Synergistic Ti₄O₇ Anode and Waste Al Can Cathode for Enhanced Phosphonate Degradation and Hardness Removal

This study proposes a hybrid electrochemical oxidation-coagulation (EOC) system that integrates a Ti₄O₇ anode with a cathode fabricated from waste aluminum cans, enabling the simultaneous degradation of phosphonates and removal of hardness ions from cooling water. Compared to standalone electrooxidation (EO) and conventional chemical coagulation (CC), the EOC system achieved 41.9% Ca²⁺ removal, 91% total soluble phosphorus (TSP) elimination, and 67.2% conversion of phosphonate to phosphate within 2 hours. Mechanistic studies revealed that the hybrid EOC system performs a synergistic effect, including anodic oxidation of antiscalant (nitrilotris methylene phosphonic acid, NTMP), and the cathodic dissolution of aluminum, generating coagulants that facilitate the concurrent removal of hardness ions and residual phosphorus. The presence of chloride ions enhanced NTMP degradation via the generation of reactive chlorine species (RCS) without impacting Ca²⁺ removal efficiency, whereas the presence of magnesium ions promoted Ca²⁺ removal via Mg(OH)₂ formation, which provides nucleation sites for co-precipitation. On top of mechanical insights, practical validation with real cooling water confirmed the practical effectiveness and robustness of the EOC system. Moreover, energy consumption analysis revealed that the EOC system significantly reduced energy demand for calcium and TSP removal by 91% and 76%, respectively, compared to the EO system. Overall, this work underscores an efficient and cost-effective electrochemical approach for industrial cooling water treatment, establishing foundational insights for scalable implementation.