Biosorption of Hexavalent Chromium by Pseudomonas aeruginosa Strain ANSC: Equilibria Isothermic, Kinetic and Thermodynamic Studies

Abstract

Pseudomonas aeruginosa strain ANSC, a non-genetically modified bacterial strain isolated from soil was used to study and evaluate biosorption potentials for hexavalent chromium (Cr[VI]) from aqueous solution. Living, heat-killed, and permeabilised cells were all used and found to be capable of reducing and sorbing Cr(VI). The influences of initial Cr(VI) ion concentration (50-150 mg/L), contact time (2 h, 10 min intervals), pH (2-8), temperature (30-60°C) and biosorbent mass (1.0-5.0 g/l) were reported. Adsorption of Cr(VI) is highly pH-and temperature-dependent, and the results indicate that the optimum pH and temperature for removal were found to be 2 and 60°C respectively. The hexavalent chromium biosorption equilibrium could be better described by Langmuir isotherm than it could by Freundlich isotherm. A comparison of kinetic models applied to the adsorption of Cr(VI) ions onto the biosorbents was evaluated for the pseudo first-order, pseudo second-order, and intra-particle diffusion kinetic models. Results show that the pseudo second-order kinetic model was evidenced to correlate better the experimental data. The rate of hexavalent chromium adsorption increased following permeabilisation of the outer and/or cytoplasmic membrane by surfactants such as Triton X100, Tween 80, toluene, sodium deoxycholate and sodium dodecyl sulphate. The adsorption process has been found endothermic, and thermodynamic parameters of Gibb's free energy (ΔG°), change in enthalpy (ΔH°) and change in entropy (ΔS°) were calculated. Pseudomonas aeruginosa strain ANSC evidenced an effective biosorbent for the removal of hexavalent chromium in aqueous form.