Removal of cadmium(II) ion from aqueous system by dry biomass, immobilized live and heat-inactivated Oscillatoria sp. H1 isolated from freshwater (Mogan Lake) Hikmet Katırcıog ˘lu a , Belma Aslım b , Ali Rehber Tu ¨ rker c, * , Tahir Atıcı a , Yavuz Beyatlı b a Department of Biology Education, Faculty of Education, Gazi University, 06500 Ankara, Turkey b Department of Biology, Faculty of Arts and Science, Gazi University, 06500 Ankara, Turkey c Department of Chemistry, Faculty of Arts and Science, Gazi University, 06500 Ankara, Turkey Received 6 December 2006; received in revised form 24 August 2007; accepted 29 August 2007 Available online 25 October 2007 Abstract Oscillatoria sp. H1 (Cyanobacteria, microalgae) isolated from Mogan Lake was used for the removal of cadmium ions from aqueous solutions as its dry biomass, alive and heat-inactivated immobilized form on Ca-alginate. Particularly, the effect of physicochemical parameters like pH, initial concentration and contact time were investigated. The sorption of Cd(II) ions on the sorbent used was exam- ined for the cadmium concentrations within the range of 25–250 mg/L. The biosorption of Cd(II) increased as the initial concentration of Cd(II) ions increased in the medium up to 100 mg/L. Maximum biosorption capacities for plain alginate beads, dry biomass, immobi- lized live Oscillatoria sp. H1 and immobilized heat-inactivated Oscillatoria sp. H1 were 21.2, 30.1, 32.2 and 27.5 mg/g, respectively. Bio- sorption equilibrium was established in about 1 h for the biosorption processes. The biosorption was well described by Langmuir and Freundlich adsorption isotherms. Maximum adsorption was observed at pH 6.0. The alginate–algae beads could be regenerated using 50 mL of 0.1 mol/L HCl solution with about 85% recovery. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Cadmium(II) removal; Biosorption; Bioaccumulation; Ca-alginate; Oscillatoria sp. H1 1. Introduction Heavy metal pollution of waters is a common environ- mental problem due to industrial processes which result in the release of heavy metals into natural water. Toxic metal ions such as Cd(II) can eventually reach the top of food chain and thus, become a risk factor for people’s health. Most of the heavy metal salts are soluble in water and form aqueous solutions and consequently cannot be separated by ordinary physical separation methods (Hus- sein et al., 2004). Conventional techniques for removing dissolved heavy metals include precipitation (Berbenni et al., 2000), adsorption (Nadeem et al., 2006), ion- exchange (Gode and Pehlivan, 2007). In recent years, alter- native methods for metal removal and recovery based on biological materials have been considered. Biosorption and/or bioaccumulation have emerged as a cost-effective and efficient alternative method. Biosorption means the passive process for adsorbing the metal ions by metaboli- cally inactive biomass, which is dependent on the affinity between the metallic species or its ionic forms and the bind- ing sites on the molecular structure of the cellular wall (Manriquez et al., 1997; Pardo et al., 2003). Bioaccumula- tion is the term usually employed to describe the active sequestering of metal ions by metabolically active biomass (Hussein et al., 2004). Microorganisms, including algae, bacteria, yeast, fungi, plant leaves and root tissues can be used as biosorbents for the removal of heavy metals (Pavasant et al., 2006; Bhano- ori and Venkateswerlu, 2000; Hussein et al., 2004; Arıca 0960-8524/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2007.08.068 * Corresponding author. Fax: +90 312 2122279. E-mail address: aturker@gazi.edu.tr (A. Rehber Tu ¨ rker). Available online at www.sciencedirect.com Bioresource Technology 99 (2008) 4185–4191