Determination of Air Filter Anti-Viral Efficiency against an Airborne Infectious Virus.

Recently, various studies have reported the prevention and treatment of respiratory infection outbreaks caused by lethal viruses. Consequently, a variety of air filters coated with antimicrobial agents have been developed to capture and inactivate virus particles in continuous airflow conditions. However, since aerosolized infectious viral-testing is inadvisable due to safety concerns, their anti-viral capability has only been tested by inserting the filters into liquid media, where infectious virus particles disperse. In this study a novel method of determining anti-viral performance of an air filter against airborne infectious viruses is presented. Initially, anti-viral air filter tests were conducted. Firstly, by an air-media test, in which the air filter was placed against an aerosolized non-infectious virus. Secondly, by a liquid-media test, in which the filter was inserted into a liquid medium containing a non-infectious virus. Subsequently, a correlation was established by comparing the susceptibility constants obtained between the two medium tests and an association was found for the air medium test with infectious virus. After ensuring the relationship did not depend on the virus species, the correlation was used to derive the results of the air-medium test from the results of the liquid-medium test.

Non-uniform filtration velocity of process gas passing through a long bag filter.

Filtration velocity is one of the dominant parameters that determine the pressure drop through a bag filter. Experimental investigation of the air flow pattern around a bag filter inside a bag house is very difficult because of the complexity of the 3-D air flow. For this reason, we numerically investigated flow characteristics along a bag filter in detail. We newly found that the filtration velocity is non-uniform along the axial direction of a long bag filter when the height of the filter is greater than 10 m. The filtration velocity is very small at the bottom of the bag filter but very large at the top. For bag filter lengths of over 10 m, 70% of total inlet flow is filtered in just the top 30% of the long bag filter. This indicates that the top section of the long bag filter could deteriorate faster than the bottom section, making it necessary to develop a new method to avoid the problem. We developed an equation that can help predict the initial pressure drop across long bag filters with different heights, but identical filtration characteristics.

Evaluation of Ag nanoparticle coated air filter against aerosolized virus: Anti-viral efficiency with dust loading.

In this study, the effect of dust loading on the anti-viral ability of an anti-viral air filter was investigated. Silver nanoparticles approximately 11 nm in diameter were synthesized via a spark discharge generation system and were used as anti-viral agents coated onto a medium air filter. The pressure drop, filtration efficiency, and anti-viral ability of the filter against aerosolized bacteriophage MS2 virus particles were tested with dust loading. The filtration efficiency and pressure drop increased with dust loading, while the anti-viral ability decreased. Theoretical analysis of anti-viral ability with dust loading was carried out using a mathematical model based on that presented by Joe et al. (J. Hazard. Mater.; 280: 356-363, 2014). Our model can be used to compare anti-viral abilities of various anti-viral agents, determine appropriate coating areal density of anti-viral agent on a filter, and predict the life cycle of an anti-viral filter.

Fabrication of an anti-viral air filter with SiO2-Ag nanoparticles and performance evaluation in a continuous airflow condition.

In this study, SiO2 nanoparticles surface coated with Ag nanoparticles (SA particles) were fabricated to coat a medium air filter. The pressure drop, filtration efficiency, and anti-viral ability of the filter were evaluated against aerosolized bacteriophage MS2 in a continuous air flow condition. A mathematical approach was developed to measure the anti-viral ability of the filter with various virus deposition times. Moreover, two quality factors based on the anti-viral ability of the filter, and a traditional quality factor based on filtration efficiency, were calculated. The filtration efficiency and pressure drop increased with decreasing media velocity and with increasing SA particle coating level. The anti-viral efficiency also increased with increasing SA particle coating level, and decreased by with increasing virus deposition time. Consequently, SA particle coating on a filter does not have significant effects on filtration quality, and there is an optimal coating level to produce the highest anti-viral quality.

Methodology for modeling the microbial contamination of air filters.

In this paper, we propose a theoretical model to simulate microbial growth on contaminated air filters and entrainment of bioaerosols from the filters to an indoor environment. Air filter filtration and antimicrobial efficiencies, and effects of dust particles on these efficiencies, were evaluated. The number of bioaerosols downstream of the filter could be characterized according to three phases: initial, transitional, and stationary. In the initial phase, the number was determined by filtration efficiency, the concentration of dust particles entering the filter, and the flow rate. During the transitional phase, the number of bioaerosols gradually increased up to the stationary phase, at which point no further increase was observed. The antimicrobial efficiency and flow rate were the dominant parameters affecting the number of bioaerosols downstream of the filter in the transitional and stationary phase, respectively. It was found that the nutrient fraction of dust particles entering the filter caused a significant change in the number of bioaerosols in both the transitional and stationary phases. The proposed model would be a solution for predicting the air filter life cycle in terms of microbiological activity by simulating the microbial contamination of the filter.

Prompt and synergistic antibacterial activity of silver nanoparticle-decorated silica hybrid particles on air filtration.

There is a significant need for materials that promptly exhibit antimicrobial activity upon contact. The large-scale fabrication of monodisperse silver nanoparticle (AgNP)-decorated silica (AgNP@SiO2) hybrid particles, and their prompt and synergistic antibacterial activity against both the Gram-negative bacteria Escherichia coli and the Gram-positive bacteria Staphylococcus epidermidis on air filtration units are presented. Monodisperse aminopropyl-functionalized silica colloids (406 nm) were used as a support material and were hybridized with AgNPs using a seeding, sorting-out, and growing strategy with Ag seeds (1-2 nm) into ∼30 nm AgNPs, successfully yielding 51 g of AgNP@SiO2 hybrid particles. Medium filter samples (glass fiber material, 4 × 4 cm2) were coated with AgNP@SiO2 particles and tested for antibacterial efficacy. SEM characterization of the bacterial morphology suggested prompt and synergistic antibacterial activity against both classes of bacteria. Moreover, antibacterial efficacies >99.99% for both bacteria were obtained using a filter sample with a coating areal density of 1 × 108 particles per cm2. Solutions of AgNP@SiO2 at 1.3% were stable even after 8 months. The hybrid particle AgNP@SiO2 and the air filter system coated with the particles are expected to be useful for future green environment applications.