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.

Effects of bentonite and yeast extract as nutrient on decrease in hydraulic conductivity of porous media due to CaCO3 precipitation induced by Sporosarcina pasteurii.

The reduction mechanism of hydraulic conductivity was investigated in porous media treated with bentonite and CaCO3 precipitates induced by growing cells of Sporosarcina pasteurii (ATCC 11859). Bentonite, the bacterial cells, and a precipitation solution, composing of 0.5 M CaCl2 and 0.5 M urea with or without 2% weight/volume yeast extract allowing the bacterial growth were sequentially introduced into the continuous-flow columns containing glass beads between 0.05 and 3 mm in diameter. The treatments reduced the hydraulic conductivity of the columns from between 8.4 × 10(-1) and 4.1 × 10(-3) cm/s to between 9.9 × 10(-4) and 2.1 × 10(-6) cm/s as the lowest. With yeast extract, the conductivity continuously decreased during four days of the experiment, while became stable after two days without yeast extract. Introduction of the bacterial cells did not decrease the conductivity. The reduction in hydraulic conductivity was inversely correlated with the volume occupied by the depositions of bentonite and CaCO3 precipitates in column, showing the same efficiency but a larger effect of the CaCO3 precipitates with increasing volume by bacterial growth. The smaller glass beads resulted in larger volume of the depositions. Bentonite increased the deposition of CaCO3 precipitates. Analysis using the Kozeny-Carman equation suggested that without yeast extract, bentonite and the CaCO3 precipitates formed aggregates with glass beads, thus increasing their diameter and consequently decreasing the pore size in the column. With yeast extract, in addition to the aggregates, the individual CaCO3 precipitates formed separately from the aggregates reduced the hydraulic conductivity.

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.