Optimum conditions for microbial carbonate precipitation

• Published in: Chemosphere (Oxford) 2010-11, Vol.81 (9), p.1143-1148
• Main Authors: Okwadha, George D.O., Li, Jin
• Format: Article
• Language: English
• Subjects: Ammonia - analysis; Ammonia - chemistry; Ammonia - metabolism; Bacteria; Bacteriology; Biological and medical sciences; Biotechnology; Calcium carbonate; Calcium Carbonate - analysis; Calcium Carbonate - chemistry; Calcium Carbonate - metabolism; Carbonates - chemistry; Carbonates - metabolism; Chemical industry. Chemical engineering; Chemical Precipitation; CO 2 sequestration; Crystals; Economics; Fundamental and applied biological sciences. Psychology; Hydrogen-Ion Concentration; Industrial applications and implications. Economical aspects; Microbial carbonate precipitation; Microbiology; Microorganisms; Miscellaneous; Optimization; Precipitation; Sporosarcina - enzymology; Sporosarcina - metabolism; Sporosarcina pasteurii; Temperature; Urea - chemistry; Urea - metabolism; Urea hydrolysis; Ureas; Urease - metabolism; Urease enzyme; Ureolytic bacteria
• ISSN: 0045-6535; 1879-1298
• DOI: 10.1016/j.chemosphere.2010.09.066

The type of bacteria, bacterial cell concentration, initial urea concentration, reaction temperature, the initial Ca 2+ concentration, ionic strength, and the pH of the media are some factors that control the activity of the urease enzyme, and may have a significant impact on microbial carbonate precipitation (MCP). Factorial experiments were designed based on these factors to determine the optimum conditions that take into consideration economic advantage while at the same time giving quality results. Sporosarcina pasteurii strain ATCC 11859 was used at constant temperature (25 °C) and ionic strength with varying amounts of urea, Ca 2+, and bacterial cell concentration. The results indicate that the rate of ureolysis ( k urea) increases with bacterial cell concentration, and the bacterial cell concentration had a greater influence on k urea than initial urea concentration. At 25 mM Ca 2+ concentration, increasing bacterial cell concentration from 10 6 to 10 8 cells mL −1 increased the CaCO 3 precipitated and CO 2 sequestrated by over 30%. However, when the Ca 2+ concentration was increased 10-fold to 250 mM Ca 2+, the amount of CaCO 3 precipitated and CO 2 sequestrated increased by over 100% irrespective of initial urea concentration. Consequently, the optimum conditions for MCP under our experimental conditions were 666 mM urea and 250 mM Ca 2+ at 2.3 × 10 8 cells mL −1 bacterial cell concentration. However, a greater CaCO 3 deposition is achievable with higher concentrations of urea, Ca 2+, and bacterial cells so long as the respective quantities are within their economic advantage. X-ray Diffraction, Scanning Electron Microscopy and Energy Dispersive X-ray analyzes confirmed that the precipitate formed was CaCO 3 and composed of predominantly calcite crystals with little vaterite crystals.