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Ammonia Emissions from Broiler Cake Stockpiled in a Naturally Ventilated Shed

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  Transactions of the ASABE. 54(5): 1893-1904. (doi: 10.13031/2013.39830) @2011
Authors:   H. Yao, S. B. Shah, D. H. Willits, P. W. Westerman, L. Wang Li, T. K. Marshall
Keywords:   Acid scrubber, Emission factor, Fick's law, Grashof's number, Integrated horizontal flux

Due to concerns about the negative environmental impacts of ammonia (NH3), the EPA may soon regulate NH3 emissions from livestock operations, including waste piles. This would require knowledge of NH3 emission rates, but there are very few field-scale studies on emission measurement from broiler waste stockpiles. This is the first study in which short-term NH3 fluxes from broiler cake stockpiled in a shed were measured, taking into account both forced and natural convection. Acid scrubbers were used to measure NH3 concentrations, while the integrated horizontal flux (IHF) method and Fick's law of diffusion were used to determine NH3 emissions due to forced and natural convection, respectively. Average daily air temperature and wind speed 0.75 m above the stockpile were 24.9°C and 0.65 m s-1 in summer and 8.5°C and 1.02 m s-1 in winter. Natural convection accounted for <0.01% of total emission, but not isolating gas concentrations during forced convection conditions generally led to overestimation of emission. In summer (7 d), NH3-N emission factors were 17 g m-2 d-1 (stockpile surface area), 30 g m-3 d-1 (stockpile volume), 1.8 g kg-1 N d-1 (initial cake N content), and 11 g AU-1 d-1 (where AU = 500 kg live weight marketed). During the first 7 d of the winter study, the emission factors were 27 g m-2 d-1, 43 g m-3 d-1, 2.1 g kg-1 N d-1, and 18 g AU-1 d-1, respectively. For the 15 d study, the emission factors changed very little. Higher emissions in winter were due to higher wind speeds, broiler cake total Kjeldahl N (TKN), and pH. While air temperature also affected emissions, stockpile temperatures (not measured) due to microbial activity were probably more important. Care should be taken in extrapolating this study's results to other stockpiles due to differences in stockpile dimensions, chemical properties, and environmental conditions.

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