Microbiologically induced calcite precipitation (MICP) in situ remediated heavy metal contamination in sludge nutrient soil

Microbiologically induced calcite precipitation (MICP), as a newly developing bioremediation technology, could redeem heavy metal contamination in diverse scenarios. In this study, MICP bacterium Sporosarcina ureilytica ML-2 was employed to suppress the pollution of Pb, Cd and Zn in municipal sludge nutrient soil. After MICP remediation, the exchangeable Cd and Zn in sludge nutrient soil were correspondingly reduced by 31.02% and 6.09%, while the carbonate-bound Pb, Cd and Zn as well as the residual fractions were increased by 16.12%, 6.63%, 13.09% and 6.10%, 45.70%, 3.86%, respectively. In addition, the extractable Pb, Cd and Zn either by diethylenetriaminepentaacetic acid (DTPA) or toxicity characteristic leaching procedure (TCLP) in sludge nutrient soil were significantly reduced. These results demonstrated that the bio-calcite generated via MICP helped to immobilize heavy metals. Furthermore, MICP treatment improved the abundance of functional microorganisms related to urea cycle, while reduced the overall abundance of metal resistance genes (MRGs) and antibiotic resistance genes (ARGs). This work confirmed the feasibility of MICP in remediation of heavy metal in sludge nutrient soil, which expanded the application field of MICP and provided a promising way for heavy metal pollution management. Municipal sludge is a repertoire of various pollutants, in which heavy metals are typical hazardous pollutants with significant biological toxicity. Our work applied the emerging microbiologically induced calcite precipitation (MICP) technology to reduce the toxicity of Pb, Cd and Zn in municipal sludge nutrient soil before land disposal. The results showed that the MICP mediated by Sporosarcina ureilytica ML-2 could convert the heavy metals from bioavailable form to insoluble carbonate-bound and residual forms, significantly reducing the bio-toxicity. This work expanded the application field of MICP and provided a promising way for heavy metal contamination management.