Dielectric barrier discharge plasma in-situ microbubble aeration with peroxymonosulfate for levofloxacin degradation: Microbubble superior performance and pH-dependent mechanism

• DBD microbubble system was constructed using a flat ceramic membrane aeration. • Enhanced O 3 transfer and PMS activation favored reactive species production. • HOrad and 1 O 2 mainly contributed to superior degradation performance. • Enhanced contribution of reactive species at various pH was quantitatively assessed. • Higher formation of HOrad, SO 4 · - , and 1 O 2 under initial pH = 8.7 conditions. In this study, a simple ceramic membrane aeration was used to realize dielectric barrier discharge/peroxymonosulfate (DBD/PMS) in-situ microbubble aeration for effective dispersion and gas–liquid transfer of highly active substances. Compared with conventional aeration, ceramic membrane aeration had 18 times fewer microbubble diameters (110–180 µm), much higher bubble densities, and 1.6–2.1 times higher aquatic O 3 concentrations at pH 4.8–10.0. Consequently, the yield of HO and SO 4 · - was 1.64–2.34 and 1.13–2.93 times, respectively, via faster O 3 transfer to the aquatic solution and enhanced PMS activation. DBD/PMS microbubble aeration outperformed conventional aeration, with a 2.52-fold increase in LEV degradation kinetics and a 2.79-fold increase in TOC removal. Quenching and EPR experiments showed that HO and 1 O 2 were the main reactive oxygen species (ROS) for LEV degradation. The yield of O 2 · - was higher at pH 6.9, while HO , SO 4 · - , and 1 O 2 was higher at pH 8.7 derived from a series of complex reactions. The LEV degradation pathway was pH-dependent, with the HO -oxidation contribution varying from 25.3% to 44.3% as the pH increased from 4.8 to 8.7, while other ROS ( 1 O 2 and O 2 · - )-oxidation decreased from 73.1% to 51.8%. Therefore, this work will advance the current understanding of the intrinsic effects of pH in the plasma/PMS microbubble process for wastewater purification.