Formation of brominated disinfection by-products and bromate in cobalt catalyzed peroxymonosulfate oxidation of phenol

Abstract

Formation of halogenated disinfection by-products (DBPs) in sulfate radical (SO4−) based oxidation processes attracted considerable attention recently. However, the underlying reaction pathways have not been well explored. This study focused on the transformation of Br− in cobalt activated peroxymonosulfate (Co2+/PMS) oxidation process. Phenol was added as a model compound to mimic the reactivity of natural organic matter (NOM). It was revealed that Br− was efficiently transformed to reactive bromine species (RBS) including free bromine and bromine radicals (Br, Br2−, etc.) in Co2+/PMS system. SO4− played a principal role during this process. RBS thus generated resulted in the bromination of phenol and formation brominated DBPs (Br-DBPs) including bromoform and bromoacetic acids, during which brominated phenols were detected as the intermediates. Br-DBPs were further degraded by excessive SO4− and transformed to bromate ultimately. Free bromine was also formed in the absence of Co2+, suggesting Br− could be oxidized by PMS per se. Free bromine was incorporated to phenol sequentially leading to Br-DBPs as well. However, Br-DBPs could not be further transformed in the absence of SO4−. This is the first study that elucidated the comprehensive transformation map of Br− in PMS oxidation systems, which should be taken into consideration when PMS was applied to eliminate contamination in real practice.