Comparative study of microbially induced carbonate precipitation under low temperature conditions

At low temperature, deposition rate induced by bacteria is often low, which restricts the practical engineering application of microbial solidification technology. The growth and reproduction characteristics and urease activity of Sporosarcina pasteurii and Bacillus megaterium are analyzed by controlling different temperature and pH value. By adding nutrients to the gelling solution and controlling urea concentration and calcium ion concentration the precipitation yields of different strains is studied, and XRD test is conducted to analyze precipitation crystal type. The solidification effect of different strains is studied by the comparison of permeability and unconfined compressive strength tests. The results show that at low temperature, the growth and reproduction of Bacillus megaterium are faster, and urease activity is higher, and the optimum pH value of Bacillus megaterium is 8, meaning that it is more suitable for alkaline environment. The precipitation yields can be increased by adding nutrients to the gelling solution, increasing concentration of urea to 1.5 M and controlling calcium acetate concentration at 0.5 M. The deposition rate of Bacillus megaterium is always higher than Sporosarcina pasteurii at low temperature, and the precipitated crystal is more stable calcite. The permeability of samples solidified by Bacillus megaterium is reduced by 3 to 4 orders of magnitude, while that with Sporosarcina pasteurii is only 2 to 3 orders of magnitude. The smaller the particle size, lower the permeability. Under the same conditions, the strength of samples solidified with Bacillus megaterium is stronger than ones solidified with Sporosarcina pasteurii. Therefore, Bacillus megaterium is more suitable for practical engineering applications at low temperature.