Circular economy in membrane technology: Using end-of-life reverse osmosis modules for preparation of recycled anion exchange membranes and validation in electrodialysis

Abstract

In the current study, the indirect recycling of discarded reverse osmosis modules as i) membrane support for the preparation of anion exchange membranes and ii) polypropylene components for the assembly of an electrodialysis stack have been investigated for the first time. In such a way, 51% of the discarded module could be recycled into an electrodialysis system composed of 54% of recycled components. Recycled anion exchange membranes have been prepared by casting and phase inversion methods using discarded reverse osmosis membranes, preconditioned as support. The influence of casting thickness and solvent evaporation time in membrane properties has been studied. Besides, a complete membrane characterization has been carried out (SEM, water content, ion exchange capacity, permselectivity, electrical resistance, diffusion coefficients and mechanical properties) to select the optimal membrane preparation conditions, obtaining recycled anion exchange membranes with a high permselectivity (87%, similar to the commercial membranes). Finally, the technical viability of the recycled membranes has been tested by brackish water desalination experiments in the assembled electrodialysis stack, achieving 84.5% of salt removal. This study could open an alternative within the recycling of discarded reverse osmosis membranes, avoiding their disposal in landfills and moving membrane technology into a circular economy.