Aerodynamic Size-Dependent Collection and Inactivation of Virus-Laden Aerosol Particles in an Electrostatic Precipitator

Abstract

Electrostatic precipitators (ESPs) may enable high particle collection efficiency with minimal pressure drop in HVAC systems. However, studies of pathogen collection and inactivation in ESPs at medium to higher flow rates are limited. Here, a single-stage, wire-plate ESP operated at flow rates of 51 and 85 m³ h^-1 was used to study the removal of virus-laden aerosol particles for three different airborne viruses: (1) bovine coronavirus (BCoV), (2) influenza A virus (IAV), and (3) porcine reproductive and respiratory virus (PRRSV). Size-resolved measurements of collection efficiency were obtained using Andersen cascade impactors (ACI) sampling upstream and downstream of the ESP. All measurements were analyzed based on three distinctive but complementary methods: (1) fluorimetry to assess physical collection, (2) RT-qPCR to assess viral RNA concentrations and (3) virus titration to assess virus viability. In general, log reductions by virus titration were highest followed by those from RT-qPCR, and last fluorimetry, suggesting that a portion of virus may be potentially inactivated in flight in the ESP. An effective migration (deposition) velocity ranging from 3.10 to 10.05 cm s^-1 was also determined using the spatially resolved measurements of virus collection on the ESP plates.

Keywords: airborne viruses; collection; electrostatic precipitator; inactivation; particle size; wind tunnel.

Figure 1

Different experimental setups (1, 2 and 3) used for virus aerosolization and aerosol sampling. The inserts labeled as (A–E) showed details including the aerosol sampling instruments, the ESP, and the sampling foils and meshes installed in the ESP.

Figure 2

Andersen cascade impactor plates sampled upstream and downstream the ESP (a); sampling foils and the holder removed from the ESP (b); Sampling foils installed into the ESP (c); Sampling foils placed into labeled Petri-dishes after sampling (d).

Figure 3

Log reduction in virus-laden particle concentrations based on fluorescence, viral RNA and viable viruses from upstream to downstream of the ESP as a function of particle diameter for porcine reproductive and respiratory syndrome virus (PRRSV), bovine coronavirus (BCoV) and influenza A virus (IAV) at different flow rates and applied voltages. (a) PRRSV, 51 m³ h^–1 and 14 kV; (b) PRRSV, 85 m³ h^–1 and 14 kV; (c) PRRSV, 51 m³ h^–1 and 12 kV; (d) BCoV, 51 m³ h^–1 and 14 kV; (e) IAV, 51 m³ h^–1 and 14 kV.

Figure 4

Comparison of log-reduction of particles in an ESP between virus-laden particles and KCl particles. The KCl measurements were carried out using a differential mobility analyzer connected in line with a condensation particle counter (D_p < 0.25 μm) and an aerodynamic particle spectrometer (D_p > 0.3 μm).

Figure 5

Relative concentration of particles collected by the ESP collecting plates as a function of the distance to the ESP inlet for different viruses, voltages and flows in the wind tunnel based on fluorimetry, RT-qPCR, and TCID₅₀ tests. The black, thick-dashed lines represent an exponential fit C(x)/C₀ = exp(−β(x – x₀)) of the fluorescence measurements for x > 20 cm.

Figure 6

Log reduction of viable virus concentration on the sampling meshes when the high voltage electrodes of the ESP operated at +7.3 kV (a) and −7.5 kV (b). Results are presented for bovine coronavirus (BCoV, green solid line with triangles), influenza A virus (IAV, blue solid line with squares), and porcine reproductive and respiratory virus (PRRSV, red solid line with circles).