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Published online 9 January 2007
Published in J Environ Qual 36:184-193 (2007)
DOI: 10.2134/jeq2006.0052
© 2007 American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America
677 S. Segoe Rd., Madison, WI 53711 USA
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TECHNICAL REPORTS

Waste Management

Evaluation of Zeolite for Control of Odorants Emissions from Simulated Poultry Manure Storage

Lingshuang Caia,b, Jacek A. Koziela,*, Yi Lianga, Anh Thu Nguyena and Hongwei Xina

a Dep. of Agricultural and Biosystems Engineering, Iowa State Univ., Ames, Iowa, 50011, USA
b Dep. of Chemistry, Wuhan Univ., Wuhan 430072, PR China. Y. Liang, current address: USDA-ARS, Pendleton, Oregon, USA

* Corresponding author (koziel{at}iastate.edu)

Received for publication February 4, 2006.

   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Poultry operations are associated with emissions of aerial ammonia (NH3), volatile organic compounds (VOCs), and odor, and the magnitude of emissions is influenced by manure management practices. As a manure treatment additive, zeolites have been shown to have the potential to control NH3. Because of their properties it is also expected that zeolites could effectively adsorb VOCs and odor. The effectiveness of zeolite in controlling odor and VOCs was qualitatively evaluated in this controlled laboratory study involving simulated poultry manure storage. In the first two trials, zeolite was topically applied on nearly fresh laying hen manure at the rates of 0, 2.5, 5, and 10% (by weight). In the third trial, zeolite was topically applied at 5% with each addition of fresh manure into the storage vessel. Headspace samples from the emission vessels were collected with solid phase microextraction (SPME) and analyzed on a multidimensional-gas chromatograph-mass spectrometry-olfactometry (MDGC-MS-O) system for identification and prioritization of poultry manure odorants. Acetic acid, butanoic acid, isovaleric acid, indole, and skatole were consistently controlled in the headspace, with the reduction rate being proportional to the zeolite application rate. Dimethyl trisulfide and phenol were consistently generated, and with a few exceptions, the rate of generation was proportional to the application rate. Average reduction of the odor caused by all odorants evaluated with SPME-GC-O was 67% (± 12%) and 51% (± 26%) for the two topical applications, respectively, while no significant reduction of VOCs and odor was detected for the layered application.

Abbreviations: GC-MS, gas chromatograph-mass spectrometer • MDGC-MS-O, multidimensional gas chromatograph-mass spectrometer-olfactometry • SPME, solid phase microextraction • VFAs, volatile fatty acids • VOCs, volatile organic compounds • FID, flame ionization detector • RT, retention time


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
EMISSIONS of aerial pollutants from high-density poultry and livestock facilities are of increasing public concern (National Research Council, 2003). The anaerobic nature of manure stabilization can cause offensive odors and release of ammonia (NH3), hydrogen sulfide (H2S), along with various volatile organic compounds (VOCs) during the collection, transfer, storage, treatment, and subsequent land application (Bicudo et al., 2002). Ammonia is the abundant gas emitted from poultry manure, but VOCs and odor are also of concern. The environmental problems associated with poultry manure could be mitigated through application of treatment additives. Numerous types of additives have been used to reduce NH3 and odor emissions from livestock wastes (McCrory and Hobbs, 2001). Zeolites are one of such additives and have a high surface area and cationic exchange properties (Mumpton and Fishman, 1977). Natural zeolite (clinoptilolite) has been shown to have the potential to control ammonium ions in wastewater (Komarowski and Yu, 1997). These properties and the abundance of low-cost zeolite-bearing deposits have made it an attractive option for a variety of applications in the treatment of livestock and poultry wastes. Clinoptilolite has been investigated as both a livestock feed additive and a topical manure additive to adsorb NH3. Application directly to the manure seems to be more effective in reducing NH3 emissions (Witter and Kirchmann, 1989; Miner et al., 1997; Liang et al., 2005), although addition through the feed is a more practical application (McCrory and Hobbs, 2001).

