Imidacloprid degradation by electro-Fenton process using composite Fe3O4–Mn3O4 nanoparticle catalyst

Imidacloprid (IMI) is a widely used systemic pesticide that acts on the central nervous system of insects. In Vietnam, IMI was imported and manufactured in large quantities for agriculture activities. The presence of high IMI levels in IMI manufacturing wastewater is an environmental concern as this chemical is highly toxic and difficult to remove by traditional methods. In this study, IMI degradation by electro-Fenton process using Fe3O4–Mn3O4 nanoparticle composite catalyst was investigated over ranges of pH, current density, reaction duration, Mn3O4/Fe3O4 ratio, catalyst dosage, and initial IMI concentration. Three kinds of electrodes (graphite-, platinum-, and boron-doped diamond) were also employed to compare their application potential. With BDD electrodes, experiment results showed that at a current density of 15.0 mA/cm2, a Mn3O4/Fe3O4 ratio of 1:3 (w/w), and a catalyst dosage of 2.5 g/l, 60.0 mg/l IMI was reduced to 0.9 mg/l after 180 min reaction at pH 4.0. Outputs of TOC and BOD5 were 0.8 ± 0.5 mg/l and 2.6 ± 0.3 mg/l, respectively, which reflects that nearly all organic compounds were mineralized in the experiment. BDD electrode also shows the best performance. In addition, it was found that catalyst dosage should be increased with the growth of IMI concentration. The limitation for this correlation was at IMI concentration of 60.0 mg/l, which corresponded to a catalyst dosage of 2.5 g/l. Some other conditions provided good performance with economic potential also found for external desire.