Rapid Mineralization of Azo-Dye Wastewater by Microwave Synergistic Electro-Fenton Oxidation Process

A method for in situ improvement of the electro-Fenton (EF) oxidation process using microwave radiation was proposed. The microwave enhanced electro-Fenton (MW-EF) degradation of azo dye wastewater with boron-doped diamond (BDD) anode was carried out in a continuous flow system under atmospheric pressure. The activation effects of microwave were studied through determining the accumulated hydroxyl radicals, electrogenerated H2O2, and the evolution of iron ions and intermediates. The results showed that, under microwave irradiation, both cathode and anode surfaces were activated efficiently. For cathode, the presence of microwave in electro-Fenton oxidation process accelerated the Fe(III)/Fe(II) redox cycles, leading to relatively steady Fe(II) recovery. Moreover, the transduction of electrons was promoted and the electrosynthesis of H2O2 from O-2 was greatly accelerated on the cathode. For BDD anode, under microwave, the blocking of electrode surface by intermediates was enormously alleviated and more active sites of producing center dot OH were formed on the electrode surface. Consequently, the concentration of center dot OH was significantly promoted in MW-EF process, which was 2.3 nines of traditional EF method. Further studies indicated that both the formation and degradation rates of intermediates in MW-EF system were obviously increased comparing with EF due to the synergistic effect between microwave irradiation and electro-Fenton. In addition, the removals of TOC and methyl orange concentration, mineralization current efficiency were respectively around 3.1, 1.1, and 3.2 times higher than that without microwave radiation. This work enriched the theory of catalytic oxidation combination technology and developed a new idea for elimination concentrated refractory organic pollutants.