Odorous emissions generated by wastewater purification plants are a highly topical problem that operators are having to deal with without the support of national legislation regulating the matter. To partially fill this gap, the Lombardy Region’s guidelines have come to the rescue, and the authors’ attention was focused on 35 plants in four geographic areas of Lombardy belonging to different potential classes. Through a questionnaire, in fact, information was collected on the most common management and plant arrangements implemented to overcome this problem. For each section, the measures undertaken and the results achieved were reported: it emerged that the units with the greatest impact are pre-treatment and dewatering and that the most widely implemented technology is the multi-stage scrubber, generally chosen for a cost/performance ratio considered advantageous. In order, furthermore, to correlate the operators’ reports (regarding seasonality and the time of occurrence, during the day, of odour episodes) with the parameters associated with the meteo-diffusivity of the atmosphere, a modelling simulation was carried out using CALPUFF, using data from the Arconate meteorological station: it was found that while day-night alternation represents a fundamentally important element in the dynamics of odour substance concentrations, seasonality, on the other hand, does not seem to have a significant effect on it. The purpose of this work is to provide the legislator with a tool to support the issuing of specific guidelines (based on the existing state of the art in much of Lombardy), which can support managers in the difficult decision-making process that must lead to correct and sustainable management of the ‘odour problem’.
