Differentiating reactive chlorine species for micropollutant abatement in chloride containing water by electrochemical oxidation process.

Electrochemical oxidation process (EOP) is promising for micropollutant degradation in water treatment, where chloride ions (Cl) are inevitable in aqueous systems, leading to the EOP/Cl system. The oxidation of Cl at anodes generates reactive chlorine species (RCS), including heterogeneous chlorine species (Cl), homogeneous free available chlorine (FAC), chlorine dioxide (ClO), and chlorine radicals (CRs). This study developed a method to differentiate various RCS responsible for the removal of carbamazepine in EOP/Cl using the RuO/IrO-Ti anode. Compared to EOP, the formation of RCS significantly enhanced the degradation of carbamazepine in EOP/Cl, primarily through heterogeneous Cl, homogeneous molecular chlorine (Cl), and CRs. The relative contribution of specific RCS to carbamazepine degradation significantly varied at different pHs, Cl concentrations, and current densities. As pH increased from 5.3 to 10.0 with 10 mM Cl, the relative contributions of Cl and CRs decreased, while Cl dominated carbamazepine degradation at pH 7.0 and 10.0. Cl was the dominant species for carbamazepine degradation at pH 5.3, while its role significantly decreased at higher pHs. The increase of Cl concentrations enhanced the relative contributions of Cl, Cl, and CRs at pH 5.3 and 18 mA/cm. The rise of current density from 18 to 39 mA/cm significantly promoted the relative contributions of Cl and CRs at pH 7.0 and 10 mM Cl. This study elucidated the specific roles of reactive species for micropollutant degradation in EOP/Cl, highlighting the significance of heterogeneous Cl and homogeneous CRs and Cl.