MODELING CONTAMINANT TRANSPORT AND BIODEGRADATION IN A LAYERED POROUS-MEDIA SYSTEM

The transport and biodegradation of an organic compound (quinoline) we re studied in a meter-scale system of layered porous media. A two-dime nsional laboratory experiment was conducted in a saturated system with two hydraulic layers with a ratio of conductivities of 1:13. A soluti on containing dissolved quinoline was injected as a front at one end o f the system, and the aqueous-phase concentrations of quinoline, its f irst degradation product (2-hydroxyquinoline), and oxygen were monitor ed over time at several spatial locations. Results from a set of ancil lary batch and small-column experiments were used to generate a mathem atical model for the microbial kinetics; these kinetics described the time rate of change of the concentrations of the two organic compounds (quinoline and 2-hydroxyquinoline), the electron acceptor (oxygen), a nd microbial biomass. This independently developed kinetic model was i ncorporated into a two-dimensional numerical model for flow and transp ort, so that simulations of the laboratory system could be conducted a nd the results compared with observed data. An analysis of the applica bility of single-phase and multiple-phase models for the description o f the microbial kinetics was conducted. The results of this analysis i ndicated that for some cases, it is not necessary to explicitly model the mass transfer between the aqueous phase and the biomass phase. A s ingle-phase model was used for simulating the laboratory system descri bed here. Favorable comparisons between the laboratory and simulation data suggested that a single-phase model was appropriate for describin g the microbially mediated reactions in this system. A method for inco rporating the effects of metabolic lag into microbial kinetics is desc ribed. Metabolic lag was explicitly accounted for in the degradation k inetics for this system; the inclusion of metabolic lag proved to be i mportant for describing transient concentration pulses that were obser ved in the low-conductivity layer.