Comparison of Legionella pneumophila and Pseudomonas fluorescens Quantification Methods for Assessing UV LED Disinfection.

This study assesses the efficacy of ultraviolet light-emitting diodes (UV LEDs) for deactivating Legionella pneumophila (pure culture) and Pseudomonas fluorescens (pure culture and biofilms) on relevant drinking water distribution system surfaces (cast iron and stainless steel). UV LED treatment at 280 nm demonstrated superior performance compared to that at 365 nm, achieving a 4.8 log reduction value (LRV) for P. fluorescens pure cultures and, for biofilms, 4.02 LRV for stainless steel and 2.96 LRV for cast iron at 280 nm. Conversely, the results were less effective at 365 nm, with suspected photolytic reactions on cast iron. Quantification of L. pneumophila yielded varying results: 4 LRV using standard plate counts, 1.8 LRV with Legiolert, and 1 LRV with quantitative polymerase chain reaction at 280 nm, while the results were less than 1.5 LRV at 365 nm. This study provides insights into managing opportunistic pathogens and biofilms, emphasizing the need for improved quantification tools to better assess treatment efficacy.

Improved disinfection performance for 280 nm LEDs over 254 nm low-pressure UV lamps in community wastewater.

Ultraviolet (UV) disinfection has been incorporated into both drinking water and wastewater treatment processes for several decades; however, it comes with negative environmental consequences such as high energy demands and the use of mercury. Understanding how to scale and build climate responsive technologies is key in fulfilling the intersection of UN Sustainable Development Goals 6 and 13. One technology that addresses the drawbacks of conventional wastewater UV disinfection systems, while providing a climate responsive solution, is UV light emitting diodes (LEDs). The objective of this study was to compare performance of bench-scale 280 nm UV LEDs to bench-scale low pressure (LP) lamps and full-scale UV treated wastewater samples. Results from the study demonstrated that the UV LED system provides a robust treatment that outperformed LP systems at the bench-scale. A comparison of relative energy consumptions of the UV LED system at 20 mJ cm-2 and LP system at 30 and 40 mJ cm-2 was completed. Based on current projections for wall plug efficiencies (WPE) of UV LED it is expected that the energy consumption of LED reactors will be on par or lower compared to the LP systems by 2025. This study determined that, at a WPE of 20%, the equivalent UV LED system would lead to a 24.6% and 43.4% reduction in power consumption for the 30 and 40 mJ cm-2 scenarios, respectively.

Immersive ultraviolet disinfection of E. coli and MS2 phage on woven cotton textiles.

Immersive ultraviolet disinfection provides a chemical-free technology for safer textiles, surfaces, and public spaces by inactivating communicable pathogens. This study examined immersive UV disinfection, using a disinfection cabinet, of E. coli and MS2 that was inoculated on white cotton T-shirts. The impact that porous materials have on UV disinfection is poorly understood with the majority of previous surface disinfection research focusing on hard, smooth surfaces. Several approaches were used in this study to characterize the light dynamics within the disinfection cabinet including colorimetric dosimetry coupons, biodosimetry, and spectroradiometry. Micro and macro geometry of porous surfaces are important factors to consider when using immersive UV technologies. The geometry of the cabinet impacted the distribution of emitted UV light within the disinfection cabinet and the physical properties of a porous material, such as the woven pattern of cotton, both contribute to UV disinfection efficiency. This work identified that light distribution is crucial for immersive UV technologies as the delivered fluence was highly variable within the disinfection cabinet and resulted in a difference of several logs of reduction for adjacent areas of T-shirt samples. Other inoculated areas achieved upwards of 1-log reductions values for MS2 and upwards of 2-log reductions for E. coli.

Specificity of UV-C LED disinfection efficacy for three N95 respirators.

The recent surge in the use of UV technology for personal protective equipment (PPE) has created a unique learning opportunity for the UV industry to deepen surface disinfection knowledge, especially on surfaces with complex geometries, such as the N95 filter facepiece respirators (FFR). The work outlined in this study addresses the interconnectedness of independent variables (e.g., UV Fluence, respirator material) that require consideration when assessing UV light efficacy for disinfecting respirators. Through electron microscopy and Fourier-transform infrared (FTIR) spectroscopy, we characterized respirator filter layers and revealed that polymer type affects disinfection efficacy. Specifically, FFR layers made from polypropylene (PP) (hydrophobic in nature) resulted in higher disinfection efficiency than layers composed of polyethylene terephthalate (PET-P) (hygroscopic in nature). An analysis of elastic band materials on the respirators indicated that silicone rubber-based bands achieved higher disinfection efficiency than PET-P bands and have a woven, fabric-like texture. While there is a strong desire to repurpose respirators, through this work we demonstrated that the design of an appropriate UV system is essential and that only respirators meeting specific design criteria may be reasonable for repurposing via UV disinfection.

Assessing the impact of multiple ultraviolet disinfection cycles on N95 filtering facepiece respirator integrity.

During the COVID-19 pandemic, N95 filtering facepiece respirators (FFRs) were recommended to protect healthcare workers when providing care to infected patients. Despite their single-use disposable nature, the need to disinfect and repurpose FFRs is paramount during this global emergency. The objectives of this study were to (1) determine if UV treatment has an observable impact on respirator integrity; (2) test the impact of UV treatment on N95 FFR user fit; and (3) test the impact of UV treatment on FFR integrity. Ultraviolet (UV) disinfection was assessed in maintaining N95 FFR integrity. Two models of FFRs were exposed to UV fluences ranging from 0 to 10,000 mJ cm-2 per side and subsequently tested for fit, respirator integrity, and airflow. Inspection of N95 FFRs before and after UV treatment via microscopy methods showed no observable or tactile abnormalities in the integrity of respirator material or straps. Tensile loading tests on UV-treated and untreated respirator straps also demonstrated no impact on breaking strength. Standardized fit test methods showed no compromise in user fit following UV treatment. Evaluation of particle penetration and airflow through N95 FFRs showed no impact on integrity, and average filtration efficiency did not fall below 95% for any of the respirator types or fluence levels. This work provides evidence that UV disinfection does not compromise N95 FFR integrity at UV fluences up to 10,000 mJ cm-2. UV disinfection is a viable treatment option to support healthcare professionals in their strategy against the spread of COVID-19.

Monitoring the influence of wastewater effluent on a small drinking water system using EEM fluorescence spectroscopy coupled with a PARAFAC and PCA statistical approach.

The potential use of a statistical approach for the investigation of complex dissolved organic matter (DOM) sources in surface water within a recycled water system monitored by excitation-emission matrix (EEM) fluorescence spectroscopy is shown. The work in this manuscript utilize information extracted from EEM spectroscopy to characterize DOM in collected surface water samples along with a wastewater treatment plant to drinking water treatment plant, discussing that humic-like and protein-like DOM sources predominate in the investigated water samples. Five different fluorescent components were resolved, describing several different types of DOM with different excitation and emission spectra that were distinct among the watershed sampling sites and indicating the influences of anthropogenic impacts. In addition, these novel fluorescence parameters have potential to improve resolution to direct more targeted water quality monitoring approaches.