Defluoridation of Moroccan groundwater by electrodialysis: continuous operation

Studies have been performed on removal of fluoride from Moroccan groundwater by electrodialysis in continuous operation using a pilot plant. The performances of two anion exchange membranes were compared. An optimisation of electrodialysis operation was carried out for various experimental conditions including, amongst others, the fluoride content in the raw water. The water quality and other parameters were followed to show the optimum operating conditions.

Fluoride removal operations by electrodialysis were conducted on Moroccan groundwater having Fig. 3. Variation of pH, Ca2+/Mg2+ ratio and LI for the three running conditions. Table 4 Recovery rate performances Running conditions at 40% of OR Scale conductivity (mS/cm) 80% of scale conductivity Recovery rate (mS/cm) (%) Without addition Addition of acid Addition of antiscalant 10.51 9.82 5.6 8.5 7.8 90.9 95.0 93.75 a fluoride content depending on the season. Using a preselected membrane, this study shows that desired drinking water can be easily obtained by electrodialysis under predetermined optimised operating conditions. Electrodialysis has the advantage of flexibility with respect to the seasonal variation of fluoride content, the relative selectivity and the low chemical demand. Moreover the recovery rates were higher than for other membrane processes such as reverse osmosis. The electrodialysis process also has the advantage that it can be started and stopped over longer periods which makes it suitable for seasonal operation when sometimes the fluoride content decreases to below the maximum admissible as happens periodically in the region where the study is conducted.