In the Flemish legislation, no odour assessment framework is implemented, despite that odour-related permit applications require the inclusion of an odour impact study. For livestock farming, odour emission factors, derived from olfactometric measurements (ou_E), are widely used. Contrastingly, the available assessment tools, based on earlier odour impact research, utilize sniffing measurements (se).

   To allow comparison between the two units of odour, it is assumed that 1 ou_E equals 1 se. For most groups of livestock animals with a rather constant growth cycle (e.g. pigs), this comparison is deemed valid and suitable for evaluating the odour impact. However, the theoretical assessment of broiler chicken emissions can be questioned, as the olfactometric emission factor of 0.33 ou_E/s.animal results in almost no odour impact.

   Competing interests: The author has declared that no competing interests exist.

   Academic editor:  Carloz N. Díaz

   Content quality: This paper has been peer-reviewed by at least two reviewers. See scientific committee here

   Citation:  N. Raes and T. Van Elst, 2021, The odour impact of broiler chickens – comparison of the theoretical approach with field panel measurements according to EN16841-2, 9th IWA Odour& VOC/Air Emission Conference, Bilbao, Spain, Olores.org.

   Copyright:  2021 Olores.org. Open Content  Creative Commons license. It is allowed to download, reuse, reprint, modify, distribute, and / or copy articles in olores.org website, as long as the original authors and source are cited. No permission is required from the authors or the publishers.

   ISBN: 978-84-09-37032-0

   Keyword: Odour emission factor, broiler chickens, sniffing measurements, impact modelling

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Abstract

   In the Flemish legislation, no odour assessment framework is implemented, despite that odour-related permit applications require the inclusion of an odour impact study. For livestock farming, odour emission factors, derived from olfactometric measurements (ou_E), are widely used. Contrastingly, the available assessment tools, based on earlier odour impact research, utilize sniffing measurements (se). To allow comparison between the two units of odour, it is assumed that 1 ou_E equals 1 se. For most groups of livestock animals with a rather constant growth cycle (e.g. pigs), this comparison is deemed valid and suitable for evaluating the odour impact. However, the theoretical assessment of broiler chicken emissions can be questioned, as the olfactometric emission factor of 0.33 ou_E/s.animal results in almost no odour impact. Therefore, the Province of West-Flanders (Belgium) ordered an odour study to compare the theoretical approach with the infield sniffing measurements. To account for the short growth cycle of broilers, resulting in discontinuous emission rates, 14 sniffing measurements each were performed in the vicinity of 8 broiler chicken farms, equally divided over the breeding schedule. From the collected data, several scenarii were compared (e.g. average value, value in function of stable type, value in function of age, …). The scenarii based on sniffing measurements resulted in a comparable impact on the environment, but compared to the theoretical value, it could be concluded that the theoretical approach serves as a major underestimation of the real odour emission. The theoretical average value of 0.33 ou_E/s was almost 4 times lower than the real average value of 1.22 su/s according to the sniffing measurements. Based on this study, and other olfactometric analyses that were made, the emission factor has been accordingly adjusted to 0.59 ou_E/s.animal, but more research is required to finetune the odour impact assessment of livestock farming.

1. Introduction

   The aim of this particular study, ordered by the Province of West-Flanders (Belgium) is to evaluate and objectify the odour problem of broiler chicken farms. The obtained information must enable the government to evaluate the actual licensing policy and possible abatement techniques, so it can result in policy adjustments.

   In Flanders, it is necessary to include an odour impact study within almost every odour-related permit application. For livestock farming nowadays, theoretical (average) odour emission factors are widely used. The main problem involving broiler chicken farms is the increasing odour emission over the growth cycle. At the cycle start, the odour emissions are very limited, but increase significantly near the end (approximately 6 weeks later). The methodology in theoretical odour studies, which is based on average emission factors, assumes that this effect is not expected tot be expressed, implying that the varying odour emissions during the growth cycle of broiler chicken farms will be insufficiently reflected in theoretical odour studies

   If this assumption is valid, it means that there is an important gap in the permit application procedure. An evaluation of the situation in practice can provide much needed support here. In the present study, the odour impact of selected farms is investigated based on sniffing measurements. The measurements took place over a longer period (2018 - 2019) and were executed in function of animal age.

   The emission factors currently used are based on olfactometric measurement results, and are expressed in ou_E/s.animal. For sniff measurements, the emission results are expressed in sniffing units (su). Because it concerns a different measuring method (with associated unit), no unambiguous relationship can be derived between the two units.

2. Materials and methods

2.1. Experimental design – selection of the broiler chicken farms

   To have a sufficiently large data set, measurements were performed at eight broiler chicken farms. Four farms with so-called “traditional” stables were selected, and four farms with the ammonia reduction technique “Heat exchanger with air mixing system for drying of the litter layer” (P-6.4.), the most common used technique in Flanders to this day. The amount of selected farms is comparable to the multi-farm apporach of the VERA-protocol (VERA Test Protocol, 2018).

