N2O emission in full-scale wastewater treatment: Proposing a refined monitoring strategy

Wenzel Gruber; Kris Villez; Marco Kipf; Pascal Wunderlin; Hansruedi Siegrist; Liliane Vogt; Adriano Joss

doi:10.1016/j.scitotenv.2019.134157

N₂O emission in full-scale wastewater treatment: Proposing a refined monitoring strategy

Sci Total Environ. 2020 Jan 10:699:134157. doi: 10.1016/j.scitotenv.2019.134157. Epub 2019 Aug 27.

Authors

Wenzel Gruber¹, Kris Villez², Marco Kipf², Pascal Wunderlin², Hansruedi Siegrist², Liliane Vogt³, Adriano Joss²

Affiliations

¹ Eawag: Swiss Federal Institute of Aquatic science and Technology, CH-8600 Dübendorf, Switzerland; Institute of Environmental Engineering, ETH Zürich, CH-8093 Zürich, Switzerland. Electronic address: wenzel.gruber@eawag.ch.
² Eawag: Swiss Federal Institute of Aquatic science and Technology, CH-8600 Dübendorf, Switzerland.
³ Eawag: Swiss Federal Institute of Aquatic science and Technology, CH-8600 Dübendorf, Switzerland; Institute of Environmental Engineering, ETH Zürich, CH-8093 Zürich, Switzerland.

PMID: 31670036
DOI: 10.1016/j.scitotenv.2019.134157

Abstract

Nitrous oxide (N₂O) emissions from wastewater treatment contribute significantly to greenhouse gas emissions. They have been shown to exhibit a strong seasonal and daily profile in previously conducted monitoring campaigns. However, only two year-long online monitoring campaigns have been published to date. Based on three monitoring campaigns on three full-scale wastewater treatment plants (WWTPs) with different activated sludge configurations, each of which lasted at least one year, we propose a refined monitoring strategy for long-term emission monitoring with multiple flux chambers on open tanks. Our monitoring campaigns confirm that the N₂O emissions exhibited a strong seasonal profile and were substantial on all three plants (1-2.4% of the total nitrogen load). These results confirm that N₂O is the most important greenhouse gas emission from wastewater treatment. The temporal variation was more distinct than the spatial variation within aeration tanks. Nevertheless, multiple monitoring spots along a single lane are crucial to assess representative emission factors in flow-through systems. Sequencing batch reactor systems were shown to exhibit comparable emissions within one reactor but significant variation between parallel reactors. The results indicate that considerable emission differences between lanes are to be expected in cases of inhomogeneous loading and discontinuous feeding. For example, N₂O emission could be shown to depend on the amount of treated reject water: lanes without emitted <1% of the influent load, while parallel lanes emitted around 3%. In case of inhomogeneous loading, monitoring of multiple lanes is required. Our study enables robust planning of monitoring campaigns on WWTPs with open tanks. Extensive full-scale emission monitoring campaigns are important as a basis for reliable decisions about reducing the climate impact of wastewater treatment. More specifically, such data sets help us to define general emission factors for wastewater treatment plants and to construct and critically evaluate N₂O emission models.

Keywords: Activated sludge; Biological nitrogen removal; Greenhouse gases; Nitrous oxide; Wastewater treatment.