world. The excess of fluorine leads to many health issues. For that reason, the World Health Organisation estimated the permissible fluoride concentration to 1.5 mg F-/dm3. In this paper defluoridation process with the use of electrodialysis was described. During research standard cation-exchange (PC-SK) and mono-anion permselctive membranes (PC-MVA) were applied. The current density was equal to 1.72 mA/cm2 (it corresponded with a current intensity equal to 0.11 A) in the course of experiments. The tested solutions contained fluoride, organic matter (humic acids) and sodium chloride. The volume of diluate and concentrate was equal to 2 dm3 each. The fluoride concentration amounted to 5, 10, 100 and 200 mg F-/dm3. The sodium chloride content amounted to 0.5 g NaCl/dm3, whereas humic acids concentration was equal to 5, 10 and 15 mg/dm3. It has been noticed that the fluoride content has influenced on the energy demand, removal efficiency and process duration. In few cases electrodialysis allowed to decrease the fluoride content under permissible level for drinking water and the F- removal efficiency was very satisfying for the most part.