A comparative adsorption/biosorption study of mono-chlorinated phenols onto various sorbents ZuÈ mriye Aksu*, JuÈ lide Yener Department of Chemical Engineering, Hacettepe University, 06532, Beytepe, Ankara, Turkey Received 24 August 2000; accepted 4 January 2001 Abstract The potential use of dried activated sludge and ¯y ash as a substitute for granular activated carbon for removing mono-chlori- nated phenols o-chlorophenol and p-chlorophenol) was examined. The pollutant binding capacity of the adsorbent/biosorbent was shown to be a function of substituted group, initial pH and initial mono-chlorinated phenol concentration. The working sorption pH value was determined as 1.0 and the equilibrium uptake increased with increasing initial mono-chlorinated phenol concentra- tion up to 500 mg dm 3 for all the mono-chlorinated phenol-sorbent systems. The suitability of the Freundlich, Langmuir and Redlich±Peterson adsorption models to the equilibrium data were investigated for each mono-chlorinated phenol-sorbent system. The results showed that the equilibrium data for all the mono-chlorinated phenol-sorbent systems ®tted the Redlich±Peterson model best within the concentration range studied. # 2001 Elsevier Science Ltd. All rights reserved. Keywords: o-Chlorophenol; p-Chlorophenol; Adsorption/biosorption; Dried activated sludge; Fly ash; Granular activated carbon 1. Introduction Chlorinated phenols are among the most common organic pollutants of waste waters that require careful treatment before being discharged into the receiving body of waters [1,2]. The most important pollution sources containing mono-chlorinated phenols are the wastewaters from pesticide, paint, solvent, pharmaceu- tics, wood preserving chemicals, and paper and pulp industries [1,2,5,13]. Phenol-containing waters develop when chlorination is used to disinfect water, which results in the formation of chlorophenols [1,5,13,17]. Traditionally, biological treatment, activated carbon adsorption and solvent extraction are the most widely used methods for removing phenols and its derivatives from wastewaters [1±5,7]. Adsorption is a well established and powerful techni- que for treating domestic and industrial euents. Acti- vated carbon is the most widely and eectively used adsorbent. A typical activated carbon particle, whether in a powdered or granular form, has a porous structure consisting of a network of interconnected macropores, mesopores, and micropores that provide a good capa- city for the adsorption of organic molecules due to its high surface area. The surface chemistry of activated carbon and the chemical characteristics of adsorbate, such as polarity, ionic nature, functional groups and solubility determine the nature of bonding mechanisms as well as the extent and strength of adsorption. A variety of physicochemical mechanisms/forces, such as van der Waals, H-binding, dipole-dipole interactions, ion exchange, covalent bonding, cation bridging and water bridging, can be responsible for adsorption of organic compounds in activated carbon [2±9]. In spite of these characteristics, activated carbon suers from a number of disadvantages. It is quite expensive and the higher the quality, the greater the cost. Both chemical and thermal regeneration of spent carbon is expensive, impractical on a large scale and produces additional euent and results in considerable loss of the adsorbent [9]. This has led many workers to search for more eco- nomic, practical and ecient techniques. Bottom ash, brick-kiln ash, ¯y ash, peat, soil, rice husk, carbonized bark, wood and montmorillonite are some new adsor- bents used for organic pollutants [5±8,10±13]. Biosorption is generally used for the treatment of heavy metal pollutants in wastewaters. Application of biosorption for organic and other pollutants could also 0956-053X/01/$ - see front matter # 2001 Elsevier Science Ltd. All rights reserved. PII: S0956-053X01)00006-X Waste Management 21 2001) 695±702 www.elsevier.com/locate/wasman * Corresponding author. Tel.: +90-312-2977434; fax: +90-312- 2992124. E-mail address: zaksu@hacettepe.edu.tr Z. Aksu).