Measurement, Analysis and Modeling of Hydrogen Sulfide Emissions from a Swine Facility in North Carolina

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Title: Measurement, Analysis and Modeling of Hydrogen Sulfide Emissions from a Swine Facility in North Carolina
Author: Blunden, Jessica
Advisors: Yang Zhang, Committee Member
S. Pal Arya, Committee Member
Viney P. Aneja, Committee Chair
David A. Dickey, Committee Member
Philip W. Westerman, Committee Member
Abstract: Annual global source contributions of sulfur compounds to the natural atmospheric environment are estimated to be 142 x 106 tons. Although not quantified, volatilization from animal wastes may be an important source of gaseous reduced sulfur compounds. Hydrogen sulfide (H2S) is a colorless gas emitted during decomposition of hog manure that produces an offensive "rotten egg" odor. Once released into the atmosphere, H2S is oxidized and the eventual byproduct, sulfuric acid, may combine with other atmospheric constituents to form aerosol products such as ammonium bisulfate and ammonium sulfate. In recent years, confined animal feeding operations (CAFOs) have increased in size, resulting in more geographically concentrated areas of animals and, subsequently, animal waste. In North Carolina and across the southeastern United States anaerobic waste treatment lagoons are traditionally used to store and treat hog excreta at commercial hog farms. Currently, no state regulations exist for H2S gaseous emissions from animal production facilities in North Carolina and the amount of H2S being emitted into the atmosphere from these potential sources is widely unknown. In response to the need for data, this research initiative has been undertaken in an effort to quantify emissions of H2S from swine CAFOs. An experimental study was conducted at a commercial swine farm in eastern North Carolina to measure hydrogen sulfide emissions from a hog housing unit utilizing a mechanical fan ventilation system and from an on-site waste storage treatment lagoon. A dynamic flow-through chamber system was employed to make lagoon flux measurements. Semi-continuous measurements were made over a one-year period (2004-2005) for a few days during each of the four predominant seasons in order to assess diurnal and temporal variability in emissions. Fan rpm from the barn was continuously measured and flow rates were calculated in order to accurately assess gaseous emissions from the system. Temperature at the fan outlet and static pressure inside the barn were measured. Lagoon samples were collected daily and analyzed for sulfide content. Lagoon parameters, temperature and pH; and atmospheric environmental parameters, ambient temperature, relative humidity, wind speed and ambient hydrogen sulfide concentration were concurrently monitored on-site. The highest barn emissions were measured during the winter and appeared to be related to the age and weight of the animals housed inside the barn. Highest lagoon emissions were measured in summer with higher sulfide content and warmer temperatures, which increase biological activity in the lagoon. The mechanistic process of H2S emissions from anaerobic liquid systems are investigated using three different modeling approaches based on the two-film theory of mass transfer: coupled Mass Transfer with Chemical Reactions Model (MTCR) with the assumption (1) pH remains constant in the liquid film (MTCR Model I), (2) pH changes from the bulk liquid phase to the air-liquid interface due to diffusion processes that occur within the film (MTCR Model II), and (3) absence of chemical reactions (MTNCR Model). Results of model predictions indicate that flux is primarily dependent on the physico-chemical lagoon properties including sulfide concentration, pH, and lagoon temperature. Low wind velocities (i.e., U10 < 3.25 m/s) and air temperature have little impact on flux. The flux was also influenced by variations in the liquid film thickness, signifying that the H2S flux is driven by resistance in the liquid-phase. Model results were compared with H2S flux measurements in order to evaluate the models' accuracy in calculating lagoon H2S emissions. All three models showed good qualitative agreement in diurnal comparison (i.e., predicting flux patterns as meteorological and lagoon conditions varied throughout the day) with flux measurements made using a dynamic flow-through chamber system during the summer. However, each model significantly over predicted the measured flux rates.
Date: 2006-08-29
Degree: PhD
Discipline: Marine, Earth and Atmospheric Sciences
URI: http://www.lib.ncsu.edu/resolver/1840.16/4022


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