Emission Characteristics of Odorous Compounds from a Swine Farm on Jeju Island, Korea

Abstract

This study investigated 26 malodorous substances emitted from a swine farm on Jeju Island, South Korea, to discern their specific emission characteristics and potential implications for workers’ health and environmental management. A detailed analysis of emissions from livestock buildings, the compost facility, and the manure storage tank was conducted. Accurate quantification involved rigorous collection methods measuring concentrations of NH₃, hydrogen sulfide (H₂S), trimethylamine (TMA), aldehyde compounds, volatile organic compounds (VOCs), volatile fatty acids (VFAs), p-cresol, indole, and skatole. High concentrations of NH₃ and H₂S, particularly in the manure storage tank, raised concerns about the health of workers. TMA levels were notably elevated in the livestock building, whereas aldehydes and VOCs remained within limits. VFAs were prevalent in the livestock building, with p-cresol, indole, and skatole in the manure storage tank. Distinct emission profiles across farm facilities highlight the need for tailored odor management strategies, ensuring worker well-being and effective environmental practices. These findings offer valuable insights for implementing targeted mitigation measures in similar agricultural settings.

1. Introduction

The livestock industry is rapidly developing around the world. Jeju Island has become a significant hub for livestock husbandry, with huge impacts on the local economy. Consequently, the number of livestock and swine facilities has increased, leading to a rise in odor emissions from manure, which has evolved into a local human and environmental issue. Livestock emissions represent a serious environmental issue on Jeju Island and globally.

Odors are composed of volatile compounds that stimulate the human sense of smell and can result in discomfort and disgust. Furthermore, the detection of even minute quantities of specific odorous substances poses a challenge in addressing their impact on odor, thereby complicating mitigation efforts. Addressing and preventing odors poses numerous difficulties. Individuals vary in their olfactory sensitivity, making it challenging to accurately assess the quality and intensity of odors through sensory methods. Specifically, odors originating from pigsties can induce mental and physiological stress in humans, resulting in adverse reactions such as nausea, headache, loss of appetite, breathing difficulties, and allergic phenomena [1,2].

Malodorous substances from swine manure encompass hundreds of compounds, including nitrogen compounds such as ammonia (NH₃) and amines, sulfurous compounds such as hydrogen sulfide (H₂S) and dimethyl sulfide (DMS), esters, ketones, and aromatic compounds [3]. NH₃ is a neurotoxin with strong negative effects on the health of animals, humans, and the environment. At high concentrations, it can cause ulceration in the eyes and severe irritation to the respiratory tract [4]. Additionally, atmospheric H₂S concentrations > 10 ppm are considered stressors for both humans and swine. For example, H₂S gas exposure can lead to neurological, respiratory, and eye diseases in animals and humans [5,6].

Odors from swine farms are principally generated by feed digestion and manure fermentation. The main components of swine feed are carbohydrates, crude protein, crude fat, crude ash, neutral detergent fiber, acid detergent fiber, non-fiber carbohydrates, and nitrogen-free extract. Among these components, crude protein is decomposed into amino acids by intestinal microorganisms, which in turn is broken down into NH₃, volatile fatty acids (VFAs), hydrogen, and carbon dioxide by the deamination of amino acids [7,8]. Furthermore, amino acids such as tyrosine, tryptophan, and phenylalanine are metabolized to generate the main components of manure odors such as indole (IND), phenol (PHE), p-cresol (p-CRE), and 4-ethyl phenol [7,8,9].

Manure also produces malodorous substances through anaerobic fermentation by microorganisms during decomposition [10]. The generated malodorous substances in this process include propionic acid (PA), sulfur compounds, NH₃ and volatile amines, VFAs, PHEs, and INDs [11,12,13,14].

Swine farms contain livestock buildings, manure storage tanks, manure composting facilities, and liquid manure treatment facilities, and diverse types and intensities of odors are generated in these facilities. Consequently, the management of odors in each facility and the construction of odor reduction systems on a swine farm demand significant expenditure in terms of costs, labor, and time [3].

