Optimum conditions for microbial carbonate precipitation

Area of Science:

• Biogeochemistry
• Environmental Microbiology
• Materials Science

Background:

• Microbial carbonate precipitation (MCP) is influenced by various factors including bacterial type, cell concentration, and chemical conditions.
• Urease enzyme activity is crucial for MCP, and its efficiency is modulated by environmental parameters.
• Optimizing MCP conditions is key for applications like carbon sequestration and construction materials.

Purpose of the Study:

• To determine the optimal conditions for microbial carbonate precipitation (MCP) using Sporosarcina pasteurii.
• To investigate the impact of bacterial cell concentration, urea concentration, and Ca(2+) concentration on CaCO(3) precipitation and CO(2) sequestration.
• To identify economically advantageous conditions for high-quality MCP results.

Main Methods:

• Factorial experiments were designed to test the influence of key parameters on urease activity and MCP.
• Sporosarcina pasteurii strain ATCC 11859 was used under controlled temperature (25°C) and ionic strength.
• Varying concentrations of urea, Ca(2+), and bacterial cells were applied, with analyses including X-ray Diffraction, SEM, and EDX.

Main Results:

• Bacterial cell concentration significantly influenced ureolysis rate (k(urea)), more so than initial urea concentration.
• Increasing Ca(2+) concentration from 25 mM to 250 mM resulted in over 100% increase in CaCO(3) precipitated and CO(2) sequestered.
• Optimal conditions identified were 666 mM urea, 250 mM Ca(2+), and 2.3×10⁸ cells mL⁻¹ bacterial concentration for MCP.

Conclusions:

• Higher concentrations of urea, Ca(2+), and bacterial cells can lead to greater CaCO(3) deposition and CO(2) sequestration, provided economic viability is maintained.
• The study identified specific optimal conditions for MCP, balancing economic factors with desired outcomes.
• The precipitate was confirmed as CaCO(3), primarily composed of calcite crystals, suitable for various applications.