Ozonation of exhausted reactive dye-bath analogues: The use of atrazine as an OH^• probe compound

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 pH12) 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^-, CO ₃^2- and particularly H₂O₂. O ₃ decomposition and consumption increased appreciably when H ₂O₂ (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 pH12 as a consequence of the stronger OH ^• scavenging effect of carbonate alkalinity at pH12.