Photon UV irradiation is promising for organic pollutant decomposition, such as disinfection by-products (DBPs). However, due to the photostability and high water solubility, chloroacetic acids (CAAs) decomposition using routine UV photolysis is very slow. The present study employed a high photon flux UV (3.13 × 104 μmol m−2 s−1) system to investigate its feasibility and suitability for enhancing CAAs (MCAA, DCAA and TCAA) decomposition. The results showed that increasing UV photon flux accelerated the photolysis remarkably. Under the condition of high UV photon flux 3.13 × 104 μmol m−2 s−1, almost complete degradation of 20 mg L−1 MCAA, 20 mg L−1 DCAA, and 20 mg L−1 TCAA in a mixed solution can be achieved within 50, 30 and 25 min, respectively. To the best of our knowledge, efficient photolytic degradation of CAAs in such short time has not been reported. The pseudo-first-order rate constant (kobs) steadily increases with the increasing of UV intensity, indicating that the utilization of light energy is efficient. In addition, the variation of pH from 3.2 to 9.0 showed minor effect on CAAs decomposition in this present studied system. The outcome of this study would be helpful for future employment of high photon flux UV systems for those photolytic resistant pollutants' decomposition.

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