Electro-oxidation mechanism profiling of humic acid by typical reactive substances

Electro-oxidation (EO) represents a promising and efficient technology for the disposal of humic acid (HA), leveraging the generation of radicals to degrade pollutants, ultimately achieving their removal or even complete mineralization. However, the detailed mechanistic profiling of the interaction between radical species (e.g. ·OH, active chlorine) and HA in the overall degradation remains significantly unclear, resulting in challenges in tuning and optimizing the treatment of HA-containing wastewater. Herein, a flow-through EO system using a Ti 4 O 7 reactive electrochemical membrane (REM) as a model electrode was constructed to investigate the degradation mechanisms of HA under ·OH or active chlorine. Under optimal conditions (HA 100 mg L −1 , current density 30 mA cm −2 , pH 7), active chlorine achieved a higher HA oxidation efficiency (76.59 %) compared to ·OH (56.60 %) at 1 h, the HA mineralization efficiency of former (53.03 %) over 3 h was lower than that of latter (67.41 %). Meanwhile, multiple techniques (UV–Vis, FTIR, etc.) revealed that ·OH degraded HA’s macromolecular polycyclic structures into aliphatic products, while active chlorine produced mainly small molecular chlorinated aromatics. Furthermore, LC-MS analysis showed that hydroxylation by ·OH is crucial for promoting ring-opening reactions of aromatic compounds, while chlorination by active chlorine proves less effective for this purpose. Adjusting the electrolyte in EO controlled reactive species generation, allowing regulation of HA degradation rates or product distribution, making EO suitable as a pretreatment or advanced treatment in other processes. This work paves a new avenue for the rational design and construction of subprocesses aimed at HA-containing wastewater treatment.