Ozonation of Exhausted Reactive Dye-Bath Analogues: the Use of Atrazine as an OH^* Probe Compound

Abstract

Ozonation and O₃/H₂O₂ treatment of a spent reactive dye–bath analogue containing aminofluorotriazine type reactive dyestuffs were examined in semi–batch experiments at different pH (2, 7 and 12), bicarbonate (0.18 M at pH7) and carbonate (0.19 M at pHl2) alkalinity. Atrazine (23.2 µM) was added as an OH* – sensitive probe compound to the reactive dye–bath analogue to evaluate the individual contributions of both direct molecular (O₃) and indirect radical (OH*) type reaction pathways for the treatment of spent dye–bath ingredients. From the obtained results it was evident that particularly de–aromatization (expressed in terms of UV₂₅₄ and UV₂₇₀ removal) kinetics were significantly retarded in the presence of HCO₃, CO₃ ^2‐ and particularly H₂O₂. O₃ decomposition and consumption increased appreciably when H₂O₂ (0.125 mM at pH7) was added as compared in the presence of carbonate/bicarbonate alkalinity when H₂O₂ was added indicating that H₂O₂ and alkalinity could act as radical chain reaction promoters (carriers) and inhibitors, respectively. Atrazine degradation and UV₂₇₀ abatement rates paralleled each other revealing that particularly de–aromatization of the spent dye–bath constituents mainly involves the action of OH*. Nitrate formation was distinctly higher at pH7 than at pH 12 as a consequence of the stronger OH* scavenging effect of carbonate alkalinity at pH12.

Keywords:

• Ozone
• Dye-Bath Effluents
• Dyestuff Removal
• Fiber Reactive Dyes
• Atrazine
• pH Effect
• Textile Wastewater
• Advanced Oxidation