Dawei Liang

The hybrid electrooxidation system driven by a wind-powered TE-HNG nanogenerator achieves high energy efficiency and more than 90% degradation of pollutants, providing a practical strategy for sustainable wastewater treatment.

Electro-oxidation (EO) is an efficient approach to removing refractory organics in wastewater. However, the interference from chlorine ions (Cl^-) can generate reactive chlorine species (RCS), potentially leading to the production of undesirable chlorinated byproducts. A novel approach involving the cathodic oxygen reduction reaction (ORR) for in situ H₂O₂ production has emerged as a promising strategy to counteract this issue. This study systematically investigated the dynamics and transformation of RCS and reactive oxygen species (ROS) in an ORR/chloride-containing EO (EO-Cl) system, elucidating their respective roles in organic removal and chlorinated byproduct minimization. Distinct generation rates and patterns were observed for free chlorine and H₂O₂ in the ORR/EO-Cl system. The rapid generation of free chlorine at the anode quickly reached a dynamic equilibrium, which contrasted with the moderate, continuous cathodic production of H₂O₂, resulting in considerable H₂O₂ accumulation over time. This difference established kinetics-driven ROS and RCS formation and distribution, influencing the subsequent organic degradation process. Three distinct stages were identified in the degradation process. In stage I, free chlorine was the primary species, along with reactive species including Cl₂^•-, ¹O₂, ClO^•, HO^•, and Cl^•. In stage II, the gradual accumulation of H₂O₂ consumed free chlorine, favoring the formation of ¹O₂ and HO^•. In stage III, excessive H₂O₂ quenched the free radicals. Insights into these multistage mechanisms reveal that the rapid degradation of chlorinated byproducts by ¹O₂ and HO^• occurs in stage II of the ORR/EO-Cl system.

Refractory organic wastewater mainly includes wastewater from papermaking, textile, printing and dyeing, petrochemical, coking, pharmaceutical and other industries, as well as landfill leachate and its membrane-treated concentrate. The traditional biochemical method is difficult to adapt to its harsh conditions such as high toxicity, high organic load and high salinity. Compared to other methods, the electro-oxidation (EO) process owns the attractive characteristics of being clean and eco-friendly, highly efficient and producing no secondary pollution. EO systems mainly include electrodes, a reactor, a power supply and other basic units. The design of reactors with different electrodes was the key link in the application of EO technology. This paper mainly reported the different configurations of electrochemical reactors (ECRs) for refractory organic wastewater treatment, and summarized the advantages and disadvantages of them, including reactor structure, flow mode, operation mode and electrode construction. Compared with traditional reactors, the improved reactors such as 3D-ECR achieve higher mass transfer efficiency by increasing the contact area between the electrode and the fluid. Additionally, it has a higher removal rate of organics and a lower energy consumption. Finally, the future perspectives of the treatment of refractory organic wastewater by ECRs is discussed. This paper is expected to provide a reliable scientific basis for the real application of EO technology in refractory organic wastewater treatment.