Inactivation of airborne viruses using vacuum ultraviolet photocatalysis for a flow-through indoor air purifier with short irradiation time

Figures & data

Table 1. Summary of studies on UV photocatalytic oxidation systems for disinfecting bioaerosols.

Light source	Target bioaerosols	Photoreactors	Irradiation time (flow rate)	Disinfection efficiency	Reference
UVA^a	Escherichia coli	TiO2-coated Pyrex tubular reactor	9–35 s (1.5–6l/min)	99.1–99.8%	(Keller et al. 2005)
UVA^a	Escherichia coli	Continuous annual reactor with TiO2-coated glass fiber filter	1.1 min (1l/min)	100%	(Pal et al. 2008)
UVA^a	Legionella pneumophila	Three-dimensional solid foam structured reactor	1.5 s (21.6l/min)	94%	(Josset et al. 2010)
UVA^a	Influenza virus H1N1	TiO2-coated porous ceramic substrate	5 min (6–24l/min)	100%	(Daikoku et al. 2015)
UVA^a	Pseudomonas aeruginosa, Staphylococcus aureus, Methicillin-resistant Staphylococcus aureus, Aspergillus fumigatus	Honeycomb structure made of P25 dip-coated cellulose acetate monoliths	15 min	74–98%	(Rodrigues-Silva et al. 2017)
UVA^a, UVC^b	Escherichia coli	TiO2-coated glass fiber substrates	∼0.5 s (20l/min)	95%	(Lin et al. 2010)
UVA^a, UVC^b	Escherichia coli	TiO2-coated filter	2–6 h	100%	(Pigeot-Remy et al. 2014)
VUV^c	MS2 phage	Spiral and pleated Pd-deposited TiO2 flow-through reactor	0.004–0.125 s (33l/min)	47.8–100%	Present study

^a UVA: 365 nm wavelength ultraviolet light.

^b UVC: 254 nm wavelength ultraviolet light.

^c VUV: 185 nm wavelength ultraviolet light.

Figure 1. Schematic diagram of the experimental setup.

Figure 2. Four types of catalyst frames with an illustration of the gas flow patterns: (a) 2 mm pleated catalyst, (b) 5 mm pleated catalyst, (c) spiral type catalyst, and (d) flat sheet type catalyst. (e) No catalyst. (f) A photograph of the photo-reactor.

Figure 3. (a) Dependence of MS2 inactivation efficiency on irradiation time for four treatments. (b) Concentration of ozone generated with different VUV irradiation times. Experimental conditions: flow rate = 33l/min, [MS2]_inlet = 1.7 × 10³ PFU/ml, RH = 40%, n = 3, *P < 0.05, ns: P ≥ 0.05.

Table 2. Specific energy input versus MS2 inactivation.

		MS2 inactivation efficiency (%)
Irradiation time (s)	Specific energy input (Wh/m^3)	VUV	UV
0.125	5.56	100	48
0.052	3.08	100	32
0.026	1.52	100	12
0.009	0.51	60	0
0.004	0.25	48	0

Experimental conditions: flow rate = 33l/min, [MS2]_inlet = 1.7 × 10³ PFU/ml, RH = 40%.

Figure 4. Dependence of MS2 inactivation and ozone degradation on catalyst frame shape. Experimental conditions: [MS2]_inlet = 1.7 × 10³ PFU/ml, [O₃]_VUV = 152 ppb, RH = 40%, flow rate = 33l/min, n = 3, *P < 0.05, ns: P ≥ 0.05.

Table 3. Specifications of the Pd-TiO₂ photo-reactors used in the present study.

Catalyst frame shape	Catalyst surface area^a (m^2)	S/V^b (m^2/m^3)	Ozone degradation efficiency (%)			MS2 inactivation efficiency (%)	Space velocity^c (/s)	Pressure drop (kPa)
2 mm pleated catalyst	0.0506	8.3 × 10^5	50.5 ± 1.8			66.9 ± 11.4	161.8	3.6 ± 0.007
5 mm pleated catalyst	0.0314	5.1 × 10^5	34.7 ± 2.8			65.4 ± 7.4	133.7	3.6 ± 0.001
Spiral type catalyst	0.0399	6.2 × 10^5	48.8 ± 3.7			40.9 ± 0.1	193.9	3.8 ± 0.034
Plate sheet catalyst	0.0134	2.0 × 10^5	20.7 ± 2.2			59.1 ± 7.0	120.8	3.6 ± 0.007
No catalyst	—	—			57.3 ± 14.8		—	3.6 ± 0.007

^a Sectional area of the reactor.

^b Ratio of catalyst area to reactor volume.

^c Space velocity is defined as the volumetric flow rate of the feed gas divided by the catalyst volume. Experimental conditions: flow rate = 33l/min, RH = 40%, [MS2]_inlet = 1.7 × 10³ PFU/ml, [O₃]_VUV = 152 ppb, n = 3.

Figure 5. The effect of RH on MS2 inactivation and O₃ degradation. Experimental conditions: [MS2]_inlet = 1.7 × 10³ PFU/ml, [O₃]_{VUV with catalyst} = 65 ppb, irradiation time = 0.009 s, flow rate = 33l/min, n = 3, *: P < 0.05, ns: P ≥ 0.05.

Figure 6. Natural decay of MS2 infectivity, with and without VUV irradiation, as a function of storage time at (a) 4ºC and (b) 25ºC, where C_o and C_t are the concentrations of viable MS2 viruses at collection and storage time t, respectively. Experimental conditions: flow rate = 33l/min, [MS2]_{No Treatment} = 1.7 × 10³ PFU/ml, [MS2]_{VUV with catalyst} = 4.1 × 10² PFU, RH = 40%, irradiation time = 0.009s, n = 3.

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