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

Ozone has been widely applied during drinldng 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 byproducts formation and control efficiency, a continuous pilot-scale system was established including conventional treatment and ozone-biological activated carbon (O-3-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 mu g/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 mu g/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 mu g/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/O-3 (g/g) of 1.0 could be possible to control both bromate and aldehydes concentrations within the standards.

Automated summary

Ozone treatment can effectively reduce odor and haloacetic acids in water, but also leads to the generation of aldehydes. The addition of hydrogen peroxide inhibits bromate formation but increases aldehydes production, which requires finding a balance point for controlling both substances simultaneously. A H2O2/O-3 (g/g) ratio of 1.0 could be a feasible option to meet the standards for both bromate and aldehydes concentrations.