Chemical Engineering Journal 162 (2010) 122–126 Contents lists available at ScienceDirect Chemical Engineering Journal journal homepage: www.elsevier.com/locate/cej Long-term chromate reduction by immobilized fungus in continuous column Rashmi Sanghi ∗ , Ashish Srivastava 302 Southern Laboratories, Facility for Ecological and Analytical Testing, Indian Institute of Technology Kanpur, Kanpur, UP 208016, India article info Article history: Received 5 February 2010 Received in revised form 1 May 2010 Accepted 10 May 2010 Keywords: Thioester Chromium reduction Fungal biomass Column Immobilization abstract The immobilized fungus Coriolus versicolor was examined in a continuous fixed bed column for long-term Cr(VI) reduction at its physiological pH. The effects of operating parameters like flow rate, glucose con- centration in the influent feed, COD, initial Cr(VI) concentration on the Cr(VI) reduction were investigated. Increase in the inlet Cr(VI) concentration and flow rate through the column led to a higher breakthrough of the Cr(VI) ions in the effluent. Cr(VI) reduction rate increased with increase in initial Cr(VI) concen- tration of up to 60 mg/L and thereafter showed a gradual decline. A Fourier transform infrared spectra were employed to elucidate the possible biosorption mechanism as well. The readiness of the thiol group of the fungal protein to interact with the Cr(VI) ion in addition to its strong reducing ability makes it a particularly important entity in the metabolism of Cr(VI). The possible role of thiol in the Cr(VI) reduction via the formation of Cr(VI) thioester is discussed. The study clearly exhibits the usage of live fungus for the long-term continuous removal of Cr(VI) as well as recovery of the metal ions from wastewater. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Chromium has been widely recognized as a toxic mutagen [1] and a carcinogen yet is an important metal, which is used in a variety of industrial applications. Chromium is a metal that can exist in oxidation states from -2 to +6, The trivalent oxidation state is the most stable form of chromium In biological systems, chromium is naturally found in its trivalent state at very vari- able levels, whereas the hexavalent form is generally a derivative of man’s activities. Cr(VI) tends to associate with oxygen gener- ating the powerful oxidants chromate (CrO 4 2- ) and dichromate (Cr 2 O 7 2- ). The biological effects of chromium are highly depen- dent on the oxidation state. Derivatives of Cr(III) are water insoluble compared to Cr(VI) derivative compounds that are highly soluble [2]. Requirements of large quantity of chemicals or energy can be a limitation for the application of physicochemical methods for removing Cr(VI). Removal of heavy metal ions using biosorption could be a promising technology and has received more and more attention in recent years [3,4,5]. Microorganisms, which are capa- ble of transforming metals from one oxidation state to another, facilitate detoxification and/or the removal of chromium, and have thus received recognition [6]. In the concept of biosorption, sev- eral chemical processes may be involved, such as bioaccumulation, bioadsorption, precipitation by H 2 S production, ion exchange, and covalent binding with the biosorptive sites, including carboxyl, ∗ Corresponding author. Fax: +91 512 2597866. E-mail address: rsanghi@gmail.com (R. Sanghi). hydroxyl, sulphydryl, amino and phosphate groups of the microor- ganisms [7]. The surfaces of fungal cells appear to act as ion exchange resins [8]. From the quantitative point of view, the surface sorption usually can contribute the larger proportion to total metal uptake, and thus binding to cell walls appears to be the most significant mechanism of sorption. Since it is energy independent, it occurs in both living and dead microbial biomass, including fungal mycelium [9]. The aim of the present work is to assess the long-term perfor- mance of thiol containing live fungus Coriolus versicolor for the continuous reduction of Cr(VI) in upflow fixed bed columns in a growth-supportive medium at physiological pH. The effects of some operating parameters, such as inlet Cr(VI) concentration, media composition, and flow rate were examined and optimized for the long-term Cr(VI)-reduction performance in the column. In this study we have used white-rot fungus C. versicolor as a biore- ductant since it has a high growth rate and can grow under a variety of environmental conditions including low pH, high pollutant con- centration. The possible mechanism for the reduction of Cr(VI) to Cr(III) by the fungus is also discussed. 2. Materials and methods 2.1. Reagents A stock solution of Cr(VI) was prepared containing 18.6736 g K 2 Cr 2 O 7 per litre of deionized water. Sterilized stock Cr(VI) solution was added to sterile medium to a desired concentration of Cr(VI) with minimal dilution of the medium. All chemicals used were of AR grade. 1385-8947/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.cej.2010.05.011