Modeling contaminant transport and biodegradation in a layered porous media system

Abstract

The transport and biodegradation of an organic compound (quinoline) were studied in a meter-scale system of layered porous media. A two-dimensional laboratory experiment was conducted in a saturated system with two hydraulic layers with a ratio of conductivities of 1' 13. A solution containing dissolved quinoline was injected as a front at one end of the system, and the aqueous-phase concentrations of quinoline, its first degradation product (2-hydroxyquinoline), and oxygen were monitored over time at several spatial locations. Results from a set of ancillary batch and small-column experiments were used to generate a mathematical 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), and microbial biomass. This independently developed kinetic model was incorporated into a two-dimensional numerical model for flow and transport, so that simulations of the laboratory system could be conducted and the results compared with observed data. An analysis of the applicability of single-phase and multiple-phase models for the description of the microbial kinetics was conducted. The results of this analysis indicated that for some cases, it is not necessary to explicitly model the mass transfer between the aqueous phase and the biomass phase. A single-phase model was used for simulating the laboratory system described here. Favorable comparisons between the laboratory and simulation data suggested that a single-phase model was appropriate for describing the microbially mediated reactions in this system. A method for incorporating the effects of metabolic lag into microbial kinetics is described. Metabolic lag was explicitly accounted for in the degradation kinetics for this system; the inclusion of metabolic lag proved to be important for describing transient concentration pulses that were observed in the low-conductivity layer. 1833 1834 WOOD ET AL' CONTAMINANT TRANSPORT AND BIODEGRADATION z V = 1.24 m d ~1 0.03 m 0.17 m ß ß ß z=0.16 m ß ß ß ß z=0.10 m 1471-1476, 1992. van Genuchten, M. T., and P. J. Wierenga, Mass transfer studies in sorbing porous media, I, Analytical solutions, Soil Sci. Soc. Am. transport model for oxygen-and nitrate-based respiration linked to substrate and nutrient availability in porous media, Water Resour. Res., 24, 1553-1565, 1988. Williams, F. M., A model of cell growth dynamics, J. Theor. Biol., 15, 190-207, 1967. Wood, B. D., and C. N. Dawson, Effects of lag and maximum growth in contaminant transport and biodegradation modeling, in

Processes in microbial transport in the natural subsurface

“…Therefore, in unstructured models the biomass is a fully penetrable volumeless component which assumes that a linear relation exists between mass of substrate consumed and mass of biomass produced and that no diffusion limitations affect the transfer of substrate mass from solution into the biomass. This approach has been taken in model construction [25,144,159,162], in column studies that focus on bacterial transport [69,120] and in intermediate-scale flow cell studies that focus on active degradation and growth and coupled transport [130,169]. For instance, Macquarrie et al [162] used this approach in treating biomass involved in aerobic degradation as a volumeless species undergoing transport, with equilibrium partitioning of biomass between aqueous and attached phases.…”

“…For instance, Macquarrie et al [162] used this approach in treating biomass involved in aerobic degradation as a volumeless species undergoing transport, with equilibrium partitioning of biomass between aqueous and attached phases. Wood et al [130] used the unstructured approach in treating the biophase as irreversibly attached, in analysis of experiments in layered medium.…”

A mixed finite element/finite volume approach for solving biodegradation transport in groundwater

“…For example, some authors assume the presence of two distinct phases, bulk flow and microbial colonies, interconnected via mass exchange [4][5][6][7][8][9]. Nevertheless, practical consider-ations have drawn attention to the fact that in several cases the characteristic time of mass exchange between aqueous solution and microbial colonies is much smaller than the characteristic time of concentration variation in bulk flow [10][11][12][13]. In the latter case it is not appropriate to distinguish between two different phases in the fluid.…”

“…Various numerical approaches for solving this class of models are documented in the literature: finite difference technique in 1D [4,5] or 2D [6,11]; optimal test function method [10]; finite elements [7,14,15]; finite elements with modified characteristic method (MMOC), [16] applied by Wood et al [9,13]. Much work has also been devoted to modelling biodegradation kinetics and their parameter calibration [7,9,12,13].…”

HYDROBIOGEOCHEM: A coupled model of HYDROlogic transport and mixed BIOGEOCHEMical kinetic/equilibrium reactions in saturated-unsaturated media

“…A metabolic lag coefficient (Kono, 1968;Wood et al, 1994) is used to allow for an acclimation period, if any, of microorganisms to new substrates:…”