A Transport-Rate-Limited Numerical Model for Simulating Cell Growth and Biodegradation Rates in Porous Soil and Rock

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The applicant proposes to examine the topic of the numerical simulation of enhanced bioremediation in hydrogeological systems. This will involve extending the multi-phase compositional numerical model CompFlow BioF to include a transport and reaction rate limited approach to simulate the stoichiometric exchange of electrons from the substrate, to the biomass, and finally to the acceptor within the void space of the soil. The objective of this biodegradation formulation is to be able to simulate the highly transient processes of pulsed air sparging to stimulate aerobic biodegradation of gasoline source zones. The problem geometry involves a variably saturated porous media or discretely fractured porous rock aquifer in which a multi-component gasoline mixture is leaked from an underground storage tank located within the vadose zone. The gasoline forms a light-non-aqueous phase (LNAPL) which subsequently mobilizes and becomes buoyant on the water table, with subsequent mass transfer and advective-diffusion transport of the gasoline components (substrate) into the pristine groundwater. As aquifer-scale mass transport of the gasoline components occurs in the groundwater, a KLA derived mass transfer coefficient for the mass transport of electron donor and acceptor from the aqueous phase within the void space of the porous media onto the biomass that is attached to the porous media. The model then reacts a stoichiometric balance of electrons from the electron donor (gasoline components as substrate) to the electron acceptor (oxygen for aerobic degradation) and removes dissolved substrate while increasing the biomass concentration. Bioreactions occur under various rate-limiting conditions including due to the following three process: electron donor-limiting mass transfer, electron acceptor-limiting mass transfer, and microbial density-limiting due to the capacity of the biomass to facilitate the electron transfer process. The transport and reaction rate limited approach allow for a continuous transition to whichever of the three processes is limiting the bioreaction process and ultimately the spatial-temporal evolution of the plume-scale biodegradation. This approach also supports quadratic converge of the Newton iteration allowing the CompFlow BioF multi-phase compositional model to simulate real-world scale aquifer issues. The outcome of this proposal is therefore to contribute to the knowledge base required for the multi-phase multi-component simulation of aerobic and anaerobic biodegradation under conditions that include technologies to enhance reactions such as atmospheric air sparging and aqueous phase nutrient injection. This outcome will enable simulation of enhanced biodegradation technologies to design, implement, and potentially optimize contaminant plume remediation systems.