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a National Swine Research Center, USDA-ARS, Ames, IA 50011
b National Soil Tilth Lab., USDA-ARS, Ames, IA 50011
c Dep. of Microbiology, Iowa State Univ., Ames, IA 50011
Corresponding author (zahn{at}nsric.ars.usda.gov)
Received for publication March 16, 2000.
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ABSTRACT |
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 TOPNOTES ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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. The concentration of VOC in air samples was highest with outdoor swine manure management systems that received a high input of volatile solids (Type 2). These systems were also shown to have the highest odor intensity levels. The emission rate for VOCs and the odor intensity associated with swine manure management systems were inversely correlated with CH4 and ammonia (NH3) emission rates. The emission rates of CH4, NH3, and VOCs were found to be dependent upon manure loading rate and were indirectly influenced by animal numbers.
Abbreviations: VOC, volatile organic compound
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INTRODUCTION |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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The purpose of this research was to develop a method to functionally classify swine manure management systems based on effluent chemical properties and emission rates of CH4, NH3, H2S, and VOC. A reliable method to functionally classify manure management systems would serve the agricultural industry as a management tool in evaluating best management practices for swine manure storage systems and would serve regulators as a rapid method to identify production sites that represent a potential air quality or nuisance concern.
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MATERIALS AND METHODS |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Description of Swine Manure Storage Facilities, Placement of Air Monitoring Equipment, and Statistical Analyses
Loading criteria and individual site descriptions for 29 swine manure management systems located in Iowa (n = 24), Oklahoma (n = 2), and North Carolina (n = 3), sampled during the months of August and September 1997, are described in Table 1. Individual manure management systems were separated into four main categories (Types 1–4) based on the concentration of total P and total S present in effluent samples. Average physical and chemical properties, as well as management attributes for these systems, are summarized in Table 1. Meteorological conditions (wind speed, relative humidity, irradiance, solution temperature at a 10-cm depth, and air temperature) were monitored continuously and the sample mean was recorded in 0.5-min intervals at the point of air sample collection by an integrated weather station (Sauer and Hatfield, 1994) that was positioned at the center of the outdoor manure storage systems. Height of the sensors was established by trajectory simulation models described in the micrometeorological flux methods section (theoretical profile shape) and was identical to the air sampling height used for micrometeorological flux measurements. Micrometeorological data was not collected for studies that employed dynamic flux chamber methods for determination of CH4 flux rates.
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Capture and Analysis of Air Pollutants from Swine Manure Management Systems
Volatile organic compounds (VOCs) were captured on a multibed adsorbent tube containing a combination of Tenax TA and Carboxen-569 (Supelco, Bellefonte, PA), according to the low-volume sampling method developed by Zahn et al. (1997). For air sampling of VOC, flow rate through individual thermal desorption tubes was precisely regulated at 1.0 L min-1 throughout the 30-min sampling period, using thermal mass flow controllers (Series 810, Sierra Instruments, Monterey, CA) that were connected to a common, high-vacuum manifold. Desorption tubes were analyzed by gas chromatography using a flame ionization or mass selective detector as previously described by Zahn et al. (1997).
