Biosorption of heavy metals (Cd2+, Cu2+, Co2+ and Mn2+) by thermophilic bacteria, Geobacillus thermantarcticus and Anoxybacillus amylolyticus: equilibrium and kinetic studies.

Two strains of thermophilic bacteria, Geobacillus thermantarcticus and Anoxybacillus amylolyticus, were employed to investigate the biosorption of heavy metals including Cd2+, Cu2+, Co2+, and Mn2+ ions. The effects of different biosorption parameters such as pH (2.0-10.0), initial metal concentrations (10.0-300.0 mg L-1), amount of biomass (0.25-10 g L-1), temperature (30-80oC), and contact time (15-120 min) were investigated. Concentrations of metal ions were determined by using an inductively coupled plasma optical emission spectrometry (ICP-OES). Optimum pHs for Cd2+, Cu2+, Co2+, and Mn2+ biosorption by Geobacillus thermantarcticus were found to be 4.0, 4.0, 5.0, and 6.0, respectively. For Anoxybacillus amylolyticus, the optimum pHs for Cd2+, Cu2+, Co2+, andMn2+ biosorption were found to be 5.0, 4.0, 5.0, and 6.0, respectively. The Cd2+, Cu2+, Co2+, andMn2+ removals at 50 mg L-1 in 60 min by 50 mg dried cells of Geobacillus thermantarcticus were 85.4%, 46.3%, 43.6%, and 65.1%, respectively, whereas 74.1%, 39.8%, 35.1%, and 36.6%, respectively, for Anoxybacillus amylolyticus. The optimum temperatures for heavy metal biosorption were near the optimum growth temperatures for both strains. Scatchard plot analysis was employed to obtain more compact information about the interaction between metal ions and biosorbents. The plot results were further studied to determine if they fit Langmuir and Freundlich models.