Immobilizing copper in loess soil using microbial-induced carbonate precipitation: Insights from test tube experiments and one-dimensional soil columns

Biomineralization as an alternative to traditional remediation measures has been widely applied to remediate copper (Cu)-contaminated sites due to its environmental-friendly nature. Immobilizing Cu is, however, a chal-lenging task as it inevitably causes inactivation of ureolytic bacteria. In the present work, a series of test tube experiments were conducted to derive the relationships of Cu immobilization efficiency versus pH conditions. The Cu speciation transformation that is invisible in the test tube experiments was investigated via numerical simulations. Apart from that, the one-dimensional soil column tests, accompanied by the X-ray diffraction (XRD) and Raman spectroscopy analysis, mainly aimed not only to investigate the variations of Cu immobilization efficiency with the depth but to reveal the underlying mechanisms affecting the Cu immobilization efficiency. The results of the test tube experiments highlight the necessity of narrowing pH ranges to as close as 7 by introducing an appropriate bacterial inoculation proportion. The coordination adsorption of Cu, while performing the one-dimensional soil column tests, is encouraged by alkaline environments, which differs from the test tube experiments where Cu2+ is capsulized by carbonate precipitates to prevent their migration. The findings highlight the potential of applying the microbial-induced carbonate precipitation (MICP) technology to Cu-rich water bodies and Cu-contaminated sites remediation.

Automated summary

Biomineralization has been widely used as an environmentally-friendly method in remediating copper-contaminated sites. However, immobilizing copper without inactivating ureolytic bacteria is challenging. This study investigated the relationship between copper immobilization efficiency and pH conditions through test tube experiments and numerical simulations. Additionally, soil column tests, along with X-ray diffraction and Raman spectroscopy analysis, were conducted to explore the mechanisms affecting copper immobilization efficiency. The findings suggest the potential of using microbial-induced carbonate precipitation technology for remediating copper-rich water bodies and contaminated sites.