Ammonia (NH3) was collected from air using two glass impingers (210 mL internal volume) arranged in series, each containing 25 g of 2-mm glass balls. Air samples were drawn by vacuum through a submerged fritted glass diffusion tube into 60 mL of 0.2 M boric acid using a Buck (Orlando, FL) IH sampling pump operated at 1.0 L min-1. The boric acid solution was replaced in 30- to 120-min intervals depending on proximity of the sampler to the emission source. Ammonium concentration was determined by the salicylate–nitroprusside technique according to USEPA Method 351.2 (USEPA, 1979). Solutions of ammonium chloride in 0.2 M boric acid were used as reference standards to determine ammonium ion concentration. Hydrogen sulfide (H2S) and CH4 were collected in 1.0-L Tedlar gas sampling bags (Supelco, Bellefonte, PA) and evaluated in the laboratory by previously described gas chromatographic methods using either a 0.32-mm x 30-m SPB-1 sulfur fused silica column with flame photometric detection (Bulletin 876, Supelco, Bellefone, PA) or a 1/8 in x 8 ft HayeSep-Q packed column (Supelco) with thermal conductivity detection (Chan et al., 1998), respectively. Air samples for H2S and CH4 analysis were drawn by vacuum into 1.0-L Tedlar gas sampling bags using a Model 1062 grab sampler (Supelco) operated at 25 mL min-1. Teflon surfaces were equilibrated with analytes (H2S and CH4) present in the air sample by performing four fill–purge cycles before collection of the final air sample. Lead acetate strips (Model #701, VICI Metronics, Santa Clara, CA) were used at the point of air sample collection (by Tedlar bag methods) to confirm gas chromatographic results for the quantification of H2S. The latter methods indicated that H2S losses due to reaction or condensation were less than 4% if samples were analyzed within 6 h of collection. The concentration of CH4 in air was also determined in real time at two of the 29 swine manure management systems noted in Fig. 1 using a tunable-diode laser system operated in the infrared region at 2968.4034 cm-1, as previously described by Simpson et al. (1995). Concentration measurements of CH4 that were determined using the tunable-diode laser were converted to flux using the theoretical profile shape micrometeorological method. All other CH4 flux measurements performed in this study used CH4 concentration measurements that were determined by the gas chromatographic method. A combination of the air sampling methods described above was used to determine recovery efficiency and to validate the H2S and CH4 sampling techniques.
Evaluation of the Odor Intensity Associated with Swine Manure Management Systems
Odor intensity was measured by the method of direct scaling in reference to an odor standard of defined intensity using three or four trained panelists (Cain et al., 1998; Degel and Koster, 1998; Liden et al., 1998; Livermore and Laing, 1998). Direct scaling was based on estimation of the intensity of olfactory sensations associated with an odor source by assigning numerical values to sensory stimuli. Sensory responses were normalized against the artificial swine odor reference standard Z2 (Zahn and DiSpirito, 2000) that consisted of 0.05 mM dimethyl disulfide, 8 mM acetic acid, 3.5 mM propionic acid, 0.5 mM isobutyric acid, 0.4 mM 2-butanol, 1.4 mM butyric acid, 0.2 mM isovaleric acid, 0.5 mM valeric acid, 0.1 mM isocaproic acid, 0.2 mM caproic acid, 0.2 mM heptanoic acid, 0.1 mM indole, 0.15 mM 3-methyl indole, 0.2 mM 4-methyl phenol, 0.12 mM 4-ethyl phenol, 0.15 mM phenol, 0.1 mM benzyl alcohol, 0.15 mM 2-amino acetophenone, 0.1 mM butylated hydroxytoluene (added as a preservative), and 8 mM ammonium acetate. Chemical composition of the artificial swine odor Z2 was optimized in a laboratory dynamic flux chamber to mimic emission parameters for VOCs emitted from a manure sample collected from a high-odor, Type 1 swine manure management system (Zahn et al., 2001). Pure compounds were dissolved in warm (45°C) water while stirring and the solution pH was frequently adjusted to pH 7.0 with 2 M potassium hydroxide. Approximately 15 mL of the solution was transferred to an amber serum vial (30 mL nominal volume), capped with a silicone–Teflon septum, and then degassed under repeated cycles of vacuum and argon to create an anaerobic headspace. Samples were stored in the dark at ambient temperatures until they were used. Panelists were provided the synthetic swine odor solution Z2 in an uncapped 30 mL-serum vial, a solution of 2 mM n-butanol in a 30-mL serum vial, and a site odor evaluation worksheet, previously described by Zahn (1997). Panelists then evaluated the n-butanol solution that was considered neutral (Grade 3/10), and the Z2 solution that was considered unpleasant (Grade 6.5/10) at a neutral distance (>1000 m) from the manure management system. Panelists were then positioned in the emission plume from the manure management system (1.5 m from the emitting source at a height of 1.5 m) and asked to compare the odor intensity with the reference standards. Numerical evaluations of the swine manure management systems ranged from neutral (3) to unbearable (10), and are reported as the sample mean. Air samples for VOC analysis were collected at the receptor (1.5 m from the emitting source at a height of 1.5 m) throughout the odor evaluation period.
