Monitoring, modelling and reducing nitrous oxide emissions from WWTPs

Towards mitigation strategies for WWTPs through intensive monitoring and modelling of N₂O emissions

Industry and society are striving to reduce the carbon footprint in response to tackling climate change. But carbon dioxide is not the only harmful greenhouse gas – nitrous oxide (N₂O) has a global warming potential  273 times greater than CO₂. Wastewater treatment plants (WWTPs) are a significant source of N₂O emissions. As a result, well-conceived long-term research is needed to better understand N₂O production in WWTPs and find technologies and strategies to reduce it.

Technology

N₂O emissions from WWTPs exhibit diurnal and seasonal variations. To better understand the processes behind its production, it is necessary to quantify the N₂O emissions. Few WWTPs in the world currently monitor N₂O emissions in real time, given that quantifying N₂O emissions from open tanks is challenging. Advanced monitoring and measurement technologies exist to detect N₂O in the gas phase, but in order to provide such analysers with representative and clean samples, a fit-for-purpose floating hood is needed to collect the off-gases in open tanks. The necessary datasets obtained can thus be used to calibrate biokinetic models that provide insight into the N₂O production pathways and processes. Furthermore, new technologies, such as artificial intelligence (AI), to accurately forecast N₂O emissions can be developed to enable potential solutions for controlling wastewater treatment processes in real time to reduce the harmful emissions.

Challenge

In this project, we will intensively monitor selected WWTPs using advanced gas analysers. We will collect high-resolution data over a long duration to understand seasonal and diurnal variations. To effectively capture the emitted N₂O gas from the open tanks of the wastewater treatment plant, we designed a fit-for-purpose floating hood which will be installed on the water surface, and connected to a gas analyser. We will combine the collected data with other measurements on the treatment processes provided by the waterboards, including the liquid phase N₂O measurements. The datasets will be used to develop digital twins for the prediction of N₂O emissions. These digital twins can be further used to develop N₂O emissions control and reduction strategies.

Solution

At several Dutch wastewater treatment plants with different biological treatment process configurations, we will conduct robust monitoring campaigns of N₂O emissions. The N₂O gas sampling are done with a state-of-the-art fit-for-purpose floating hood, which is equipped with the necessary sensors (such as temperature and pressure) to record the sampling conditions and includes preventive maintenance mechanisms to ensure the collection of high-quality and representative gas samples. These samples are then analysed with industry-standard analytical equipment to measure the concentration of the emitted N₂O. In doing so, we use equipment from KWR and new equipment from Douna Machinery B.V and Emerson Process Management B.V.

The data collected will allow us to determine the emission factor for N₂O at different WWTPs. With the development of models and digital technologies, valuable insights into the processes of N₂O production and emissions will be gained, leading to the development of effective N₂O mitigation strategies. This project also provides important and complementary knowledge to the versnellingsprogramma in the Netherlands aiming at monitoring N₂O emissions from WWTPs nationwide.