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Fluence (UV Dose) Required to Achieve Incremental Log Inactivation of Bacteria, Protozoa, Viruses and Algae
... (1) The UV doses selected were based on the vastly reported MS-2 inactivation data in water samples tabulated by Malayeri et al. [13]. The MS-2 stock solution had a concentration of approximately 10 9 PFU/mL and was transferred to the surfaces with a Figure 1 displays the spread of UV 254 irradiance by the Trojan UV collimated beam. ...
... (1) The UV doses selected were based on the vastly reported MS-2 inactivation data in water samples tabulated by Malayeri et al. [13]. The MS-2 stock solution had a concentration of approximately 10 9 PFU/mL and was transferred to the surfaces with a cotton swab. ...
... The equivalence tests were run three times using different "practically zero" values, which were determined by data sets published in the literature [2,13,22]. Practical equivalence was determined by p-values below 0.05. These values were taken from peer-reviewed publications and standards as an acceptable range of k values for MS-2 inactivation in water. ...
The COVID-19 pandemic highlighted the limitations in scientific and engineering understanding of applying germicidal UV to surfaces. This study combines surface characterization, viral retention, and the related UV dose response to evaluate the effectiveness of UV254 as a viral inactivation technology on five surfaces: aluminum, ceramic, Formica laminate, PTFE and stainless steel. Images of each surface were determined using SEM (Scanning Electron Microscopy), which produced a detailed characterization of the surfaces at a nanometer scale. From the SEM images, the surface porosity of each material was calculated. Through further analysis, it was determined that surface porosity, surface roughness, contact angle, and zeta potential correlate to viral retention on the material. The imaging revealed that the aluminum surface, after repeated treatment, is highly oxidized, increasing surface area and surface porosity. These interactions are important as they prevent the recovery of MS-2 without exposure to UV254. The dose response curve for PTFE was steeper than ceramic, Formica laminate and stainless steel, as inactivation to the detection limit was achieved at 25 mJ/cm2. These findings are consistent with well-established literature indicating UV reflectivity of PTFE is maximized. Statistical testing reinforced that the efficacy of UV254 for surface inactivation varies by surface type.
... While the National Sanitation Foundation/American National Standards Institute (NSF/ANSI) 55 standards designate UV systems with a fluence >40 mJ/cm 2 as class A and >16 mJ/cm 2 as class B, most pathogens are inactivated at 5−10 mJ/cm 2 . 29 However, water quality parameters (e.g., UV transmittance, turbidity) and the type of microbial contaminant can have a significant effect on the effectiveness of the UV system. 29 In this study, we only used fecal indicator bacteria (total coliforms and E. coli). ...
... 29 However, water quality parameters (e.g., UV transmittance, turbidity) and the type of microbial contaminant can have a significant effect on the effectiveness of the UV system. 29 In this study, we only used fecal indicator bacteria (total coliforms and E. coli). Microorganisms more resistant to UV light (e.g., Adenovirus) may be present, 29 and therefore, a system with a higher fluence should be used when possible. ...
... 29 In this study, we only used fecal indicator bacteria (total coliforms and E. coli). Microorganisms more resistant to UV light (e.g., Adenovirus) may be present, 29 and therefore, a system with a higher fluence should be used when possible. If a UV system with a low fluence is used (e.g., 16 mJ/cm 2 ), households should ensure that the total flow rate at a single point-in-time is as low as possible. ...
UV water treatment can be a viable option for point-of-entry applications among households utilizing contaminated private water sources, including roof-harvested rainwater. However, limited data is available on UV system effectiveness and costs. Therefore, Love City Strong, an NGO in the US Virgin Islands, piloted a UV access program which included free UV systems with prefiltration along with installation and monthly household visits for up to 12 months, including water quality testing. In addition, a pilot study was conducted to evaluate the effectiveness of UV systems without prefiltration. Results from the UV access program demonstrated that E. coli was not detected in 95.1% of tap or spigot samples (n = 268). Among water quality parameters, household characteristics, and premise plumbing dynamics, no factor was significantly higher among samples with detections of E. coli or total coliforms. Among all samples from the pilot study of UV systems without prefiltration, no E. coli was detected (N = 24). Finally, there was a wide range of costs─first year and annual─when comparing different types and configurations of UV systems. Given these data, UV systems may be a viable option for generating potable water; however, clear purchasing and operational guidelines are important to reduce user error.
