The formation and control of ozonation by-products during drinking water advanced treatment in a pilot-scale study

Ozone has been widely applied during drinking water treatment for organic pollutants removal, however, the ozonation by-products such as bromate, aldehydes, and carboxylic acids could be produced. To investigate the ozonation by-products formation and control efficiency, a continuous pilot-scale system was established including conventional treatment and ozone-biological activated carbon (O₃-BAC) treatment processes in a waterworks that receives bromide-bearing source water from the Yellow River in northern China. It was found that ozonation could reduce the threshold odour number and the haloacetic acids formation potential effectively. As 1.8-2.6 mg/L of ozone was applied, the bromate concentration would exceed the standard of 10 μg/L. Simultaneously, ozonation led to a large number of formaldehyde, methylglyoxal and other aldehydes. At the ozone dosage of 3.0 mg/L, the total concentration of aldehydes reached the highest of 45.4 μg/L. Ammonia and hydrogen peroxide (H₂O₂) addition could inhibit the formation of bromate effectively. The application of H₂O₂ induced an increase in aldehydes concentration reaching a maximum concentration of 57.6 μg/L. During the BAC treatment, the removal rate of aldehydes would reach 19%-41%. The addition of H₂O₂ inhibited the formation of bromate but increased the production of aldehydes, thus it is important to search a balance point for controlling bromate and aldehydes simultaneously. The H₂O₂/O₃ (g/g) of 1.0 could be possible to control both bromate and aldehydes concentrations within the standards.