Comparative study of the formation of brominated disinfection byproducts in UV/persulfate and UV/H 2 O 2 oxidation processes in the presence of bromide

Abstract

The objective of this research was to compare the transformation of Br⁻ and formation of brominated byproducts in UV/persulfate (PS) and UV/H₂O₂ processes. It was revealed that Br⁻ was efficiently transformed to free bromine which reacted with humic acid (HA) or dihydroxybenzoic acid resulting in the formation of brominated byproducts such as bromoacetic acids (BAAs) in UV/PS system. In contrast, no free bromine and brominated byproducts could be detected in UV/H₂O₂ system, although the oxidization of Br⁻ was evident. We presumed that the oxidation of Br⁻ by hydroxyl radicals led to the formation of bromine radicals. However, the bromine radical species could be immediately reduced back to Br⁻ by H₂O₂ before coupling to each other to form free bromine, which explains the undetection of free bromine and BAAs in UV/H₂O₂. In addition to free bromine, we found that the phenolic functionalities in HA molecules, which served as the principal reactive sites for free chlorine attack, could be in situ generated when HA was exposed to free radicals. This study demonstrates that UV/H₂O₂ is more suitable than UV/PS for the treatment of environmental matrices containing Br⁻.

Graphical abstract

Graphical abstract

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