While effective indoor air filtration technologies have long been a necessity in health care, school, transportation, and other settings, COVID-19 brought the need for clean and safe air to the forefront. However, the pandemic also revealed the limitations of traditional options, such as HEPA filters and ultraviolet light disinfection devices, to effectively remove pathogens from the air. These inadequacies led researchers at North Carolina State University (NC State) to develop a filtration technology that presents a viable alternative for air cleaning in the 21st century.
NC State’s development combines the best performance characteristics of HEPA filters and ultraviolet (UVC) light devices into a single technology. The result is a 2D, lightweight, non-thermal, plasma-enhanced textile called SPAR, which stands for smoke and pathogen air removal (formerly known as FIL-TEX). The filter is proficient at both capturing and killing bacteria, viruses, and other contaminants with a 99.9% efficiency.
The drawbacks of traditional air-cleaning solutions
While HEPA filters with high MERV ratings have long been the gold standard for air filtration, they are an imperfect solution for today’s needs. Although HEPA filters offer a 99.9% efficiency rating when it comes to collecting small particles and pathogens, they do not deactivate live bacteria and viruses, which makes replacing these filters a potentially hazardous task.
“Because HEPA filters merely capture particulates and pathogens and focus them in one place, there is a strong likelihood that any collected bacteria or viruses will be re-aerosolized when replacing the filter,” said Warren Jasper, a professor in the Textile Engineering Chemistry and Science Department at the Wilson College of Textiles at NC State.
In addition, HEPA filters are frequently located in the air-handling system, which is often located far from the rooms or settings from which collection is necessary, meaning they are a whole-building solution versus an intermediate one.
“Essentially, they are often placed too far away to provide protection to areas where people are congregating,” said Jasper. “If someone coughs in a crowded classroom, the fact that there is clean air near the air handler doesn’t really protect the individuals from the airborne particulates that have just been released into the room.”
UVC disinfection technologies are growing in popularity because they successfully deactivate live pathogens and microorganisms by destroying their DNA; however, these systems utilize UV light mechanisms, which can cause adverse health effects, such as headaches and skin cancer, in individuals who are overexposed, making UVC a poor choice in health care, educational, and other highly populated settings.
In addition, when UVC technologies are combined with HVAC systems, as is often the case, operational and maintenance expenses may increase due to higher power requirements and costly bulb replacements.
An air-cleaning technology for the 21st century
Understanding the drawbacks of these traditional technologies, which date back to the 1930s and ’40s, researchers at NC State have developed an effective and contemporary method of providing clean and safe air that is suitable for today’s post-pandemic needs.
“Filtration of airborne particulates can be divided into two camps: active and passive,” Jasper said. “We decided to take the best performance characteristics from passive technologies that capture particulates and active technologies that purify the air and combine them into a single, more modern air-cleaning solution.”
He said SPAR is comprised of woven, knit, or non-woven structures where nonconductive yarns combine with conductive yarns that serve as electrodes. When a voltage is applied to these conducting yarns, a non-thermal plasma (NTP) is produced.
NTP, often called cold plasma, is an electrically energized form of matter that remains cool to the touch but is composed of a partially ionized gas that reacts with pathogens, chemicals, odorants, and other contaminants and converts them into harmless oxidized forms. So, when airborne pathogens pass through the SPAR filter, the NTP reacts with the sheath membrane of the microorganisms, deactivating the virus or destroying the cell wall of the bacterium, essentially killing any airborne pathogens while also safely collecting them.
In addition, because it operates like a magnet that attracts, deactivates, and removes unwanted contaminants from the air, SPAR technology does not emit any additives or substances into the air.
Proven air-cleaning results
Following the COVID-19 pandemic, technology that effectively eliminates aerosolized pathogens is extremely important in confined spaces where people congregate.
“While good air circulation helps reduce the likelihood of the transmission of airborne viruses and bacteria, effective filtration is crucial in locations where there is not much air turnover and in which we pack a lot of people,” said Dr. Frank Scholle, associate professor of biological sciences at NC State. “Close quarters without proper ventilation, such as gateways between the airport and airplane, buses or subways, classrooms, and exam or waiting rooms in health care settings, provide an ideal environment for very contagious respiratory pathogens, such as COVID-19, chicken pox, and measles, to transmit between people.”
Based on these needs, NC State researchers in Scholle’s virology lab tested the effectiveness of SPAR, which was originally developed to remove smoke and particulates, against respiratory pathogens and were more than satisfied with the results.
An aerosolized coronavirus, similar in genetic makeup to the virus responsible for COVID-19 infections, was introduced into an enclosed laboratory-scale tunnel with SPAR situated between the inlet and outlet. A sampling of the air before and after passing through SPAR demonstrated encouraging post-filtration effectiveness of the novel technology.
“We had nearly a 3-log reduction in infectious virus after the SPAR filter — to be specific, up to a 99.7% effectiveness,” said Scholle. “The destruction of infectious virus was a truly significant level of success and was beyond our initial expectations.”
Following NC State tests, SPAR was sent to CREM Co Labs, an independent research and development laboratory specializing in antimicrobial testing, which conducted similar analyses and found equally impressive results.
According to the report, SPAR was proven to remove over 99.9% of airborne viruses, such as COVID-19, and 99.9% of airborne bacteria, such as staph, while deactivating 98% of viruses found on the filter’s surface.
SPAR has also been shown to rapidly absorb continuous smoke and particulates, such as oil, carbon, soot, ash, and tar, in enclosed spaces where venting is not an option, making it an effective air-cleaning technology with many potential applications.
Applying the SPAR technology
SPAR combines NTP technology with a 2D textile filter that can be made from cotton, polyester, polypropylene, Kevlar, or other fabrics, so it is lightweight and flat with a thickness of about 2 mm. The textile filter is designed in such a way that air can pass through the system at a high rate and requires very little power, making it an effective and energy-efficient component suitable for a number of air cleaning devices and systems. These could include a wall- or ceiling-mounted device, or can be used in conjunction with HVAC systems.
