Sodium and potassium removal from brackish water by nanofiltration membrane: single and binary salt mixtures

Abstract

In this study, the removal efficiency of sodium (Na+) and potassium (K+) by nanofiltration (NF) process was investigated. The experiments was conducted by variation of influent concentration of Na+ and K+, flow rate, solution pH and also co-existing anions and cations. The results showed that with increasing influent concentration of Na+ from 200 to 400 mg/L, the removal efficiency decreased from 68.9 to 63.1 and K+ removal efficiency declined from 89.1 to 83.4 with increasing concentration from 20 to 60 mg/L. As the solution pH was raised from 4 to 9, the Na+ and K+ removal efficiency increased from 66.5 to 74.1 and 87.5 to 93.5 and correspondence with deceasing the concentration of Na+ and K+ in permeate water from 67.1 mg/L to 51.8 mg/L and from 2.51 mg/L to 1.32 mg/L, respectively. In addition, as the flow rate was varied of 0.4 L/min to 0.8 L/min, the Na+ and K+ rejection by NF descended approximately 5. The most important of effective co-exist anions and cations on Na+ and K+ rejection were nitrate and magnesium, respectively. Consequently, the NF process was recognized as efficient, convenience and low cost method for Na+ and K+ removal from brackish water.