Microbially-Induced Cementation of Sands by Denitrification

Project: Research project

Description

Improvement of granular soils by microbially induced carbonate precipitation (MICP) has attracted significant attention among geotechnical engineers over the past few years. MICP offers the potential for a wide variety of cost-effective soil improvement applications in granualr soil, including stabilizing liquefiable soils, reducing seismic settlement potential, increasing bearing capacity, reducting lateral earth pressures, controling soil erosion and scour, improving basal stability of excavations, and facilitating tunneling in running or flowing sands [1]. MICP may be especially useful near or beneath existing structures, where the application of traditional soil improvement techniques is limited because of the associated ground deformations and/or high cost associated with these traditional techniques. MICP is known to improve the strength and stiffness of granular soils naturally over a geologic time frame. However, case histories of fouling of treatment plant filters, mineral scale on pipes, and clogged drainage systems at landfills, mines, and dams suggest that MICP can yield changes of engineering significance over a time frame of engineering relevance. The engineering challenges in developing beneficial applications of MICP involve identifying the appropriate process and inducing it in the location of interest over a timeframe of engineering relevance. Several research groups around the world [e.g. 2, 3] have been working on MICP using ureahydrolyzing bacteria, a process referred to herein as ureolysis. Because the production of the urea hydrolyzing enzyme, urease, by soil microorganisms is retarded by a lack of oxygen, application of ureolysis in an anaerobic environment, e.g. below the ground water table, may be limited or may require supplemental oxygenation, e.g. air sparging. In research initiated under a National Science Foundation (NSF) sponsored Small Grant for Exploratory Research, the Co-Principal Investigators (Co-PIs) on this project initiated work on an alternative means of MICP. The work at ASU has focused on reducing nitrate to nitrogen to increase alkalinity and precipitate carbonate, an anaerobic process referred to herein as denitrification. There are a variety of situations where an anaerobic process would be preferable to ureolysis, most notably when the soil to be improved is below the water table. Therefore, this proposal is focused upon further development of MICP by denitrification as a soil improvement process.

Description

This REU supplement will be used to train an undergraduate interested in going to graduate school in geotechnical engineering, and more specifically interested in the emerging field of biogeotechnical engineering, in the techniques required to conduct laboratory testing associated with microbially induced calcite precipitation (MICP). MICP plays a prominent role in the emerging field of biogeotechnical engineering. However, most civil engineering students are not trained in the techniques required to conduct experiments involving biogeotechnical processes, including techniques involving geochemistry, microbiology and geology, e.g. culturing bacteria strains, bacterial cell counts, mass spectrometry, and electron microscopy. The undergraduate research assistant will primarily be responsible for performing the following laboratory duties under the direction of a graduate research assistant: assisting in set-up, sampling, breaking down, and analyzing sand columns employed in MICP experiments; assisting in preparing chemical and nutrient mediums; assembly and disassembly of test equipment; and recording and analyzing data. An interest in graduate study in geotechnical engineering will be a prerequisite for employment in this position. The successful candidate is also expected to be able to demonstrate good writing and communication skills. Outreach will be made to underrepresented groups (e.g. women and minorities) in identifying candidates for this position.
StatusFinished
Effective start/end date8/15/097/31/14

Funding

  • National Science Foundation (NSF): $335,054.00

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cementation
denitrification
carbonate
sand
engineering
soil improvement
geotechnical engineering
soil
water table
air sparging
bacterium
oxygenation
earth pressure
soil microorganism
civil engineering
microbiology
scour
electron microscopy
bearing capacity
cost