   A total of 14 sniffing measurements were performed per farm, taking animal age into account. At broiler farms, a cycle consists of approximately 6 weeks, and a vacancy is foreseen after every six weeks. The setup was made to have two measurements per company per weekly cycle, with the aim of having one of these measurements in the summer period. By the end of the measuring round (weeks 5 to 6), a part of the animals (approximately 20 to 30 %) is already unloaded to create more space for other animals. As a result, fewer animals will be kept on the farm in the last week.

   Aside from the ammonia reducing technique (P-6.4 vs. traditional), a numerous range of criteria was used to select the different broiler farms in the study:

• Location : the study was ordered by the Province of West-Flanders, implying that the farms had to be established in the West-Flanders region;

• Location compared to other farms : the aim is to identify the unique odour plume of the selected farm. So, there may be no interference with odour emissions of other farms;

• Size : it is necessary that the farms are large enough to be able to identify the odour plume in the surrounding area.

• All-in, all-out-system : the animals need to have the same age. In this case, there is a direct link between the observed odour impact during the sniffing measurements and age.

   An overview of the selected broiler chicken farms with their specifications is listed in Table 1.

Table 1: Overview of the selected farms.

   For most of het broiler chicken farms, the ventilation system is a combination of ridge and length ventilation. When P-6.4. is used, an amount of air is also ventilated through the heat exchanger system. Length ventilation is mostly used in very particular circumstances (high temperature, end of the growth circle, high ventilation rate). Farm 5 differs from the other, and uses only length ventilation.

2.2. Sniffing measurements

   The odour impact was determined by field observations, so called sniffing measurements using the dynamic method. This is a standardised method that was followed, and is described in a Flemish code of good practice “determining the odour dispersion using sniffing team measurements” (Bilsen et al., 2012) and the prEN168412 “Determination of odour ambient air by using field inspection: plume method” (CEN, 2015). A review of the experience with this method in Belgium is also described in Van Elst & Delva (2016).

2.3. Data processing and modelling

   After each sniffing team measurement, relevant source characteristics concerning the broiler chicken farms was collected. This involves the age of the animals, the amount of animals, the temperature in the stables and the ventilation rate (including division of the ventilation over the different fans).

   Based on these source characteristics, the results of the sniffing measurement and the meteorological circumstances at the time of measurement, the odour emission (in su/s) can be calculated for each individual measurement. Calculation was performed with the Flemish model IMPACT and is based on bi-gaussian dispersion formulas and rely on dispersion classes of Bultynck and Malet.

   Based on this individual calculations, a ventilation volume and emission can be calculated for every animal present, but also for the maximum amount of animals that can be present. For permit purposes the odour calculation is in Flanders based on the maximum permit level. Therefore, the results in this paper are based on the maximum amount of animals allowed.

   A large data set of emission factors and ventilation rates is collected. Based on this data collection, different scenarii can be determined :

• Scenario 1 : total odour emission factor regardless of age and stable type (this is overall average of the total data set);

• Scenario 2 : total odour emission factor, but discriminating in stable type (traditional vs. P- 6.4);

• Scenario 3 : average odour emission factor for every cycle week (no distinction between stable type);

• Scenario 4 : average odour emission factor for every cycle wee (with distinction between the stable types);

• Scenario 5 : the theoretical odour emission factor (0.33 ou_E/s).

   To evaluate and compare the different scenarii, a long term odour impact assessment was modelled with IMPACT based on the average emission and ventilation factors. The model calculates the occurrence of odour in a grid of points around the source, taking into account the meteorological data of a number of years (2007-2011). In addition to the odour concentration, the frequency of perception is also calculated.

3. Results and discussion

3.1. Odour emission and ventilation factors

   Table 2 summarizes the odour emission factor and ventilation rate for each individual broiler chicken farm. These results are expressed in function of the maximum allowed amount of animals according to the permit.

Table 2: Overview of results for the individual farms.

   Compared to the theoretical emission factor (0.33 ou_E/s.animal), the odour emission that is calculated for the different broiler chicken farms is significantly higher. The theoretical ventilation ratio (2,4 Nm³/h) is somewhat higher, but that difference is less pronounced.

   Between the different broiler chicken farms there is also a rather large variation in odour emission factor, with Farm 3 having the lowest emission factor. This is probably due to the presence of dust containers that are placed at the end of the stables. Therefore the air flow is obligated to rise, with a better dispersion of the air (and thus lower impact on the vicinity). Farm 6 has the highest odour emission factor, and is the only farm that has length ventilation only. The air is emitted horizontal, without dispersion and as a consequence a higher impact (and thus higher emission factor).

   The results of the different scenario, as described earlier, are shown in Table 3. As mentioned earlier, farm 6 has much higher emissions compared to the others.

   Therefore the results are also shown without farm 6.

Table 3: Overview of results of the different scenarii (between brackets : without farm 6).

   From the results, it is obvious that during the cleaning and preparation period of the stables (empty stables), the odour emissions are not present. The only exception is the moment litter is removed via opened doors out of the stable. This can be accompanied with odour emissions, but in that case there is no ventilation at work. The odour impact during this short notice of time is therefore rather limited.

