Pollution of the water resources by nitrate ion is an important and severe threat for human health. Among other methods considered for removal of nitrate ions, Nanofiltration (NF) has proved to be a promising and efficient method for this purpose. This process falls between Ultrafiltration (UF) and Reverse Osmois (RO). In this study, the effects of different parameters of operational temperature and pressure as well as pH of the on nitrate removal efficiency and water permeability through NF90 nanofiltartion membrane were investigated. To conduct the experiments both synthesized and ground water with nitrate ion concentration of 100 and 95 mg/l, respectively, were used. Response surface methodology (RSM) and Central composite design (CCD) method were used to find the optimum condition of the process to reach simultaneous optimum values for nitrate removal and permeability. In addition, the economical evaluation and optimization of the process was performed by using Verberne cost model. According to the obtained results, the minimum and maximum water permeability for the synthesized water were 16.5 and 84.3 (L.m -2 .h -1 ), respectively. These marginal values for nitrate removal were found to be 44.1 and 78.4, respectively. Also, as expected the permeability and nitrate removal both were enhanced with increase in the operational pressure. The temperature had a reverse effect on the nitrate removal, where it decreased with increasing temperature. Increasing the pH had a negligible effect on the permeability whereas it improved nitrate removal. By comparing the results of the two kinds of water, it was found that the effects of parameters are nearly the same except the effect of pH. For natural ground water in contrast to the synthesized water, permeability decreased with increasing pH. The experimental results showed that permeability and nitrate removal for the case of groundwater were generally lower than those of the synthesized water. This could be due to the effects of concentration polarization and fouling of the membrane in the case of groundwater. The economic evaluation of the process showed that increasing capacity of the process leads to higher capital and operating costs while it results in decreasing of producing cost for each cubic meter of water. Also, increasing the operational pressure causes higher capital cost. In fact, the cost of producing each cubic meter of purified water decreases with increasing the pressure from 3 to 7 bar, whereas it increases at higher pressures. Therefore, the optimum pressure of the process was found to be 7 bar. However, further economic evaluation of the membrane process showed the lowest cost of water treatment can be achieved by conducting the process in the temperatures range of 13 to 27 °C.
