Cd2 + and Pb2+ immobilization via microbially induced carbonate precipitation by a novel biomineralizing bacterium Proteus mirabilis D2

Electroplating wastewater has a complex composition and contains high levels of free heavy metal ions. Conventional strains struggle to survive in the contaminated water and show limited effectiveness in removing heavy metals. To address this issue, the biomineralizing bacterium Proteus mirabilis D2, isolated from heavy-metal-contaminated soil, was employed to immobilize Cd 2+ and Pb 2+ in multi-heavy-metal-contaminated electroplating wastewater via microbially induced carbonate precipitation (MICP). The results indicated that Proteus mirabilis D2 demonstrated high urease activity (2168.70 U/mL) and strong resistance to heavy metals, with minimum inhibitory concentrations (MICs) of 600 mg/L and 900 mg/L for Cd 2+ and Pb 2+ , respectively. Single-factor experiments revealed that temperature, pH, and urea concentration are key environmental factors affecting heavy metal immobilization. After optimizing these factors using response surface methodology (RSM), Proteus mirabilis D2 achieved removal efficiencies of up to 97.98% for Cd 2+ under the conditions of 38.43°C, pH 6.65, and 2.62% urea concentration, and up to 98.87% for Pb 2+ under 39.2°C, pH 6.75, and 2.2% urea concentration. Characterization and analysis of the biomineralization products, identified as otavite (CdCO 3 ) and Cd-bearing calcite (Ca 0.67 Cd 0.33 CO 3 ), revealed that the mineralization pathway of Cd 2+ involved isomorphous substitution for Ca 2+ and coprecipitation with calcium carbonate. In contrast, the mineralization of Pb 2+ mainly relied on bioadsorption by extracellular polymeric substances (EPS) and the formation of cerussite (PbCO 3 ). In conclusion, this study provides a novel strain ( Proteus mirabilis D2) for the efficient removal of multiple heavy metals (Cd 2+ and Pb 2+ ) from electroplating wastewater and offers valuable insights for the optimization of environmental factors. • Proteus mirabilis D2 exhibits strong Cd 2+ (600 mg/L) and Pb 2+ (900 mg/L) tolerance. • RSM optimized MICP conditions (temperature, pH, urea) for heavy metal removal. • MICP achieved efficient removal of Cd 2+ (97.98%) and Pb 2+ (98.87%). • SEM–EDS & XRD confirmed Cd 2+ (CdCO₃, Ca₀.₆₇Cd₀.₃₃CO₃) and Pb 2+ (PbCO₃) precipitates.