Simultaneous removal of calcium, fluoride, nickel, and nitrate using microbial induced calcium precipitation in a...

In this research, an immobilized biofilm reactor was established for the simultaneous removal of calcium (Ca²⁺), fluoride (F^-), nickel (Ni²⁺), and nitrate (NO₃^--N) by microbial induced calcium precipitation (MICP). The operating parameters of the reactor, hydraulic retention time (HRT: 4, 8, and 12 h), influent Ca²⁺ concentration (36.0, 108.0, and 180.0 mg L^-1), and influent Ni²⁺ concentration (0.0, 3.0, and 6.0 mg L^-1) were discussed. Under the HRT of 12 h, influent Ca²⁺ concentration of 180.0 mg L^-1, and influent Ni²⁺ concentration of 3.0 mg L^-1, the removal ratios of Ca²⁺, F^-, Ni²⁺, and NO₃^--N reached 45.31%, 79.55%, 85.11%, and 55.29%, respectively, which was the reactor stable operation performance. The SEM revealed the morphology of calcium-precipitated bio-crystals. XPS showed the Ca²⁺ and Ni²⁺ precipitate components and XRD further revealed the formation of CaCO₃, Ca₅(PO₄)₃OH, and NiCO₃ precipitation. Nitrogen (N₂) was the main gas produced in the reactor. Fluorescence spectroscopy manifested that extracellular polymers played an important role in the organism nucleation. High-throughput sequencing exhibited that Acinetobacter sp. H12 was the dominant bacterial group. This study provided a new insight for simultaneous remediation of Ca²⁺, F^-, Ni²⁺, and NO₃^--N in water bodies.