While evaluating the effects of an odour control system the remaining emission to atmosphere should be introduced in an atmospheric dispersion modelling analysis. Pure air solutions can perform such modelling using e.g. the US EPA ISC3 series of software packages which are fully approved by licensing authorities. Meteorological data which is valid for the region needs to be used. Building influences as well as the heat burden of the emission need to be taken into account. The current approach in most European countries for permissible odour emission (=concentration at ground level) for an industrial area with food industry and nearby scattered residential areas is 1 OUE/m3 at 98 percentile. Indeed, based on that reference, we have good experiences as to the result of the odour control effect, in other words the significant reduction and even absence of further odour nuisance complaints. Should a contract be finalised, at extra cost, Pure Air Solutions can undertake such modelling to confirm the chosen height of the stack. Procurement of meteorological and terrain data is the responsibility of the client.
Odour is usually quantified in terms of odour units. A solution to an odour nuisance problem is always a combination of dedicated measures within the boundary limits of a plant and the atmospheric dilution under various ambient conditions valid for the particular location of the plant. Background odour (other sources like industrial activities and traffic) can enhance or reduce the odour perception as well as influence the appreciation of the type of odour. In practical terms one must accept that an odour abatement system can do no better than remove the odour from the raw gas at an efficiency of 85 to 99% in terms of Odour Units.
The remaining odour load in the cleaned gases should be reduced by dilution with ambient air, such that under most atmospheric conditions the odour from the particular source cannot be perceived in a residential or other sensitive area.