Application of the nitrogen-to-argon ratio to understand nitrogen transformation pathways in landfills under in-situ stabilization

Susan Yi*, Nathali Meza, Julia Gebert

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

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Abstract

The ratio of nitrogen (N2) to argon (Ar) in landfill gas was compared to the atmospheric gas ratio to quantify the balance between N2 generating (anaerobic ammonium oxidation, denitrification) and N2 consuming (nitrogen fixation) processes on three landfills undergoing in-situ stabilization. In the aerated landfills, as much as 22% of the extracted N2 could be explained by net denitrification, with coexisting aerobic and anaerobic domains fostering nitrification-dependent denitrification. Nitrogen fixation was also occasionally observed. Removal of nitrogen via the gas phase exceeded nitrogen removed via the leachate by up to a factor of 33. Contrastingly, the anaerobic landfill under leachate recirculation showed a net reduction of N2 in relation to Ar, indicating nitrogen fixation as the dominant mechanism, equivalent up to 28% of the nitrogen in the extracted landfill gas. The balance between denitrification and nitrogen fixation in the aerated sites varied seasonally, likely caused by increased evapotranspiration in the summer, allowing greater air intrusion through the cover soil, resulting in higher NO3– and NO2– availability for denitrification and anammox. No such variability was observed for the landfill under liquid recirculation. The nitrogen transforming microbial community comprised of species responsible for nitrification, ammonification, denitrification, and anammox, indicating all processes may coexist. The findings show aeration supports nitrogen removal through the gas phase, but also suggest that nitrogen fixation adds nitrogen to the waste body in anaerobic domains. This could delay reaching environmental compliance criteria for leachate nitrogen, both for in-situ treatment by aeration and by leachate recirculation.
Original languageEnglish
Pages (from-to)13–23
Number of pages11
JournalWaste Management
Volume194
DOIs
Publication statusPublished - 2025

Keywords

  • Landfill stabilization
  • Nitrogen transformation
  • Denitrification
  • Nitrogen fixation
  • Landfill aeration
  • Leachate recirculation
  • Landfill bioreactors

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