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N2O Science and Biology

N2O Science 

Nitrous oxide (N2O) is a very strong greenhouse gas and may count for up to 90 % of the carbon footprint of individual wastewater treatment plants (WWTPs).

N2O is an undesired greenhouse gas due to two facts.

  • N2O has a global warming potential that is about 320 times greater than CO2

  • N2O is involved in the reaction with ozone resulting in ozone depletion. 
Since the atmospheric concentration of N2O continues to increase due to the persistent input of nitrogen compounds to the environment, e.g. from fertilizers and wastewater, the global warming from N2O is expected to increase even further in the future.  

The extent of N2O formation in wastewater treatment is complex and depends on multiple factors but it is well recognized that N2O emissions from the biological treatment processes can be very significant. Today, modern wastewater treatment plants therefore have an uncontrolled emission of N2O to the atmosphere, which is a major problem for regulators, plant owners, and technology providers. Despite the relatively small amount of N2O that is released to the atmosphere, it contributes significantly to the climate impact from wastewater treatment.
Therefore, N2O emission must be accounted for as part of the total carbon footprint management and also mitigated. Furthermore the impact from N2O varies significantly from plant to plant and during the season, wherefore the use of standard values is inappropriate to estimate the impact of N2O.

WWTP infographic

The overall scientific conclusion at IWA-2014 was therefore that the best way to calculate emissions and climate impact from N2O is by measuring it!