Technical-economic comparison of nanofiltration and reverse osmosis in the reduction of fluoride ions from groundwater: experimental, modeling, and cost estimate

Abstract

The fluoride content in many regions of Morocco exceeds acceptable standards, especially in phosphate regions like Benguerir. In this region, the hermetic effect of dental fluorosis is widespread among the population supplied directly by the wells. Fluoride contamination is attributed to phosphate deposition. In Morocco, the maximum acceptable concentration of fluorides in drinking water is 1.5 mg/L. In this context, the first aim of this work concerns the technical and economic comparison of nanofiltration and reverse osmosis in the reduction of fluoride ions. Three commercial membranes were involved in this study. This study confirms the performances of these membranes in the fluoride reduction and the compositions of the produced water obtained are similar. The Spiegler–Kedem model was applied to determine the constants of the model, namely the reflection coefficient and the coefficient of permeability for all the membranes used. In addition, the Hermia model was applied to identify the fouling mechanism of the three membranes. The parameters of the two models were optimized using the Levenberg–Marquardt algorithm which solves non-linear least-squares problems using an iterative technique. Good agreement between experimental results and model predicted results were obtained. For three membranes tested the transport mechanism is predominant by diffusion and the mechanism that describes the fouling is the cake-forming model. The technical-economic comparison of nanofiltration and reverse osmosis was performed on the basis of produced water with a fluoride content of 0.7 mg/L and the cost of the produced cubic meter by the three membranes is almost the same.