Removal of chemical oxygen demand from ethylenediaminetetraacetic acid cleaning wastewater with electrochemical treatment

Abstract

Removing chemical oxygen demand (COD) from ethylenediaminetetraacetic acid (EDTA) cleaning wastewater is difficult. In this study, an electrochemical treatment device was designed to condition EDTA cleaning wastewater, which mainly consisted of direct current (DC) power supply, iron anode, aluminum cathode, and magnetic stirrer. Four parameters, namely, initial pH, inter-electrode distance, current density, and H2O2 concentration, were investigated. The best COD removal efficiency of 86.31% in single-factor experiments was obtained at initial pH of 5, inter-electrode distance of 2 cm, current density of 60 A/m2, and H2O2 concentration of 30 mmol/L. On the basis of single-factor experimental results, a model with a methodological strategy was established using a central composite design to check these factors and their effects. The model described the changes of COD removal efficiency according to the same four parameters. The ranges for the initial pH, inter-electrode distance, current density, and H2O2 concentration are 3–5, 1–3 cm, 40–60 A/m2, and 20–40 mmol/L, respectively. The optimum conditions could be obtained from the model, which are 4.4, 1.5 cm, 52.8 A/m2 and 38.0 mmol/L, whose COD removal efficiency was 94.63%, and relative importance of parameters was in the order: current density > H2O2 concentration > initial pH > inter-electrode distance. FTIR and MS were performed to indent the intermediate products formed during this process and XRD was performed to indent the precipitates, a possible degradation pathway and mechanism of EDTA were proposed.