Chemical Engineering Journal 128 (2007) 163–167 Competitive adsorption of reactive dyes from solution: Equilibrium isotherm studies in single and multisolute systems Y. Al-Degs a , M.A.M. Khraisheh b , S.J. Allen c , M.N. Ahmad c , G.M. Walker c,∗ a Chemistry Department, The Hashemite University, P.O. Box 150459 Zarqa, Jordan b Department of Civil and Environmental Engineering, University College of London, Gower Street, London WCIE 6BT, UK c The Queen’s University of Belfast, School of Chemistry and Chemical Engineering, David Keir Building, Stranmillis Road, BT9 5AG Northern Ireland, UK Received 28 March 2006; received in revised form 15 September 2006; accepted 7 October 2006 Abstract Experimental data of the adsorption of reactive dyestuffs onto Filtrasorb 400 activated carbon (FS400) were determined in an equilibrium isotherm study. As most industrial wastewater contains more than one pollutant, an investigation into the effect of multisolute systems (using the unhydrolysed form of the reactive dyes) on the adsorption capacity was undertaken. Equilibrium isotherm models were employed to describe the adsorption capacities of single, binary and ternary dye solutions. The results of these analyses showed that adsorption of reactive dyes from single and multisolute systems can be successfully described by Langmuir, and Redlich–Peterson equilibrium isotherm models. Experimental data indicated that competitive adsorption for active sites on the carbon surface results in a reduction in the overall uptake capacity of the reactive dyes investigated. © 2006 Elsevier B.V. All rights reserved. Keywords: Reactive dyes; Competitive adsorption; Langmuir isotherm 1. Introduction Waste effluent from the textile industry can be particularly problematic due to the presence of colour in the final effluent. This colour on entering the waterways is highly visible and thus undesirable. Conventional treatment facilities are often unable to remove certain forms of colour, particularly arising from reactive dyes due to their high solubility and low biodegradability. The failure of conventional physiochemical methods as a technique for treating reactive dye waste could be overcome by adsorption. Hence, adsorption is recommended as a viable means for reactive dye removal [1,2]. Reactive dyes are characterised by nitrogen-to-nitrogen dou- ble bonds, azo bonds (N N), and used mainly for dyeing cellu- lose fibres. The colour of the azo dyes is due to this azo bond and associated chromophores [3]. The dyes are first absorbed onto the cellulose and then react with the fibre. The reaction occurs by the formation of a covalent bond between the dye molecule and the fibre. The reactive systems of these dyes react with ionised hydroxyl groups on the cellulose substrate [4]. How- ∗ Corresponding author. Tel.: +44 2890 974172; fax: +44 2890 974627. E-mail address: g.walker@qub.ac.uk (G.M. Walker). ever, hydroxyl ions present in the dye bath due to alkaline dyeing conditions compete with the cellulose substrate, resulting in a percentage of hydrolysed dyes which can no longer react with the fibre [5] and [4]. Activated carbon adsorption is widely used in the chemi- cal process industries and is playing important role in cleaning up plant effluent and municipal wastewater. Within literature a numerous number of research papers have considered adsorption processes for single component systems. However, due to com- plexity of the textile effluent and the variability of the dyeing process little successes have been reported in using this tech- nique as a full scale process to decolourise textile wastewater [1,6–9]. Hence, this study was undertaken to address the prob- lems associated with multi component adsorption from aqueous solutions. This is essential for accurate design of adsorption sys- tems as the effect of multicomponent interactions in the process effluent may cause deterioration in the adsorption capacity of activated carbon for dyestuffs. 2. Experimental 2.1. Carbon and dyes Filtrasorb 400 activated carbon (FS400) was used as obtained from manufacturers (Chemviron) without any chemical or phys- 1385-8947/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.cej.2006.10.009