Ureolytic Consortium enriched from contaminated soil: Identification, acclimatization and its potential for immobilization of heavy metals

Heavy metal contamination is widespread in the environment and poses a significant threat to the ecosystem. Microbially induced calcite precipitation (MICP) method is known to immobilize heavy metals through co-precipitation with CaCO 3 . To enhance heavy metal tolerance and environmental adaptability, the ureolytic Consortium HMsoil-01 was enriched from certain heavy metal contaminated soil, subsequently acclimatized and identified, and its role in mediating ureolytic-driven MICP for heavy metals immobilization was examined. The optimal growth conditions of Consortium HMsoil-01 were achieved at a cultivation time of 28 h, a temperature of 31 °C, and pH=7.0. The Consortium HMsoil-01 efficiently immobilized heavy metals in aqueous solution via co-precipitation with CaCO 3 , achieving a removal ratio above 74.3, 74.5, and 99.0% for Cu 2+ , Cd 2+ , and Pb 2+ at initial concentrations from 100 to 800 mg/L. Mineralogical analysis showed that heavy metals were primarily immobilized by incorporation into the calcite and vaterite in aqueous solution. Due to the limited pore space in the soil structure, well-defined micron-sized spherical and rhombohedral crystals were not detected in the soil; however, fine nano-sized calcite crystals were observed. Heavy metals in contaminated soil can be effectively immobilized by CaCO 3 through co-precipitation and physical encapsulation into the mineral matrix, resulting in the leaching concentrations of Cd 2+ , Cu 2+ , and Pb 2+ decreasing by 8.3%, 18.9%, and 28.2%, respectively. Meanwhile, this co-precipitation pathway could transform the weak acid-extractable metals into the residual fraction, reducing the potential toxicity of heavy metals. These findings demonstrated the promising application potential of Consortium HMsoil-01 in immobilizing heavy metals.