Modeling of fluoride rejection from aqueous solution by nanofiltration process: Single and binary solution

This study was aimed at the investigation of fluoride (F^–) rejection from single and binary solution by nanofiltration process (NF). The influence of various parameters such as the effect of solution pH, initial F^– concentration, applied pressure, feed flux, and accompanying cations and anions in feed water has been reported. Besides, the solute rejection and Spiegler–Kedem models were applied for the better understanding of NF performance. In a single solution, the laboratory study demonstrated F^– rejections with NF membranes to be higher than 85%. Moreover, as applied pressure and feed flux increased F^– rejection was observed to increase marginally whereas the opposite trend was observed when initial F^– concentration in feed water was increased. Further, the depletion of F^– rejection at 15 mg/L of F^– was found to be associated with the presence of co-existing cation and anion in the feed water. The estimated average of pore radius and Δx/A_k of the NF membrane were 0.12 ± 0.02 nm and 47.84 ± 25.22 mm, respectively.