Measurement of Methane Flux, Volatile Organic Compound Concentration, and Odor Intensity from 29 Swine Manure Management Systems
An initial screening study was completed at 29 swine manure management systems to measure the flux rate of CH4, odor intensity, concentration of VOCs in air at the point of the odor intensity measurements, and analytes in the effluent fraction. The flux rate of CH4, for this initial screening study, was measured at 29 manure management systems (lagoons, earthen basins, cement-lined basins, steel-lined tanks, and confinement pits) using a flux chamber described by DiSpirito and Zahn (1999). The dynamic flux chamber method was found to be most suitable for screening large sample numbers due to the minimum operation requirements, portability, and reliability for measurement of nonreactive gases such as CH4 (Chan et al., 1998). The dynamic flux chamber was positioned near the center of the swine manure management system, with the exception of deep and shallow pit systems, which were sampled at the pump-out positions near the wall of the pit. Chamber operational parameters were modified from semistatic to dynamic mode by installation of a sweep gas manifold. Compressed air (containing 1.1 parts per million by volume or 0.77 mg m-3 CH4) sweep gas was provided to the enclosure at a flow rate of 2.0 L min-1 in a demand mode. Air pressure within the chamber was maintained at barometric pressure through the use of a silicone oil (impinger) purge valve, positioned on the gas supply manifold. The static pressure differential was maintained at 0 ± 1.5 kPa throughout the collection period with the use of a mercury manometer. Gases were removed from the chamber through 0.635-cm i.d. Teflon tubing that was attached to a vacuum pump through an inline mass flow controller set at 2.0 L min-1, following a 1-h chamber equilibration period. Six individual air samples (about 750 mL each) were collected over a 3-h sampling period. Samples were analyzed for CH4 concentration by gas chromatography within 6 h of sample collection. The concentration of CH4 in air samples was converted to trace gas flux density (f) through the equation:
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Detailed Studies of Gas Flux Rates from Four Swine Manure Management Systems
The flux rate of CH4, H2S, NH3, and VOCs was measured continuously at four swine manure management systems throughout a 24-h period using the theoretical profile shape micrometeorological flux measurement method. The four sites chosen for this comprehensive study represented each of the four classes of swine manure management systems defined in Table 1. The theoretical profile shape method was chosen instead of chamber methods, since the latter methods adversely affected VOC emission profiles. Higher flux rates of disulfide compounds (dimethyl disulfide and dimethyl trisulfide) and lower flux rates of sulfide compounds (methyl mercaptan) were consistently observed with flux chamber methods when compared with micrometeorological methods. This observation indicated that the chamber surfaces were potentially the site of oxidation reactions for reactive gases (H2S, NH3, and VOCs). These results are consistent with previous studies that show significant reduction in the concentration of VOCs collected from air if samples were drawn through glass or polymeric tubing (Zahn et al., 1997).
The flux of NH3, H2S, CH4, and VOCs from the lagoon was measured using the theoretical profile shape method described by Wilson et al. (1982). The emission rate of gases from a circular source plot was calculated with the following equation:
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is the nondimensional normalized horizontal flux predicted by the trajectory simulation model, and (uc)measured is the product of the measured average wind velocity and air concentration of analyte in m s-1 and µg m-3, respectively (Majewski et al., 1989; Majewski, 1990). Flux measurements were completed at the center of swine waste management systems with a circular shape. System classification based on the concentration ratio of phosphorus to sulfur (Table 1) and the requirement for circular manure management systems served as the major criteria for selecting the four swine waste management systems that were sampled for follow-up studies. The surface roughness was determined before the sampling period began by performing mean wind velocity profile measurements at 0.2, 0.5, 1.0, 2.0, and 3.0 m for a period of 1 h at the center of the swine manure management system with cup anemometers (Model 03101-5, R.M. Young Co., Traverse City, MI). The mean value for roughness length at the surface of outdoor swine manure management systems, during periods of neutral atmospheric stability (mid-morning), was 0.10 ± 0.02 cm (mean ± standard error). The following measurement parameters were used to establish the sampling height: Type 1 = total mechanically ventilated exhaust flow rate = 110000 m3 h-1, sampling position at the fan orifices (four total); Type 2 = 39-m-diam. basin, z = ZINST (0.1 cm roughness length, 1950 cm radius = 70 cm sampling height); Type 3 = 92-m-diam. lagoon, z = ZINST (0.1 cm roughness length, 4600 cm radius = 189 cm sampling height); Type 4 = a primary 100-m-diam. photosynthetic lagoon, z = ZINST (0.1 cm roughness length, 5000 cm radius = 191 cm sampling height). Error in measurement height that was associated with temporal changes in roughness length for the lagoon surface was estimated to cause a maximum error of 8% in the height parameter for emission measurements.