The same physicochemical properties that make zeolite so attractive for NH3 abatement are also expected to enhance adsorption of VOCs and odor emitted from poultry and livestock wastes. The mechanism of VOCs and odor control from livestock slurries has been attributed to the high adsorptive capacities of zeolites (Pain et al., 1987). Japanese farmers have sprinkled zeolite on farmyard and manure piles for years to control both odor and moisture content (Mumpton, 2006). Miner and Stroh (1976) evaluated several materials including clinoptilolite and erionite as surface applications to cattle feedlots for NH3 and odor control. These two zeolites were then judged to be somewhat effective for odor control (Miner and Stroh, 1976). The use of erionite is currently phased out due to inhalation health hazards. No significant reduction of odor concentration and odor emissions were found from broiler houses where zeolite was used simultaneously as feed additive and topical litter treatment (applied only in week 1, 4, 5, and 6 of the study) in a broiler operation in Slovenia (Amon et al., 1997). A reduction of odor intensity was observed when a simple air scrubber packed with clinoptilolite was used inside a laying hen house (Koelliker et al., 1980).

The majority of the literature related to VOCs emitted from livestock manure stem from studies of swine manure (Schaeffer, 1977; O'Neal and Phillips, 1992; Schiffman et al., 2001). To date, relatively little is known about the chemical nature of odorous compounds in poultry manure beyond the early studies when gas chromatography became available (Deibel, 1967; Burnett, 1969; Banwart and Bremner, 1975; Smith et al., 1977; Yasuhara, 1987). Deibel (1967) found that butyric acid, ethanol, and acetoin were the main volatile components in stored poultry manure. Burnett (1969) found mercaptans, sulfides, and diketones in the headspace of accumulated liquid poultry manure, and volatile fatty acids (VFAs), indole, and skatole in the liquid. Banwart and Bremner (1975) reported that volatile sulfur compounds such as H2S, methyl mercaptan (MM), dimethyl sulfide (DMS), and dimethyl disulfide (DMDS) were detected from poultry manure under anaerobic conditions. Various alcohols, ketones, esters, and carboxylic acids together with DMS and DMDS were found when poultry manure was incubated in an Ar atmosphere (Smith et al., 1977). Yasuhara (1987) reported 72 compounds identified in poultry manure with a gas chromatograph-mass spectrometer (GC-MS). Branched alipathic alcohols, many esters, dimethyl trisulfide (DMTS), and alkanamides were then detected for the first time. Yasuhara (1987) identified butyric acid, isovaleric acid, DMTS, indole, and skatole as the most important odorous components using the odor impact factor defined as the ratio of concentration to the odor detection threshold value.

Several different sampling and sample preparation techniques were used for characterization of the volatile fraction of poultry manure, such as solvent extraction, trap tube (Smith et al., 1977), steam distillation (Deibel, 1967), and freeze vacuum distillation (Yasuhara, 1987). Standard air sampling methods were also modified to quantify VOCs in and around swine operations (Schiffman et al., 2001; Zahn et al., 2001; Blunden et al., 2005). However, caution should be exercised when standard methods are modified for determination of VOCs and semi-VOCs in livestock environments. This is because livestock gases are often polar, reactive, and can interact with each other, moisture in the air, and the sampling container materials (Trabue et al., 2005; Koziel et al., 2005; McConnell and Trabue, 2006; Trabue et al., 2006). The EPA TO-17 method utilizing sorbent tubes and active sampling often used for ambient air sampling was not specifically developed for the compounds of interest in this study: carboxylic acids, sulfides, amides, indolics, phenolics, branched ketones, and high molecular weight aldehydes (Woolfenden and McClenny, 1999). Whole air sampling utilizing evacuated canisters and air sampling bags can be associated with poor sample recoveries for typical malodorous gases found in livestock environments (Keener et al., 2002; Koziel et al., 2005; Trabue et al., 2006). Some improvement in sample recoveries can be achieved for sulfides with special surface treatments in canisters. However, the presence of moisture appears to lower sample recoveries with storage time (Trabue and Scoggin, 2006).

