Harnessing Electrochemistry Synergy in Reverse Osmosis: Modulating Ammonium Localized Oxidation and Restricted Transport

The unsatisfactory selectivity of reverse osmosis (RO) membranes toward ammonium poses a critical challenge in water safety when reclaiming water from domestic wastewater. Herein, we developed a novel integrated electrochemical-assisted RO (ECRO) system using the electrically treated feed spacer and permeate carrier as electrodes. This system enhanced ammonium removal efficiency significantly while maintaining low energy consumption, increasing from 94.36% at 0 V to 99.91% at 4 V. The improvement was primarily attributed to localized oxidation and restricted transport of ammonium ions. Specifically, the permeate carrier anode facilitated the indirect oxidation of ammonium through active chlorine via the breakpoint chlorination pathway, notably localized on the permeate side to prevent damage to the separation layer of the RO membrane and simultaneously avoid additional chemical additives. Furthermore, the restricted ammonium ion transport was responsible for its improved enthalpic barrier, as evidenced by both experimental investigation and Monte Carlo simulation. This rise in enthalpic barrier was primarily driven by the reverse electric field force across the RO membrane, coupled with the constrained ion migration near the membrane surface and ion diffusion within the membrane. This study offers new insights and a theoretical foundation for the optimization of electrochemistry synergy membrane systems, highlighting the potential for enhancing ammonium removal in wastewater reclamation in a green and low-energy manner.