Degradation of Acid Orange 7 in aqueous solution by a novel electro/Fe2+/peroxydisulfate process

A novel process in which electrochemistry (EC) was coupled with ferrous ion activation of peroxydisulfate (Fe(2+)/S(2)O(8)(2-)) was proposed for the decolorization of Acid Orange 7. In this process, the reaction between peroxydisulfate and externally added ferrous ion results in the production of sulfate free radical as well as ferric ion, and at the same time ferrous ion could be electro-regenerated at the cathode by the reduction of ferric ion. Color removal by the Fe(2+)/S(2)O(8)(2-) process was significantly enhanced in the presence of applied current. The effects of some important reaction parameters such as initial pH, current density, S(2)O(8)(2-) concentration and Fe(2+) concentration on the decolorization of Acid Orange 7 by EC/Fe(2+)/S(2)O(8)(2-) process were investigated. The results showed that the decolorization efficiency was not significantly affected by the initial pH value, and the decolorization efficiency increased with the increase of S(2)O(8)(2-) concentration and Fe(2+) concentration. The current densities had little effect on the decolorization of Acid Orange 7 at the beginning of the reaction, while it improved the decolorization efficiency after 60min reaction. The GC-MS analysis was employed to identify the intermediate products and a plausible degradation pathway is proposed. The chemical oxygen demand (COD) removal efficiency was 57.6% after 60min reaction and it reached 90.2% when the reaction time was extended to 600min. Toxicity test with Daphnia magna showed that the acute toxicity of the solution increased during the first stage of the reaction, and then gradually decreased with the progress of the oxidation.