Microbubble-Enhanced Ozone/Peroxymonosulfate Oxidation for DEET Degradation: Mass Transfer–Reaction Coupled Radical Generation, Oxidant Contributions and Energy Efficiency

Micro-O 3 /PMS increased DEET k o b s to 9.32 times that of millibubble O 3 . • PMS activation was co-controlled by O 3 mass transfer and O 3 -PMS reaction kinetics. • Increasing pH and PMS dosage promoted interfacial PMS activation. • ·OH and SO 4 ·- jointly contributed 81%∼98% to DEET oxidation. • Micro-O 3 /PMS showed EE/O of 1.63∼11.20 kWh/m 3 under all conditions. The ozone/peroxymonosulfate (O 3 /PMS) process can simultaneously generate hydroxyl radicals (·OH) and sulfate radicals (SO 4 ·- ), but its oxidative efficiency is often limited by ozone mass transfer and utilization. In this study, a ceramic-membrane-based Micro-O 3 /PMS system was developed for the degradation of N,N -diethyl- m -toluamide (DEET), a refractory micropollutant. Micro-O 3 /PMS achieved the highest DEET degradation rate constant ( k o b s ) of 7.95 × 10 3 M -1 and the lowest EE/O of 1.94 kWh/m 3 , with 2.64∼9.32-fold higher degradation kinetics and 46.4%∼85.7% lower energy demand than those of the comparison systems of Milli-O 3 , Milli-O 3 /PMS and Micro-O 3 . Compared with Milli-O 3 /PMS, the generation efficiencies of ·OH and SO 4 ·- in Micro-O 3 /PMS increased by 4.49 and 11.42 times, respectively. Microbubbles enhanced k L a , while the lower k L increased the Hatta number and extended PMS activation from the bulk liquid into the liquid film. Interfacial O 3 –PMS reactions enhanced O 3 absorption, creating positive feedback that promoted PMS activation and radical generation. Increasing the pH and PMS dosage further strengthened PMS interfacial activation, resulting in higher radical generation. Oxidant contribution analysis demonstrated that ·OH and SO 4 ·- were the dominant oxidants for DEET degradation under the tested conditions, jointly contributing 81%∼98%, whereas O 3 and other unquantified oxidation pathways made only minor contributions. As pH increased from 5 to 8, the k o b s of DEET increased from 1.57 × 10 3 to 9.36 × 10 3 M -1 , while EE/O decreased from 11.20 to 1.63 kWh/m 3 . When the PMS dosage increased from 50 to 200 μM, k o b s increased from 5.31 × 10 3 to 10.04 × 10 3 M -1 ; however, the lowest EE/O was obtained at 100 μM PMS, indicating diminishing energy benefits at higher dosages. Cl - , HCO 3 - /CO 3 2- , humic acid, and real water matrices inhibited DEET degradation and increased EE/O to 3.09∼9.00 kWh/m 3 . This study elucidates the ozone-microbubble-induced regulation mechanism of PMS activation and the characteristics of radical generation, confirms the application potential of Micro-O 3 /PMS for DEET control in water, and thereby provides a promising strategy for the removal of refractory micropollutants.