Improved and virus-disabling air filtration systems

Summary

The virus that causes COVID-19 can be spread from one person to another through tiny particles of water called aerosols and the virus. We make these aerosols when we breathe and more when we talk, shout or sing. Aerosols are different from larger droplets that spread COVID-19. Larger droplets fall to the ground quickly, going three to six meters away from the person making them. Aerosols can float in the air for hours and travel long distances. Aerosols contain fewer viruses than larger droplets, so you have to inhale more aerosols to get sick. Aerosols can build up if the air inside is not circulated properly. Airborne transmission of viruses increases during the winter months because people spend more time indoors and it is often too cold to keep windows open. In winter, the air is drier, especially in heated interiors. Dry air damages the lining of the respiratory tract and can facilitate the entry of the virus into the airways. It also means that smaller aerosols float longer in the air. Therefore, airborne transmission of COVID-19 is expected to be more common during the winter months. If you are not fully vaccinated, wearing face masks and staying at least one meter away from other people, as well as good air circulation (ventilation) in buildings, schools and homes, and air purifiers made using nanotechnology will reduce the spread of COVID-19 in aerosols.

Key words/phrases:  air filtration systems, nanotechnology, COVID-19

1. Introduction

COVID-19 has forced the human population to rethink the way of life. The threat posed by the potential spread of the virus through the airborne mode of transmission through ventilation systems in buildings and confined spaces has been recognized as a major concern. To mitigate this threat, researchers have discovered different technologies and methods that can eliminate or reduce the concentration of the virus in ventilation systems and indoor spaces. Although many technologies and methods have already been researched, some are currently commercially available, but their effectiveness and safety concerns have not been fully investigated. This article contains a brief review of various applicable technologies and methods for combating airborne viruses in ventilation systems and indoor spaces, in order to gain a broader view and overview of the current research and development situation. It includes efficient air filtration, air ionization, environmental control, ultraviolet germicidal irradiation, non-thermal plasma and reactive oxygen species, filter coatings, chemical disinfectants and heat inactivation. In this article, information will be given about air filtration systems that prevent viruses.

COVID-19 has forced the human population to adapt rapidly in the wake of the new and highly contagious virus. The modes of transmission are not fully understood; however, it is accepted that the virus can be transmitted into the air by direct contact with another person or by evaporating respiratory droplets as droplet nuclei that can remain suspended for a long time as aerosols [23, 20, 7]. These aerosols may pass through ventilation systems in buildings and confined spaces, eventually invading other areas away from infected persons [6, 14]. While there is some debate about the seriousness of the threat posed by these airborne droplets, it is recognized that this form of transmission for typically confined spaces cannot be ignored. Moreover, a recent study even suggests that airborne transmission may be the dominant mode of transport (Fig. 1) [6].

Although COVID-19 is not fully understood, many lessons have been learned from previous airborne viruses such as tuberculosis and various strains of influenza [14, 21]. From a very basic understanding of how viruses spread, it follows that a certain amount of virus must enter an uninfected individual in order to increase the viral load and establish a new infection. Traditionally, this is defined in the epidemiological literature as a quantum, the number of infectious airborne particles required to infect 63% of individuals in a confined space [22], and serves as a baseline criterion for many models attempting to quantify the probability of infection without exposure to a pathogen. This model is based on a well-mixed chamber assumption supported in the literature [19, 2, 26]. And it simply assumes that the particles are uniformly dispersed throughout an enclosed space rather than creating a small cloud of aerosols that diffuse around an infected individual. The spread and effect of the infection are determined by factors such as viral load, inhalation rate, droplet volume concentration expelled from the infected individual, the number of viral particles required to initiate an infection, and the volume of the enclosed space.

Figure 1. Risk of infection by airborne droplets.

Mathematically, the quantum emission rate is determined by viral load, inhalation rate, droplet volume concentration expelled from the infected individual, and the number of viral particles required to initiate an infection. The effects to reduce the possibility of infection are factors such as air exchange, air filtration rate, droplet settling, droplet settling rate, inactivation rate, and particle radius.