... Some papers reported the UV dose and response data. The UV disinfection of different spores and protozoa at different degrees of Log I was published by Malayeri et al. (2016). This current research aims to develop a simple and universal model to systematically predict the fluence required to achieve specific reduction log I by using the spores sensitive index (SPSI) and protozoan sensitive index (PSI) during UV disinfection. ...
... The database developed by Malayeri et al. (2016) was used to obtain a uniform set of first-order inactivation rate constants of spores and protozoa during UV disinfection. The inactivation rate constants of other spores and protozoa were divided by the mean k r as a reference spores and protozoa to derive their corresponding SPSI. ...
... By using the database which compiled by Malayeri et al. (2016), the inactivation UV dose at different Log I was modelled through a linear correlation analyses using SPSS of the IBM. The inactivation rate constant of each spore and protozoan were divided by the corresponding inactivation rate constants of the reference spores such as Bacillus subtilis, or the reference protozoa such as Cryptosporidium parvum, respectively. ...
During UV disinfection, the required UV dose in terms of fluence depends upon the species of bacteria spore and protozoa. To rank their UV disinfection sensitivity, spore sensitivity index (SPSI) and protozoan sensitivity index (PSI) are defined. For spores, shoulder effect exists, therefore, SPSI is defined as the ratio between the ki of any spores for the linear portion of the dose response curve to the kir of Bacillus subtilis as the reference spore. After statistical analysis, the fluence of any spore can be predicted by SPSI through equation, H = (0.8358 ± 0.126)*LogI*SPSI + H0. PSI is defined as the ratio between the inactivation rate constants of a protozoa in reference to that of Cryptosporidium parvum. The equation predicting the fluence of any protozoa in reference to Cryptosporidium parvum is: H = 107.45*(3.86 ± 2.68)*LogI/PSI. Two regression equations suggest that protozoa require significantly higher UV dose than bacteria spores.
HIGHLIGHTS
UV sensitivity index of bacteria spore and protozoa were defined.;
The UV fluence could be predicted by the UV sensitivity indexes.;
Protozoa required significantly higher UV dose than that required by spores.;
... The fluence level (UV dose) of the system evaluated in this study was >40 mJ/cm 2 while other locally available UV systems may provide a fluence as low as 30 or 16 mJ/cm 2 . While the National Sanitation Foundation/American National Standards Institute (NSF/ANSI) 55 standards designate UV systems with a fluence >40 mJ/cm 2 as class A and >16 mJ/cm 2 as class B, most pathogens are inactivated at 5-10 mJ/cm 2 (Malayeri et al., 2016). However, the type of microbial contaminant can have a significant influence on the effectiveness of the UV system (Malayeri et al., 2016). ...
... While the National Sanitation Foundation/American National Standards Institute (NSF/ANSI) 55 standards designate UV systems with a fluence >40 mJ/cm 2 as class A and >16 mJ/cm 2 as class B, most pathogens are inactivated at 5-10 mJ/cm 2 (Malayeri et al., 2016). However, the type of microbial contaminant can have a significant influence on the effectiveness of the UV system (Malayeri et al., 2016). In this study, we only used fecal indicator bacteria (total coliforms and E. coli). ...
... In this study, we only used fecal indicator bacteria (total coliforms and E. coli). Microorganisms more resistant to UV light (e.g., Adenovirus) may be present (Malayeri et al., 2016) and therefore a system with a higher fluence should be used when possible. If a UV system with a low fluence is used (e.g., 16 mJ/cm 2 ), households should . ...
UV water treatment can be a viable option for point-of-entry applications among households utilizing private water sources. In the US Virgin Islands (USVI), the primary water source is roof-harvested rainwater, collected in large cisterns and supplied to household taps via a pump. While diversification of water sources provides increased resilience to climate change, literature suggests rainwater catchment systems are at high risk of microbial contamination. One option USVI households have is UV systems. However, limited data is available on UV system effectiveness for USVI installations while these systems can be expensive. Therefore, Love City Strong, a local NGO, piloted a multi-year UV access program which included free UV systems with prefiltration along with installation and monthly household visits for up to 12 months including water quality testing. In addition, due to the significant costs associated with the prefiltration portion of the system, a pilot study was conducted to evaluate the effectiveness of the UV systems without prefiltration.
