1. Introduction
The poultry industry is transforming towards more sustainable and ethical practices, driven by consumer demand for ethically sourced products and heightened concerns about animal welfare [
1,
2,
3,
4]. Cage-free (CF) housing systems have emerged as a promising alternative to caged housing environments, offering hens the freedom to roam, perch, and engage in natural behaviors, leading to improved welfare and potentially enhanced egg production. Despite the numerous benefits, adopting CF systems introduces new challenges, particularly in ensuring optimal indoor air quality (e.g., particulate matter) within hen houses [
5,
6,
7,
8].
The accumulation of particulate matter (PM) constitutes a significant concern in CF environments, encompassing various airborne pollutants such as dust, feathers, and dander [
6,
9,
10,
11]. These particles can adversely affect the respiratory health of hens, leading to respiratory issues, reduced productivity, and compromised well-being [
12,
13,
14,
15,
16]. Moreover, PM poses health risks to farmworkers [
6,
15,
17,
18], contributes to environmental pollution [
15,
19], and may affect the safety and quality of egg products, ultimately impacting consumer trust. Addressing this pressing concern requires innovative air quality management solutions that effectively reduce PM emissions while maintaining a conducive and healthy indoor environment for the hens. Researchers and practitioners have explored various technologies to mitigate PM in poultry facilities, each with their own level of efficacy. These measures include oil and water spraying [
20,
21,
22,
23], scrubbers [
24], air filtration [
25,
26,
27], proper manure management [
28,
29], and electrostatic particle ionization (EPI) [
30,
31,
32,
33].
Oil spraying systems with handheld spraying lances have shown the capability to remove up to 94% of PM
2.5 (PM size ≤ 2.5 µm) and 82% of PM
10 (PM size ≤ 10 µm) [
34]. However, the mixture of oil and PM is trapped inside housing necessitating frequent house cleaning to prevent worker hazards. Acidic electrolyzed water spraying systems have demonstrated up to 89% removal efficiencies for total PM in CF poultry facilities [
23]. Wet scrubbers with packed-bed configurations exhibit high removal efficiencies of up to 90% for PM
2.5 and 93% for PM
10 [
24], but they tend to become easily clogged, require significant water usage, and raise concerns over liquid waste compared to the air pollution problem. Filtration is a commonly used technique, effectively removing up to 60% of fine dust in poultry layer facilities [
35]. However, this method is susceptible to frequent clogging and particle resuspension.
Among the emerging technologies, electrostatic charging systems have garnered attention as a potential solution to reduce airborne particles in various experimental and commercial settings [
30,
31,
32,
33,
34,
36,
37,
38,
39]. Electrostatic particle ionization systems utilize electrostatic charges to attract and neutralize airborne particles, providing a promising avenue for mitigating PM in CF henhouses. Studies have reported significant PM reductions in broiler houses, with electrostatic charging systems achieving up to 43% reduction in PM levels [
31]. Research in other broiler houses demonstrated a reduction of 36% for PM
10 and 10% for PM
2.5 using an electrostatic charging system [
38]. Furthermore, specific studies have evaluated electrostatic charging systems’ effectiveness in hatching cabinets, with a reduced dust concentration of up to 79% [
37]. In a recent study, a prototype electrostatic precipitator effectively reduced the levels of PM
2.5 and PM
10 up to 97.8% and 99.0%, respectively [
40]. Similarly, Bist et al. [
39] found that the EPI with the longest length had reduced PM
2.5 by 31.7% and PM
10 by 32.7%, respectively.
