In this study, the Pb 2+ biosorption potential of live and dead biosorbents of the hydrocarbondegrading strain Rhodococcus sp. HX-2 was analyzed. Optimal biosorption conditions were determined via single factor optimization, which were as follows: temperature, 25˚C; pH, 5.0, and biosorbent dose, 0.75 g L −1. A response surface software (Design Expert 10.0) was used to analyze optimal biosorption conditions. The biosorption data for live and dead biosorbents were suitable for the Freundlich model at a Pb 2+ concentration of 200 mg L −1. At this same concentration, the maximum biosorption capacity was 88.74 mg g −1 (0.428 mmol g −1) for live biosorbents and 125.5 mg g −1 (0.606 mmol g −1) for dead biosorbents. Moreover, in comparison with the pseudo-first-order model, the pseudo-second-order model seemed better to depict the biosorption process. Dead biosorbents seemed to have lower binding strength than live biosorbents, showing a higher desorption capacity at pH 1.0. The order of influence of competitive metal ions on Pb 2+ adsorption was Cu 2+ > Cd 2+ > Ni +. Fourier-transform infrared spectroscopy analyses revealed that several functional groups were involved in the biosorption process of dead biosorbents. Scanning electron microscopy showed that Pb 2+ attached to the surface of dead biosorbents more readily than on the surface of live biosorbents, whereas transmission electron microscopy confirmed the transfer of biosorbed Pb 2+ into the cells in the case of both live and dead biosorbents. It can thus be concluded that dead biosorbents are better than live biosorbents for Pb 2+ biosorption, and they can accordingly be used for wastewater treatment.
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