Plasma-generated reactive water mist for disinfection of N95 respirators laden with MS2 and T4 bacteriophage viruses

Abstract

Due to the shortage of personal protective equipment (PPE) during the COVID-19 pandemic, the interest and demand for sterilization devices to reuse PPE has increased. For reuse of face masks, they must be effectively decontaminated of potential infectious agents without compromising its filtration ability during sterilization. In this study, we utilized an atmospheric pressure pulsed dielectric barrier discharge (DBD), combined with nebulized liquid microdroplets to generate plasma-activated mist (PAM). MS2 and T4 bacteriophages were used to conduct the decontamination tests on two types of N95 respirators. Results showed at least a 2-log reduction of MS2 and T4 on N95 respirators treated in one cycle with 7.8% hydrogen peroxide PAM and at least a 3-log reduction treated in 10% hydrogen peroxide PAM. In addition, it was found that there was no significant degradation in filtration efficiency of N95 respirators (3M 1860 and 1804) treated in 10% hydrogen peroxide PAM found after 20 cycles. In terms of re-useability of masks after treatment as determined, it was shown that the elastic straps of 3M 1804 were fragmented after 20 treatment cycles rendering them unusable, while the straps of 3M 1860 were not negatively affected even after 20 disinfection cycles.

Figure 1

Schematic of plasma system. It consists of three chambers: large 53-L open area for the PPE, the plasma chamber (#1–6) and heating chamber (#7–9): 1. Fan forcing the air into the plasma chamber. 2. Exit from the plasma chamber where droplets, mixed with plasma-generated reactive oxygen and nitrogen species (RONS) are introduced into the area with the PPE. 3. Plasma is generated with a 20 kHz, 3,000 V dielectric barrier discharge. 4. Ultrasonic nebulizer is used to generate water microdroplets with mean diameter of ~ 5 µm. 5. Water microdroplets form a dense fog that is produced immediately after the plasma zone and mixed with RONS. 6. Each cycle consumes 1 ml of DI water or other solutions and our current prototype has a 750 ml container. 7. For the heated air cycle, the air (containing residual RONS and moisture) is sucked in from the chamber with the PPE. 8. The air-RONS-moisture is heated to 50 °C to facilitate removal of the residual reactive chemistry and drying of the PPE. 9. Warm air is forced into the chamber with the PPE by a fan.

Figure 2

Decontamination efficiency of MS2 and T4 on N95 respirators treated by different compositions of PAM. N95 1804 treated in 7.8% hydrogen peroxide mist without plasma was not tested on MS2. All treatments were found to significantly reduce MS2 or T4 on N95 1804 or 1860 compared to untreated group (P < 0.05, independent t-test).

Figure 3

Ozone concentration measured in the sample placed chamber (left) and in the DBD reactor chamber (right) during one operation cycle.

Figure 4

Temperature and humidity of one cycle treatment with DI water PAM.