Electrochemical degradation kinetics of cleaning wastewater containing ethylene diamine tetraacetic acid

Abstract

The electrochemical degradation kinetics of cleaning wastewater containing ethylene diamine tetraacetic acid (EDTA) is complicated. In this study, the kinetics of EDTA degradation was conditioned on an experiment device designed for the electrochemical treatment of EDTA cleaning wastewater, and five parameters, namely, initial pH, electrode distance, current density, supporting electrolyte concentration and H2O2 concentration, were investigated. The single-factor experimental results indicated that an acidic initial pH or a small electrode distance is beneficial to electrochemical degradation, the supporting electrolyte concentration is changing the rate for the initial stage of reaction, and high current density or excessive H2O2 concentration could reduce the oxidation efficiency. On the basis of single-factor experiments, three factors that affect the reaction rate significantly were taken as variable factors in the Box–Behnken experimental design (i.e. initial pH (X1 = 3–5), current density (X2 = 40–60 A/m2) and H2O2 concentration (X3 = 20–40 mmol/L)). The optimum condition could be obtained at the initial pH of 4.3, the current density of 53.0 A/m2 and the H2O2 concentration of 37.6 mmol/L, and degradation constants k, k1, k2 and k3 are 0.0247, 0.0134, 0.2077 and 0.0256 min−1, respectively. The SEM and EDX analyses were performed on the precipitate and scum after electrochemical treatment, and a possible degradation mechanism of EDTA was proposed.