UV-C Device Research Articles

The Decontamination of N95 Masks as an Occupational Safety Strategy

Objective: This study aimed to monitor the use of a short-wave ultraviolet (UV-C) decontamination device for N95 masks at the João de Barros Barreto University Hospital, Belém, Pará, Brazil. The research investigated the reuse of masks, storage methods, and the perception of healthcare professionals regarding the decontamination protocol using UV-C after each work shift. Theoretical Framework: The research is based on theories related to biosafety and occupational health, focusing on the importance of decontamination processes in hospital settings to enhance the protection of healthcare workers and reduce infection risks. Method: A cross-sectional study was conducted with 295 nursing professionals, including nurses, technicians, and assistants. Data were collected through a questionnaire addressing the reuse of N95 masks, storage between uses, and opinions on the use of the UV-C device for decontamination. Results and Discussion: All participants (n=295) agreed that UV-C decontamination improves biosafety by reducing the handling of potentially contaminated masks. The acceptance of the device was unanimous, confirming its feasibility both in high-demand scenarios, such as the Covid-19 pandemic, and in routine hospital practices. Research Implications: This study demonstrates that implementing UV-C decontamination systems is a practical and effective solution for hospitals, with the potential to increase occupational safety and reduce infectious waste generation. Originality/Value: The study contributes to the literature by highlighting the feasibility and benefits of reusing N95 masks with UV-C decontamination, promoting greater safety in hospital environments.

Portable UV-C Device to Treat High Flow of Infectious Aerosols Generated during Clinical Respiratory Care.

Respiratory interventions including noninvasive ventilation, continuous positive airway pressure and high-flow nasal oxygen generated infectious aerosols may increase risk of airborne disease (SARS-CoV-2, influenza virus) transmission to healthcare workers. We developed/tested a prototype portable UV-C254 device to sterilize high flows of viral-contaminated air from a simulated patient source at airflow rates of up to 100 l/m. Our device consisted of a central quartz tube surrounded 6 high-output UV-C254 lamps, within a larger cylinder allowing recirculation past the UV-C254 lamps a second time before exiting the device. Testing was with nebulized A/PR/8/34 (H1N1) influenza virus. RNA extraction and qRT-PCR showed virus transited through the prototype. Turning on varying numbers of lamps controlled the dose of UVC. Viability experiments at low, medium and high (100 l/min) flows of contaminated gas were conducted with 6, 4, 2 and 1 lamp activated (single-pass and recirculation were tested). Our data show 5-log reduction in particle forming units from a single lamp (single- pass and recirculated conditions) at high and low flows. UVC dose at 100 l/m was calculated at 11.6 mJ/cm2 single pass and 104 mJ/cm2 recirculated. The protype device shows high efficacy in killing nebulized influenza virus in a high flow of contaminated air.

Synergistic electrochemical and optical properties of a UVC class quaternary nanocomposite incorporating graphene oxide and samarium chromium oxide perovskite

This research presents a comprehensive investigation into a novel quaternary nanocomposite comprising graphene oxide (GO), samarium chromium oxide perovskite (SmCrO3), silicon dioxide (SiO2), and tin dioxide (SnO2). The nanocomposite was synthesized using a modified Stöber method. In order to assess its potential applications in supercapacitors and UVC devices, an extensive analysis of its electrochemical and optical properties was conducted. The crystal structure and phase identification were analyzed using X-ray diffraction (XRD) and Rietveld refinement with X'pert HighScore Plus software, confirming the successful formation of the nanocomposite. Scanning electron microscopy (SEM) provided valuable insights into the structural morphology, while energy dispersive X-ray spectroscopy (EDS) confirmed the presence of constituent elements. Fourier transform infrared (FTIR) analysis and Raman Spectroscopy elucidated the functional groups and chemical bonds, confirming the successful synthesis of the nanocomposite. UV–Vis spectroscopy and photoluminescence (PL) spectroscopy revealed its strong UV radiation absorption and intensified fluorescence properties and confirming the band gap of SmCrO3 and GO/SmCrO3/SiO2/SnO2 quaternary nanocomposite as ∼5.4 eV and 4.84 eV respectively. The potential of nanocomposite potential as a supercapacitor material was evaluated through cyclic voltammetry (CV) measurements and electrochemical impedance spectroscopy (EIS) analyses. Remarkably, the specific capacitance of the nanocomposite reached 253.75 Fg−1 at a scan rate of 10 mVs−1, and electrochemical surface area of 507 cm2, highlighting its exceptional charge storage capability and promising prospects for high-performance energy storage devices. This comprehensive study addresses a significant knowledge gap, providing a profound understanding of the electrochemical and optical behavior of the quaternary nanocomposite. The observed exceptional results underscore its suitability for supercapacitor applications and expected favorable material for UVC device technologies.

