Studies On Microorganism - Strontium, Uranium Interactions And Mechanisms

The contamination of wastewaters by radionuclide is a worldwide environmental problem. Biosorption, as an alternate method, is becoming one of the more attractive methods for the removal of radioactive nuclide ions from wastewaters. But few literatures have focused on the biosorption of microorganism under culture conditions. The biosorption and bioaccumulation of strontium and uranyl ions by selected and acclimated microorganisms, the interaction and tolerance mechanisms were studied in this dissertation. The main results were showed as follows:(1) Eight strains of yeast cell were acclimated after Flash X-ray radiation through stress induction.The selected and acclimated microbes showed good strontium ions and uranyl ions biosorption and bioaccumulation capacity with >90% biosorption efficiency under culture conditions. The cell wall was the main biosorption sites, wich accout for 90% uptake quantity; while the cell may bioaccumulate the strontium or uranyl ions in cytoplasm, which contributed 10% uptake quantity. The strontium and uranyl ions would partly interact with the culture medium and produced pesudo-biosorption effect. A new bioaccumulation model was proposed based on the biosorption and bioaccumulation mechanism under culture conditions.(2)The simulated middle and low radioactive wastewater showed low toxic to selected microorganisms in short time under culture conditions. The selected microbes showed high selective biosorption and bioaccumulation capacity with >90% biosorption efficiency for Sr²⁺, while the bisorption quantity for Fe³⁺, Ni²⁺, Cr³⁺ was larger than Sr²⁺. The biosorption equibrium met isotherm equations. The pseudo-second order kinetic model and new bioaccumulation model were used to describe the biosorption and bioaccumulation kinetics.(3)The calcium alginate immobilized yeast cell particles showed >80% biosorption efficiency for Sr²⁺. The static adsorption results showed that the packed column had high adsorption quantity. The average adsorption ratio was 88%. The chromatography with packed column had carried out two runs (four cycles per run) and the results showed that the immobilized yeast cell beads packed column had good chromatography performance with high adsorption ratio, high elution ration, good readsorption ratio and perfect manipulation stability.(4) The mesoscopic analytic results revealed that the strontium or uranyl ions first bind to the cell surface, then the strontium or uranyl ions may transport into the cytoplasm and bioaccumulate in the vacuole of the cell through metabolism - dependent ways. The AFM results suggested that the strontium ions may form nanometer level mineral particles such as SrCO₃. The simulated radioactive wastewater or uranyl ions may form precipitate on the cell surface.(5) The FTIR results revealed that yeast cell wall was the major sorption sites and the–O-H,–C=O and–PO^2- contributed to the major binding groups. The strontium and uranyl ions may form coordination complex with O, N or P of the active groups on yeast cell surface. The XPS results proved that the ions exchange was one of the bisoorption mechanisms. The strontium ions may interact with free anions in culture medium to form precipitate and active groups on cell surface to form coordination complex.(6)The ashing and XRD results showed that the strontium existed in the ash of incinerated yeast cell sedimentation as SrSO₄ or Sr₃(PO₄)₂, which was a result of strontium interaction with free anions in culture medium and active groups on cell surface. So uranyl or strontium ions may form precipitate or biomineral particles on the cell surface as a cell detoxicant manner.(7) The volume decreasing ratio (VDR) showed that the biosorption may lead to great volume decreasing ratio. The VDR results showed that the biosorption by yeast cell combined with incineration/ashing was a potential radioactive waste disposal method for further treatment such as solidification.The results proved that the biosorption and bioaccumulation under culture conditions was an efficient and quick volume decreasing methods for radioactive wastewater disposal. But the biosorption was a complex process including ion-exchange, coordinate and complexation biosorption, bioaccumulation, biomineration, precipitating with culture medium etc. under culture conditions.