A Review of Wastewater for Hydrogen Production by Electrochemical Processes

Wastewater electrochemical processes and electrolysis—defined here as direct electrochemical water splitting using wastewater as the electrolyte, without biological hydrogen-producing pathways or external organic oxidation processes—have emerged as compelling dual-function strategies for renewable hydrogen generation and advanced wastewater treatment. Unlike broader electrochemical and bioelectrochemical systems such as microbial electrolysis cells or photoelectrochemical reactors, wastewater electrolysis relies solely on anodic and cathodic electrochemical reactions driven by applied potential, while leveraging the intrinsic conductivity and ionic/organic constituents of wastewater to reduce energy demand. This review synthesizes recent progress in hydrogen production across diverse wastewater matrices, including municipal effluents, agro-industrial wastewaters (olive mill, vinegar fermentation, and cheese whey), and industrial streams like metal-plating effluents. Emerging wastewater types—textile and dairy effluents, landfill leachate, tannery and pharmaceutical effluents, petrochemical wastewater, acid mine drainage, and desalination brine—are evaluated for their suitability as electrolytes. Key parameters governing performance, including conductivity, organic load, pH, and the presence of metals and inhibitory species, are examined alongside electrode materials, fouling and corrosion mechanisms, energy efficiency, and environmental implications. Challenges such as wastewater variability, electrode degradation, and chlorine evolution in saline matrices are discussed with emphasis on future research needed to integrate wastewater electrolysis within the circular economy. In essence, wastewater-driven hydrogen production represents a promising route toward sustainable, distributed energy systems while delivering co-benefits for water quality improvement.