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Odour studies at broiler farms: theory tested against practice
Theory tested against practice
Issue
Flemish legislation does not include a legal assessment framework concerning odour. Nevertheless, it is necessary to conduct an odour impact study in almost every environmental permit application in which odour is a significant aspect. A problem in this regard is also the method used to quantify odour.
For livestock files, this usually uses theoretical odour emission factors derived from olfactometric (lab) measurements (ouE). In contrast, the available assessment tools, based on previous odour impact research, use field panel measurements (se).
To allow comparison between the two odour units, it is assumed that 1 ouE is equal to 1 se. For most groups of animals with fairly constant growth cycles (e.g., pigs), this approach is considered more or less acceptable and realistic. The theoretical approach can therefore be used as a good measure to evaluate odour impact in such cases.
Broiler problem
However, the theoretical assessment of broiler emissions can be strongly questioned. Using the olfactometric emission factor (previously 0.33 ouE/s.animal, recently adjusted to 0.59 ouE/s.animal), after model calculations, almost no odour impact is observed. Nevertheless, multiple applications involving these types of barns often leads to action groups being set up, and the odour complaints are numerous.
The main problem in broilers is the short growth cycle (around 6 weeks), resulting in highly variable emissions and flow rates. Odour emission is very limited at the beginning of a cycle. At the end, emissions increased significantly. Because of the methodology used in the theoretical odour studies (based on average emission factors), this effect is not adequately addressed.
Research conducted
A study was therefore conducted by OLFASCAN on behalf of the Province of West Flanders to compare this theoretical approach with practice (based on sniff measurements). To best assess the effect of periodic emissions, 14 sniff measurements were conducted near 8 broiler farms. These measurements were evenly distributed over six weeks of the breeding round.
At present, barns must be low in ammonia emissions. One of the most commonly used techniques involves the use of a heat exchanger (type P-6.4.). To assess the effect of this technique, it was therefore decided to select 4 companies equipped with a traditional barn system, and 4 farms with the P-6.4 barn type.
The results of the individual companies are shown in Table 1, which clearly demonstrate that there are large differences between individual companies.
Determination of odour emission rate
Based on the obtained results of the sensory environment studies, several possible scenarios were worked out (including difference traditional – P-6.4, variation emissions according to weekly age, etc.). One of the scenarios was to use the average of all sniff measurements, regardless of housing system and weekly age. This most closely approximates the current methodology, where a single emission figure is also used.
This averaging resulted in an average emission factor of 1.22 se/s.animal, which is considerably higher than the theoretical emission rate (which was set at 0.33 ouE/s.animal at the time of the study).
Comparison of practice and theory
The figures compare the odour impact of company 4 between the emission factor from the study and the emission factor (at that time). For illustrative purposes, the captured odour plumes determined during the sensory survey are also shown.
This clearly shows that the theoretical approach reflects a substantial underestimate of the real odour impact of broiler farms (almost factor 4). To obtain a more realistic picture, it will therefore be necessary to increase the emission factor.
Consequence
Based on the conclusion from this study, combined with analyses and considerations made, the emission factor has since been adjusted to 0.59 ouE/s.animal.
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