WP2 – Minimization of nitrous oxide

Nitrous oxide is a powerful greenhouse gas that has a climat impact of 300 times larger than CO2 and therefore the need to reduce its emissions is crucial.

Its emissions can be mapped by implementing online measurements from both the aeration tanks and the treated wastewater. Danish-developed N2O sensor has been employed to measure and collect data in real-time, with an aim to improve carbon footprint.

The measurement of nitrous oxide is of major importance to ensure a balanced energy savings in the aeration tanks and carbon harvesting (WP 1) in the primary stage.  Low oxygen levels and carbon depletion in the aeration tanks can significantly increase the emissions of nitrous oxide. In this work package, nitrous oxide level is initially monitored based on a reference line, and with the use of emission’s models the real-time emission of nitrous oxide is calculated, which together with current power consumption / production provides the basis for estimating the realtime footprint. Subsequently, effects of the belowmentioned process-actions will be documented and optimized in proportion to total environmental impact :

• Increased carbon harvesting to digesters (WP 1) that could potentially minimize carbon loading for the biological nitrogen removal.

• Better control of the biological nitrogen removal in relation to oxygen level and phase control.

• Better control of the side stream processes for nitrogen removal (WP 4 – Anammox), for minimizing the nitrous oxide emissions.

The methane emission is also included in the real-time model in the form of discharge of unburned methane from digesters. The remaining discharge of methane from the process tanks is difficult to be monitored online and is expected to give a smaller contribution to the overall environmental impact. This can be validated with the spot-metering of the total emission of climate gases from the plant.