Efficient treatment of an electroplating wastewater containing heavy metal ions, cyanide, and organics by H₂O₂ oxidation followed by the anodic Fenton process

A real electroplating wastewater, containing heavy metals, cyanide, and organic contaminants, was treated by electrocoagulation (EC), H₂O₂ oxidation, H₂O₂ pre-oxidation followed by EC, and the anodic Fenton process and the efficacy of the processes was compared. Concentration of cyanide, Cu, Ni, Zn, and Cr was largely decreased by EC within 5 min. When the reaction time was extended, removal of residual cyanide, Cu, and Ni was limited. In H₂O₂ oxidation, the concentration of cyanide decreased from initial 75 to 12 mg L⁻¹ in 30 min. The effluents from the H₂O₂ oxidation were further treated by EC or anodic Fenton. In EC, the concentration of total cyanide, Ni, and Cu decreased to below 0.3, 0.5, and 1.5 mg L⁻¹, respectively. Removal efficiency of chemical oxygen demand by EC was less than 20.0%. By contrast, there was 73.5% reduction by the anodic Fenton process with 5 mM H₂O₂ at 30 min; this can be attributed to the oxidation induced by hydroxyl radicals generated by the reaction of H₂O₂ with the electrogenerated Fe²⁺. Meanwhile, residual cyanide, Cu, and Ni can also be efficiently removed. Transformation of organic components in various processes was analyzed using UV-visible and fluorescence excitation-emission spectra.