Comparison of dispersion models for assessing odour from municipal solid wastes

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Abstract
This paper assesses the dispersion of odour from a waste transfer station in the North London area, UK. The basic models used for analysing the extent of dispersion were UK-ADMS (version 1.5) and US-EPA's MPTER (A Multiple Point Gaussian Dispersion Algorithm with Optional Terrain Adjustment). The two models have been extensively run for various meteorological conditions and source values based on site measurements. It has been observed that the two models compare very well at distances downwind greater than 500 m within a range of 29.0% to 40.0% up to 3.0 km. The two models differ substantially near the source; the physics of UK-ADMS representing the scenario better close to the source. The results indicate that with a wind velocity of 5.0 m s-1 the mean odour level, in odour units (ou), can fall down sharply from 1695.0 ou m-3 at the source to 0.5 ou m-3 at about 1.5 km from the source along the centreline. A dynamic dilution olfactometer with six panellists was used to characterize the odour strength of the source. Simultaneously, an intensity test was used to assess the number of times the odour would need to be diluted to achieve a reasonable expectation of 'no complaints' from the site operations. Measurements of intensity were determined by a 'sniffing' panel using a subjective scale (usually 0 to 6) from very faint to very strong. It has been observed that the emitted odour intensity reduces from a distinct odour to a faint odour as the odour concentration decrease from 10 to 4 ou m-3 and these levels are greatly exceeded at the point of emission. According to calculations, an odour intensity of 6 ou m-3 averaged for 15 min could be expected up to a distance of 470.0 m downwind along with a crosswind spread of + 80.0 m to - 80.0 m about a source of strength 1695.0 ou m-3 and average wind velocity of 5 m s-1.

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