#08-259

Complete

Date Full Report Received

04/10/2012

Date Abstract Report Received

04/10/2012

Investigation

Institution:
Primary Investigator:

This project investigated manure composition and emissions potential of swine manure in opposing contexts of desired and undesired methane generation. In the main study, the full-scale treatment effects of anaerobic digestion on the air emissions potential of swine manure were investigated to improve our understanding of the practical air quality implications of digesting manure. The project also facilitated detailed analysis of swine manure from deep-pit finishing barns across the Midwest in support of a multi-state effort to find a cause behind increased incidence of foam in such facilities. This foam, which consists of methane and other pit gases, has undesirable consequences for facility management and has been implicated in a number of flash fires.

In the first study, manure slurry and digester effluent samples were collected from a pork production facility in eastern Nebraska that utilizes a complete-mix anaerobic digester to treat the manure and produce biogas for generating electricity. Samples were collected from three sites in the manure stream (below-barn pit, digester outlet, and holding pond) over a 15-month period to observe changes in manure composition as a result of manure treatment and over time. When compared for each sampling date, the concentration of manure constituents usually decreased as the manure was digested and stored. This pattern held true on eight of the twelve sampling dates, but for three consecutive sampling events the methane digester was not functioning well and produced little methane. When the digester was operating as designed, chemical oxygen demand was reduced by an average of 45%, odorous volatile fatty acids were reduced by an average of 66%, and ammonia increased by an average of 58%. These results affirm that organic matter is being broken down as desired in the digester. One implication for pork producers is that a functional digester clearly provides a basis for controlling odor during storage of [digested] manure, with subsequent benefits expected for land application as well. The results of this study also reinforced a greater need for conserving nitrogen 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.

This project also facilitated extensive analyses of twenty-six manure and foam samples collected from deep-pit pork production facilities in Iowa, Illinois, Minnesota and Nebraska. The analyses included a standard manure analysis (for pH, solids contents, and macro/micronutrient levels); a feed analysis (for protein, fiber and energy composition); and a fat analysis (for levels of 45 different volatile fatty acids). In subsequent statistical analysis by the University of Minnesota, correlations were found between fat content and foam, but no other correlations could be established. While the manure and foam analyses did not identify a specific manageable cause for this facility management problem, they did help narrow down the scope for future study.
Contact: Rick Stowell, University of Nebraska, (402) 472-3912, rstowell2@unl.edu