Enhancing Dust Control for Cage-Free Hens with Electrostatic Particle Charging Systems at Varying Installation Heights and Operation Durations

: The poultry industry is shifting towards more sustainable and ethical practices, including adopting cage-free (CF) housing to enhance hen behavior and welfare. However, ensuring optimal indoor air quality, particularly concerning particulate matter (PM), remains challenging in CF environments. This study explores the effectiveness of electrostatic particle ionization (EPI) technology in mitigating PM in CF hen houses while considering the height at which the technology is placed and the duration of the electric supply. The primary objectives are to analyze the impact of EPI in reducing PM and investigate its power consumption correlation with electric supply duration. The study was conducted in a laying hen facility with four identical rooms housing 720 laying hens. The study utilized a Latin Square Design method in two experiments to assess the impact of EPI height and electric supply durations on PM levels and electricity consumption. Experiment 1 tested four EPI heights: H1 (1.5 m or 5 ft), H2 (1.8 m or 6 ft), H3 (2.1 m or 7 ft), and H4 (2.4 m or 8 ft). Experiment 2 examined four electric supply durations: D1 (control), D2 (8 h), D3 (16 h), and D4 (24 h), through 32 feet corona pipes. Particulate matter levels were measured at three different locations within the rooms for a month, and statistical analysis was conducted using ANOVA with a signiﬁcance level of ≤ 0.05. The study found no signiﬁcant differences in PM concentrations among different EPI heights ( p > 0.05). However, the duration of EPI system operation had signiﬁcant effects on PM 1 , PM 2.5 , and PM 4 concentrations ( p < 0.05). Longer EPI durations resulted in more substantial reductions: D2—17.8% for PM 1 , 11.0% for PM 2.5 , 23.1% for PM4, 23.7% for PM 10 , and 22.7% for TSP; D3—37.6% for PM 1 , 30.4% for PM 2.5 , 39.7% for PM 4 , 40.2% for PM 10 , and 41.1% for TSP; D4—36.6% for PM 1 , 24.9% for PM 2.5 , 38.6% for PM 4 , 36.3% for PM 10 , and 37.9% for TSP compared to the D1. These ﬁndings highlight the importance of prolonged EPI system operation for enhancing PM reduction in CF hen houses. However, utilizing 16 h EPI systems during daylight may offer a more energy-efﬁcient approach while maintaining effective PM reduction. Further research is needed to optimize PM reduction strategies, considering factors like animal activities, to improve air quality and environmental protection in CF hen houses.


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].
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.

Ethical Approval
Before commencing the study, all procedures were approved by the Institutional Animal Care and Use Committee at the University of Georgia.

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).
(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.

Ethical Approval
Before commencing the study, all procedures were approved by the Institutional Animal Care and Use Committee at the University of Georgia.

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).

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

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.

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.

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].

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.

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].

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 PM 1 (PM size ≤ 1 µm), PM 2.5 (PM size ≤ 2.5 µm), PM 4 (PM size ≤ 4 µm), PM 10 (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.

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; Y ijk 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; α i is the effect of ith rooms; β j is the effect of jth trials or WOA; γ l is the effect of lth EPI heights or electric supply duration; and ε ijk represents the random error term corresponding to Kth Latin letter in the (i,j)th cell.

Experiment 1 3.1.1. Environment Parameters
The study compared the influence of different EPI height treatments (H1, H2, H3, and H4) on temperature, RH, and the LMC (Table 3).The study observed slight variations in temperature among the different treatments.The average values ranged from 21.82 • C for H2 to 23.19 • C for H1.The differences observed could be attributed to various factors, including the heat generated using the different treatments.Similarly, the study identified slight differences in RH levels among the various treatments.The average RH values ranged from 43.94% for H2 to 47.64% for H1.As with temperature, these differences in RH, although relatively small, can impact certain experiments or processes sensitive to humidity variations.
Contrary to the observed variations in temperature and RH, there were no significant differences in LMC among the treatments (p = 0.946), and percentages ranged from 10.05% to 10.36% across all treatments.One possible explanation for the consistent LMC values across treatments could be the environmentally controlled housing [6,42] and the same length of EPI system used.The housing system's ability to regulate temperature and RH precisely may contribute to the stable LMC observed in the study.The controlled housing minimizes external factors that could otherwise influence humidity levels, ensuring a reliable and reproducible experimental environment.

