Decolorization effects of six azo dyes by O3, UV/O3 and UV/H2O2 processes

The decolorization of six azo dyes by means of O3, UV/O3 and UV/H2O2 processes was performed successfully with all of the tested dyes decolorizing effectively. However, dyes with dis-azo links (i.e. C.I. Direct Yellow 4 and C.I. Acid Black 1) were more difficult to decolorize than mono-azo dyes. During the processes, the pH value changed from 5.4 to 3.5, thus becoming more acidic. The increased acidity resulted from the oxidation and breakdown of the R+-(SO3−) bond in the azo dye structure. The removal of 95% color was the level chosen to compare the energy efficiency. The results showed that UV/H2O2 used the most energy, 5-11 times, than that of UV/O3 process, and 265-520 times more than that of the ozonation process.