Evaluation of the Odour Emission Rate from Wastewater Aerated Tanks: a Methodological Approach

Accuracy in the characterisation of odour-emitting sources is particularly significant for the implementation of a truly representative odour impact study. The selection of sampling techniques to measure odour concentrations, along with an accurate method to assess Odour Emission Rate, is closely linked to the type of source under investigation. The distinction between active and passive sources is not always obvious, such as in the case of biological oxidation tanks. This kind of emissive source, commonly classified as a passive source, is characterised by convective flow that is generally not intense. Indeed, the flushing of a known airflow within a dynamic hood, such as a wind tunnel system, necessary to simulate the wind action on the surface of the tank, may not be the driving force of the system. The aim of the present study is to evaluate the emissive contributions of biological oxidation tanks, focusing on the phenomenon of aeration and the effect of wind on the liquid surface of an oxidation basin. Using different sampling methodologies, through different field measurements, the Specific Odour Emission Rates, associated with each contribution, were measured and compared. The results indicate that the stripping phenomenon due to the convective flow generated by aeration can account for up to 96% of the odorous emission contribution.