Chemical Engineering Journal 155 (2009) 62–67 Contents lists available at ScienceDirect Chemical Engineering Journal journal homepage: www.elsevier.com/locate/cej Electro-Fenton decoloration of dyes in a continuous reactor: A promising technology in colored wastewater treatment E. Rosales, M. Pazos, M.A. Longo, M.A. Sanromán ∗ Department of Chemical Engineering, University of Vigo, Isaac Newton Building, Campus As Lagoas, Marcosende 36310, Vigo, Spain article info Article history: Received 13 March 2009 Received in revised form 11 June 2009 Accepted 18 June 2009 Keywords: Bubble reactor Continuous reactor Dye Electro-Fenton treatment Effluent Kinetic abstract This study focuses on the application of Electro-Fenton technique for the remediation of wastewater contaminated with synthetic dyes. A bubble reactor was designed to develop this treatment operating in continuous mode. In order to increase the efficiency of Electro-Fenton treatment, the effect of key parameters (iron dosage and pH) that play an important role in this process was investigated for Lissamine Green B decoloration in batch mode. Operating at the optimal conditions, determined for Lissamine Green B, several dyes (Methyl Orange, Reactive Black 5 and Fuchsin Acid) were decolorized by using Electro- Fenton process. A first-order kinetic model was used to simulate the experimental results operating at different pH, and iron concentration of 150 mg L -1 . This kinetic model for Lissamine Green, Methyl Orange and Reactive Black 5 was successfully used in the progression of the process from batch to continuous mode. About 80% color removal was achieved for Lissamine Green and Methyl Orange with a residence time of 21h. The decoloration for Reactive Black 5 was lower, reached a value around 60% at the same residence time. Nevertheless in all assays a good agreement between experimental results and proposed model in a continuous bubble reactor was detected. In addition a continuous treatment with a mixture of dyes was carried out. Operating with a residence time of 21h the obtained decoloration was close to 43% which is squared with a TOC reduction around 46%. Therefore, the results provide fundamental knowledge for the treatment of a real wastewater stream. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Synthetic dyes are used to color many different products such as textiles, paper, cosmetics and drugs [1]. The discharge of these colored compounds in the environment causes considerable non- aesthetic pollution and serious health-risk factors [2]. Conventional wastewater treatment plants cannot degrade the majority of these pollutants and generating large volumes of sludge, thus causing secondary loading of environmental pollutants [3,4]. Advanced oxidation processes (AOPs) offer effective and rapid alternative treatments for various contaminants. The AOPs are based on the in situ generation of hydroxyl radicals ( • OH), a highly powerful oxidizing agent, and are effective in treatment of per- sistent organic pollutants aqueous solutions until their overall mineralization [5]. Among these AOPs, the Fenton reaction with hydrogen peroxide and transitional metals, especially the ferrous ion, in an acidic aqueous system has been investigated in numer- ous studies [6]. However, this system generally offers effective contaminant removal only at high rates of hydrogen peroxide ∗ Corresponding author. Tel.: +34 986 812383; fax: +34 986 812380. E-mail address: sanroman@uvigo.es (M.A. Sanromán). and soluble iron consumption due to the stoichiometric reaction [7]. Currently, some research groups have reported Electro-Fenton oxidation offering significant advantages as well as solving prob- lems, without requirement for special equipment, and high efficiency in organic pollutants removal [8–10]. Electro-Fenton process consists of treating wastewater in situ with H 2 O 2 electro- generated in the presence of catalytic amounts of Fe(II) [11]. According to Fenton’s reaction (Eq. (1)), hydroxyl radicals ( • OH) are formed. These radicals are high oxidant species, they attack most organic molecules with rate constants usually in the order of 10 6 –10 9 L mol -1 s -1 [12]: Fe 2+ + H 2 O 2 + H + → Fe 3+ + H 2 O + • OH (1) This new hybrid technology employs the electricity which is a clean energy source so the overall process does not create secondary pollutants and is compatible with the environment [13]. Furthermore, in situ generation of H 2 O 2 avoids the need for transport and storage of this hazardous substance, offers safer oper- ation by virtue of providing diluted H 2 O 2 solutions, enhances the mixing of solution [11]. There are many reports on Electro-Fenton process application for the degradation of phenol [14], aniline [15] and azo dyes [10,16]. Nevertheless to our knowledge there is no application of this hybrid 1385-8947/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.cej.2009.06.028