Great care must be taken whenever swine manure is handled, transported and applied, not only for the safety of the pigs and people, but also to minimize odor and gas emissions.
Researchers at the University of Nebraska recently investigated swine manure composition and emissions. In the main study, the full-scale treatment effects of anaerobic digestion on the air emissions potential of swine manure, particularly methane, were investigated to gain a better understanding of the practical air quality implications of digesting manure.
Manure slurry and digester effluent samples were collected from a production facility in eastern Nebraska equipped with a complete-mix anaerobic digester to treat the manure and produce biogas to generate electricity. Samples were collected from three points in the manure stream — barn pit, digester outlet and holding pond — over a 15-month period. Changes in manure composition per treatment and over time were recorded.
The concentration of manure constituents generally decreased as the manure was digested and stored. This pattern held true on eight of the 12 sampling dates, but for three consecutive sampling events the methane digester was not fully functional and little methane was produced.
When the digester was operating
as designed, chemical oxygen demand was reduced by an average of
45%, odorous volatile fatty acids were reduced by 66% and ammonia increased by 58%, reports Rick Stowell,
University of Nebraska animal environment engineer.
Clearly, a functional digester provides a basis for controlling odor during storage of digested manure, with subsequent benefits expected for land application, Stowell adds.
“The results of this study also reinforced a greater need for conserving nitrogen (N) in digested manure. While digesters improve the plant availability of manure nitrogen by converting organic N into ammonia, much of this fertilizer benefit may be lost through ammonia volatilization during storage and application of the digester effluent,” he adds.
Researchers also conducted a detailed analysis of manure from deep-pit finishing barns across the Midwest to identify the causes of excessive foaming in deep manure pits. This foam, consisting of methane and other pit gases, has been implicated in a number of flash fires and explosions.
Twenty-six manure and foam samples were collected from deep-pit facilities in Iowa, Illinois, Minnesota and Nebraska. Standard manure analysis for pH, solids and macro- and micro-nutrient levels was conducted. Diets were analyzed for protein, fiber and energy composition, and 45 different volatile fatty acids.
Statistical analysis at the University of Minnesota found correlations between fat content and foam, but no other correlations could be established. While researchers were unable to identify a specific, manageable cause, researchers were able to narrow the scope of the foaming problem for future studies.
Agitate and Pump with Care
Slow decomposition of liquid manure creates several gases, including methane and hydrogen sulfide — both potentially dangerous gases. During manure agitation and pumping, the rate at which these gases are released can be drastically increased. This is particularly true of hydrogen sulfide, which can have a lethal, paralyzing effect.
When excessive foam accompanies the agitation and pumping process, there is grave concern about rapid gas release, explains Iowa State University Extension program specialist Angela Rieck-Hunt and Extension agricultural engineer Shawn Shouse. The presence of substantial foam in deep pits may trap methane, which can be quickly released during agitation or power washing.
“The rapid release of methane mixing with fresh air can create an explosive mixture,” ISU researchers note. If the mixture comes in contact with an ignition source, it can cause a flash fire or explosion.
Following is a list of precautions for anyone working with or handling manure:
• Develop an emergency action plan (go to www.extension.iastate.edu/Publications/PM1859.pdf for assistance).
• Before agitating or pumping a manure pit, make sure all workers are out of the building; tag all doors with a warning that the building is unsafe. Never enter a building or storage structure when liquid manure is being agitated or pumped.
• Operate ventilation fans at maximum capacity during agitation/pumping.
• If substantial foam is present, consider pumping the pit without agitation.
• Do not agitate manure until manure is pumped down to a level at least 2 ft. below the slats.
• During agitation, keep the jet of pressurized manure below the surface; do not let the jet of manure strike pit walls or columns.
• Stop agitation when the manure level does not allow agitation below the liquid surface.
• Continue maximum ventilation for 30 to 60 minutes after pumping has ended and before allowing anyone to enter the building.
A video, “Foaming and Deep-Pit Manure Pumping Safety,” can be found at http://vimeo.com/15463270.