From May 2006 to December 2006 an odour exposure study using field panel observations according to German standard EN3940 was carried out around an installation for reception and sorting of urban solid waste and treatment of the organic fraction using anaerobic digestion and composting, with a capacity of 240.000 tonnes of waste annually.

The exposure study covered an area of 2000 × 4000 meters, including the residential area of Ripollet, the Can Salvatella industrial estate and a rural area with various animal production facilities. The results were compared with the German criteria for residential and industrial areas of 10% and 15% odour hours respectively. These criteria were exceeded in the vicinity of the installation, including part of the industrial area of Can Salvatella, but not exceeded in the residential area of Ripollet.

The odour impact was also modelled using dispersion modelling. Two models were applied, ISCST as an example of the more traditional Gaussian plume model and CALPUFF in 3 dimensional mode as an example of more advanced modelling.

The meteorology in the area is challenging, from the modelling point of view, with frequent calms and low wind velocities, combined with a pronounced day/night circulation pattern. The results of the three methods of odour impact assessment are applied and the model results are compared and validated against the observed odour frequencies over the six month period of the study. The Gaussian ISCST model proved to be unable to effectively predict the odour footprint as determined by direct field observations of exposure, overestimating the distance of impact substantially in the direction of prevailing winds. The CALPUFF model in 3D mode did predict the area of measurable odour hour frequencies quite well. The 98 percentile for 3 ouE·m-3 appears to be a bit more restrictive than the German <10% odour hours criterion applied in German regulation.

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