Sonochemical decomposition of phenol: Evidence for a synergistic effect of ozone and ultrasound for the elimination of total organic carbon from water

Advanced oxidation processes (AOPs) for water and wastewater treatment are often handicapped by their inability to completely eliminate total organic carbon (TOC). In order to explore the capability of the combination of ultrasonic irradiation with ozone for the rapid removal of TOC, we examined the degradation rates of dissolved phenol (C6H5OH) in water with high-frequency ultrasound over the range of 200-1000 kHz, with ozone and with the combined application of sonication and ozonation. When ozone and ultrasound are applied simultaneously, a pronounced synergistic effect is observed that leads to the complete and rapid elimination of TOC at enhanced reaction rates. At longer reaction times, phenol oxidation by O-3 leads to oxalate and formate, which accounts for the majority of the residual TOC. However, the combination of US (ultrasound) and ozone together readily oxidizes HCO2- and C2O42- to CO2 while they prove to be relatively resistant to further oxidation to CO2 by O-3 alone.