Importance of H2O2/Fe2+ ratio in Fenton's treatment of a carpet dyeing wastewater

The effectiveness of the Fenton's reagent (H2O2/Fe2+) in the treatment of carpet dyeing wastewater was investigated under different operational conditions, namely, H2O2 and FeSO4 concentrations, initial pH and temperature. Up to 95% COD removal efficiency was attained using 5.5 g/l FeSO4 and 385 g/l H2O2 at a pH of 3, temperature of 50 °C. The H2O2/Fe2+ ratio (g/g) was found to be between 95 and 290 for maximum COD removal. It was noteworthy that, keeping H2O2/Fe2+ ratio constant within the range of 95–290, it became possible to decrease FeSO4 concentration to 1.1 g/l and H2O2 concentration to 96.3 g/l, still achieving nearly the same COD removal efficiency. The relative efficiencies of Fenton's oxidation and coagulation stages revealed that Fenton's coagulation removed organic compounds which were not removed by Fenton's oxidation, indicating that the Fenton's coagulation acted as a polishing step.