Bioremediation of cadmium in a sandy and a clay soil by microbially induced calcium carbonate precipitation after one week incubation

Abstract

Microbially induced calcium carbonate precipitation (MICP) method can convert heavy metals from mobile forms into more stable crystals. This study was conducted to investigate the removal of cadmium (Cd) by Sporosarcina pasteurii through the urea hydrolysis pathway. Cd removal from solution containing 0.5, 1, and 2 mmol l⁻¹ of Cd (as CdCl₂.5H₂O) were measured firstly, and then the amount of Cd removal was studied in two sandy and clay soils containing 10, 20, 40, and 50 mg kg⁻¹ of Cd. The experiments were arranged in complete randomized design with three replications. Minimum inhibitory concentration (MIC) of Cd for bacteria growth was attained as 2 mmol l⁻¹, after 48 h of incubation. Cd removal efficacy was 99.6% in 0.5 mmol l⁻¹ and 99.8% in 1 and 2 mmol l⁻¹ Cd solutions. In both soils that were inoculated with bacteria, Cd concentration decreased in solution-exchangeable fraction significantly (p ≤ 0.05). The Cd concentration in the solution-exchangeable fraction of sandy and clay soils were decreased to 85.9, 61.1, 74.3, 80.3% and 89.3, 86.6, 76, 75.6% of its initial values (i.e., 10, 20, 40, and 50 mg kg⁻¹), respectively. The amount of Cd in carbonate fraction in both sandy and clay soil increased significantly in the presence of bacteria (p ≤ 0.05). The results revealed that MICP-based removal of heavy metals via co-precipitation with calcite not only immobilized Cd in studied soils but also improved the microbial and enzymatic activities.

Keywords:

• Biomineralization
• calcite
• Sporosarcina pasteurii
• urease

Acknowledgments

The authors are thankful to the University of Guilan, Rasht, Iran for the financial support and providing facilities to carry out this research.