Ti4O7 reactive electrochemical membrane for humic acid removal: Insights of electrosorption and electrooxidation

• Ti 4 O 7 REM was studied as anode for electrochemical treatment of humic acid (HA). • The HA removal was ascribed to the synergy between electrosorption and oxidation. • Faster mineralization rates were observed in Cl – medium compared to SO 4 2– medium. • Both active chlorine species and OH contribute to the removal of HA in Cl – medium. Electrochemical advanced oxidation processes (EAOPs) are regarded as a promising technology for the treatment of landfill leachate containing high concentrations of humic acid (HA). Herein, a Ti 4 O 7 -based porous reactive electrochemical membrane (REM) system was developed and explored for the rapid and effective removal of HA. The relationship between the electrolyte medium (Na 2 SO 4 or NaCl) and the adsorption/oxidation capacity of the REM system for HA removal was comparatively studied under different ionic strengths. An unprecedented trade-off phenomenon was revealed between the electrosorption and electrooxidation induced by chloride ions. On one hand, the pH value of the aqueous solution increased due to the loss of Cl − (NaCl → NaOH) during the electrolysis process in the NaCl medium, which weakened the electrosorption ability of REM on HA and further led to deterioration of the effluent quality. On the other hand, the introduction of chlorine significantly strengthened the mineralization performance of HA adsorbed on the anode surface because the anode enabled the oxidation of Cl − into powerful active chlorine species. Current density, membrane permeability, solution pH, and initial HA concentration were identified as the key parameters affecting the overall degradation performance. The active radicals ( Cl and OH) involved in the REM system were systematically studied and generation pathways were proposed accordingly. This study facilitates understanding of the surface catalytic behavior of the Ti 4 O 7 REM in a NaCl medium and confirms that this is a powerful and efficient technology for HA removal.