The results from the UV system access program demonstrated that E. coli was not detected in 95.2% of tap samples (n=271). Among samples with detectable levels of E. coli and total coliforms, turbidity was lower compared to samples with non-detections. Field teams reported user error was often identified in association with E. coli detections (e.g., bypass was opened). Among all samples from the pilot study of UV systems without prefiltration, no E. coli was detected (n=24). Total first-year costs for locally available UV systems with and without prefiltration ranged from 1,645 and 1,183, respectively, while operation and maintenance (O& M) costs ranged from 266 and 146, respectively. Given these data, UV systems may be a viable option for generating potable water; however, clear purchasing and installation protocols are needed as well as simple O&M guidelines for households to reduce user error.
Synopsis
Point-of-entry UV systems were able to produce water for domestic use with no detectable E. coli in 95.2% of samples among USVI households using roof-harvested rainwater.
... For example, vegetative bacterial cells such as Bacillus subtilis are much more sensitive than their spores [8]. Tabular overviews exist, which list the common irradiation doses required to reduce known pathogens [8,9]. However, these tables focus on bacteria and viruses. ...
... In the study presented here, the results of already published UVC inactivation studies are compiled and standardized in their presentation. The existing overviews by Kowalski and Malayeri et al. [8,9] mainly presented data that was obtained with 254 nm UVC radiation from low-pressure mercury vapor lamps. However, other UV spectral ranges also exhibit antimicrobial properties, and the same is true for visible violet or blue light, if the applied dose is high enough [19,20]. ...
Nearly two million people die each year from fungal infections. Additionally, fungal crop infections jeopardize the global food supply. The use of 254 nm UVC radiation from mercury vapor lamps is a disinfection technique known to be effective against all microorganisms, and there are surveys of published UVC sensitivities. However, these mainly focus on bacteria and viruses. Therefore, a corresponding overview for fungi will be provided here, including far-UVC, UVB, UVA, and visible light, in addition to the conventional 254 nm UVC inactivation.
The available literature was searched for photoinactivation data for fungi in the above-mentioned spectral ranges. To standardize the presentation, the mean log-reduction doses were retrieved and sorted by fungal species, spectral range, wavelength, and medium, among others. Additionally, the median log-reduction dose was determined for fungi in transparent liquid media.
Approximately 400 evaluable individual data sets from publications over the last 100 years were compiled. Most studies were performed with 254 nm radiation from mercury vapor lamps on Aspergillus niger, Candida albicans, and Saccharomyces cerevisiae. However, the data found were highly scattered, which could be due to the experimental conditions.
Even though the number of individual data sets seems large, many important fungi have not been extensively studied so far. For example, UV irradiation data does not yet exist for half of the fungal species classified as “high priority” or “medium priority” by the World Health Organization (WHO). In addition, researchers should measure the transmission of their fungal suspensions at the irradiation wavelength to avoid the undesirable effects of either absorption or scattering on irradiation results.
... UV-LED technology has several advantages over conventional mercury UV lamps, such as diversity of radiating wavelengths (from deep UV to near UV regions; 210-360 nm), small point light source, mercury-free, durability, compactness, extremely short warm-up time (intermittent-flow friendly), allowing versatile integration, lower energy consumption, and longer lifetime 20,25,26 . Since disinfection depends on the spectral sensitivity of the target microorganism rather than the UV source, the efficacy of LEDs for disinfection of protozoa, viruses, and bacteria was proven to be at least as effective as low-pressure UV lamps for a given wavelength and dose combination [27][28][29][30][31][32][33][34] . ...
... Bacteria (including biofilm-formers) and protozoa such as Cryptosporidium and Giardia that pose a health risk are easily inactivated at low UV doses, while viruses inactivation require higher doses 27 . UV-LEDs wavelength output is tunable based on their material composition 25 , making them an ideal technology for optimization of treatment objectives, as the response of each microorganism to different wavelengths is unique 32,33 . ...
Crop irrigation with treated wastewater effluent using drip irrigation has become common as demand for water supplies has increased. Because of the quality characteristics of treated wastewater and the narrow...
... We hypothesized that use of a microfiber cloth (Sanny Shop, Longmont, CO) dampened with water to wipe surfaces prior to UV-C irradiation (Surfacide, Waukesha, WI) would address soiling, and thus, that UV-C would be a noninferior approach to targeted surface disinfection with a microfiber cloth soaked in quaternary ammonium and alcohol chemicals (PDI Healthcare, Woodcliff Lake, NJ), regardless of horizontal orientation to the emitters or increased height from the floor of the environmental target. Our secondary hypothesis was that the dose of UV-C delivered would be sufficient for bactericidal activity against a variety of pathogens [17]. We conducted a laboratory study using the more pathogenic S. aureus ST5 to test these hypotheses [15]. ...
