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.

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.

Inactivation of biofilm-bound Pseudomonas aeruginosa bacteria using UVC light emitting diodes (UVC LEDs).

Ultraviolet light emitting diodes (UV LEDs) are a promising technology for the disinfection of water and wetted surfaces, but research into these applications remains limited. In the drinking water field, UV LEDs emitting at wavelengths ranging from 254 nm to 285 nm (UVC LEDs) have been shown to be effective for the inactivation of numerous pathogens and pathogen surrogate organisms at UV doses comparable to conventional germicidal UV lamps. Surface disinfection with UV light, from UVC LEDs or from conventional UV lamps, is not as well understood. As the technology underlying the design and construction of UV LEDs matures and their energy efficiency improves, it is likely that they will become ubiquitous in small scale water treatment applications and surface disinfection in various industries, including the medical and dental fields. A simple, easily replicated methodology was developed and optimized to grow, irradiate, and recover biofilms from coupons. It was hypothesized that higher UV doses would be required to inactivate biofilm-bound bacteria than planktonic (free-floating) bacteria because the biofilm would provide some degree of protection from the effects of UVC irradiation. Indeed, UV LED irradiation at 265 nm achieved 1.3 ±â€¯0.2 log inactivation of biofilm-bound Pseudomonas aeruginosa at a UV dose of 8 mJ/cm2. This inactivation level is lower than those that have been reported by researchers using UVC LEDs to inactivate planktonic P. aeruginosa, a finding that can be explained by the higher resistance of biofilm-bound bacteria to UV inactivation. A dose-response curve was developed and fitted to three disinfection models: the Chick-Watson model, the multi-target model, and the Geeraerd model. This last, which posits a subpopulation of organisms that are resistant to treatment, was a good fit to the dose-response data. ATP results obtained using the biomass recovery ATP method (ATPBR), a method that includes a 4 h incubation period after treatment, was well correlated to the results of conventional plate counts.