Advanced oxidation of a reactive dyebath effluent: Comparison of O₃, H₂O₂/UV-C and TiO₂/UV-A processes

In the present study the treatment efficiency of different AOPs (O₃/OH^-, H₂O₂/UV-C and TiO₂/UV-A) were compared for the oxidation of simulated reactive dyebath effluent containing a mixture of monochlorotriazine type reactive dyes and various dye auxiliary chemicals at typical concentrations encountered in exhausted reactive dyebath liquors. A₅₂₅ (color), UV₂₈₀ (aromaticity) and TOC removal rates were assessed to screen the most appropriate oxidative process in terms of reactive dyebath effluent treatment. Special emphasis was laid on the effect of reaction pH and applied oxidant (O₃, H₂O₂) dose on the observed reaction kinetics. It was established that the investigated AOPs were negatively affected by the Na₂CO₃ content (=867mg/L) which is always present at high concentrations in dyehouse effluents since it is applied as a pH buffer and dye fixation agent during the reactive dyeing process. The ozonation reaction exhibited almost instantaneous decolorization kinetics and a reasonable TOC reduction rate. It appeared to be stable under the investigated advanced oxidation conditions and outranked the other studied AOPs based on the above mentioned criteria. Besides, the electrical energy requirements based on the EE/O parameter (the electrical energy required per order of pollutant removal in 1m³ wastewater) was calculated for the homogenous AOPs in terms of decolorization kinetics. In view of the electrical energy efficiency, ozonation and H₂O₂/UV-C oxidation at the selected treatment conditions appear to be promising candidates for full-scale dyehouse effluent decolorization.