Nitrous oxide from wastewater treatment plants – Eutrophication is more than nutrient loading

Nitrous oxide (N₂O), a potent greenhouse gas and ozone-destroying agent, is produced during nitrogen transformations in both natural and human-constructed environments. Wastewater treatment plants (WWTPs) remove nitrogenous nutrient compounds, but produce and emit N₂O into the atmosphere during the process. Reducing nutrient inputs to coastal waters, therefore, is a double-edged sword. By measuring N₂O concentrations at a monthly resolution over a year in the Potomac River Estuary, a tributary of Chesapeake Bay in the eastern United States, we found a strong seasonal variation in N₂O concentrations and fluxes: N₂O concentrations were larger in fall and winter but fluxes were larger in summer and fall. Hotspots of N₂O emissions were revealed downstream of WWTPs. N₂O concentrations were higher at stations downstream of WWTPs compared to other stations (median: 21.2 nM vs 16.2 nM) despite the similar concentration of dissolved inorganic nitrogen, suggesting the direct discharge of N₂O from WWTPs into the aquatic system or a higher N₂O production yield in waters influenced by WWTPs. Meta-analysis of N₂O measurements associated with WWTPs globally revealed variable influence of WWTPs on downstream N₂O concentrations and emissions. Other waste management systems, e.g., agriculture and animal husbandry, likely cause analogous hotspots and variable N₂O emissions. Since wastewater production is projected to rise with the growing population, efficient N₂O removal, in addition to dissolved nitrogen removal, should be an essential part of wastewater quality control.

Presentation Preference: Oral

Primary Presenter: Weiyi Tang, University of South Florida (weiyitang@usf.edu)

Authors:

Weiyi Tang, University of South Florida  (weiyitang@usf.edu)

Jeff Talbott, Virginia Department of Environmental Quality  (Jeff.Talbott@deq.virginia.gov)

Timothy Jones, Virginia Department of Environmental Quality  (Timothy.Jones@deq.virginia.gov)

Bess Ward, Princeton University  (bbw@princeton.edu)