Kinetics and mechanism of sulfate radical- and hydroxyl radical-induced degradation of Bisphenol A in VUV/UV/peroxymonosulfate system

Abstract

The degradation of Bisphenol A (BPA) in the vacuum ultraviolet/ ultraviolet/ peroxymonosulfate (VUV/UV/PMS) process based on a mini-fluidic VUV/UV photoreaction system has been comprehensively investigated focusing on the degradation performances and kinetics in this study. With 20 min reaction at pH 7.0 in VUV/UV/PMS process, the removal efficiency and the apparent degradation rate constant (kapp) of BPA were > 95.2 % and 0.145 min−1 (R2 = 0.9935). In addition, the impacts of operational parameters and co-existing constituents on BPA degradation are systematically evaluated. Importantly, the effective degradation of BPA (> 96.1 % at least) achieved at the test pH conditions (5–11) after 30 min reaction and achieved the highest BPA removal rate at pH = 11 (0.243 min−1, R2 = 0.9952). The electron paramagnetic resonance and radical scavenger experiments confirmed that both hydroxyl radical (OH) and sulfate radical (SO4−) are the predominant reactive radicals in VUV/UV/PMS process. The second-order reaction rate constants of BPA with OH and SO4− under different pH conditions were determined to be 0.74–1.86 × 1010 M−1 s−1 and 2.92–5.01 × 109 M−1 s−1 via the competition kinetics. Meanwhile, the relative contribution rate of OH decreased from 97.2 %–33.1 % with the increasement of pH from 5.0 to 11.0, while the relative contribution rate of SO4− rose from 1.7 % to 48.9 %. The present study demonstrated that the VUV/UV/PMS process, as a new advanced oxidation process, has potential applications for micropollutants removal in water.