Effect of cell density on decrease in hydraulic conductivity by microbial calcite precipitation

The effect of number of cells deposited on decrease in hydraulic conductivity of porous media using CaCO₃ precipitation induced by Sporosarcina pasteurii (ATCC 11,859) was examined in columns packed with glass beads in the range of 0.25 mm and 3 mm in diameter. After resting Sporosarcina pasteurii cells were introduced into the columns, a precipitation solution, which consisted of 500 mM CaCl₂ and 500 mM urea, was introduced under continuous flow conditions. It was shown that hydraulic conductivity was decreased by formation of microbially induced CaCO₃ precipitation from between 8.37 * 10^-1 and 6.73 * 10^-2 cm/s to between 3.69 * 10^-1 and 1.01 * 10^-2 cm/s. The lowest hydraulic conductivity was achieved in porous medium consisting of the smallest glass beads (0.25 mm in diameter) using the highest density of cell suspension (OD₆₀₀ 2.25). The number of the deposited cells differed depending on the glass bead size of the columns. According to the experiments, 7 * 10^-9 g CaCO₃ was produced by a single resting cell. The urease activity, which led CaCO₃ precipitation, depended on presence of high number of cells deposited in the column because the nutrients were not included in the precipitation solution and consequently, the amount of CaCO₃ precipitated was proportional with the cell number in the column. A mathematical model was also developed to investigate the experimental results, and statistical analysis was also performed.