... Changes in the UV-C delivery configuration and/or treatment time as described in this study may impact the delivered dose of irradiation. Increases in the delivered dose may increase the risk of photo reactivation and reduce the practicality of clinical implementation, while reduced dose delivery may reduce efficacy against ST5 and additional vegetative, spore-forming, and/or fungal pathogens [17,26]. ...
Background: We hypothesized that ultraviolet-C (UV-C) irradiation (Surfacide, Waukesha, WI) following use of microfiber cloths (Sanny Shop LLC, Longmont, CO) soaked in water would be noninferior to surface disinfection wipes containing a quaternary ammonium compound and alcohol (PDI Healthcare, Woodcliff Lake, NJ) for the pathogenic Staphylococcus aureus (S. aureus) sequence type 5 (ST5).
Methods: This was a randomized laboratory study of disinfection approaches for S. aureus ST5. A total of 270 polycarbonate slides loaded with ST5 were prepared for the standard surface disinfection group (N=18) and water-soaked microfiber cloths and UV-C treatment group (N=144), along with positive and negative microbiological controls.
Results: All 18 samples of S. aureus ST5 bacteria treated with standard chemical wipes showed complete disinfection (colony forming units (CFU) = 0). All 144 treatments with water-soaked microfiber wipes followed by UV-C exposure showed complete disinfection (CFU =0) regardless of soiling, height from the floor, or orientation to the emitters. The upper 95% exact one-sided confidence limit for any CFU >0 was 2.1%.
Discussion: These data affirm our hypothesis that surface wiping with a damp cloth followed by triangular UV-C irradiation delivery is noninferior to surface disinfection for S. aureus ST5 using germicidal wipes, even when UV-C is compromised by height from the floor and orientation to the emitters and surface disinfection is targeted.
Conclusion: Removing bioburden with chemical-free microfiber cloths followed by triangular UV-C delivery is a noninferior strategy to targeted surface disinfection with chemical disinfecting wipes for the pathogenic S. aureus ST5 strain in the laboratory setting.
... In recent years, UVGI has received renewed interest after decades of underutilization and neglect [32]. The efficacy of UVGI systems is known to be affected by different parameters such as microorganism susceptibility, environmental factors, duct surface reflectance, etc. Different pathogens require a different UV-C irradiation dose for successful inactivation [34], [35], black surface than in clean ducts [36]. The disinfection efficacy of in-duct UV-C lamps can be increased by 20% with a reflective duct wall compared to under non-reflection conditions [37]. ...
... At first sight, a minor effect of the virus was instead noticed. The main difference may rely on the different UV-C susceptibility of the microorganism, which strongly depends on other different factors, such as the ability of different microorganisms to recover UV radiation-induced damage, the UV dose, fluence rate, temperature, RH, exposure time, and the particulate/moisture present in the air [34], [35], [39], [47]. ...
Improving the air quality of indoor environments (IAQ) is of utmost importance to safeguard public health as people spend about 80–90% of their time indoor. Efficient Ultraviolet germicidal irradiation (UVGI) system represents a strategic and sustainable solution to protect from recurrent and new airborne pathogens. Here, we present a new approach to design highly efficient UVGI systems, which can be installed in existing Air Treatment Units (ATU) plants with minimal effort. The increased efficiency relies on the concept of an optical cavity, thanks to its shape and source position. The internal volume consists of a highly reflective cavity illuminated with UV-C lamps. Optical simulations permitted the variation of the parameters to maximize the internal irradiance and, thus, the performance. The sanitation efficacy of the system was assessed on a full-scale pilot system. Tests were carried out under normal operating conditions against various microorganisms showed an inactivation rate of > 99%. The benefits of such systems are triple and encompass economic, environmental, and societal aspects. Since the system requires little energy to operate, its application for air disinfection may yield significant energy savings and ensure a balance between energy sustainability and good IAQ.
... UV radiation is common in water treatment and is employed globally in small to large-scale systems. The UV fluence and deactivation rate for common water pathogens are well established (Haji Malayeri et al., 2016). UV radiation damages the DNA and RNA of microorganisms and forms pyrimidine dimers, preventing replication and transcription. ...
