Irradiation Conditions Simulated Radionuclide Sr < Sup > 2 + < / Sup > Microbial Adsorption Study

As one of most hazardous nuclide ions from global sedimentation radionuclide originated from nuclear explode and nuclear accident etc., radioisotope of Strontium has its characteristic concealment and hysteresis. For achieving efficient microbial adsorbent and exploring the feasibility of biosorption of Sr2+using microbes under radioactive environment, some living microorganism from nature (soli) and dead thalli from industry waste yeast were chose as study objects in this PhD dissertation.47strains from soli were isolated, in which one strain of fungus and eleven strains of bacteria were confirmed have better biosorption efficiencies to Sr2+. The growth rate, biosorption efficiency and biosorption rate of these12kinds of strains were increased under domesticated intimidation stress in aqueous stable isotope of strontium. The appearance time of their highest growth rate was accelerated0.5d, while the appearance time of biosorption equilibrium was accelerated1.0～2.5d as they appeared at2.0-3.0d. The optimized biosorption condition for soli strains to Sr2+was pH=6.0～7.0, Vi=0.5mL/25mL (1/50) and C0=25mg/L～100mg/L.The kinetic processes of different strains are composed of initial biosorption equilibrium, fast biosorption increasing and second biosorption equilibrium. These three biosorption phases were all consistent with pseudo-second order adsorption kinetics. The results showed that the biosorption process of living cells to Sr2+was extremely complex due to its complex biosorption mechanism and its complex biosorption system. The biosorption of different strains to Sr2+were all better consistent with Langmuir adsorption isotherm than Freundlich adsorption isotherm, R>0.98. However, the analysis to qmax showed that the model of Langmuir adsorption isotherm still had some limits for describing the biosorption Sr2+by living cells.The adsorption isotherm type parameters (KR) of experimental strains to Sr2+were all less than0.82ensured the experimental condition was propitious to biosorption activity of different strains to Sr2+. Under experimental condition of303K and pH7.0, The biosorption activities of Sr2+were spontaneously due to Gibbs free energy change (ΔG0) of different stains were all below zero.Although the growth of twelve strains soil microbes were restrained obviously under the radiant dose of0.5kGy and1.0kGy, there were no distinct evidence show the effects of Sr2+on bacteria colony formation under experimental radiation condition. The strain of6#has best radiation-resistant ability. This strain was subject to Bacillus according to analysis results of16S rDNA was100%accordance with GeneBank database of Bacillus pumilus.As for the whole kinetic biosorption curves, under the radiation dose of1.0kGy, bacterial growth rates of test groups have retardation phenomena comparing to the control groups without radiation. The radiation effect of test groups of inoculated12.Oh in advance was weaker than the test groups of inoculated1.0h. The experimental results of radiation after adsorbed Sr2+showed that the radiation effect of different strains at initial biosorption stage (1.0～2.0d) were more obvious than anaphase biosorption stage, while the results of adsorption Sr2+after radiation showed that biosorption time has more obvious effect than radiation.FTIR analysis results under different radiation condition showed that the characteristic peaks of amylase, protein amide and lipids on bacteria cells were slightly shifted. These indicated that bacteria cells were damaged by radiation and Sr2+has cooperation damage effects with radiation in aqueous condition.Batch experiments about biosorption Sr2+on baker’s yeast showed that the optimized adsorption condition as following:pH=4.0-5.5, T=20℃-40℃, Cm=2.0-6.0g/L, C0=0.25-].Ommol/L. FTIR results showed that its existent chemical adsorption in the biosorption process to Sr2+. The changes observed in the spectra indicated the possible involvements of functional groups on the surface of the biomass in biosorption process, and the further analysis showed that amylose and protein amide have more important roles in the biosorption of Sr2+on yeast cells.With the radiant dose of1.0kGy, the biosorption of baker’s yeast and control groups without radiation to Sr2+were all better consistent with Langmuir adsorption isotherm and Freundlich adsorption isotherm. The analysis results of adsorption isotherm type parameters (0.88<KR<0.11) ensured that there is favor to Sr2+on baker’s yeast. The Gibbs free energy change (ΔG0) analysis showed that ΔG0of baker’s yeast were all below zero, and the ΔG0values of radiation groups were less than the control groups without radiation groups. Firstly, these can ensure that the biosorption process to Sr2+is spontaneously. At the same time, these showed that experimental temperature and radiation conditions can be favor to the spontaneous biosorption of baker’s yeast to Sr2+The kinetic analysis showed that the biosorption of baker’s yeast to Sr2+was a fast reaction process. As the whole biosorption process, qt is being the relation at different experimental temperatures as30℃>20℃>10℃. The biosorption effect to Sr2+on baker’s yeast after radiation was better than the control groups without radiation. The biosorption analysis results of baker’s yeast to Sr2+were all consistent with pseudo-second order adsorption kinetics at different experimental temperatures, as R>0.999. The activation energy Ea of biosorption to Sr2+can be calculate as9.955kJ/mol and9.162kJ/mol before and after radiated to baker’s yeast. These indicated that an experimental radiation condition is favor to the spontaneous biosorption of baker’s yeast to Sr2+The analysis results of biosorption five kinds of heavy metal ions and Sr2+showed that baker’s yeast has similar adsorption activity to bivalent ions. At the relative optimized experimental conditions as pH=4.5, Cm=4.0g/L and Co=1.0mmol/L, the biosorption kinetics of six ions on baker’s yeast showed that qt and n have the relation as following: Pb2+>Cd2+>Sr2+> Cu2+>Zn2+> Ni2+.This study obtained some strains from soli without radiation pollution. Their biosorption abilities to Sr2+increased after domestication of intimidation stress. Some of them have satisfactory biosorption efficiencies to Sr2+under the conditions of low to moderate, even high radioactivity. As industry waste, although baker’s yeast have not the similar high biosorption efficiencies to Sr2+as strains from soli, it has advantages of easily obtained, low-cost and fast adsorption, etc.. On the other hand, dry yeast cells are favor to transport and is able to bear radiation; these indicated baker’s yeast may become one kind of excellent biosorbent to Sr2+in the future.