In Korea, 22 target offensive odorants have been officially specified for the management of odor emissions in industrial and surrounding areas. These 22 malodorous substances are regulated based on the permissible emission standards set by the Odor Prevention Law, with a particular focus on sulfur compounds, NH₃, volatile amines, VOCs, aldehydes, and VFAs [15]. However, PHEs and INDs, which are the main malodorous substances generated from swine farms, are excluded, making it difficult to manage livestock odors.

On Jeju Island, 259 swine farms were operating in 2022, with farms with <3000 swine accounting for 85% (220 swine farms) of this total. By region, Hallim-eup, Jeju City, has 128 swine farms, accounting for 49% of the total. As there are numerous swine farms in this small area and as the number of livestock has increased, odor complaints have increased accordingly.

To achieve the sustainable development of the livestock industry globally, systematic livestock odor management is required to solve air quality deterioration, health issues, and odor complaints. Consequently, this research focused on swine farms on Jeju Island, characterized by an average breeding scale within a region exhibiting a dense distribution of swine farms. To achieve this objective, samples were collected and analyzed for malodorous substances. A comprehensive set of 26 substances, including 22 malodorous compounds specified by the Korean Ministry of Environment, two types of PHEs, and two types of INDs, were examined. These samples were derived from a swine farm comprising a livestock building, a compost facility, and a manure storage tank. The analysis aimed to identify the distinctive characteristics of the primary malodorous substances associated with each facility and their respective contributions to odor.

2. Materials and Methods

2.1. Sampling Sites and Substances

This study was performed at a commercial swine facility on Jeju Island (33°36′ N, 126°31′ E), located in Geumak-ri, Hallim-eup, Jeju City, South Korea. The swine farm comprised approximately 350 sows, which produce 4000–5000 market pigs (i.e., 100~110 kg per pig) per year. The swine farm comprised various buildings, including thirteen pig houses, two manure treatment facilities (a compost facility and manure storage tank), and management/administration offices. The total area of the swine farm was approximately 4200 m². In addition, the total area of the pig house structures, the compost facility, and manure storage were 2800, 495, and 330 m², respectively. Each pig house was a closed structure constructed with concrete materials, devoid of windows, and operated using a deep-pit manure removal system. Additionally, the buildings had fully slatted floors. Approximately 400–500 pigs are reared in each pig house. The volume of the manure storage tank was 5000 m³, which was operated using an oxygen aeration system, and manure was transferred to the tank from the pig house. The water level in the manure storage tank was maintained at 60–70%.

Samples were collected from inside the livestock building (nursery, growing, and finishing pig houses), compost facility, and manure storage tank. The samples were collected four times, from February to September 2023. The prevalent meteorological conditions during sample collection are shown in

Table 1. Basic information regarding the five sampling sites selected for the research of malodor composition in the investigated swine farm.

Sampling Site	Sampling Point	Sampling Date	Sampling Time	Temperature (°C)	Humidity (%)
Nursery pig house	Indoor center, Ventilation fan off	17/Feb/2023, 21/Apr/2023 11/Aug/2023, 07/Sep/2023	9:00–11:00	14.1–29.9	71–75
Growing pig house	Indoor center, Ventilation fan off	17/Feb/2023, 21/Apr/2023 11/Aug/2023, 07/Sep/2023	9:00–11:00	18.2–32.2	70–73
Finishing pig house	Indoor center, Ventilation fan off	17/Feb/2023, 21/Apr/2023 11/Aug/2023, 07/Sep/2023	9:00–11:00	17.6–32.3	70–78
Compost Facility	Indoor center, Composting	17/Feb/2023, 21/Apr/2023 11/Aug/2023, 07/Sep/2023	9:00–11:00	18.2–39.3	51–67
Manure storage tank	Tank entrance, Aerating	17/Feb/2023, 21/Apr/2023 11/Aug/2023, 07/Sep/2023	9:00–11:00	14.0–35.7	51–65

.

