Transformation of iodide and formation of iodinated by-products in heat activated persulfate oxidation process

- I− can be transformed to free iodine by SO4−.
- Free iodine attacks phenol leading to I-DBPs.
- Iodophenols are precursors of iodoform and TIAA.
- DIAA is formed via disparate pathway other than from iodophenols.

Formation of halogenated disinfection by-products (DBPs) in sulfate radical-based advanced oxidation processes (SR-AOPs) have attracted considerable concerns recently. Previous studies have focused on the formation of chlorinated and brominated DBPs. This research examined the transformation of I− in heat activated PS oxidation process. Phenol was employed as a model compound to mimic the reactivity of dissolved natural organic matter (NOM) toward halogenation. It was found that I− was transformed to free iodine which attacked phenol subsequently leading to iodinated DBPs such as iodoform and iodoacetic acids. Iodophenols were detected as the intermediates during the formation of the iodoform and triiodoacetic acid (TIAA). However, diiodoacetic acid (DIAA) was formed almost concomitantly with iodophenols. In addition, the yield of DIAA was significantly higher than that of TIAA, which is distinct from conventional halogenation process. Both the facts suggest that different pathway might be involved during DIAA formation in SR-AOPs. Temperature and persulfate dose were the key factors governing the transformation process. The iodinated by-products can be further degraded by excessive SO4− and transformed to iodate. This study elucidated the transformation pathway of I− in SR-AOPs, which should be taken into consideration when persulfate was applied in environmental matrices containing iodine.

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