Hydrogen peroxide suppresses the formation of brominated oxidation by-products in heat-activated peroxydisulfate oxidation process

Formation of halogenated oxidation by-products (OBPs) in sulfate radical based advanced oxidation process (SR-AOPs) has raised growing concern. In the present study, we found that brominated OBPs (Br-OBPs) were generated in heat-activated peroxydisulfate (PDS) oxidation of humic acid (HA) in the presence of Br − . The yields of bromoform, dibromoacetic acid, and tribromoacetic acid reached 2.52, 2.01, and 0.11 μM, respectively, in 2 h at a working temperature of 60 °C with an initial Br − , PDS, and HA concentrations of 0.1 mM, 5.0 mM, and 2.0 mg/L, respectively. Similar results were found when HA was replaced by 3,5-dihydroxybenzoic acid (DHBA) as the substrate, suggesting that the phenolic moieties in HA molecules are the reactive sites for halogenation. Almost no Br-OBPs could be detected when 5.0 mM H 2 O 2 was added to the reaction solutions. The reduced Br-OBPs formation was due to the reduction of free bromine by H 2 O 2. Both experimental data and kinetic modeling indicated that the concentration of free bromine decreased significantly in the presence of H 2 O 2 . However, H 2 O 2 did not eliminate the formation of organic bromines completely. Certain brominated DHBA intermediates formation in the presence of H 2 O 2 was even higher than that with H 2 O 2 absent. Bromine radicals, such as Br 2 − and HBrO − , are presumed responsible for the organic bromines. Without free bromine, these organic bromines were relative stable and could not be further degraded to small molecule Br-OBPs. The findings of this study indicate that adding H 2 O 2 to SR-AOPs can significantly suppress the generation of halogenated-OBPs. However, the formation of organic bromines is still a concern.