Therefore, several key factors can be considered as possible methods of removing viral particles from a confined space to reduce the likelihood of an infection. These are (Fig. 2):

• increase the supply of fresh air and consequently decrease the quantum concentration;
• increase the filtration rate for an HVAC system;
• increase the deposition rate of viral particles to surfaces;
• increase viral inactivation.

Figure 2. Improving indoor air quality to prevent COVID-19.

 

Although different in definition, increasing the deposition rate of viral particles can be considered similar to increasing the sedimentation rate. Sedimentation refers to the settling of particles on the ground or other surfaces due to gravitational forces. However, airborne particles can also accumulate on walls and other surfaces due to mechanisms such as unnatural diffusion for particle sedimentation. The Centres for Disease Control and Prevention (CDC) and the World Health Organization (WHO) confirm the removal of viral particles through air exchange [8, 4]. And recommend increasing the supply of fresh air as a simple way to reduce the concentration of viral particles in a confined space. Air ionization can also be used to increase the rate of removal of viral particles from a confined space by increasing filtration efficiency and particle deposition. Various methods are available to sterilize the air and render the virus harmless, thereby increasing the rate of viral inactivation and reducing the need to remove particles from the air. In this regard, the following can be listed.

• • Ultraviolet Germicidal Irradiation (UVGI).This is a traditionally popular technology for fighting airborne viruses (Fig. 3).
  • Control of temperature and relative humidity. It has also been suggested that directly controlling the environmental conditions of an area creates an unfavourable environment for viruses, thereby increasing the natural rate of viral inactivation. This includes controlling the temperature and relative humidity of an area to maintain an especially generally hostile environment.
  • Non-thermal plasma and reactive oxygen species. These offer other alternatives for viral inactivation that have proven effective against bacteria and other microbes.
  • Filter coatings use. Another possible method uses filter coatings that facilitate viral inactivation by mechanisms such as the materials’ inherent antiviral properties or by directly damaging the virus.
  • Chemical disinfectants. Chemical disinfectants have also been proven to effectively remove viruses from surfaces and may provide other solutions to increase viral inactivation.
  • Superheated sterilization. Superheated sterilization may offer another viable solution for inactivating viral particles, although it has traditionally been used to sterilize surgical equipment on a smaller scale.

Figure 3. Improving living and work space ventilation and air filtering to help prevent transmission of COVID-19

2. Air filtration and SARS-CoV-2

In various applications, air filtration has become a critical intervention in managing the spread of the 2019 coronavirus disease (COVID-19). However, the proper placement of air filtration has been hampered by a poor understanding of its principles. These misunderstandings have led to uncertainty about the effectiveness of air filtration in stopping potentially infectious aerosol particles. A proper understanding of how air filtration works is critical for making further decisions regarding its use in managing the spread of COVID-19. The problem is significant because recent evidence has shown that severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) can stay in the air longer and travel farther than previously expected in the COVID-19 pandemic, with reduced concentrations and viability. SARS-CoV-2 virions are around 60-140 nm in diameter, while larger respiratory droplets and air pollution particles (>1 µm) have been found to harbour virions. Removal of particles that can carry SARS-CoV-2 from the air is possible with air filtration based on natural or mechanical movement of air. Among the various types of air filters, high efficiency particulate trap (HEPA) filters have been recommended. Other types of filters are less or more effective and, accordingly, easier or more difficult to move the air. The use of masks, respirators, air filtration modules and other special equipment is an important intervention in the management of the spread of COVID-19. It is critical to consider air filtration mechanisms and understand how aerosol particles containing SARS-CoV-2 virions interact with filter materials in order to identify best practices for using air filtration to reduce the spread of COVID-19.

There is growing evidence that severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) can remain suspended in the air for long periods of time. Some of the airborne SARS-CoV-2 virions remain viable for at least 3 hours after aerosolization [31]. Polymerase chain reaction positive SARS-CoV-2 was detected in aerosol particles larger than 1 μm in diameter in rooms where patients with coronavirus disease 2019 (COVID-19) were staying [5]. In another study, SARS-CoV-2 RNA was detected in the aerosol phase at a distance of at least 3 m from infected people indoors [15]. SARS-CoV-2 RNA has also been found in air pollution particles circulating in the air [24].

