Characterization of dust generation in livestock houses based on field monitoring and numerical approach

Abstract

The evaluation of airborne dust is of concern because it can result in a deteriorated indoor air quality (IAQ) within livestock houses and compromises the respiratory welfare of both livestock workers and animals. To create adequate aero-environmental conditions inside the livestock houses, an understanding of the mechanisms of dust generation according to a complicated combination of variables is very important. However, investigations based on the single correlation between dust concentration and environmental factors have been mostly carried out up to date

there have been few comprehensive and detailed studies that have statistically investigated various dust generation factors simultaneously. In addition, in spite of the demand of legislation pertaining to the occupational exposure limit for dust level in primary industries, such as agriculture, only few studies are available as the backgrounds related to observation of the dust concentrations within livestock houses in South Korea. In this thesis, as a first step, comprehensive literature reviews on source of airborne dust within livestock houses, factors leading to generation of airborne dust, adverse effects on livestock farmers, animals and neighboring society, Computational fluid dynamics (CFD) application in agricultural fields and CFD analyses on dust behavior in airspace were intimately conducted to build the foundation and to suggest the appropriateness of the study. Intensive and long-term field monitoring of airborne dust defined as total suspended particle (TSP), PM10, inhalable particulate, and respirable particulate were carried out to determine the key factors affecting dust generation in different size fractions in commercial nursery pig house, mechanically ventilated broiler house, naturally ventilated broiler house, dairy cattle and Korean native cattle farm which are typical type of livestock houses in South Korea. From field observations and statistical analyses in nursery pig house, statistical analysis results showed that ventilation was the most influential factor for variation of TSP and PM10. Activity of animals, number of animals, and ventilation were found to be significant factors for the concentration of inhalable particulate, while the ventilation, indoor air temperature, and activity of animals were significant factors for the concentration of respirable particulate. From the statistical models, adjusting the ventilation rate or improving the systematic characteristics of ventilation were identified as effective and practical components of dust reduction strategy in terms of their productivity and economic feasibility. With respect to strategy of ventilation control, CFD technique was used to evaluate the dust reduction efficiencies of conceptual pipe-exhaust systems during feed supply based on Eulerian-Eulerian multiphase model. Boundary and initial conditions for numerical model were constructed from the field measured data and statistically derived equations in this thesis. From the computation of dust concentrations and dust removal efficiencies according to the application of the pipe-exhaust system and their operation methods, the application of the pipe-exhaust system was shown to effectively improve the IAQ, especially for inhalable particulate concentrations in the experimental nursery pig house. Combined use of the pipe-exhaust system and conventional roof-exhaust dust ventilation system produced 31.0% decrease of particulate phase with 20 μm AED (Aerodynamic equivalent diameter) in contrast to single operation of the conventional roof-exhaust duct ventilation system when minimum ventilation rate was adopted. In case of the field observations and statistical analyses for experimental broiler houses, increase in activity of the broilers, indoor absolute humidity and ventilation were influential factors for variation of the inhalable particulate, while outdoor humidity level, activity of the broilers, ventilation rate and age of broilers were influential factors for respirable particulate in the mechanically ventilated broiler house. Considering the practical operation and their effectiveness, controlling of humidity level inside the facility was effective manner for dust reduction strategies for mechanically ventilated broiler house. For the naturally ventilated broiler house, ventilation rate and activity of broilers were influential to the inhalable particulate, while, indoor air temperature and outdoor absolute humidity level were statistically significant to the variation of the respirable particulate. From the additional chamber experiment to investigate the effect of water contents of bedding materials on dust generation, approximately 45 and 50% of water content levels was found to be a threshold level for generation of the inhalable and the respirable particulate, respectively. Restrictive and temporal application of the droplets spraying on bedding materials is able to be proper options to reduce the respiratory risk for workers especially during shipment works, considering perils of micro-organisms proliferation. For the experimental cattle farms, statistical analyses were not carried out due to the limited research periods and outbreak of Foot-and-mouth disease (FMD) during research periods. Relatively low dust concentrations were observed in dairy cattle farm and Korean native cattle farm in contrast to other species. However, substantial quantities of the dust concentrations that exceeded the occupational exposure limit for respiratory health of workers were especially found during hoof actions of the animals and TMR (Total mixed ration) process for feed particulates. Water content of bedding materials were also related to the degree of dispersion of the larger particulates such as inhalable particulate fractions. In case of the TMR processing, size of the feed materials and supply method were strongly related to level of dust concentrations.