From reclaimed water to renewable hydrogen: Treatment optimisation for electrolyser performance

Green hydrogen production requires a secure supply of high-purity water, posing significant challenges in regions increasingly affected by water scarcity. Reclaimed urban wastewater is a sustainable, locally available alternative that can decouple hydrogen production from freshwater abstraction. This study assesses the technical feasibility of producing electrolyser-grade water from tertiary-treated urban wastewater for anion-exchange membrane (AEM) electrolysis using a multistage treatment train comprising ultrafiltration (UF), reverse osmosis (RO), and electrodeionisation (EDI). The pilot system was installed at an urban wastewater treatment plant and operated using tertiary effluent as feedwater. RO achieved substantial removal of dissolved salts and micropollutants; however, trace levels of benzotriazole and methyl-benzotriazoles remained in the permeate, resulting in an average conductivity of approximately 15 µS/cm. The subsequent EDI polishing step further reduced ionic content, producing water with conductivity ≤ 1 µS/cm and achieving an overall micropollutant removal efficiency of (98 ± 3) %, thus meeting ASTM Type II quality standards regarding electrical conductivity. To evaluate the impact of water quality on electrolyser durability, accelerated degradation tests were performed using RO permeate (RO-P), EDI permeate (EDI-P), and ultrapure water as a reference. Operation with RO-P resulted in a severe performance loss (~82%), indicating catalyst deactivation and increased internal resistance due to residual contaminants. In contrast, EDI-P limited degradation to ~2%, comparable to ultrapure water. These findings demonstrate that advanced polishing is essential to ensure stable anionic exchange membrane (AEM) operation and confirm the feasibility of wastewater-to-hydrogen pathways, positioning wastewater treatment plants as strategic hubs within the circular water-energy nexus.