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Abstract Microbially Induced Desaturation and Precipitation (MIDP) through denitrification is an emerging ground improvement method in which indigenous nitrate reducing bacteria are stimulated to introduce biogas, biominerals and biomass in the soil matrix. In this study, a numerical model is developed to evaluate the effect of biogas, biominerals and biomass on the hydraulic properties of soils treated with MIDP. The proposed model couples the biochemical conversions to changes of porosity and water saturation and predicts changes in permeability through two separate power law equations. Experimental studies from the literature are used to calibrate the model. Comparing the results with other studies on bioclogging or biomineralization in porous media reveals that the combined production of biogas, biomass, and biominerals results in efficient clogging, in the sense that only a small amount of products leads to a substantial permeability reduction. Based on this comparison, the authors postulate that biogenic gas bubbles preferably form within the larger pore bodies. The presence of biogenic gas in the larger pore bodies forces calcium carbonate minerals and biomass to be formed mainly at the pore throats. The interaction between the different phases results in more efficient clogging than observed in other studies which focus on a single product only.
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Evaluation of Biogenic Gas Formation by Denitrification in Centrifuge
Microbially induced desaturation and precipitation (MIDP) via denitrification has the potential to reduce earthquake-induced liquefaction potential by two mechanisms: calcium carbonate precipitation to mechanically strengthen soil and biogenic gas production to desaturate and dampen pore pressure changes in soil. Lab-scale tests have demonstrated effective desaturation and improved mechanical strength by MIDP. However, in laboratory tests, gas pockets and lenses form causing upheaval as a result of low overburden pressures. The characteristics of biogenic gas formation, distribution, and retention need to be evaluated to gain comprehensive understanding of the effectiveness of this treatment at depth before and after an earthquake event. MIDP treatment during centrifuge loading conditions is being performed to simulate field stress conditions, prior to complete process scale-up for field application. A simplified numerical model was developed to evaluate the scaling effects on biogenic gas generation between the centrifuge model and prototype scale. The results indicate that diffusion of soluble N2 is negligible at both the model and prototype scales for the simulated reaction rate. However, the simplified model did not consider other pore-scale influences and mixing from liquid-gas transfer and transport. Future modeling work will need to add these features.
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- Award ID(s):
- 1520581
- PAR ID:
- 10398109
- Date Published:
- Journal Name:
- UNSAT 2018 The 7th International Conference on Unsaturated Soils
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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