Flux measurements using the theoretical profile shape method were based on the concentration of airborne analytes present at a measurement height (z) and meteorological data, collected at the same point (Majewski, 1990). Measurement height (z) was calculated by trajectory simulation models and was based on system surface area and roughness length (Wilson et al., 1982). In addition to the air samples that were collected over the emitting source, two to five air samples were collected at the beginning of each sampling period, upwind from each manure storage system, to assess background air concentrations of target analytes and to confirm the source of these emissions. Background analyte concentrations were assumed to remain constant throughout the sampling period and were subtracted from analyte concentrations that were observed above each emitting source. Background concentrations for analytes at each of the four sites sampled in follow-up studies were as follows. Type 1: 6.0 parts per billion by volume (ppbv) (8.5 µg m-3) H2S, 15.0 ppbv (11.1 µg m-3) NH3, and 1.3 parts per million by volume (ppmv) (0.91 mg m-3) CH4. Type 2: 15 ppbv (21.3 µg m-3) H2S, 11.0 ppbv (8.1 µg m-3) NH3, and 1.3 ppmv (0.91 mg m-3) CH4. Type 3: 12 ppbv (17.1 µg m-3) H2S, 7.0 ppbv (5.2 µg m-3) NH3, and 1.2 ppmv (0.84 mg m-3) CH4. Type 4: 9.0 ppbv (12.8 µg m-3) H2S, 8.0 ppbv (5.9 µg m-3) NH3, and 1.3 ppmv (0.91 mg m-3) CH4. The concentration of VOCs in background air samples was below the detection limit of 0.2 ppb for all samples that were analyzed.
Flux rate measurements for the mechanically ventilated deep-pit swine manure management system (animal confinements) were performed by continuously monitoring exhaust flow rate during the sample collection period at two pit fan and two ventilation fan orifices using a three-dimensional sonic anemometer (Campbell Scientific, Logan, UT). Air samples were collected near the lower sensor arm on the anemometer in the exhaust stream.
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RESULTS AND DISCUSSION |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Classification of 29 Swine Manure Management Systems Based on Solution-Phase Chemistry and Methane Emission Rate
The concentration range for elements found in the swine manure storage systems sampled in this study were found to be similar to those previously reported by Giusquiani et al. (1998), Japenga and Harmsen (1990), and Zahn et al. (1997) (Table 1). There was a weak positive correlation observed between volatile solids loading rate and concentration of elements for each of the samples evaluated (Table 1). Individual correlations between element concentration and volatile solids loading rate indicated that volatile solids loading rate could account for 48 to 76% of the variability observed with effluent concentration of elements. This inadequacy of volatile solids loading rate to account for differences in effluent elemental composition for various swine manure management systems, in addition to the low-throughput of volatile solids measurements, indicated that the solution concentration of elements may provide a more appropriate means to classify swine manure management systems.
In the search for useful effluent chemical classification criteria, 45 pairwise comparisons were made between the concentrations of elements present in the 29 site samples. The nonparametric measure of association for each pairwise comparison is shown in Table 2. In general, a lower level of correlation was observed for pairwise comparisons made between elements showing opposite partitioning behavior (Table 2). For example, transition metal ions have been shown to partition strongly into the sludge or particulate fraction of the manure, while sodium (Na), potassium (K), and to a lesser extent, phosphorus (P), magnesium (Mg), and sulfur (S), demonstrate neutral or preferential partitioning behavior into the supernatant fraction of the manure (Giusquiani et al., 1998; Zahn et al., 1997). Therefore, the concentration of transition metal ions in samples is highly dependent upon the concentration of suspended solids, while Na and K are nearly independent of the concentration of suspended solids. High correlation coefficients were observed for pairwise comparisons between several transition metals, for several transition metals and a small number of main group elements, and finally, for P and S concentrations in the 29 site samples. However, only one pairwise comparison (P and S) demonstrated clear functional clustering of manure management systems based on system CH4 emission rate, air concentration of VOCs, or odor intensity (Fig. 2 , Table 2).
