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Modeling the Biodegradation Kinetics of Dissolved Organic Contaminants in a Two-Dimensional Heterogeneous Aquifer

The goal of this dissertation was to develop a versatile groundwater transport model capable of incorporating various types of biodegradation kinetic sub-models, and to use the model to examine the interaction between transport and biodegradation processes in a two-dimensional heterogeneous aquifer. Operator splitting, which involves splitting the transport and kinetic equations and solving each with an appropriate method, was the numerical technique chosen because of the ease at which different bi ode gradation kinetic models can be changed. The differences between the Monad and biofilm kinetic models were shown to be negligible by model simulations and dimensionless analysis for realistic groundwater parameter ranges.

For dual limitation, two forms of the Monod model were examined, namely, the minimum-rate and multiplicative Monod models. Differences between the models could be quantified apriori by examining the kinetic parameters and substrate concentration values; maximum differences occur when one or both substrates are at sub saturation concentrations.

The effects of heterogeneity were quantified by studying transport in a two-layer stratified domain. The effects of dispersion were found to be significant when electron acceptor was injected into a background concentration of electron donor due to increased mixing of the two substrates. Biomass accumulated at the interface between the slow and fast layers due to transverse dispersion of the electron acceptor from the fast into the slow layer.

The effect of adsorption was studied in a one-dimensional system in which electron acceptor was input into a background of electron donor. In general, increased retardation of the electron donor increased the amount of biodegradation. An initial period of rapid biological growth was followed by a pseudo-steady-state behavior. The lag time to the initial period of rapid biological growth increased with increasing retardation and decreasing velocity. Once the lag time was complete, the rate of bi ode gradation increased with increasing retardation factor. This increase was due mainly to the reservoir of adsorbed electron donor substrate, but was enhanced by greater overlap of the retarded donor and nonretarded acceptor fronts.