... UV radiation damages the DNA and RNA of microorganisms and forms pyrimidine dimers, preventing replication and transcription. Lowpressure UV treatment decreases cell counts measured by both HPC and flow cytometry (Haji Malayeri et al., 2016). Medium-pressure UV treatment causes alterations to the drinking water microbiome, resulting in a decrease in the relative abundance of Proteobacteria and dominance of UV-resistant Actinobacteria (Nocker et al., 2018;Pullerits et al., 2020aPullerits et al., , 2020b. ...
... Table 3 shows the UV dose expressed in mJ/cm 2 required for a 99.99% reduction in exposed microorganisms. The cited references illustrate the highest doses listed in the perpetual inventory maintained by the International UV Association (Abshire et al., 1981;Blatchley III et al., 2016;Bounty et al., 2012;Chang et al., 1985;Clauß, 2006;Gerba et al., 2002;Linden et al., 2009;Malayeri et al., 2018;Nwachuku et al., 2005;Park et al., 2011;Qian et al., 2004;Shin et al., 2005;Thurston-Enriquez et al., 2003;Wilson, 1992). ...
... In a bio-mineral pool, disinfection is ensured by treatment based on ultraviolet (UV) radiation with additional oxidation such as photocatalytic UV. The UV dose required for the elimination of 99.99% of E. coli is 7.2 ± 2.55 mJ/cm 2 according to the synthesis of 48 studies carried out by Malayeri et al. (2018). The combination of the impoverishment of the medium in order to limit bacterial proliferation, a UV treatment delivering a minimum of 25 mJ/cm2, and a hydraulic circuit making it possible to treat the entire volume of water repeatedly in accordance with the legislation makes it possible to limit the contribution of bacteria by swimmers. ...
In this review, we depict the state of the art concerning the water quality management of bio-mineral bathing pools, and compare these to traditional swimming pools. Bio-mineral pools use a combination of mechanic filtration, bio-filtration, and UV-treatment to disinfect the water. Studies in test tanks have shown that bio-filtration is effective in maintaining the water quality with regard to the treatment of organic pollution. Concerning biological risks, the bio-mineral pool relies on UV-treatment to degrade bacteria. Unlike chemical disinfectant treatments, UV disinfection does not lose its effectiveness in the event of high traffic in the pool. However, as only the water taken up by the filtration system is disinfected, it is essential that all the water in the pool is filtered. If the pool has a dead zone, its water is not disinfected and there is a risk of localized pathogen development. As the development of bio-mineral pools spreads in Europe, legislation gradually follows. The health parameters measured differ slightly from one country to another, but there are constants: the measurement of Escherichia coli, Enterococci, and Pseudomonas aeruginosa. In terms of biological swimming pools, regulatory homogeneity across Europe does not exist. From these comparisons, Austrian legislation segmenting water quality into 4 categories ranging from “excellent” to “poor” represents legislation that combines health and safety with indications of possible malfunctions. Next, a study of three real sites of bio-mineral pools is presented. It appears that whatever the type of pool, bio-mineral filtration makes it possible to achieve performances comparable to those encountered in chlorinated swimming pools concerning the risks associated with fecal contamination and external pollution. On the other hand, when frequentation is high, as is the case in small pools used for aquafitness, monitoring the risks of inter-bather contamination, as illustrated by the presence of Staphylococcus aureus, reveals a recurring problem. Knowing that this parameter is not evaluated in bathing waters in the natural environment and that numerous studies show that Staphyloccocus aureus are always detected, even on beaches, we propose the definition of three thresholds: i.e., 0 CFU/100 mL (threshold value in Wallonia) for water of excellent quality, less than 20 CFU/100 mL (threshold value in France) for water of very good quality, less than 50 CFU/100 mL (contribution of bathers by simple immersion) for good quality water, and more than 50 CFU/100 mL for poor quality water. This document could therefore be converted into a manual for operators on the use and management of bio-mineral baths.
... As of 2016, seven studies using UVC lamps determined the fluence of MS2 ATCC15977-B1 in host E. coli ATCC15977, the same organisms used in this study, to be 72 to 97 mJ/cm 2 to achieve 4 LRV. 76 Because MS2 is more resistant to UV disinfection, it is considered a conservative surrogate to human viruses and was proposed as a standard for UV reactor validation in the United States. 50 Unlike viruses, bacteria are able to protect against, or repair, sunlight damage, but ultimately can be inactivated after exposure to both UVA and UVB wavelengths. ...
