Biosorption of lead by E. coli strains expressing Vitreoscilla hemoglobin: Isotherm modeling with two- and three-parameter models

Biosorption is presented as an alternative choice to traditional physicochemical means for removing toxic metals from groundwater and wastewaters. Removal of lead (Pb) from solutions was studied using Escherichia coli (parental) and Vitreoscilla hemoglobin (VHb)-expressing E. coli (transformed) cells. Pb biosorption was increased in bacterial hemoglobin-expressing E. coli cells grown in Luria broth B containing different concentrations of Pb²⁺. The maximum Pb²⁺ biosorption of transformed and parental cells was determined to be 612 and 370 μg Pb/g biomass, respectively. The inhibitory effect of Pb²⁺ on the parental strain was determined at 10 ppm. However, in transformed cells, Pb²⁺ was lethal at 100 ppm. The optimum aeration required for the transformed cells was lower than that for the parental strain on a growth yield basis. A linear correlation was established between the biosorption and uptake amounts. The biosorption process was analyzed using two-parameter (Langmuir, Freundlich, Temkin) and three-parameter models (Sips, Redlich-Peterson, Toth). The chi-square test was used to compare these models. It was demonstrated that the three-parameter model is better in describing biosorption equilibria, while the Sips equation showed the best description for both types of cells.