Evaluation of decolorization, mineralization, and toxicity reduction of Tropaeolin O in water by ozonation with UV irradiation

The combination of ozonation with UV irradiation can remove Tropaeolin O (AO6) and its by-products effectively and completely. The ozone dose affects the rate of decolorization, AO6 species removal, and dissolved organic carbon (DOC) reduction significantly. After 240 minutes of ozonation, the average DOC removal efficiency (ηDOC) for O3 alone was about 0.79, while ηDOC for O3/UV was 1.0. The average DOC removal rate was low at early stage of ozonation due to decolorization and low DOC. At later stage of ozonation, average DOC removal rate decreases because of the formation of persistent intermediates. The ozone consumption was consistent with ηDOC. The ratio of ozone consumption to ozone applied decreased from 14 to 12% when ηDOC <40% because the decolorization in the early stage of the ozonation of AO6 may consume a relatively large amount of ozone. It was found that NO2, NO, CO2, and small amount of SO2 was detected in the off-gas. The effective concentration (EC50) increased from 23.48% to 100%, suggesting that the toxic reduction was achieved, and O 3/UV system was superior to O3 alone system.