Modelling wastewater treatment plant odour dispersion in weak wind conditions: importance of high-resolution meteorological data

Odour emissions from wastewater treatment plants (WWTPs) represent one of the major causes of community's complaints since they can spread over large distances, influenced by air dispersion phenomena and particular topographic or meteorological conditions. The modelling tools, normally used for simulating odour emissions, can be affected by some limitations, often due to the refinement of input meteorological data, thus requiring an accurate evaluation. To investigate this aspect, a measurement campaign was performed at a WWTP located in Northern Italy, where a comparison between a conventional (CA) vs. a 3D ultrasonic anemometer (UA) was carried out from 14 June to 17 July 2018. Even if the UA has been already used in other odour-related studies, to the authors' best knowledge, this represents the first investigation where the results, obtained by feeding dispersion models with CA and UA input data, were compared. The location, the site complex orography and the presence of a conventional meteorological station installed at the plant were the main factors taken into account for the WWTP choice. These features, shared by many other worldwide sites, contribute to make this site representative of a common situation. The comparison showed a huge difference in modelled odour concentrations between the two measurements, suggesting that the use of high-resolution meteorological data, as an input to modelling tools, could help the plant managers to adopt smart strategies for minimizing odour nuisance spread (e.g. a more suitable definition of the daily hours to evacuate the sludge from the plant), therefore reducing community's complaints.