| Summary: | The chlorination of dissolved amino acids can generate disinfection by-products (DBPs). To prevent the formation of DBPs, we examined the UV-induced degradation of tryptophan (Trp). In order to further understand the impact of UV disinfection on Trp, the effects of initial concentrations of Trp, pH, temperature, concentrations of NO<sub>3</sub><sup>−</sup>, HCO<sub>3</sub><sup>−</sup> and Cl<sup>−</sup> on Trp removal were investigated, and a degradation mechanism was also proposed. The results demonstrated that degradation fitted a pseudo first-order reaction kinetic model. The degradation of Trp was mainly caused by direct UV degradation. The apparent rate constant k<sub>obs</sub> decreased with the increase in initial Trp concentration and increased with increases in pH and temperature. The thermal degradation activation energy was 19.65 kJ/mol. Anions in water also had a significant influence on the degradation of Trp. HCO<sub>3</sub><sup>−</sup> and NO<sub>3</sub><sup>−</sup> contributed to the k<sub>obs</sub> of Trp, but Cl<sup>−</sup> inhibited the degradation rate. By electron paramagnetic resonance (EPR) spectroscopy, ·OH was proven to be formed during the degradation of Trp by UV. Based on the intermediate products of C<sub>11</sub>H<sub>15</sub>NO<sub>3</sub>, C<sub>10</sub>H<sub>15</sub>N and C<sub>9</sub>H<sub>13</sub>N detected by LC-MS-MS, the degradation pathway of Trp was speculated.
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