| | Odour is fundamentally a matter of opinion. Although there may be a common consensus as to what constitutes a “good” or “bad” smell, the tolerance level for odours varies from individual to individual. A person who grew up in a rural community, for example, may have a higher tolerance for livestock derived odour than a lifelong urbanite who has just bought a rural acreage. On the other hand, there are cases in which just the opposite might be true, or the opinion could vary depending on the species of livestock.
Generally, the degree to which an odour is considered “strong” or “weak” is determined by its intensity, persistence and concentration. But what if science could find a way to measure odour by isolating the components which contribute to these factors and predict its dispersion from the source?
The result would likely be increased confidence when judging the potential odour impact of a livestock operation, says Ike Edeogu. “It would allow requirements for siting livestock operations to be applied based on objective scientific standards rather than subjective or experience based standards. Odour is treated as a nuisance under the regulations and being able to quantify odour would assist in the expansion and development of the livestock industry.
Measuring with confidence
Researchers in Canada generally follow European odour standards as a benchmark when determining the concentration of livestock odour. However, Edeogu says there is a need for homegrown standards to better reflect the rural situation in Canada and to help refine regulations on odour.
It was this need which drove a project by a province-wide network of odour researchers in Alberta, including the AgTech Centre in Lethbridge, to investigate ways to measure odour with confidence. The following were the significant findings:
Persistence a factor. “Because odour is typically presented as concentration, odour mitigation is usually considered to be a reduction in odour concentration,” says Edeogu. “However, in this project the persistence of different livestock odours was found to differ. A more persistent odour will not dissipate as quickly in the atmosphere compared to a less persistent odour. This suggests that persistence levels could be used to scientifically determine the nuisance value of various types of livestock as stipulated in the regulations.”
Odour intensity and concentration. A more scientifically accurate relationship between odour intensity and concentration was developed. “This means odour intensity measurements can be converted to units of odour concentration. This is significant because it helps us relate the impact of odour emissions from livestock operations to their downwind concentrations measured in the field away from the operation. It may also be used to scientifically define the concentrations associated with separation distances specified by the regulations.”
Electronic nose shows potential. Odour concentrations measured with a commercial desktop electronic nose combined with a hydrogen sulphide sensor and an ammonia sensor showed a good relationship. A commercial handheld electronic nose, however, failed to show the same performance. “The alternative may be to design and fabricate a patentable electronic nose,” says Edeogu.
Artificial livestock odour (ALO). This was developed as a reference odour to improve the accuracy of odour measurements compared to the accuracy based on the use of non-agricultural reference substances such as n-butanol. Although the ALO has yet to be extensively tested in a wide variety of applications, results suggested that n-butanol continues to be the most accurate reference compound for odour.
Higher measurement accuracy. Rigorous odour measurement protocols were developed to achieve higher measurement accuracy. These included maintaining odour sample quality in new and reused bags, maintaining reliable olfactometer operation, odour evaluation directly in the field, and measurement of representative
odour concentrations from buildings and manure storage.
Normalizing odour measurement. Dr. G. Qu, previously with the Alberta Research Council, demonstrated that panellist responses from various labs across North America and Europe could be normalized, in other words, corrected for the variability between individuals. “This is significant because recruiting panellists that comply with the internationally recognized European standards is difficult,” says Edeogu. “Normalization of odour measurements results in more accuracy when using less experienced panellists, enabling us to continue to measure odour confidently and objectively.”
Measuring emission rates
Another aspect of the research focused on emission rates at the barn level, from manure storage facilities and other sources with large surface areas. These were the notable findings:
Monitoring ventilation rates. A reliable monitoring system for measuring ventilation rates from mechanically entilated buildings was developed. “These measurements were used to determine odour emission rates from such buildings,” says Edeogu. “It’s a cost-effective pitot-tube system that can be easily installed for either ceiling or wall mounted exhaust fans.”
Ventilation model developed. A ventilation model accounting for variables such as livestock species, number of animals, mass and outdoor and indoor carbon dioxide concentrations was developed to accurately predict daytime ventilation rates in naturally ventilated livestock housing.
Vented flux chamber technique. This was developed to improve the accuracy of odour emission rate calculations from earthen manure storages, feedlot surfaces and similar surface sources.
Emission rate database. A database of odour emission rates was created. It represents emission rates from dairy, poultry and pig operations.
Development of a scientific planning tool for siting livestock operations
The purpose of this project was to develop a planning tool for siting confined feeding operations (CFOs) using science-based information and methodologies. The three main steps included selecting a standard industrial dispersion model, gathering data from a CFO site in order to verify and calibrate the model, and developing a dispersion model as a planning tool to site CFOs.
The ISC Prime dispersion model was selected as a model suitable for the development of a scientific planning tool, while the research was conducted at a pig CFO using trained odour sniffers to record odour intensities in the field downwind from the CFO.
Key to the research was the ability to accurately predict odour levels downwind from livestock operations. In this respect, says Edeogu, the dispersion model was unsuitable because of the highly variable data affecting its accuracy. Although a simple to use, easy to modify planning tool for siting CFOs was developed, Edeogu says the limitations of dispersion models suggests that the tool should not be used to replace AOPA regulations for determining separation distances at this time.
Predicting odour dispersion
Air dispersion models are routinely used to estimate the position and value of a pollutant emitted into the atmosphere. The main finding of this project, which sought to test the reliability of a promising dispersion model for planning the siting of livestock operations, is that such models are generally unreliable for predicting the dispersion of livestock odours in the atmosphere and reveal highly variable results.
“Based on the odour emission rate data and measurements of odour intensity, the ISC dispersion model was unable to predict livestock odour concentrations downwind from a livestock operation that agreed with concentrations measured by trained human sniffers,” says Edeogu. “The outcome leaves little doubt that based on the way odour is measured today, air dispersion models cannot be reliably used as planning tools to site new CFOs or expand existing CFOs.” |
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