We measured a total of 26 malodorous substances, including 22 components designated by the Korean Ministry of Environment (22 offensive odor compounds): NH₃, trimethylamine (TMA), H₂S, methyl mercaptan (CH₃SH), DMS, dimethyl disulfide (DMDS), acetaldehyde (ACHO), propionaldehyde (PCHO), butyraldehyde (BCHO), iso-valeraldehyde (iso-VCHO), n-valeraldehyde (n-VCHO), styrene (STY), toluene (TOL), xylene (XYL), methyl ethyl ketone (MEK), methyl iso-butyl ketone (MIBK), butyl acetate (BuAc), iso-butyl alcohol (iso-BuAl), PA, n-butyric acid (n-BA), iso-valeric acid (iso-VA), and n-valeric acid (n-VA), as well as the following four main offensive odor compounds: PHE, p-CRE, IND, and skatole (SKT).

2.2. Sampling Method

Diverse methods were applied to collect samples of 26 malodorous substances from the swine facility. First, absorption solutions were used to collect NH₃, TMA, and VFAs (PA, n-BA, iso-VA, n-VA) with a low-volume air sampler (Yotsubishi Corp., KP–10O, Tokyo, Japan). The absorption solutions used were 0.5% boric acid for NH₃, 0.1 M sulfur acid for TMA, and a 0.1 M NaOH absorption solution for VFAs.

Air samples containing sulfur compounds (H₂S, CH₃SH, DMS, and DMDS) were collected using a 5 L polyester aluminum sampling bag (BMS, 5 L, Tokyo, Japan), which was placed in a vacuum chamber (Supelco Inc., 10642, Bellefonte, PA, USA). VOCs (STY, TOL, XYL, MEK, MIBK, BuAc, iso-BuAl), PHEs, p-CRE, IND, and SKT were collected at 0.1 L/min for 5 min by connecting an absorption tube (Supelco Inc., Tenax-TA, Bellefonte, PA, USA) to a low-volume air pump (Sibata Scientific Technology Ltd., MP-∑30KNII, Tokyo, Japan).

Aldehyde compound samples, such as ACHO, PCHO, BCHO, iso-VCHO, and n-VCHO, were collected at 1.0 L/min for 5 min by connecting an absorption cartridge (Supelco Inc., LpDNPH S10, Bellefonte, PA, USA) and an ozone scrubber (1.5 g potassium iodide) to a low-volume air pump (Sibata Scientific Technology Ltd., MP-∑10H, Tokyo, Japan).

2.3. Analysis Method

Analytical methods for determining various components in air samples and absorption tubes were based on a preconcentration step followed by subsequent separation and detection using gas chromatography, whereas absorption solutions were analyzed using a UV/vis spectrophotometer.

NH₃ was collected and absorption solutions were analyzed at 640 nm using a UV/vis spectrophotometer (Shimadzu Corp., UV-1280, Kyoto, Japan). TMA was analyzed using the Headspace System (PerkinElmer Inc., Turomatrix 40, Shelton, CT, USA) and GC-NPD (PerkinElmer Inc., Clarus 690, Shelton, CT, USA). Sulfur compounds were analyzed using the thermal desorber system (Markes International Ltd., Unity-xr/Air Server, Bridgend, UK) and GC-FPD (PerkinElmer Inc., Clarus 690, Shelton, CT, USA). Aldehydes were analyzed using a high-performance liquid chromatograph (HPLC) coupled with a photodiode array detector (Waters Corp., e2695/2998, Milford, MA, USA) at a 360 nm absorption wavelength. VOCs, PHEs, and INDs were analyzed using GC/MSD (PerkinElmer Inc., Clarus 690/Clarus SQ8T, Shelton, CT, USA) connected to a thermal desorber system (PerkinElmer Inc., Turbomatrix 650, Shelton, CT, USA). VFAs were analyzed using the Headspace System (PerkinElmer Inc., Turomatrix 40, CT, USA), and GC/MSD (PerkinElmer Inc., Clarus 680/Clarus SQ8T, Shelton, CT, USA) was used for the analysis of TMA. The analytical conditions of these components are listed in

Table 2. Analytical conditions of instruments.

