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

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_hetero), homogeneous free available chlorine (FAC), chlorine dioxide (ClO₂), and chlorine radicals (CRs). This study developed a method to differentiate various RCS responsible for the removal of carbamazepine in EOP/Cl^- using the RuO₂/IrO₂-Ti anode. Compared to EOP, the formation of RCS significantly enhanced the degradation of carbamazepine in EOP/Cl^-, primarily through heterogeneous Cl_hetero, homogeneous molecular chlorine (Cl₂), 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_hetero and CRs decreased, while Cl_hetero dominated carbamazepine degradation at pH 7.0 and 10.0. Cl₂ 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_hetero, Cl₂, and CRs at pH 5.3 and 18 mA/cm². The rise of current density from 18 to 39 mA/cm² significantly promoted the relative contributions of Cl_hetero 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_hetero and homogeneous CRs and Cl₂.