Evaluation of an Air Cleaning Device Equipped with Filtration and UV: Comparison of Removal Efficiency on Particulate Matter and Viable Airborne Bacteria in the Inlet and Treated Air

Abstract

Since the COVID-19 pandemic, improving indoor air quality (IAQ) has become vital for the public as COVID-19 and other infectious diseases can transmit via inhalable aerosols. Air cleaning devices with filtration and targeted pollutant treatment capabilities can help improve IAQ. However, only a few filtration/UV devices have been formally tested for their effectiveness, and little data is publicly available and UV doses comparable. In this research, we upgraded a particulate matter (PM) air filtration prototype by adding UV-C (germicidal) light. We developed realistic UV dose metrics for fast-moving air and selected performance scenarios to quantify the mitigation effect on viable airborne bacteria and PM. The targeted PM included total suspended particulate (TSP) and a coarse-to-fine range sized at PM₁₀, PM₄, PM_2.5, and PM₁. The PM and viable airborne bacteria concentrations were compared between the inlet and outlet of the prototype at 0.5 and 1.0 m³/s (low and high) air flow modes. The upgraded prototype inactivated nearly 100% of viable airborne bacteria and removed up to 97% of TSP, 91% of PM₁₀, 87% of PM₄, 87% of PM_2.5, and 88% of PM₁. The performance in the low flow rate mode was generally better than in the high flow rate mode. The combination of filtration and UV-C treatment provided 'double-barrier' assurance for air purification and lowered the risk of spreading infectious micro-organisms.

Keywords: UV disinfection; UV254; UVGI; air pollution control; biosecurity; disease control; indoor air quality; occupational health; ultraviolet light.

Figure 1

FastAir prototype for air treatment (top view). Untreated air enters on both sides and is filtered and irradiated by UV-C lamps. The air blower facilitates untreated air suction and ejection on treated air.

Figure 2

(A): Front view of the upgraded FastAir prototype with UV-C lamps enclosed and a controller box attached above the air outlet. (B): Side view of the upgraded FastAir prototype. MERV-8 filters can be seen at the air inlet. (C): After MERV-8 filters were removed, MERV-13 filters can be seen as the second filtration layer. Aluminum mesh filters follow MERV-13 filters to protect MERV filters from degradation caused by long-term UV irradiation. (D): Eight UV-C light bulbs were installed on each side of the FastAir prototype. Each light fixture supported twin UV-C light bulbs. The air blower can be seen downstream from the UV-C lamp. The gradient of the air flow arrows signifies progressively cleaner air (from (B–D)).

Figure 2

(A): Front view of the upgraded FastAir prototype with UV-C lamps enclosed and a controller box attached above the air outlet. (B): Side view of the upgraded FastAir prototype. MERV-8 filters can be seen at the air inlet. (C): After MERV-8 filters were removed, MERV-13 filters can be seen as the second filtration layer. Aluminum mesh filters follow MERV-13 filters to protect MERV filters from degradation caused by long-term UV irradiation. (D): Eight UV-C light bulbs were installed on each side of the FastAir prototype. Each light fixture supported twin UV-C light bulbs. The air blower can be seen downstream from the UV-C lamp. The gradient of the air flow arrows signifies progressively cleaner air (from (B–D)).

Figure 3

The schematic of UV irradiation inside the FastAir prototype. The filtered air entered three UV treatment zones, A, B, and C (upstream from lamps, in the near vicinity of lamps, and downstream of lamps).

Figure 4

Details of FastAir prototype for air treatment (one symmetrical side shown) following the air flow direction. Treated air can be sampled after each treatment phase (e.g., filtration and UV) for PM and viable airborne bacteria. The red arrow indicates the air sampling location for the inlet (room air), and the green arrows indicate two air sampling locations for different configuration options: (a.) after “filtration only”, (b.) after “UV” or after “filtration + UV”.

Figure 5

Six air cleaning configuration options were used for testing of FastAir prototype in high (top three panels) and low (bottom three panels) air flow rate modes, with both modes having filtration + UV, filtration only, and UV only options. Red and green arrows signify the sampling locations of the inlet and exhaust (treated) air, respectively, for PM and viable airborne bacteria. Each of the six configuration options was tested three (n = 3) times in experimental trials.

Figure 6

The experimental setup for collecting viable airborne bacteria and PM at a teaching room that housed ~150 laying hens at ISU Poultry Teaching and Research Facility. The red cart was used to deploy the FastAir prototype into the testing room. The brown cart (behind) held all sampling equipment (vacuum pumps, manifolds, and BioSamplers^®).