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Odor intensities and VOC concentrations in Type 2 systems were consistently higher than measurements performed on Type 1 systems. This result was not entirely consistent with effluent P and S concentrations or with system CH4 emission rates, which predicted Type 1 systems to have the highest odor intensities and air concentrations of VOCs. Gas transfer coefficients for CH4 and VOCs are known to differ by several hundred-fold (MacIntyre et al., 1995). In addition to large differences in gas transfer coefficients for CH4 and VOCs, surface exchange rate for some VOCs is known to be influenced by effluent chemical events that include ionization (pH), hydrogen bonding, and surface slicks (MacIntyre et al., 1995). For these reasons, CH4 emission rate is not an appropriate criterion for predicting VOC volatilization potential between swine manure management systems. Wind, temperature, and irradiance are known to be major factors in the emission rate of sparingly soluble gases (VOCs) from liquid or semisolid surfaces (MacIntyre et al., 1995; Zahn et al., 1997). Based on the VOC transfer coefficient calculations from MacIntyre et al. (1995), the difference due to wind and temperature exposures between outdoor and indoor manure management systems can account for between 51 and 93% of the observed differences in VOC emissions. This analysis provides evidence that exposure factors can account for differences observed in VOC flux rates, VOC air concentrations, and odor intensity between Type 1 and 2 systems.
Swine manure management systems are often designed to release gases produced in anaerobic decomposition processes into the atmosphere. Within these systems, a complex consortium of microorganisms (anaerobic food chain) decompose complex biological waste material to end-products including CH4, H2S, CO2, and NH3 (Gottschalk, 1988; Lana et al., 1998; Mackie et al., 1998; Fenchel and Finlay, 1994). The anaerobic food chain is often functionally separated into microorganisms catalyzing acid-producing reactions from complex organic substrates and Archaea, which catalyze CH4–producing reactions from products formed in the breakdown of complex organic substrates (Deppenmeier et al., 1996; Fenchel and Finlay, 1994). The emission rate of CH4 and partially decomposed microbial substrates (volatile fatty acids) has been previously employed as an indicator to assess functional coupling between processes in the anaerobic food chain in anaerobic digesters (Hill and Bolte, 1989). Overloaded anaerobic digestion processes have been correlated with high emission rates of VOCs and low emission rates of CH4, while optimum loading rates promote high bioconversion efficiencies of complex organic matter into CH4 (Hill and Bolte, 1989). Data in Fig. 2 and Table 1 provide evidence that the biological processing events occurring in high-load systems (Type 1 and Type 2) may result from the functional decoupling of the anaerobic food chain. This observation is further supported by the fact that these same systems show an accumulation of organic (particulate C, H, N) material (Table 1) and high air concentrations of VOCs (Fig. 3 ; Table 3). In contrast, the high emission rates for CH4 and low liquid-phase organic content (particulate C, H, N) associated with Type 3 and 4 systems (Table 1) indicate that the environment in these systems provides for relatively more efficient bioconversion of complex organic substrates into CH4.