Disinfection of needleless connectors for catheters in one second using a hand-held UV device

The standard of care for disinfecting needleless connectors (NCs) of central venous catheters includes alcohol-containing caps or up to a 15-second scrub with alcohol or chlorhexidine. Due to the clinical impact and high cost of treating Central line-associated bloodstream infections (CLABSI), reducing the incidence of CLABSI is a priority for public health and of the Centers for Disease Control. Alcohol-containing caps have been demonstrated to disinfect external NC surfaces, but not the internal surface. Ultraviolet light (UV-C) is a strategy for disinfection of NC internal and external surfaces. Four clinically relevant bacteria (Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli,Pseudomonas aeruginosa) and Candida albicans were inoculated on NCs. Disinfection efficacy was measured after exposure to one second of 285nm UV-C light at 48mW/cm2 in a proprietary handheld device and UV-C transparent NC or standard of care. Disinfection of internal and external surfaces of NC inoculated with S aureus using alcohol caps, and UV-C was also compared. A 4-log reduction in colony forming units (CFUs) on the interior and exterior surfaces of the UV-transparent NC of clinically relevant pathogens was observed with UV-C light at this power for 1second. We demonstrated the efficacy of UV-C for the disinfection of NCs in one second using the UV-C device in benchtop studies. This device holds promise for reducing CLABSI, and clinical studies are planned.

Preclinical safety evaluation of continuous UV-A lighting in an operative setting.

Germicidal ultraviolet (UV-C) light has been shown as an effective modality for disinfection in laboratory settings and in the operative room. Traditionally, short-wavelength UV-C devices, which have previously been shown to cause DNA damage, are utilized only for disinfection in pre- and post-operative settings and are not continuously active during operations. Continuous use of intraoperative UV light has potential to decrease pathogens and subsequent surgical site infections (SSIs), which arise in approximately 5-15% of operative cases. SSIs are a significant determinant of patient morbidity, readmission rates, and overall cost. Therefore, a method of UV light disinfection with a low risk of DNA damage is needed so that greater antimicrobial protection can be afforded to patients during the entirety of their surgical procedures. A new disinfection device that harnesses longer-wavelength UV-A light to disinfect the surgical field throughout the entirety of the procedure, including pre- and post-operation has been developed. This study aimed to determine if UV-A light administered intraoperatively was safe, as defined by the minimal presence of DNA damage and safe amounts of reflection upon medical personnel. Using in vitro models, we examined the differential impacts of UV-C and UV-A light on DNA damage and repair pathways. In a murine model, we looked at the production of DNA damage photoproduction in relation to UV-A versus UV-C exposure. Our results show UV-A light does not induce a significant amount of DNA damage at the cellular or tissue level. Furthermore, a preclinical porcine study showed that surgical personnel were exposed to safe levels of UV-A irradiance from an overhead UV-A light used during an operation. The amount of UV-A transmitted through surgical personal protective equipment (PPE) also remained within safe levels. In conclusion, we found that UV-A may be safe for intraoperative use.

