Evaluating the Performance of UV Disinfection across the 222-365 nm Spectrum against Aerosolized Bacteria and Viruses.

Bioaerosols play a significant role in the transmission of many infectious diseases, especially in enclosed indoor environments. Ultraviolet (UV) disinfection has demonstrated a high efficacy in inactivating microorganisms suspended in the air. To develop more effective and efficient UV disinfection protocols, it is necessary to evaluate and optimize the effectiveness of UV disinfection against aerosolized bacteria and viruses across the entire UV spectrum. In this study, we evaluated the performance of UV disinfection across the UV spectrum, ranging from 222 to 365 nm, against aerosolized bacteria and viruses, including Escherichia coli, Staphylococcus epidermidis, Salmonella enterica, MS2, P22, and Phi6. Six commonly available UV sources, including gas discharge tubes and light-emitting diodes with different emission spectra, were utilized, and their performance in terms of inactivation efficacy, action spectrum, and energy efficiency was determined. Among these UV sources, the krypton chloride excilamp emitting at a peak wavelength of 222 nm was the most efficient in inactivating viral bioaerosols. A low-pressure mercury lamp emitting at 254 nm performed well on both inactivation efficacy and energy efficiency. A UV light-emitting diode emitting at 268 nm demonstrated the highest bacterial inactivation efficacy, but required approximately 10 times more energy to achieve an equivalent inactivation level compared with that of the krypton chloride excilamp and low-pressure mercury lamp. This study provides insights into UV inactivation on bioaerosols, which can guide the development of effective wavelength-targeted UV air disinfection technologies and may significantly help reduce bioaerosol transmission in public areas.

Home-made masks with filtration efficiency for nano-aerosols for community mitigation of COVID-19 pandemic.

OBJECTIVES: The novel coronavirus disease 2019 (COVID-19) epidemic that emerged in December 2019 has rapidly evolved in recent months to become a worldwide and ongoing pandemic. Shortage of medical masks remains an unresolved problem. This study aims to investigate the filtration efficiency (FE) of home-made masks that could be used as alternatives for community mitigation of COVID-19. STUDY DESIGN: Experimental observational analytic study. METHODS: The FE of home-made masks and medical masks (as the control) were tested under laminar flow within a scaled air duct system using nebulised NaCl aerosols sized 6-220 nm. The size-resolved NaCl aerosol count was measured using a scanning mobility particle-sizer spectrometer. Home-made masks with an external plastic face shield also underwent a splash test. In addition, the fibre structures of medical masks were studied under an electron microscope after treatment with either 75% alcohol or soap and water at 60 °C. RESULTS: The FE of the home-made masks at 6-200 nm were non-inferior to that of medical masks (84.54% vs 86.94%, P = 0.102). Both types of masks achieved an FE of 90% at 6-89 nm. A significantly higher FE was achieved when one piece of tissue paper was added adjacent to the inner surface of the medical mask than medical mask alone (6-200 nm: 91.64% vs 86.94%, P < 0.0001; 6-89 nm: 94.27% vs 90.54%, P < 0.0001; 90-200 nm: 82.69% vs 73.81%, P < 0.0001). The plastic face shield prevented the home-made mask from fluid splash. The fibre structures of the external surface of medical masks were damaged after treatment with either 75% alcohol or soap and water at 60 °C. CONCLUSIONS: The home-made masks in this study, which were made of one piece of tissue paper and two pieces of kitchen towels, layered from face to external, had an FE at 6-200 nm non-inferior to that of medical mask materials, which had a certified FE of ≥95% at 3 µm. In the current COVID-19 pandemic with the shortage of medical masks, these home-made masks combined with an external plastic shield could be used as an alternative to medical masks for community mitigation. In addition, one piece of tissue paper could be placed adjacent to the inner surface of a medical mask to prolong effective lifespan of the medical mask. These demand reduction strategies could be used to reserve medical masks for use in healthcare and certain high-risk community settings, such as symptomatic persons, caregivers and attendees to healthcare institutions.

Emission strength of airborne pathogens during toilet flushing.

The flushing of toilets generates contaminated aerosols, the transmission of which may cause the spread of disease, particularly in the immunocompromised or the elderly. This study investigated the emission strength of three types of airborne bacteria, namely Staphylococcus epidermidis, Escherichia coli, and Pseudomonas alcaligenes, during toilet flushing in a custom-built toilet under a controlled environment. Flushing was activated by a flushometer operated at two pressure levels, 400 kPa (high pressure [HP]) and 200 kPa (low pressure [LP]), and by a water cistern tank placed 95 cm (high tank [HT]) and 46 cm (low tank [LT]) above the toilet seat. The pathogens emitted by the first flush were calculated, with the correlations between airborne pathogen emissions and droplet concentration (HP, r=0.944, P<.001; LP, r=0.803, P<.001, HT, r=0.885, P<.05) and bacterial size (HP, r=-0.919, P<.001; LP, r=-0.936, P<.001; HT, r=-0.967, P<.05) in the different conditions then tested. The emission strength in the HP condition was statistically greater than that in the LP condition, whereas the cistern tank system produced less emissions than the flushometer system, and tank height was not found to be a sensitive parameter.