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Relationships between Emission Chemistry and Odor Intensity
Several recent investigations have attempted to define relationships between chemical concentration of specific gases and odor concentration or intensity (Hobbs et al., 1995; Jacobson et al., 1997a,b; Obrock-Hegel, 1997; Pain et al., 1990). Obrock-Hegel (1997) found that nutritional manipulation of amino acid intake reduced NH3, cresols, and indoles measured in air samples from production environments. However, no reduction in odor concentration was observed between control and treatment samples. Schulte et al. (1985) and Hobbs et al. (1995) linked high levels of ammonia (NH3) to odor. Unfortunately, the latter authors noted that the relationship between NH3 and odor could not be universally applied to all farms, especially when they differed in the type of manure management system used. The use of hydrogen sulfide (H2S) as a surrogate of livestock manure odor has also proven to be a formidable challenge. Jacobson et al. (1997b) evaluated odor and H2S concentration in air from approximately 60 different pig, dairy, beef, and poultry manure storage units on farms in Minnesota. Low correlation was observed between H2S and odor concentration for manure storages based on a species comparison and for production systems grouped according to manure management system type (pit, basin, and lagoon). The study further suggested the possibility that chemical odorants other than H2S (i.e., VOCs) were responsible for swine odor. In support of this conclusion, Powers et al. (1999) recently demonstrated that effluent concentrations of several VOCs present in anaerobic digester effluent were correlated with odor intensity. However, effluent concentration of VOC did not predict odor intensities well enough to suggest that human panels should be eliminated. Data quality in the latter study was probably negatively influenced by the fact that correlations were not performed in a similar matrix (air vs. liquid). Previous studies have established that effluent measurements often provide an inaccurate representation of malodor potential and therefore represent an inappropriate comparison (Zahn et al., 1997).
To test the potential relationship between airborne VOCs and swine manure odor, odor intensity and air concentration of VOCs were determined simultaneously at the 29 swine production facilities. Figure 2C shows the relationship between average odor intensity, assessed through direct scaling techniques using a defined odor intensity, and the total air concentration of VOCs present at the receptor. The relationship between mean odor intensity and air concentration of VOCs was observed to obey Michaelis–Menten kinetics, with a Michaelis constant (Km) of 95 µg m-3 VOCs and receptor saturation occurring at 1250 µg m-3 VOCs (Fig. 2). The saturation properties showed typical second-order kinetics and were characteristic of a receptor–ligand process. A qualitative analysis of VOCs present at sites representing the four classes of swine manure management systems is shown Fig. 3 and Table 3. The gas chromatography–flame ionization detector (GC–FID) chromatograms from deep pits or basins produced high odor intensities and relatively intense signal responses but were chemically simplistic in nature when compared with chromatograms from lagoons (Fig. 3; Table 3). These results provide evidence that chemical concentration rather than diversity is the largest determinate in the odor intensity response associated with swine manure odor. This observation is important since the ability to define odorant synergisms and antagonisms has been suggested to be the most significant obstacle in applying chemical methods in odor measurement (Mackie et al., 1998). Data presented in Fig. 2C provide evidence that the total air concentration of nonmethane VOCs can be used to predict the odor intensity associated with swine manure management systems evaluated in this study.
Odor measurement methods using human olfactory senses are based on the use of psychophysical theory. As the name implies, psychophysical methods are based on relationships between psychological and physical attributes of sensory stimuli. The intensity of olfactory stimuli reported by an individual is related to stimulus magnitude. For many odorants used in the food and fragrance industry, there is a linear relationship between log olfactory intensity reported by the individual and the air concentration of the odorant(s) present in air (Turk and Hyman, 1991). This relationship between perceived olfactory stimuli and intensity of sensation is referred to as the fundamental psychophysical law (Stevens, 1957, 1962). Data reported in Figure 2C show that the total air concentration of VOCs correlate well with the log stimulus intensity and therefore conform with the fundamental psychophysical law. In agreement with other olfactory studies, we observed that data quality was influenced by variables associated with the subjective nature of intensity scales, fatigue, sex, age, race, and visual cues (Cain et al., 1998; Degel and Koster, 1998; Liden et al., 1998; Livermore and Laing, 1998; Turk and Hyman, 1991). However, the use of the defined odor standard Z2 was found to reduce most of the sampling variability associated with intensity scales. Evidence for this conclusion was provided by the low average standard deviation reported by panelists for site evaluations (avg. std. dev. = 0.14 odor units). A prerequisite that underlies all olfactory methods is the ability to define and properly sample chemical odorants that constitute a particular odor. Accomplishing this objective has been a formidable challenge, since it requires the use of both olfactory and analytical methods to validate sampling methods. The results of this study demonstrate utility of chemical methods in odor analysis and in the validation of air sample collection methods (i.e., Teflon bag sampling).
