Electro-Fenton method for the removal of Malachite Green: effect of operational parameters

This study aims to evaluate the degradation and mineralization of Malachite Green (MG) in an electro-Fenton process (EFP). We studied the influence of several important parameters including solution pH (2–11), current density (0–20 mA/cm2), H2O2 concentration (0–200 mg/L) and MG concentrations (200, 600, 1000, 1500, 2000, 3000 mg/L) at different reaction time (2.5–30 min). The intermediates produced during the degradation were determined by GC–MS. The optimum pH, current density and H2O2 concentration were found to be approximately 3, 10 mA/cm2 and 50 mg/L, respectively. It was concluded that acidic pH was required to increase the efficiency of the EFP. At optimum conditions and a reaction time of 15 min, MG was completely removed without any significant variation in the corresponding maximum wavelengths or new absorption bands. Due to formation of intermediates, almost all the organic compounds were completely mineralized (95.3%) to CO2 and water at reaction time of 30 min. Results indicated the effect of hydroxyl radical (·OH) on MG degradation is greater than that of superoxide radical scavenger (O2·-\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ {\text{O}}_{2}^{ \cdot - } $$\end{document}). The results showed that the degradation process of MG followed pseudo-first-order kinetic model and the treatment time required in EFP was 4.6 times lower than ECP. Furthermore, the results showed that EFP was an extremely efficient process for degradation and mineralization of a high concentration of MG (1000 mg/L) at a short reaction time (30 min).