Study On The Performance Of Carbonate-Mineralized Bacteria Combined With Eggshell For Immobilizing Pb and Cd in Water And Soil

Microbially induced carbonate precipitation (MICP) is an advanced bioremediation approach to remediate heavy metals (HMs) contaminated water and soil. In this study, metal tolerant urease-producing bacterial isolates, namely UR1, UR16, UR20 and UR21, were selected based on their urease activity. The efficiency of these isolates in water for Pb and Cd immobilization was explored. Our results revealed that UR21 had the highest removal rates of Pb (81.9%) and Cd (65.0%) in solution within 72 h through MICP. The scanning electron microscopy-energy dispersive x-ray and x-ray diffraction analysis confirmed the structure and the existence of PbCO 3 and CdCO 3 crystals in the precipitates. In addition, the strain UR21, in combination with urea/eggshell waste (EGS) or both, was further employed to investigate the effect of MICP on soil enzymatic activity, chemical fractions and bioavailability of Pb and Cd. The outcomes indicated that the applied treatments reduced the proportion of soluble-exchangeable Pb and Cd, resulted an increment in carbonated bound Pb and Cd in the soil. The DTPA extractable Pb and Cd was reduced by 29.2% and 25.2% with the treatment of UR21 + urea + EGS as compared to the control. Besides, the application of UR21 and EGS significantly increased the soil pH, cation exchange capacity, and enzyme activities. Our findings may provide a novel perceptive for an eco-friendly and sustainable approach to remediate heavy metal contaminated environment through a combination of metal-resistant ureolytic bacterial strain and EGS.