Bromate formation potential during ozonation of wastewater treatment plant effluents

Ozonation is an established advanced treatment process to transform organic micropollutants present in wastewater treatment plant effluents. In the presence of bromide, ozone treatment can cause formation of the oxidation byproduct bromate. Due to its potential carcinogenicity, its concentration in drinking water is regulated and limited to 10 μg/L in the European Union. Understanding relevant influences on bromate formation and potential control options is crucial to ensuring surface water quality and safe drinking water in case of semi-closed water cycles. This study investigates the bromate formation potential for four wastewater treatment plant effluents of the largest German city Berlin. Laboratory-scale ozonation experiments were conducted with varying ozone doses and bromide concentrations to determine bromate formation for different conditions that might occur during real operation. The results show native bromide concentrations of 0.14 to 0.32 mg/L and bromate concentrations of 0.3 to 1.3 μg/L for ozone consumptions around 0.7 mg/mg O 3 /DOC at pH values between 7 and 8. This corresponds to bromate yields of 0.2 to 0.6% (mg/mg bromate/bromide). Splitting the ozone dose into multiple smaller doses proved to be an efficient bromate control option for high specific ozone consumptions, with up to 48% less bromate formation. The results underline that the bromate formation potential in Berlin wastewater treatment plants does not limit ozonation as advanced wastewater treatment, since bromate concentrations of all plants were significantly below the drinking water limit of 10 μg/L for specific ozone consumptions around 0.7 mg/mg O 3 /DOC, even at artificially elevated bromide concentrations. • Investigation of bromate formation potential of four wastewater treatment plants • Bromate levels uncritical at typical ozone doses, even with bromide >1 mg/L • Ozone dose more relevant to control bromate formation than bromide concentration • Reduction of bromate yields by splitting of the total ozone dose • Correlation of bromate yields with UVA 254 -specific ozone consumption