Simultaneous Degradation of Aqueous Trichloroacetic Acid by the Combined Action of Anodic Contact Glow Discharge Electrolysis and Normal Electrolytic Processes at the Cathode

Abstract

To enhance the removal of trichloroacetic acid (TCA) by anodic contact glow discharge electrolysis (CGDE), the combined degradation of TCA by the action of anodic CGDE, denoted anodic degradation, and normal electrolytic processes at the cathode, denoted cathodic degradation, was investigated. Here, this overall process is termed simultaneous degradation. Compared to anodic degradation, in simultaneous degradation, the reduction rates for TCA and total organic carbon (TOC) increased from 65.32% and 62.03% to 91.82% and 73.03%, respectively. Meanwhile, the dechlorination rate rose from 64.6 to 80.12%. For simultaneous degradation, the disappearance of TCA, the reduction in the TOC, and the dechlorination of TCA, followed first-order kinetics. The reaction intermediates were detected and, based on the intermediates and the observed kinetics, the effects of the simultaneous degradation of TCA, TOC, and dechlorination of TCA are discussed. The cathode materials, length of the anode dipped into the electrolyte, and Pd loading on the Ni cathode all affected the simultaneous degradation of TCA significantly. The effect of the addition of Fe2+ was also investigated. The additive and synergistic effects of the combination of anodic and cathodic degradations on simultaneous degradation are discussed. Based on these results, an analysis of the degradation of TCA suggests that ·OH and ·H/e aq − generated by the action of anodic CGDE, as well as the ·Hads generated on the Pd-loaded Ni cathode surface, are the key species responsible for the dechlorination of TCA. Furthermore, possible mechanistic routes for the simultaneous degradation of TCA are proposed.