A COMPARISON OF ODOR DISPERSION MODELLING RESULTS USING EMISSION DATA FROM WIND TUNNEL AND FLUX HOOD

Odor impact from sewage treatment plants can be predicted using air dispersion models such as Ausplume or ISCIII. In this study, a flux hood and a portable wind tunnel system were used together with forced choice dynamic olfactometry to determine odor emission rates from various processing units at a medium sized sewage treatment plant. In all cases, the olfactometry measurements conformed to the requirements of the most recent draft European and Australian standard on odor concentration measurement using dynamic olfactometer. Both sets of emission results were used as input data to the Ausplume air dispersion model. The odor emission rates determined using the portable wind tunnel system were adjusted for ambient wind speeds to take into account the empirically demonstrated, theoretical relationship between wind speeds and odor emission rates from open surface area sources. Odor concentration isopleths were calculated using meteorological data recorded on site, and, alternatively, synthetic meteorological data for both the wind tunnel and flux hood cases. Concentration levels for odor isopleths based on wind tunnel measurement inputs were found to be about four fold greater than the ones based on flux hood measurements. In both cases, the modelling results showed little difference using both recorded and synthetic meteorological data. The results of the case study suggest the development of alternative assessment criteria for modelling results derived from flux hood measurements would not offer a satisfactory solution as the relative contributions of the various sources were substantially different for the wind tunnel and flux hood. The wind tunnel is preferred for emission sampling as the results can be adjusted in the model for the actual ground level wind speeds and the fetch lengths of area sources. This is not possible with the flux hood. Synthetic meteorological data simulate possible weather conditions and provide a useful tool in air dispersion modelling.