Airborne transmission is considered to be one of the primary factors contributing to the spread of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus responsible for coronavirus disease (COVID-19). This is especially true in the current scenario, where more transmissible SARS-CoV-2 variants such as the Delta and Omicron strains are in circulation.
The need for high-efficiency and low-pressure filter technologies is essential to remove aerosols in indoor environments such as restaurants, convention halls and hospitals to effectively reduce viral transmission, primarily through airway droplets.
Examination: Demonstration of hollow fiber membrane-based air purification in an enclosed space for capturing an aerosolized synthetic SARS-CoV-2 mimic and pseudovirus particles. Image Credit: NokkieVector / Shutterstock.com
Apart from purifying the air from contaminated bioaerosols, removal of suspended particles from the air is also imperative. In fact, particles measuring 2.5 micrometers (μm) or less in diameter can also carry viral aerosols, increasing the risk of severe COVID-19.
Conventional polymeric materials can be easily modified to improve surface functionalization and adjust membrane surface properties. In addition, these materials can be modified by adding specific enzymes or nanoparticles to improve their surface functionality. Controlling the thickness, pore size, structure and porosity of polymeric materials can help control the transport properties of the membrane and reduce the cut-off for filtering viruses more efficiently.
Hollow fiber membranes (HFMs) are cylindrical, semipermeable membranes where transport takes place radially across the membrane. HFMs are an ideal solution for high throughput scenarios due to their cylindrical geometry with a high surface area to volume ratio. For this purpose, HFMs can maintain large filtration areas for small footprints while remaining effective for low pressure operations.
No study to date has shown viral aerosol capture using HFM modules with different properties. As a result, researchers in a recent ACS ES&T Engineering study demonstrates their efforts to redesign HFM filters and innovate methods for removing / deactivating viral aerosols, which could be cheaper alternatives to high-efficiency particulate air filtration (HEPA) systems with higher aerosol removal efficiency than standard heating, ventilation and air conditioning (HVAC) filtration.
About the study
The current study examined three hollow fiber membrane (HFM) modules for viral aerosol separation in enclosed spaces.
All pipe connections and valves were made of brass or stainless steel. Aerosol size distributions were measured in inside diameter (ID) of approx. three inches. The polytetrafluoroethylene (PTFE) tube served as a pressure relief chamber to avoid pressure damage to the pump in the optical particle counter.
Pore structures were characterized by scanning electron microscopy. In addition, the particle removal efficiency was characterized by aerosols generated by a constant output collision atomizer from a defined mixture of three kinds of synthetic nanoparticles, including 50 nanometer (nm) lipoic acid-coated gold nanoparticles, 100 nm COOH-functionalized polystyrene latex nanoparticles, and 500 nmalized nanoparticles polystyrene latex nanoparticles that also included fluorescently labeled SARS-CoV-2 imitations.
Aerosol concentrations were measured using an optical particle counter operated in differential mode, showing different aerosol sizes for a better understanding of particle size filtering.
HFM1, which consisted of polyvinylidene fluoride with pores in the range of 50-1300 nm, showed an efficiency in the range of 96.5-100% for aerosols between 0.3-3 micrometers (μm) in size at a flow rate of approx. 18.6 ± 0.3 standard liters per minute (SLPM). In comparison, HFM2, which consisted of polypropylene with pores about 40 nm in size, and HFM3, which consisted of hydrophilized polyether sulfone with pores in the size range of about 140-750 nm, showed efficiencies between 99.65-100% and 98 , 8-100% at flow rates of 19.7 SLPM and 19.4 SLPM, respectively.
The filters could produce clean air with minimal soiling when demonstrated using ambient aerosols over two days. Finally, the filtration efficiency of each module was evaluated with a vesicular stomatitis virus (VSV) aerosol that acted as a pseudovirus to mimic SARS-CoV-2.
To this end, the HFM1, HFM2 and HFM3 filters demonstrated an efficiency of 99.3%, 99.8% and 99.8%, respectively, to reduce active viral titers as a direct target for removing viral particles and keeping the surrounding air clean.
Studies like these help provide innovative solutions for purifying ambient air, especially during the current COVID-19 pandemic, where aerosolized viral particles directly contribute to increases in transmission rates. The results of this study provided an insight into the aerosol separation efficiency of HFMs, while also highlighting the need for further studies of these membranes in the real world.
- Baldridge, KC, Edmonds, K., Dziubla, T., et al. (2022). Demonstration of hollow fiber membrane-based air purification in an enclosed space for capturing an aerosolized synthetic SARS-CoV-2 mimic and pseudovirus particles. ACS EST Engineering. doi: 10/1021 / acsestengg.1c00369.