Removal of fluoride from contaminated groundwater by cross flow nanofiltration: Transport modeling and economic evaluation S. Chakrabortty a , M. Roy b , P. Pal a, ⁎ a Environment and Membrane Technology Laboratory, Department of Chemical Engineering, National Institute of Technology Durgapur 713209, India b Department of Management Studies, National Institute of Technology Durgapur 713209, India HIGHLIGHTS ► Mathematical model developed for fluoride separation by nanofiltration ► Model has successfully predicted the system performance with less than 0.1 relative errors. ► The system has been found to remove more than 98% of fluoride from water. ► Achieved flux was reasonably high for industrial acceptance. abstract article info Article history: Received 8 September 2012 Received in revised form 5 December 2012 Accepted 18 December 2012 Available online xxxx Keywords: Fluoride removal Cross-flow module Membrane fouling Nanofiltration modeling A modeling and simulation study along with economic evaluation was carried out for removal of fluoride from contaminated groundwater in a flat sheet cross flow nanofiltration membrane module. Mathematical model was developed based on extended Nernst–Planck equation and with the help of ‘concentration polarization modulus’ equation. Linearized approach in modeling reduced computation time significantly. Effects of trans- membrane pressure, cross-flow rate, pH and concentration of the solute of interest on membrane charge density, solute rejection and solvent flux were investigated. The membrane module was successful in yielding a pure water flux as high as 158 lm -2 h -1 removing more than 98% of the fluoride at a transmembrane pressure of only 14 kgf cm -2 and at a pH of 10.01 for a volumetric cross flow rate of 750 L h -1 . The membrane module not only removed fluoride effectively but also brought down high pH of groundwater to the desired level. The developed model corroborated well with the experimental findings as reflected in the very low relative error (b 0.1) and high value of overall correlation coefficient (R 2 > 0.98). Economic analysis indicated that such a mem- brane filtration system could be quite promising in purifying fluoride-contaminated groundwater at low cost. © 2012 Elsevier B.V. All rights reserved. 1. Introduction High fluoride concentration in drinking water has been found to cause severe human health hazards. Fluoride occurs in groundwater in the form of fluorine, biotite, cryolite, fluoro-apatite and villiaumite (NaF) [1,2]. The problem of high fluoride concentration in groundwater resources has now become one of the most serious toxicological and geo environmental issues in several countries featuring India as the most dominant one. Over the last three decades, the high fluoride con- centration in drinking water and the resultant disease ‘fluorosis’ have been highlighted considerably throughout the world. Intake of excess fluoride (>10 ppm) in the human body may cause dental, skeletal and non-skeletal ‘fluorosis’. Again lack of fluoride in groundwater (less than 0.5 ppm) may cause dental caries [3]. WHO has already recommended the highest desirable and maximum permissible contaminant level (MCL) of fluoride in drinking water to be 1 ppm and 1.5 ppm respectively with the consideration of proper safeguard limit of fluoride in drinking water [4]. This has thrown a challenge to the scientific community to purify water with extremely high degree of efficiency to bring down concentration of fluoride to the safe limit where groundwater has been found to contain twenty times the per- missible limits. Occurrence of fluoride in groundwater and the related problems of contaminated drinking water have been widely published [5–9]. Technologies such as precipitation, adsorption, and ion exchange [10–14] have been well studied for separation of fluoride from contam- inated groundwater. Membrane based technologies such as electro dial- ysis, reverse osmosis and nanofiltration have also been examined and identified [15–18] in the recent years as the potential technologies for fluoride separation from contaminated drinking water. Among these membrane processes, nanofiltration stands to be one the most effective technologies as it can remove a number of other contaminants also from groundwater at a relatively low transmembrane pressure using low priced membranes. Nanofiltration (NF) membranes which have the op- erational properties in between those of ultrafiltration membranes and Desalination 313 (2013) 115–124 ⁎ Corresponding author. Tel.: +919434469750; fax: +913432547375. E-mail address: parimalpal2000@yahoo.com (P. Pal). 0011-9164/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.desal.2012.12.021 Contents lists available at SciVerse ScienceDirect Desalination journal homepage: www.elsevier.com/locate/desal