Tracing N&lt;sub&gt;2&lt;/sub&gt;O formation in full-scale wastewater treatment with natural abundance isotopes indicates control by organic substrate and process settings

Gruber, Wenzel; Magyar, Paul M.; Mitrovic, Ivan; Zeyer, Kerstin; Vogel, Michael; von Känel, Luzia; Biolley, Lucien; Werner, Roland A.; Morgenroth, Eberhard; Lehmann, Moritz F.; Braun, Daniel; Joss, Adriano; Mohn, Joachim

doi:10.1016/j.wroa.2022.100130

Tracing N₂O formation in full-scale wastewater treatment with natural abundance isotopes indicates control by organic substrate and process settings

Gruber W, Magyar PM, Mitrovic I, Zeyer K, Vogel M, von Känel L, Biolley L, Werner RA, Morgenroth E, Lehmann MF, Braun D, Joss A & Mohn J

Citation

Gruber, W., Magyar, P. M., Mitrovic, I., Zeyer, K., Vogel, M., von Känel, L., … Mohn, J. (2022). Tracing N₂O formation in full-scale wastewater treatment with natural abundance isotopes indicates control by organic substrate and process settings. Water Research X, 15, 100130 (11 pp.). https://doi.org/10.1016/j.wroa.2022.100130

Persistent URL https://www.dora.lib4ri.ch/eawag/islandora/object/eawag:24521

Nitrous oxide (N₂O) dominates greenhouse gas emissions in wastewater treatment plants (WWTPs). Formation of N₂O occurs during biological nitrogen removal, involves multiple microbial pathways, and is typically very dynamic. Consequently, N₂O mitigation strategies require an improved understanding of nitrogen transformation pathways and their modulating controls. Analyses of the nitrogen (N) and oxygen (O) isotopic composition of N₂O and its substrates at natural abundance have been shown to provide valuable information on formation and reduction pathways in laboratory settings, but have rarely been applied to full-scale WWTPs.
Here we show that N-species isotope ratio measurements at natural abundance level, combined with long-term N₂O monitoring, allow identification of the N₂O production pathways in a full-scale plug-flow WWTP (Hofen, Switzerland). Heterotrophic denitrification appears as the main N₂O production pathway under all tested process conditions (0-2 mgO₂/l, high and low loading conditions), while nitrifier denitrification was less important, and more variable. N₂O production by hydroxylamine oxidation was not observed. Fractional N₂O elimination by reduction to dinitrogen (N₂) during anoxic conditions was clearly indicated by a concomitant increase in site preference, δ¹⁸O(N₂O) and δ¹⁵N(N₂O). N₂O reduction increased with decreasing availability of dissolved inorganic N and organic substrates, which represents the link between diurnal N₂O emission dynamics and organic substrate fluctuations. Consequently, dosing ammonium-rich reject water under low-organic-substrate conditions is unfavorable, as it is very likely to cause high net N₂O emissions.
Our results demonstrate that monitoring of the N₂O isotopic composition holds a high potential to disentangle N₂O formation mechanisms in engineered systems, such as full-scale WWTP. Our study serves as a starting point for advanced campaigns in the future combining isotopic technologies in WWTP with complementary approaches, such as mathematical modeling of N₂O formation or microbial assays to develop efficient N₂O mitigation strategies.