Enhancing the operational robustness of continuous salinity gradient energy-reverse electrodialysis, SGE-RED, in real effluent streams through in-situ cleaning approaches

Reverse electrodialysis (RED) can enable salinity gradient energy recovery in coastal wastewater treatment plants, overcoming operational challenges associated with fouling and instability. This study demonstrates the long-term operation of a pilot-scale RED system (TRL6) integrated into a wastewater treatment plant, using tertiary-ultrafiltration treated municipal effluent as low-concentration stream and natural seawater as high-concentration stream. The system accumulated more than 100 h of effective operation under stable voltage and current conditions. The key contribution is the in-situ validation of cleaning and maintenance protocols adapted to real feedwaters. The post-RED effluent exhibited consistently low turbidity, limited organic content, and stable microbiological quality, supporting reliable system operation. During continuous operation, at matched flow rates of 500 L/h the system delivered a stable gross power density, reaching a maximum of 0.88 W/m 2 . Pressure losses indicated limited deposit accumulation (~0.5 bar). Reversible performance losses were effectively mitigated through periodic clean-in-place procedures. The protocol combined alkaline backflushing with potassium hydroxide solutions to remove organic foulants, and when necessary acidic cleaning with citric acid or hydrochloric acid at ambient temperature to control inorganic scaling. These interventions restored both electrochemical output and flow conditions without membrane degradation. The post-RED effluent complied with regulatory criteria for non-potable water reuse, demonstrating that integrating advanced tertiary wastewater treatment with RED supports scalable energy recovery within circular water management frameworks.