Despite these promising findings, the application of EPI in CF hen houses remains relatively unexplored, necessitating comprehensive research to evaluate its efficacy and practical implementation. The success of EPI technology in this specific context is influenced significantly by crucial factors such as the facility’s layout and the height at which the electric supply is situated above the litter floor. However, the efficacy of EPI technology with respect to height in CF hen houses has yet to be fully explored. Ritz et al. (2006) recommend placing the EPI technology closer to the litter floor where dust is generated. In this study, the goal is to evaluate the effectiveness of EPI technology in reducing PM concentration while considering the height at which the technology is placed. Similarly, several studies used 24 h of electric supply [
30,
31,
38,
39]. However, it is worth questioning whether running the system 24 h a day is necessary, especially when the birds show no activity during the dark period. Thus, the hypothesis is that the reduction in PM concentration significantly depends on the duration of the electricity supply and the height at which EPI technology is placed. Hence, the objectives of this research study were to:
- (a)
Test the effect of EPI on dust control with a particular emphasis on the influence of varying electric supply durations and system installation heights in research CF facilities.
- (b)
Investigate the optimal management of EPI system for dust control for CF hens;
- (c)
Analyze the power consumption of the EPI system and its correlation with the duration of electric supply employed within CF hen facilities.
The findings of this study aim to provide practical insights that can guide poultry farmers and industry stakeholders in developing effective air quality management strategies, ultimately fostering improved animal welfare, increased egg production, and sustainable practices in the poultry industry. This research can potentially drive significant advancements toward a more responsible and ethical approach to egg production by addressing the crucial challenge of maintaining optimal indoor air quality in CF environments.
2. Materials and Methods
2.1. Ethical Approval
Before commencing the study, all procedures were approved by the Institutional Animal Care and Use Committee at the University of Georgia.
2.2. Experimental Setup
The study was conducted at the University of Georgia Poultry Research Center in a laying hen facility with four identical rooms. Each room measured 7.3 m long, 6.1 m wide, and 3.1 m high (
Figure 1a). Within these rooms, 720 laying hens (Hy-line W-36) were placed at a higher stocking density than the recommended minimum space to promote their natural behaviors. The study focused on hens aged 68 to 76 weeks of age. The care and management of the hens adhered to the Hy-Line W-36 commercial layers management guidelines. In addition, each room was provided with pine wood shavings as bedding and A-shaped perches. The rooms were equipped with Chore-Tronics Model 8 controllers to regulate temperature, lighting, and ventilation rates, with exhaust ventilation fans and a heater programmed to control temperature and relative humidity. The light turned on at 5 am and turned off at 9 pm, providing a 16 h light period. Circulating fans were used to ensure continuous air and temperature distribution. In addition, the EPI system was hung from the ceiling and connected to the EPI device (EPIAir, Columbia, MO, USA) for particle ionization (
Figure 1b).
2.2.1. Experiment 1
Experiment 1 utilized the Latin Square Design (LSD) method to conduct the study, considering the limited availability of rooms (
Table 1). The available rooms were provided with four distinct height treatments of EPI: 5 feet (H1 = 1.5 m), 6 feet (H2 = 1.8 m), 7 feet (H3 = 2.1 m), and 8 feet (H4 = 2.4 m) above the litter floor. These heights were selected based on suggestions from previous studies, including 7 ft [
31] and 8 ft [
30,
38], and additional heights of 5 ft and 6 ft, closer to the average human height, were also included. The lower heights were recommended by Ritz et al. [
31] for increased dust reduction efficiency. However, the 9 ft EPI height was not used due to the presence of different equipment in the experimental rooms, and heights below 5 ft were avoided to prevent harm to the hens as they tend to jump and fly around. A manual winch was installed to adjust the EPI height, allowing caretakers to raise or lower the system safely when entering the farm to avoid accidents. Each trial lasted one week and involved a continuous electricity supply throughout the treatment rooms except for control. To ensure the hens did not sit on the corona pipe, bird-repellent spikes were thoughtfully placed above it. In addition, the EPI system was carefully positioned 0.3 m away from the walls and 2.4 m away from each other to minimize electric field effects on nearby objects. The configuration involved two rows of 5.5 m long corona pipes, resulting in 11 m for the entire EPI system.
