Engineering properties and environmental safety of biostimulated MICP-treated lead-contaminated soil

With the acceleration of urbanization, the remediation, development and reuse of heavy metal-contaminated sites have attracted increasing attention. Taking the typical heavy metal contaminant lead as the research object, the effects of lead concentration on the bacterial activity indexes such as pH of soil, number of viable cell, concentration of urea and ammonium are investigated by using the biostimulated MICP method. The unconfined compressive strength, permeability and toxicity leaching concentration of the solidified lead-contaminated soil are used to evaluate the solidification effects. The findings demonstrate that the biostimulation method can realize the enrichment of ureolytic bacteria in low lead concentration contaminated soils. The number of viable cell can reach 10⁹ CFU/g after 7 days of enrichment, but the high concentration of lead contaminants significantly inhibits the growth and activity of microorganisms. The strength and impermeability show an increasing trend with solidifying time, and the strength of 40 mM lead-contaminated soil increases significantly and the permeability coefficient can be decreased to 6.5×10^-6 m/s after solidifying for 14 days. The leaching concentration also decreases with solidifying time, and the leaching concentration of the low lead concentration-contaminated soil solidified for 14 days can be lower than 0.1 mg/L in neutral or weakly acidic environment. Based on the engineering properties and environmental safety tests, the solidification mechanism of the lead-contaminated soil treated by the biostimulated MICP is revealed by combining the scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and microbial 16 s whole genome resequencing.