Studying Fenton oxidation kinetics of mixed dyes wastewater and salt effect by online spectrophotometry

Fenton oxidation is an efficient process for dye wastewater treatment. Dye processing wastewater containing both Rhodamine B (RhB) and Methylene Blue (MB) dyes was treated by Fenton oxidation and analyzed using fast online spectrophotometry. The RhB and MB molecules were simultaneously decomposed by Fenton oxidation. The best experimental conditions for highest dye degradation were found to be 10 mg/L of FeSO4, 20 mg/L of H2O2 and a solution pH of 3. Under these conditions, nearly 100% color removal and 53% removal of chemical oxygen demand were achieved after 30 min of Fenton oxidation. It was found that the presence of NaCl had a negative effect on the color removal. Compared with the Fe2+/H2O2 process, the Fe3+/H2O2, Cu2+/H2O2 and Co2+/H2O2 Fenton-like processes showed very low dye removal efficiency. A first-order model and hyperbola model were used to describe the reaction kinetics. The hyperbola model showed outstanding performance in the description of the dye degradation with fitting coefficients of over 0.95. Based on the hyperbola model, the reactive activation energies of the RhB and MB degradation by the Fenton process were found to be 33.64 and 33.86 kJ/mol, respectively, with an Arrhenius fitting coefficient of over 0.99.