The degradation of micropollutants and the formation of bromate (a probable human carcinogen) by the UV/O₃ process at low ozone doses and the cobaltous-activated KHSO₅ process were studied in bench-scale experiments. _{3 3} ^{-1 -1} ₃...[ Read more ]

The degradation of micropollutants and the formation of bromate (a probable human carcinogen) by the UV/O₃ process at low ozone doses and the cobaltous-activated KHSO₅ process were studied in bench-scale experiments.

Micropollutants including nitrobenzene, NDMA and NPyr could be removed effectively by the UV/O₃ process at low ozone doses in undisinfected real water at pH 7. The degradation of NB was improved by the UV/O₃ process compared with ozonation alone at low ozone doses (0.3 and 0.5 mg L^-1). Dissolved organic carbon (DOC), bicarbonate and bromide were important parameters in suppressing NB degradation. At an ozone dose of 0.5 mg L^-1, no bromate was detected by the UV/O₃ process in undisinfected real water at pH 8. On the other hand, compared with UV irradiation, no enhancement of NDMA degradation by the UV/O₃ process was observed at an ozone dose of 0.5 mg L^-1. The improvement of NPyr degradation by the UV/O₃ process was obtained at an ozone dose of 1.0 mg L^-1. The extended study of NPyr degradation showed that the C-N and N-N bonds of NPyr were broke down in ozonation.

The cobaltous-activated KHSO₅ process was effective for NDMA and NPyr abatement. Low pH level (pH ≈ 3.6) and the use of phosphate buffer reduced the effectiveness of NPyr degradation. Both inhibitive and promotive effects of bicarbonate and chloride on NPyr elimination were observed, depending on the experimental conditions. Apart from sulfate radicals, OH radicals were found of importance for NPyr degradation in phosphate buffered testing solution. Furthermore, the cobaltous-activated KHSO₅ process could produce considerable amounts of bromate (>10 μg L^-1). The bromate formation should also be taken into account when the Fe⁰-activated KHSO₅ process is used for micropollutant degradation.