Efficient removal of high concentrations of sulfate, chloride, and total hardness from industrial effluents using nanofiltration membrane technology

Sulfate ions, chloride ions, and water hardness represent significant challenges in the treatment of industrial effluents. In this study, a polyamide spiral-wound nanofiltration membrane was applied under various operating conditions to remove these contaminants. Removal performance for sulfate and chloride ions, total hardness reduction, electrical conductivity reduction, and water recovery was assessed, with pH, feed flow rate, and operating pressure selected as key process variables. The experimental results were analyzed using the Response Surface Methodology–Central Composite Design (RSM–CCD) approach, and a face-centered design was employed to determine the relationships between input variables and output responses. Process optimization identified the optimal operating conditions as 7 bar pressure, 10 L/min feed flow rate, and pH 4.62. Under these conditions, water recovery, sulfate ion removal, total hardness removal, chloride ion removal, and electrical conductivity reduction reached 29.9%, 99.4%, 97.7%, 80.9%, and 92.23%, respectively. Recovery rate increased with higher operating pressure and decreased with increased feed flow rate, with minimal dependence on pH. Sulfate removal was strongly dependent on pressure, showing a slight decrease at higher pH values, while total hardness removal followed a similar trend with weaker pH sensitivity. Chloride removal exhibited lower pressure dependence but increased with pH. Given the high contaminant removal efficiencies achieved without the use of chemical additives and with moderate energy consumption, the polyamide spiral-wound nanofiltration process is demonstrated to be an effective and sustainable method for treating industrial effluents.