Transformation of end-of-life RO membranes into NF and UF membranes: Evaluation of membrane performance

Abstract

Economic and environmental concerns demand the recycling and reuse of fouled, end-of-life, reverse osmosis (RO) membranes. Different dry stored coupons of commercial TM720-400 membranes were subjected to the chemical attack of NaOCl (124ppm free chlorine), acetone solution (10,000ppm) or N-methyl-2-pyrrolidone solution (10,000ppm). The best permeability results were achieved with NaOCl solution and consequently it was used as the key reagent for further analysis. The effect of pH and membrane storage on the transformation process was evaluated. Membrane permeability and rejection coefficients were tested filtering synthetic brackish water containing NaCl (2,000ppm), MgSO4 (2,000ppm) and dextrose (250ppm). The basic pH showed the highest effect on the membranes performance therefore, experiments were carried out up to 410h exposure time. The transforming process was repeated for five different commercial membrane brands, stored wet. Most of the transformed membranes achieved permeability and rejection like nanofiltration (NF) membranes up to 50h exposure time and performed like ultrafiltration (UF) membranes after 242h exposure time. It was observed that permeability and rejection coefficients were affected by the storage condition. This treatment may provide a cost effective and eco-friendly method of recycling end-of-life RO membrane process, at lab scale.