Group	Preprocessing Instrument	Analytical Instrument	Column and Oven Method
Ammonia		UV-visible spectrophotometer
Amine	Headspace system	GC/NPD	Elite-5AMINE (30 m × 0.53 mm × 3 μm)
Sulfur	Thermal desorber	GC/FPD	CP-SIL 5CB (60 m × 0.32 mm × 5 μm)
Aldehyde		HPLC/PDA	CAPCELL PAK C18 UG120 S-5 (250 mm × 4.6 mm × 5 μm)
VOCs	Thermal desorber	GC/MSD	DB-heavywax (60 m × 0.32 mm × 0.25 μm)
Phenol
Indole
VFAs	Headspace system	GC/MSD	DB-heavywax (60 m × 0.32 mm × 0.25 μm)

, and the reliability of the analysis is presented in

Table 3. Method detection limit (MDL) and coefficient of variation (CV) for the analysis of odorous compounds (n = 7).

Group	Compounds	Short Name	MDL (ppb) *	CV (%)
Nitrogenous	Ammonia	NH3	0.012 ppm	4.0
	Trimethylamine	TMA	0.035	1.0
Sulfur	Hydrogen sulfide	H2S	0.026	1.6
	Methyl mercaptan	CH3SH	0.033	1.9
	Dimethyl sulfide	DMS	0.061	3.4
	Dimethyl disulfide	DMDS	0.023	1.4
Aldehyde	Acetaldehyde	ACHO	1.680	5.6
	Propionaldehyde	PCHO	1.534	5.0
	Butyraldehyde	BCHO	1.680	5.7
	iso-Valeraldehyde	iso-VCHO	2.566	2.6
	n-Valeraldehyde	n-VCHO	1.534	1.5
VOCs	Styrene	STY	0.143	2.2
	Toluene	TOL	0.147	2.2
	Xylene	XYL	0.221	3.4
	Methyl ethyl ketone	MEK	0.183	2.8
	Methyl iso-butyl ketone	MIBK	0.229	3.6
	Butyl acetate	BuAc	0.190	3.1
	iso-butyl alcohol	iso-BuAl	0.124	2.0
Phenols	Phenol	PHE	0.206	3.2
	p-Cresol	p-CRE	0.157	2.5
INDs	Indole	IND	0.164	2.6
	Skatole	SKT	0.185	2.9
VFAs	Propionic acid	PA	6.040	3.8
	Butyric acid	n-BA	4.334	2.8
	iso-Valeric acid	iso-VA	2.953	1.9
	n-Valeric acid	n-VA	3.262	2.0

* In ppb unless stated otherwise.

, including the method detection limit (MDL) and coefficient of variation (CV), as specified in the Odor Prevention Law of the Korean Ministry of Environment [15].

3. Results and Discussion

3.1. Nitrogen Compounds

The results for the NH₃ components measured in the samples collected from the livestock building (nursery, growing, and finishing pig houses), compost facility, and manure storage tank in the investigated swine farm on Jeju Island are shown in Figure 1. High concentrations of NH₃ were observed in the following order: manure storage tank (373.4 ± 191.4 ppm) > nursery pig house (15.3 ± 4.0 ppm) > finishing pig house (12.3 ± 3.3 ppm) > growing pig house (12.1 ± 5.1 ppm) > compost facility (10.4 ± 7.9 ppm). The manure storage tank exhibited the highest NH₃ concentration (373.4 ppm), which was far above the short-term exposure limit (STEL) concentration of 35 ppm set by the Korean Ministry of Environment and the American Conference of Governmental Industrial Hygienists (ACGIH). Exposure to an NH₃ concentration exceeding 100 ppm can result in irritation to the eyes, nose, and skin, emphasizing the importance of managing concentrations with due regard to worker health. Additionally, NH₃ generated from the manure storage tank is likely to affect surrounding areas; its concentration in the rest of the livestock building and the compost facility was 10.4–15.3 ppm, with a level similar to that of the NH₃ concentration in a general swine farm [16,17].

TMA concentrations were observed in the following order: growing pig house (6.5 ± 1.9 ppb) > nursery pig house (6.4 ± 1.3 ppb) > finishing pig house (5.7 ± 2.4 ppb) > manure storage tank (1.3 ± 0.6 ppb) > compost facility (1.1 ± 0.6 ppb; Figure 2). The TMA concentrations were similar in the livestock building, including the growing pig house, nursery pig house, and finishing pig house, whereas the NH₃ concentration was high and that of TMA was relatively low in the manure storage tank. In the livestock building (i.e., nursery, growing, and finishing pig houses), the correlation coefficient (r) between the NH₃ and TMA was 0.75, indicating a good correlation; this result may have been due to urea decomposition in the intestines of the livestock, which results in the generation of these two components.

