Performance of commercial nanofiltration membranes in the removal of nitrate ions

In the Mediterranean region of Spain, the number of wells with nitrate ion concentration over the maximum allowed limit of 50 mg-NO3− · L−1 has been increasing. The aim of the present work was to study the efficiency of the nitrate removal by three commercial nanofiltration membranes, NF90, NF270 (Dow-FilmTec) and ESNA1-LF (Hydranautics). Nitrate ion rejection was studied using NaNO3 model solutions at different concentration. The results were contrasted with a natural water. NF270 gave very high flux but very low nitrate rejection, even at the lowest concentrations in the feed. NF90 and ESNA1-LF membranes produced a rejection high enough to obtain good quality water. Additionally, an experimental design was carried out to determine the effect of pH, nitrate and sulphate ion concentration on the nitrate rejection. The pH was the most influent factor for both membranes and the increase in the sulphate ion concentration always caused a decrease on the nitrate rejection; however, the membranes presented different performance. Important differences were observed in the membrane performance when comparing the model solutions results with those of the groundwater. This confirms the convenience of experimental tests on pilot plant with the groundwater to be treated in order to select the most adequate membrane. As a conclusion, the application of the nanofiltration technology can be useful to produce drinking-water from brackish water with nitrate ion concentration below 150 mg · L−1.