Study on engineering properties and environmental safety of bio-stimulated 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 bacterial activity indexes such as soil pH, viable cell number, urea and ammonium concentration were investigated by biostimulated MICP method. The unconfined compressive strength, permeability, and toxicity leaching concentration of the solidified lead-contaminated soil were used to evaluate the solidification effect. The findings demonstrated that the biostimulation method could realize the enrichment of ureolytic bacteria in low lead concentration contaminated soils. The viable cell number could reach 109 CFU/g after 7 days of enrichment, but the high concentration of lead contaminants would significantly inhibit the growth and activity of microorganisms. The strength and impermeability showed an increasing trend with solidifying time, and the strength of 40 mM lead-contaminated soil increased significantly and the permeability coefficient could be decreased to 6.5×10-6 m/s after solidifying for 14 days. The leaching concentration also reduced with solidifying time, and the leaching concentration of 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 lead-contaminated soil treated by biostimulated MICP was revealed by combining scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and microbial 16s whole genome resequencing.