Revealing the defluoridation efficacy of a ureolytic bacterium Micrococcus yunnanensis MLN22 through MICP driven biomineralization for sustainable groundwater development

Groundwater contamination by fluoride (F⁻) poses a notable hazard to the environment, agriculture and human well-being. The present study investigates the potential use of urease-driven microbially induced carbonate precipitation (MICP) for defluoridation from natural groundwater. Previous reports have shown that the urease driven MICP technique can naturally mineralize heavy metal contaminants from the environment, but no such work exists for fluoride ions. For this study, the highly F⁻ resistant ureolytic bacterium Micrococcus yunnanensis MLN22 was isolated and characterized for its urease and CaCO₃ production activity. In batch experiments using MICP technique, strain MLN22 showed a maximum F⁻ removal efficacy of 83.4% at optimal conditions (5.0 mg L⁻¹ initial F⁻ concentration, 250 mg L⁻¹ Ca²⁺, 15 g L⁻¹ urea and pH 8.0). The dense and less porous aggregates indicate the morphological features of F⁻ treated bioprecipitates characterized by microscopic analysis using SEM. Moreover, F⁻ is adsorbed and precipitated in two different form of biological crystals (BC) such as CaF₂ and Ca₅(PO₄)₃F, which was confirmed by microscopic (SEM and SEM–EDS) and spectroscopic (FTIR and XRD) analysis. Freundlich's isotherm model best described the adsorption mechanism of F⁻ onto BC and showed a multi-layered heterogeneous adsorption pattern. Highlighting its potential for practical applications, the optimized BC extracted from M. yunnanensis MLN22 was used in natural groundwater contaminated with F⁻ (4.95 mg L⁻¹) and reached maximum removal ability of 98.4% at a BC dose of 1.5 g L⁻¹ after 48 h. The final statement of this research is that the urease-driven MICP technique contributes to the production of BC in the defluoridation of F⁻ contaminated groundwater and represents a sustainable and cost-effective solution for fluoride remediation.