Reduction Of U(â…¥) By Shewanella Oneidensis MR-1 Imbedded In PVA

A dense mass of wastewater containing uranium was generated in uranium mining, which presents or could present serious harm to environment and humans. How to use the cost-effective ways to remove the radioactive nuclide from wastewater, even to recycle the metal resources, such as uranium, is currently the problems of security and environment to be solved. The traditional physical and chemistry methods could remove uranium, but it also has some problems, such as the high cost of chemicals and easy to cause secondary pollution. Bioremediation treatment methods have been brought to the focus, for its advantages of sufficient raw materials, low cost, high treatment efficiency and no secondary pollution.Heavy metal ions such as Cr(VI) and Hg(II) and radioactive nuclide such as U(VI) and Tc(VII) could be efficiently reduced by Shewanella. It has broad prospects which heavy metal ions and radioactive nuclide could be reduced and removed by Shewanella. Our group has researched the characteristics of reduction of U(VI) by Shewanella oneidensis. In this test Shewanella oneidensis was used as reducing bacteria and polyvinyl alcohol was used as imbedding material. Shewanella oneidensis was imbedded in polyvinyl alcohol. The optimal imbedding conditions andthe characteristics of reduction of U(VI) by the embedding microspheres were determined.The results indicated that Shewanella oneidensis imbedded in could efficiently reduce U(VI). The optimum conditions for the embedding microspheres was as follow: polyvinyl alcohol 10%; Ca Cl2 4%; crosslinking time 4h, in terms of the difficulty of forming beads, mechanical stability and mass transfer characteristics. It’s benefit for the embedding microspheres to add 0.5% sodium alginate. The highest removal rate of U(VI) by imbedded microspheres could reach 96.22% in the condition of C0(U)=15mg/L, VMR-1=6m L and VMR-1:VPVA=1:2. Scanning electron microscope showed that the surface of microsphere is damaged after the reduction, means U(VI) has toxic action on Shewanella oneidensis. The crystals were sedimented on the surface and inner. Electron spectrum showed that the absorption peak of uranium appears after the reduction. Comprehensive analysis the crystals are U(IV), which is reduced by Shewanella oneidensis and sediments. Coexisting metal ions(Cu2+,Mn2+,Ca2+) had different impact on the imbedded microspheres. There was weak promotion on the imbedded microspheres to reduce the U(VI) when the Ca2+ concentration is 2.0mmol/L. On the contrary, equal concentrations of Cu2+ and Mn2+ could cause varying degrees of inhibition of U(VI) reduction.