The Study On Interaction Mechanisms Of Chromium,Uranium With Bacillus Thuringiensis 016

With the rapid development of industry,the pollution of heavy metal has become more and more serious.Bioremediation has attracted the attention of many scholars due to their strong self-reproduction ability,low cost,environmental friendliness and suitable for real-time field treatment of large-area pollution.In this paper,Bacillus thuringiensis was used as the research object,its repairing effect on chromium and uranium was studied,and the related mechanism also was explored.The main contents are as follows:?1?Bacillus thuringiensis 016 had a good adsorption effect on uranium.When the initial concentration of uranium was 100 mg/L,the adsorption efficiency was 100%,and U?VI?was mineralized into uramphite[?NH₄??UO₂?PO₄?3H₂O]eventually.The adsorption of uranium by B.thuringiensis 016 was a non-enzymatic process in which the functional groups such as carboxyl,amino and phosphate groups played a key role.High concentrations of uranium have no significant influence on the adsorption process.The mineralization of uranium by B.thuringiensis 016 was the result of the interaction of enzyme and cell metabolism.At the same time,it was found that B.thuringiensis 016 has only adsorption ability for the high concentration of uranium.In addition,when pH=5,B.thuringiensis 016 had the best adsorption and mineralization effect on uranium.Besides,the reaction of B.thuringiensis 016with uranium was a rapid process consisting of extracellular bioadsorption and intracellular biomineralization.After reacted 1 h,uranium can be adsorbed on the surface of bacteria in the form of flake compounds.After reacted 8 h,these compounds gradually entered the interior of the cells.Furthermore,by tracking the concentration of soluble U?VI?in the cells,it was confirmed that the amorphous compounds,formed on the cell surface,were in an insoluble form when entering the cells.?2?B.thuringiensis 016 can effectively reduce hexavalent chromium to trivalent chromium.When the initial concentration of chromium is 25 mg/L,the reduction efficiency was close to 100%,and the fixed efficiency was about 92%.The trivalent chromium was likely to be combined with functional groups on the surface of the bacteria or other organic substances to form an organic trivalent chromium compound.In addition,pH had little effect on reduction and immobilization of chromium by B.thuringiensis 016.Whether in strong acid or strong alkali environment,the reduction and fixation efficiency of bacteria to chromium can reach more than 80%.The cell debris played a major role in reduction and immobilization of chromium.Protein denaturation experiments further demonstrated that the reduction of chromium by B.thuringiensis 016 is an enzymatic reaction.?3?We compared the effects of several microorganisms on the reduction of chromium.The results showed that Bacillus thuringiensis and Ochrobactrum anthropic had better reduction and fixation effects on chromium,and the reduction efficiency was above 90%,the fixation efficiency was above 80%.In addition,the reduced trivalent chromium cannot be completely fixed,and some organic trivalent chromium remained in the supernatant.The zeta potential showed that the organic chromium were negative at different pHs.Among the soil minerals,kaolin and illite had almost no reduction and fixation effect on chromium.However,after adding minerals to the reaction system of bacteria and chromium,the reduction and fixation of chromium by kaolin can be promoted almost 2%³.6%and 5%¹5%,respectively.After the addition of illite in the system of B.thuringiensis 016 with chromium,the reduction rate was reduced by 32%and the fixation rate was reduced by 34%.