Comparison of nitrous oxide (N 2 O) emissions calculations at a Swedish wastewater treatment plant based on water concentrations versus off-gas concentrations

Total nitrous oxide (N2O) emissions from a conventional active sludge process were calculated using a mathematical emission model and dissolved N2O in the water phase by a N2O water sensor. Calculated emissions showed good agreement with measured emissions based on concentrations and airflow in the off-gas ventilation system from the covered process. Various tests for a wide range of potentially affecting parameters indicated robust and reliable emission estimations by the model. Thus, common uncertainties in input data would still provide good emission estimations. Measurements of dissolved N2O required low maintenance and N2O emission monitoring based on such measurements might therefore be considered as a significant practical improvement. This would be advantageous especially in non-enclosed wastewater treatment plants (WWTPs) otherwise requiring complex off-gas measurements. As the sensor is connected directly to the WWTPs monitoring and control system, emissions calculations could be incorporated.