Removal of phenol from wastewater by high-gravity intensified heterogeneous catalytic ozonation with activated carbon

In this study, the high-gravity technique is used to intensify the heterogeneous catalytic ozonation with activated carbon (AC) as the catalyst for removal of phenol from wastewater in a rotating packed bed (RPB), and the effects of high-gravity factor, inlet O₃ concentration, liquid-gas ratio, and initial pH on the degradation and mineralization of phenol at room temperature are investigated. It is revealed that the degradation rate of phenol reaches 100% at 10 min and the removal rate of total organic carbon (TOC) reaches 91% at 40 min under the conditions of high-gravity factor β = 40, inlet O₃ concentration = 90 mg·L^-1, liquid flow rate = 80 L·h^-1, and initial pH = 11. Compared with the bubbling reactor (BR)/O₃/AC and RPB/O₃ systems, the mineralization rate of phenol by the RPB/O₃/AC system is increased by 24.78% and 34.77%, respectively. Free radical quenching experiments are performed using tertiary butanol (TBA) and benzoquinone (BQ) as scavengers of ·OH and O₂^-, respectively. It is shown that the degradation and mineralization of phenol are attributed to the direct ozonation and the indirect oxidation by ·OH generated from the decomposition of O₃ adsorbed on AC surface, respectively. ·OH and O₂^·- are also detected by electron paramagnetic resonance (EPR). Thus, it is concluded that AC-catalyzed ozonation and high-gravity technique have a synergistic effect on ·OH initiation, which in turn can significantly improve the degradation and mineralization of organic wastewater.