Modeling of Enhanced Biodegradation in Unsaturated Soil Zone

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Abstract
In an attempt to simulate the mitigation of chemical contamination by microbial enrichment in existing unsaturated soil systems, two important characteristics, i.e., the influence of microorganisms on soil water flow and chemical removal rates, were incorporated into a mathematical model (BIOSOIL). Variablestep and variable‐order Gear's Method was employed as a numerical approximation to solve the set of four differential equations. The resulting mathematical model described the behavior of the biosoil system under varying input condititons. From this modeling study of chemical removal, the following conclusions were drawn: (1) The depth of the unsaturated soil zone, a significant consideration in waste disposal practices, seems to be less crucial under bioremediation than generally thought; and (2) microbial distribution in a vertical column of soil is as important as the total population size of soil microorganisms. Study results suggest a guideline for the development of vertically well distributed biosoil systems: apply a limiting substrate at high concentration, at fast rates, and in infrequent cycles.