Solid phase microextraction (SPME) is an alternative to conventional sampling techniques such as adsorbent tubes (Koziel et al., 1999) and offers easy handling, high selectivity, and sensitivity for quantitative analysis of airborne compounds (Koziel et al., 2000; Koziel and Pawliszyn, 2001; Augusto et al., 2003). It is especially suitable for qualitative and quantitative analysis of VOCs requiring exposure of a fiber to the headspace above the sample for a suitable period of time, followed by direct thermal desorption in the heated injection port of a GC (Matich, 1999). Quantitative air sampling with SPME can be affected by competitive adsorption, sampling variables such as air velocity and temperature (Jia et al., 2000; Koziel et al., 2000; Koziel and Pawliszyn, 2001). However, air velocity and temperature effects can be minimized when SPME is used as a time-weighted average sampling device (Martos and Pawliszyn, 1999). Competitive adsorption and displacement caused by limited sorption capacity of porous SPME fibers can be minimized by using short sampling times (Jia et al., 2000). The reproducibility of SPME methods was compared with the standard NIOSH method (NIOSH, 1994) and the comparison showed that the SPME methods were generally better than that of the conventional charcoal tube methods (Jia et al., 2000; Koziel and Pawliszyn, 2001) for air samples with target VOCs. Review of air sampling methods utilizing SPME for VOCs in indoor air is presented elsewhere (Koziel and Novak, 2002). To date, limited progress has been made with SPME applications to quantification of odorous gases in and around livestock and poultry operations. SPME has been useful for qualitative characterization and screening of livestock gases. Sampling of livestock VOCs and odorants with SPME has been used to characterize swine dust odorants (Cai et al., 2006), downwind odor impact of a beef cattle feedlot (Wright et al., 2005), and downwind odor impacts of swine finisher operations (Bulliner et al., 2006; Koziel et al., 2006).

Odors from livestock wastes are due to a complex mixture of volatile compounds arising from anaerobic degradation of plant fiber and protein in the feed (Spoelstra, 1980; Hammond et al., 1989). Identification of odorous compounds in livestock wastes is very important to improve the understanding of the potential of malodor generation. Livestock odor results from hundreds of compounds and their possible interactions with each other (Schiffman et al., 2001; Zahn et al., 2001). Wright et al. (2005) demonstrated that SPME combined with a multidimensional GS-MS-olfactometry (MDGC-MS-O) system can be used for sampling, identification, and prioritization of specific odorants associated with livestock. Although livestock odors are made up of hundreds of compounds (Schiffman et al., 2001), only a handful of compounds are responsible for the characteristic beef cattle and swine odor (Wright et al., 2005) and downwind impact of beef cattle and swine operations (Koziel et al., 2006; Bulliner et al., 2006). Odor reduction for livestock and poultry wastes could be directed toward the most significant characteristic odor-causing components to facilitate development of odor control technologies. Concentrations of key odorous compounds are often very low, e.g., in low ppb range or less. However, odor thresholds of these compounds are even lower. Therefore, suitable sampling/sample preparation and analytical methods are required for the identification of the key odorous compounds.

The objective of this research was to qualitatively evaluate the effectiveness of natural zeolite as a topical manure additive to control odor and VOCs during simulated laying hen manure storage. The zeolite was applied to fresh laying hen manure at a rate of 0, 2.5, 5, or 10% (by weight). Headspace samples from the storage/emission vessels were collected with SPME 85 µm Carboxen/PDMS and analyzed on a MDGC-MS-O for the identification and prioritization of poultry manure odorants.

The approach used in this study allowed for qualitative evaluation of odor reduction associated with specific odorants that were separated with GC and identified with MS-O. Measurements of odor concentration with triangular forced-choice olfactometry were not in the scope of this study (ASTM, 2001). This ASTM E697–91 standard method is not suitable for specific odorant identification and prioritization. Parker et al. (2005) reported poor correlations between measured odor concentrations, odor intensity, and odor hedonic tones when the triangular forced-choice olfactometry was applied to beef cattle odor. The MDGC-MS-O approach could provide additional information related to the specific odorant identity, odor prioritization, and ranking (Wright et al., 2005; Bulliner et al., 2006).


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Emission Apparatus
The emission vessel system has been previously described in detail by Liang et al. (2005). Eight 19-L emission vessels were operated under positive pressure, with headspace mixing achieved by small 12VDC fans. Fresh air with a constant flow rate of 3 L min–1 was introduced into each vessel. The vessels were housed in a laboratory with temperature maintained between 21 and 25°C.

