An in-depth insight into the simultaneous oxidation of sulfamethoxazole and reduction of Cr (VI) by one system of water film DBD plasma: The interaction effect, role of active species, and their dominant to pathways

This study aims to deeply investigate the simultaneous elimination of sulfamethoxazole (SMZ) and Cr (VI) through one system of water film dielectric barrier discharge (WFDBD) plasma. The interaction effect of SMZ degradation and Cr (VI) reduction and dominant effect of active species were highlighted. Results showed that the oxidation of SMZ and the reduction of Cr (VI) directly promote each other. When the concentration of Cr (VI) raised from 0 to 2 mg L−1, the degradation rate of SMZ enhanced from 75.6% to 88.6%, respectively. Similarly, when the concentration of SMZ improved from 0 to 15 mg L−1, the removal efficiency of Cr (VI) improved from 70.8% to 84.3%, respectively. ·OH, 1O2 and ·O2− play crical roles for SMZ degradation, and e−, ·O2−, ·H and H2O2 dominated to the Cr (VI) reduction. The variations of pH, conductivity and TOC during the removal process were also explored. The removal process was studied by UV–vis spectroscopy and a three-dimensional excitation-emission matrix. Based on DFT calculation and LC-MS analysis, free radicals dominated SMZ degradation pathways in the WFDBD plasma system were clarified. Besides, the influence of Cr (VI) on SMZ degradation pathway was clarified. The ecotoxicity of SMZ and the toxicity of Cr (VI) into Cr (III) were greatly reduced. This study provides a significant reference value for the application and mechanism of plasma simultaneous removal of organic pollutants and heavy metals in wastewater.