Efficient removal of Cu-EDTA complexes from wastewater by combined electrooxidation and electrocoagulation process: Performance and mechanism study

In this study, combined electrooxidation and electrocoagulation (EO-EC) reactor using RuO2-IrO2/Ti and Al electrodes has been built for treatment of Cu-EDTA wastewater. Effects of current density, electrolyte, NaCl concentration, pH and initial concentration on EO-EC performance were investigated. In this study, Cu-EDTA removal efficiency increased with a higher current density. The electrolyte type exerted a significant role in EO-EC process, compared with Na2SO4 and NaNO3, NaCl was a superior supporting electrolyte because the oxidation of Cl- into Cl2 provided additional highly reactive oxidant ClO- for Cu-EDTA oxidation or mineralization. In neutral or alkaline solution, EO-EC reactor performed better than when it was acid. At the condition of current density 10.29 mA cm-2, C0(NaCl) 1 g L-1, C0(Cu) 50 mg L-1 and pH 7, the Cu and COD removal efficiency reached 99.85% and 85.01%, respectively within 60 min. The possible mechanism of Cu-EDTA removal was proposed based on SEM, EDS, XRD, FTIR and XPS analysis of the products. Cu-EDTA chelates were degraded or mineralized by direct charge transfer, chemisorbed M(OH) and active chorine species produced on anode surface, in which degradation intermediates and mineralization products of Cu-EDTA were generated. Meanwhile, residual degradation intermediates and mineralization products were removed by electrocoagulation. In this study, EO-EC process has been proved to be an effective way for the treatment of Cu-EDTA contaminated wastewater.