   Comparing the two stable systems (scenario 2), the traditional system has lower odour emissions but a higher ventilation rate. After removing the outlier farm 6, the results are closer to each other, but week 6 still results in a large difference between the two. The odour emission factor is much higher for P-6.4. compared to the traditional type, which also explains the deviations in scenario 2. No direct explanation for this difference could be found.

   In the beginning of the growth cycle (first two weeks) the emissions and ventilation rates are the lowest. Compared to scenario 5 (theoretical assumption) however, the derived odour emission values are already higher based on the sniffing measurements. But the ventilation rate is very low, and therefore the total amount of emitted odour will be minor, and mostly no odour complaints will occur during this period.

   From week 3 on, the emission factors are higher, but in the rest of the cycle they seem to stay rather stable (bases on the permit amount of animals).

3.2. Reality-check

   The comparison between the theoretical and the practical approach indicates that there are major differences involving the odour emission factor. The theoretical approach seems to result in a large underestimation of the odour emission factor. Therefore, it is important to determine how the obtained results match with reality.

   To make this evaluation, long term modelling was performed on the results of the different scenarii. The odour impact (98-P) was calculated for every farm and for every scenario as the 98-percentile (98-P), indicating wherein the real concentration is only in 2 % of the time higher than the calculated value. When comparing the 1 su/m³ (as 98-P) contour with the individual plumes (of every sniffing measurement) most of them should be inside the contour. In the best case scenario, a minimum of 0 to 2 plumes is allowed outside of the contour (“outliers”). Table 4 gives an overview of these so-called “outliers”.

Table 4:Amount of measurements exceeding 1 su/m³ (as 98-P)

id.	amount of measurements	scenario 1	scenario 2	scenario 3	scenario 4	scenario 5
1	8	3	3	3	2	7
2	14	2	2	2	2	8
3	14	1	1	1	1	7
4	14	1	1	1	1	9
5	15	0	0	0	0	8
6	15	5	4	4	4	8
7	15	0	0	0	0	9
8	15	2	2	2	2	10

   A major part of the plumes of scenario 5 (theoretical approach) are outside the 1 su/m³ (98-P) contour. This confirms the idea that the theoretical odour emission factor, as used today, gives a large underestimation of the real impact of broiler chicken farms.

   The differences between scenarii 1 until 4 are almost negligible. Some of the farms have more “outliers” (e.g. farm 6) compared to others (e.g. farm 5). This is due to the fact that the individual odour emission factor of farm 6 is higher than the overall emission factor derived from all farms. The farms with less “outliers” have an individual odour emission factor lower than the overall emission factor.

   Figure 1 gives the visual comparison of the long term odour impact of scenario 1 en 5 for broiler chicken farm 4. The colored lines indicate distances (500 m ranges) from the farm, the plumes are the actual sniffing measurements, and the filled areas are the result of the long term modelling. The green filled area indicates the 1 su/m³ (98-P) odour contour. The length of the plumes differ in function of the age of the chickens. Figure 1 clearly shows the used theoretical odour emission factor of 0.33 ou_E/s.animal results in an underestimation of the real odour impact of the broiler chicken farms. Scenario 1 gives a much more comprehensive/matching output.

Fig. 1.: Comparison of long term impact farm 4 – scenario 1 vs. scenario 5.

 

4. Conclusions

   To evaluate the discrepancy between the low calculated impact based on the theoretic emission factor and the numerous complaints around certain broiler chicken farms a large amount of sniffing measurements (field panel measurement) were conducted around these farms. During the measurements the different growth cycles were evaluated around 8 farms in 2018 – 2019.

   Based on the large data set, several scenarii based on the sniffing measurements were evaluated and resulted in a comparable impact on the environment of the farm. But compared to the theoretical value, the main conclusion of the study was that the theoretical approach can be considered as a major underestimation of the real odour emission. The theoretical average value of 0.33 ou_E/s was almost 4 times lower than the real average value of 1.22 su/m³ (when excluding farm 6)

   For now, a follow-up study is in progress, involving other animal categories, in order to finetune the odour impact assessment of livestock farming.

 

5. References

   Bilsen, I., De Fré, R. & Bosmans, S., 2008, Code van goede praktijk: bepalen van de geurverspreiding door middel van snuffelploegmetingen. VITO, expertisecentrum milieumetingen 2008/MIM/R/022, 47p.

   CEN, 2015, prEN 16841-2. Determination of odour in ambient air by using field inspection: plume method. CEN TC264 WG27.

   International VERA Secretariat, 2018. VERA Test Protocol for Livestock Housing and Management Systems. https://www.vera-verification.eu/app/uploads/sites/9/2019/05/VERA_Testprotocol_Housing_v3_2018.pdf

   Van Elst, T. & Delva, J. 2016. The European Standard prEN 16841-2 (Determination of Odour in Ambient Air by Using Field Inspection : Plume Method) : a Review of 20 Years Experience with the Method in Belgium. Chemical Engineering Transactions, 54, 175-180.