The diameter of SARS-CoV-2 virions is around 60-140 nm [39]. However, many exhaled respiratory droplets that may contain virions are significantly larger than the virions themselves. However, airborne droplet evaporation reduces their size [39], allowing potentially infectious particles to remain in the air for significantly longer. It was observed that dry droplets with a diameter of about 4 μm formed speech-derived wet droplets of 12 μm to 21 μm due to drying. It took about 8 minutes for these dry droplets to fall only 30 cm in still air [35]. At low ambient temperature, exhaled breath with high humidity can become supersaturated. The moisture then condenses on the particles emitted by a person, causing them to turn into droplets or larger diameter ice crystals. In such droplets or ice crystals, SARS-CoV-2 virions may survive longer, and this is an important hypothesis that future research needs to test. Therefore, environmental conditions and aerosol dynamics can profoundly alter the wide range of inhaled particle sizes and the viability of SARS-CoV-2 virions in aerosol particles that mediate indoor and outdoor airborne transmission. COVID-19 outbreaks in slaughterhouses and ski resorts may be due, at least in part, to cold air aerosol dynamics.

Removing particles that may harbour SARS-CoV-2 from the air using specialized air filtration equipment and masks or respirators is an important intervention in managing the spread of COVID-19. However, a poor understanding of how air filtration works and misunderstandings about the concept of filtration efficiency for aerosol particles of different sizes hinder effective deployment of air filtration. To identify best practices for the use of air filtration in the management of the spread of COVID-19, it is critical to consider air filtration mechanisms and understand how aerosol particles containing SARS-CoV-2 virions interact with filter materials.

For air filtration, efficient air filters (EPA), high efficiency air filters (HEPA) (Fig. 4) filters and ultra-low penetration air filters (ULPA) have been widely used in various industries and applications for many years [25]. HEPA filters are recommended for infection control in healthcare settings [13, 10] based on a balance of higher filtration efficiencies and lower pressure drops compared to ULPA. HEPA filters are also commonly used in non-health environments where airborne infectious agents may be present. Examples include filtration of recirculated air on passenger aircraft and biosafety cabinets in laboratories, including where SARS-CoV-2 research is being conducted [37].

Generally, the abbreviation HEPA is interpreted as “high efficiency particulate air”. Both versions of the underlying term are widely used and there is no difference between them. The United States Department of Energy and the United States Environmental Protection Agency (EPA) define HEPA based on a minimum 99.97% efficiency when tested with an aerosol with a diameter of 0.3 μm [36]. The United States EPA defines a diameter of 0.3 µm as “the most penetrating particle size” (MPPS). However, the MPPS can vary around 0.3 μm with an absolute value depending on the nature of the aerosol particles, the type of filter material and the flow rate [25]. Particles larger or smaller than MPPS are helded with an efficiency greater than 99.97% [32]. The concept of MPPS goes against the common misconception that filtration efficiency drops for particles smaller than MPPS (for example, smaller than 0.3 µm). This misunderstanding contributed to early policies that were misled by the assumption that SARS-CoV-2 virions were too small to be effectively filtered from the air.

Figure 4. HEPA filter.

It is recommended to install HEPA filters at the outlets of ventilators used in the intensive care of people infected with SARS-CoV-2. The use of fixed (building ventilation) and portable HEPA filtration systems with and without air recirculation (indoor air purifiers) is recommended for use in healthcare settings by the United States Centres for Disease Control and Prevention and the World Health Organization, including where SARS-CoV-2 patients are present [10]. National and international standards govern the minimum filtration efficiency specifications of HEPA filters. The two most widely used standards are the international ISO 29463 standard and the European EN1822 standard. The differences between the two standards can be reconciled. For example, a HEPA filter certified to EN 1822, filter class H14, must retain at least 99.995% of aerosol particles in the MPPS. Comparable to EN 1822, filter class H14 standard, ISO 45 H. Multi-step test protocols are available to verify the compliance of filters with the requirements of the standards [12, 18]. When mechanical air movement occurs between filters, it can be important to ensure that strong directional flows or drafts of filtered air do not occur. Recently, concerns have been raised that such directional flows could entrain unfiltered air, which may contain infectious particles, and push them faster and farther than they could diffuse in still air [11].

