The efficient abatement of contaminants of emerging concern by LED-UV275nm/electrochemical chlorine for wastewater reuse: kinetics, degradation pathways, and cytotoxicity

Treating wastewater to augment surface water can be a practicable solution to water scarcity, while the residual contaminants of emerging concern (CECs) and inorganic ions put forward new requirements to the treatment methods. Electrochemical chlorine process (EC/Cl 2 ) utilizes the remaining Cl − in wastewater to generate free chlorine and radicals, which could be further improved in conjunction with LED UV 275nm irradiation (UV-EC/Cl 2 ). Compared to UV only and EC/Cl 2 , UV-EC/Cl 2 could effectively decompose the selected CECs at higher rates due to the much higher yield of reactive chlorine species (Cl • , ClO • , and Cl 2 •− ). A MATLAB R2021a programming method was developed to estimate the order of magnitude of these radicals, and Cl 2 •− was the most abundant radical. In the UV-EC/Cl 2 system, CECs with phenolic or aniline moieties were mainly degraded by electrochemical oxidation (EC), ClO • , and Cl 2 •− ; and the CECs with weakly electron-donating moieties were predominately decomposed by EC , • OH, and Cl • . The degradation pathways of levofloxacin, diclofenac, carbamazepine (CBZ), and ibuprofen were proposed according to the transformation products (TPs) detected by LC/Q-TOF-MS. Moreover, the cytotoxicity of spiked CBZ in real water samples, that were discharged to surface water, was significantly reduced by UV-EC/Cl 2 . Interestingly, the electrical energy per order (E E/O ) for CBZ decomposition by LED UV 275nm -EC/Cl 2 (1.46 kWh m −3 order −1 ) is lower than that by UV/Cl 2 , EC/Cl 2 , and UV 254nm -EC/Cl 2 . The results indicate that UV-EC/Cl 2 could be used as a promising method to remediate CECs during the tertiary treatment and reuse of wastewater for augmenting surface water.