Potential of Bio-mediated Calcite Precipitation Methods for Heavy Metal Immobilization and Strength Enhancement of Contaminated Soils

Microbially induced calcite precipitation (MICP) has emerged as a promising technique for heavy metal immobilization along with improving the strength of contaminated soils. MICP involves the use of microorganisms that are capable of producing calcite or other minerals in the presence of calcium ions and carbon dioxide. These microorganisms can be introduced into contaminated soils, where they can bind with heavy metal ions and convert them into insoluble minerals that are less likely to leach into groundwater or be taken up by plants. This article includes two major studies, demonstrating the novel objectives of heavy metal immobilization and simultaneous strength enhancement of contaminated soil. These studies also include investigations with two different microbial conditions for biotreatment, i.e., a single type of bacteria strain used to execute biogeochemical reactions and different bacteria strains used with Algae to understand the consortium effect in biocementation. First study includes immobilization of Pb, Zn, and Cr(VI) using Sporosarcina pasteurii bacteria and second study includes the investigation of Pb immobilization using consortia of Algae Nostoc commune and bacteria (Sporosarcina pasteurii and Bacillus sphaericus). The toxicity characteristic leaching procedure (TCLP) results demonstrated that the lead immobilization was 92–99% and Cr(VI) immobilization was 94%. On the other hand, Zn was observed mobile/leachable as ZnCO₃ was not stable for pH less than 5. Additionally, unconfined compressive strength (UCS) test results showed significant improvement in biocemented contaminated sand, in both studies. Overall, MICP is a promising approach for the immobilization of heavy metals and strength enhancement of contaminated soils, and further research is needed to optimize the process and evaluate its effectiveness in different scenarios.