Ventilation and control of airborne pathogens in indoor environments for human and animal health

By Lingying Zhao

The COVID-19 pandemic has painfully made us recognize how critical air quality is to our health. Office buildings, classrooms, most public facilities, and even our homes are not equipped to deal with the airborne transmission of infectious diseases. One sick family member at home may put the whole household at risk. One sick worker may easily spread the virus to coworkers. One sick animal may quickly infect many other animals in large-scale animal production facilities. We need solutions to address these emerging and pressing challenges. Ventilation and/or air pollution mitigation technologies can be developed to control COVID-19 and other types of airborne infectious disease transmission in indoor spaces. Ohio State University researchers are developing innovative ventilation and air disinfection technologies for homes and animal production facilities to improve human and animal health.

Ventilation

Ventilation is an intentional air exchange process that introduces fresh air in, and exhausts stale air out, of an indoor space. It is the most fundamental means to control indoor environmental quality. Both the amount of fresh air and the uniform distribution of airflow are key factors for achieving effective ventilation. Ventilation system failures can result in unhealthy indoor environments due to lack of oxygen, uncomfortable temperatures, high concentrations of air pollutants, and presence of various pathogenic microorganisms and viruses, such as the COVID-19 virus. 

The American Society of Heating, Refrigerating and Air-Conditioning Engineers has recommended sufficient ventilation, even increased ventilation, to reduce the spread of the COVID-19 virus in enclosed spaces such as homes, airplanes, and classrooms. 

Prior to the pandemic, typical ventilation systems in offices, homes, classrooms, and animal facilities were operated under the mixing model of air distribution, which is intended to create a uniform indoor environment. However, the nature of the mixing model of air distribution also promotes transmission of airborne infectious diseases. Given this critical issue, new ventilation systems are needed to prevent transmission of airborne diseases in indoor spaces. 

For example, disease outbreak is a serious threat that the poultry industry is facing. In 2014, highly pathogenic H5 avian flu infected approximately 57 million birds in the U.S., resulting in a disastrous loss to the layer and turkey industries. It was suspected that the rapid spread of the avian flu was partially due to the fact that HPAI viruses can be transmitted through ventilation airflow within poultry houses and even between farms. The current mixing ventilation systems in poultry houses, including cross and tunnel ventilation systems, transport dust laden air throughout the poultry house and therefore cannot effectively control disease transmission. Avian flu remains a significant threat to the poultry industry and new ventilation systems are needed in layer houses to not only provide comfortable and uniform indoor environments, but also prevent significant losses due to disease outbreaks.  

OSU research on innovative ventilation

To improve indoor air quality and control disease outbreaks, an upward airflow displacement ventilation (UADV) system has been developed for commercial manure-belt layer houses. With this new ventilation system, fresh air is supplied into cages, heated up by laying hens inside the cages, moves into the aisles, flows upward in aisles,  and exits the layer house via exhaust fans installed on the roof, with minimum interactions with birds in other cages. This ventilation design creates the shortest pathways for contaminated air and efficiently removes heat, moisture, air pollutants, and viruses compared to existing tunnel and cross ventilation systems. The performance of the new UADV system was preliminarily simulated using a Computational Fluid Dynamics (CFD) model in terms of possible disease transmission under different weather conditions. It was found that the new system can reduce disease transmission probabilities from 29.8% to 2.7% in the summer and from 61.4% to 44.3% in the winter in layer houses in comparison with the existing tunnel ventilation system. Further efforts are needed to test the UADV system in commercial laying hen farms. 

Mitigation of airborne pathogens

In addition to diluting air pollutants in indoor environments and removing them from indoor spaces, directly removing air pollutants from airstreams and deactivating pathogens are necessary to improve health. In the process of ventilating office or home spaces, the majority of the air will need to be recirculated. Therefore, active cleaning of the returning air to maintain supply air free of any harmful air pollutants, especially airborne pathogens, is very important to ensuring occupant health in an indoor environment. In the process of ventilating animal production facilities, removal of dust particles and/or bioaerosols with bacteria and viruses attached is very important to maintaining human, animal, and environmental health.

Various air pollution control technologies have been used to control indoor air quality, such as high efficiency particulate air (HEPA) and activated carbon filters, ultraviolet (UV) light, and air ionization. Airborne pathogens often attach themselves to larger inert particles in the air to avoid becoming isolated in the airstream, which allows them to be active for long time and transport themselves over a long distance. Therefore, particulate matter or aerosol control is essential for effective microorganism control.

OSU has developed two type of electrostatic precipitation technologies, namely electrostatic precipitators (ESPs) and electrostatic spray scrubbers (ESS), to collect particulate matter and deactivate pathogens in poultry production facilities. ESP systems use high voltage electrodes and collection plates to form electric fields. Charged dust particles or aerosols pass through the electric fields which then collect the particles on collection plates that are oppositely charged. ESS systems use electrodes at high voltage to charge water droplets that are sprayed through the electric field. The charged droplets are then used to capture dust particles in an airstream that is slightly oppositely charged. Both the ESP and ESS technologies have been optimized for collecting dust particles in egg production facilities with more than 90% in dust removal efficiency. In addition to dust removal, the ESP and ESS technologies have potentials to deactivate pathogens directly. We are testing their performances on deactivation of pathogens in poultry production environments.  

In summary, COVID-19 pandemic reminds us that the control of pathogens in indoor environment is a critical, but challenging task that cannot be accomplished by the existing ventilation systems of buildings. Mitigation of particulate matter and airborne pathogens in animal production environments is also very critical to animal, human and environmental health. Ohio State researchers have developed an innovative upward airflow displacement ventilation (UADV) system for better indoor environmental control and more limited disease transmission in layer houses. In addition, electrostatic precipitation-based dust and pathogen control technologies are under development to improve human, animal, and environmental health. 

Lingying Zhao, Professor and Extension Agricultural Engineer, can be reached at zhao.119@osu.edu. This column is provided by the OSU Department of Food, Agricultural and Biological Engineering.

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