Emission Rate of Air Pollutants from Swine Manure Management Systems
Analysis of CH4 emission rates, airborne VOC concentration, and odor intensity for the 29 swine manure management systems evaluated in this study indicated that manure management systems could be functionally classified according to the ratio of P to S concentrations. This analysis, however, provided limited insight into the differences in microbial processes associated with these systems. In an effort to further elucidate chemical and biological differences associated with the system classification, a detailed evaluation of effluent characteristics and gases (H2S, NH3, CH4, VOCs) was conducted at four swine manure management systems that represented each of the four system classes. Each of the swine manure management systems chosen for the follow-up study were shown to exhibit the same relative profiles in CH4 emission rate regardless of the flux measurement strategy employed (Table 1, chamber-based vs. Table 4, micrometeorological-based). These results provided additional support that manure management loading parameters influenced bioconversion efficiency. In systems with relatively low emission rates of CH4 and NH3 (Type 1 and 2 systems, Tables 3, 4, and 5), high concentrations of organic carbon and nitrogen (particulate C, H, N) were found to accumulate in the solution phase (Table 1). These systems were also observed to have the highest odor intensities. In contrast, Type 3 and 4 systems showed a lower tendency to accumulate effluent organic material (Fig. 3; Tables 1 and 3) and a much higher emission rate of CH4 (Fig. 2; Table 1).
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Manure management systems with high loading rates and relatively low CH4–producing activity showed up to a 26-fold increase in total VOC emissions when compared with low-odor photosynthetic lagoons (Fig. 2 and Table 5). The data indicate that VOCs are more likely to be of concern with systems employing high loading rates, while CH4 and NH3 are likely to be more problematic with systems employing lower loading rates. In addition to nuisance concerns, elevated VOC concentrations may present a concern to human health. A small number of regulated industrial pollutants are present in airborne emission streams from swine production facilities (Table 3). The air concentrations for these compounds at the source were found to be at least one order of magnitude below exposure levels established for safe work environments by occupational health organizations (Plog, 1988, p. 770–783). However, the use of industrial exposure indices may not be appropriate for assessing exposure to animal waste emissions due to the following considerations. First, several agricultural waste pollutants are unique to agricultural systems and thus have no established exposure indices. Second, bioactive airborne pollutants, such as microbial secondary metabolites, remain largely uncharacterized from swine production systems. Bioactive compounds have been identified as a serious human health risk, since many of these compounds have been shown to influence mammalian cell physiology in the part per billion and sub–part per billion range (Andersson et al., 1998). Third, there is a lack of information on the acute and chronic toxicological effects of VOCs derived from swine manure on children and individuals of compromised health. This concern is reflected in recent epidemiological studies that have shown a higher incidence of psychological dysfunction and health-related problems in individuals residing near large-scale swine production facilities (Thu et al., 1997; Schiffman et al., 1995).
Ammonia emissions from the four intensively studied swine production systems were found to violate release reporting requirements for NH3 under the USEPA Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) (USEPA, 2000). Emergency Planning and Community Right-to-Know Act (EPCRA) Section 329(4) defines facility to include stationary structures on a single site, or on contiguous or adjacent sites owned or operated by the same person. Under this definition, the aggregated emission rate of registered hazardous substances (i.e., NH3, H2S, VOC, particulate matter) from all swine production facility point sources is subject to release reporting requirements. The current reporting requirements for NH3 (and H2S) are set at 100 lb (about 45 kg) of NH3 d-1 (USEPA, 2000). The range for NH3 emissions from the four intensively studied swine production sites ranged from 101.7 kg NH3 d-1 (224 lb NH3 d-1) to 369.2 kg NH3 d-1 (813.9 lb NH3 d-1). The observed aggregate emission rates for swine production facilities evaluated in this study exceed the CERCLA reporting requirements for NH3 by 55 to 88%. Under Section 304 of EPCRA, the "owner or operator" of a facility is required to report immediately to the appropriate state emergency response commissions and local emergency planning committees when there is a release of a CERCLA hazardous substance. The results indicate that NH3 emissions from swine production facilities have the potential to exceed release reporting requirements enforced by the USEPA.
