Utilizing Indigenous Microorganisms to Stabilize Humus Soil from a Municipal Solid Waste Landfill with Optimized Microbial Strain Selection

A major challenge in utilizing humus soil excavated from municipal solid waste (MSW) landfills for landscaping is stabilizing heavy metals while preserving beneficial soil properties. Microbially induced calcium carbonate precipitation (MICP) technology offers a promising solution for this. In this study, seven indigenous urease producing bacteria were isolated from humus soil and their effectiveness in stabilizing the soil was evaluated. A comparative analysis was conducted between Bacillus pasteurii (BA) and the seven indigenous strains. All strains thrived and effectively performed MICP in the humus soil leachate environment, contributing to solidification/stabilization. Some strains outperformed BA in specific parameters. Among them, Brucella oryzae (Q2-9) exhibited the best performance, with urease activity reaching 52.38 mmol/L, bacterial concentration (OD600) reaching 2.446, and optimal solidification/stabilization effects on humus soil. Following treatment, the unconfined compressive strength of specimens increased to 2.983 MPa, while average particle size rose to 0.91 mm. The heavy metal fixation rates for Cr, Pb, Cu, Zn, Cd, Ni and Mn were 85.03%, 99.50%, 63.24%, 80.75%, 93.92%, 77.23% and 71.21% respectively, with leaching concentrations all meeting Class IV of the Standard for groundwater quality (GB/T 14848-2017). Consequently, Q2-9 is a preferred strain for MICP-based stabilization of humus soil. This strain has been deposited at the China Center for Type Culture Collection under the accession number CCTCC M 2021810 Q2-9.