Abstract
The biochemical properties of CaCO3 precipitation induced by Sporosarcina pasteurii, an ureolytic type microorganism, were investigated. Effects of calcium source on the precipitation process were examined, since calcium source plays a key role in microbiologically induced mineralization. Regardless of the calcium source type, three distinct stages in the precipitation process were identified by Ca2+, NH4+, pH and cell density monitoring. Compared with stage 1 and 3, stage 2 was considered as the most critical part since biotic CaCO3 precipitation occurs during this stage. Kinetics studies showed that the microbial CaCO3 precipitation rate for calcium lactate was over twice of that for calcium nitrate, indicating that calcium lactate is more beneficial for the cell activity, which in turn determines urease production and CaCO3 precipitation. X-ray diffraction analysis confirmed the CaCO3 crystal as calcite, although scanning electron microscopy revealed a difference in crystal size and morphology if calcium source was different. The findings of this paper further suggest a promising application of microbiologically induced CaCO3 precipitation in remediation of surface and cracks of porous media, e.g., cement-based composites, particularly by using organic source of calcium lactate.
Highlights
Since the phenomenon that CaCO3 precipitation could be induced by many soil bacteria was revealed (Boquet et al, 1973), research on microbial mineral plugging of porous media has been extensively carried out, especially on the application of bioremediation materials in civil engineering
It is observed that bacteria in medium with calcium lactate was more active than in medium with calcium nitrate, for the cell density of group L-B was always two times of that of group N-B
It was considered that the biochemical process of microbiologically induced CaCO3 precipitation consists of three distinct stages with similar pattern, regardless of the type of calcium source (Figure 1)
Summary
Since the phenomenon that CaCO3 precipitation could be induced by many soil bacteria was revealed (Boquet et al, 1973), research on microbial mineral plugging of porous media has been extensively carried out, especially on the application of bioremediation materials in civil engineering. What is more to the point, self-repair can be achieved by using microbial induced deposition (Jonkers et al, 2010). The mechanism of microbial deposition has been revealed and the feasibility of crack repairing in concrete by Bacillus pasteurii immobilized in polyurethane foam was verified (Stocks-Fischer et al, 1999; Bang et al, 2001; Bachmeier et al, 2002). It has been shown that the capillary water adsorption and gas permeability of concrete can be reduced effectively by surface treatment from microbiological mediated deposition, and the composition of bacterial culture medium has a Microbial CaCO3 Precipitation
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