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 (kobs) were 0.0931 and 0.1938 min−1at pH 6.0 in the UV/PDS system. The sulfate radical (SO4•−) and hydroxyl radical (•OH) were identified as the major reactive radicals. The pH-dependent reaction rate constants of ACY and ATL with•OH and SO4•−were measured via the competing kinetics. Meanwhile, the contributions of•OH and SO4•−for ACY and ATL degradation were calculated by the radical steady-state hypothesis, and the results revealed that SO4•−occupied a decisive position (>84.5%) for the elimination of ACY and ATL. The contribution of•OH became more significant with the increasing pH, while SO4•−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.Keywords:UV/PDS;micropollutants;radical contribution rates;kinetic models;degradation pathways