Insights into the Kinetics, Theoretical Model and Mechanism of Free Radical Synergistic Degradation of Micropollutants in UV/Peroxydisulfate Process

The degradation of acyclovir (ACY) and atenolol (ATL) in the UV/peroxydisulfate (UV/PDS) process has been systematically considered, focusing on the degradation kinetics, theoretical models, and reaction pathways via applying a microfluidic UV reaction system. The removal efficiencies of ACY and ATL were >94.8%, and the apparent degradation rate constants (k(obs)) were 0.0931 and 0.1938 min(-1) at pH 6.0 in the UV/PDS system. The sulfate radical (SO4 center dot-) and hydroxyl radical ((OH)-O-center dot) were identified as the major reactive radicals. The pH-dependent reaction rate constants of ACY and ATL with (OH)-O-center dot and SO4 center dot- were measured via the competing kinetics. Meanwhile, the contributions of (OH)-O-center dot and SO4 center dot- for ACY and ATL degradation were calculated by the radical steady-state hypothesis, and the results revealed that SO4 center dot- occupied a decisive position (>84.5%) for the elimination of ACY and ATL. The contribution of (OH)-O-center dot became more significant with the increasing pH, while SO4 center dot- was still dominant. Moreover, ACY and ATL degradation performance were systematically evaluated via the experiments and Kintecus model under different operational parameters (Cl-, Br-, HCO3-, NOM, etc.) in the UV/PDS process. Furthermore, the plausible reaction pathways of ACY and ATL were elucidated based on the Fukui function theory and ultra-performance liquid chromatography-tandem quadrupole time-of-flight mass spectrometry (UPLC-QTOF-MS) analysis. The UV/PDS process has been demonstrated to be an efficient and potential application for micropollutants mitigation.