Experimental study on the effect of light source arrangements on the disinfection performance of upper-room 222 nm Far-UVC.

The air disinfection efficacy of upper-room 222 nm Far-UVC was experimentally investigated in a real-size chamber under well-mixed air conditions. Two bacteria (Escherichia coli, Staphylococcus epidermidis) and two bacteriophages (MS2, and P22) were selected for the test. The study considered different lamp source arrangements, including single and double sources, stationary and rotating operating modes, and an overlapping mode with a 45° irradiation angle. A numerical view-factor model was developed to analyze the irradiance distributions. Four irradiation angles, 30°, 45°, 60°, and 90°, were chosen. The results show that the lamps operating with an irradiation angle of 45° provide the highest chamber-averaged irradiance. This suggests an optimal irradiance level for a given room dimension, as inferred from the view factor model. Experimental results indicated that the overlapping mode with a 45° irradiation angle consistently outperformed both the stationary mode and rotating mode in disinfection. This can be attributed to the higher chamber-averaged irradiance, which is also supported by the numerical model predictions. The increment ratios ranged from 14.9 % to 42.9 % compared to the stationary mode. The susceptibility constants of Escherichia coli, Staphylococcus epidermidis, MS2, and P22 were measured as 0.572 m2/J, 0.099 m2/J, 0.060 m2/J, and 0.081 m2/J respectively.

An efficient lattice Boltzmann model for indoor airflow and particle transport.

The three-dimensional multiple-relaxation-time LB (MRT-LB) and Lagrangian particle tracking methods were applied to simulate turbulent airflow and particle dispersion in a ventilated room with a partition. The turbulent airflow was simulated by large eddy simulation (LES) using the MRT-LB method with the Smagorinsky model. This method was verified by comparing it with experimental and other numerical results. Good agreement was observed between airflow simulation and experimental data. It is also demonstrated that the LES carried out by the MRT-LB method can produce airflow results very similar to the RNG LES and provide better prediction than the standard and RNG k-ε models. In order to further improve the efficiency of the MRT-LB method, the multi-block grid refinement (MBGR) technique was used. The accuracy and efficiency of the MBGR and the consistency of physical quantities across the interface were investigated. In simulation of particle dispersion in the model room, particles with diameters of 1 and 10 µm were considered. It is shown that this model can successfully capture dispersion characteristics of particles.

Synergistic disinfection of aerosolized bacteria and bacteriophage by far-UVC (222-nm) and negative air ions.

Air ionizers and 222-nm krypton-chlorine (KrCl) excilamp have proven to be effective disinfection apparatus for bacteria and viruses with limited health risks. We determined inactivation efficiencies by operating them individually and in combined modules. Gram-positive and gram-negative bacteria, non-enveloped dsDNA virus, and enveloped dsRNA virus were examined in a designed air disinfection system. Our results showed that the bioaerosols were inactivated efficiently by negative ionizers and far-UVC (222-nm), either used individually or in combination. Among which the combined modules of negative ionizers and KrCl excilamp had the best disinfection performance for the bacteria. The aerosolized virus P22 and Phi 6 were more susceptible to 222-nm emitted by KrCl excilamp than negative air ions. Significant greater inactivation of bacterial bioaerosols were identified after treated by combined treatment of negative air ion and far-UVC for 2 minutes (Escherichia coli, 6.25 natural log (ln) reduction; Staphylococcus epidermidis, 3.66 ln reduction), as compared to the mean sum value of inactivation results by respective individual treatment of negative ionizers and KrCl excilamp (Escherichia coli, 4.34 ln; Staphylococcus epidermidis, 1.75 ln), indicating a synergistic inactivation effect. The findings provide important baseline data to support the design and development of safe and high-efficient disinfection systems.

A pilot study on the disinfection efficacy of localized UV on the flushing-generated spread of pathogens.

The process of toilet-flushing can generate flushing-associated water droplets which can potentially expose humans to pathogen-laden aerosols. Very little is known about such aerosol dissemination or the means for minimizing exposure to these aerosols. This study has evaluated the efficacy of ultraviolet waveband C (UV-C) for disinfection of flushing-generated pathogen-laden aerosols through tests with localized disinfection systems for airborne and surface contaminations. Three types of bacteria were chosen for investigation: Staphylococcus epidermidis, Escherichia coli, and Salmonella typhimurium. Tests were conducted with UV-C tubes of 5 W and 10 W. High levels of disinfection efficacies were observed, ranging from 76% to 97% for bacteria-laden aerosols at sources of emission, and efficiencies of 53% to 79% for surface samples in localized systems. The results from the localized systems were further compared with those obtained with an upper-room ultraviolet germicidal irradiation (UVGI) system. As it is important to note, the UV-C doses and ozone emissions for the localized systems were found well below the limits recommended in current guidelines. This research has shown that the disinfection of flushing-generated pathogen-laden aerosols in proximity to the source of emission was more effective than at the more distant sites where aerosols may be dispersed to the environment.

