How I– alters UV and UV/VUV processes' redox capacities: Evidences from iodine species evolution, hydrogen peroxide formation, and oxyhalides degradation?

Abstract

Although UV and/or VUV tandem I– are often proposed as advanced reduction processes (ARPs) to eliminate micropollutants by generating eaq–, the fate of I– and its byproducts formation remain to be explored. Therefore, this study investigated the iodine species evolution during UV/I– and UV/VUV/I– processes under different influencing factors. Results show that UV/VUV oxidized most of I– to IO3– whereas UV only oxidized a portion of I– to intermediate reactive iodine species (RISs, including I2, HOI, and I3–); meanwhile, substantial H2O2 was generated only in UV/VUV/I– process but not in UV/I– process, proving that UV/VUV owns stronger oxidation ability than UV alone. Spiking I– into water exerted triple-sided effects by consuming •OH, generating eaq–, and shielding light, thus complicating the systems. Holistically, increasing pH or decreasing dissolved oxygen converted oxidizing environment into reducing condition and caused less RISs formation, especially for UV/VUV/I–. For oxyhalides, neither UV/I– nor UV/VUV/I– degraded ClO4–. While UV/I– cannot remove ClO3–, UV/VUV/I– reduced ClO3– to Cl–. Expectedly, both UV/I– and UV/VUV/I– reduced BrO3– to Br– more efficiently than UV and UV/VUV, confirming that I– can enhance the reduction capacities of UV/VUV and UV technologies.