Immobilization of Chromium Present in Contaminated Soils Through Bioprecipitation in Calcite Lattice

Soil pollution due to the presence of toxic elements in the soil is a major concern as it is dangerous for the ecosystem and harms living beings directly or indirectly. Bioremediation and bioprecipitation methods can be potentially used to treat polluted soils contaminated with heavy metals. The present study comprises an investigation of the capability of the bacterially/microbially induced calcite precipitation (MICP) method for immobilizing Chromium (Cr(VI)) in artificially contaminated sand. The Cr(VI) contaminated sand with 1000 and 2000 mg/kg concentrations were treated using Sporosarcina (S.) pasteurii bacteria and reagent solution for up to 18 days. The bioprecipitation mechanism and immobilization efficiency was explored using the toxicity characteristic leaching process (TCLP) test. The simultaneous strength enhancement along with the precipitation of calcite was determined through an unconfined compression (UC) test. The microstructural characterization using XRD and SEM was also conducted for bioprecipitated soil. The results demonstrated that the Cr(VI) immobilization was 79% and 94% in 2000 mg/kg and 1000 mg/kg concentration contaminated sand, respectively. The strength of 1000 mg/kg concentration contaminated specimen showed higher UC strength than 2000 mg/kg specimen due to a higher amount of bioprecipitation of calcite. The XRD results confirmed the Cr(VI) to Cr(III) conversion and the calcite crystal’s presence was observed through SEM images. Overall, the MICP method was found to be applicable to heavy metal contaminated soils for immobilization and strength improvement.