Antiviral properties can be added to filter materials. However, once the aerosol particles are collected on the filter fibres, almost none of them leaves and passes through the filter during or after proper use [25]. Thus, the antiviral properties of the fibres have almost no effect on airborne removal of live SARS-CoV-2 virions. Particles accumulated on previously collected particles do not come into contact with the filter material, eliminating any antiviral properties. Therefore, imparting antiviral properties to HEPA filter materials may not add value except when people come into direct contact with these filters during or shortly after use.

The mechanisms of aerosol particle filtration in the gas phase—inertial impingement, diffusion, arresting, electrostatic deposition, and sieving [25, 12, 18]—have been explored in depth over decades of research. These mechanisms have varying contributions to the overall particle arresting efficiency of filters, depending on the particle aerodynamic diameter, other particle properties, and the filtration medium. The combined effect of all these filtration mechanisms in HEPA filters explains the high filtration efficiency and MPPS phenomenon across the entire aerosol size spectrum [25]. Various types of aerosol particles are filtered with high efficiency in accordance with relevant standards, regardless of their biogenic or non-biogenic origin [12, 18].

It is known, based on numerous published studies, that some respiratory infections occur more frequently when people breathe more polluted air, and that the healing process and outcomes of some respiratory infections are adversely affected by air pollution. An association between long-term level of particulate air pollution and higher COVID-19 mortality has already been demonstrated [39]. Breathing polluted air is also strongly associated with adverse effects on respiratory and cardiovascular functions [17]. Air filtration-based interventions using adequate equipment should be widely implemented both to reduce the spread of SARS-CoV-2 through the aerosol phase and to improve the health status and outcomes of people exposed and infected with COVID-19.

3. Air purifiers and filters

It is estimated that the use of air filters and purifiers will reduce the viral load in the environment. Air purifiers can be used in patient rooms, which can reduce the likelihood of infection by healthcare workers due to deficiencies in PPE. It can reduce the likelihood of re-infection in a patient due to airborne transmission of viruses. This type of filtration system can also be used in public transport, in the hospital setting, anywhere in the aerosol generating procedure, in closed vehicles and at home. Liquid droplets when coughing or sneezing from an infected person are typically 5 microns or more in size. The smallest particle of concern is the single virion (not attached to any liquid droplet) with a diameter of about 0.12 microns. The smallest particle to worry about is a single virion (not attached to any liquid droplet) with a diameter of about 0.12 microns. These can be reasonably filtered by a HEPA (high efficiency particulate air) filter [3]. ULPA (ultra-low penetration air) filters are more advanced at trapping almost 99.99% of particles 0.12 micron and above. The use of nanotechnology further increases the virus capture capacity and purification of such air purifiers and filters. It has produced an efficient filter based on nickel (Ni) foam to capture and kill airborne viruses and microbes, including SARS-CoV-2 and Bacillus anthracis. Since the SARS-CoV-2 virus cannot survive at temperatures above 70 °C, the air filter is designed to operate at 200 °C by heating Ni-foam. The efficiency of the designed filter is claimed to be 99.8% for SARS-CoV-2 virus and 99.9% for Bacillus anthracis [3].

Recent studies show that, in addition to its use in cleaning products and PPE, nanotechnology has also been used in the development of air cleaners to prevent airborne transmission of the SARS-CoV-2 virus. In this context, the TeqAir 200 air ionizer developed by the France-based company TEQOYA is already on the market (Fig. 5). Since the size of SARS-CoV-2 is close to the median of particle sizes for which TEQOYA air cleaners are efficient, they are expected to reduce the concentration of SARS-CoV-2 in the air.

Figure 5. TeqAir 200 air ionizer.

3.1. Nanofiber technology

Mack Antonoff HVAC has designed air purification and filtration systems using nanofiber technology and UV radiation to combat COVID-19 [16]. Turnkey Environmental Consultants have developed an air filtration system based on a dense nanofiber network (IQAirHyperHEPA® filtration technology) that captures polluting particles of all sizes. It is claimed to capture 99.5% of contaminants, including bacteria and viruses with a size of approximately 0.003 microns [16].

