Oxychlorides induced over-evaluation of electrochemical COD removal performance over dimensionally stable anode (DSA): The roles of cathode materials

Abstract

The electrochemically generated toxic oxychlorides would induce an over-evaluation of electrochemical oxidation performance in terms of COD removal when treating saline wastewater, which has not yet drawn any attention in environmental community. In this study, the interference extent of oxychlorides on COD determination was revealed in the DSA-based electrochemical oxidation (EO) system, which was related to the choice of cathode materials (i.e., Ti, stainless steel, Cu/Zn). Noticeably, the TOC removal efficiency was similar in the systems with different cathode materials at current density of 20∼40 mA cm−2, while the apparent COD removal efficiency was followed a decreased trend in the order of Ti, stainless steel, Cu/Zn cathode. The above cathode-dependent trend of COD removal efficiencies all returned to the similar levels after reductive removal of the oxychlorides (ClO− and ClO3−) by sulfite. The control experimental results indicate that ClO3− exhibited a more evident interference on COD determination than ClO−. The less over-evaluation of EO performance in COD removal efficiency with Cu/Zn cathode were attributed to the higher reduction ability of Cu/Zn cathode toward ClO− and ClO3−. Generally, although Cl− can be regarded as a “accelerant” for electrochemical pollutant degradation, the over-evaluation of electrochemical oxidation performance for COD removal should be also deserved attention.