Bio-augmented microbial induced carbonate precipitation for immobilizing Pb contaminants in soil

Abstract Heavy metal contamination, particularly lead (Pb), poses severe threats to ecosystems due to its persistence and bioaccumulation. This study investigates the remediation of Pb-contaminated soil using bio-augmented microbial induced carbonate precipitation (MICP). The effects of Pb concentration and soil depth on bacterial activity (viable cell counts and urease activity) were evaluated. Furthermore, the impact of different calcium sources and Pb concentrations on immobilization efficiency was assessed via unconfined compressive strength (UCS) tests. The results indicate that the bacterial tolerance threshold for Pb is 50 mmol/L, beyond which the MICP process is significantly inhibited. However, within this threshold, bio-augmented MICP effectively enhances soil strength, achieving a UCS of 0.94 MPa in soil with 50 mmol/L Pb. Microstructural and physicochemical analyses reveal that the remediation mechanism involves the precipitation of carbonate, co-precipitation, and the transformation of macropores into capillary pores. Notably, this study elucidates the distinct advantages of bio-augmentation, particularly its robust tolerance to Pb toxicity and sustained mineralization capability, in reducing the bioavailability of Pb in contaminated soil matrices.