Photoelectrochemical activation of free chlorine utilizing vacancies-engineered BiVO₄ photoanode for simultaneous pharmaceuticals and personal care products (PPCPs) degradation and bacterial inactivation: An integrative batch and continuous flow reactor study

Conventional water treatment plants are found to be incapable of degrading pharmaceuticals and personal care products (PPCPs), thereby imposing high risks to human health. As a solution to the deficiency of conventional water treatment plants, although the photocatalysis (PC)/chlorine process has been demonstrated to be feasible for incorporating PPCP degradation and disinfection, its development has been limited by the rapid recombination of charge carriers, secondary pollution, and intense formation of disinfection byproducts (DBPs). To overcome these limitations of the PC/chlorine process, we have developed a novel photoelectrochemical (PEC)/chlorine system with enhanced charge separation forced by external bias in this study. A dual-vacancy-engineered BiVO₄ (V_Bi,O-BiVO₄) photoanode with improved PEC properties was synthesized for the PEC/chlorine system, which can prevent secondary disinfection by immobilizing the photocatalyst. The effectiveness of the PEC/chlorine system is shown by achieving an enhanced carbamazepine (CBZ, a PPCP) degradation rate constant of 0.065 min⁻¹ (compared with 0.041 min⁻¹ for the PC/chlorine system) and complete inactivation of 3-log/mL E. coli within 1 min in a batch reactor. The mechanistic study reveals that both photogenerated electrons and holes engage in chlorine activation, producing ^[rad]OH and ^[rad]OCl as the predominant reactive species for PPCP degradation. Notably, compared to the PC/chlorine process, the PEC/chlorine system reduces DBP formation by 44.6 %, ensuring the safety of the treated water. Furthermore, the scalability of the PEC/chlorine system from a batch to continuous flow reactor is proven by achieving excellent performance in PPCP degradation and E. coli disinfection with a low power-intensive UV light source. This study provides detailed insights into the potential applications of the PEC/chlorine process for PPCP degradation and disinfection in future water treatment processes.