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The Potential Causes of Manure Pit Foaming in Pig Finishing Barns

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

Citation:  Paper number  131620730,  2013 Kansas City, Missouri, July 21 - July 24, 2013. (doi: @2013
Authors:   Larry D Jacobson, Bo Hu, MI Yan, Neslihan Akdeniz
Keywords:   Manure Foaming Deep Pit Pig Housing Flash Fires.

Abstract. Since 2009 numerous upper Midwest pork producers have experienced foaming manure in deep pits beneath their swine wean-to-finish and grow-finish barns. The prevalence of this phenomenon seems to be increasing and has primarily occurred in Midwestern states. A major safety concern occurs when the foam is disturbed, as is the case during pit pumping or agitation. This action results in a sudden release of dissolved gases, especially methane which has been captured by the foam during normal anaerobic processes in the stored manure. This can result in methane concentrations in the barn between 5 and 15%, which are the lower and upper explosive levels for methane respectively. If an ignition source is present (heater pilot light or spark from light switch or fan, welder or cigarette), an explosion or flash-fire will occur. Foaming of manure is due to a variety of complex interactions. Collection of manure samples were done from farm manure pits with and without foaming manure. Manure compositional changes were found between foaming and non-foaming, especially total solids and organic nitrogen. Also surfactants, either generated by filamentous bacteria or present in the diet, were found in the foaming manure layer. A microbial community analysis was also completed and revealed differences between foaming and non-foaming manure samples. Fundamentally, foaming occurs because methane gas is generated as a result of anaerobic digestion, the presence of surfactants (oil or fatty acids) that significantly decrease the surface tension along with very small fibers that act as foam stabilizers that are generated by bacteria or present in the pig feed. The increase use of dried distiller grains solubles (DDGS) and other by-products in pig diets may be the source of excess surfactants (oil) and/or fiber which are needed to generate or produce foam. Also, DDGS and other by-products diets results in greater solids in the manure which also can enhance methane production.

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