Cr(VI) biosorption from aqueous solutions using free and immobilized biomass of Lentinus sajor-caju: preparation and kinetic characterization

The potential use of the free and immobilized mycelia (in carboxymethylcellulose (CMC)) of Lentinus sajor-caju to remove hexavalent form of chromium ions, Cr(VI), from aqueous solutions was evaluated using CMC bead as a control system for immobilised form of fungus. The CMC beads containing immobilized fungus mycelia were incubated for the uniform growth on the beads surface at 30 °C for 3 days. Effects of pH, biosorption time, initial concentration and biosorbent dosages on the biosorption of Cr(VI) ions were studied. The biosorption of Cr(VI) ions on the biosorbents showed a highest value at around pH 2.0. The biosorption of Cr(VI) ions on both free and immobilized L. sajor-caju biomass (mg/g) was increased as the initial concentration of Cr(VI) ions increased in the medium. Biosorption equilibrium was established in about 2.0 h. The determined maximum biosorption capacities of the free and immobilized fungus were 18.9 and 32.2 mg/g dry weight, respectively. The biosorption equilibrium was also represented with Langmuir and Freundlich adsorption isotherms. The biosorption of Cr(VI) on these biomasses follows pseudo-second-order kinetics. The temperature change in the range of 5–40 °C affected the biosorption capacities of the biosorbents. The biosorbent systems can be regenerated using 0.1 M NaOH, with more than 95% recovery, the biosorbents reused in five biosorption–desorption cycles without any considerable loss in the biosorption capacity.