3.2. Sulfur Compounds

The concentrations of the main sulfur-based malodorous substances such as H₂S, CH₃SH, DMS, and DMDS were measured in the livestock building, compost facility, and manure storage tank, and the results were compared (Figure 3). H₂S (63,915.1 ppb) and CH₃SH (227.4 ppb) showed the highest concentrations in the manure storage tank; the concentrations were likely high because the manure undergoes anaerobic decomposition with an oxygen aeration system. H₂S is detectable by its odor at 0.01–0.7 ppm, irritates the eyes and respiratory tract with an exposure of 50–100 ppm for 1 h, can be fatal in the case of exposure for 8–48 h at a concentration of 150 ppm, and causes rapid death at an exposure of 700–2000 ppm [18,19]. Therefore, considering the health of workers in manure storage tanks is necessary [19].

In the manure storage tank, if the H₂S concentration is between 50 and 100 ppm, eye and upper respiratory irritations, headaches, nausea, vomiting, and diarrhea may occur; the exposure of workers should be carefully managed. The concentrations of H₂S and CH₃SH reached their lowest levels in the compost facility, with values of 60.9 and 2.9 ppb, respectively. This reduction can be attributed to the anaerobic decomposition of manure in that specific area. In the rest of the livestock building, the concentrations of H₂S and CH₃SH were 1050.0–2186.0 and 18.8–22.6 ppb, respectively, similar to the concentrations in livestock buildings in other general farms [20,21,22]. Moreover, DMS and DMDS were detected below the emission limit value of 10 and 9 ppb, respectively, set by the Korean Ministry of Environment. These components were not considered the main malodorous substances generated from the swine farm.

In the livestock building, compost facility, and manure storage tank, the r values of H₂S and CH₃SH, DMS, and DMDS were 0.96, 0.82, and 0.65, respectively, indicating a good correlation, probably because these components had the same origin.

3.3. Aldehyde Compounds

Figure 4 shows the results of the analysis for aldehyde compounds such as ACHO, PCHO, BCHO, iso-VCHO, and n-VCHO. The livestock building, compost facility, and manure storage tank had ACHO and PCHO concentrations of 8.5–28.8 and 1.3–52 ppb, respectively; however, these concentrations were lower than the emission limit value set by the Ministry of Environment (50 ppb). Additionally, BCHO, iso-VCHO, and n-VCHO were not detected. Consequently, aldehyde compounds were not considered principal malodorous substances at the swine farm.

3.4. Volatile Organic Compounds (VOCs)

VOCs such as STY, TOL, XYL, MEK, MIBK, BuAc, and iso-BuAl—generated from the nursery pig house, growing pig house, finishing pig house, compost facility, and manure storage tank—were analyzed, and the results are shown in Figure 5. The concentration ranges were as follows: STY: 1.0–20.6 ppb, TOL: 8.0–219.3 ppb, XYL: 2.4–77.3 ppb, MEK: 9.4–132.7 ppb, MIBK: 1.3–21.2 ppb, BuAc: 0.1–4.7 ppb, and iso-BuAl: 1.6–5.9 ppb. These components showed trace levels that were far below the emission limits set by the Ministry of Environment at 400, 10,000, 1000, 13,000, 1000, 1000, and 900 ppb, respectively. Therefore, VOCs were not the main malodorous substances generated in the swine farm, similar to aldehyde compounds.

3.5. Volatile Fatty Acids (VFAs)

VFAs are produced in the dissolution process of proteins and carbohydrates. In the digestive tract, a neutral pH (pH 6–7) is typical; however, VFAs occur from the deamination of amino acids [23]. Miller and Varel [24] reported that VFAs or aromatic substances were the main contributors to swine manure odor.

