In present study, the free and immobilized cells of Bacillus megaterium were used as biosorbent for the removal of Pb(II) ions from the aqueous solution. The adsorption studies of bacterium were compared in batch mode. Optimum biosorption conditions were determined as a function of pH, temperature and contact time. The equilibrium adsorption data was analyzed by the Langmuir, Freundlich, Tempkin, Dubinin-Radushkevich, Redlich-Peterson and Sips isotherm models. The values of the regression coefficient of the isotherms gave the best fit (free cells R2=0.998 and immobilized cells R2=0.999) with the Langmuir isotherm. The maximum monolayer adsorption capacity (qe) of the biosorbents (free and immobilized cells), as obtained from the Langmuir adsorption isotherm, was found to be 166 and 200 mg/g, respectively at 5h contact time, 7.0 pH, 0.4 g/L bacterial dose, and 300C temperature. The energy of adsorption, E (free = 9.911KJ/mol and immobilized = 11.174 KJ/mol) obtained from the Dubinin-Radushkevich isotherm suggested a chemical ion exchange mechanism. Kinetics of adsorption followed both first- and second-order rate equations with intra-particle diffusion processes. Biosorbent could be regenerated using 0.1 M NaOH solution, with up to 60% recovery. The performance of this biosorbent was compared with many other reported biosorbents for lead removal and it was observed to be most effective.