... 13 As of 2016, 11 studies using lamps in the UVC range observed fluences from 4.5 to 10.3 mJ/cm 2 were able to reduce E. coli ATCC11229, the strain that we used, by 4 LRV in suspensions and water/wastewater samples. 76 No literature was identified on E. coli inactivation by sunlight on surfaces; thus, it is difficult to compare our data with observed inactivation times. One study modeling E. coli reductions derived from bench-scale tests using the solar disinfection water FIGURE 5. Cloudy data. ...
Ultraviolet (UV) radiation systems, commonly used to disinfect surfaces, drinking water, and air, stem from historical practice to use sunlight to disinfect household items after contagious illness. Currently, it is still recommended in viral outbreak contexts such as COVID-19, Ebola, and Marburg to expose soft surfaces to sunlight after washing with detergent or disinfecting with chlorine. However, sunlight that reaches the Earth's surface is in the UVA/UVB wavelengths, whereas UV disinfection systems typically rely on biocidal UVC. Our goal was to fill the evidence gap on the efficacy of sunlight disinfection on surface materials common in low-resource healthcare settings by seeding four surfaces (stainless steel, nitrile, tarp, cloth) with three microorganisms (viral surrogate bacteriophages Phi6 and MS2 and Escherichia coli bacteria), with and without soil load, and exposing to three sunlight conditions (full sun, partial sun, cloudy). We conducted 144 tests in triplicate and found: solar radiation averaged 737 W/m2 (SD = 333), 519 W/m2 (SD = 65), and 149 W/m2 (SD = 24) for full sun, partial sun, and cloudy conditions; significantly more surfaces averaged ≥ 4 log10 reduction value (LRV) for Phi6 than MS2 and E. coli (P < 0.001) after full sun exposure, and no samples achieved ≥ 4 LRV for partial sun or cloudy conditions. On the basis of our results, we recommend no change to current protocols of disinfecting materials first with a 0.5% chlorine solution then moving to sunlight to dry. Additional field-based research is recommended to understand sunlight disinfection efficacy against pathogenic organisms on healthcare relevant surfaces during actual outbreak contexts.
... The reciprocity law assumes that the rate of the photochemical reaction process is proportional to the light irradiance (linear stochastic process) such that the amount of the process depends only on the D. While this is true for most primary photochemical reaction processes at light irradiances which do not induce nonlinear effects, there are many reactions that do not obey the reciprocity law over any significant range of reaction conditions, such as radical polymerizations 8 . Furthermore, the inactivation rate constants of many bacteria and viruses by UV irradiation reported in the literature vary widely, even for studies in which the same wavelength of irradiation and the same types and strains of bacteria and viruses were used [9][10][11] . These wide range of reported values seem to suggest that the physical mechanism of UV inactivation cannot be described by the simple time-dose reciprocity law; instead, a secondary inactivation process must be identified to clarify the scientific basis 7 . ...
... D. To prove that ROS play a role in inactivation, it is necessary to quantify and measure the amount of ROS by UV irradiation. Various values of the inactivation rate constant for the UV inactivation of a bacterium and/or virus have been reported, even when the same light source and irradiation wavelength are used [9][10][11] . One reason for this discrepancy might be the difference in strains and their environments of the bacteria. ...
There is a great demand for developing and demonstrating novel disinfection technologies for protection against various pathogenic viruses and bacteria. In this context, ultraviolet (UV) irradiation offers an effective and convenient method for the inactivation of pathogenic microorganisms. The quantitative evaluation of the efficacy of UV sterilization relies on the simple time-dose reciprocity law proposed by Bunsen-Roscoe. However, the inactivation rate constants reported in the literature vary widely, even at the same dose and wavelength of irradiation. Thus, it is likely that the physical mechanism of UV inactivation cannot be described by the simple time-dose reciprocity law but requires a secondary inactivation process, which must be identified to clarify the scientific basis. In this paper, we conducted a UV inactivation experiment with Escherichia coli at the same dose but with different irradiances and irradiation durations, varying the irradiance by two to three orders of magnitude. We showed that the efficacy of inactivation obtained by UV-light emitting diode irradiation differs significantly by one order of magnitude at the same dose but different irradiances at a fixed wavelength. To explain this, we constructed a stochastic model introducing a second inactivation rate, such as that due to reactive oxygen species (ROS) that contribute to DNA and/or protein damage, together with the fluence-based UV inactivation rate. By solving the differential equations based on this model, the efficacy of inactivation as a function of the irradiance and irradiation duration under the same UV dose conditions was clearly elucidated. The proposed model clearly shows that at least two inactivation rates are involved in UV inactivation, where the generally used UV inactivation rate does not depend on the irradiance, but the inactivation rate due to ROS does depend on the irradiance. We conclude that the UV inactivation results obtained to date were simply fitted by one inactivation rate that superimposed these two inactivation rates. The effectiveness of long-term UV irradiation at a low irradiance but the same dose provides useful information for future disinfection technologies such as the disinfection of large spaces, for example, hospital rooms using UV light, because it can reduce the radiation dose and its risk to the human body.