2.2.2. Experiment 2
Experiment 2 employed the LSD, dividing the rooms into four different treatments: control (D1), 8 h (D2), 16 h (D3), and 24 h (D4) of EPI operation (
Table 2). These durations were selected based on several studies that used a 24 h electric supply [
30,
31,
38]. However, considering that laying hen housing provided a 16 h light period, it is worth questioning whether running the system 24 h a day is necessary, especially when the birds show no activity during the dark period (8 h). Moreover, the inclusion of an 8 h duration treatment was based on the half-light period time to assess whether using 8 h can yield similar PM reduction compared to other treatments. Each trial lasted one week, and an EPI system was placed at 8 feet to accommodate existing equipment in the rooms.
2.3. Working Mechanism of EPI
Electrostatic particle ionization technology offers a revolutionary approach to improving air quality by releasing negative ions into the surrounding atmosphere. These negative ions play a critical role in charging and surrounding airborne particles, causing them to be attracted to grounded or negatively charged surfaces. As a result, the charged particles either adhere to surfaces or settle on the ground, leading to noticeably cleaner and safer air to breathe. EPI systems include a 2.0 mA power supply, a sharp-point corona pipe, insulators, and a −30 KV high-voltage direct current with a current limit of 2 mA for safety [
41]. This highly cost-effective technology operates with power consumption comparable to a 100-watt light bulb and can connect to standard electrical services. EPI systems emit an impressive volume of negative ions (10
16 ions/second) into the air, effectively saturating airborne particles and inducing charge shifts. This process causes PM to adhere to surfaces or descend to the ground, significantly improving air cleanliness. Designed specifically for agriculture, EPI technology creates a protective barrier in the airspace, safeguarding animals and workers from various airborne contaminants. Treating airspace with negative ions naturally attracts and polarizes airborne particles, facilitating their bonding and adhesion to surfaces they encounter. The details of the EPI system were mentioned in [
39].
2.4. Electricity Consumption by EPI
This research focused on examining EPI system’s power consumption and its relation to the duration of the electric supply in the laying hen facility. The study aimed to understand how the duration and height of the electric supply influence the EPI system’s power consumption in this specific context. In Experiment 1, the length and duration of EPI systems were the same, resulting in no difference in electric consumption. However, the duration of the EPI system is critical information that holds significance for poultry producers, as it facilitates the selection of an appropriate EPI duration that balances effectiveness in mitigating airborne pollutants with energy expenditure. The digital power monitor meter (Zhengzhou Paiji Technology, Henan Province, China) was used in each treatment room to measure electricity consumption accurately. This meter operated at 120 V, 60 Hz, and up to 15 A, providing real-time data of the EPI system’s power use. The power consumption analysis was carried out throughout the study to assess the power requirements and efficiency of the EPI system. Monitoring electricity usage in kilowatt-hours (KWh) provides valuable insights into the relationship between the duration of the electric supply and the EPI system’s energy consumption. These findings play a crucial role in assisting poultry producers in making informed decisions, enabling them to optimize the air quality management in their facilities while ensuring energy conservation and sustainable poultry production practices.
2.5. Environment Parameter Measurements
Temperature and relative humidity (RH) of inside and outside rooms were monitored using Onset HOBO data loggers programmed to continuously collect data every 10 min. Data loggers were placed 1.2 m above the floor inside the room and 1.8 m above the ground outside. Temperature and RH data were monitored daily via phone to ensure a comfortable environment for the birds.
The litter moisture content (LMC) significantly impacts the levels of air pollutants within poultry housing. To measure the LMC, 100 g litter samples were collected weekly from four locations within each room and placed into Ziplock bags. The detailed procedure for LMC analysis is mentioned in [
39].
2.6. Particulate Matter Measurement
PM levels were monitored twice a week using an optical PM sensor, specifically the DustTrak DRX Aerosol Monitor 8533 from TSI Incorporated in Shoreview, MN, USA. The PM sensor was capable of measuring various sizes of PM, including PM1 (PM size ≤ 1 µm), PM2.5 (PM size ≤ 2.5 µm), PM4 (PM size ≤ 4 µm), PM10 (PM size ≤ 10 µm), and TSP (Total Suspended Particulates; PM size ≤ 100 µm), allowing for a comprehensive assessment of airborne pollutants. The measurements were taken at three locations inside each room, strategically chosen to represent different activity areas and potential particle concentrations. These locations included positions near the perch, between the feeder and drinker, and near the exhaust ventilation. For Experiment 1, we collected the PM data twice a week and only once during the sampling day at three different locations. For Experiment 2, we collected the PM data twice a week and four times during the sampling day (1 h before and after the first 8 h of the light period, and 1 h before and after the 16 h of the light period, which also included the dark period PM data) at three different locations.
