Towards sustainable management of end-of-life membranes: Novel transformation of end of life (EoL) reverse osmosis membranes for efficient dye/salt separation

Effective management of end-of-life (EoL) membranes is crucial for addressing environmental and economic concerns. A novel approach has been proposed in this study to transform discarded EoL reverse osmosis (RO) membranes into loose nanofiltration (NF) membranes that exhibit high flux and effective dye/salt fractionation. The proposed method involves oxidative treatment followed by a one-step co-deposition of polydopamine (PDA) and polyethylene glycol (PEG). Rigorous chemical and morphological characterization techniques have verified the successful transformation of the EoL membranes. The study's findings demonstrate the great potential of this method, as the transformed EoL membranes achieved high pure water permeability of 67 LMH/bar after only a 5 hour coating process, representing a remarkable 2.5-fold increase in permeability compared to the uncoated membrane. A 20-hour coating produced a denser film that reduced the permeability to 19 LMH/bar but increased the potential for dye/salt separation. The transformed membranes exhibited high rejection rates of dyes and ultra-low salt rejection, making them highly efficient for dye/salt separation. Moreover, the enhanced hydrophilicity of the transformed membranes inhibited foulant accumulation, resulting in excellent fouling resistance with a flux recovery ratio of 93.6 %. This novel approach offers a promising solution for treating dye contaminated wastewater and promoting circular economy in membrane technology.