Microbial Mineralization Remediation Technology And Demonstration Of Compound Heavy Metal Contaminated Farmland Soil

Heavy metals are a kind of potentially harmful chemical pollutants,which are mainly introduced into soil through chemical fertilizer and pesticide application,sewage irrigation,and unreasonable disposal of garbage,and thus lead to deterioration of the environmental quality of soil ecosystem.Soil in northern China is also faced with environmental challenges such as drought,high wind erosion and high salinity,making remediation techniques that are effective in the south not applicable in the north.In this study,the farmland soil contaminated by complex heavy metals caused by sewage irrigation around Guanjiang Village,Baotou City,Inner Mongolia was used as the research object,and the bacteria powder produced in the laboratory was used to repair the soil contaminated by complex heavy metals.The optimum conditions for the growth of fungus powder and the tolerance degree of heavy metals were determined by studying the environmental adaptability of fungus powder.To drop village officer ten acres experimental sample plot investigation and analysis of soil physical and chemical properties and heavy metal content,based on the microbial mineralization repair technology,to exert demonstration zone soil bacterium agent,additives,bacterium agent to add fertilizer combination treatment,on the repair of heavy metals in the soil before and after the curing efficiency,at the same time,combined with modern molecular biology techniques of microbial community diversity research,The growth indexes of the restored plants were verified.The main results obtained are as follows:(1)The study on the environmental adaptability of Monceoeae powder showed that the optimal concentration of urea and Ca ion was 0.4 mol/L and 0.2 mol/L,respectively.The mineralized product of monceoeae powder was confirmed to be calcium carbonate precipitation with calcite as the main crystal type by XRD,SEM and FTIR analysis.The tolerance of Pb,Zn and Cd to single heavy metal stress was up to 4 mmol/L,3 mmol/L and0.5 mmol/L,respectively.The tolerance degree of bacteria under combined heavy metal stress decreased.Monseyotrophic bacteria had good removal effect on three kinds of heavy metals,among which,the removal effect on heavy metal Pb was the best,and the highest removal rate could reach 74.21 %.(2)The demonstration area is farmland soil covering an area of 10 mu.A total of 42 sampling sites are set up in the demonstration area.Among them,Pb content ranges from32.09 mg/kg-312.29 mg/kg,20 sites exceed the soil screening value,and Zn content ranges from 82.71 mg/kg-791.66 mg/kg.Thirty-one sites exceeded the soil screening value,and the content of Cd ranged from 0.14 mg/kg to 1.02 mg/kg,and 20 sites exceeded the soil screening value,While Cr,As and Hg did not exceed the standard.The soil p H value ranged from 7.96-9.14,with an average of 8.54,and was alkaline soil.The distribution of soil nutrient contents in N,P and K levels was uneven,with N at grade 4 and grade 5,namely,medium and low level.P is at grade 3 and 4,namely above and middle level;K at level 2 means high level and abundant.(3)Soil samples were collected after the end of the remediation cycle to verify the solidification effect of heavy metals.After the microbial agent remediation,the leaching toxicity of heavy metals decreased by more than 20 %,the morphology of heavy metals changed,the content of exchangeable states with easy migration decreased,and the carbonate binding state increased.At the same time,the physical structure of soil was improved,the formation of soil aggregates was promoted,the nutrient index of soil was improved,the organic matter content was increased by 14.27 %-28.91 %,the inorganic carbon content was increased by 21.96 %-110.74 %,and the total carbon content was increased by 6.07 %-45.81 %.(4)Using metagenomic analysis of soil microbial community diversity in the study area after bioreremediation.It was found that remediation of soil contaminated by complex heavy metals by microbial mineralization would affect the structure of indigenous microbial community.After exogenous microbial agents were added,the species abundance of microorganisms changed,and Firmicutes became the species with the largest phylum level abundance,while the species abundance of the group with only additives did not change significantly compared with the control group.At the same time,through αdiversity and β diversity analysis,it can be concluded that after the addition of biological agents,The biodiversity and abundance of soil microorganisms were significantly lower than that of the control group.(5)After soil remediation,Chinese cabbage was planted.The results showed that the growth condition of Chinese cabbage could be significantly improved after soil remediation.The weight per square meter of Chinese cabbage was increased by 234.15 %to 656.09 %.Improve photosynthetic pigment content and soluble protein and other plant nutritional indicators.After restoration,the enrichment of Pb,Zn and Cd in the root of pakchoi was verified,and the enrichment in the root was significantly higher than that in the leaf of pakchoi in the control group.The heavy metal Pb content in the leaf of pakchoi in the control group was 0.5 mg/kg,and the heavy metal Pb content in all groups of pakchoi after treatment was lower than 0.3 mg/kg.It meets the requirements of GB2762-2017 national Standard for Food Safety-Limits of Contaminants in Food,and heavy metals Zn and Cd also do not exceed the standard,indicating that it is feasible to use microbial mineralization remediation technology to rehabilitate large-scale complex heavy metal contaminated farmland soil.