Specific protocols were strictly followed before each measurement to ensure the accuracy and reliability of the data collected. The PM sensor was carefully positioned at a consistent height of 36 cm above the floor and covered with a protective plastic shield to prevent dust buildup or external interference that might compromise the readings. Furthermore, to maintain precise calibration and data integrity, the PM sensor underwent manufacturer calibration before the research commenced, and regular maintenance was upheld throughout the study. This maintenance routine involved periodic cleaning and filter replacement every two weeks. The first 30 s of each reading were excluded from the data analysis process to avoid potential interference from sensor relocation within the rooms during the initial measurement moments. By adhering to these rigorous procedures, the research team ensured that the collected PM measurements provided accurate and reliable insights into the indoor air quality of the laying hen facility.
2.7. Statistical Analysis
In this research, four floor-raised rooms were arranged in an LSD way, with room and trial serving as blocking factors, and four different EPI heights (H1, H2, H3, and H4) or electric supply durations (D1, D2, D3, and D4) considered as treatments. Statistical analyses were conducted using R-studio (version 4.1.0) to assess the impact of varying heights or electric supply durations on PM levels, litter moisture content (LMC), and electricity consumption within the laying hen facility. ANOVA was employed to analyze the PM, LMC, and electricity consumption data collected from each room, followed by post hoc analysis using the LSMeans Tukey HSD method to determine significant differences between the treatments. Differences were considered significant at a
p-value of ≤0.05. The study aimed to gain insights into the effectiveness of EPI technology in mitigating airborne pollutants and maintaining optimal litter conditions, providing valuable information for enhancing indoor air quality and overall well-being in the laying hen environment.
where:
i = 1,…,
K;
j = 1,…,
K,
l = 1,…,
K;
K represents the Latin letter for treatment in the (
i,
j)th cell of the Latin Square;
Yijk represents the LMC, PM, or electricity consumption corresponding to
Kth Latin letter in the (
i,
j)th cell;
μ is the overall mean of the LMC, PM, or electricity consumption;
αi is the effect of
ith rooms;
βj is the effect of jth trials or WOA; γ
l is the effect of
lth EPI heights or electric supply duration; and
εijk represents the random error term corresponding to
Kth Latin letter in the (
i,
j)th cell.
4. Conclusions
The study’s results demonstrated that the EPI system consistently reduced PM concentrations within CF hen rooms, irrespective of the height at which it was implemented. This finding indicates that the EPI system’s performance remained stable and uniform, providing effective PM reduction across all tested heights. On the other hand, the duration of EPI system operation significantly influenced PM1, PM2.5, and PM4 concentrations, with longer durations leading to more substantial reductions. While PM10 and TSP did not show statistically significant variations, trends suggested a reduction in PM concentrations with extended operation. Therefore, employing the EPI system for a prolonged period is essential for achieving enhanced PM reduction.
Despite the benefits of 24 h EPI system usage, the study highlighted that continuous electric supply did not show significant differences compared to using the EPI system for 16 h. This observation presents an important practical implication concerning energy consumption. Opting for 16 h EPI system operation during daylight can lead to significant energy cost savings without compromising the system’s effectiveness in reducing PM. Considering the need for sustainable practices, this insight can guide decision-makers in the poultry industry to strike a balance between achieving effective PM reduction and managing energy consumption. Nevertheless, the study acknowledges the scope limitations and suggests further research to explore additional factors, such as the impact of animal activities on PM dynamics within the EPI system. By gaining a more comprehensive understanding of PM generation and neutralization in relation to hen activities, researchers can optimize PM reduction strategies and contribute to improved air quality and environmental protection in CF hen houses.