Simulering av lustgasutsläpp med processmodell över Kalmar avloppsreningsverk : En undersökning av driftstrategier

Sammanfattning

The European Parliament’s Urban Wastewater Treatment Directive imposes stricter requirements on wastewater treatment plants (WWTPs) to monitor and reduce greenhouse gas emissions. Nitrous oxide is a potent greenhouse gas with a global warming potential 273 times higher than carbon dioxide (for a 100-year time horizon) and can be emitted during WWTP processes.This study analyzed nitrous oxide emissions from Kalmar WWTP using a process model to identify emission hotspots and evaluate operational strategies for emission reduction. Four strategies were examined: flexible zones in the activated sludge (AS) lines, adjustment of the dissolved oxygen (DO) setpoint in the mixing tank “Aeration 9”, modification of the calculation interval for aeration control in the AS lines, and changes to the equation determining the DO setpoint in the AS lines.Only adjustment of the DO setpoint in Aeration 9 significantly reduced emissions. Shutting off aeration in the mixing tank is estimated to reduce emissions by 0,53-3,55 tCO2eq/week, while increasing the oxygen concentration from 0.5 to 1.5 gO2/m3 is estimated to reduce emissions by up to 2.72 tCO2eq/week. However, full-scale implementation may introduce complications not captured by the model.Although the remaining strategies did not significantly affect total emissions, differences between individual process units were observed, with Aeration 9 appearing most sensitive.Model estimates corresponded to 50% of drone-based estimates and 84% of estimates from Svenskt Vatten’s climate calculation tool. The modelled emission factor was 0.79% of the incoming total nitrogen load.