Establishment of ureolytic biofilms and their influence on the permeability of pulse-flow porous media column systems
Wheeler, Laura Allison.
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As the population of the world has increased, energy consumption and greenhouse gas emissions have increased as well. One possible way to reduce the amount of greenhouse gases emitted into the atmosphere is through the geologic sequestration of carbon dioxide. During geologic sequestration, supercritical carbon dioxide is injected into different types of underground formations. Inherent cracks in these formations may lead to the upward leakage of CO 2, and a controllable engineered strategy is needed to reduce this potential leakage. Currently, biomineralization has been used in many different environmental applications but not for the sequestration of carbon dioxide. The goal of this research is to establish biofilm communities of ureolytic bacteria that promote CaCO 3 precipitation in a pulse-flow porous media column system with the intent of reducing the porosity and permeability of the porous media. Pulse-flow column systems were inoculated with different species of ureolytic bacteria: S. pasteurii, B. sphaericus #21776, or B. sphaericus #21787. The bacteria were allowed to grow in the column for five days before a calcium-containing medium was introduced. Flow rate, pH, ammonium concentration, calcium concentration, culturable bacteria, and protein concentration were monitored over the course of the entire experiments. It was shown that all ureolytic species were capable of growing, utilizing urea, and creating an environment that facilitated calcium carbonate precipitation in 1mm diameter glass bead packed columns at room temperature and atmospheric pressure. To better understand the effect of pore space on biomineralization columns packed with 0.1 mm diameter glass beads were constructed and inoculated with S. pasteurii. Within days of calcium introduction, the permeability of the columns was reduced to the point where no more fluid would drain from the column. These results indicate that the ureolytic bacteria are capable of surviving, facilitating calcium carbonate precipitation, and reducing the permeability of the pulse-flow porous media column system. While further study is needed, the precipitation of calcium carbonate through ureolysis may offer a controllable engineered strategy to reduce the permeability of underground formations used for geologic sequestration.