A fluidised-bed Fenton process was utilised for the homogeneous and heterogeneous Fenton degradation of three azo dyes: CI Reactive Black 5, CI Reactive Orange 16 and CI Reactive Blue 2. The effects of the concentration of Fe2+ and hydrogen peroxide on the decolorisation and degradation of the azo dyes were examined. More than 96% of colour removal of the azo dyes was achieved using the fluidised-bed Fenton process. Chemical oxygen demand (COD) removal of the three azo dyes followed pseudo-second-order kinetics at various Fe2+ and hydrogen peroxide concentrations. COD removal of the three azo dyes increased with increasing Fe2+ concentration and was more than 85%. In addition, the COD removal efficiency of the three types of azo dyes first increased and then decreased as the hydrogen peroxide concentration increased. Presumably, the scavenging effect of hydrogen peroxide on hydroxyl radicals occurs at high concentrations of hydrogen peroxide. The most efficient COD removal was found at 160220 mg/l hydrogen peroxide. More than 80% of the COD was eliminated at pH 3 in 20 mg/l Fe2+ and 160 mg/l hydrogen peroxide for CI Reactive Black 5, 25 mg/l Fe2+ and 160 mg/l hydrogen peroxide for CI Reactive Orange 16 and 20 mg/l Fe2+ and 160 mg/l hydrogen peroxide for CI Reactive Blue 2.
