Available online at www.sciencedirect.com Colloids and Surfaces B: Biointerfaces 62 (2008) 97–104 Biosorption of Ni(II) from aqueous solutions by living and non-living ureolytic mixed culture Mustafa Is ¸ik ∗ Aksaray University, Engineering Faculty, Environmental Engineering Department, 68100 Aksaray, Turkey Received 25 July 2007; received in revised form 13 September 2007; accepted 19 September 2007 Available online 25 September 2007 Abstract The present study explores the ability and the comparison of living and non-living ureolytic mixed culture (UMC) to remove Ni(II) from aqueous solution. Time dependency experiments for the Ni(II) uptake showed that adsorption equilibrium was reached almost 110 and 60 min after addition Ni(II) of 100 mg/L. The kinetic data were analyzed in term of pseudo-first-order and pseudo-second-order expressions. Ni(II) sorption of living UMC was appropriate with pseudo-first-order kinetic (k 1 = 2.15 h -1 , R 2 = 0.93) while non-living UMC sorbed Ni(II) with respect to second-order kinetics (k 2 = 1.64 g/mg h, R 2 = 0.98). Also, comparison between the biosorption capacity of untreated living and non-living biomass was conducted for removal of Ni(II). The biosorption process was investigated in equilibrium batch tests for Langmiur, Freundlich and Temkin isotherm models. The data pertaining to the sorption dependence upon Ni(II) ion concentration ranged from 5 to 320 mg/L could be fitted to a Freundlich isotherm model. The capacity constants K of Freundlich model for living and non-living UMC were 1.55 and 0.38 mg/g, respectively; the affinity constants 1/n were 0.47 and 0.75, respectively. Based on the results, the UMC appear to be a potential biosorbent for removal of Ni(II) from wastewater. © 2007 Elsevier B.V. All rights reserved. Keywords: Biosorption; Living; Non-living; Ureolytic; Nickel; Kinetics 1. Introduction Enhanced industrial activity after the industrial revolution has led to the discharge of chemicals, which causes environmen- tal and public health problems. The important group of toxic chemicals is heavy metals, due to their high toxicity, pose a serious threat to biota and the environment. The presence of heavy metals in the environment is of major concern because of their extreme toxicity and tendency for bioaccumulation in the food chain even in relatively low concentrations [1,2] Heavy metals pollute the environment from various industries such as metal plating, electroplating, mining, ceramic, batteries, pig- ment manufacturing [3]. Although there are many methods for the removal of metal ions from solutions, such as chemical precipitation, complexation, solvent extraction and membrane processes, biosorption processes show many advantages over these methods. It is selective, effective and cheap and is able to remove very low levels of heavy metals from solutions [4]. In ∗ Tel.: +90 382 2150953/132; fax: +90 382 2150592. E-mail address: misik@aksaray.edu.tr. addition, most of these processes are not eco-friendly because of the production of sludge causing a solid disposal problem [5]. Recently, bioadsorbents have emerged as an eco-friendly, effective and low cost material option. These bioadsorbents include some agricultural wastes, fungi, algae and bacteria. Stud- ies using bioadsorbents have shown that both living and dead microbial (non-living) cells are able to adsorb metal ions and offer potential inexpensive alternative to conventional adsor- bents [6]. However, living cells are subject to toxic effect of the heavy metals, resulting in cell death. Moreover, living cells often require the addition of nutrients and hence increase the biochemical oxygen demand (BOD) and/or chemical oxygen demand (COD) in the effluent. For these reasons, the use of non-living biomaterials or dead cells as metal-binding com- pounds has been gaining advantage because toxic ions do not affect them. In addition, dead cells require less care, mainte- nance and they are cheaper. Furthermore, dead biomass can be easily regenerated and reused [6]. Microbial metal uptake generally involves the rapid, metabolism-independent uptake of metals to cell walls and other external surfaces (passive uptake), followed by a slow, metabolism-dependent transport across the cell membrane 0927-7765/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.colsurfb.2007.09.022