Synergistic effect on simultaneous treatment of Cr(VI) and chloramphenicol using a non-thermal plasma technology

Toxic organic and heavy metal contaminants commonly exist in industrial waste stream and the treatment is of great challenge. In this study, a dielectric barrier discharge (DBD) non-thermal plasma was employed for the simultaneous treatment of two important contaminants, chloramphenicol (CAP) and Cr(VI) in an aqueous solution through redox transformations. More than 70% of CAP and 20% of TOC were degraded in 60 min, while Cr(VI) was completely removed in 10 min. The hydroxyl radicals could be the main active species for the degradation. Meanwhile, the consumption of hydroxyl radicals was beneficial to the reduction of Cr(VI). The synergistic effect was investigated between CAP degradation and Cr(VI) reduction. The reduction of Cr(VI) would be enhanced in the presence of CAP with a low concentration and could be inhibited under a high concentration of CAP, because part of hydroxyl radicals could be consumed by a low concentration of CAP and the obtained intermediates with a higher kinetic rate. However, CAP with a high concentration could also react with some reductive species, such as eaq- and •H, which could compete with Cr(VI) and inhibit the reduction of Cr(VI). In addition, the presence of Cr(VI) could enhance the degradation and mineralization of CAP, and the identification of obtained intermediates indicated that the presence of Cr(VI) could change the degradation path of CAP as Cr(VI) would react with reductive species and enhance the generation of hydroxyl radicals, leading to more hydroxylation reactions. Moreover, the mechanism for the simultaneous redox transformations of CAP and Cr(VI) was illustrated. This study indicates that the DBD non-thermal plasma technology could be one of better solutions for simultaneous elimination of heavy metal and organic contaminants in aquatic environment.