Model Development and Simulation of Bioremediation in Soil Beds with Aggregates

One method of remediating contaminated soil and ground water is through management of the subsurface environment so that indigenous microorganisms can biodegrade organic contaminants. Modeling and simulation offer promising means of assessing the migration and attenuation of such contaminants being treated in situ in the subsurface. In this paper, a macropore flow model has been developed to account for bioremediation in the interstitial spaces among soil aggregates. This model has been combined with another bioremediation model which accounts for diffusion and Biodegradation in the micropores and soil particles in the aggregates. The combined model comprises a system of six coupled equations, of which three are nonlinear ordinary differential equations and three are nonlinear partial differential equations. Dimensional analysis of these equations has yielded useful dimensionless parameters for evaluating the relative significance of each mechanism in remediation. Numerical experiments have been conducted to evaluate the effects of initial contaminant concentration, aggregate size, and soil-water partition factor. The total time of remediation has been found to depend on the rate at which contaminants are consumed within the large aggregates which, in turn, depends on the Biodegradation kinetics and the rates of diffusion of substrate and oxygen in the aggregates. For soil with aggregates whose radius is 1 cm or larger, the results of simulation indicate that the remediation time for the aggregates is significantly longer compared to the corresponding result for homogeneous soil. For contaminants with large partition coefficients, the estimated time for remediation achieved through microbial oxidation in situ is much shorter than that achieved through purely diffusional transport of the contaminants out of the soil bed.