Modeling Enhanced Denitrification in Groundwater Through Electron Competition Among Nitrogen Species

Nitrate pollution in groundwater is a global issue with far-reaching effects on ecological balance and human health. Stimulation of indigenous denitrifying populations using emulsified vegetable oil (EVO) has shown promise for treating nitrate plumes, but the potential for secondary effects, such as release of nitrous oxide and discharge of dissolved carbon, are not yet well understood. This study adapts an electron competition model for use in flow and transport modeling to better understand those potential secondary effects as the electron competition framework has been shown to better describe the dynamics of nitrogen intermediates, when applied in the context of wastewater treatment. The model decouples the description of carbon oxidation and nitrogen reduction to describe nitrogen and carbon emissions over the duration of treatment following the introduction of EVO as a permeable reactive barrier. Model simulations indicate that nitrous oxide emissions may be influenced by the balance between oxidized and reduced electron carriers, modulated by biomass activity and carbon substrate availability. The hydrolysis of EVO is identified as the rate-limiting step in sustaining denitrification, but incomplete denitrification can occur even at high carbon availability. This research advances the understanding of microbially mediated denitrification mechanisms and provides model-based insights for managing nitrate-containing groundwater in ways that minimize nitrogen oxide emissions and downstream impacts by limiting carbon discharge.