An efficient UV-C device for photoinactivation of human Corona and Influenza virus: Solution for small-scale reuse of personal protective equipment (PPE)

The world has recently witnessed a significant surge in the use of non-recyclable items such as Personal Protective Equipment (PPE) due to the COVID-19 pandemic. This has increased environmental pollution and caused a massive burden on the global waste management system. Hence, an effective strategy to address the demand-supply disparity and provide road map for sustainable management of used PPE are the need of the hour. In the present work, we aimed to develop a cost-effective, convenient, and effective strategy to safely reuse PPE by engineering an in-house UV-C-based Sanitization Device (UVSD) and systematically evaluating its potential to disinfect virus-contaminated PPE. To this end, we tested the capacity of the UVSD to disinfect single-use PPE and N95 face masks, experimentally soiled with the human Influenza (A/PR/8/1934/H1N1) and human Coronavirus (HCoV-OC43). For this, the UV-C-based photoinactivation of both viruses was assessed by in vitro cell protection, quantification of viral gene transcript, and residual viral load by plaque-forming assay. Further, Indirect immunofluorescence and viral hemagglutination assays were also performed to visualize and quantify the viral titers at different post-exposure (UV-C) time points. Our results demonstrate that 15 min exposure to the virus-contaminated simple or complex PPE within the UVSD cabinet could effectively inactivate both the H1N1 and HCoV-OC43 viruses.

Tolerance of clinical vancomycin-resistant Enterococcus faecium isolates against UV-C light from a mobile source

BackgroundAdmission to a room previously occupied by patients carrying environmentally robust pathogens implies an increased risk of acquiring those pathogens. Therefore, ‘No-touch’ automated room disinfection systems, including devices based on UV-C irradiation, are discussed to improve terminal cleaning. It is still unclear if clinical isolates of relevant pathogens behave differently under UV-C irradiation compared to laboratory strains used in the approval process of disinfection procedures. In this study we analysed the susceptibility of well characterized clonally divergent vancomycin-resistant enterococci (VRE) strains, including a linezolid-resistant isolate, against UV-C radiation.MethodsSusceptibility against UV-C of ten clonally divergent clinical isolates of VRE was determined in comparison to the commonly used test organism Enterococcus hirae ATCC 10541. Ceramic tiles contaminated with 105 to 106 colony forming units/25 cm² of the different enterococci were positioned at a distance of 1.0 and 1.5 m and irradiated for 20 s, resulting in a UV-C dose of 50 and 22 mJ/cm², respectively. Reduction factors were calculated after quantitative culture of the bacteria recovered from treated and untreated surfaces.ResultsSusceptibility to UV-C varied considerably among the strains studied, with the mean value of the most robust strain being up to a power of ten lower compared to the most sensitive strain at both UV-C doses. The two most tolerant strains belonged to MLST sequence types ST80 and ST1283. The susceptibility of the laboratory strain E. hirae ATCC 10541 ranged between the most sensitive and most tolerant isolates for both irradiation doses. However, for UV-C dose of 22 mJ/cm², the reduction of the most tolerant isolate of ST1283 was statistically significantly lower compared to E. hirae ATCC 10541. The most susceptible strains belonged to the MLST sequence types ST117 and ST203.ConclusionsThese results indicate that UV-C doses reported in the literature are sufficient for the reduction of commonly used reference strains of enterococci but could be insufficient for the reduction of tolerant patient VRE-isolates in a hospital setting. Therefore, for future studies, the most tolerant clinical isolates should be used to validate automated UV-C devices or longer exposure times should be expected to ensure efficacy in the real world.

Can a UV-C box help the cinema industry by disinfecting video cameras?

UV-C has proven to be an effective virucide and microbicide, and its cost-effectiveness allowed it to spread as a disinfecting procedure in different environments. The study aims to determine the microbicide activity on Staphylococcus aureus, Escherichia coli and SARS-CoV-2 of the UV-C Boxer by Cartoni S.p.A. Three separate experiments were performed to assess the effectiveness of the UV-C disinfection device on different materials, directly on surfaces of a video camera and on a specific carrier for SARS-CoV-2. In all three experiments, a significant abatement of bacterial and viral contamination was reached after 60 seconds on carriers and after 3 minutes on all examined surfaces of the video camera, with a higher reduction on glass carriers. UV-C devices may be a valuable tool to implement in the working routine to achieve a higher level of safety in work environments.

Real-Life Assessment of the Ability of an Ultraviolet C Lamp (SanificaAria 200, Beghelli) to Inactivate Airborne Microorganisms in a Healthcare Environment.

