Characterizing ammonia emissions from swine farms in eastern North Carolina: Reduction of emissions from water-holding structures at two candidate superior technologies for waste treatment
Introduction
Atmospheric ammonia (NH3) is a very important alkaline constituent, and has a significant influence on a variety of environmental processes (Aneja et al., 2006a, Aneja et al., 2006b). Ammonia reacts with a variety of acidic atmospheric species, such as sulfuric acid (H2SO4), nitric acid (HNO3), and hydrochloric acid (HCl), to form ammonium aerosols, namely, ammonium bisulfate (NH4HSO4), ammonium sulfate ((NH4)2SO4), ammonium nitrate (NH4NO3), and ammonium chloride (NH4Cl).
Ammonia and ammonium are removed from the atmosphere through both wet and dry deposition processes. Wet deposition occurs by either below cloud scavenging (washout) or by rainout (in-cloud processes). Atmospheric NH3 and its deposition lead to a variety of environmental consequences such as fine particulate matter formation, soil acidification and aquatic eutrophication.
Ammonia is emitted by a large variety of sources such as soils and agricultural crops, synthetic fertilizers, animal waste, biomass burning, fossil-fuel combustion, and human excreta (Oliver et al., 1996; Bouwman et al., 1997). Domestic animal waste is the leading source of global atmospheric ammonia. Studies suggest that it contributes between 20 and 35 Tg of nitrogen per year (Bouwman et al., 1997; Warneck, 2000). In North Carolina, swine waste is the dominant source accounting for 47% of all ammonia emissions, and it is estimated that about 75 000 tons of nitrogen per year are released by hog waste (Aneja et al., 1998). These emissions are related to a rapid increase in hog population, from approximately 3 million in 1992 to 10 million in 1997, when a moratorium was placed. The increase in hog population has been concentrated in the coastal plain region of North Carolina, which contains about 85% of the current pig population (Aneja et al., 2000). The lagoon and spray technology (LST) is the system currently employed to manage hog waste in North Carolina. It consists of an anaerobic lagoon to store and biologically treat the hog waste, which is then sprayed on nearby crops as a source of nutrients.
Due, in part, to the environmental problems associated with ammonia/ammonium emissions from LST farms, a moratorium in 1997 was placed on the construction of swine facilities and the expansion of existing swine facilities until September 2007.
In order to develop sustainable solutions to this problem, an agreement between the North Carolina Attorney General and several commercial hog farming companies was reached to develop potential environmentally superior technologies (ESTs) for hog facilities (Williams, 2001). Program OPEN (Odor, Pathogens, and Emissions of Nitrogen) was an integrated study of the emissions of ammonia, odor and odorants, and pathogens from potential ESTs for hog facilities. Its objectives were to evaluate 16 potential ESTs at swine facilities to determine if they would be able to substantially reduce atmospheric emissions of NH3, pathogens, and odor from their observed or estimated emissions from the conventional LST used at selected conventional farms in different (warm and cool) seasons or observation periods. Previous papers present the results for the conventional LST farms (Aneja et al., 2007a), and the evaluation of six potential ESTs, that would need improvements/modifications to qualify as ESTs (Aneja et al., 2007b). This paper focuses on characterizing and quantifying emissions of NH3 from water-holding structures at two ESTs that met the specified performance standards (Williams, 2004) for ammonia emissions reduction, and therefore qualified as ESTs. This evaluation was achieved by comparing them with projected emissions from two conventional (also called, baseline) LST farms. The evaluated ESTs are: (1) Super Soils at Goshen Ridge; and, (2) Environmental Technologies at Red Hill. The water-holding structures for both of these ESTs contain no conventional anaerobic lagoon. Therefore, these might be considered to be most effective for reducing ammonia.
Section snippets
Approach to evaluate ammonia emissions at EST farms
Ammonia flux measurements were conducted during 2-week periods representing different seasons (characterized here as warm and cool) at two EST sites in eastern North Carolina and also at two conventional farms (Stokes Farm and Moore Farm), which are also referred to as “baseline” sites for comparison with EST sites (for locations see Fig. 1). Measurements at the different sites were made at different times of the year. Therefore, to compare the EST and LST sites, the different environmental
NH3 fluxes and emissions from water-holding structures
Water-holding structure emissions from two EST farms (Goshen Ridge and Red Hill) were calculated from measurements of NH3 flux from EST farms, water-holding structure surface areas, and farm production data (number of pigs, feed consumed, and average pig weight) during experimental periods representing both cool and warm seasons. Emissions at the EST farms were normalized to steady-state live animal weight (lw) in the units of kg N week−1(1000 kg lw)−1. Average fluxes and total estimated emissions
Conclusions
Two potential ESTs with no conventional anaerobic lagoon component were evaluated to determine if they would substantially reduce atmospheric emissions of ammonia at the hog facilities and meet the performance standards as compared with estimated or projected emissions from the conventional LST used at two selected hog farms in two different (warm and cool) measurement periods. Both farms showed substantial reductions in NH3 emissions from their water-holding structures. The Environmental
Acknowledgments
Financial support provided by the North Carolina State University Animal and Poultry Waste Management Center (APWMC) is greatly appreciated. We sincerely acknowledge the help and support provided by Ms. Lynn Worley-Davis. We thank the technology PIs, farm owners, Cavanaugh & Associates, and Mr. Bundy Lane, C. Stokes, and P. Moore for their cooperation.
We also thank the various people who assisted in fieldwork including, Hilawe Semunegus, Wesley Stephens, and Srinath Krishan.
We acknowledge the
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