Rapid degradation of methyl p-hydroxybenzoate by dielectric barrier discharge synergized with persulfate: Performance, mechanism, pathway and toxicity assessment

Abstract In this study, a dielectric barrier discharge reactor was designed for the rapid and efficient degradation of methylparaben (MeP), an organic pollutant in wastewater. The superiority of the degradation performance against MeP was jointly evaluated by degradation, voltage-current waveform plots, kinetic curves, energy efficiency and synergy factor. The single DBD discharge performance was investigated and it was determined that the coaxial electrode structure achieves an optimal energy consumption of 0.28 g/kWh at a dielectric tube thickness of 1 mm gas gap of 2 mm peak voltage of 21 kV.The degradation rate of MeP reached 70.1% after 15 min of treatment at discharge frequency of 7.8 kHz, aeration flow rate of 8 L/min, initial MeP concentration of 30 mg/L and pH=7. The DBD synergized persulfate (PS) system conforms to first-order kinetics, with a kinetic constant increase of 0.080 min-1 over single DBD. The highest synergy factor was 2.50 at a PS addition of 15 mM, and the highest energy efficiency was 0.99 g/kWh at an initial concentration of 90 mg/L of MeP. Common inorganic anions, CO2-3 promoted degradation, SO2- 4 inhibited degradation, Cl-and HPO2-4 had little effect. •OH, •O-2, and SO-4• all participate in the reaction, with •O-2 contributing the most. H2O2 and O3 were equally involved in degradation.The actual intermediates of the degradation process were identified by LC-MS and combined with DFT calculations to predict the MeP degradation pathway, and toxicity analysis by QSAR model.