Study On The Removal Of U(?)?Co(?)?Cr(?) By Microorganisms

In recent years,with the accelerating pace of human life,the development and utilization of mineral resources,the rapid development of industrial production,heavy metal contaminants enter the environment through various channels,leading to soil pollution by heavy metals,microbial remediation of heavy metal contaminated also pushed on the boom.In this study,Bacillus cereus,Citrobacter freundii and Serratia marcescens`s growth and the ability of removing U(?),Co(?),Cr(?)were studied under the condition of single U(?),Co(?)and Cr(?).The changes of morphology and elemental composition of microorganisms and heavy metals were analyzed by scanning electron microscopy-energy dispersive X-ray spectroscopy(SEM)and transmission electron microscopy(TEM).The tolerance and removal ability of Serratia marcescens to U(?),Co(?)and Cr(?)were studied systematically under single and mixed heavy metal conditions.The effect of prodigiosins on the removal of Cr(?)produced by Serratia marcescens was investigated,the effect of ethanol and the Serratia marcescens on the removal of Cr(?)was studied.The main results are as follows:(1)The tolerance and removal ability of microorganisms to single heavy metals: The growth of Bacillus cereus,Citrobacter freundii and Serratia marcescens and the removal of U(?),Co(?)and Cr(?)were investigated by UV spectrophotometry under single heavy metal concentration.The results showed that the removal rate was 90% at least under 50.0 mg/L U(?),the growth of Serratia marcescens was promoted at 30mg/L Co(?),Cr(?)exhibited strong biotoxicity.(2)Electron microscopic analysis of the interaction between microorganisms and heavy metals: The morphology and the morphological changes of cell surface of Bacillus cereus,Citrobacter freundii and Serratia marcescens before and after exposure to U(?),Co(?),Cr(?)was studied by scanning electron microscopy-energy dispersive X-ray spectroscopy.The morphological changes of the cells were studied by transmission electron microscopy(TEM).The results of SEM showed that U(?)mainly interacted with extracellular secretions and forms flocculent precipitates.the lamellar structure on the cell surface was formed by deposion or crystallization of Cr(?).The results of TEM showed that the plate crystal in the cells was formed by the interaction of Serratia marcescens and Cr(?).(3)Study on tolerance and removal ability of Serratia marcescens to single and mixed heavy metals: The tolerance and removal ability of the Serratia marcescens to single heavy metal U(?),Co(?),Cr(?)and mixed heavy metals U(?)-Co(?),U(?)-Cr(?),Co(?)-Cr(?),U(?)-Co(?)-Cr(?)was stuied.Results showed that: stick quality Shara's bacteria on single U(?),and Co(?)of tolerance sex and the removal capacity high,stick quality Shara's bacteria on U(?)of highest removal rate are can reached 90% above,low concentration of Co(?)also will promote stick quality Shara's bacteria of growth,and Cr(?)performance out has strong of biological toxicity.Mixed heavy metals under the action of U(?),Co(?)on the growth of Serratia bacteria,Cr(?)on the growth inhibition.(4)The effect of prodigiosins and ethanol on the removal of heavy metals by Serratia marcescens: The study concluded that when the temperature was 30?,p H=7,the rotary speed was 120 rpm,the yield of prodigiosins was highest;the prodigiosins was beneficial to the removal of a single heavy metal,the removal of the Cr(?)by Serratia marcescens can be promoted by 3.70% after adding ethanol.In conclusion,Serratia marcescens had the good tolerance and removal ability to U(?)and Co(?),which can produce prodigiosins,the low concentration of Co(?)can promote the growth of Serratia marcescens,prodigiosins and ethanol had a positive effect on the removal of heavy metals.The mechanism of microbial to remove the heavy metals included the interaction of extracellular secretions and heavy metals,deposion or crystallization to precipitated on the cell surface.This will provide a technical reference for microbial remediation of heavy metals(U(?),Co(?),Cr(?))contamination.