Résumé
Currently, nanofiltration (NF) is gaining increasing importance in water treatment and can replace reverse osmosis especially in the case of brackish water. It is generally appreciated for its low energy consumption, good selectivity and high productivity. The purpose of this study aimed at evaluating the best performance of NF to remove fluoride ions using model solutions in order to treat a South-Algerian groundwater in the optimal conditions. WHO guidelines recommend a limit concentration of 1.5 mg.L−1 in drinking water. A commercial NF membrane (NF90) was investigated to study its efficiency in treating synthetic and natural brackish waters in a cross-flow NF membrane process at a pressure range from 3 to 15 bar using a bench scale NF pilot. The membrane performance was determined by the permeation flux and the rejection capacity as a function of trans-membrane pressure. The results showed that productivity and rejection increase with pressure for NF90. The latter parameter leveled off at a trans-membrane a pressure of 11 bar. The defluorination efficiency was about 98% from a synthetic solution with a permeate flux of 64.8 L/h.m2, an F−concentration of 10−3 M (42 mg/L) and pH = 7.2. In the same conditions, NF90 can retain more than 88% of fluoride ions from natural groundwater water (Robbah) at its natural pH (7.85) in the presence of other ions. The F−content was 0.35 mg/L well below the WHO threshold.