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Mechanisms of Gas Releases from Swine Wastes

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

Citation:  Transactions of the ASABE. 52(6): 2013-2025. (doi: 10.13031/2013.29203) @2009
Authors:   J.-Q. Ni, A. J. Heber, A. L. Sutton, D. T. Kelly
Keywords:   Air quality, Ammonia, Bubble-release model, Carbon dioxide, Convection mass transfer, Hydrogen sulfide, Sulfur dioxide

Knowledge about release mechanisms of pollutant gases from animal manure is important for modeling and predicting gas release and emission, improving measurement accuracy, developing abatement technologies, and ensuring farm safety. This article presents research results on release behaviors of ammonia (NH3), hydrogen sulfide (H2S), carbon dioxide (CO2), and sulfur dioxide (SO2) from swine manure. The study was conducted in a laboratory using 138 L laboratory reactors at 20°C for 260 d. Gas release behaviors were investigated under transient conditions when manure was suddenly disturbed and under steady-state conditions at different reactor ventilation rates. Distinguishing release behaviors were observed and related to the different releases mechanisms of these gases. Convective mass transfer release governed NH3 release and influenced H2S and CO2 releases. Solubility of gases played an important role in the convective releases. Higher solubility was related to higher convective release. "Bubble-release" was dominant in the releases of H2S, SO2, and CO2. A new Bubble-release model was developed to explain release behavior characteristics related to these gases. Bubble-release was responsible for the reported phenomenon of "H2S Burst-release" that had been defined as sudden increases in H2S release by more than 100% as compared with previous releases in less than 1 h in deep-pit swine barns. Interactive release occurred among different gases via their different effects on the pH of surface manure. This study demonstrated that gas production in liquid manure and gas release from liquid medium into the immediate free air stream are two different processes that should be distinguished when addressing air pollution. Liquid manure containing dissolved gases and micro air bubbles serves as a reservoir before the gases are released to the free air stream. A "Reservoir-effect" was found to be considerable in this study because it held gaseous H2S for about 10 d before H2S bubbles started to release. Understanding gas release mechanisms can help to improve air quality sampling methodology. For example, to obtain accurate H2S emission factors at swine buildings, long-term monitoring with high-frequency (or continuous) and multipoint measurement is necessary to cope with temporal and spatial variations of the gas due to its Bubble-release behavior.

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