Comparison of methods for nitrous oxide emission estimation in full-scale activated sludge

Area of Science:

• Environmental Engineering
• Environmental Chemistry
• Wastewater Treatment

Background:

• Nitrous oxide (N₂O) is a potent greenhouse gas emitted from wastewater treatment plants (WWTPs).
• Accurate estimation of N₂O emissions is crucial for climate change mitigation strategies.
• Quantifying N₂O gas transfer requires understanding the volumetric mass transfer coefficient (K_La).

Purpose of the Study:

• To correlate liquid phase N₂O concentrations with gas phase N₂O emissions in a full-scale WWTP.
• To compare different methods for determining the K_La for N₂O.
• To evaluate the accuracy of N₂O emission estimation using experimentally determined O₂ K_La.

Main Methods:

• Simultaneous measurement of dissolved and off-gas N₂O and O₂ using a novel method.
• Calculation of K_La using three distinct approaches: empirical, O₂-based, and static best fit.
• Comparison of estimated N₂O emissions against measured values.

Main Results:

• Trends in local emitted N₂O closely matched trends in local dissolved N₂O.
• The O₂ method, with a static correction factor, provided the most accurate N₂O emission estimation.
• Estimated N₂O emissions using the O₂ method showed a root mean square error (RMSE) of 70.5 and a maximum 28% error.

Conclusions:

• The method of K_La determination significantly impacts N₂O emission estimations.
• The O₂-based K_La method, when corrected, offers a reliable approach for estimating N₂O emissions from WWTPs.
• Accurate monitoring and modeling of N₂O transfer are essential for effective greenhouse gas management in wastewater treatment.