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

Abstract

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/Cl2) utilizes the remaining Cl− in wastewater to generate free chlorine and radicals, which could be further improved in conjunction with LED UV275nm irradiation (UV-EC/Cl2). Compared to UV only and EC/Cl2, UV-EC/Cl2 could effectively decompose the selected CECs at higher rates due to the much higher yield of reactive chlorine species (Cl•, ClO•, and Cl2•−). A MATLAB R2021a programming method was developed to estimate the order of magnitude of these radicals, and Cl2•− was the most abundant radical. In the UV-EC/Cl2 system, CECs with phenolic or aniline moieties were mainly degraded by electrochemical oxidation (EC), ClO•, and Cl2•−; 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/Cl2. Interestingly, the electrical energy per order (EE/O) for CBZ decomposition by LED UV275nm-EC/Cl2 (1.46 kWh m−3 order−1) is lower than that by UV/Cl2, EC/Cl2, and UV254nm-EC/Cl2. The results indicate that UV-EC/Cl2 could be used as a promising method to remediate CECs during the tertiary treatment and reuse of wastewater for augmenting surface water.