Adsorption (2007) 13: 159–169 DOI 10.1007/s10450-007-9017-5 Competitive adsorption and desorption of a bi-solute mixture: effect of activated carbon type Özgür Akta¸ s · Ferhan Çeçen Received: 29 March 2006 / Revised: 6 July 2007 / Accepted: 9 July 2007 / Published online: 8 September 2007 © Springer Science+Business Media, LLC 2007 Abstract This study aims to clarify the effects of carbon activation type and physical form on the extent of adsorp- tion capacity and desorption capacity of a bi-solute mix- ture of phenol and 2-chlorophenol (2-CP). For this pur- pose, two different PACs; thermally activated Norit SA4 and chemically activated Norit CA1, and their granular counter- types with similar physical characteristics, thermally acti- vated Norit PKDA and chemically activated Norit CAgran, were used. The thermally activated carbons were better ad- sorbers for phenol and 2-CP compared with chemically ac- tivated carbons, but adsorption was more reversible in the latter case. 2-CP was adsorbed preferentially by each type of activated carbon, but adsorption of phenol was strongly suppressed in the presence of 2-CP. The simplified ideal adsorbed solution (SIAS) model underestimated the 2-CP loadings and overestimated the phenol loadings. However, the improved and modified forms of the SIAS model could better predict the competitive adsorption. The type of carbon activation was decisive in the application of these models. For each activated carbon type, phenol was desorbed more readily in the bi-solute case, but desorption of 2-CP was less compared with single-solute. This was attributed to higher energies of 2-CP adsorption. Keywords Activated carbon · Activation method · 2-chlorophenol · Competitive adsorption · Desorption · Irreversible adsorption · Phenol · SIAS model Ö. Akta¸ s( ) · F. Çeçen Bo˘ gaziçi University Institute of Environmental Sciences, 34342 Bebek ˙ Istanbul, Turkey e-mail: ozgura@boun.edu.tr 1 Introduction Phenolic hydrocarbons are widely used in pharmaceutical, petrochemical, pulping industries and other chemical man- ufacturing processes (Chern and Chien 2002). Due to their strong toxicity, persistence in the environment and suspected carcinogenicity (Quan et al. 2005), wastewaters containing phenolic compounds should be treated before discharge into water bodies. Particularly, chlorophenols are an important class of aromatic pollutants in industrial wastewaters be- cause of their wide use in the production of preservers, pes- ticides and biocides (Quan et al. 2005). Chlorinated phe- nols can exist up to 100–200 mg/L in contaminated en- vironments (Sahinkaya and Dilek 2005). However, pheno- lic compounds are usually poorly degraded in conventional wastewater treatment systems. But, they can be effectively removed by activated carbon adsorption (Carvalho et al. 2001). In the application of adsorption processes, reversibility of adsorption is usually as important as adsorption. There are two possible mechanisms leading to irreversible adsorption. One of them is the high energy bonding of adsorbate mole- cules to specific functional groups on the active sites of car- bon surface resulting in covalent bonding. This phenomenon is called chemisorption. Second is the oxidative polymeriza- tion of phenolic compounds onto activated carbon due to the presence of oxygen (Akta¸ s 2006). A previous study showed that carbon activation type was very important in terms of adsorption capacity of phenol (Akta¸ s and Çeçen 2006a). Desorption capacity, or in other words reversibility of adsorption, was also very much re- lated to the activated carbon type, particularly to the acti- vation method (Akta¸ s and Çeçen 2006a). In particular, des- orption capacity was of crucial importance because biore- generation of activated carbon in systems combined with