Swine production represents approximately 40% of the world's meat production, and its wastes contain high concentrations of organic carbon, nitrogen (N), and phosphorus (P). Anaerobic digestion is an increasingly popular technology for treating animal wastes while simultaneously generating energy. Its propagation and ability to solubilize organic N and P make adding a struvite recovery process attractive. Recovering struvite (MgNH4PO4) from anaerobically digested swine waste can address global P shortages, meet P discharge guidelines, and produce slow-release fertilizer, which can be sold for revenue. Anaerobic digesters were operated with at organic loading rates of 3.4-3.9 g volatile solids per liter per day to provide consistent effluent for struvite precipitation studies. Three research questions about struvite precipitation were addressed in this study, specifically what is the (1) required Mg:PO4 ratio, (2) effect of organic matter, and (3) effect of storage time and conditions on struvite precipitation from effluent of anaerobically digested swine manure? Mg:PO4 ratios between 1.3-1.8 were determined to be the economic optimum and precipitated 81-90% of P from synthetic wastewater with calcium phosphate minerals dominating. Under P-limited conditions, a chemical equilibrium model (Visual MINTEQ v.3.0) predicted over 99% P removal with a precipitate mixture of struvite, calcium phosphates, and magnesite. Synthetic wastewater experiments without organic matter removed approximately 85% P with a precipitate mixture of struvite, dolomite, calcite, brucite, and calcium phosphates. Real swine effluent removed more than 95% of P and had a similar mixture of precipitates as synthetic wastewater, but in different concentrations. Organic acids were suspected to prevent struvite formation. Stored anaerobically digested swine wastewater under varying conditions all suggest calcium phosphates form naturally over time. Precipitation of struvite is best carried out as soon as possible to increase the purity of struvite. Although struvite recovery was possible, the conditions for struvite precipitation must be controlled carefully to obtain highly pure struvite.

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Master of Science / Department of Agronomy / Jay M. Ham / The potential environmental impact of animal feeding operations on air quality has created the need for accurate air emissions measurements. Of particular concern are ammonia emissions from cattle feedlots, operations that contribute a large portion of the agricultural ammonia emissions inventory. Micrometeorological methods are ideal for emissions measurements from large, open-source areas like feedlot pens; however, theoretical assumptions about the boundary layer must be made, which may not hold true above the heterogeneous, fetch-limited surface of the feedlot. Thus, the first objective of this work was to characterize the surface boundary layer of an open-air cattle feedlot and provide insight into how micrometeorological techniques might be applied to these non-ideal sites. Eddy covariance was used to measure fluxes of momentum, heat, water, and carbon dioxide from a commercial cattle feedlot in central Kansas. Data supported the use of eddy covariance and similar methods (i.e., relaxed eddy accumulation) for flux measurements from both cattle and pen surfaces. The modeled cumulative source area contributing to eddy covariance measurements at a 6 m sample height was dominated by just a few pens near the tower, making the characteristics of those pens especially important when interpreting results. The second objective was to develop a system for measuring ammonia fluxes from feedlots. A new type of relaxed eddy accumulation system was designed, fabricated, and tested that used honeycomb denuders to independently sample ammonia in up-moving and down-moving eddies. Field testing of the relaxed eddy accumulation system at a feedlot near Manhattan, KS showed fluxes of ammonia ranged between 60 and 130 μg m-2 s-1 during the summer of 2007. Even in the high ammonia environment (e.g., 300-600 μg m-3), the honeycomb denuders had enough capacity for the 4-hour sampling duration and could be used to measure other chemical species that the denuders could be configured to capture. Results provide a foundation for emissions measurements of ammonia and other gases at cattle feedlots and help address some of the challenges that micrometeorologists face with any non-ideal source area.