Removal of Acid Orange 7 in simulated wastewater using a three-dimensional electrode reactor: Removal mechanisms and dye degradation pathway

The removal of Acid Orange 7 (AO7) in simulated wastewater was experimentally investigated using a three-dimensional electrode reactor with granular activated carbon as the particle electrode, ACF (activated carbon fiber)/Fe as the anode, and ACF/Ti as the cathode. Particular attention was paid to the reaction mechanisms and the dye degradation pathway in the system. The removal of AO7 in the system was mainly dependent on the oxidation by the produced active substances (OH, etc.) and the coagulation by Fe(II) or Fe(III) dissolved from the anode. The former mechanism was predominant. A possible pathway for AO7 degradation was proposed by monitoring the temporal evolution of intermediates in the solution, with the use of some techniques including GC/MS, FTIR and HPLC. The AO7 molecule was observed to be firstly decomposed to aromatic intermediates, further degraded to ring opening products and finally mineralized to CO2, H2O and inorganic salts. The intermediates increased the biodegradability of the wastewater, which was proved by the increase of the BOD/COD value after electrolysis treatment. The three-dimensional electrode method can be considered an effective alternative to dye wastewater pretreatment prior to the biological process.