Simultaneous humic acid removal and bromate control by O3 and UV/O3 processes

• UV irradiation with addition of ozone, generated by the UV lamp, was proposed
• Bromate formations in UV/O3 and ozone processes were comparatively studied
• Residual ozone was proved to be important to bromate formation in UV/O3 process.

Bromate is a potential carcinogen that forms during the treatment of bromide-containing water using ozone-based technologies. A study of humic acid (HA) removal and bromate formation in UV/O3 and ozone processes was conducted relative to a variety of operational conditions, such as ozone dosage, pH and initial concentrations of HA and Br−. Additionally, UV irradiation with the addition of ozone, which was generated by the same low-pressure mercury lamp (emitting 254 nm and 185 nm), was studied. Bromate concentrations during the UV/O3 process were 17.1–77.6 μg/L, which was 2.1–2.9 times the concentration for the O3 process, when ozone at concentrations ranging from 1.5 to 6.3 mg/L was continuously applied to water to which no HA was added. UV radiation reduced the concentration of the residual ozone, which was important for the formation of bromate. HA inhibited bromate formation, which was especially dramatic in UV/O3 process, and increasing the initial concentration of Br− accelerated the bromate formation in both processes; however, enhancement of bromate formation after increasing the pH was only observed for O3 process. Reducing the ozone dosage in UV/O3 process lessened both residual ozone concentration and hydroxyl radical (OH) exposure; changing this parameter led to a slight drop in the rate of HA removal but also caused a significant decrease in the bromate formation. Therefore, the combination of UV irradiation and low doses of ozone represented a promising method for the simultaneous control of bromate formation and HA removal. Because the UV lamp can also generate a low concentration of ozone, combining UV irradiation with the internally generated ozone is recommended.