Carbonate-activated hydrogen peroxide oxidation process for azo dye decolorization: Process, kinetics, and mechanisms

Advanced oxidation processes offer effective solutions in treating wastewater from various industries. This study is the first time to investigate the potential of carbonate-activated hydrogen peroxide (CAP) oxidation process for the removal of organic pollutant from highly alkaline wastewaters. Azo dye acid orange 7 (AO7) was selected as a model pollutant. The influences of various parameters on AO7 decolorization by the CAP oxidation were evaluated. Furthermore, the active species involved in AO7 degradation were explored using scavenger experiments and electron spin resonance analysis. Additionally, AO7 degradation products by the CAP oxidation were identified to elucidate possible transformation pathways. Results showed that the CAP oxidation had better AO7 decolorization performance compared to bicarbonate-activated hydrogen peroxide method. The AO7 decolorization efficiency augmented from 3.70 ± 0.76% to 54.27 ± 2.65% when carbonate concentration was increased from 0 to 50 mM at pH 13.0, and then changed slightly with further increasing carbonate concentration to 70 mM. It increased almost linearly from 5.95 ± 0.32% to 94.03 ± 0.39% as H2O2 concentration was increased from 5 to 50 mM. Moreover, trace amount of Co(II) could facilitate AO7 decolorization by the CAP reaction. Superoxide and carbonate radicals might be the main reactive oxygen species involved in the CAP process. Finally, a possible degradation pathway of AO7 by the CAP oxidation was proposed based on the identified products.