Ozonation of aqueous Bomaplex Red CR-L dye in a semi-batch reactor Ensar Oguz a, * , Bu¨lent Keskinler b , Zeynep C¸ elik c a Atatu ¨rk University Environmental Problems Research Center, 25240 Erzurum, Turkey b Gebze Institute of Technology, Environmental Engineering Department, 41400 C ¸ ayirova, Kocaeli, Turkey c Atatu ¨rk University, Environmental Engineering Department, 25240 Erzurum, Turkey Received 2 January 2004; received in revised form 12 March 2004; accepted 22 April 2004 Available online 19 July 2004 Abstract The ozonation of synthetic wastewater containing Bomaplex Red CR-L dye has been realized in a semi-batch reactor. In this study, the dye and COD removal from synthetic textile wastewater has been studied by ozonation as functions of initial dye concentration (400, 600, 800 and 1000 mg L ÿ1 ), temperature (18, 40 and 70  C), ozoneeair flow rate (5, 10 and 15 L min ÿ1 ), pH (3, 6, 9.3 and 12) and ozone generation percentage (0.7, 1.1 and 1.4 O 3 %). The efficiency of dye removal has increased with increasing pH, ozone generation rate, and decreased with increasing temperature, but not changed with increasing ozoneeair flow rate and initial dye concentration. The efficiency of COD removal from synthetic wastewater has increased with increasing pH, ozone generation percentage, but scarcely changed with increasing initial dye concentration and ozoneeair flow rate, but the efficiency of COD removal decreased with increasing temperature. In this study, dye removal from synthetic wastewater in excess of 99% was obtained at an oxidation time of 15 min. The efficiencies of COD removal were between 56 and 35% at an oxidation time of 30 min. At the end of the study, it was concluded that ozonization is an efficient process for dye removal from synthetic wastewater of Bomaplex Red CR-L, but alone ozonization was not an efficient method to remove all the COD from the textile wastewater. Ó 2004 Elsevier Ltd. All rights reserved. Keywords: Ozonation; Dye; Oxidation; Wastewater; COD 1. Introduction The oxidation potential of ozone (2.07 V) is 1.52 times higher than that of chlorine. The high oxidation potential allows it to degrade most organic compounds [7]. The oxidizing ability of ozone is derived from the third, or nascent, oxygen atom [1]. Ozone and hydroxyl radicals (OH c ) generated in the aqueous solution are able to open the aromatic rings. The use of ozone in textile effluent treatment appears as a very attractive alternative with considerable appli- cation potential. Ozone is a powerful oxidizing agent (E  = 2.08 V), and can react with several classes of compounds through direct or indirect reactions [12]. The chromophore groups generally are organic compounds with conjugated double bonds that can be broken by ozone (directly or indirectly) forming smaller molecules, which decrease the effluent color. The more complex environmental problems asso- ciated with the textile industry are due to wide utili- zation of carcinogenic or mutagenic reactive dyes, which are resistant to microbial degradation [5]. Some reactive dyes are either toxic or can be modified biologically to toxic or carcinogenic compounds [11]. The nonbiode- gradability of textile wastewater is due to its high content of dyestuffs, surfactants and additives. There are no universally useful methods available for treatment of dye wastes, probably because of the complex and very varied chemical structures of these compounds [11]. * Corresponding author. Tel.: C90 442 231 4601. E-mail address: eoguz@atauni.edu.tr (E. Oguz). 0143-7208/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.dyepig.2004.04.009 Dyes and Pigments 64 (2005) 101e108 www.elsevier.com/locate/dyepig