An experimental and numerical modeling investigation was conducted to
study interactions between microbial dynamics and transport processes in variably
saturated porous media. These interactions are important in a variety of applied
problems such as water and wastewater treatment, bioremediation, and oil-field
recovery operations. These processes and interactions also have great ecological
significance, with global scale implications for carbon cycling in the environment
and the related issue of climate change.
Experiments were conducted under variably saturated flow conditions in
columns and 2D light-transmission chambers packed with translucent quartz sand.
A bioluminescent Pseudomonas fluorescens bacterium was utilized in the
experiments and bioluminescence was used as a non-destructive measure of
bacterial density and distribution. In the column experiments, pressure heads
increased (became less negative) at all measured depths, but significant changes in
apparent volumetric water contents were only observed in the upper 5 cm of the
columns. Permeability was reduced by a factor of 40 within one week during
growth on glucose. In the chamber experiments, aqueous-phase saturations
decreased by 7-9% in the region of primary colonization and the capillary fringe
dropped by 5 cm during the 6-day experiment. The colonized region expanded
laterally by 15 cm and upward against the flow by about 7-8 cm. The desaturation
phenomenon resulted in increased lateral spreading of solutes around the colonized
region.
A numerical model was developed and used to help interpret the experimental
data. Water flow was modeled using the single-phase Richards equation. Solute and
bacterial transport, cell growth, substrate consumption, and gas diffusion were
modeled using advection-dispersion-reaction equations. Observed changes in
saturations and pressure heads were reproduced approximately using fluid-media
scaling to represent an apparent surface-tension lowering effect, which was
assumed to be due to sorption of cells and/or biosurfactants at gas-liquid interfaces.
Microbial dynamics, and substrate and oxygen consumption were represented using
first-order reversible kinetics for cell attachment/detachment, and dual Monod-type
kinetics for cell growth and substrate and oxygen consumption. Reasonably good
matches were obtained between the observed and simulated results. / Graduation date: 2003
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/31485 |
| Date | 17 May 2002 |
| Creators | Rockhold, Mark L. |
| Contributors | Selker, John S. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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