A novel strategy using sulfite for bromate control during UV/persulfate oxidation of bromide-containing waters

The ultraviolet/persulfate (UV/PS) process has attracted more and more attention for water treatment. However, it runs the risk of producing bromate in the presence of bromide ions. In this work, we propose a new strategy using sulfite to inhibit bromate formation. The results show that the addition of sulfite significantly reduced the formed bromate in the UV/PS system by 61.2% and 24.5% in 30 min and 120 min, respectively. Increasing sulfite dosage or pH could enhance bromate control. From the standpoint of reaction kinetics, sulfite is likely to inhibit bromate formation by reducing bromine radicals (Br) back to bromide ions, the energy profile of which was quantified by density functional theory (DFT) calculations. In the UV/PS/sulfite system, the conversion of SO3− to HO was observed, indicating that sulfite also served as a source of reactive radicals. Moreover, sulfite apparently promoted the degradation of benzoic acid and phenol in a UV/PS system, showing advantages over other inorganic reductants. As a result, we discovered that sulfite could not only help control bromate formation in UV/PS but also improve the system's oxidation capacity.