Ozonation of some dyes in aqueous solution and toxicological assessment of their oxidation products

The effects of ozonation on the degradation processes of a lot of dyes in aqueous solution were studied. The results demonstrated that ozonation was a highly effective way to remove the colour of dye solution, and kinetic analysis indicated that decolourization rates of these dyes were all approximated as pseudo-first-order kinetics. During ozonation process, sharp increase of conductivity and rapid decrease of pH revealed the formation of inorganic ions and acidic by-products. Acetate, sulfate, oxalate, and nitrate were identified as main ozonation products of Direct Red Brown RN by ion chromatography (IC). The toxicity of by-products was determined by a bioluminescence inhibition assay With Photobacterium phosphoreum. The results showed that there was an increase, and then, a decrease in toxicity after zonation, and their toxicity generally followed the order acid dyes > direct dyes > reactive dyes.