The goal of this research was to mathematically simulate the ability of
bioaugmented microorganisms to aerobically cometabolize a mixture of chlorinated
aliphatic hydrocarbon (CAH) compounds during in-situ treatment. Parameter values
measured from laboratory experiments were applied to the transport model with
biotransformation processes included. In laboratory microcosm studies, a butane-grown,
enriched culture was inoculated in soil and groundwater microcosms and
exposed to butane and several repeated additions of 1,1,1-trichloroethane (TCA), 1,1-dichioroethylene (DCE), and 1,1-dichloroethane (DCA) at aqueous concentrations of
200 ��g/L, 100 ��g/L, and 200 ��g/L, respectively. Microcosms containing the
bioaugmented culture showed 1,1-DCE to be rapidly transformed, followed by slower
transformation of 1,1-DCA and 1,1,1-TCA. After most of the butane had been
consumed, transformation of these latter CAHs increased, indicating strong inhibition
by butane. With repeat biostimulations, butane utilization and CAH transformation
accelerated, showing the increase in cell mass. These trends occurred in two sets of
microcosm triplicates. No stimulation was observed in controls containing only the
microorganisms indigenous to Moffett Field, confirming that activity seen in the
bioaugmented microcosms was a result of the introduced culture's activity.
Batch reactor results were simulated using differential equations accounting for
Michaelis-Menten kinetics, transformation product toxicity, substrate inhibition, butane
utilization, and CAH transformation. The equations were solved simultaneously by
Runge-Kutta numerical integration with parameter values adjusted to match the
microcosm data.
Having defined the parameter values from laboratory studies, the
biotransformation model was combined with 1-D advective-dispersive transport to
simulate behavior of the culture and the substrates within an aquifer. The model was
used to simulate the results of field studies where the butane-utilizing culture was
injected into a 7 m subsurface test site and exposed to alternating pulses of oxygen and
butane, along with the contaminant mixture studied in the microcosms. Monitoring
wells spaced at 1 m, 2.2 m, and 4 m from the injection well allowed temporal and
spatial changes in substrate concentrations to be determined. Model simulations of the
field demonstration were performed to determine how well the biotransformation/solute
transport model predicted actual field observations.
To model the influences of solute transport, simulations were run and compared
to breakthrough test data (prior to bioaugmentation) to determine the values for
advection, dispersion, and sorption. The simulations showed that flow ranged from 1.0
to 1.5 m��/day (average linear velocity of 2.0 m/day). Dispersion was estimated as 0.31
m��/day. Sediment sorption partitioning coefficients for 1,1-DCE, 1,1-DCA, and 1,1,1-TCA were determined to be approximately 0.69, 0.50, and 0.50 L/kg, respectively. It
was more difficult to determine an appropriate value of the mass transfer rate
coefficient for non-equilibrium sorption, so simulations were run to compare
equilibrium and non-equilibrium cases. Results indicated that non-equilibrium (with
mass transfer rate coefficient of approximately 0.2 day�����) better simulated the field data.
Using these transport parameters and the biotransformation values determined
from the laboratory experiments, simulations of the field data showed that the model
was capable of simulating the effects of transformation rates, butane inhibition, and
1,1-DCE product toxicity. Simulations for varying pulsing cycles and durations
provided possible improvements for future field demonstrations.
Overall, this work proved that there is good potential in extrapolating laboratory
based kinetics to simulate biotransformation at a field scale. Although the complexity
of such systems makes modeling difficult, such simulations are useful in understanding
and interpreting field data. / Graduation date: 2003
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/31659 |
| Date | 26 September 2002 |
| Creators | Mathias, Maureen Anne |
| Contributors | Semprini, Lewis |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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