Experimental Procedure
Manure Treatment
Nearly fresh hen manure was collected from a commercial belt cage layer facility located in Central Iowa. About 2.5 kg of fresh manure was loaded into a 3.8-L container with 0.02 m2 surface area. Different amounts of zeolite (grade 14 x 40, Bear River Zeolite Company, Thompson Falls, MT) of 0, 62.5, 125, or 250 g, i.e., 0, 2.5, 5, and 10% by weight, respectively, were surface-applied on top of the manure, corresponding to an application rate of 0, 3.125, 6.25, or 12.5 kg·m–2 manure surface. Each container was placed inside an emission vessel. Two vessels were used for each of the dosages. Two trials (Trials A and B) were conducted to achieve four replicates of each treatment. In Trial C, fresh manure (5-cm thickness and 2.5 kg per layer) was loaded to 19-L vessels (as opposed to the smaller 3.8-L container, then placed inside the vessel) every other day for four layers to simulate periodic manure addition and zeolite application to manure storage. Zeolite (125 g, 5% by weight) was surface-applied on top of each layer in four of the eight vessels while the others served as control. Zeolite application rate was equivalent to 2.55 kg·m–2 manure surface in Trial C. The air exchange rates ranged from 11 to 21 air changes per hour in each vessel as a result of the increasing manure volume from manure addition and decreasing headspace volume.

Sampling and Analysis of Volatile Organic Compounds and Odor
Carboxen/PDMS 85 µm SPME fiber (Supelco, Bellefonte, PA) was used for sampling headspace above the poultry manure in the emission vessels. New fibers were conditioned according to the manufacturer's instructions. The SPME fiber assemblies had their tensioning spring removed and samples were collected manually. Before each sampling, SPME fibers were desorbed in a GC injector for 5 min at 260°C, and then SPME collections were performed by direct fiber exposure in the dynamic headspace of the emission vessels for 10 min. The selection of sampling time was based on the preliminary tests of control headspaces with varying SPME sampling times. The 10 min sampling time consistently resulted in detectable amounts of all major odorants and odorous VOCs associated with poultry manure. The effects of limited SPME sorbent capacity were also tested with SPME sampling from static headspaces. No competitive extraction and displacement were observed for all target compounds for sampling up to 10 min, except for methyl mercaptan and dimethyl sulfide.

The headspace SPME sampling was performed at room temperature and was immediately followed by sample analyses on a MDGC-MS-O system (Microanalytics, Round Rock, TX). The system integrated GC-O with conventional GC-MS (Agilent 6890N GC/5973 MS, Agilent, Wilmington, DE) as the base platform with the addition of an olfactory port. The system was equipped with a nonpolar precolumn and polar analytical column in series as well as system automation and data acquisition software (MultiTrax V. 6.00 and AromaTrax V. 6.61, Microanalytics and ChemStation, Agilent). The general run parameters used were as follows: injector, 260°C; flame ionization detector (FID), 280°C; column, 40°C initial, 3 min hold, 7°C min–1, 220°C final, 10 min hold; carrier gas, helium. Mass/charge (m/z) ratio range was set between 33 and 280 amu (atomic mass units). Spectra were collected at 6 scans sec–1 and electron multiplier voltage was 1200 to 1350 V. The detector was auto-tuned weekly.

During each trial headspace of all vessels was sampled once only. Two headspace samples (one control and one treatment) were taken on other days. Headspace samples for the same one control and one 10% treatment emission vessel for Trial A were performed on Day 1, Day 2, Day 3, Day 8, and Day 9. Problems with the GC motherboard prevented more frequent sampling for this trial between Day 3 and Day 8. Headspace of all eight vessels were sampled on Day 2. For Trial B, headspace of the same one control and one 10% treatment emission vessel were sampled daily between Day 1 and 7. For Trial C, headspace of the same one control and one 5% treatment emission vessel were sampled daily between Day 1 and 8, and then on Day 10, 12, and 14, respectively. Headspace sampling of all eight vessels was performed on Day 3 for Trials B and C.

The identity of compounds was verified by combination of (a) high purity reference standards (Sigma-Aldrich, Fisher, and Fluka) and matching their retention time on the MDGC capillary column and mass spectra; (b) matching mass spectra of unknown compounds with BenchTop/PBM (Palisade Mass Spectrometry, Ithaca, NY) MS library search system and spectra of pure compounds; and (c) matching the description of odor character.