Airborne-mediated microbial diseases represent one of the major challenges to public health. Ultraviolet C radiation (UVC) is among the different sanitation techniques useful to reduce the risk of infection in healthcare facilities. Previous studies about the germicidal activity of UVC were mainly performed in artificial settings or in vitro models. This study aimed to assess the sanitizing effectiveness of a UVC device (SanificaAria 200, Beghelli, Valsamoggia, Bologna, Italy) in 'real-life' conditions by evaluating its ability to reduce microbial loads in several hospital settings during routine daily activities. The efficacy of the UVC lamp in reducing the bacterial component was evaluated by microbial culture through the collection of air samples in different healthcare settings at different times (30 min-24 h) after turning on the device. To assess the anti-viral activity, air samplings were carried out in a room where a SARS-CoV-2-positive subject was present. The UVC device showed good antibacterial properties against a wide range of microbial species after 6 h of activity. It was effective against possible multi-drug resistant microorganisms (e.g., Pseudomonas spp., Acinetobacter spp.) and spore-forming bacteria (e.g., Bacillus spp.). In addition, the UVC lamp was able to inactivate SARS-CoV-2 in just one hour. Thanks to its effectiveness and safety, SanificaAria 200 could be useful to inactivate airborne pathogens and reduce health risks.

Epitaxial hexagonal boron nitride with high quantum efficiency

Two-dimensional (2D) hexagonal boron nitride (h-BN) is one of the few materials showing great promise for light emission in the far ultraviolet (UV)-C wavelength, which is more effective and safer in containing the transmission of microbial diseases than traditional UV light. In this report, we observed that h-BN, despite having an indirect energy bandgap, exhibits a remarkably high room-temperature quantum efficiency (∼60%), which is orders of magnitude higher than that of other indirect bandgap material, and is enabled by strong excitonic effects and efficient exciton-phonon interactions. This study offers a new approach for the design and development of far UV-C optoelectronic devices as well as quantum photonic devices employing 2D semiconductor active regions.

Enhanced Photoresponsivity UV-C Photodetectors Using a p-n Junction Based on Ultra-Wide-Band Gap Sn-Doped β-Ga2O3 Microflake/MnO Quantum Dots.

Solar-blind self-powered UV-C photodetectors suffer from low performance, while heterostructure-based devices require complex fabrication and lack p-type wide band gap semiconductors (WBGSs) operating in the UV-C region (<290 nm). In this work, we mitigate the aforementioned issues by demonstrating a facile fabrication process for a high-responsivity solar-blind self-powered UV-C photodetector based on a p-n WBGS heterojunction structure, operating under ambient conditions. Here, heterojunction structures based on p-type and n-type ultra-wide band gap WBGSs (i.e. both are characterized by energy gap ≥4.5 eV) are demonstrated for the first time; mainly p-type solution-processed manganese oxide quantum dots (MnO QDs) and n-type Sn-doped β-Ga2O3 microflakes. Highly crystalline p-type MnO QDs are synthesized using cost-effective and facile pulsed femtosecond laser ablation in ethanol (FLAL), while the n-type Ga2O3 microflakes are prepared by exfoliation. The solution-processed QDs are uniformly dropcasted on the exfoliated Sn-doped β-Ga2O3 microflakes to fabricate a p-n heterojunction photodetector, resulting in excellent solar-blind UV-C photoresponse characteristics (with a cutoff at ∼265 nm) being demonstrated. Further analyses using XPS demonstrate the good band alignment between p-type MnO QDs and n-type β-Ga2O3 microflakes with a type-II heterojunction. Superior photoresponsivity (922 A/W) is obtained under bias, while the self-powered responsivity is ∼86.9 mA/W. The fabrication strategy adopted in this study will provide a cost-effective means for the development of flexible and highly efficient UV-C devices suitable for energy-saving large-scale fixable applications.

Field Study and Evaluation of KrCl* Far UV-C Device Capability for Inactivation of Phi6 Bacteriophage.

