Factors Affecting Efficiency of Microbially Induced Calcite Precipitation

Microbially induced carbonate precipitation (MICP) using ureolytic bacteria shows promise in the field of geotechnical engineering for several different applications, such as ground improvement and groundwater control. This study examined optimal use and efficient control of Sporosarcina pasteurii to induce the precipitation of ${\mathrm{CaCO}}_3$ in open environments. Laboratory tests were conducted to investigate the effect of changing treatment factors, such as chemical concentrations, retention times, and effective input rates ($\mathrm{mol}/\mathrm{L}/\mathrm{h}$) on chemical efficiency. Chemical efficiency was measured based on weight measurements of ${\mathrm{CaCO}}_3$ precipitation compared with the amount of chemical reactants injected to samples. Based on the experimental results, the optimal time required for the precipitation process to take place in porous media for a specific range of bacterial optical density was determined. Results show that, below a certain urea and ${\mathrm{CaCl}}_2$ input rate ($0.042\mathrm{mol}/\mathrm{L}/\mathrm{h}$) and for a bacterial optical density (${\mathrm{OD}}_{600}$) between 0.8 and 1.2, the reaction efficiency remained high and the amount of precipitation was not affected by the liquid medium concentration (for input concentrations up to 1 M). However, the precipitation pattern at the pore scale was found to be affected by the injected concentration. Scanning electron microscopy images taken of different samples at different levels of cementation showed that, for the same amount of precipitation, the use of lower chemical concentrations in injections resulted in better distribution of calcite precipitation, especially at lower cementation levels. This variation in precipitation pattern is expected to affect the use of MICP for different applications.