Division of Environmental Science and Engineering, Pohang University of Science and Technology (POSTECH) , Pohang 37673, Korea.
Environ Sci Technol. 2017 Aug 1;51(15):8368-8375. doi: 10.1021/acs.est.7b00915. Epub 2017 Jul 13.
Bromate is a common disinfection byproduct formed during ozonation. Reducing bromate into bromide can remove this toxic pollutant, however, not many studies have been done for its environmental fate. In this work, we demonstrate a new transformation pathway that bromate can be efficiently reduced to bromide in frozen solution in the presence of organic reductants like humic substances (HS). The results showed that bromate in frozen solution could be removed by 30-40% in dark condition and 80-90% in irradiation condition (λ > 300 nm) in 24 h, while around 1% bromate was reduced in aqueous solution. The bromate reduction by HS induced a partial oxidation of HS, which was confirmed by X-ray photoelectron spectroscopic analysis of the HS sample recovered from the frozen solution. Photoluminescence analysis of HS revealed that the fluorescence quenching by bromate was observed only with very high concentration of bromate (0.1-0.2 M) in aqueous solution whereas the quenching effect in frozen solution was seen with much lower bromate concentration (5-100 μM). The highly enhanced removal of bromate in ice is ascribed to the freeze concentration effect that bromate and HS are concentrated by orders of magnitude to accelerate the bimolecular transformation in the ice grain boundary region. Freezing process in cold environments would provide a unique chemical mechanism for the removal of persistent bromate.
溴酸盐是臭氧氧化过程中形成的一种常见的消毒副产物。将溴酸盐还原为溴化物可以去除这种有毒污染物，但对于其环境归宿，研究并不多。在这项工作中，我们证明了一种新的转化途径，即在存在有机还原剂（如腐殖质）的情况下，溴酸盐可以在冷冻溶液中被有效地还原为溴化物。结果表明，在 24 小时内，黑暗条件下冷冻溶液中溴酸盐的去除率为 30-40%，光照条件下（λ>300nm）的去除率为 80-90%，而在水溶液中仅还原了约 1%的溴酸盐。HS 诱导的溴酸盐还原导致 HS 的部分氧化，这通过从冷冻溶液中回收的 HS 样品的 X 射线光电子能谱分析得到证实。HS 的光致发光分析表明，只有在水溶液中溴酸盐浓度非常高（0.1-0.2M）时，才观察到溴酸盐对荧光的猝灭，而在冷冻溶液中，在低得多的溴酸盐浓度（5-100μM）下就观察到猝灭效应。溴酸盐在冰中高度去除归因于冷冻浓缩效应，该效应使溴酸盐和 HS 按数量级浓缩，以加速冰晶粒边界区域的双分子转化。寒冷环境中的冷冻过程为去除持久性溴酸盐提供了一种独特的化学机制。
