Equilibrium and kinetic studies of Cu(II) and Ni(II) sorption on living Euglena gracilis

Abstract

Biosorption and bioaccumulation involve the decrease in concentration or removal of metals from aqueous solution through the sequestering of ions by active or metabolically inert biomass. In this study, the potential use of Euglena gracilis, a free-floating, flagellated unicellular species of protist, to remove Cu and Ni ions at environmentally relevant levels from aqueous solutions was investigated. Adsorption isotherms were used in a batch system to describe the kinetic and equilibrium characteristics of metal removal. The effects of pH and initial concentration of metal ions on the adsorption of Cu and Ni ions were examined. Results indicate that the sorption reaction occurred quickly (<30 min) in both Cu and Ni monometallic systems, and adsorption followed a pseudo-second-order kinetics model for both metals. Comparable metal sorption was found at pH 5 and 7.5, suggesting that metal sorption onto live Euglena cells is not pH dependent. No significant differences in metal sorption were found at pH 5 and 7.5. Removal efficiencies for Cu decreased with higher initial concentrations (3–30 μg L−1) and conformed to the Freundlich sorption model. Ni removal was found to increase with greater initial concentration values (5–110 mg L−1) and conformed to the Freundlich isotherm. The removal efficiency for Cu and Ni was 58 ± 3 and 44 ± 6%, respectively. In bimetallic systems, sorption of both metals were equivalent, suggesting that E. gracilis may be appropriate for mining effluent metal removal due to their ability to simultaneously tolerate, sorb, and accumulate multiple metals in solution in a range of environmental conditions.