| Microbial induced carbonate deposition(MICP)is an application of biomineralization.The basic principle of the technology is to rely on the biological enzymes produced by microbial metabolism to promote the production of carbonate ions and combine with calcium ions in the environment to form a calcium carbonate precipitation.Calcium carbonate can adsorb and wrap the exchangeable heavy metals in the soil during the deposition process,thereby achieving the purpose of repairing heavy metal contaminated soil.In this paper,the Sporosarcina pasteurii was used as the target strain.Firstly,the growth characteristics of bacteria in heavy metal environment were studied,and then the strains were screened and domesticated.The remediation effect parameters were obtained through the remediation experiments on heavy metal liquids and soils,and the post-remediation pollution was obtained.The soil was tested for acid stability and freeze-thaw cycle stability.The microscopic analysis and qualitative testing techniques were used to investigate the mechanism of the remediation of manganese and chromium contaminated soil by MICP method and the mechanism of acid stability.Finally,the on-site grouting test was carried out to evaluate the Environmental effects of MICP method.The main conclusions are as follows:(1)Appropriate amount of Mn2+can promote the growth of Sporosarcina pasteurii,while Cr6+ can inhibit the growth and reproduction of bacteria,and Cr6+ has greater biotoxicity to the target strain than Mn2+.When the concentrations of Mn2+and Cr6+ in the medium reached 1100 mg/L and 700 mg/L,the rapid propagation period of the target strain was not observed,and the cells gradually lost their activity.Through the screening and domestication of strains,the highest tolerance concentrations of Mn2+and Cr6+ were 1300mg/L and 900mg/L.(2)With the increasing concentration of manganese and chromium pollutants,the remediation effect of microbial mineralization methods is gradually reduced.The exchangeable removal rates of manganese and chromium contaminated soil were 85.64%and 77.56%after three bioremediation.The remediation effect in soil was related to the remediation effect in water.The microbial mineralization method can effectively remove the exchangeable state in heavy metal contaminated soil and convert it into other relatively stable forms.Increasing the number of repairs can enhance the remediation effect on manganese and chromium contaminated soil.(3)The micro region analysis of the sediments produced under different conditions shows that the CaCO3 mineralized vaterite and calcite in the basic sediment coexist,the pores of the fine vaterite and the microporous structure on the surface of the calcite crystal can adsorb a large amount of heavy metals.The biomineralization remediation method fixes the manganese ions by surface adsorption and coprecipitation;while the chromium remediation is achieved by surface adsorption to fix the chromium ions;When the contaminated liquid contains both manganese and chromium,the specific gravity of manganese and chromium ions contained in the sediment is reduced,and the two metals interact with each other.(4)Both the acidic environment and the freeze-thaw cycle conditions can transform the manganese and chromium heavy metals in the repaired soil from carbonate-bound to exchangeable,and the acidic environment has a great influence on the stability of the restored soil.The occurrence of chemical action in an acidic environment results in the release of the exchangeable heavy metals adsorbed and the precipitation of calcium sulfate.Under the conditions of freezing and thawing,heavy metals are precipitated again due to physical destruction of the soil.(5)The by-product ammonia nitrogen produced by the biological grouting method has a certain impact on the surrounding water quality.Rainfall conditions will accelerate the migration of ammonia nitrogen,and the proper setting of the barrier wall prevent the spread of microbial remediation agents. |
PDF Full Text Request