Biosorption of heavy metals from single and multimetal solutions by free and immobilized cells of Bacillus megaterium

Biosorption capacity of immobilized and free cells of bacterium Bacillus megaterium has been assessed for the removal of Pb2+, Cr2+ and Cd2+ ions from single, binary and ternary metal solutions at varying initial metal ion concentrations, incubation time, pH and temperature regimes. From single metal solution biosorption capacity followed the order Pb > Cd > Cr and it was maximum 96.83%, 77.16% and 55.28% for Pb2+, Cd2+ and Cr2+ ions respectively by immobilized cells and 76.29%, 54.59% and 32.18% by free cells at optimum conditions i.e. pH 7, temperature 400C for 50 ppm metal ion concentration. Mutual interference effects were probed using equilibrium adsorption capacity ratios, qe?/qe where the prime indicates the presence of one or two other metal ions. The combined action of the metals was found to be antagonistic. Multimetal adsorption behavior was successfully described by extended Langmuir Model. In binary metal solution, 10, 30 and 50 ppm of Cr2+ ions inhibited both Pb2+ and Cd2+ ions, Pb2+ ions being more influenced. In contrast, Cr2+ ions sorption remained unaffected at varying concentrations of competing metals. Thus in binary system, sorption order was Pb>Cr, Cd>Cr and Pb~Cd while interference dominance followed the order PbCd>Cr, and inhibition dominance was found to be Cr>Pb>Cd. Study revealed that the findings could assist devising toxic metal cleansing by bacterial sorption especially in immobilized state.