"Far UV-C" is an effective disinfection method that can be deployed in occupied areas. Commercially available Krypton Chloride (KrCl*) excimer lamps filtered to emit at 222 nm are effective in disinfecting pathogens and safe for human exposure up to an allowable threshold exposure, which is much longer than for conventional UV lamps emitting at 254 nm. Laboratory and controlled field testing of a filtered KrCl* excimer lamp for disinfection of a virus suspended in a thin film aqueous solution in an occupied office setting was conducted. Complete inactivation of almost 6 log (99.9999%) of Phi6 bacteriophage virus was achieved in ~20 min of exposure time in a field setting, equivalent to a dose of about 10 mJ cm-2 . The Phi6 inactivation rate constant for the field test results were not statistically different from laboratory values (P > 0.05, paired t-test). When positioned at 1 m distance from possible human exposure, this device can be used safely for almost 4.5 h of continuous direct exposure without any acute or long-term adverse health effects. This study illustrates the applicability and deployment of Far UV-C for pathogen reduction and can help in decision making for implementation of Far UV-C for disinfection in human-occupied environments.

Self-reported Side-effects of Ultraviolet-C Disinfection Devices.

The COVID-19 pandemic increased sales of portable UV-C devices as a means of inactivating the SARS-CoV-2 virus. Research suggests that excessive UV-C exposure to the eyes and skin can lead to side-effects, primarily photokeratitis and erythema, but these findings are limited to case studies. This study explores self-reported side-effects of UV-C devices by collating five waves of UK consumer survey data from April 2020-December 2021 (N=26 864). 30%-46% of owners report a side-effect after using a device claiming to emit UV-C. However, detailed analysis of Wave 4 data (N =309) highlights inconsistencies between reported and plausible side-effect(s) associated with skin or eye exposure from UV-C devices. Alternative explanations are considered, namely that the reported side-effect(s) were psychosomatic or misattributed to direct exposure of UV-C radiation. Data regarding awareness of warnings about device side-effect(s) supports the misattribution explanation. For risk assessment purposes, limited reliable information about specific irritation or injury to the eye and skin was found from self-reporting surveys. To optimize future data collection, we recommend addressing recall errors by: reducing the period under investigation, supplementing responses with empirical measures, and incentivizing respondents to provide accurate information about the make and model of the UV-C device.

Stylish UV-C lamp for disinfecting household objects

Abstract Background Considering the current pandemic situation, the growing problem of antibiotic resistance and the increase in healthcare costs, attention to daily disinfection is becoming increasingly important. This study aimed to evaluate the bactericidal efficacy of a modern and stylish UV-C device designed for the home environment. Methods The experimental study was conducted between July-August 2020 on four bacterial strains: Staphylococcus aureus, Salmonella typhymurium, Klebsiella pneumoniae and Escherichia coli. The UV-C device consist of a protective dome with a reflective coating, a UV-C lamp (placed in the device base) and three reflective holders. Different positions and exposure times were tested using two different carriers holder for the bacterial inoculum (plastic and stainless steel) to estimate the germicidal efficency related to UV-C lamp exposure, with direct and reflected (from the dome coating) light. Results The experiment showed that the higher bacterial inactivation effect (3.5 to 7 log10) was achieved for all four strains at 3 minutes, but even at 1 minute, there is a marked reduction in the bacterial load with the only exception of Klebsiella pneumoniae. After 45 and 30 seconds, steel carriers contaminated by Escherichia coli and Staphylococcus aureus on the opposite side of the UV-C source showed significant reductions in the range between 99 and 99,9%. Conclusions The device has proven to be effective for the disinfection of various everyday objects placed into the lamp and introduces beauty to the household environment. Key messages • In this study, UV-C device proved to be a valuable tool for disinfecting household items and enhancing safety for everyday health. • UV-C device proved to be a valuable tool for disinfecting household items and enhancing safety for everyday health.

Efficacy of Ultraviolet Radiations against Coronavirus, Bacteria, Fungi, Fungal Spores and Biofilm

