Physical Collection Efficiency of Filter Materials for Bacteria and Viruses

Abstract

The purpose of this study was to determine the physical collection efficiency of commercially available filters for collecting airborne bacteria, viruses, and other particles in the 10-900 nm (nanometer) size range. Laboratory experiments with various polytetrafluoroethylene (PTFE), polycarbonate (PC) and gelatin filters in conjunction with Button Inhalable samplers and three-piece cassettes were undertaken. Both biological and non-biological test aerosols were used: Bacillus atrophaeus, MS2, polystyrene latex (PSL), and sodium chloride (NaCl). The B.atrophaeus endospores had an aerodynamic diameter of 900 nm, whereas MS2 virion particles ranged from 10 to 80 nm. Monodisperse 350 nm PSL particles were used as this size was believed to have the lowest filtration efficiency. NaCl solution (1% weight by volume) was used to create a polydisperse aerosol in the 10-600 nm range. The physical collection efficiency was determined by measuring particle concentrations size-selectively upstream and downstream of the filters. The PTFE and gelatin filters showed excellent collection efficiency (>93%) for all of the test particles. The PC filters showed lower collection efficiency for small particles especially <100 nm. Among the tested filters, the lowest collection efficiencies, 49 and 22%, were observed for 1 and 3-microm pore size PC filters at the particle sizes of 47 and 63 nm, respectively. The results indicate that the effect of filter material is more significant for the size range of single virions than for bacteria. The effect of filter loading was examined by exposing filters to mixtures of PSL particles, which aimed at mimicking typical indoor dust levels and size distributions. A 4-h loading did not cause significant change in the physical collection efficiency of the tested filters.

Air sampling filtration media: Collection efficiency for respirable size-selective sampling

“…Gentry et al (1982) found that the penetration of Nuclepore filters with 2 and 5 μ m pore size varied from 40% to 76% (~23%–60% collection efficiencies) and 70%–86% (~14%–30% collection efficiencies) at face velocities in range of 0.8–6.6 cm s −1 . Burton et al (2007) also found that the polycarbonate filter showed low collection efficiency for particles <100 nm. The lowest collection efficiencies, 49% and 22% were observed for 1 and 3 μ m pore size polycarbonate filter when a flow rate of 4 l min −1 was used.…”

Total Concentrations of Virus and Bacteria in Indoor and Outdoor Air

“…While Griffin et al 14 collected air samples directly onto a 0.02-μm pore size filter, we used a 0.2-μm pore size filter with lower pressure drop due to concerns about noise from the sampling pump in indoor, occupied environments. Based on studies of membrane filters with similar or larger pore sizes than 0.2 μm, 35–37 we expect the collection efficiency to be >99% for both virus- and bacteria-sized particles, so the use of filters with different pore sizes should not bias the comparison. The VBR of 1.4 in outdoor air in Blacksburg, Virginia is 7% higher than in the Caribbean and 58% lower than in Korea.…”

Evaluation of applicability of the Sartorius Airport MD8 sampler for detection of Bacillus endospores in indoor air

“…The different criteria for selection of an appropriate surrogate for B. anthracis endospores have been already proposed; among them, a risk of use, genetic and morphological similarity to B. anthracis , and response to various chemical and environmental challenges seemed to be most important (Greenberg et al 2010). An aerodynamic diameter of B. atrophaeus endospore is about 0.9 μm and is slightly smaller when compared to B. anthracis endospores (Burton et al 2007; Carrera et al 2006). B. atrophaeus is considered as nonpathogenic and is classified as a BSL-1 organism.…”