| In this work, the environmental-friendly bacteria (Bacillus thuringiensis and Bacillus cereus) were selected as target strains. The interaction mechanisms between bacteria and environmental pollutants (lead, uranium and methylene blue) were investigated. The related influence factors of heavy metals (lead and uranium) biosorption and biomineralization as well as methylene blue decolorization and biodegradation by bacteria were further explored.The main results were as follows:(1) B. cereus 12-2 (isolated from lead-zinc mine tailings) and B. thuringiensis 016 (laboratory preservation) have good ability of lead biosorption, the maximum biosorption capacity were 226 and 156 mg/g, respectively. As the pH value was 3.0, the adorption amount of lead by B. cereus 12-2 was up to 340 mg/g. The zeta potential analyses indicated that pH value could affect the surface charge of bacteria, which played an important role in the lead(Ⅱ) biosorption. Meanwhile, K+, Mg2+ and Na+ inside the bacteria could contribute to the lead(Ⅱ) biosorption through ionic exchange or transport from extracellular to intracellular. Functional passivation experiments and fourier transform infrared spectroscopy (FT-IR) showed that the carboxyl, amino and phosphate groups were also involved in the biosorption of lead(Ⅱ). Besides, the granular sediments on the bacterial surface and interior was observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analysis. X-ray powder diffraction (XRD) confirmed that these sediments were nano lead-hydroxyapatite mineral [Ca2.5Pb7.5(OH)2(PO4)6]. The protein denaturation experiments show that after protein denaturation, the capacity of lead(Ⅱ) biosorption could decrease in different degrees. Furthermore, the denatured biomass could not transform the accumulated lead(Ⅱ) into mineral of calcium lead hydroxide phosphate [Ca2.5Pb7.5(OH)2(PO4)6], suggesting a enzyme-mediated lead(II) biomineralization process by bacteria.(2) The micromechanism of uranium biosorption and biomineralization by B. thuringiensis 016 was investigated in this work. It was found that the maximum uranium biosorption capacity of B. thuringiensis 016 was 209 mg/g at pH 5.0, and it was a rapid biosorption process. The carboxyl, amino and phosphate groups of bacteria could play an important role in uranium biosorption, while the coexistence of Fe3+and CO32- ions in the solution could greatly inhibite biosorption of uranium. The valence of uranium was not changed during the process of biosorption. Moreover, the accumulated uranium could be further mineralized into uramphite [(NH4)(UO2)PO4·3H2O] by B. thuringiensis 016 when initial uranium concentration was low (100 mg/L). However, the uramphite could not form when initial uranium concentration was higher than 100 mg/L. Besides, the coexisting ions could promote the mineralization of uranium by B. thuringiensis 016.(3) It was found that methylene blue could not affect the growth of B. thuringiensis 016 at the concentration ranging from 5-25 mg/L. Further studies indicated that B. thuringiensis 016 biomass possessed strong ability of methylene blue decolourization with a quick process. The pH value, temperature as well as rotation speed could affect the decolourization of methylene blue in a large extent. UV-visible, FT-IR spectroscopy analyses, liquid chromatography as well as microscopic investigations suggested that the decolourization of methylene blue could be divided into two steps as follows:1) Rapid biosorption of methylene blue on B. thuringiensis 016 biomass through electrostatic attraction or chelating activity of functional groups; 2) Methylene blue was further degraded by B. thuringiensis 016 through enzyme-mediated or couple with the metabolism process. |
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