Chemical Engineering Journal 166 (2011) 662–668 Contents lists available at ScienceDirect Chemical Engineering Journal journal homepage: www.elsevier.com/locate/cej Wastewater treatment of reactive dyestuffs by ozonation in a semi-batch reactor M.T.F. Tabrizi ∗ , D. Glasser, D. Hildebrandt Centre of Material and Process Synthesis, School of Chemical and Metallurgical Engineering, University of the Witwatersrand, Private Bag 3, WITS 2050 Johannesburg, South Africa article info Article history: Received 3 August 2010 Received in revised form 7 November 2010 Accepted 8 November 2010 Keywords: Advanced oxidation Ozonation Reactive dye Bath effluent Wastewater Semi-batch abstract Water is quickly becoming both scarce and very expensive. Thus, it has become necessary for every industry to examine proposals for the purification and re-use of their wastewater and effluent streams. The Textile industry is one of the largest industrial consumers of water. Predominantly, wastewater from textile industry contains large amounts of dye and dyeing agents, as well as mordant and sizing agents. Current advanced oxidation processes (AOPs) which include ozone, photochemical and photo cat- alytic oxidation are techniques used for the treatment of such wastewater. Although AOPs are relatively expensive, they appear to be the most likely candidates for full-scale dye house effluent decolouration. The ozonation of wastewater containing four different textile reactive dyestuffs in a semi-batch reactor have been studied. Various ozonation conditions – ozone dose, ozone consumption efficiency, etc. – were explored and studied for these various types of dyestuffs. The mass transfer coefficient of ozone in water and its relationship to the ozone efficiency was studied. Pseudo-first order decolouration rate constants for all dyestuffs were determined experimentally. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Water is considered as the most constructive and in terms of volume, the leading solvent in textile manufacturing. During the wet processing steps, large amounts of water has to be used in the textile manufacturing for methods such as sizing and desizing, bleaching, mercerising, dyeing, printing and finishing of fabrics and dyed yarns. The major industrial consumers of water are textile mills. To create 1 kg of finished goods in textile industry, nor- mally 0.2–0.5 m 3 of water is required. The chemical and mechanical action during processing is used to treat most impurities that are in the form of dirt, salts, oil, greases, and colours of natural fibres, used and dead dyestuffs, chemicals, polymers and fibres. Textile manufacturing as well as many other industries including phar- maceutical, food, paper and ink manufacturing use over 30 000 industrial dyes with 8000 varying chemical structures and more often than not they are released in waste water [1]. Approximately 10–20% of the dyes used in textile manufacturing do not adhere to the fibres during the dyeing process and are therefore discharged into the aquatic atmosphere [2]. These potentially toxic organic and mineral compounds form wastewater which is returned to the environment [3–5]. Due to water resources being very limited, costly and with many governments initiating more stringent governmental regulations, it is necessary for every industry to formulate and study suggestions ∗ Corresponding author. Tel.: +27 834583456; fax: +27 880118800373. E-mail address: tabrizisa@gmail.com (M.T.F. Tabrizi). for purification of their wastewater treatment and effluent streams [6]. The advanced oxidation process (AOPs) is presently the most applicable technology for full-scale dye house sewage decolourisa- tion [7]. Hydroxyl radicals are believed to be the most important oxidants for the degradation of these biological wastes in the AOPs [8]. Ozonation one of the advanced oxidation processes (AOPs) is considered by many as the most competent treatment application for effluent decolourisation [9–16]. It is also possible for dye formulas to include auxiliary ingre- dients for desizing, scouring, mercerising and so on. Colour and salts may remain virtually unaltered when typical organic treat- ment techniques are employed and these substances, along with heavy metals, can be lethal to aquatic life [17,18]. Therefore, it must be recognised that manufacturing textile wastewater is an intri- cate combination of compounds and non-living salts which must be cleansed using cutting edge purification techniques [19]. In the present work, four representative reactive dyestuffs groupings were hydrolyzed and ozonated to the point of complete colour removal. The mass transfer coefficient for the dissolution of the ozone in the water was also measured as was the stoichiometry for one dye. 2. Materials and methods 2.1. Reactive dye and synthetic dye effluent Four reactive dyestuffs (Table 1) were provided as samples by Dye Star (Durban, South Africa). 1385-8947/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.cej.2010.11.043