Human panelists were used to sniff separated compounds simultaneously with chemical analyses. Odor evaluations consisted of qualitative comparisons of (a) the number of separated odor events and (b) the total odor defined here as sum of the product of odor intensity and odor event duration for all separated odor events recorded in an aromagram (Cai et al., 2006; Bulliner et al., 2006). In this approach, odor intensity and odor character are recorded and measured for each compound in an air sample causing odor without considering potential odorant interactions. The total odor was not compared with actual odor concentrations. An aromagram was recorded by a panelist utilizing the human nose as a detector. Odor events resulting from separated compounds eluting from the column were characterized for odor descriptor with a 64-descriptor panel and odor intensity with Aromatrax software (Microanalytics, Round Rock, TX). The olfactory responses of a panelist were recorded using Aromatrax software by applying an odor tag to a peak or a region of the chromatographic separation. The odor tag consisted of editable odor character descriptors, an odor event time span (odor duration) and perceived odor intensity.

The relative % reduction was used to evaluate the effectiveness of different zeolite application rates. Relative amount of volatiles present in the headspace above the manure was measured as peak area counts under peaks of characteristic single ions for separated gases. Treatment effectiveness of specific VOCs and potential odor control measured with the GC-O approach was expressed as percentage reduction, i.e., as the ratio of the difference between the control and treatment to the control, of the form:

Formula 1[1]

where:

Ci = peak area count of compound or odor "i" for the control hen manure, and
Ti = peak area count of compound or odor "i" for the zeolite-treated hen manure.

Positive value of % reduction means the zeolite treatment was effective for that particular compound. Negative numbers signify that the treatment was not effective, i.e., treatment generated a particular compound instead of reducing it. The relative reduction did not refer to specific concentrations.

Reproducibility of HS-SPME Method for Volatile Organic Compounds Emitted from Poultry Manure
Reproducibility of the method was tested, expressed as relative standard deviation (RSD) for 24 target VOCs typically present in the headspace of poultry manure. Five replicate samples were collected at room temperature from the headspace of the same control vessel using the same 85 µm Carboxen/PDMS fiber and 10 min extraction time, followed with analysis on a GC-MS. The RSD ranged from 2.0 to 28.3% for all 24 target compounds with the exception of phenol (44.9%). Average RSD was 12.7%. Values of RSD ranged from 5.2 to 12.8% for aldehydes, 9.1 to 12.5% for VFAs, 6.4 to 44.9% for phenolics, 10.6 to 13.0% for indolics, and 2.0 to 19.7% for sulfide compounds.


   RESULTS AND DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
CONCLUSIONS
 REFERENCES
 
Effects of Zeolite Application Rates on Volatile Organic Compounds
A total of more than 90 volatile compounds were identified from the headspace air. Among those compounds only several chemical groups contributed to the offensive odor of poultry manure, including short-chain VFAs, volatile sulfur compounds, and phenolic and indolic compounds. Eight characteristic compounds which significantly contributed to the malodor of poultry manure, including acetic acid, butanoic acid, isovaleric acid, DMTS, dimethyl sulfone, phenol, indole, and skatole, were selected for comparisons of the effect of zeolite application rates. Effects of the three application rates of the natural zeolite on target VOCs are shown in Table 1. Data in Table 1 represent the reduction (%) for different zeolite application rate (2.5, 5, and 10%, by weight) of target odorants and characteristic odors for Trial A and B evaluated with GC-MS-O. Close inspection of the data in Table 1 shows that acetic acid, butanoic acid, isovaleric acid, indole, and skatole were controlled by zeolite application. The reduction of those compounds and its statistical significance was generally proportional to the zeolite application rate. However, DMTS and phenol were generated, and the rate of generation was proportional to the application rate, except for phenol at 10% application rate.


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  		Table 1. Reduction (%) of different zeolite application rate (2.5%, 5% and 10%, by weight) on target odorants and characteristic odors for Trial A and B evaluated with GC-MS-O.

