Mitigation of N2O Wastewater Emission

Unisense Environment

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Unisense Environment has developed the world's only N2O (nitrous oxide) Wastewater Sensor for direct measurement in wastewater treatment processes. Nitrous oxide is a strong green house gas 300 times more potent than CO2 and emissions from N2O can account for as much as 90% of total carbon footprint from wastewater treatment. The N2O Wastewater System from Unisense Environment enables real-time and on-site quantification of dissolved N2O and emission from wastewater treatment processes. New state-of-the-art bioprocess and emission mitigation controls can be developed using N2O sensor input yielding a clear environmental advantage over standard control regimes. Unisense Environment was established in 2014 by a team of university scientists with more than 20 years of experience in developing, constructing, and applying microsensors primarily in environmental research. We have in-house development and production, and a strong outreach in international collaborations.

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Nitrous oxide emission contributes with about 42% of the CO2 footprint from Danish WWTPs, emphasizing earlier years underestimation of the impact of N2O and the importance of control strategies targeted at understanding and reducing N2O emissions from WWTPs.

Danish studies support the increased IPCC 2019 wastewater N2O emission factor, but also elucidate the large temporal and WWTP site variations. In the VARGA study, N2O emission control has shown an up to 65% CO2 footprint reduction potential, while other WWTP sites shows lower N2O emission. Overall a reduction potential of 25% in CO2 footprint is expected in Denmark and this number will increase with the new IPCC 2019 wastewater N2O emission factor. However, with the site and temporal variations that exist, online monitoring and control strategies are essential for harvesting this reduction potential.

The Danish project VARGA has implemented and tested a number of new controls for minimizing nitrous oxide at the Avedøre WWTP and demonstrated a 30% reduction (4,260 Ton of CO2 equivalents) early in the project. The full minimization potential is expected to be even greater – up to a 30-65% reduction. Similarly, multiple Unisense Environment clients have demonstrated N2O minimization potentials between 25% and 90% by controlling aeration, loading, and carbon resources more balanced by integration of the N2O wastewater sensor.
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Unisense Environment
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