Chlorine-induced organic wastewater treatment via redox electrochemical processes: Mineralization or detoxification?

Chloride-induced electrochemical advanced oxidation processes (EAOPs) have gained widespread attention for efficient pollutant degradation via in-situ generated reactive chlorine species (RCS), despite the drawback of forming chlorinated transformation products (TPs). In particular, the rapid reaction between electro-synthesized H₂O₂ and anodically produced HOCl has been shown to effectively suppress the formation of chlorinated TPs. However, given that H₂O₂ simultaneously compromise degradation efficiency, a direct evaluation targeting their trade-off in efficiency and toxicity is currently lacking. Here, we compare an electrochemical reduction (EO-Cl-Reduction) system with a metal alloy cathode to an electrochemical oxygen reduction (EO-Cl-ORR) system using a natural air-diffusion cathode for treating chlorine-induced organic wastewater. We systematically investigated their primary oxidative contribution, reaction kinetics, degradation pathways, and toxicity assessment. Results indicated that the EO-Cl-Reduction system achieved excellent pollutant removal and coexists with elevated transient toxicity. However, elevated levels of RCS and reactive oxygen species (ROS) can further destruct the newly formed chlorinated TPs, thereby reducing their associated risks. Conversely, the EO-Cl-ORR system exhibits a safer degradation pathway with minimal chlorinated TPs but requires higher energy consumption and reduced efficacy for persistent compounds like bisphenol AF. This study provides insights into harnessing inherent chloride in industrial wastewater for tailored EAOPs, simultaneously eliminating parent contaminants and reducing overall toxicity, ideally with lower energy consumption. It aims to overcome the trade-offs between degradation efficiency and toxicity reduction for two common chlorine-induced EAOPs, providing insights that design electrochemical water treatment applications across diverse scenarios.