 
Six characteristic odors present in the poultry manure were then selected to further evaluate the effects of zeolite application rates on odor impact (Table 1). The odor shown in Table 1 was defined as the product of odor intensity (%) and odor duration (min) for each characteristic odor recorded in the aromagram (Cai et al., 2006). Six characteristic odors were correlated with corresponding compounds, i.e., ‘onion/garlic’ (DMTS), ‘fatty acid/body odor’ (butanoic acid), ‘body odor’ (isovaleric acid), ‘phenolic’ (phenol), ‘barnyard’ (indole), and ‘naphthalenic’ (skatole). Apparent reduction in odor caused by VFAs, skatole, and indole was consistent with the chemical analyses shown in Table 1. Similarly, the reduction of odor was typically proportional to the rate of application. The odor intensity from acetic acid was much smaller compared with the six characteristic compounds. The ‘vinegar, acidic’ odor character for acetic acid is also less offensive compared with higher molecular weight fatty acids. Thus, acetic acid is not shown in Table 1. Among the dosages tested, 10% zeolite was the most effective in controlling VOCs and odors emitted from poultry manure as evaluated with the GC-MS-O approach.

Comparing Average Effectiveness of Ten Percent Zeolite Treatment for Trials A and B
Thirty compounds belonging to seven chemical groups, such as ketone (2), aldehyde (3), VFAs (6), phenolic (5), indolic (2), N-containing compounds (5), and S-containing compounds (7), were selected to evaluate the effectiveness of a 10% zeolite treatment. Figure 1 shows the comparison of total ion chromatograms (TICs) of 10% zeolite treatment and control. Table 2 summarizes the comparison of the average effectiveness of 10% zeolite treatment for each of the target 30 compounds for Trials A and B. Twenty two out of 30 compounds including two ketones, benzaldehyde, six VFAs, four phenolics, two indolics, five N-containing compounds, and two S-containing compounds were consistently controlled in Trials A and B. However, some sulfur compounds, such as MM, DMS, DMDS, 1-propanethiol, and especially DMTS, were generated over time in both trials. A possible reason is that zeolite changed the pH of poultry manure and resulted in the generation of sulfur compounds. Also, sulfur compounds could have been generated because the surface-applied zeolite layer could facilitate formation of an anaerobic condition in the manure. Banwart and Bremner (1975) reported that volatile sulfide compounds such as H2S, MM, DMS, and DMDS were emitted from poultry manure under anaerobic conditions. Some authors reported apparent sulfur compound generation associated with the use of Carboxen/PDMS fiber coatings, also known to be the most suitable fiber for analyzing sulfur compounds (Lestremau et al., 2004). This fiber coating is known for artifact DMDS formation of as much as 25% (Lestremau et al., 2004). Carboxen coatings contain between 1 and 4% of sulfur material (Dettmer and Engelwald, 2002). In this study, the possible artifact formation should be offset (and not affect the % reduction estimates) by qualitative comparisons of treatment and control and the use of Eq. [1]. Phenol is the only compound generated in Trial A and controlled in Trial B. Analysis of headspace of only the zeolite material used in this study showed that phenol was emitted from zeolite. Thus, the variability of treatment/generation observed for phenol might be attributed to its presence in zeolite.


Figure 1
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  		Fig. 1. Comparison of total ion chromatogram (TIC) between 10% zeolite treatment and control.

 

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  		Table 2. Qualitative comparison of average reduction (%) estimated with Eq. [1] of 10% zeolite treatment for entire Trial A and Trial B. Number in parentheses is the single ion of each compound used for peak area count integration.{dagger}

