Purification of organic pollutants in cationic thiazine and azo dye solutions using plasma-based advanced oxidation process via submerged multi-hole dielectric barrier discharge

Abstract

Due to industrialization and population growth, water shortage has emerged as a critical global issue. Pollution of existing water supplies is a critical part of this issue, and organic contaminants are one of the main causes of water pollution. The non-thermal plasma-based advanced oxidation process (AOP) is one of the most widely studied and best developed processes owing to its simple structure and ease of operation. In this study, a plasma-based AOP was stably generated using submerged multi-hole dielectric barrier discharge (DBD) and added to an aqueous solution. Using a plasma system, the complexity of the process for generating hydroxyl radicals (OH) can be simplified by allowing ozone, hydrogen peroxide, ultraviolet light (UV), and OH to be generated simultaneously in one device. The electrical properties and concentrations of the active species were analyzed to establish optimal plasma operating conditions. Among the organic pollutants, methylene blue (MB) and methyl orange (MO) were selected as experimental targets because they are representative cationic thiazine and azo dyes, respectively. The results were analyzed by measuring the absorbance of UV–Vis, total organic carbon (TOC), chromaticity, and changes in solution properties. The effects of hydroxyl radical (OH) scavengers (D-mannitol) on the MB and MO degradation rates were also investigated. Based on these results, degradation mechanisms of MB and MO are proposed. After 3 min of plasma treatment, the concentration, chromaticity, and TOC of MB and MO rapidly decreased. Consequently, we believe that plasma-based AOP using submerged multi-hole DBD has advantages as an alternative technology for treating organic pollutants.