... If data from other microorganisms had been used, the values would probably have been slightly different, but it is unlikely that anything would have changed in general, as the antimicrobial effectiveness of all UVC sources is roughly in the same order of magnitude. In any case, this also fits in quite well with our own previously published results and those of other research groups [14][15][16][17][18][19]. ...
Abstract: The recently much noticed Far-UVC spectral range offers the possibility of inactivating pathogens without necessarily posing a major danger to humans. Unfortunately, there are various Far-UVC sources that differ significantly in their longer wavelength UVC emission and, subse-quently, in their risk potential. Therefore, a simple assessment method for Far-UVC sources is pre-sented here. In addition, the temporal intensity stability of Far-UVC sources was examined in order to reduce possible errors in irradiation measurements. For this purpose, four Far-UVC sources and a conventional Hg UVC lamp were each spectrally measured for about 100 h and mathematically evaluated for their antimicrobial effect and hazard potential using available standard data. The two filtered KrCl lamps were found to be most stable after a warm-up time of 30 min. With regard to the antimicrobial effect, the radiation efficiencies of all examined (Far-) UVC sources were more or less similar. However, the calculated differences in the potential human hazard to eyes and skin were more than one order of magnitude. The two filtered KrCl lamps were the safest, followed by an unfiltered KrCl lamp, a Far-UVC LED and, finally, the Hg lamp. When experimenting with these Far-UVC radiation sources, the irradiance should be checked more than once. If UVC radiation is to be or could be applied in the presence of humans, filtered KrCl lamps are a much better choice than any other available Far-UVC sources.
... The abundance of human pathogenic viruses can be highly variable depending on processes, operating conditions of a WWTP, and the shedding behavior within the serviced community. Concentrations in raw sewage can vary from 10 1 to 10 8 genomic copies per 100 mL for human adenoviruses, norovirus GII, enteroviruses, and papillomaviruses (Sommer et al., 1998;Malayeri et al., 2006;Hijnen et al., 2006, U.S. EPA, 2020Pirnie et al., 2006,McCall et al., 2020 In this study, the nucleic acids of adenoviruses, enteroviruses, rotaviruses, polyomaviruses, SARS-CoV-2 as well as PMMoV, TMV and CrAss-phage Ho et al. Water Research 267 (2024) 122429 could be detected in raw sewage. ...
In this study, we evaluated the ability of various pilot-scale treatment train combinations to meet the microbial
requirements of the new European non-potable water reuse regulation 2020/741. The study utilized nondisinfected
secondary effluent from the wastewater treatment plant in Schweinfurt, Germany, as feedwater for
two pilot-scale treatment trains. The first, a reference treatment train (Train A), consisted of filtration and UV
disinfection as specified for reclaimed water class A in the EU regulation. The second, an advanced treatment
train (Train B), included ceramic ultrafiltration (UF), ozonation, biological activated carbon filtration (BAC), and
final UV disinfection. Based on a Monte Carlo simulation for Train A, the EU requirements for pathogen removal
were not met when an average UV dose of 400-600 J/m² was applied. This shortcoming was likely due to a
moderate transmittance range (50–65 %), resulting in decreased UV fluence. These findings suggest that operational
conditions for disinfection should be more clearly specified to ensure consistent pathogen inactivation
both during validation and regular operation. In contrast, treatment train B successfully met the requirements of
the EU regulations by reducing pathogens to below the detection limit. The UF membrane demonstrated a
positive effect on the overall log reduction values (LRVs) throughout the water reclamation system. It also
enhanced the efficiency of downstream processes, such as ozonation and UV disinfection, by lowering total
suspended solids and turbidity. However, even without the UF membrane, treatment train B was still able to meet
the pathogenic EU requirements for non-potable reuse applications. Furthermore, the study observed that the
inclusion of biologically activated carbon (BAC) filtration requires a final disinfection step (e.g., UV disinfection)
to prevent the potential occurrence of heterotrophic bacteria that proliferate in the BAC filter. For process
validation it is recommended to use at least two different virus surrogates (MS2 and PhiX174), rather than just
one or total coliphage as required in the EU regulation.
