Modelling the effects of nanofiltration membrane properties on system cost assessment for desalination applications

Nanofiltration (NF) membranes have been successfully used in various applications in water and wastewater treatment as well as other industries. In desalination plants, NF membranes were found to be suitable for pre-treatment application prior to the desalination process. In general NF membranes can be characterized in terms ofthe effective pore radius (r_p), effective charge density (X_d) and permeability (P_m). NF membranes available in the market show a wide range of these properties and thus this variation affects the membrane performance significantly. Through a predictive model such as the Donnan-Steric-Pore-Dielectric-Exclusion (DSPM-DE) model, the performance of NF membranes can be predicted in terms of the solute rejections, fluxes and applied pressure. In addition, for desalination application, the osmotic effect due to the high concentration of salt can also be included in such model. The osmotic effect is taken into account by using the Vant Hoff equation and this is incorporated in the modified DSPM-DE model to allow for approximation of the reduced permeate flux. In this study, the modified DSPM-DE model was used in conjunction with an economic assessment model to analyse the effect of the NF membrane characteristics (r_p, X_d and P_m) on the cost of the NF membrane system with a particular emphasis on desalination application. Detailed analyses of the economic assessment shows that r_p can play a major role in reducing the cost of an NF system provided that the minimum rejection requirement is met.