Numerical Simulation of Air Sparging for Enhanced Aerobic Biodegradation of Gasoline in the Subsurface

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The applicant proposes to contribute to extend the multi-phase compositional model CompFlow BioF to include a non-equilibrium flux-based biodegradation formulation and simulate pulsed air sparging for enhanced aerobic biodegradation of gasoline source zones. The problem geometry involves a variably saturated porous-media-only aquifer in which a multi-component gasoline mixture is leaked from an underground storage tank located within the vadose zone. The gasoline forms an 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 mass transport of the gasoline components occurs in the aqueous phase, the diffusive flux-based biodegradation model reacts a stochiometric 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, electron donor-limiting, electron acceptor-limiting, and microbial density-limiting. The diffusive flux-based mass transport approach allows for the aqueous and biomass phases to be in disequilibrium with respect to another, and evolve their composition in a highly transient manner. This is a significant improvement over the conventional Monod-based approach which assumes a quasi-steady-state approximation for determining the bioreaction rate. The objective 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. The outcome will be to enable simulation of enhanced biodegradation technologies to design, implement, and potentially optimize contaminant plume remediation systems.