Predictive Model for Propagation of Beneficial Microbes in Variably Saturated Soils

Abstract

Abstract

Bioremediation of contaminated soils by pumping-in beneficial microorganisms to degrade and eventually remove undesirable organic pollutants is gaining popularity for soil treatment. One critical step of bioremediation involves introducing beneficial microbes, such as bacteria and fungi, into soils to break down contaminants as the microbes carry out their life functions. The current state of knowledge on this subject has been built primarily on experimental work, and the development of a numerical method that is capable of accurately analyzing and predicting bacterial propagation in variably saturated soils has not been adequately explored. Within this background, this article presents the development of a finite element method (FEM)-based model for determining the mobility and growth of bacterial microbes in variably saturated soils. This numerical model captures three major propagation mechanisms of bacteria in a variably saturated soil as a porous medium, including natural diffusion, bacterial growth, and bacterial convective transport, which were successfully coupled in the nonlinear partial deferential governing equation of the model. Temperature, as an important environmental factor, was modeled explicitly in the model. A FEM model was validated experimentally and then used to evaluate the propagation of bacterial species in soils under different environmental conditions. It was found that soil temperature and moisture movement are among the major factors that influence the evolutionary behavior of bacteria. The example application given at the end of the work shows that the developed model is useful for designing the best-performance bioremediation strategies for subsurface zones contaminated by organic matters.