Oxidation of commercial reactive azo dye aqueous solutions by the photo-Fenton and Fenton-like processes

Abstract

This paper evaluates the degradation of two azo reactive dyes, C.I. Reactive Yellow 84 (RY84) and C.I. Reactive Red 120 (RR120) by photo-Fenton and Fenton-like oxidation. All experiments were performed on a laboratory scale set-up. The effects of different reaction parameters such as initial pH, contact time, effect of light and hydrogen peroxide concentrations on the oxidation of the dye aqueous solutions have been assessed. Effective system conditions were found to be pH of 3, hydrogen peroxide-to-iron molar ratio of 20:1 and UV or solar irradiation. The color removal efficiency at the optimum conditions during different Fenton-like processes was also evaluated. The results show that the color removal of RY84 after 15 min reaction time follows the decreasing order: solar/Fe(II)/ H 2O 2>UV/Fe(II)/ H 2O 2>UV/Cu(II)/Fe(III)/ H 2O 2>UV/Fe(III)oxalate/H 2O 2>UV/Fe(III)/ H 2O 2>dark/Fe(II)/ H 2O 2>solar/Fe(III)oxalat/H 2O 2>UV/H 2O 2>UV/Fe(II)=UV. During the same reaction period the relative order for RR120 removal rate was slightly different: solar/Fe(II)/ H 2O 2>UV/Fe(II)/ H 2O 2>UV/Fe(III)/ H 2O 2=UV/Cu(II)/Fe(III)/ H 2O 2>UV/Fe(III)oxalate/H 2O 2=UV/H 2O 2>UV. The toxic potential of the dye’s degradation was investigated by the bioluminescence test using the LUMIStox 300 instrument and results were expressed as the percentage inhibition of the luminescence of the bacteria Vibrio fisheri. Formate and oxalate, identified as fragmental oxidation products of investigated dyes, could also be detected after 15 min irradiation time.