Biogeochemical Modeling of Microbially Induced Desaturation and Precipitation

Earthquake-induced soil liquefaction poses a significant global threat, especially to vulnerable populations. There are no existing cost-effective techniques for mitigation of liquefaction under or around existing infrastructure. Microbially Induced Desaturation and Precipitation (MIDP) via denitrification is a potentially sustainable, non-disruptive bio-based ground improvement technique under existing structures. MIDP has been shown to reduce liquefaction triggering potential under lab conditions in two ways: 1) biogenic gas desaturation in the short-term (treatment within hours to days) and 2) calcium carbonate precipitation and soil strengthening in the long-term (treatment within weeks to months). However, these experiments have not considered MIDP behavior under field stresses and pressures, nor have they considered challenges from process inhibition or microbial competition that may be encountered when upscaled to field applications. This study presents results from centrifuge experiments and simplified modeling to explore scaling effects on biogenic gas formation, distribution, and retention when simulating field pressures and stresses. Experimental results from the centrifuge demonstrated MIDP’s potential to mitigate the potential liquefaction triggering through desaturation. This study also includes the development of a biogeochemical model to explore the impact of water constituents, process inhibition, and alternative biochemical metabolisms on MIDP and the subsequent impact of MIDP on the surrounding environment. The model was used to explore MIDP behavior when varying the source-water used as the substrate recipe solute (i.e., groundwater and seawater) and when varying the electron donor (i.e., acetate, glucose, and molasses) in different substrate recipes. The predicted products and by-products were compared for cases when desaturation was the targeted improvement mechanism and for the case when precipitation was the primary targeted ground improvement mechanism. From these modeling exercises, MIDP can be applied in all tested natural environments and adjusting the substrate recipe may be able to mitigate unwanted long-term environmental impacts. A preliminary techno-economic analysis using information gained from the modeling exercises was performed, which demonstrated MIDP’s potential as a cost-effective technique compared to currently used ground improvement techniques, which can be costly, impractical, and unsustainable. The findings from this study are critical to develop treatment MIDP plans for potential field trials to maximize treatment effectiveness, promote sustainability and cost-effectiveness, and limit unwanted by-products.