Analysis Of Microbial Diversity And Isolation Of Cr(?) Leaching Strain In Soil

With the rapid development of China's economy,the demand for minerals and other commodities continues to strengthen.From mining to end products,some heavy metals are not used but become pollutants,of which hexavalent chromium pollution has become one of the most toxic and migratory pollutants.In this paper,four aspects were studied: the influence of hexavalent chromium pollution on microbial diversity and community structure,the screening of chromium-tolerant bacteria and the interaction mechanism between chromium-tolerant bacteria and hexavalent chromium,and the separation of microorganisms that can promote the leaching of hexavalent chromium in soil,the optimization of leaching conditions and leaching mechanism of leaching bacteria,the screening of the best biological additives to enhance the leaching of microorganisms and the study of leaching mechanism;In order to explore the continuous impact of hexavalent chromium pollution on soil environment and efficient and green microbial leaching technology.The conclusions of the study are as follows:Studies on microbial diversity have revealed that a certain degree of hexavalent chromium pollution will stimulate the increase of microbial diversity,while higher pollution will lead to the difficulty in the survival of many microorganisms.At the same time,all microorganisms will adapt to different degrees of environmental pollution and lead to changes in relative abundance.Some microorganisms,such as Bacteroides,Acinetobacter,Actinomyces and Sclerotinia,will become the dominant phylum due to their better adaptation to chromium pollution.In the experiment of screening chromium-tolerant bacteria and studying the interaction mechanism between chromium-tolerant bacteria and hexavalent chromium,eight chromium-tolerant microorganisms were screened and separated,and all of them had no reduction effect on hexavalent chromium.Among them,four microorganisms had a certain adsorption effect on hexavalent chromium,and Beauveria bassiana had the best adsorption effect on hexavalent chromium.When the initial hexavalent chromium concentration was50mg/L,the adsorption rate reached the maximum of 94.6%,and the adsorption effect decreased with the increase of the initial hexavalent chromium concentration.The adsorption of hexavalent chromium by Beauveria bassiana was mainly through the extracellular group adsorption.The remaining four microorganisms had a certain role in promoting the leaching of hexavalent chromium in soil.Fusarium solani had the best leaching effect on hexavalent chromium in soil,and the removal rate reached 69.91% after three days.According to the infrared spectrum measurement,the secreted total organic matter mainly contains amide,carboxyl and hydroxyl groups,and the effective component is a glycolipid substance;and the Fusarium solani can physically adsorb soil particles,so that the dispersibility in the leaching process is improved.In that optimize experiment of leaching condition.Under the condition of rotating speed of 200 rpm,liquid/soil ratio of 15: 1,temperature of 35?,and p H of 7,the maximum removal rate reaches 80.00%.After leaching,there are still leaching effective substances in the soil,the exchangeable and carbonate-bound forms of total chromium in the soil are greatly reduced(both content is less than 1%),and there is no obvious change in the soil crystal structure after leaching.In the optimal adjuvant screening experiment,the hexavalent chromium in the soil was leached by Fusarium solani by adding tea saponin,rhamnolipid,sophoolipid and glucose.The results showed that when the amount of tea saponin was 2g/100 ml,the removal rate by leaching reached the maximum of 85.31%.After leaching,through SEM and mapping analysis,the soil became obviously loose and porous,and the relative contents of Cr,Mn and Fe in the soil decreased from 8%,7% and 19% to 6%,6% and 13%,respectively.The exchange state and carbonate binding state were further reduced,and the soil crystal structure was not significantly changed.The concentration of hexavalent chromium leach by“the sulfuric acid-nitric acid method”(HJ/T299)is reduced from 49.10 to 0.43mg/L of the original soil,which is high than the class III standard limit of 0.05 mg/L in “the groundwater quality standard”(GB/T 14848-2017)for in-situ backfilling.The hexavalent chromium concentration leach by “the acetic acid buffer solution method”(HJ/T300)is reduce from35.90 of the original soil to 0.28mg/L,which is far lower than the admission limit of 1.5mg/L in “the pollution control standard for domestic waste landfill”(GB 16889-2008)and meets the standard for entering a waste landfill.