Modeling enhanced denitrification in groundwater through electron competition among nitrogen species to identify N2O emissions

Nitrate contamination in groundwater is a pervasive environmental issue with significant ecological and potential human health implications.  Emulsified vegetable oil (EVO) has shown promise for nitrate plume remediation through simulation of indigenous denitrifying populations, but the potential for secondary effects such as nitrous oxide emissions and discharge of dissolved carbon are not well understood. This study is the first adaptation of an electron competition model with steady-state biomass developed for modeling denitrification in wastewater treatment facilities to denitrification in the subsurface environment with biomass growth. The goal of the model is to quantify carbon and nitrogen emissions over the lifetime of a treatment. The model integrates EVO hydrolysis with substrate availability and electron carrier dynamics, incorporating microbial interactions between hydrolyzers and denitrifiers. Key findings reveal that nitrous oxide emissions are significantly 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 microbial-mediated denitrification mechanisms and provides insights for identifying the conditions that favor nitrous oxide emissions in Permeable Reactive Barriers (PRBs) for nitrate-contaminated groundwater remediation.