Ultra-violet (UV) C (200–280 wavelength) light has long been known for its antimicrobial and disinfecting efficacy. It damages DNA by causing the dimerization of pyrimidines. A newly designed technology (MUVi-UVC; Mobile UV Innovations Pty Ltd., Melbourne, VIC, Australia) that emits UVC at 240 nm is composed of an enclosed booth with three UVC light stands each with four bulbs, and has been developed for disinfecting mobile medical equipment. The aim of this project was to examine the spectrum of antimicrobial activity of this device. The experiments were designed following ASTM E1052-20, EN14561, BSEN14476-2005, BSEN14562-2006 and AOAC-Official-Method-966.04 standards for surface disinfection after drying microbes on surfaces. The disinfection was analyzed using Staphylococcus aureus (ATCC 6538), Pseudomonas aeruginosa (6294), Candida auris (CBS 12373), spores of Aspergillus niger (ATCC 16404), coronavirus (SARS-CoV-2 surrogate ATCC VR-261) as well as a methicillin-resistant Staphylococcus aureus (SA31), a carbapenem- and polymyxin-resistant Pseudomonas aeruginosa (PA219), Escherichia coli K12 (ATCC 10798) and Salmonella typhi (ATCC 700730). The parameters of time, the number of lights and direction of the sample facing the lights were examined. The MUVi-UVC was able to kill 99.999% of all of the tested bacteria, fungi, coronavirus and bacteria in the biofilms if used for 5 min using all three lights in the setup with the glass slides in a vertical position. However, for fungal spores, 30 min were required to achieve 99.999% killing. There was a small but insignificant effect of having the surface horizontally or vertically aligned to the UV lights. Therefore, this UVC device is an effective technology to disinfect medical devices.

Protocol for Evaluating the Microbial Inactivation of Commercial UV Devices on Plastic Surfaces.

With the plethora of commercially available UV-C devices exhibiting different intensity and lifespans, it is critical to consumer safety that companies verify and clearly communicate the efficacy of their devices as per the intended use. The purpose of this study was to define a low-cost protocol for investigating the antimicrobial efficacy of commercial UV devices for industry use. The tested devices included: a wall-mounted unit (Device A), a troffer unit (Device B), and an induction lamp unit (Device C). The devices were installed within an enclosed tower to prevent the transmission of UV-C radiation outside of the testing area. The procedure details determining the devices′ antimicrobial efficacy using plastic coupons inoculated with Escherichia coli or Staphylococcus aureus. The protocol includes suggested time–distance treatments according to the potential application of each device type and reports the results as log CFU/mL reduction or percent reduction.

Reduction in Operating Room Airborne Particle Burden and Time-Dependent Contamination of Sterile Instrument Trays With the Use of a Novel Air Filtration System.

IntroductionPostoperative infections represent a substantial burden to patients and healthcare systems. To improve patient care and reduce healthcare expenditures, interventions to reduce surgical infections must be employed. The crystalline C-band ultraviolet (UV-C) air filtration technology (Aerobiotix Inc., Miamisburg, OH, USA) has been designed to reduce airborne bioburden through high-quality filtration and germicidal irradiation. The purpose of this study was to assess the ability of a novel UV-C air filtration device to reduce airborne particle counts and contamination of surgical instrument trays in an operating room (OR) setting.Materials and methodsThirty sterile instrument trays were opened in a positive-air-flow OR. The trays were randomly assigned to one of two groups (UV-C or control, n=15 per group). In the UV-C group, the UV-C filtration device was used and in the control, it was not. All trays were opened with the use of a sterile technique and left exposed in the OR for four hours. Air was sampled by a particle counter to measure the numbers of 5µm and 10µm particles. Culture specimens were obtained from the trays to assess for bacterial contamination. Outcome data were collected at 30-minute intervals for the duration of the four-hour study period.ResultsUse of the UV-C device resulted in statistically significant reductions in the numbers of 5µm (average of 64.9% reduction when compared with the control, p<0.001) and 10µm (average of 65.7% reduction when compared with the control, p<0.001)-sized particles detectable in the OR. There was no significant difference in the overall rates of contamination (33.3% in the control group vs. 26.7% in the UV-C group, p=1.0) or the time to contamination (mean survival of 114 minutes in the control group vs. 105 minutes in the UV-C group, p=0.72) of surgical instrument trays with the use of the UV-C device.ConclusionsThe results demonstrate that the UV-C filtration device can successfully reduce airborne bioburden in standard ORs, suggesting that it may have the potential to reduce the risk for wound and hardware infections. Further clinical trials are necessary to better determine the effect of this air filtration system on postoperative infection rates.

