Effects Of Microbial Induced Carbonate Precipitation On Soil Aggregates And Microbial Communities

With the massive exploitation of mineral resources,the accumulation of tailings and the leakage of waste liquid around the mining area,the heavy metals in the tailings not only cause serious damage to the surrounding soil environment,but also bring a serious threat to food security.At present,the remediation technology of heavy metal pollution in soil is mainly physical and chemical,but it has some disadvantages,such as large engineering quantity,secondary pollution and so on.Bioremediation has gradually become the mainstream repair technology because of its advantages of economy and environmental protection.In this paper,through the laboratory simulation experiment,Microbial induced carbonate precipitation technology(MICP)was used to stabilize the Pb in the soil,the screening method and CT technology were used to study the effect of MICP on the soil physical structure,and the modern molecular biology technology was used to study the microbial community.To comprehensively evaluate the effect of MICP on the stabilization of heavy metals in soil and its effect on soil ecological environment.(1)By analyzing the stabilization effect of MICP on Pb,it is shown that MICP can reduce the content of available Pb in soil.The leaching rate of Pb in the soil decreased by up to 76.34%,and the proportion of available heavy metal Pb decreased by 41.64%.The content of carbonate-bound Pb increased by 13.24%.Through scanning electron microscope(SEM)and X-ray diffraction(XRD)analysis,it can be observed that Pb and calcium carbonate coprecipitated and attached to the surface of soil particles and were fixed.At the same time,MICP technology has a great influence on the basic physical and chemical properties of soil,such as pH,electrical conductivity and the content of organic matter.It significantly increased the soil electrical conductivity and the content of various nutrients.(2)The sieving method was used to analyze the soil particle size composition and water stability.After MICP remediation,the soil particle size increased,the content of macroaggregates increased,and the soil water stability after bioremediation was stronger,and the fragmentation rate of soil aggregates was lower.Therefore,MICP remediation technology can not only stabilize heavy metals,but also improve soil physical structure,enhance the mechanical stability and water stability of soil aggregates,thus improve the ability of soil to resist wind erosion and water erosion,and make the stability of heavy metals in soil stronger.CT analysis showed that MICP bioremediation significantly increased the total porosity and total number of pores of aggregates,especially the porosity occupied by macropores.The total porosity increased by 42.07%,73.78% and 50.61% respectively compared with the control group,and the number of soil pores increased by 11.13%,11.13% and 31.38%,respectively.The increase of macropores increases the soil ventilation,improves the hydraulic conductivity,and makes the soil structure better.(3)Using 16 S rRNA to analyze soil microbial communities before and after remediation,the study found that MICP technology to repair soil heavy metal pollution will affect the indigenous microbial community.Due to the addition of specific nutrients,soil microbial diversity and abundance are reduced.At the same time,through the analysis at the door level and the genus level,the biological treatment will change the soil microbial composition.The main dominant bacterial groups in the soil with different treatment methods are different;through the PICRUSt function prediction analysis.The metabolic function of the soil microbial community is very rich,and there is no change in the functional composition,and the functional abundance is significantly reduced after bioremediation.After adopting MICP bioremediation,the dominant genes in the functional genes of the soil microbial community are carbohydrate transport and metabolism,inorganic ion transport and metabolism,transcription,etc.Therefore,although MICP bioremediation has certain effects on the composition and function of the microbial community in the soil environment of the soil,will not affect the overall ecological function of soil microorganisms.