Efficiency and mechanism of oxidative degradation of typical UV filters by ozone micro-nano bubbles

Ozone micro-nano bubbles are known for their beneficial traits, such as high ozone utilization and mass transfer rates. In this study, ozone micro-nano bubbles were utilized to degrade the ultraviolet filter, diethylamino hydroxybenzoyl hexyl benzoate (DHHB). The characteristics of ozone micro-nano bubbles and their degradation mechanism on DHHB were studied by varying dissolved gas modes and liquid-phase ozone concentrations, and the impacts of temperature, pH, natural organic matter and different ion strengths on the degradation efficiency were explored. The results indicated that the oxidation efficiency of ozone micro-nano bubbles exceeded that of conventional ozone bubbles. The concentration of liquid-phase ozone, hydroxyl radicals, hydroxyl radical yield, and ozone utilization rate in the system increased significantly. The DHHB removal rate achieved 87.3% within 60 min at 25 °C, with a gas-phase ozone concentration of 10.22 mg/L and pH of 11. The removal effectiveness was 2.02 times greater than that of traditional ozone bubbles. Natural organic matter and bicarbonate ions inhibited the degradation of DHHB to different extents. According to the quenching test, 65.2% of DHHB degradation was contributed by hydroxyl radicals and 14.9% by superoxide radicals. This study confirms the feasibility of utilizing an ozone micro-nano bubble system for treating DHHB in water, and offers a theoretical basis for the practical implementation of this system.