Effectiveness of facemasks to reduce exposure hazards for airborne infections among general populations.

Facemasks are widely used as a protective measure by general public to prevent inhalation of airborne pathogens including seasonal, swine and other forms of influenza and severe acute respiratory syndrome (SARS), etc. However, scientific data on effectiveness of facemasks in reducing infections in the community are extremely limited and even inconsistent. In this work, two manikins labelled as 'source' and 'susceptible' were used to measure the protection provided by facemasks under various emission scenarios. The source was modified to generate polydisperse ultrafine particles, whereas the susceptible was modified to mimic a realistic breathing pattern. The facemask was challenged by both pseudo-steady and highly transient emissions generated by an expiratory process where parameters, such as separation distance between manikins, emission velocity and expiratory duration, were controlled and measured systematically. Performances of four different types of facemask fits, varying from ideal to normal wearing practice, were also investigated. Under the pseudo-steady concentration environment, facemask protection was found to be 45 per cent, while under expiratory emissions, protection varied from 33 to 100 per cent. It was also observed that the separation between the source and the manikin was the most influential parameter affecting facemask protection.

Minimizing the exposure of airborne pathogens by upper-room ultraviolet germicidal irradiation: an experimental and numerical study.

There has been increasing interest in the use of upper-room ultraviolet germicidal irradiation (UVGI) because of its proven effectiveness in disinfecting airborne pathogens. An improved drift flux mathematical model is developed for optimizing the design of indoor upper-room UVGI systems by predicting the distribution and inactivation of bioaerosols in a ventilation room equipped with a UVGI system. The model takes into account several bacteria removal mechanisms such as convection, turbulent diffusion, deposition and UV inactivation. Before applying the model, the natural die-off rate and susceptibility constants of bioaerosols were measured experimentally. Two bacteria aerosols, Escherichia coli and Serratia marcescens, were tested for this purpose. It was found out that the general decay trend of the bioaerosol concentration predicted by the numerical model agrees well with the experimental measurements. The modelling results agree better with experimental observations for the case when the UVGI inactivation mechanism dominates at the upper-room region than for the case without UVGI. The numerical results also illustrate that the spatial distribution of airborne bacteria was influenced by both air-flow pattern and irradiance distribution. In addition to predicting the local variation of concentration, the model assesses the overall performance of an upper-room UVGI system. This model has great potential for optimizing the design of indoor an upper-room UVGI systems.

A new mathematical model for irradiance field prediction of upper-room ultraviolet germicidal systems.

There has been an increasing interest in the use of upper-room ultraviolet germicidal irradiation (UVGI) system because of its proven disinfection effect for airborne microorganisms. To better design and explore further potential applications of UVGI systems, it is of critical importance to predict the spatial UV intensity in enclosures. In this paper, we developed a new mathematical model to predict spatial radiation intensity for upper-room ultraviolet germicidal irradiation systems. The detail geometries of the lamp and the reflector were removed and replaced by introducing a fictitious irradiation surface near louver slots. The view factor approach was applied to evaluate the UV irradiance in a three-dimensional space with different louver configurations. With this approach no detail meshing of the fixture is required and this leads to significant simplification of the entire systems from modeling perspectives. To validate the model, experiments were performed in a full-scale environmental controlled chamber in which one UVGI fixture was mounted on a sidewall. The UV irradiance was measured by a radiometer. The results predicted by the present model agree very well with the experimental measurements. Factors affect the accuracy of the model was also discussed.

Particle deposition indoors: a review.

Particle deposition indoors has received increasing attention recently because of increasing concern about the effects of particle exposure on human health. Deposition is a positive phenomenon from the perspective of human health, as deposited particles cannot be inhaled unless resuspended. There are studies showing strong correlation between the prevalence of biological-origin airborne particles and the prevalence of some specific sick building syndrome (Menzies et al., 1998; Teeuw et al., 1994). In the literature, the amount of research effort put on particle deposition indoors which is directly related to human health and microcontamination control is far less than the amount of research on deposition in small diameter tube/channel. This is a summary of the full-length version which will appear on the home page. The full-length paper aims to provide an up-to-date revision for both experiment and modeling on particle deposition indoors. This paper summarizes the experimental studies for particle deposition indoors for non-industrial environments. In section 2, 'Background', an overview of the different mechanisms of particle deposition, focusing on indoor environments is addressed. In section 3, 'Experimental Study Review', a survey of aerosol deposition experiments in small experimental chambers and real houses (or large-scale chambers) is presented. Detailed experimental measurements are addressed for the real house studies. The experimental techniques of particle generation, particle labeling and detection methods are discussed. Although the present paper focuses on experimental studies, it would be more complete to include some discussions on the modeling of the term particle eddy diffusivity and it is reviewed in section 4, 'Modeling Review'.