Applying model solutions

Estimating emission rate is the hardest part of an odour control study. This is particularly true of wastewater treatment plants, food manufacturing facilities and animal rendering plants, where robust measurements are required but the emission rates and source concentrations are likely to be low.

The introduction of user-friendly environmental dispersion models such as the Atmospheric Dispersion Modelling System (ADMS), has made dispersion studies more straightforward. Dispersion modellers replicate peaks in odour concentration by calculating hourly average concentrations and then assuming a factor of +10 or, as in the case of pungent chemicals, a factor of +30 for the peaks. By using the fluctuations module of ADMS, it is possible to estimate the probability of concentrations at a specific point exceeding odour thresholds.

For example, Fig 1 illustrates the concentrations arising from 0.3mg of highly pungent ethyl acrylate from a 25m-high vent stack used to discharge gases from a metal coating process oven. ADMS v3 was used for this study. Ethyl acrylate has an odour threshold of around 0.02ppb – around 25 times stronger than hydrogen sulphide (H₂S) – typical windy and cloudy weather conditions have been assumed and concentrations multiplied by 10 to account for peaks in concentrations.

From these calculations, it is unlikely there will be a serious odour nuisance from this site. However, as the concentration contour lies relatively close to the residential area a more detailed assessment of the effect of weather conditions would be necessary.

Food for thought

A major manufacturer of food ingredients needed a cost-effective solution to deal with malodorous aqueous effluent generated by its production process. Eutech carried out a wastewater review to investigate the effluent handling procedure. After considering at-source as well as end-of-pipe treatments, the consultancy recommended the installation of a biofilter on the vent from the holding tank as the best option.

As a result, the manufacturer is confident the odours are now successfully eliminated from the effluent-handling process and now enjoys an enhanced relationship with the regulatory authority.