Journal of Photochemistry and Photobiology A: Chemistry 161 (2003) 87–93 Oxidation of commercial reactive azo dye aqueous solutions by the photo-Fenton and Fenton-like processes Mariana Neamtu a,b,∗ , Ayfer Yediler a , Ilie Siminiceanu b , Antonius Kettrup a,c a GSF-National Research Center for Environment and Health, Institute of Ecological Chemistry, Ingolstaedter Landstrasse 1, 85764 Neuherberg, Germany b Technical University of Iasi, Faculty of Industrial Chemistry, 71 Bd. D. Mangeron, 6600 Iasi, Romania c Technical University of Munich, Chair of Ecological Chemistry, 85350 Freising-Weihenstephan, Germany Received 15 May 2003; received in revised form 15 May 2003; accepted 21 May 2003 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 2 O 2 > UV/Fe(II)/H 2 O 2 > UV/Cu(II)/Fe(III)/H 2 O 2 > UV/Fe(III)oxalate/H 2 O 2 > UV/Fe(III)/H 2 O 2 > dark/Fe(II)/H 2 O 2 > solar/Fe(III)oxalat/H 2 O 2 > UV/H 2 O 2 > UV/Fe(II) = UV. During the same reaction period the relative order for RR120 removal rate was slightly different: solar/Fe(II)/H 2 O 2 > UV/Fe(II)/H 2 O 2 > UV/Fe(III)/H 2 O 2 = UV/Cu(II)/Fe(III)/H 2 O 2 > UV/Fe(III)oxalate/H 2 O 2 = UV/H 2 O 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. © 2003 Elsevier B.V. All rights reserved. Keywords: Azo dyes; Photo-Fenton; Decolourization; UV; Solar light 1. Introduction There are several methods currently used to decolorize textile wastewater [1] but they are not universally applicable and they are not cost-effective for all dyes. The azo dyes contained in industrial dye wastewaters could be treated by adsorption onto activated carbon or by chemical coagulation. Unfortunately, these classic methods mainly transferred the contaminant from wastewater to solid wastes. Advanced oxidation processes (AOP), such as the H 2 O 2 /UV, O 3 /UV, and H 2 O 2 /O 3 /UV procedures, employ UV photolysis of H 2 O 2 and/or O 3 in order to generate HO radicals. These oxidation methods can be considered as a potential alternative in decolorizing the textile dyeing and finishing effluents [2–4]. However, the high electrical en- ergy demand and/or the consumption of chemical reagents ∗ Corresponding author. Tel.: +49-89-3187-2675; fax: +49-89-3187-3371. E-mail address: neamtu@gsf.de (M. Neamtu). are common problems among all the AOPs. Specially, the production of photons with artificial light sources require an important energy input [5]. Fenton-type reactions using H 2 O 2 as an oxidant in the presence of iron ions at acidic pH have been among the most common homogeneous systems [6,7]. The main advantage of Fenton’s reaction compared to other AOPs is that this sys- tem offers a cost effective source of hydroxyl radicals and it is easy to operate and maintain. It is particularly advanta- geous in situation where textile wastewater contains a high concentration of suspended solids due to the limited depth of photon penetration. The generation of hydroxyl radicals from H 2 O 2 in pres- ence of Fe(II) has been shown to be enhanced in the presence of light. Under irradiation, Fe 3+ ions are constantly reduced to Fe 2+ and the Fenton reaction is improved by the partic- ipation of photogenerated Fe 2+ . In the presence of H 2 O 2 , the photo-Fenton reaction is continuously promoted. Kang et al. [8] reported that the Fenton process could be adopted readily in a textile wastewater treatment system, 1010-6030/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/S1010-6030(03)00270-3