Carbonate Mineral Precipitation for Soil Improvement through Microbial Denitrification

Abstract

Microbially induced calcium carbonate precipitation (MICP) is attracting increasing attention as a sustainable means of soil improvement. While there are several possible MICP mechanisms, microbial denitrification has the potential to become one of the preferred methods for MICP because complete denitrification does not produce toxic byproducts, readily occurs under anoxic conditions, and potentially has a greater carbonate yield per mole of organic electron donor than other MICP processes. Denitrification may be preferable to ureolytic hydrolysis, the MICP process explored most extensively to date, as the byproduct of denitrification is benign nitrogen gas, while the chemical pathways involved in hydrolytic ureolysis processes produce undesirable and potentially toxic byproducts such as ammonium (NH 4 + ). This thesis focuses on bacterial denitrification and presents preliminary results of bench-scale laboratory experiments on denitrification as a candidate calcium carbonate precipitation mechanism.The bench-scale bioreactor and column tests, conducted using the facultative anaerobic bacterium Pseudomonas denitrificans, show that calcite can be precipitated from calcium-rich pore water using denitrification. Experiments also explore the potential for reducing environmental impacts and lowering costs associated with denitrification by reducing the total dissolved solids in the reactors and columns, optimizing the chemical matrix, and addressing the loss of free calcium in the form of calcium phosphate precipitate from the pore fluid.ii The potential for using MICP to sequester radionuclides and metal contaminants that are migrating in groundwater is also investigated. In the sequestration process, divalent cations and radionuclides are incorporated into the calcite structure via substitution, forming low-strontium calcium carbonate minerals that resist dissolution at a level similar to that of calcite. Work by others using the bacterium Sporosarcina pasteurii has suggested that in-situ sequestration of radionuclides and metal contaminants can be achieved through MICP via hydrolytic ureolysis. MICP through bacterial denitrification seems particularly promising as a means for sequestering radionuclides and metal contaminants in anoxic environments due to the anaerobic nature of the process and the ubiquity of denitrifying bacteria in the subsurface.iii ACKNOWLEDGMENTS I am deeply grateful for the assistance and guidance provided by my committee members Dr. Edward Kavazanjian, Dr. Bruce Rittmann, and Dr.Everett Shock. I would like extend a special thanks to Dr. Kavazanjian for all his efforts including the countless hours spent providing a deeper and broader understanding of geotechnical engineering that can only come from fruitful years of academic work bolstered by equally impressive years in industry. I would also like to thank Dr. Rittmann for allowing me the opportunity to work and train in his laboratory, and affording me much needed guidance. As a pioneer in his field, Dr. Rittmann has provided me wi...

Geochemical evidence of microbial activity within ooids

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Construction Biotechnology: a new area of biotechnological research and applications

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