Degradation of high-concentration simulated organic wastewater by DBD plasma

In this study, a high-concentration simulated organic wastewater, made by dissolving methyl violet in water, was degraded using dielectric barrier discharge (DBD) plasma generated in air and O₂ respectively. The decoloration rate and chemical oxygen demand (COD) of wastewater were evaluated during plasma treatments with the initial concentration of methyl violet of 300 mg L^-1. Results showed that the highest decoloration rate of around 100% within 10 min and the highest COD decrease of 33% within 60 min could be achieved with the O₂ plasma treatment at the discharge voltage of 10 kV, while air plasma treatment showed lower efficiency in decolorizing the methyl violet solution and lower COD decrease (24%) after 60 min treatment. UV-Vis spectroscopy and chemical analysis of generated by-products during the plasma-enabled degradation process revealed that the methyl violet molecules could be completely decomposed into some refractory organics in the solution. Based on the experimental results and literature review, a pathway of methyl violet degradation attributed to energetic electrons and highly reactive species generated by DBD was proposed.