Comprehensive Characterization of the Transformation of Wastewater Effluent via Advanced Oxidation Processes Using Nontarget Mass Spectrometric Analysis

Advanced oxidation processes (AOPs) have been extensively studied, employing preselected target compounds to evaluate their performance; however, this might overestimate their performance in real water. Herein, we applied nontarget mass spectrometric analysis to characterize the transformation of wastewater effluent during UV/H₂O₂ and UV/peroxydisulfate (PDS) processes. A total of 8,986 detected features, including 169 identified micropollutants, were categorized as stable features, unstable features, and transformation products (TPs) based on their transformation behaviors. Approximately 40% of the detected features were resistant to both AOPs, highlighting their need for additional treatment. The UV/H₂O₂ process eliminated a wider range of organic compounds than the UV/PDS process with the participation of H₂O₂-related nonradical reactive species, while the UV/PDS process exhibited high selectivity in degrading organic compounds at a faster rate. Oxygen addition and dealkyl group reactions were the most common reaction types in the AOPs. Linkage analysis with the four representative reactions of toxic TPs implied the higher probability of the UV/PDS process yielding high-toxicity products compared with the UV/H₂O₂ process. This study provides a comprehensive view of the two AOPs and is helpful to improving understanding of their performance in treating wastewater effluent.