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

Abstract

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.

Keywords: CaCO3; Column; Glass beads; Hydraulic conductivity; Microbial clogging; Microbially induced calcium carbonate precipitation; Number of cells; Optical density; Sporosarcina pasteurii.

Fig. 1

Experimental setup revised from Eryürük et al.

Fig. 2

Hydraulic conductivities of glass beads before treatment (closed circle) and after treatment using 500 mM of CaCl₂ and 500 mM urea, and cell suspension as OD₆₀₀ 0.15 (cross sign), OD₆₀₀ 0.75 (closed triangle), OD₆₀₀ 2.25 (plus sign)

Fig. 3

The number of cells deposited into the columns packed with different diameter of glass beads for OD₆₀₀ 0.15 (cross sign), OD₆₀₀ 0.75 (closed triangle), OD₆₀₀ 2.25 (plus sign)

Fig. 4

Change in hydraulic conductivity in time for the experiments conducted with a OD₆₀₀ 2.25, b OD₆₀₀ 0.75, and c OD₆₀₀ 0.15

Fig. 5

Relationship between cell densities of OD₆₀₀ 0.15 (cross sign), OD₆₀₀ 0.75 (closed triangle), OD₆₀₀ 2.25 (plus sign) introduced into the column and the proportion of the hydraulic conductivity of the treated column to the initial hydraulic conductivity

Fig. 6

The number of cells deposited and the amount of CaCO₃ precipitated

Fig. 7

Estimated hydraulic conductivity using modified Kozeny-Carman equation and measured hydraulic conductivity for a OD₆₀₀ 2.25, b OD₆₀₀ 0.75, and c OD₆₀₀ 0.15

Fig. 8

Optimal conditions

Fig. 9

Surface plot of OD₆₀₀ (A), glass beads size (B)