Journal of the Taiwan Institute of Chemical Engineers 51 (2015) 152–158 Contents lists available at ScienceDirect Journal of the Taiwan Institute of Chemical Engineers journal homepage: www.elsevier.com/locate/jtice Modeling and optimization of Reactive Green 19 oxidation on a BDD thin-film electrode Elisabetta Petrucci, Luca Di Palma, Roberto Lavecchia, Antonio Zuorro ∗ Department of Chemical Engineering Materials & Environment, Sapienza – University of Rome, Via Eudossiana 18, 00184 Rome, Italy article info Article history: Received 4 November 2014 Revised 28 December 2014 Accepted 6 January 2015 Available online 7 February 2015 Keywords: Reactive Green 19 Azo dye BDD electrode Response surface methodology Color removal TOC removal abstract A membrane-free electrochemical reactor with a boron-doped diamond (BDD) anode was used to degrade Reactive Green 19 (RG19), an azo dye widely used in the textile industry. Oxidation experiments were carried out under galvanostatic conditions according to a central composite design. The factors investigated were current density (100–500 A/m 2 ), pH (3–11), chloride concentration (0–0.5 M) and agitation rate (250– 750 rpm), while the response variables were the efficiencies of color and TOC removal. Color removal was strongly affected by chloride concentration and, to a lesser extent, by current density and stirring rate. In contrast, current density was the factor with the greatest influence on TOC removal, followed by pH and chloride concentration. Under optimal degradation conditions, the efficiencies of color and TOC removal reached values close to 90% and 80%, respectively. Taken together, the results of this study suggest that the anodic oxidation of RG19 on a BDD thin-film electrode can be a suitable method to degrade this dye, once the optimum operating conditions have been established. © 2015 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved. 1. Introduction Azo dyes constitute the largest class of synthetic dyes used in the textile, paper, leather and plastic industries, with the textile sec- tor accounting for over 70% of the total dyestuff market [1]. During textile dyeing, large amounts of dye are lost in water due to poor fixation on the fibers and the competitive hydrolysis reaction [2]. In some cases, such as the dyeing of cellulosic fabrics with sulfonated azo dyes, dye losses can reach values as high as 50% [3]. Being specif- ically designed to withstand long-term exposure to environmental conditions and repeated washings, azo dyes are highly resistant to light, microbial attack and most oxidizing agents. Accordingly, treat- ment of dyeing wastewater by conventional biological (e.g., activated sludge) or physico-chemical (e.g., adsorption, flocculation, oxidation) methods is often inadequate or economically unfeasible [4]. In addition to the negative aesthetic impact on receiving waters, the release of azo dyes into the environment is of great concern due to their toxic, mutagenic and carcinogenic properties [5,6]. These rea- sons and the introduction of increasingly stringent environmental regulations have prompted researchers to investigate more efficient methods for the treatment of textile effluents. Among them, photocat- alytic [7,8] and electrochemical [9,10] technologies such as electro- Fenton (EF) and anodic oxidation (AO) processes, have received great ∗ Corresponding author. Tel.: +39 06 44585598; fax: +39 06 4827453. E-mail address: antonio.zuorro@uniroma1.it (A. Zuorro). attention due to their versatility, environmental compatibility and the possibility to operate under mild conditions. The boron-doped diamond (BDD) electrode is considered an ideal anode for the electrochemical oxidation of organic compounds [11–13]. It possesses a number of attractive features, including a wide electrochemical potential window, low background current, high chemical inertness and long-term response stability [14]. Fur- thermore, it allows the production of large amounts of highly reac- tive hydroxyl radical ( • OH) species that are weakly absorbed on the electrode surface [15]. Recently, some investigations have been per- formed on the use of BDD electrodes for the removal of synthetic dyes from aqueous solution [16–19] and real wastewater [20]. The results of these studies indicate that the oxidation of azo dyes on BDD electrodes is affected by many factors including, among others, pH, temperature, agitation rate, dye and chloride concentrations, and that the process needs to be properly optimized in order to achieve high removal efficiencies [18,19,21]. In particular, while the chromophoric groups in the dye molecule can be relatively easily destroyed, leading to fast decolorization of the solution, complete dye mineralization is more difficult to achieve and requires more severe treatments. In this paper we investigate the degradation of Reactive Green 19 (RG19) on a BDD thin-film electrode. Because of its cost effective- ness and excellent wash and light fastness properties, the use of this dye in the textile industry has increased steadily over the last few years. However, RG19 is extremely resistant to degradation and most attempts to remove it from aqueous solution by microbial [22], pho- tocatalytic [23] or UV/H 2 O 2 [24,25] methods have met only limited http://dx.doi.org/10.1016/j.jtice.2015.01.005 1876-1070/© 2015 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.