Experimental design to optimize the degradation of the synthetic dye Orange II using Fenton’s reagent J. Herney Ramirez, Carlos A. Costa, Luis M. Madeira * LEPAE-Departamento de Engenharia Quı ´mica, Faculdade de Engenharia da Universidade do Porto, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal Available online 22 August 2005 Abstract The experimental design methodology was applied having in mind the optimization of the azo dye Orange II degradation using the Fenton’s reagent (mixture of H 2 O 2 and Fe 2+ ). The variables considered were the temperature, H 2 O 2 concentration and Fe 2+ :H 2 O 2 ratio, for a dye concentration of 0.3 mM and pH 3. The multivariate experimental design allowed to develop quadratic models for: (i) color removal and (ii) total organic carbon (TOC) reduction (both after 2 h of reaction), which were adequate to predict responses in all the range of experimental conditions used. Under the optimum conditions, performances of 99.7 and 70.7% for color and TOC removal, respectively, were experimentally reached. It was found that both H 2 O 2 concentration and temperature have an important effect in the organic matter degradation efficiency. # 2005 Elsevier B.V. All rights reserved. Keywords: Experimental design; Orange II; Fenton’s reagent; Hydrogen peroxide; Oxidation 1. Introduction The textile industry, of great importance in the Portuguese economy, produces large quantities of effluents that contain significant concentrations of organic matter. These wastewaters often contain some color after treatment, being then directly launched into the rivers and others water courses. However, more problematic than the aesthetic aspect is the environmental impact that a discharge of this type of compounds has, because some of them are toxic for certain species [1]. Therefore, the removal/degradation of dyes from wastewaters is a great challenge for the related industries. The main currently used techniques for decontamination of waters proceeding from the textile industry involve adsorption processes with activated carbon. However, these processes may be costly, inefficient and often produce a high amount of secondary wastes. Ozone and hypochlorite oxidations are efficient decolorizing methods, but they are not desirable because of the high cost of equipment, operating costs and the secondary pollution arising from the residual chlorine [2]. Recent progress in the removal of dyes has led to the development of advanced oxidation processes (AOPs). Among them, the oxidation using Fenton’s reagent has proved to be a promising and attractive treatment method for the effective decolorizing and degradation of dyes, as well as for the destruction of a large number of hazardous and organic pollutants [1–4]. Besides, the process is simple and non-expensive, taking place at low temperatures and atmospheric pressure [5]. Oxidation with Fenton’s reagent is based on ferrous ion and hydrogen peroxide, and exploits the very high reactivity of the hydroxyl radical produced in acidic solution by the catalytic decomposition of H 2 O 2 [6]: Fe 2þ þ H 2 O 2 ! Fe 3þ þOH  þOH  (1) However, to achieve high performances, the experimental conditions must be optimized. And this is not an easy task since in Fenton oxidation several parameters affect the oxidation efficiency, like the pH of the reaction medium, the temperature, the hydrogen peroxide concentration and www.elsevier.com/locate/cattod Catalysis Today 107–108 (2005) 68–76 * Corresponding author. Tel.: +351 22 5081519; fax: +351 22 5081449. E-mail address: mmadeira@fe.up.pt (L.M. Madeira). 0920-5861/$ – see front matter # 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.cattod.2005.07.060