PM Concentration
The study's results showed no statistically significant differences in PM concentrations among different heights within the EPI system, indicating that the treatments (H1, H2, H3, and H4) did not cause substantial variations in PM levels (Table 4).The controlled parameters, including an equal corona pipe length and uniform discharge of charged particles, likely ensured the consistent exposure and interaction of air pollutants with the EPI system, leading to a relatively uniform neutralization of PM throughout the treatment (Figure 2).As a result, the treatments consistently reduced PM 1 , PM 2.5 , PM 4 , PM 10 , and TSP levels, regardless of the height of implementation.However, it is crucial to acknowledge the study's limited scope, focusing on specific treatments within the EPI system.Further investigations are needed to comprehensively understand PM dynamics and potential PM mitigation strategies.

Environment Parameters
The study compared temperature, RH, and the LMC of different EPI duration treatments (D1, D2, D3, and D4).The rooms exhibited similar temperatures across all treatments, with average values ranging from 22.54 to 23.24 °C (Table 5).Additionally, the RH levels in the rooms were consistent, showing average values between 43.58% and 48.10%.These findings suggest that the environmentally controlled housing significantly provided consistent temperature and humidity levels throughout the study period [6,42], irrespective of the treatment applied.Note: EPI-electrostatic particle ionization; CF-cage-free; H1 = 5 ft (1.5 m), H2 = 6 ft (1.8 m), H3 = 7 ft (2.1 m), and H4 = 8 ft (2.4 m) high above the litter.PM-particulate matter; PM 1 -PM with a diameter of ≤1 micrometer, PM 2.5 -PM with a diameter of ≤2.5 micrometers, PM 4 -PM with a diameter of ≤4 micrometers, PM 10 -PM with a diameter of ≤10 micrometers, TSP-Total Suspended Particles.

Experiment 2 3.2.1. Environment Parameters
The study compared temperature, RH, and the LMC of different EPI duration treatments (D1, D2, D3, and D4).The rooms exhibited similar temperatures across all treatments, with average values ranging from 22.54 to 23.24 • C (Table 5).Additionally, the RH levels in the rooms were consistent, showing average values between 43.58% and 48.10%.These findings suggest that the environmentally controlled housing significantly provided consistent temperature and humidity levels throughout the study period [6,42], irrespective of the treatment applied.Note: EPI-electrostatic particle ionization; CF-cage-free; RH-relative humidity; LMC-litter moisture content; D1 = control (0 h), D2 = 8 h, D3 = 16 h, and D4 = 24 h electric supply into EPI corona pipes.
Furthermore, the study found consistent LMC values across all treatments, with average percentages ranging from 10.55% to 11.12%.The absence of statistically significant differences in LMC among the treatments (p = 0.731) further supports the notion that the housing system maintained a stable and uniform moisture content within the EPI system.Thus, it highlights the housing system's robust performance in controlling and stabilizing humidity levels, resulting in a constant and optimal LMC across the different treatments.Overall, the study's results demonstrate that similar environmentally controlled housing tended to yield similar temperature and RH levels [6,43] with comparable LMC percentages, providing valuable insights into the importance of environmentally controlled housing systems in offering reliable and reproducible experimental conditions.This benefit significantly contributes to research endeavors that demand a consistent and stable environment.

PM Concentration
The study aimed to evaluate the impact of different durations of the EPI system operation on PM concentrations, specifically focusing on PM 1 , PM 2.5 , PM 4 , PM 10 , and TSP.The results revealed significant differences in PM concentrations among the various durations for PM 1 , PM 2.5 , and PM 4 (p-values: 0.0103, 0.0074, and 0.0473, respectively), while PM 10 and TSP did not show statistically significant variations at the 5% significance level (Table 6; Figure 3).In the control treatment (D1), the average concentrations of PM 1 , PM 2.5 , PM 4 , PM 10 , and TSP were measured as 2.98 ± 0.49 mg/m 3 , 2.83 ± 0.39 mg/m 3 , 3.63 ± 1.1 mg/m 3 , 6.59 ± 2.25 mg/m 3 , and 16.80 ± 5.59 mg/m 3 , respectively.Comparing the other treatments (D2, D3, and D4) to D1, the percentage reductions were calculated to better understand the differences in PM levels.The 8 h duration treatment (D2) showed reductions of 17.8% for PM 1 , 11.0% for PM 2.5 , 23.1% for PM 4 , 23.7% for PM 10 , and 22.7% for TSP.With a 16 h duration (D3), the reductions significantly increased to 37.6% for PM 1 , 30.4% for PM 2.5 , 39.7% for PM 4 , 40.2% for PM 10 , and 41.1% for TSP.The 24 h duration treatment (D4) resulted in percentage reductions of 36.6% for PM 1 , 24.9% for PM 2.5 , 38.6% for PM 4 , 36.3% for PM 10 , and 37.9% for TSP compared to the control.During nighttime, when the lights are off and no activities are taking place, there is minimal opportunity for PM emissions to occur [6,44], resulting in negligible differences between D3 and D4.These findings suggest that extending the EPI system operation duration can substantially reduce PM 1 , PM 2.5 , and PM 4 concentrations, essential for effective air quality management and environmental protection efforts.However, further investigation is needed to better understand the factors influencing PM 10 and TSP concentrations and optimize PM reduction strategies.

