Degradation of iodinated disinfection byproducts by VUV/UV process based on a mini-fluidic VUV/UV photoreaction system.

This study investigated the VUV/UV photodegradation of three iodinated disinfection byproducts (I-DBPs), namely, triiodomethane (TIM), diiodoacetamide (DIAcAm) and triiodoacetic acid (TIAA), based on a mini-fluidic VUV/UV photoreaction system (MVPS). The pseudo-first-order rate constants (k) of TIM, DIAcAm and TIAA under VUV/UV irradiation (1769, 1301 and 1174 m einstein, respectively) were higher than those under UV irradiation (1003, 832 and 766 m einstein, respectively). The enhancement of photodegradation could be attributed to the indirect HO oxidation rather than the direct VUV photolysis. As a whole, compared with the indirect HO oxidation, the direct UV photolysis had a relatively greater contribution to the degradation of the three I-DBPs, especially DIAcAm and TIAA (ca. 57% and 60%, respectively). The two electron-withdrawing groups in DIAcAm and TIAA (i.e., acylamino and carboxyl) decreased the electron density of the C-I bonds, thus weakening the electrophilic attack of HO. The iodine in the three I-DBPs was released to form I and a small fraction (< 6%) of I was oxidized to IO, indicating that HO preferred to break the C-I bonds rather than oxidize I. The direct UV photolysis proceeded via HO-catalyzed deiodination reactions, while the indirect HO oxidation proceeded via deiodination reactions along with HO addition. The VUV/UV photodegradation of the three I-DBPs was more favored at an acidic pH but inhibited by the water matrix components (i.e., NOM, Cl and alkalinity) to different extents.