Abstract
Microbially induced calcium carbonate precipitation (MICP) is a bio-geochemical process involving calcium carbonate precipitation and possible co-precipitation of other metals. The study investigated the extent to which a urease-positive bacterium, Sporosarcina pasteurii, can tolerate a range of metals (e.g., Cu, Zn, Pb, Cd, and Sr), and analyzed the role of calcium carbonate bioprecipitation in eliminating these divalent toxicants from aqueous solutions. The experiments using S. pasteurii were performed aerobically in growth media including urea, CaCl2 (30 mM) and different metals such Cu, Zn, Pb, and Cd (0.01 ∼ 1 mM), and Sr (1 ∼ 30 mM). Microbial growth and urea degradation led to an increase in pH and OD600, facilitating the precipitation of calcium carbonate. The metal types and concentrations contributed to the mineralogy of various calcium carbonates precipitated and differences in metal removal rates. Pb and Sr showed more than 99% removal efficiency, whereas Cu, Zn, and Cd showed a low removal efficiency of 30∼60% at a low concentration of 0.05 mM or less. Thus the removal efficiency of metal ions during MICP varied with the types and concentrations of divalent cations. The MICP in the presence of divalent metals also affected the mineralogical properties such as carbonate mineralogy, shape, and crystallinity.
Highlights
Heavy metal and radionuclide pollution in subsurface environments is a serious environmental concern
Regardless of the types of metals, a higher metal content tended to be included on the surface of the carbonate mineral particles precipitated under high metal concentrations. These results indicate that the removal effect may vary depending on the type of metal, the metal ions can be co-precipitated in calcium carbonate and removed from the aqueous solution via Microbially induced calcium carbonate precipitation (MICP) and/or chemical processes
During the 2-week microbial reaction, Pb and Sr showed more than 99% removal efficiency, whereas a low removal efficiency of 30 ∼ 60% was observed at a low concentration of 0.05 mM or less of Cd, Cu, and Zn
Summary
Heavy metal and radionuclide pollution in subsurface environments is a serious environmental concern. The toxic metals are removed via direct precipitation leading to metal carbonate formation, or by coprecipitation incorporating metals such Cu2+, Cd2+, Zn2+, Pb2+, and Fe2+ in the lattice structure of calcium carbonate via substitution of Ca2+ (Kang et al, 2014b; Krajewska, 2018). The emergence of MICP as a promising in-situ remediation technology has led investigators to explore the use of microorganisms in the removal of toxic metals and radionuclides effectively. Li et al (2013) demonstrated high removal rates (ranging from 88% to 99%) of Ni, Cu, Pb, Co, Zn, and Cd within 48 h using metalresistant strains via MICP. The results demonstrated that elevated pH and calcium precipitation were strongly linked to the removal of Zn and Cd, but only partially affected the elimination of Pb and Cu (Mugwar and Harbottle, 2016)
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