VFAs, including PA, n-BA, iso-VA, and n-VA, were analyzed and their concentrations were compared (Figure 6). PA (231.9 ± 81.0 ppb) and iso-VA (28.9 ± 23.8 ppb) exhibited the highest concentrations in the growing pig house, and n-BA (194.6 ± 94.1 ppb) and n-VA (35.8 ± 19.5 ppb) had the highest concentrations in the finishing pig house. The VFA components had the lowest concentrations in the manure storage tank.

The r values among VFA components were >0.90 in the livestock building, compost facility, and manure storage tank, demonstrating a good correlation because they had the same origin. The concentrations of VFAs were higher in the livestock building than in the compost facility and manure storage tank because of the leftover feed and high temperature in the livestock building, which causes carbohydrates and proteins in the manure to undergo catabolism and initiates anaerobic degradation processes [25].

3.6. Phenolic and Indole Compounds

PHE and PHE compounds such as p-CRE occur during the bacterial degradation of amino acids such as tyrosine and phenylalanine in the animal intestine [26]. The metabolism of tryptophan produces IND acetate, which is converted to SKT (3-methyl IND) and IND by several types of bacterial flora [10].

The concentration of PHE was prevalent in the following order (Figure 7): growing pig house (12.4 ± 4.8 ppb) > finishing pig house (11.4 ± 4.8 ppb) > nursery pig house (6.4 ± 1.5 ppb) > manure storage tank (5.0 ± 3.7 ppb) > compost facility (2.9 ± 2.2 ppb). The PHE concentration was high in the livestock building. However, p-CRE had a high concentration in the manure storage tank, while showing a concentration pattern in the following order: manure storage tank (158.8 ± 198.1 ppb) > finishing pig house (146.2 ± 68.5 ppb) > growing pig house (117.7 ± 43.7 ppb) > nursery pig house (73.8 ± 29.3 ppb) > compost facility (12.7 ± 10.5 ppb); these results indicate that PHE and p-CRE components had different patterns.

The IND and SKT components had the highest concentrations in the manure storage tank at 5.9 and 100.6 ppb, respectively, and had the lowest concentrations in the compost facility (Figure 8). The PHE, p-CRE, IND, and SKT components had low MDL concentrations at 0.28, 0.054, 0.30, and 0.0056 ppb, respectively. As SKT has a lower MDL compared to other components, it can trigger displeasure even at low concentrations when perceived by olfactory sensors.

3.7. Estimation of Odor-Causing Substances According to Pigsty Type

As malodorous substances exhibit distinct threshold limit values for each component, assessing the extent of their contribution to odor relies on the concentration of detected malodorous substances [27,28]. Primary odor-causing substances can be predicted by calculating the odor quotient (OQ). The OQ is derived by dividing the concentration of each individual malodorous substance, as determined through instrumental analysis using the threshold limit value for that particular substance, by the sum of the odor quotients (SOQ) [29]. Here, threshold limit values refer to the data provided by the Korean Ministry of Environment [4]. PHE, p-CRE, IND, and SKT have threshold limit values of 0.28, 0.054, 0.30, and 0.0056 ppb, respectively [23]. If the OQ is >10, a weak odor is perceived, but if it is >100, a strong odor is perceived. Therefore, components with an OQ of 100 or more can be considered major odor-causing substances [30].

$$\mathrm{O}\mathrm{d}\mathrm{o}\mathrm{r}\mathrm{Q}\mathrm{u}\mathrm{o}\mathrm{t}\mathrm{i}\mathrm{e}\mathrm{n}\mathrm{t}\left(\mathrm{O}\mathrm{Q}\right)=\frac{\mathrm{O}\mathrm{d}\mathrm{o}\mathrm{r}\mathrm{c}\mathrm{o}\mathrm{n}\mathrm{c}\mathrm{e}\mathrm{n}\mathrm{t}\mathrm{r}\mathrm{a}\mathrm{t}\mathrm{i}\mathrm{o}\mathrm{n}\left(\mathrm{p}\mathrm{p}\mathrm{b}\right)}{\mathrm{T}\mathrm{h}\mathrm{r}\mathrm{e}\mathrm{s}\mathrm{h}\mathrm{o}\mathrm{l}\mathrm{d}\mathrm{l}\mathrm{i}\mathrm{m}\mathrm{i}\mathrm{t}\mathrm{v}\mathrm{a}\mathrm{l}\mathrm{u}\mathrm{e}\left(\mathrm{p}\mathrm{p}\mathrm{b}\right)}$$

