Spatial Disorder and Degradation Kinetics in Intrinsic Biodegradation Schemes

Abstract

The restoration of contaminated soils by intrinsic biodegradation employs microorganisms in the subsurface that degrade the contaminant substrate infiltrating the subsurface matrix. The outcome of intrinsic biodegradation has been difficult to predict. We examine a source of the difficulty with a computational model of diffusive-reactive transport that introduces spatial disorder in the arrangement of the degrading microorganisms. Spatial disorder alone, even on the small scales that characterize the distance between aggregates of microorganisms, is enough to induce a wide range of times to complete the degradation to an arbitrary limit. The mean time for the concentration to achieve the limit becomes twice that for the case of spatial order. Bounds on the range of the effective degradation kinetics can be obtained by computing the distribution of times to complete degradation.

Attached and Unattached Microbial Communities in a Simulated Basalt Aquifer under Fracture- and Porous-Flow Conditions

“…A combined modeling and physical experimentation approach using a single bacterial population has indicated that organism partitioning influences the transport of dissolved substances through a porous medium (41). Strict modeling studies have shown that the distribution of degradative microorganisms attached to porous media can profoundly affect the fate of soluble organic contaminants in porous media (34). The effect of the distribution of attached microorganisms on a mobile contaminant can be further contrasted with that of a homogeneous distribution of unattached degrading organisms moving with a contaminant plume.…”

Dynamics of Coupled Microbial and Contaminant Transport.

“…Basagaoglu et al (1999) develop a new simplified modeling approach for keeping track of solute diffusion effects in such media, as it affects the availability of solute hydrocarbon for anaerobic degradation. Field-scale transport in the subsurface involves uncharacterized heterogeneities in physical and chemical properties governing flow and transport (Cushman and Hu, 1997;LaViolette et al, 1999;Cushman and Ginn, 2000), and upscaling the biodegradation processes here requires careful treatment of the dynamic couplings between flow, transport, growth, and bacterial adhesion; a field-scale modeling framework for this is provided through streamtube-ensemble modeling approach (Ginn, 2000) that approximates transport in the field via use of a series of streamtubes. The streamtube approximation allows the reduction in the dimensionality of the problem from three-dimensions to (a series of) onedimensional effective streamtubes.…”

Self-Organized Network of Chemical Reactions: A Model of Contaminated Converging and Diverging Flows in Fractured Media

“…Contaminants spilled into the vadose zone may react with and be degraded by communities of native microorganisms resident throughout the vadose zone, which may themselves also impact the flow of contaminants . Theoretical (i.e., statistical mechanics) and computational studies , of the reaction−diffusion equations that describe microbial degradation of contaminants (which were introduced only once into a diffusive flow in a saturated porous medium, with a static population of degradation sites) found that the disorder in the spatial distribution of the degradation sites strongly influenced the degradation kinetics. Here, we studied a model of the degradation of contaminants continually introduced into a driven flow in fractured nonporous unsaturated media, combined with a dynamic population of microbial degradation sites.…”

“…Instead of saturating with zeroth-order kinetics at high concentrations (as in Michaelis−Menten kinetics), we assume that the microorganisms are poisoned and degradation ceases from those sites. These assumptions have been discussed in the literature, for example, refs and −16. Second, we assume that the flow in fractured media can be convergent as well as divergent.…”