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Advanced modelling and control of nitrous oxide emissions from wastewater treatment plants

Periodic Reporting for period 1 - AMACONOE (Advanced modelling and control of nitrous oxide emissions from wastewater treatment plants)

Berichtszeitraum: 2018-08-01 bis 2020-07-31

The production and emissions of nitrous oxide (N2O), one of the main chemical compounds leading to ozone layer depletion and a significant greenhouse gas with a global warming effect 265 times stronger than CO2, significantly increase the carbon footprint of wastewater treatment plants (WWTPs). Currently, the development of technological solutions to decrease N2O emissions is impaired, due to the lack of a solid fundamental understanding of the rather complex N2O production pathways. Moreover, a reliable simulation tool capable of accurately predicting N2O emissions is not available to generate and test novel ideas and customized solutions for WWTPs to mitigate carbon footprint.

This project aims to put together a database of full-scale N2O emissions from different WWTPs and develop a unified N2O model able to predict the multiple N2O production pathways. The unified N2O model will then be incorporated to issue a new plant-wide model, which will be implemented to optimize plant design for minimum carbon footprint. Through applying data-based and model-based analyses, carbon footprint mitigation strategies will be proposed for WWTPs of different process configurations. The developed control strategies will be implemented at full scale to evaluate their applicability in directing the operation of real WWTPs.
Work performed:
• Work Package 1 – Collected full-scale N2O data from a number of publications.
• Work Package 1 – Collected and analyzed long-term N2O data from Avedøre WWTP (Denmark).
• Work Package 2 – Evaluated a unified N2O model and applied it to assess N2O production from different biological nitrogen removal systems (e.g. autotrophic nitrogen removal granular sludge systems).
• Work Package 2 – Developed a plant-wide model with incorporation of N2O production pathways in the modelling platform Sumo2.
• Work Package 3 – Compared different WWTP configurations and proposed prospective WWTP designs for carbon footprint mitigation.
• Work Package 4 – Proposed a potential control concept and performed its full-scale testing.

Main results achieved:
o Work Package 1 – Published a database containing full-scale N2O emission data from different WWTPs and revealed the mechanisms and driving forces for N2O emissions from activated sludge oxidation ditch process with alternating aerobic and anoxic phases (like Avedøre WWTP studied in this project).
o Work Package 2 – Obtained a unified N2O model and revealed the mechanisms of N2O production from autotrophic nitrogen removal granular sludge systems.
o Work Package 3 – Revealed that when proper control strategies were implemented, the predenitrification WWTP configuration was able to reduce the N2O emissions by 17.2%, compared to the postdenitrification WWTP configuration.
o Work Package 4 – Obtained an effective N2O control strategy able to reduce 60% of N2O emissions from activated sludge oxidation ditch process with alternating aerobic and anoxic phases.
Progress beyond the state of the art:
• Not only proposed an effective N2O control strategy but also tested it on site of the WWTP studied in this project, which has been rarely done before.

Expected results:
o A database of full-scale N2O emissions from different WWTPs.
o Several plant designs for carbon footprint mitigation.
o Identified control strategies for carbon footprint mitigation for some different WWTP process configurations.
o Four journal papers (Three have been published, and the fourth one is under review).
o Two IWA conference presentations (2018 IWA World Water Congress and 2019 IWA Watermatex Conference).
o One co-supervised Master thesis.

Potential impacts:
• The long-term monitored full-scale N2O emission data and analysis results obtained in Work Package 1 will provide important practical support for the upcoming legislation on greenhouse gas (GHG) emission from WWTPs in the Nordic region.
• The European Union (EU) has set the ambitious goal of reducing its GHG emissions to 20% below 1990 levels by 2020. Therefore, WWTPs in the EU have a huge interest in effective N2O control strategies. The control strategy obtained in Work Package 4 is extremely important to reducing the contribution of WWTPs to the global GHG stock and represents a huge contribution to the field, especially considering the wide application of this particular activated sludge oxidation ditch process (like Avedøre WWTP studied in this project) which is being applied in more than 80 WWTPs in Europe alone.