(1)

$$\mathrm{S}\mathrm{u}\mathrm{m}\mathrm{o}\mathrm{f}\mathrm{O}\mathrm{d}\mathrm{o}\mathrm{r}\mathrm{Q}\mathrm{u}\mathrm{o}\mathrm{t}\mathrm{i}\mathrm{e}\mathrm{n}\mathrm{t}\left(\mathrm{S}\mathrm{O}\mathrm{Q}\right)=\sum \mathrm{O}\mathrm{d}\mathrm{o}\mathrm{r}\mathrm{Q}\mathrm{u}\mathrm{o}\mathrm{t}\mathrm{i}\mathrm{e}\mathrm{n}\mathrm{t}\left(\mathrm{O}\mathrm{Q}\right)$$

(2)

$$\mathrm{O}\mathrm{d}\mathrm{o}\mathrm{r}\mathrm{C}\mathrm{o}\mathrm{n}\mathrm{t}\mathrm{r}\mathrm{i}\mathrm{b}\mathrm{u}\mathrm{t}\mathrm{i}\mathrm{o}\mathrm{n}(\mathrm{\%})=\frac{\mathrm{O}\mathrm{Q}}{\mathrm{S}\mathrm{O}\mathrm{Q}}\times 100$$

(3)

The computed OQ and SOQ values in the livestock building (nursery, growing, and finishing pig houses), compost facility, and manure storage tank are compared in

Table 4. Comparison of SOQ, OQ, and OC at the swine facilities.

	Odor Quotient (OQ)/Odor Contribution (OC%)
	Nursery Pig House	Growing Pig House	Finishing Pig House	Compost Facility	Manure Storage Tank
1st	H2S (4358/49.3)	H2S (2561/27.4)	H2S (5332/41.8)	SKT (243/18.1)	H2S (155,890/84.6)
2nd	p-CRE (1366/15.5)	p-CRE (2179/23.4)	p-CRE (2708/21.2)	p-CRE (235/17.5)	SKT (17,958/9.8)
3rd	SKT (1065/12.1)	SKT (1632/17.5)	SKT (1863/14.6)	iso-VA (197/14.7)	NH3 (3774/2.0)
4th	n-BA (638/7.2)	n-BA (1017/10.9)	n-BA (1024/8.0)	n-BA (175/13.0)	CH3SH (3248/1.8)
5th	iso-VA (466/5.3)	iso-VA (781/8.4)	iso-VA (695/5.4)	H2S (148/11.0)	p-CRE (2941/1.6)
6th	CH3SH (278/3.2)	n-VA (397/4.3)	n-VA (459/3.6)	n-VA (139/10.3)	iso-VA (142/0.1)
7th	n-VA (255/2.5)	CH3SH (322/3.5)	CH3SH (269/2.1)	NH3 (104/7.7)	n-VA (79/0.04)
8th	TMA (200/2.3)	TMA (204/2.2)	TMA (179/1.4)	CH3SH (41/3.1)	TMA (40/0.02)
9th	NH3 (153/1.7)	NH3 (122/1.3)	NH3 (123/1.0)	TMA (34/2.5)	DMS (36/0.02)
10th	PA (27/0.3)	PHE (44/0.5)	PHE (41/0.3)	PHE (10/0.8)	n-BA (24/0.01)
11th	PHE (23/0.3)	PA (41/0.4)	PA (37/0.3)	ACHO (6/0.4)	IND (20/0.01)
12th	ACHO (17/0.2)	ACHO (17/0.2)	ACHO (19/0.2)	PA (4/0.3)	PHE (18/0.01)
13th	IND (7/0.1)	IND (12/0.1)	IND (8/0.1)	PCHO (1/0.1)	ACHO (6/0.003)
14th	PCHO (5/0.1)	PCHO (2/0.02)	PCHO (2/0.02)	IND (1/0.1)	DMDS (2/0.001)
15th	DMS (1/0.01)	DMS (1/0.01)	STY (1/0.005)	DMS (1/0.1)	PCHO (2/0.001)
16th	DMDS (1/0.01)	DMDS (1/0.01)	DMDS (1/0.004)	DMDS (1/0.1)	PA (2/0.001)
17th	Others (1/0.01)	Others (0/0.003)	Others (1/0.02)	Others (3/0.2)	Others (2/0.001)
SOQ	8832	9332	12,763	1345	184,183

. The results of the calculated odor contributions are presented in Figure 8.