3.2. Photo electrochemical oxidation technology

Researchers from the University of South Florida have developed an air-purifying device “Molekule” that is claimed to effectively destroy air pollutants, including bacteria, mould spores and viruses [9]. The air cleaner uses photo electrochemical oxidation (PECO), in which UV-A light is used to activate a catalyst in the nanoparticle coated filter to generate free radicals that oxidize air pollutants [9]. These PECO-based air purifiers have enormous potential to slow the spread of the virus, predominantly in healthcare facilities.

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References

1. Bazant, M. Z., & Bush, J. W. (2021). A guideline to limit indoor airborne transmission of COVID-19. Proceedings of the National Academy of Sciences, 118(17).
2. Buonanno, G., Stabile, L., & Morawska, L. (2020). Estimation of airborne viral emission: Quanta emission rate of SARS-CoV-2 for infection risk assessment. Environment international, 141, 105794.
3. Chaudhary, V., Royal, A., Chavali, M., & Yadav, S. K. (2021). Advancements in research and development to combat COVID-19 using nanotechnology. Nanotechnology for Environmental Engineering, 6(1), 1-15.
4. Centres for Disease Control and Prevention, Feb. 9, 2021. COVID-19 ventilation FAQs, pp. 1–8 [Online]. Available. https://www.cdc.gov/coronavirus/2019-ncov /community/ventilation.html. (Accessed 4 May 2021).
5. Chia, P. Y., Coleman, K. K., Tan, Y. K., Ong, S. W. X., Gum, M., Lau, S. K., … & Marimuthu, K. (2020). Detection of air and surface contamination by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in hospital rooms of infected patients. MedRxiv.
6. Correia, G., Rodrigues, L., Da Silva, M. G., & Gonçalves, T. (2020). Airborne route and bad use of ventilation systems as non-negligible factors in SARS-CoV-2 transmission. Medical hypotheses, 141, 109781.
7. Dancer, S. J., Tang, J. W., Marr, L. C., Miller, S., Morawska, L., & Jimenez, J. L. (2020). Putting a balance on the aerosolization debate around SARS-CoV-2. The Journal of Hospital Infection, 105(3), 569.
8. Ding, J., Yu, C. W., & Cao, S. J. (2020). HVAC systems for environmental control to minimize the COVID-19 infection. Indoor and Built Environment, 29(9), 1195-1201.
9. Elias, B., & Bar-Yam, Y. (2020). Could air filtration reduce COVID-19 severity and spread. New England Complex Systems Institute, 9.
10. EMW filtertechnik. ISO 29463: new test standard for HEPA filters [cited 2020 Jun 3]. Available from: https://www.emw.de/en/filter-campus/iso29463.html.
11. Ham, S. (2020). Prevention of exposure to and spread of COVID-19 using air purifiers: challenges and concerns. Epidemiology and Health, 42.
12. Hick, J. L., Hanfling, D., Wynia, M. K., & Pavia, A. T. (2020). National Academy of Medicine. Duty to Plan: Health Care, Crisis Standards of Care, and Novel Coronavirus SARS-CoV.
13. Hinds, W. C. (1999). Aerosol technology: properties, behavior, and measurement of airborne particles. John Wiley & Sons.
14. Li, Y., Leung, G. M., Tang, J. W., Yang, X., Chao, C. Y. H., Lin, J. Z., … & Qian, H. (2007). AC 587 Sleigh, H.-JJ Su, J. Sundell, TW Wong, PL Yuen, Role of ventilation in airborne transmission of 588 infectious agents in the built environment-a multidisciplinary systematic review. Indoor Air, 17(589), 2-18.
15. Liu, Y., Ning, Z., Chen, Y., Guo, M., Liu, Y., Gali, N. K., … & Lan, K. (2020). Aerodynamic analysis of SARS-CoV-2 in two Wuhan hospitals. Nature, 582(7813), 557-560.
16. Look, M., Bandyopadhyay, A., Blum, J. S., & Fahmy, T. M. (2010). Application of nanotechnologies for improved immune response against infectious diseases in the developing world. Advanced drug delivery reviews, 62(4-5), 378-393.
17. Nadadur, S. S., & Hollingsworth, J. W. (Eds.). (2015). Air pollution and health effects. Springer.