Improvement and standardization of disinfection in hospital theatre with ultraviolet-C technology

The level of disinfection between operating sessions is important to prevent cross-contamination risk in operating theatres. To assess the difference in microbial contamination between different disinfection levels, before (T0) and after (T1) application of a UVC device (UVC-D). A cross-sectional study was conducted between December 2019 and August 2020 in a clinic. Three disinfection levels - no disinfection after surgery, after in-between cleaning, and after terminal cleaning - were compared to assess the reduction of microbial presence at T0 and T1 according to the use of UVC-D for 3-5min per bedside. A total of 260 Petri dishes, divided into a preliminary phase followed by a probabilistic model-driven experiment, were used in three operating theatres, and colony-forming units (cfu) were counted. The Mann-Whitney test was performed in the preliminary phase to establish UVC exposure time. Using the probabilistic model, descriptive statistics and percentage and log10 reduction were calculated. The multivariate analysis of variance (MANOVA) for repeated measures was performed to verify the 95% statistical difference between T0 and T1, combined with the disinfection levels and different operating theatres. The Mann-Whitney test showed no cfu difference between 3 and 5min of UVC exposure time; the MANOVA test showed no significant difference between disinfection levels in T0 - T1 cfu reduction with a mean cfu reduction of 72% (95% confidence interval: 61.7-84.9) regardless of the disinfection level applied previously. UVC-D has improved environmental disinfection in all initial conditions. Together with the classic sanitizing procedures already present, it improves and standardizes the level of environmental hygiene.

Inactivation of biofilm-bound bacterial cells using irradiation across UVC wavelengths

Opportunistic pathogens (OPs), such as Pseudomonas spp., Legionella spp., and mycobacteria, have been detected in biofilms in drinking water distribution systems and water storage tanks and pose potential risks to finished drinking water quality and safety. Emerging UV technologies, such as UV light emitting diodes (LEDs) and krypton chloride (KrCl*) excimers, could provide an alternative to chemical-based secondary disinfection (i.e., chlorine or chloramines) for controlling biofilm-bound OPs. UV systems offer long lifetimes, ability to select wavelength, small size with high power density, and limited-to-no disinfection by-product formation. In this study, inactivation of biofilm-bound Pseudomonas aeruginosa cells across different maturities was investigated using five UVC devices with different peak emission wavelengths, including a KrCl* excimer (222 nm), a low pressure mercury vapor lamp (254 nm), and three UV LEDs (260 nm, 270 nm, and 282 nm). The UV transmittance and absorbance through the biofilm structure was also documented for the first time using a unique approach. Our results show all UVC devices can inactivate biofilm-bound P. aeruginosa cells up to a point, among which the UV LED with peak emission at 270 nm provided the best disinfection performance. UV sensitivities of biofilm-bound cells decreased with biofilm maturity and while initial rates of inactivation were high, no more than 1.5-2.5 log reduction was possible. Re-suspended biofilm bacteria in aqueous solution were highly sensitive to UV, reaching greater than 6 log reduction. UV shielding by biofilm constituents was observed and was likely one of the reasons for UV resistance but did not fully explain the difference in UV sensitivity between biofilm-bound cells versus planktonic cells. This study improves upon fundamental knowledge and provides guidance for innovative designs using emerging UV technologies for biofilm and pathogen control in water distribution systems.

Analysis of the efficiency improvement of 273 nm AlGaN UV-C micro-LEDs

UV-C LEDs have great application prospects in the fields of sterilization, disinfection, and non-line-of-sight solar-blind communication. However, their efficiency is currently not high enough to satisfy these applications and needs to be improved. In this work, AlGaN based UV-C LEDs (273 nm) with size from 8 to 200 μm were fabricated to evaluate the size effect of external quantum efficiency (EQE). Higher EQE was detected in smaller-size UV-C micro-LEDs. Simulations on EQE were performed. The analysis on experimental data and the simulation results reveals that higher EQE originates from both higher internal quantum efficiency at high current densities due to better current spreading and higher light extraction efficiency (LEE) due to the larger proportion of sidewall. From the efficiency improvement mechanism, it is concluded that the most sever current density non-uniformity and LEE loss of UV-C devices compared with visible or near ultraviolet LEDs can be effectively restrained by preparing micro-LEDs. Our work helps to optimize the efficiency characteristics for UV-C applications.