 
The average treatment effectiveness evaluated with SPME-GC-O approach for seven chemical groups in both trials were 47% for ketones, 23% for aldehydes, 89% for VFAs, 57% for phenolics except for phenol, 77% for indolics, 98% for amines, 42% for sulfur-oxidation compounds, and –532% for sulfides, respectively. Statistical analyses were performed using a paired t test to detect the significance of observed difference. The control of acetic acid, skatole, and dimethyl sulfone was significant (p < 0.05) for 10% zeolite treatment in both Trials A and B. Few compounds were significantly reduced in one of the trials only. In Trial A, 3-octanone and propanamide were significantly (p < 0.05) controlled. In Trial B, propanoic, isobutyric, butanoic, isovaleric, pentanoic acids, phenol, p-cresol, 4-ethyl phenol, 4-vinyl phenol, guaiacol, indole, skatole, acetamide, propanamide, 2-methyl-propanamide, butanamide, and trimethyl amine were controlled (p < 0.05). Methyl mercaptan, DMS, and 1-propanethiol were generated (p < 0.05). However, 23 out of 30 target odorous compounds showed significant difference (p < 0.05) between control and treatment for pooled Trial A and B (Table 2). The average standard deviations of removal means for all selected compounds except for DMTS in both trials were calculated. The average standard deviation (except for DMTS) of Trial A was greater than that of Trial B (48 vs. 25%). The variability is likely due to the degradation of manure and/or SPME sampling without septa causing the concentration of the headspace to change, as well as possible variations in extraction efficiency for different SPME fibers.

Figure 2 (A and B) show the effectiveness of 10% zeolite application rate treatment for five representative compounds over time for Trials A and B. Trimethyl amine, acetic acid, skatole, indole and DMTS were selected for evaluation of the effectiveness. For all the selected compounds, the effectiveness changed over time. However, different compounds showed different changing trends, i.e., upward trend (acetic acid), downward trend (indole and skatole), and consistent trend (trimethyl amine and DMTS), respectively.


Figure 2
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  		Fig. 2. Effects of 10% zeolite treatment on characteristic compounds emitted from manure over time for Trial A (part A) and Trial B (part B).

 
The percentage reduction of specific compounds reported in this article is based on qualitative evaluations according to Eq. [1] without estimating actual compound concentrations. However, it could be assumed that percentage reduction estimated with this qualitative approach is not significantly different from the percentage reduction that would be obtained if % reduction was estimated based on estimates of concentrations. This is because no significant effects of competitive adsorption were observed on the SPME fiber coatings used for the same sampling time and sampling temperature. Potential biases associated with selective extractions and the use of different SPME fibers (Jia et al., 2000) should also be relatively insignificant when an equation is used for qualitative comparisons. More research is warranted to test these assumptions with suitable air sampling and analysis methods.

Comparison of Total Odor and Odor Events between Ten Percent Zeolite Treatment and Control
Figures 3A and 3B show the comparison of total odor and odor events between 10% zeolite treatment and control in Trials A and B. The total odor was estimated as the summation of the products of odor duration and odor intensity for all odor events found in all headspace samples of poultry manure. Total odor from the control was always higher than that from the 10% zeolite treatment over time in both trials. The total odor for Trial A and B showed significant difference (p = 0.0016) between control and treatment. Average reduction of the odor caused by all odorants evaluated with SPME-GC-O was 67 (± 12%) and 51% (± 26%) for Trials A and B, respectively. The same trend was observed for the total number of odor events. The apparent reduction in the estimate of odor and the total number of odors detected was consistent for both trials. Thus, the overall odor in poultry manure appeared to be controlled by 10% zeolite application. Average reduction of the total odor evaluated with SPME-GC-O approach for 2.5, 5, and 10% treatment was 33, 50, and 83% for Trial A, and –29, 3, and 55% for Trial B, respectively, when headspace of all treatments was compared. This apparent correlation between the loading rate and the reduction of the total odor is consistent with the similar trend observed for several target VOCs. It is interesting to mention that the effectiveness of zeolite treatment in the 7-d cumulative ammonia emission for 2.5, 5, and 10% treatment were 68, 81, and 96% of control, respectively. The effectiveness of ammonia reduction decreased as storage time went by, possibly due to its decreased capacity (Liang et al., 2005). The better performance of zeolite in controlling ammonia emission from poultry manure storage might be associated with its natural selectivity for ammonia by zeolite.


Figure 3
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  		Fig. 3. Effects of 10% zeolite treatment on the total odor evaluated with GC-O for Trial A (part A) and Trial B (part B). Total odor was defined as the sum of all separated odor peak areas (product of separated odor intensity and odor duration on an aromagram).

