Emission and dispersion of odour from swine operations
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Odour emissions and instantaneous downwind odour plumes were measured on two 3000-sow swine farrowing farms located in a flat area of southern Manitoba, one farm (Farm A) with open earthen manure storage (EMS) and another (Farm B) with negative air pressure (NAP) covered EMS. Three commonly used dispersion models (ISCST3, AUSPLUME, and INPUFF-2) were used to predict downwind odour distributions on the two farms. Dispersion predictions were based on the measured odour emission data for each farm and on-site weather data recorded by a portable weather station. The peak-to-mean ratios of downwind odour intensity were computed from field odour intensity measurements and analysed against averaging time, downwind distance, and atmosphere stability class. It was found that the average odour emission rate from the negative pressure covered earthen manure storage (NAP EMS) was negligible in comparison with the open EMS (0.3 vs 20.3 OU/ s-m2). Downwind odour intensity measured by trained human sniffers on Farm A with covered manure storage was significantly (P<0.05) lower than that on Farm B with open manure storage at 100 and 500 m, but the difference in odour intensity at 1000 m was not significant (P>0.05) between the two farms. A 46% difference in odour emission rate between Farms A and B resulted in a 14% difference in the separation distance for odour annoyance-free between the two farms. When three commonly used dispersion models, namely AUSPLUME, ISCST3, and INPUFF-2, were used to predict downwind odour from the farms, the percentage of agreement between model predictions and field measurements was adequate for downwind distances of 500 and 1000 m, but relatively low for 100 m for all three models. Since the long-distance (>1000 m) predictions are of more practical value, all three models were considered to be adequate in predicting odour downwind from the swine operations. The peak-to-mean ratios of downwind odour intensity were computed from field odour intensity measurements and analysed against averaging time, downwind distance, and atmospheric stability class. The peak-to-mean ratio of field odour intensity increases with averaging time and downwind distance, and unstable atmospheric conditions.