Ozonation and O-3/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 muM) was added as an OH. - sensitive probe compound to the reactive dye-bath analogue to evaluate the individual contributions of both direct molecular (O-3) 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-, CO32- and particularly H2O2. O-3 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 pH12 as a consequence of the stronger OH. scavenging effect of carbonate alkalinity at pH12.