 
Comparing Average Effectiveness of Five Percent Zeolite Treatment for Trial C
In Trial C, 5% zeolite application rate was surface-applied on top of each manure layer (zeolite addition interval of 2 d, 4 layers in total). This was done in an attempt to simulate manure collection and treatment in a typical layer barn with belt manure removal and storage. The evaluation of the effects of zeolite application simulating periodic application is displayed in Table 3. Twenty two compounds were selected to evaluate the effectiveness of zeolite treatment using Eq. [1]. Only trimethyl amine was controlled over the 14-d trial duration. Skatole and diacetyl were randomly controlled. Average treatment effectiveness for the remaining compounds was negative. Figure 4 shows comparison of total odor area count between treatment and control. Total odors evaluated with the SPME-GC-O approach on Days 1, 2, 3, 5, 8, and 12 in treatment were higher than that in the control. The total odor for trial C showed no significant difference (p = 0.1439) between control and treatment. Average reduction of the total odor was actually negative (–9%) (standard deviation ± 21%). These results indicated that there was no apparent odor and VOCs control with the layered 5% zeolite application. However, there were three compounds, i.e., trimethyl amine, DMTS, and skatole which showed significant difference (p < 0.05) (Table 3). It is noteworthy that fresh manure was loaded directly into the 19-L vessel with 0.05 m2 manure surface in Trial C (as opposed to the smaller 3.8-L container in Trials A and B). Zeolite application rate was equivalent to 2.55 kg·m–2 manure surface for 5% application rate, which was much less than the equivalent 6.25 kg m–2 (5% by weight) rate in Trials A and B. Hence, the total zeolite adsorption capacity in Trial C was presumably much lower than that in Trials A and B.


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  		Table 3. Reduction (%) of 4-layer treatment for Trial C estimated with Eq. [1]. Number in parentheses is the single ion of each compound used for peak area count integration.{dagger}

 

Figure 4
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  		Fig. 4. Effects of four layer 5% zeolite treatment on the total odor evaluated with GC-O for Trial C.

 
Caution should be exercised when interpreting qualitative odor comparisons in this study. The total odor was defined here as sum of the product of odor intensity and odor event duration for all separated odor events recorded in an aromagram for each air sample (Cai et al., 2006; Bulliner et al., 2006). In this approach, odor intensity and odor character were recorded and measured for each compound in an air sample causing odor without considering potential compound interactions and its potential effect on odor concentrations. This approach is useful in determination of specific compound or compounds causing specific odors in complex air samples associated with livestock odor (Wright et al., 2005). The total odor was not compared with actual odor concentrations. Research is warranted to determine the effect of individual odorous compounds typically found in livestock odor on measured odor concentrations.


   CONCLUSIONS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
REFERENCES
 
The following conclusions were drawn from this study:

Sampling with SPME and analysis with GC-MS-O is a useful qualitative approach for testing of treatment effectiveness of zeolite applications to control VOCs and specific odorants from simulated poultry manure storage.
Topical application of zeolite to laying hen manure showed the potential for reducing emissions of acetic acid, butanoic acid, isovaleric acid, dimethyl sulfone, phenol, indole, and skatole from the manure storage, with the effectiveness of treatment being proportional to the zeolite application rate.
Sulfide compounds including DMS, DMDS, DMTS, MM, 1-propanethiol were generated with the rate of generation being generally proportional to the application rate.
Specific odors caused by VFAs, skatole, and indole, i.e., fatty acid/body odor (butanoic acid), body odor (isovaleric acid), barnyard (indole), and naphthalenic (skatole) were controlled by 10% topical zeolite treatment.
Ten percent zeolite application rate is most effective at controlling specific odorants emitted from poultry manure among the tested application rates. Average reduction of the total odor measured with the GC-O approach was 67 (± 12%) and 51% (± 26%) for Trials A and B, respectively.


   ACKNOWLEDGMENTS
 
This research was funded in part by the Women in Science and Engineering Program at the Iowa State University, the Midwest Poultry Research Program, and a Special USDA-CSREES Air Quality Research Grant.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 




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Y.-C. M. Lo, J. A. Koziel, L. Cai, S. J. Hoff, W. S. Jenks, and H. Xin
Simultaneous chemical and sensory characterization of volatile organic compounds and semi-volatile organic compounds emitted from swine manure using solid phase microextraction and multidimensional gas chromatography-mass spectrometry-olfactometry.
J. Environ. Qual., March 1, 2008; 37(2): 521 - 534.
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