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 mu M, respectively, in 2 h at a working temperature of 60 degrees 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 H2O2 was added to the reaction solutions. The reduced Br-OBPs formation was due to the reduction of free bromine by H2O2. Both experimental data and kinetic modeling indicated that the concentration of free bromine decreased significantly in the presence of H2O2. However, H2O2 did not eliminate the formation of organic bromines completely. Certain brominated DHBA intermediates formation in the presence of H2O2 was even higher than that with H2O2 absent. Bromine radicals, such as Br-2(-center dot) and HBrO-center dot, 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 H2O2 to SR-AOPs can significantly suppress the generation of halogenated-OBPs. However, the formation of organic bromines is still a concern.

Automated summary

The formation of halogenated oxidation by-products in sulfate radical based advanced oxidation process has raised concerns. Addition of hydrogen peroxide can significantly suppress the generation of halogenated-OBPs, but the formation of organic bromines is still a concern.