Study On Microbacterium Sp.YL3 Combined With CS/PPy Composite For Remediation Of Cr(Ⅵ) Contaminated Soil

The remediation of Cr（Ⅵ）contaminated soil has attracted extensive attention.The combination of physicochemical and biological remediation has many advantages such as environmental protection and high efficiency.In this paper,the isolated and screened Cr（Ⅵ）reducing strain Microbacterium sp.YL3 and the prepared chitosan/polypyrrole（CS/PPy）composite were applied to Cr（Ⅵ）contaminated soil,and achieved good remediation effect.The research mainly includes the following contents:（1）A Cr（Ⅵ）reducing bacterium was screened and isolated from a chromium contaminated soil in Anyang city,Henan Province.It was identified as Microbacterium sp.And named YL3.The physiological characteristics of Microbacterium sp.YL3 strain were studied.The colony morphology of Microbacterium sp.YL3 is yellowish round,the optimum p H is 7-8,the optimum salinity is 1%（10 g/L）,the optimum growth temperature is 30℃,and the growth reaches logarithmic stage for 42 h.In the liquid environment of 50mg/L,Cr（Ⅵ）was 100%reduced at 60 h,and the highest tolerance concentration of Cr（Ⅵ）was 300 mg/L.The main mechanism of Cr（Ⅵ）removal by strain YL3 is reduction,but not adsorption.The reduction process mainly occurs in the cell,and there are reductase or reductive substances in the cytoplasm and cell membrane,and the reduction of Cr（Ⅵ）mainly occurs in the cytoplasm.（2）CS/PPy was obtained by in-situ oxidation polymerization with chitosan as matrix and Fe Cl₃ as oxidant,and its structure was loose and spongy.In 2.5 g chitosan,CS/PPy prepared with 1.0 m L pyrrole has good adsorption performance,with a specific surface area of 42.6 m²/g and a zero potential about 6.3 m V.Decreasing p H and increasing reaction temperature are beneficial to the removal of Cr（Ⅵ）.The adsorption process of Cr（Ⅵ）by CS/PPy conforms to the quasi-second-order kinetic model（R²>0.99）,and is a spontaneous endothermic process in which the disorder degree of the reaction system increases.The removal of Cr（Ⅵ）in solution by CS/PPy can be divided into three processes:adsorption of Cr（Ⅵ）,reduction of adsorbed Cr（Ⅵ）to Cr（III）,and the generation of Cr（III）after reduction.（3）In this chapter,YL3 and CS/PPy composite materials were combined for the remediation of 200 mg/kg simulated Cr（Ⅵ）contaminated soil.After 15 days of remediation,100%removal of Cr（Ⅵ）could be achieved,which was 2.5 times and 1.1times of YL3 and CS/PPy alone.With the BCR step extraction method,it was found that the content of residual Cr in soil increased,and Cr element tended to be more stable and less toxic.Synergistic remediation significantly increased the activities of soil dehydrogenase,sucrase and urease,and increased the number of soil microorganisms.High-throμghput sequencing results showed that CS/PPy increased microbial abundance in contaminated soil,and YL3+CS/PPy corrected the negative effects of YL3 addition on soil microbial abundance.The results showed that fresh weight,stem length,root length,contents of chlorophyll and chromium content in ryegrass were 11.1,1.29,1.07,1.56 and0.22 times of CK group,respectively,and the growth of ryegrass even exceeded that of unpolluted soil.In this study,the combination of chemical remediation materials and microorganisms was innovatively applied to Cr（Ⅵ）contaminated soil,and 100%removal of 200 mg/kg Cr（Ⅵ）contaminated soil could be completed within 15 days,without bringing potential harm to soil and affecting soil reuse performance.It provides an idea for the application of multiple technologies in soil remediation.