Study on the simultaneous removal of fluoride, heavy metals and nitrate by calcium precipitating strain Acinetobacter sp. H12

Highlights: • The study explored the mechanism for simultaneous removal of F^-, Ca²⁺, Ni²⁺ and NO₃^- by Acinetobacter sp. H12. • The highest removal ratio of F^- was 75.00% under the optimum conditions. • The removal of F^-, Ca²⁺, Ni²⁺ and NO₃^- is closely related to the contribution of biological metabolism. • The bacteria was encapsulated by precipitation (CaCO₃ and CaF₂, etc) to form biological crystal seeds. • Ni²⁺ are removed by substitution to form nickel elements and NiCO₃. The removal properties and mechanisms of fluoride (F^-) and nickel (Ni²⁺) were studied by biomineralizing bacteria (Acinetobacter sp. H12). The results showed that the removal ratio of F^-, Ca²⁺ and Ni²⁺ reached 75% (0.031 mg·L⁻¹·h⁻¹), 84.96% (2.123 mg·L⁻¹·h⁻¹), and 56.67% (0.024 mg·L⁻¹·h⁻¹) after 72 h, respectively. The removal ratio of nitrate (NO₃^-) reached 100% (0.686 mg·L⁻¹·h⁻¹) after 24 h. SEM and XRD images indicated that bioprecipitation of CaF₂, Ca₅(PO₄)₃F, Ca₅(PO₄)₃(OH), NiCO₃, CaCO₃ and Ni were formed, and some of these precipitation used bacteria as nucleation sites to form biological crystal seeds. N₂ was the primary product in gas chromatography analysis. Meanwhile, both the fluorescence spectroscopy and fourier transform near-infrared spectroscopy analysis proved that strain H12 had good ability to remove fluoride and nickel ions simultaneously.