Contribution of free radicals to ozonation of spent reactive dyebaths bearing aminofluorotriazine dyes

Laboratory-scale ozonation of spent dyebath simulations bearing aminofluorotriazine-type reactive dyes was investigated. It was particularly aimed at interpreting the kinetic behaviour of ozone by applying a simple fractional hydroxyl radical scavenger (carbonate/bicarbonate alkalinity) test at varying pH in the absence and presence of sodium carbonate. Complete decolorisation (first-order decolorisation rate constant k_D, 0.5-1.0 1/min at λ 436 nm) as well as partial mineralisation (TOC removal, 5-9%) and dearomatisation (UV₂₅₄ removal, 55-83%) could be achieved after 1 h of ozonation, whereas detoxification was only improved from ED₂₀ 30 to 53%. This study demonstrated that in the presence of sodium carbonate, neither molecular ozone nor hydroxyl radicals play an important role in dye oxidation. It has been proposed that other free radicals (carbonate or bicarbonate radicals) might be the dominant oxidising agents.