Tracing N 2 O formation in full-scale wastewater treatment with natural abundance isotopes indicates control by organic substrate and process settings

Water Research X

article

Wenzel Gruber¹  Paul M. Magyar¹  Ivan Mitrovic¹  Kerstin Zeyer¹  Michael Vogel¹  Luzia von Känel¹  Lucien Biolley¹  Roland A. Werner¹  Eberhard Morgenroth¹  Moritz F. Lehmann¹  Daniel Braun¹  Adriano Joss¹  Joachim Mohn¹ 

[1]Eawag, Swiss Federal Institute for Aquatic Science and Technology

关键词: Nitrification;    Denitrification;    Stable isotopes;    Isotopomer analysis;    Nitrous oxide;    GHG mitigation;   

DOI  :  10.1016/j.wroa.2022.100130

学科分类：社会科学、人文和艺术（综合）

来源: Academic Press

【 摘 要 】

Nitrous oxide (N 2 O) dominates greenhouse gas emissions in wastewater treatment plants (WWTPs). Formation of N 2 O occurs during biological nitrogen removal, involves multiple microbial pathways, and is typically very dynamic. Consequently, N 2 O 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 N 2 O 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 N 2 O monitoring, allow identification of the N 2 O production pathways in a full-scale plug-flow WWTP (Hofen, Switzerland). Heterotrophic denitrification appears as the main N 2 O production pathway under all tested process conditions (0–2 mgO 2 /l, high and low loading conditions), while nitrifier denitrification was less important, and more variable. N 2 O production by hydroxylamine oxidation was not observed. Fractional N 2 O elimination by reduction to dinitrogen (N 2 ) during anoxic conditions was clearly indicated by a concomitant increase in site preference, δ 18 O(N 2 O) and δ 15 N(N 2 O). N 2 O reduction increased with decreasing availability of dissolved inorganic N and organic substrates, which represents the link between diurnal N 2 O 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 N 2 O emissions. Our results demonstrate that monitoring of the N 2 O isotopic composition holds a high potential to disentangle N 2 O 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 N 2 O formation or microbial assays to develop efficient N 2 O mitigation strategies.

【 授权许可】

CC BY|CC BY-NC-ND