Synergistic enhancement of cadmium immobilization and soil fertility through biochar and artificial humic acid-assisted microbial-induced calcium carbonate precipitation

Microbially induced carbonate precipitation (MICP) is emerging as a favorable alternative to traditional soil remediation techniques for heavy metals, primarily due to its environmental friendliness. However, a significant challenge in using MICP for farmland is not only to immobilize heavy metals but also to concurrently enhance soil fertility. This study explores the innovative combination of artificial humic acid (A-HA), biochar (BC), and Sporosarcina pasteurii (S. pasteurii) to mitigate the bioavailability of cadmium (Cd) in contaminated agricultural soils through MICP. X-ray diffraction (XRD) and scanning electron microscope (SEM) analyses revealed that the integration of BC and A-HA significantly enhances Cd immobilization efficiency by co-precipitating with CaCO3. Moreover, this treatment also improved soil fertility and ecological functions, as evidenced by increases in total nitrogen (TN, 9.0-78.2%), alkaline hydrolysis nitrogen (AN, 259.7-635.5%), soil organic matter (SOM, 18.1-27.9%), total organic carbon (TOC, 43.8-48.8%), dissolved organic carbon (DOC, 36.0-88.4%) and available potassium (AK, 176.2-193.3%). Additionally, the relative abundance of dominant phyla such as Proteobacteria and Firmicutes significantly increased with the introduction of BC and A-HA in MICP. Consequently, the integration of BC and A-HA with MICP offers a promising solution for remediating Cd-contaminated agricultural soil and synergistically enhancing soil fertility. This study presents a groundbreaking approach to remediating cadmium (Cd)-contaminated agricultural soils using a combination of biochar (BC), artificial humic acid (A-HA), and Sporosarcina pasteurii. By promoting microbial-induced calcium carbonate precipitation (MICP), the research demonstrates significant advancements in immobilizing Cd, thereby reducing its bioavailability. This process not only detoxifies the soil but also enhances its fertility and ecological functions, as evident from improvements in soil organic matter, nitrogen content, and microbial diversity. Importantly, it offers an eco-friendly alternative to conventional heavy metal remediation methods, reducing the environmental footprint associated with soil decontamination efforts and promoting sustainable agricultural practices.