Journal of Hazardous Materials 179 (2010) 113–119 Contents lists available at ScienceDirect Journal of Hazardous Materials journal homepage: www.elsevier.com/locate/jhazmat Removal of acid green dye 50 from wastewater by anodic oxidation and electrocoagulation—A comparative study E-S.Z. El-Ashtoukhy ∗ , N.K. Amin Chemical Engineering Department, Faculty of Engineering, Alexandria University, Alexandria, Egypt article info Article history: Received 7 October 2009 Received in revised form 14 January 2010 Accepted 22 February 2010 Available online 1 March 2010 Keywords: Electrochemical oxidation Electrocoagulation Decolourization Wastewater treatment Acid green dye abstract The present work represents a comparative study for removing acid green dye 50 by anodic oxidation and electrocoagulation using a new batch self gas stirred electrochemical cell. The effect of operating param- eters such as current density, initial dye concentration, NaCl concentration and pH on the efficiency of colour removal has been examined. The chemical oxygen demand (COD) reduction under suitable oper- ating conditions was also calculated and found to be reduced by 68% and 87% in case of electrochemical oxidation and electrocoagulation methods, respectively. The results indicate that electrocoagulation is more economic than anodic oxidation, energy consumption ranged from 2.8 to 12.8 kWh/kg dye removed in case of electrocoagulation while in case of anodic oxidation it ranged from 3.31 to 16.97 kWh/kg dye removed. Although the mechanisms of electrocoagulation and anodic oxidation are different, results show that the first-order rate equation provides the best correlation for the decolourization rate of acid green 50 by the two methods. © 2010 Elsevier B.V. All rights reserved. 1. Introduction The production of textiles represents one of the big consumers of high water quality. Textile industry actually represents a range of industries with operation and processes as diverse as its prod- ucts. Fabrics, after its manufacturing, are subjected to several wet processes collectively known as “finishing” and it is in these fin- ishing operations that the major waste effluents are produced [1]. Wastewater from textile dyeing and finishing factories is a significant source of environmental pollution because its high con- centration of organic compounds can damage seriously aqueous ecosystems. Textile wastewater is characterized by high chemical oxygen demand (COD), low biodegradability and high-salt con- tent. It is the source of aesthetic pollution related to colour. There are many processes to remove dyes from coloured effluents such as adsorption, precipitation, chemical degradation, photodegra- dation, biodegradation and chemical coagulation [2,3]. However, these processes are quite expensive and involve several oper- ational problems. For these reasons there has been increasing interest in the use of new methods. Electrochemical methods have advantages such as they require of no chemicals before and after treatment, thus producing no sludge, requirement of small area and low investment cost [4]. One of these methods is the electro- chemical oxidation of wastewater containing organic compounds ∗ Corresponding author. Tel.: +20 3 592555 203 5925557; fax: +20 3 59211853. E-mail address: elsayed elashtoukhy@hotmail.com (E.-S.Z. El-Ashtoukhy). [5–15]. In the electrochemical oxidation process, the pollutants are destroyed by either the direct or indirect oxidation process. In a direct anodic oxidation process, the pollutants are first adsorbed on the anode surface and then destroyed by the anodic electron transfer reaction. In an indirect process, strong oxidants such as hypochlorite/chlorine, ozone, and hydrogen peroxide are electro- chemically generated. The pollutants are then destroyed in the bulk solution by oxidation reaction of the generated oxidant [8]. In presence of chloride, oxidation of organic compounds is medi- ated by active chloro species. The main reactions at the electrodes are [16,17]: anode : 2Cl - → Cl 2 + 2e - (1) cathode : 2H 2 O + 2e - → H 2 + 2OH - (2) In the solution bulk Cl 2 hydrolysis takes place as follows: Cl 2 + H 2 O ↔ HOCl + H + + Cl - (3) HOCl ↔ H + + OCl - (4) At the anode O 2 evolution competes with Cl 2 evolution accord- ing to the reaction: H 2 O → 2H + + 1 2 O 2 + 2e (5) Electrocoagulation technique uses a direct current source between metal electrodes immersed in polluted water. The elec- trical current causes the dissolution of metal plates including iron or aluminum into wastewater. The metal ions, at an appropriate pH, 0304-3894/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jhazmat.2010.02.066