An electrostatic precipitator (ESP) is effective in mitigating airborne spread of pathogens under farm conditions, a new study says. Montserrat Torremorell, department chair and professor of the Department of Veterinary Population Medicine at the University of Minnesota, led this study evaluating the utility of an ESP to remove airborne particles from aerosols, including porcine reproductive and respiratory syndrome virus (PRRSV).
The study, funded by the Swine Health Information Center Wean-to-Harvest Biosecurity Research Program, in partnership with the Foundation for Food & Agriculture Research and Pork Checkoff, demonstrated high effectiveness, comparable to or slightly exceeding a MERV-16 filter, in removing airborne particles and over 99% removal of PRRSV.
According to SHIC, the study focused on assessing the detailed capabilities of the ESP system to remove airborne particles. When compared to the MERV-16, respected for high-efficiency filtration in controlled environments, the ESP prototype achieved similar or enhanced performance using its non-mechanical, electrostatic method.
“These results suggest potential opportunities for farms to shift to technologies that would be highly effective without the rapid pressure drop and replacement burden associated with using mechanical air filtration,” researchers report.
The Set-Up
A commercially available ESP was used and tested for its ability to collect airborne particles in the ASHRAE 52.2 wind tunnel in the UMN Department of Mechanical Engineering. Not only was the ESP assessed in a controlled laboratory setting to assess the particle collection efficiency but it also confirmed particle size distribution.
SHIC says the size distribution measurements were conducted using a Size Mobility Particle Scanner and Optical Particle Scanner, covering a particle range from 10 nm to 10 µm.
“After laboratory characterization of the ESP was completed, the ESP was installed within a wean-to-finish barn,” the researchers say. “The barn was mechanically ventilated and used air filtration in the inlets, which were located in the attic. To evaluate the ESP performance, the filter bank in one of the ventilation boxes was replaced with the ESP setup.”
To evaluate the ESP’s performance in capturing viruses in the field, PRRSV was aerosolized and introduced at the ESP inlet. Two trials were performed at a temperature of 59 °F with 47% relative humidity. The airflow rate was maintained at 1200 cfm. After collection, samples were analyzed for viable virus by titration and for viral RNA through PCR testing, the study says.
How Did it Work?
With an above 99% collection efficiency for particles greater than 1 µm, the ESP was determined to be highly effective. For particles less than 1 µm, collection efficiency varied by temperature, with higher efficiencies generally observed at lower temperatures.
The on-farm feasibility assessment using the ESP under field conditions included a cost comparison of purchasing, installing and operating the equipment compared to those of air filtration. Other considerations included operational sustainability as well as the upkeep and maintenance of the equipment, the researchers report. ESPs operate by electrically charging and collecting particles onto plates and must be regularly cleaned to maintain efficiency.
An economic analysis including assumptions on acquisition, installation, operation, maintenance and replacements costs for the ESP and filter systems, concluded that the ESP system had a $299,553 greater net present value over a 15-year period, resulting in approximately $0.25 additional cost per weaned pig, when compared to air filtration.
“This costing model is based on the assumptions around current technology,” the study says. “Future engineering advances may make this model more economically viable in the future.”
Scalability of the ESP for on-farm use involves moving the technology from laboratory- or pilot-scale units to systems capable of handling the significant air volumes necessary for large commercial farms. Experts say this requires robust engineering solutions that maintain high efficiency of ESP while operating continuously under real-world weather and climate variability.
“Overall, the ESP tested in this study was highly effective at removing airborne particles with collection efficiencies similar and marginally superior to those of a MERV-16 filter,” SHIC reports. “The path to commercialization and more broad scale use of ESP is dependent upon successfully resolving the complex logistical and engineering challenges of scalability, design integration, long-term maintenance, and cost-effectiveness for producers. Further commercial exploration is needed to fully optimize ESP designs and maintenance protocols for practical applications to improve biosecurity within commercial pig farms.”
