The development of industrial factories has led to increasing the entry rate of non-degradable compounds into the environment. Natural sorbents have been used extensively to remove heavy metals under optimal conditions. In the present research, the lead-resistant bacteria (Delftia lacustris Strain-MS3) were isolated and identified and the ability of this novel strain to tolerate different concentrations of Pb+2 were evaluated. Kinetics, thermodynamic study and the optimal conditions for lead uptake by isolated strain were statistically described. Factors affecting optimum operational conditions of lead biosorption were analyzed using response surface methodology (RSM), based on the Box-Behnken design (BBD) model. The maximum lead removal measured at pH value of 6.6, bacterial biomass to lead ratio of 22:3, and residence time of 180 min. There was a significant difference between the growth rates of Strain-MS3 in different treatments. Results illustrate the high accuracy of the selected model to determine the optimal experimental conditions in the metal biosorption process. The adsorption results match with the pseudo-second-order kinetics, suggesting that lead ions were uptake to the adsorbent in monolayers due to their chemical affinity. The thermodynamic parameters were also determined by the Gibbs free energy function, confirming that the adsorption process was spontaneous and accompanied by endothermic nature.
