New understanding of the main active substances and the promotion mechanism in the degradation of phenol by Fe–C micro-electrolysis systems

The mechanism of phenol degradation by micro-electrolytic systems can be fully understood by evaluating the oxidation of active substances from the two aspects of phenol bond-breaking and mineralization, and the direction of promoting the generation of active substances is pointed out. In this article, the effects of H2O2, O2-•, ·OH and 1O2 in the degradation of phenol were analyzed using phenol and chemical oxygen demand (COD) removal rates as judgment indicators, respectively. And the addition of C6O8H6 to the micro-electrolysis system was adopted to promote the generation of active substances. The experimental results showed that the active substances which played a dominant effect in the process of phenol bond-breaking and mineralization were changed. While 1O2 is dominant in the bond-breaking of phenol, •OH is dominant in the mineralization of phenol. After adding C6O8H6 (1 mmol/L), the removal rates of phenol and COD were increased by 7.35 and 4.85%, respectively. This was attributed to the autoxidation reaction of C6O8H6 and the continuous supply of H+ while reducing Fe3+ to Fe2+. Additionally, the C6O8H6 regulated the reaction pathway to improve the utilization of H2O2. This study provides a new perspective for the understanding of active substances in micro-electrolysis systems. HIGHLIGHTS The main active substances in the bond-breaking and mineralization are different.; is the main active substance in the phenol bond-breaking process.; •OH is the main active substance in the phenol mineralization process.; C6O8H6 can promote the formation of active substances in the system.; C6O8H6 can promote the Fe2+/Fe3+ cycle and improve the utilization of •OH.;