Significant enhancement of bromate removal in drinking water: Implications for the mechanism of sonocatalytic reduction

Bromate (BrO ₃ ⁻ ) is a potential carcinogenic compound that can form during the disinfection of drinking water. For the first time, the sonocatalytic reduction of BrO ₃ ⁻ were studied through examining the effect of the important operational parameters such as ultrasound (US) frequency, TiO ₂ loading, pH, temperature and other anions. By observing sonoluminescence (SL) at various frequencies and measuring H ₂ production rates, a new reduction mechanism for BrO ₃ ⁻ is also proposed. The kinetic results presented that the BrO ₃ ⁻ reduction rates enlarged as the measured H ₂ production rate increased for all parameters, and the slopes between the BrO ₃ ⁻ reduction and H ₂ production rates for sonocatalysis were much higher than those for sonolysis. Interestingly, sonolysis could be limited by the amount of H ₂ production, but sonocatalysis could increase the BrO ₃ ⁻ reduction rate because of additional electrons (e ⁻ ) from the surface of TiO ₂ via SL. The highest SL intensities for H ₂ production and BrO ₃ ⁻ reduction rates occurred at an ultrasound frequency of 500 kHz, implying that an increase in SL intensity caused by ultrasound cavitation enhanced H ₂ production and increased the e ^- released to the conduction band of TiO ₂ . At 500 kHz, BrO ₃ ⁻ reduction rate (6.84 × 10 ⁻²  min ⁻¹ ) by sonophotocatalysis was 5.2 times higher than that (1.32 × 10 ⁻²  min ⁻¹ ) of sonolysis. Investigation into the effect of anion species showed that BrO ₃ ⁻ reduction was inhibited or enhanced depending on the type of anions present. In real application, sonocatalytic reduction of BrO ₃ ⁻ could be advantageous, as it has higher reduction rates than those reported for photocatalysis.