Development of a rate expression for predicting decolorization of C.I. Acid Black 1 in a UV/H 2 O 2 process Hung-Yee Shu * , Ming-Chin Chang Department of Environmental Engineering, Hungkuang University, No. 34 Chung-Chie Road, Shalu, Taichung County 433, Taiwan, ROC Received 23 September 2004; received in revised form 14 April 2005; accepted 24 April 2005 Available online 21 June 2005 Abstract A kinetic rate expression was developed by the experimental results of photochemical reactions that decolorize model azo dye, C.I. Acid Black 1. The decolorization was efficient by UV irradiation with hydrogen peroxide addition. The observed reaction rate constants were determined and correlated as a function of volumetric UV dosage and initial hydrogen peroxide concentration. The decolorization rate follows pseudo-first order kinetic with respect to dye concentration. The rate increases linearly by volumetric UV dosage, yet nonlinearly by hydrogen peroxide concentration. The proposed rate expression model, which considers both the kinetic mechanism and operation parameters, can predict the experimental results well. The prediction and experimental data are in a very good agreement. Besides, this model also integrates the correlation of pH and initial dye concentration in order to enlarge more versatile applications while various dye concentrations and pH range in the real case. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Rate expression equation; Azo dye; Decolorization; UV/H 2 O 2 ; AOPs; Oxidation 1. Introduction Textile industry is one of the most important industries among Taiwan’s economics since last few decades. There are about 10,000 dyes used in textile industry. Among these dyes, azo dyes constitute the largest and the most important class of commercial dyes. Effluents of textile dyeing and finishing industries often contain high intensity of color and high chemical oxygen demand (COD), which are objectionable if they were discharged without proper treatment. Therefore, the efficient treatment of dyeing and finishing wastewater becomes the major environmental concern of textile industries. The Taiwan EPA issues stricter effluent standards to enforce textile industries decolorize and eliminate pollutants in wastewater before discharge to surface water. Because of the regulatory enforcement, technol- ogies of dye wastewater decolorization become more and more important. The textile dyeing and finishing wastewater contaminated with azo dyes was typically treated in a conventional wastewater treatment system. Textile dyestuffs have complicated aromatic structures which resist degradation in biological system. It was first reported by U.S. Water Engineering Research Labora- tory of EPA that 11 out of 18 studied azo dyes were substantially unaffected by the activated sludge process [1]. Further studies on biodegradability showed that azo dyes were very difficult to biodegrade under aerobic conditions [2,3]. Consequently, alternative technologies to treat these refractory azo dyes have to be explored. Advanced oxidation processes (AOPs) are widely used to decompose various hazardous organics in industrial * Corresponding author. Tel.: C886 4 26318652/4111; fax: C886 4 26525245. E-mail address: hyshu@sunrise.hk.edu.tw (H.-Y. Shu). 0143-7208/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.dyepig.2005.04.002 Dyes and Pigments 70 (2006) 31e37 www.elsevier.com/locate/dyepig