Reducing hydraulic conductivity of porous media using CaCO₃ precipitation induced by Sporosarcina pasteurii.

The effect on hydraulic conductivity in porous media of CaCO3 precipitation induced by Sporosarcina pasteurii (ATCC 11859) was investigated using continuous-flow columns containing glass beads between 0.01 mm and 3 mm in diameter. Resting S. pasteurii cells and a precipitation solution composed of 0.5 M CaCl2 and 0.5 M urea were introduced into the columns, and it was shown that the subsequent formation of CaCO3 precipitation reduced hydraulic conductivity from between 8.38 × 10(-1) and 3.27 × 10(-4) cm/s to between 3.70 × 10(-1) and 3.07 × 10(-5) cm/s. The bacterial cells themselves did not decrease the hydraulic conductivity. The amount of precipitation was proportional with the bacterial number in the column. The specific CaCO3 precipitation rate of the resting cells was estimated as 4.0 ± 0.1 × 10(-3) μg CaCO3/cell. Larger amounts of CaCO3 precipitation were deposited in columns packed with small glass beads than in those packed with large glass beads, resulting in a greater reduction in the hydraulic conductivity of the columns containing small glass beads. Analysis using the Kozeny-Carman equation suggested that the effect of microbially induced CaCO3 precipitation on hydraulic conductivity was not due to the formation of individual CaCO3 crystals but instead that the precipitate aggregated with the glass beads, thus increasing their diameter and consequently decreasing the pore size in the column.