Lagoons with established anoxic bacterial photosynthetic populations (Type 4 systems; bacteriochlorophyll a concentrations above 40 nmol mL-1) showed lower odor intensities, lower air concentrations of VOCs, and lower emission rates of VOCs when compared with other swine manure management systems (Fig. 3; Tables 3 and 4). Photosynthetic bacteria carry out the process of photosynthesis under anaerobic conditions. These requirements for photosynthesis differ greatly from algae and plant species that use water as an electron source for photosystem II and evolve oxygen in this reaction (Kobayashi and Kobayashi, 1995). Instead of using water as a reductant, anoxic photosynthesis is dependent on substrates such as H2S, hydrogen (H2), and VOCs to provide reducing equivalents, while light from the sun provides the energy source (Gottschalk, 1988). Bacteria capable of anoxic photosynthesis are categorized into one of four major groups (purple sulfur, purple nonsulfur, green sulfur, and green-gliding) based on the presence of specific types of bacteriochlorophyl, phylogenetic characteristics, and metabolic capabilities (Gottschalk, 1988; Siefert et al., 1978). All four groups of photosynthetic bacteria are able to utilize organic substrates (VOCs) as a source of carbon and the green-gliding and purple bacteria are able to use organic substrates as proton donors. However, a novel species of Rhodobacter (Rhodobacter sp. PS9) dominates the photosynthetic population (about 20% of the total microbial community structure) in all photosynthetic swine lagoon systems examined in this study (Do et al., 1998, 1999). The physiological characteristics of this purple nonsulfur photosynthetic bacterium provide evidence for the observed degradation of VOCs and decreased odor emissions from photosynthetic swine waste lagoons.
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CONCLUSIONS |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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ACKNOWLEDGMENTS |
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NOTES |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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K. L. Conn, E. Topp, and G. Lazarovits Factors Influencing the Concentration of Volatile Fatty Acids, Ammonia, and Other Nutrients in Stored Liquid Pig Manure J. Environ. Qual., January 25, 2007; 36(2): 440 - 447. [Abstract] [Full Text] [PDF]
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D. N. Miller and B. L. Woodbury A Solid-Phase Microextraction Chamber Method for Analysis of Manure Volatiles J. Environ. Qual., October 27, 2006; 35(6): 2383 - 2394. [Abstract] [Full Text] [PDF]
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S. L. Trabue, J. C. Anhalt, and J. A. Zahn Bias of Tedlar Bags in the Measurement of Agricultural Odorants J. Environ. Qual., August 9, 2006; 35(5): 1668 - 1677. [Abstract] [Full Text] [PDF]
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B. J. Kerr, C. J. Ziemer, S. L. Trabue, J. D. Crouse, and T. B. Parkin Manure composition of swine as affected by dietary protein and cellulose concentrations J Anim Sci, June 1, 2006; 84(6): 1584 - 1592. [Abstract] [Full Text] [PDF]
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T. M. DeSutter and J. M. Ham Lagoon-Biogas Emissions and Carbon Balance Estimates of a Swine Production Facility J. Environ. Qual., January 1, 2005; 34(1): 198 - 206. [Abstract] [Full Text] [PDF]
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 Y. S. Do, T. M. Schmidt, J. A. Zahn, E. S. Boyd, A. de la Mora, and A. A. DiSpirito Role of Rhodobacter sp. Strain PS9, a Purple Non-Sulfur Photosynthetic Bacterium Isolated from an Anaerobic Swine Waste Lagoon, in Odor Remediation Appl. Envir. Microbiol., March 1, 2003; 69(3): 1710 - 1720. [Abstract] [Full Text] [PDF]
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L. Merrill and L. J. Halverson Seasonal Variation in Microbial Communities and Organic Malodor Indicator Compound Concentrations in Various Types of Swine Manure Storage Systems J. Environ. Qual., November 1, 2002; 31(6): 2074 - 2085. [Abstract] [Full Text] [PDF]
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J.A. Zahn, A.A. DiSpirito, Y.S. Do, B.E. Brooks, E.E. Cooper, and J.L. Hatfield Correlation of Human Olfactory Responses to Airborne Concentrations of Malodorous Volatile Organic Compounds Emitted from Swine Effluent J. Environ. Qual., March 1, 2001; 30(2): 624 - 634. [Abstract] [Full Text] [PDF]
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