Effects of additives on the degradation of methylene blue using DBD

The simulated wastewater of methylene blue (MB) with initial mass concentration of 100 mg/L was treated using a cylindrical falling-film dielectric barrier discharge (DBD) reactor. By examining how discharge voltage and the rate of liquid flow influence MB degradation by the falling-film DBD, the optimal conditions for the reaction were identified as a discharge voltage of 70 V and a pump rotation speed of 100 r/min. Under the optimal conditions, the effects of acid and alkali on MB’s breakdown rate were analyzed, revealing that H2SO4 accelerated MB’s degradation during the initial phase of DBD discharge, while NaOH markedly increased MB's degradation in the final stage. The resultant improvement of the degradation process with acid and alkali inputs in the form of H2SO4 at the pre-discharge stage and NaOH at the late stage of discharge resulted in a methylene blue degradation rate of up to 92% within 1 h. The effect and energy utilization of the addition of H2O2, O3 and tert-butanol on the degradation of MB by DBD were investigated. The results indicated that H2O2 and O3 had a promotional effect on MB’s degradation, while tert-butanol clearly hindered MB’s degradation. Additionally, H2O2 and O3 significantly improved the DBD reaction device’s energy consumption. The highest energy utilization rate was 587.698 mg/(kW·h) for 30 min with 400 μL of H2O2, or 307.600 mg/(kW·h) for 30 min with 600 mL/min of O3. Raman spectroscopy distinctly revealed that combining H2O2 and O3 with DBD resulted in increased ·OH production, leading to the deduction of three routes for MB degradation by additives linked to DBD from the mass spectrometry analysis.