A novel mechanism of bisphenol A removal during electro-enzymatic oxidative process: Chain reactions from self-polymerization to cross-coupling oxidation

• Electro-enzymatic method can effectively improve BPA removal with humic acid (HA).
• Removal of BPA achieved 100% within 2 min reaction at an optimal condition.
• A novel mechanism of BPA removal is proposed during electro-enzymatic process.
• HA provides a pathway of BPA self-polymers incorporated into HA matrix.
• Chain reactions from BPA self-polymerization to cross-coupling oxidation.

The catalyzed removal of bisphenol A (BPA) by a horseradish peroxidase (HRP) cathode in the presence of humic acid (HA) was investigated. At an optimal condition, the removal of BPA achieved 100% within 2 min reaction. In the electro-enzymatic process, products were analyzed by high performance liquid chromatography with diode array detector (HPLC-DAD) and high performance size exclusion chromatography (HPSEC). HPLC-DAD results showed that BPA was oxidized into self-polymers and then self-polymers as important intermediate products decreased and disappeared. HPSEC results showed the order of molecular weight (MW): HA + BPA cross-coupling products > HA self-coupling products > initial HA. According to above results, a novel mechanism of BPA transformation in the presence of HA was proposed in electro-enzymatic process. In summary, under oxidation of in situ hydrogen peroxide on HRP electrode, the BPA first are polymerized into self-polymers, and then, the polymers may be incorporated into HA matrix and finally larger MW of BPAn-HA might be formed. The presence of HA can provide chain reactions from BPA self-polymerization to cross-coupling oxidation. Therefore, in the presence of HA, the electro-enzymatic oxidation is an effective way to improve BPA removal.