Degradation of metronidazole in water using dielectric barrier discharge synergistic with sodium persulfate

Abstract

A series of water pollution problems caused by antibiotic wastewater need to be solved urgently. Dielectric barrier discharge (DBD) is one of the advanced oxidation processes (AOPs) with the advantages of rapid reaction, stable discharge. Sodium persulfate (PS) is a reagent with strong oxidation and good water solubility, but need to be activated in order to effectively used in wastewater treatment. DBD can activate PS. The effects of technological parameters (input power, air velocity, Metronidazole (MTZ) initial concentration, discharge gap), material of external electrode and sodium persulfate addition amount on the degradation rate and energy efficiency were investigated for MTZ in simulate antibiotic wastewater and a self-made immersed DBD reactor alone or in synergy with PS. Under the optimized conditions of input power of 12 W, air velocity of 150 mL·min−1, MTZ initial concentration of 50 mg·L-1 and discharge gap of 2.0 mm, the maximum degradation rate of MTZ was 60.71 % and 58.68 % for copper wire and nickel–chromium wire as external electrode, respectively. The maximum synergistic degradation rate was 96.48 % and 90.30 % with copper or nickel–chromium external electrode, respectively, when the molar ratio of PS to MTZ was 50. The contributions of O3, ·OH and SO4-· free radicals in the process of DBD synergistic degradation of MTZ with PS were explored via Indigo sodium disulfonate spectrophotometry and free radical scavenger methanol, tert-butyl alcohol. The ozone concentration in the solution can reach 2.965 × 10-2 mmol·L-1. The contributions of ·OH and SO4-· free radicals were 46.73 % and 29.69 %, respectively. The probable degradation paths of MTZ were also proposed based on intermediate product analysis with LC-MS.