Formation control of bromate and trihalomethanes during ozonation of bromide-containing water with chemical addition: Hydrogen peroxide or ammonia?

Abstract

To ensure the safety of drinking water, ozone (O3) has been extensively applied in drinking water treatment plants to further remove natural organic matter (NOM). However, the surface water and groundwater near the coastal areas often contain high concentrations of bromide ion (Br−). Considering the risk of bromate (BrO3−) formation in ozonation of the sand-filtered water, the inhibitory efficiencies of hydrogen peroxide (H2O2) and ammonia (NH3) on BrO3− formation during ozonation process were compared. The addition of H2O2 effectively inhibited BrO3− formation at an initial Br− concentration amended to 350 µg/L. The inhibition efficiencies reached 59.6 and 100% when the mass ratio of H2O2/O3 was 0.25 and > 0.5, respectively. The UV254 and total organic carbon (TOC) also decreased after adding H2O2, while the formation potential of trihalomethanes (THMsFP) increased especially in subsequent chlorination process at a low dose of H2O2. To control the formation of both BrO3− and THMs, a relatively large dose of O3 and a high ratio of H2O2/O3were generally needed. NH3 addition inhibited BrO3− formation when the background ammonia nitrogen (NH3N) concentration was low. There was no significant correlation between BrO3− inhibition efficiency and NH3 dose, and a small amount of NH3N (0.2 mg/L) could obviously inhibit BrO3− formation. The oxidation of NOM seemed unaffected by NH3 addition, and the structure of NOM reflected by synchronous fluorescence (SF) scanning remained almost unchanged before and after adding NH3. Considering the formation of BrO3− and THMs, the optimal dose of NH3 was suggested to be 0.5 mg/L.