Microbially Induced Carbonate Precipitation Using Microorganisms Enriched from Calcareous Materials in Marine Environments and Their Metabolites

Microbially induced Ca-carbonate precipitation (MICP) in general, refers to a process in which the urease secreted by microbes hydrolyzes urea to ammonium and carbon dioxide. The main objectives of this study were to identify the environmental factors (e.g., microbial growth, cell/metabolite presences, and calcium sources) that control Ca-carbonate formation and to investigate the mineralogical characteristics of the Ca-carbonate precipitated using ureolytic microorganisms cultured in marine environments. The two types of carbonate-forming microorganisms (CFMs), mixed cultures hydrolyzing urea, were enriched from calcareous materials in marine environments. The experiments using a CFM, Sporosarcina pasteurii, was also used for comparison. All the microbes were cultured aerobically in D-1 growth media that included urea. To investigate the effect of microbial growth states on Ca-carbonate precipitation, Ca-acetate was injected into the media before (i.e., lag phase) and after (i.e., stationary phase) microbial growth, and into the soluble microbial products (SMP) solution, respectively. XRD, FT-IR, and SEM-EDS analyses were used for mineralogical characterization of the precipitated Ca-carbonates. Results indicated that the Ca-carbonates, vaterite and/or calcite, precipitated under all the experimental conditions. The fastest precipitation of Ca-carbonates occurred in the SMP solution and formed calcite (size = 5–15 μm). When the concentrations of added Ca-acetate were varied from 0 to 0.5 M, the highest amounts of calcite, 22.8 g/L, were produced when 0.3 M Ca-acetate was injected. Therefore, the environmental factors (e.g., microbial growth, cell/metabolite presences, and calcium sources) could have an effect the rate of formation of Ca-carbonate and the types of carbonate minerals formed. Moreover, the use of cell-free SMP solution is expected to be applicable to Ca-carbonate precipitation in an environment where microbial growth is unfavorable.