Comparative evaluation of iodoacids removal by UV/persulfate and UV/H ₂ O ₂ processes

To develop a cost-effective method for post-formation mitigation of iodinated disinfection by-products, degradation of iodoacids by UV, UV/PS (persulfate), and UV/H ₂ O ₂ was extensively investigated in this study. UV direct photolysis of 4 iodoacids followed first-order kinetics with rate constants in the range of 2.43 × 10 ⁻⁴ −3.02 × 10 ⁻³  cm ²  kJ ⁻¹ . The derived quantum yields (Ф ₂₅₄ ) of the 4 iodoacids range from 0.13 to 0.34, respectively. A quantitative structure-activity relationship (QSAR) model was subsequently established and applied to predict the direct photolysis rates of 6 other structurally similar iodoacids whose standards are commercially unavailable. At a UV dose of 140 mJ cm ⁻² which is typically applied for disinfection of drinking water, the removal percentages of 4 iodoacids were only between 3.35% and 34.7%. Thus, ICH ₂ CO ₂ H (IAA), the most photo-recalcitrant species, was selected as the target compound for removal in the UV/PS and UV/H ₂ O ₂ processes. The IAA degradation rates decreased with increasing pH from 3 to 11 in both processes. Humic acid (HA) and HCO ₃ ⁻ had inhibitory effects on IAA degradation in both processes. Cl ⁻ adversely affected the IAA degradation in the UV/PS process but had no effect in the UV/H ₂ O ₂ process. Generally, in the deionized (DI) water, surface water, treated drinking water, and secondary effluent, UV/PS process is more effective than UV/H ₂ O ₂ process for IAA removal, based on the same molar ratio of oxidant: IAA. SO ₄ [Formula presented] ⁻ generated in the UV/PS process yields a greater mineralization of IAA than [Formula presented] in the UV/H ₂ O ₂ process. IO ₃ ⁻ was the predominant end-product in the UV/PS process, while I ⁻ was the major end-product in the UV/H ₂ O ₂ process. The respective contributions of UV, [Formula presented], and SO ₄ [Formula presented] ⁻ for IAA removal in the UV/PS process were 7.8%, 14.7%, and 77.5%, respectively, at a specific condition (1.5 μM IAA, 60 μM oxidant, and pH 7). Compared to UV/H ₂ O ₂ process, UV/PS was also observed as more cost-effective process based on the electrical energy per order (EE/O) and chemical cost.