Electricity Consumption
The study's results demonstrated significant variations in the electric consumption of the EPI system based on its operation duration (p < 0.001, Figure 4).The system consumed 3.79 ± 0.25 Kwh for 8 h, 7.58 ± 0.58 Kwh for 16 h, and the highest energy consumption of 11.37 ± 0.48 Kwh for 24 h throughout the EPI treatment.The findings underscore the direct correlation between operation duration and energy consumption, with longer durations requiring more energy to sustain the treatment process.As decision-makers evaluate the optimal operation duration for the EPI system, it becomes crucial to carefully weigh the bal- Although PM 10 and TSP did not show statistically significant variations among treatments at the 5% significance level, they exhibited a trend toward reducing PM concentrations.However, at a 10% significance level, these treatments significantly reduced PM concentrations, highlighting the importance of a prolonged duration of operation for enhanced PM reduction.Longer durations may lead to a higher release of charged particles, resulting in more effective PM neutralization.Interestingly, there was no significant difference between D1 and D2, as well as among D2, D3, and D4.The lack of difference between D3 and D4 could be attributed to the absence of hen activities during the dark period [6,44].As the activities of hens were limited during the dark period, this could have contributed to the similarity in PM concentration between D3 and D4.Therefore, the EPI duration of D3 seems to be a promising duration requirement with minimum electricity consumption in mitigating PM and enhancing sustainability.However, further research is necessary to explore additional variables and external factors, including the impact on animal activities and behaviors.

Electricity Consumption
The study's results demonstrated significant variations in the electric consumption of the EPI system based on its operation duration (p < 0.001, Figure 4).The system consumed 3.79 ± 0.25 Kwh for 8 h, 7.58 ± 0.58 Kwh for 16 h, and the highest energy consumption of 11.37 ± 0.48 Kwh for 24 h throughout the EPI treatment.The findings underscore the direct correlation between operation duration and energy consumption, with longer durations requiring more energy to sustain the treatment process.As decision-makers evaluate the optimal operation duration for the EPI system, it becomes crucial to carefully weigh the balance between achieving effective PM reduction and the associated increase in energy consumption.Therefore, the D3 treatment results in appropriate treatment to reduce similar PM reduction with significantly less electric consumption than D4.The EPI system has demonstrated effective PM reduction capabilities, and the study highlights the importance of evaluating its energy consumption to ensure overall sustainability and cost-effectiveness.Therefore, energy saving reduces the electricity cost to poultry producers [45].Achieving a balance between desired PM reduction and energy conservation measures will be pivotal for implementing the EPI system on a larger scale and maximizing its benefits in improving air quality and promoting environmental protection.

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 ex-

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 PM 1 , PM 2.5 , and PM 4 concentrations, with longer durations leading to more substantial reductions.While PM 10 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.

Figure 3 .
Figure 3. Impact of EPI duration treatments on PM concentrations in CF rooms with varying hen's weeks of age.EPI-electrostatic particle ionization; CF-cage-free; RH-relative humidity; LMC-litter moisture content; D1 = control (0 h), D2= 8 h, D3 = 16 h, and D4 = 24 h electric supply into EPI corona pipes; PM-particulate matter; PM 1 -PM with a diameter of ≤1 micrometer, PM 2.5 -PM with a diameter of ≤2.5 micrometers, PM 4 -PM with a diameter of ≤4 micrometers, PM 10 -PM with a diameter of ≤10 micrometers, TSP-Total Suspended Particles.

Figure 4 .
Figure 4. Electricity consumption differences between EPI durations during the entire study.Different alphabets in the figure represent significantly different.

Figure 4 .
Figure 4. Electricity consumption differences between EPI durations during the entire study.Different alphabets in the figure represent significantly different.

Table 1 .
Experimental LSD setup for EPI heights among four CF hen experimental rooms.

Table 2 .
Experimental setup for EPI duration electric supply in four CF hen experimental rooms using LSD.

Table 3 .
Environmental parameters in CF hen rooms with varying EPI heights.

Table 5 .
Environmental parameters in CF hen rooms with varying EPI duration.

Table 4 .
Effect of EPI heights on PM concentrations (mg m −3 ) in CF hen rooms.

Table 5 .
Environmental parameters in CF hen rooms with varying EPI duration.

Table 6 .
Effect of EPI duration treatments on PM concentrations (mg m −3 ) in CF hen rooms.