The Experiment And Mechanism Study Of Remediation Of Heavy Metal Contaminated Soil By Sporosarcina Pasteurii Based On MICP

In this paper,based on the microbial induced carbonate deposition（MICP）technology,using Sporosarcina pasteurii as the test strain,the effect and mechanism of mineralization and fixation of heavy metals copper,cadmium and lead ions were studied.First,select the most suitable growth conditions for bacteria and obtain bacteria with higher tolerance to heavy metals,then use domesticated bacteria to study the removal effect of Cu²⁺,Cd²⁺and Pb²⁺in water,and explore the removal mechanism through microscopic analysis;Above,the mineralization fixation characteristics of Cu²⁺,Cd²⁺and Pb²⁺in soil were studied through soil-water ratio test,oscillatory leaching test and soil column test,and the mineralization fixation mechanism was further explored through microscopic analysis.The paper obtained the following conclusions:（1）The optimal culture conditions for Sporosarcina pasteurii are:the culture temperature is 30°C,the culture time is 48h,the p H of the medium is 8.0;the increase in urea concentration and Ca²⁺concentration is beneficial to the growth of Sporosarcina pasteurii,the increase of Cu²⁺,Cd²⁺and Pb²⁺concentration is not conducive to grow.（2）When the concentration of urea in the liquid culture substrate is 1.0 mol/L and the concentration of Ca²⁺is 1.5 mol/L,the overall removal effect of Cu²⁺by Sporosarcina pasteurii is best,and the removal rate of Cu²⁺in water by Sporosarcina pasteurii is between61.30%and 86.80%.When the concentration of urea in the liquid medium is 1.0 mol/L and the concentration of Ca²⁺is 0.5 mol/L,the overall removal effect of Cd²⁺by Sporosarcina pasteurii is best.The removal rate of Cd²⁺in water by Sporosarcina pasteurii is between 49.1%and 99.95%.When the concentration of urea in the liquid medium is 0.5 mol/L and the concentration of Ca²⁺is 0.5 mol/L,the overall removal effect of Pb²⁺by Sporosarcina pasteurii is best;the removal rate of Pb²⁺in water by Sporosarcina pasteurii is between 40.88%and 99.99%.（3）In the soil-water ratio test,the fixation rate of Cu²⁺contaminated soil by Sporosarcina pasteurii is between 94.79%and 99.11%,and the fixation rate of Cd²⁺contaminated soil is between 82.88%and 99.31%,and the fixation rate of Pb²⁺contaminated soil is between 99.05%and 100.00%;in the shaking test,the fixation rate of Cu²⁺contaminated soil by Sporosarcina pasteurii is 91.27%～95.60%,and the fixation rate of Cd²⁺contaminated soil by Sporosarcina pasteurii is 85.73%～98.88%,the fixation rate of Pb²⁺contaminated soil is 91.35%～98.46%;in soil column test research,the fixation rate of Cu²⁺-contaminated soil column by Sporosarcina pasteurii is 99.44%～99.72%,and the fixation rate of Cd²⁺-contaminated soil column by Sporosarcina pasteurii is 99.50%～99.68%,and the fixation rate of Pb²⁺-contaminated soil column by Sporosarcina pasteurii is99.45%～99.75%.（4）The sediments obtained by Sporosarcina pasteurii removing heavy metal ions in the water are mainly composed of Ca CO₃ calcite and vaterite,and there are no other minerals containing heavy metal elements.This may be because the heavy metal ions are adsorbed on the surface of the bacteria.It is also covered by calcite and vaterite;the proportion of the two minerals in the sediment obtained by removing different heavy metal ions is different;the type of heavy metal will affect the particle-to-particle binding in its sediment.（5）The soil sample obtained by fixing the heavy metal ions from the soil with Sporosarcina pasteurii has only calcite minerals of Ca CO₃,but no vaterite;the soil samples obtained by fixing the heavy metal ions from the soil with Sporosarcina pasteurii also have no minerals containing heavy metal.Further verified that the mechanism of microbially induced carbonate precipitation（MICP）technology to repair heavy metals is because heavy metal ions are adsorbed on the surface of bacteria and covered by carbonate minerals,so heavy metal ions are deposited along with bacteria and carbonate minerals.This reduces the heavy metal concentration.