Transforming end-of-life SWRO desalination membranes into nanofiltration membranes for the treatment of brackish water and wastewater
Anissa Somrani, Zaineb Mohamed, Kholoud Abohelal, Sara Larhrib, Noreddine Ghaffour, Maxime Pontié
Abstract
In this study, we explore the possibility of reusing end-of-life seawater reverse osmosis (RO) membranes to treat brackish water and industrial effluent. Prior to cleaning the end-of-life RO membranes, we conducted several autopsies in order to assess the extent of degradation. Based on these results, three cleaning protocols were tested and Ultrasil10 and/or chlorine solution were selected for further investigation. The cleaning capacity of the chlorine treatment at 4000 ppm.h was tested but proved inefficient as it leads to a denser cake and a significant decrease in hydraulic permeability. Therefore, we recommend commencing chemical cleaning with Ultrasil10 to remove foulants, thereby reconditioning the end-of-life RO membranes to meet nanofiltration membrane specifications. The cleaned end-of-life RO membranes exhibited enhanced hydraulic permeability (1.97 L·h⁻¹·m⁻²·bar⁻¹) and achieved a salt rejection of 85% for brackish water (6 g/L NaCl). With a molecular weight cutoff of 86 Da, these membranes effectively reduced brackish water conductivity to below 1000 µS/cm at 10 bars, complying with Tunisian drinking water standards (300-2500 µS/cm). Additionally, they demonstrated high efficiency in treating industrial effluents, achieving turbidity levels below 2 NTU and conductivity of 180 µS/cm. Operating at lower pressures, these membranes provided cost-effective, sustainable solutions and performed comparably to commercial new NF membranes, validating their potential for reuse in brackish water and wastewater treatment applications.