The Stimulation of a Ureolytic Denitrifying Microbial Community for Microbially Induced Carbonate Precipitation
This dissertation investigates the potential for stimulating ureolytic and denitrifying microbes concurrently (i.e., stimulating a ureolytic, denitrifying microbial community) for a more efficient microbially induced carbonate precipitation (MICP) process. Three sand columns were run for a treatment period of six weeks with a continuous flow of nutrient solution containing calcium nitrate, calcium acetate, calcium chloride, magnesium sulfate, tryptic soy broth and trace metals. The first and third columns served as control columns, within which only denitrification processes were at work. The first column was used for periodic sampling to measure the pH, ion concentrations, and total nitrogen over time. The third column was used to measure compressional (P-) and shear (S-) wave velocities to monitor cementation and desaturation over time. The second column was subject to initial conditions identical to the other two columns except that urea was added to the nutrient solution to stimulate ureolysis and was also subject to sampling. This was done to determine whether the use of the combined MICP processes resulted in increased efficiency of precipitation. Results from ion chromatography analysis, acid digestion and scanning electron microscope imaging did not show an increase in the amount of carbonate precipitated for the second column, possibly due to nitrite inhibition and abiotic hydrolysis of the urea from sterilization of the nutrient solution through autoclaving. However, the stimulation of denitrification and ureolysis in combination was achieved, and the amount of carbonate precipitation per mol of nitrate reduced increased, which in a sense increased the efficiency of the system. Ultimately, more experimentation is needed to determine if this combination is beneficial for MICP.