Effect of Fenton’s reagent on the degradability of CI Reactive Yellow 15 Zeynep Eren* and Filiz Nuran Acar Environmental Engineering Department, Engineering Faculty, Ataturk University, Erzurum 25240, Turkey Email: zeren@atauni.edu.tr Received: 30 January 2006; Accepted: 2 June 2006 As an advanced oxidation method, Fenton’s reagent has an advantage that it combines both oxidation and coagulation techniques. The aim of this study was to efficiently operate Fenton’s reagent oxidation to degrade a reactive dye, CI Reactive Yellow 15, which is non-biodegradable and has high chemical oxygen demand. In addition, performance of the Fenton oxidation process for dye solution was determined by measuring the chemical oxygen demand and colour removal. The influence of the main operating parameters, iron sulphate and hydrogen peroxide concentration, pH, temperature and dye concentration have been studied, in a batch-type operation. The results obtained show that the best pH value for decolorisation was pH 3, with an average decolorisation of 98.7% and average removal of chemical oxygen demand ca. 93.3% at 15 °C for a 0.065 molar ratio of Fenton’s reagent. An increase in temperature resulted in higher removal rates. Introduction Textile industry wastewater contains large amounts of dyestuff [1]. There are many kinds of dyestuffs on the market for various applications and they can generally be characterised into vat, reactive, direct, acid, disperse and cationic dyes [2]. The large consumption of reactive dyes in the textile industry and the practice of discharging exhausted dyebaths with residuals of unfixed dyestuff and spent chemicals result in a great problem for environmental engineers and water quality managers [3]. The presence of unfixed dye in textile effluent is an environmental problem not only because these dyes are relatively resistant to conventional treatment methods, but also because some of them produce carcinogenic by-products [4]. Thus, the ecosystem of streams can be seriously affected [5]. Other pollutants from dyeing are characterised by high levels of chemical oxygen demand, colour and concentration of suspended solids [6]. As discharge standards are becoming more stringent, the development of technological systems for minimising the concentration of dyes and their breakdown products in wastewater is necessary [7]. In the past two decades, advanced oxidation processes involving hydroxyl radicals as the primary oxidant have emerged as a promising new technology for the degradation of organic pollutants [8]. In these processes, Fenton’s reagent is known to be a very effective process in the removal of many hazardous organic pollutants from wastewater. The main advantage is the complete destruction of contaminants to harmless compounds, e.g. carbon dioxide, water and inorganic salts. The Fenton reaction causes the dissociation of the oxidant and the formation of highly reactive hydroxyl radicals ( • OH) that attack and destroy the organic pollutants [9]. Research has demonstrated that the oxidation mechanism using Fenton’s reagent involved the reactive hydroxyl radical generated in an acidic solution by the catalytic decomposition of hydrogen peroxide. Its mechanism is given in Eqns 1–5 [10]. H 2 O 2 þ Fe 2þ ! Fe 3þ þ  O þ  OH ð1Þ RH þ  OH ! R  þ H 2 O ð2Þ R  þ Fe 3þ ! R þ þ Fe 2þ ð3Þ Fe 2þ þ  OH ! Fe 3þ þ  OH ð4Þ R þ þ H 2 O ! ROH þ H þ ð5Þ The hydroxyl radical attacks the organic compounds, RH and decomposes them chemically. The Fenton oxidation process has the advantages of both oxidation and coagulation processes. Thus, ferric ions formed during redox reactions and the remaining decolorised dye molecules in wastewater can be coagulated and precipitated. In the literature, there are many studies on degradation of dye and organic material by Fenton oxidation with vat blue BO [2], azo dye [6], Reactive Black 5 [11], trihalomethanes [12], phenol [13] and atrazine [14]. Among the commercial dyes used for textile applications, reactive dyes are of great environmental concern because of their widespread use. Additionally, these dyes are the most problematic pollutants of textile wastewater because they have an azo group consisting of two nitrogen atoms (N¼N) which is non- biodegradable for conventional biological treatment methods [15]. Decolorisation of wastewater, polluted with reactive dyes, is closely related to the cleavage of C¼C and N¼N double bonds or heterocyclic and aromatic rings [16]. In this study, Fenton oxidation (FeSO 4 /H 2 O 2 ) was used to degrade a commercial reactive dye, CI Reactive Yellow 15. The optimal Fenton oxidation conditions, e.g. dye, H 2 O 2 and FeSO 4 concentration, pH and temperature were determined by examining the removal of colour and COD. doi: 10.1111/j.1478-4408.2006.00036.x ª 2006 The Authors. Journal compilation ª 2006 Society of Dyers and Colourists, Color. Technol., 122, 259–263 259