Journal of Hazardous Materials B119 (2005) 219–229 Modification of surface properties of Lentinus sajor-caju mycelia by physical and chemical methods: evaluation of their Cr 6+ removal efficiencies from aqueous medium G¨ ulay Bayramo ˘ glu ∗ ,G¨ okc ¸e C ¸ elik, Emine Yalc ¸ın, Meltem Yılmaz, M. Yakup Arıca Biochemical Processing and Biomaterial Research Laboratory, Faculty of Science, Kırıkkale University, 71450 Yah¸ sihan-Kırıkkale, Turkey Received 22 September 2004; received in revised form 20 December 2004; accepted 21 December 2004 Available online 23 January 2005 Abstract The hexavalent chromium biosorption onto untreated and heat-, acid- and alkali-treated Lentinus sajor-caju mycelia were studied from aqueous solutions. The particles sizes of the fungal mycelia ranged from 100 to 200 m. The effect of pH, temperature, biosorbent dose, initial concentration of chromium ions, contact time parameters were investigated in a batch system. Biosorption equilibrium was established in about 4 h. The surface charge density of the fungal preparations varied with pH, and the maximum absorption of chromium ions on the fungal preparations were obtained at pH 2.0. The biosorption of chromium ions by the tested fungal preparations increased as the initial concentration of chromium ions increased in the medium. The maximum biosorption capacities of the untreated and heat, HCl- and NaOH-treated fungal biomass were 0.363, 0.613, 0.478 and 0.513 mmol Cr 6+ per gram of dry biomass, respectively. The correlation regression coefficients and the Langmuir constant values show that the biosorption process can be well defined by Langmuir equation. The chromium adsorption data were analysed using the first- and the second-order kinetic models. The first-order equation is the most appropriate equation to predict the biosorption capacities of all the fungal preparations. In addition, the polarity and surface energy of the untreated and all the modified biomass film preparations were determined by contact angle measurement. All the tested fungal biomass preparations could be regenerated using 0.1 M NaOH solution. © 2005 Elsevier B.V. All rights reserved. Keywords: White-rot fungus; Lentinus sajor-caju; Biosorption; Cr 6+ ; Chemical and physical treatment; Contact angle; Surface energy 1. Introduction Heavy metals are toxic because they are present as ions in an aqueous system and can be readily absorbed into the human body. Even a very small amount can cause severe physiological or neurological damage. One of the most dan- gerous metal ions for human life is Cr 6+ which is found in industrial wastewater because of the extensive use of chro- mate and dichromate in electroplating, leather tanning, metal finishing, nuclear power plant, textile industries and chro- ∗ Corresponding author. Tel.: +90 318 3572477; fax: +90 318 3572329. E-mail address: gbayramoglu@kku.edu.tr (G. Bayramo ˘ glu). mate preparation [1,2]. Chromium, Cr 6+ , is a powerful car- cinogenic agent that modifies the DNA transcription process causing important chromosomic aberrations. The Cr 6+ may also cause epigastric pain, nausea, vomiting, severe diarrhea, and hemorrhage [3]. Portable waters containing more than 0.05 mg/l of chromium are considered to be toxic [4,5]. Thus, the removal of metal ions from wastewaters has become an important and widely studied area where a number of tech- nologies have been developed over the years. The most im- portant of these methods include reverse osmosis, ion ex- change adsorption, chemical precipitation and electro depo- sitions [6]. These methods are highly expensive. Therefore, the use of microbial biomass for removal of toxic heavy metal ions from wastewaters has emerged as an alternative to the 0304-3894/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.jhazmat.2004.12.022