First, a comparison of the SOQ values of each facility indicated the following order of odor intensity: manure storage tank > finishing pig house > growing pig house > nursery pig house > compost facility, indicating that the intensity was the highest in the manure storage tank. Furthermore, a comparison of the odor index per livestock building indicated that H₂S showed the highest odor index at the nursery, growing, and finishing pig houses, followed by p-CRE, SKT, and n-BA. The main malodorous substances (OQ > 100) in the livestock buildings were the same components, such as H₂S, p-CRE, SKT, n-BA, iso-VA, CH₃SH, n-VA, TMA, and NH₃. Sulfur compounds showed the highest odor contribution (30.9–52.5%) in the livestock buildings, followed by PHEs, VFAs, INDs, and nitrogen compounds, accounting for more than 99% of the total. Therefore, five types of aldehyde compounds and seven types of VOCs were not considered key malodorous substances.

As shown in Figure 8, SKT, p-CRE, iso-VA, n-BA, H₂S, n-VA, and NH₃ were confirmed to be the primary malodorous substances (OQ > 100) in the compost facility, and SKT, which is an IND, showed the highest odor index. In the compost facility, contributions of VFAs, PHEs, INDs, sulfur compounds, and nitrogen compounds were 38.3, 18.2, 18.2, 14.2, and 10.3%, respectively.

The H₂S component had the highest odor quotient in the manure storage tank—especially H₂S and SKT, which generated strong odors with an odor quotient of over 10,000. The main malodorous substances were confirmed to be H₂S, SKT, NH₃, CH₃SH, p-CRE, and iso-VA. Sulfur compounds showed the highest odor contribution (86.4%), followed by INDs and nitrogen compounds.

4. Conclusions

This study investigated the characteristics of malodorous substances generated from a livestock building (nursery, growing, and finishing pig houses), a compost facility, and a manure storage tank on a swine farm located in a region with high concentrations of swine farms on Jeju Island. A total of 26 malodorous substances, including 22 malodorous substances designated by the Korean Ministry of Environment, two types of PHEs, and two types of INDs, which are known as key malodorous substances in swine farms, were collected and analyzed.

The concentration of NH₃ in the manure storage tank was the highest, and it caused irritation to the eyes, nose, and skin, requiring environmental and health care for workers. TMA exhibited a high concentration in the growing pig house. Four types of sulfur compounds exhibited the highest concentrations in the manure storage tank; H₂S was at levels that irritate the eyes and respiratory tract of workers. Aldehyde compounds and VOCs were not detected or were below the emission limits set by the Ministry of Environment; they were thus not considered key malodorous substances on swine farms. VFAs exhibited high concentrations in the livestock building, but low concentrations in the manure storage tank. High concentrations of p-CRE, IND, and SKT were observed in the manure storage tank, but had low concentrations in the compost facility.

Swine farms on Jeju Island mainly target and manage NH₃ and H₂S. However, in livestock buildings, sulfur compounds most significantly contribute to odor emissions, followed by VFAs, PHEs, and INDs—all of which contribute more than nitrogen compounds. In the compost facility, the contributions of VFAs, PHEs and INDs surpassed those of nitrogen or sulfur compounds, underscoring the need for the effective management of VFAs, PHEs, and INDs. Furthermore, in the manure storage tank, sulfur compounds accounted for 86.4% of the odor contribution, emphasizing the more urgent need for targeted odor management related to a series of sulfur compounds compared to other components. These findings highlight the variability in the types and quantities of odors generated depending on the specific facility within a swine farm. Therefore, we recommend tailoring odor management strategies on swine farms based on the unique characteristics of each facility and the source of emissions.