Degradation and sludge production of textile dyes by Fenton and photo-Fenton processes Robert Liu a , H.M. Chiu a , Chih-Shiuc Shiau a , Ruth Yu-Li Yeh a , Yung-Tse Hung b, * a Department of Chemical Engineering, Ming Hsin University of Science and Technology, Hsin-chu 304, Taiwan, ROC b Department of Civil and Environmental Engineering, Cleveland State University, Cleveland, Ohio 44115-2214, USA Received 8 July 2005; received in revised form 13 September 2005; accepted 7 October 2005 Available online 23 November 2005 Abstract The degradation and decolorization of direct dye (Everdirect supra turquoise blue FBL), acidic dye (Isolan orange S-RL) and vat dye (Indanthrene red FBB) have been investigated by Fenton and UV/Fenton processes. The effects of solution pH, Fe 2þ dosages and H 2 O 2 dosages have been studied by jar-test experiments. A comparative study for Fenton and UV/Fenton reactions by photoreactor has also been carried out by scale-up the optimum conditions, obtained through jar-test experiments. Fenton process is highly efficient for color removal for three dyes tested and for TOC removal of FBB and FBL. UV/Fenton showed slighter increase in treatment efficiency than that of Fenton process for both FBB and FBL dye solutions. S-RL improved much more TOC removal% by UV-irradiation. Sludge productions were compared for FeCl 3 -, FeSO 4 - coagulation and Fenton reaction in order to prove the dual role of FeSO 4 in Fenton process. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: AOP (Advanced oxidation process); Fenton process; Photo-Fenton process; Free radicals 1. Introduction Wastewater from textile and dye industries [1] are highly polluted by suspended solids (SS), high chemical oxygen de- mand values (COD), high biochemical oxygen demand values (BOD), heat, acidity, basicity and other soluble substances. Most of pollutants, except color, can be reduced by chemical, physical or biological methods. Therefore, the color problem of some textile wastewater caused by the residual dyes during the dyeing process needs more effort to be studied and investigated. Conventional treatment methods in the textile dyeing indus- try for color removal include coagulation/flocculation, and activated carbon adsorption [1e6]. Both coagulation and adsorption generate large amounts of sludge and waste which need further treatment for disposal. Biotreatment is still considered as an appropriate method for meeting discharge standard but it still remains a color problem [7]. Also, ozona- tion [8e10] effectively decolorizes dyes but does not remove COD well and may produce exhausted ozone in the water and thereby, increase the cost of treatment. Recently, Fenton’s reagent (Fe 2þ /H 2 O 2 ) among AOPs is applied for treatment of dye wastewater [11e15]. It not only has the advantages of both coagulation and catalytic oxidation, but also generates oxygen in water. Hydrogen per- oxide reacts with Fe 2þ in acid media and thus forms an extremely efficient oxidizing agent. The most important part of the oxidizing agent, Fenton’s reagent, is the hydroxyl free radical, cOH. The oxidizing capacity of cOH exceeds that of ozone and is only slightly inferior to that of fluorine. Photo-Fenton, which is also a newly emerged AOP, has been applied to the treatment of dye stuffs [15e20]. This photoca- talytic degradation of dyes involves several pathways includ- ing reduction which makes it more important among AOPs [21e23]. * Corresponding author. Tel.: þ1 216 687 2596; fax: þ1 216 687 5395. E-mail address: yungtsehung@yahoo.com (Y.-T. Hung). 0143-7208/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.dyepig.2005.10.002 Dyes and Pigments 73 (2007) 1e6 www.elsevier.com/locate/dyepig