18. Nazarenko, Y. (2020). Air filtration and SARS-CoV-2. Epidemiology and health, 42.
19. Nicas, M., & Miller, S. L. (1999). A multi-zone model evaluation of the efficacy of upper-room air ultraviolet germicidal irradiation. Applied Occupational and Environmental Hygiene, 14(5), 317-328.
20. Peters, A., Parneix, P., Otter, J., & Pittet, D. (2020). Putting some context to the aerosolization debate around SARS-CoV-2. The Journal of Hospital Infection, 105(2), 381.
21. Riley, R. L. (1982). Indoor airborne infection. Environment international, 8(1-6), 317-320.
22. Riley, E. C., Murphy, G., & Riley, R. L. (1978). Airborne spread of measles in a suburban elementary school. American journal of epidemiology, 107(5), 421-432.
23. Santos, A. F., Gaspar, P. D., Hamandosh, A., Aguiar, E. B. D., Guerra Filho, A. C., & Souza, H. J. L. D. (2020). Best practices on HVAC design to minimize the risk of COVID-19 infection within indoor environments. Brazilian Archives of Biology and Technology, 63.
24. Setti, L., Passarini, F., De Gennaro, G., Barbieri, P., Perrone, M. G., Borelli, M., … & Miani, A. (2020). SARS-Cov-2RNA found on particulate matter of Bergamo in Northern Italy: first evidence. Environmental research, 188, 109754.
25. Stadnytskyi, V., Bax, C. E., Bax, A., & Anfinrud, P. (2020). The airborne lifetime of small speech droplets and their potential importance in SARS-CoV-2 transmission. Proceedings of the National Academy of Sciences, 117(22), 11875-11877.
26. Stilianakis, N. I., & Drossinos, Y. (2010). Dynamics of infectious disease transmission by inhalable respiratory droplets. Journal of the Royal Society Interface, 7(50), 1355-1366.
27. URL-1: https://aeramaxpro.com/covid19-1/
28. URL-2: https://www.usatoday.com/in-depth/graphics/2020/10/18/improving-indoor-air-quality-prevent-covid-19/3566978001/
29. URL-3:https://www.sentryair.com/blog/indoor-air-quality/improving-ventilation-and-air-filtration-to-help-prevent-covid-transmission-in-the-workplace/
30. URL-4: https://www.microcovid.org/blog/hepafilters
31. URL-5: https://product.statnano.com/product/11653/teqoya-teqair-200-air-ionizer
32. S. Department of Energy. DOE-STD-3020-2005, specification for HEPA filters used by DOE contractors; 2015 [cited 2020 Jul 15]. Available from: https://www.standards.doe.gov/standards-documents/3000/3020-astd-2005
33. Van Doremalen, N., Bushmaker, T., Morris, D. H., Holbrook, M. G., Gamble, A., Williamson, B. N., … & Munster, V. J. (2020). Aerosol and surface stability of SARS-CoV-2 as compared with SARS-CoV-1. New England journal of medicine, 382(16), 1564-1567.
34. Vejerano, E. P., & Marr, L. C. (2018). Physico-chemical characteristics of evaporating respiratory fluid droplets. Journal of The Royal Society Interface, 15(139), 20170939.
35. Wells, W. F. (1934). ON AIR-borne infection: study II. Droplets and droplet nuclei. American journal of Epidemiology, 20(3), 611-618.
36. World Health Organization. Laboratory biosafety guidance related to coronavirus disease 2019 (COVID-19): interim guidance, 12 February 2020 [cited 2020 Jun 3]. Available from: https://apps.who.int/iris/handle/10665/331138.
37. World Health Organization. (2020). Severe acute respiratory infections treatment centre: practical manual to set up and manage a SARI treatment centre and a SARI screening facility in health care facilities(No. WHO/2019-nCoV/SARI_treatment_center/2020.1). World Health Organization.
38. Wu, X., Nethery, R. C., Sabath, B. M., Braun, D., & Dominici, F. (2020). Exposure to air pollution and COVID-19 mortality in the United States: A nationwide cross-sectional study. medRxiv 2020.04. 05.20054502.
39. Zhu, N., Zhang, D., Wang, W., Li, X., Yang, B., Song, J., … & Tan, W. (2020). A novel coronavirus from patients with pneumonia in China, 2019. New England journal of medicine.