Integration of Urease-Producing Bacteria with Biochar for Enhanced Heavy Metal Immobilization

Soil heavy metal contamination poses a severe threat to agricultural safety, ecosystems, and public health.In situ immobilization using pyrolyzed biochar has emerged as a cost-effective, sustainable remediation strategy.Pristine biochar derived from agricultural waste like crop straw stabilizes heavy metals through physical adsorption, electrostatic attraction, surface precipitation, ion exchange, and complexation.However, limited adsorption capacity and aging-induced re-release risks necessitate functional modifications.Physical (e.g., ball milling, steam activation), chemical (e.g., acid, alkali, oxidant, and sulfur/phosphorus impregnation), and biochar-based composite approaches significantly enhance specific surface area, porosity, and oxygen-containing functional groups.Furthermore, incorporating microbial biomineralization-such as ureolytic bacteria (Sporosarcina pasteurii) that catalyze urea hydrolysis to precipitate calcium carbonate-further locks heavy metals into stable mineral lattices.Despite these advances, environmental factors including acid rain, dynamic redox shifts, dissolved organic matter, and biotic interference from plant roots or earthworms can degrade biochar efficacy over time.Long-term field evaluations and standardized risk assessments remain essential to optimize modified biochar and biomineralization technologies for durable, field-scale soil restoration.