Removal of fluoride from contaminated groundwater by cross flow nanofiltration: Transport modeling and economic evaluation

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 transmembrane 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 1m(-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 (<0.1) and high value of overall correlation coefficient (R-2>0.98). Economic analysis indicated that such a membrane filtration system could be quite promising in purifying fluoride-contaminated groundwater at low cost. (C) 2012 Elsevier B.V. All rights reserved.