... Concerning the efficacy of UV treatment in reducing the number of viable cells, our results of 4.5 mJ cm for a 1-log reduction of E. coli (Supplementary Table S3) compare well with those previously reported for various E. coli strains in 15 different studies using UV-C light emitting at 255 nm , where a 1-log reduction was achieved at 3.9 1.9 mJ cm [35]. Regarding the survival curves (Figure 2), the initial rapid decline in viable organisms indicates that UV exposure to low doses effectively reduces the microbial population; however, as the UV dose increases beyond a certain threshold, the rate of reduction slows down or "tails off". ...
This study examines the inactivation kinetics and stress responses of Gram-positive and Gram-negative waterborne bacteria using ultraviolet (UV)-B and UV-C LEDs at varying fluences. Our findings show that UV-light-emitting diodes (LED) treatment effectively inactivates both bacterial types, achieving over 4-log reductions at 255 nm and 285 nm wavelengths. Notably, inactivation rates at 285 nm, especially at higher fluences, are comparable to or exceed those at 255 nm. Additionally, UV-B treatment at 285 nm requires shorter exposure times for the same UV dose due to its deeper penetration into water and higher radiant flux. Stress responses varied between species: 255 nm exposure caused more direct DNA damage, triggering the SOS response with recA upregulation, particularly in Gram-positive L. innocua; while 285 nm exposure primarily induced oxidative stress, leading to soxS upregulation, especially in Gram-negative bacteria. These results suggest that UV-B complements UV-C effects by causing reactive oxygen species (ROS) formation in addition to DNA damage, challenging DNA repair. Given the higher cost of UV-C LEDs, our results support the optimization of water treatment systems using UV-B LEDs, which is a promising approach for improving bacterial inactivation while reducing exposure time and energy use.
... and E. coli, two common microorganisms in poultry litter. The UV-C dose required for killing Salmonella is around 152 J/m 2 , and E. coli is about 66 J/m 2 [61]. In order to select the proper lamps, we used the following equations. ...
The traditional aviary decontamination process involves farmers applying pesticides to the aviary’s ground. These agricultural defenses are easily dispersed in the air, making the farmers susceptible to chronic diseases related to recurrent exposure. Industry 5.0 raises new pillars of research and innovation in transitioning to more sustainable, human-centric, and resilient companies. Based on these concepts, this paper presents a new aviary decontamination process that uses IoT and a robotic platform coupled with ozonizer (O3) and ultraviolet light (UVL). These clean technologies can successfully decontaminate poultry farms against pathogenic microorganisms, insects, and mites. Also, they can degrade toxic compounds used to control living organisms. This new decontamination process uses physicochemical information from the poultry litter through sensors installed in the environment, which allows accurate and safe disinfection. Different experimental tests were conducted to construct the system. First, tests related to measuring soil moisture, temperature, and pH were carried out, establishing the range of use and the confidence interval of the measurements. The robot’s navigation uses a back-and-forth motion that parallels the aviary’s longest side because it reduces the number of turns, reducing energy consumption. This task becomes more accessible because of the aviaries’ standardized geometry. Furthermore, the prototype was tested in a real aviary to confirm the innovation, safety, and effectiveness of the proposal. Tests have shown that the UV + ozone combination is sufficient to disinfect this environment.
... Since the UVC system should at least lead to a disinfection rate of 90% (corresponding to a reduction of 1-log), to achieve a decrease in bacteria up to 99.9% (corresponding to reduction of 3-log), a 200% increase in the exposure time or irradiance per square meter should be adopted [52]. Malayeri et al. [53] examined the fluence data (UV dose) required to achieve the log-incremental inactivation of bacteria, protozoa, viruses, and algae; the authors highlighted, as several studies have shown, that a fluence below 20 mJ/cm 2 is sufficient to achieve a 90% kill rate (1-log reduction) for microorganisms, but it is sometimes necessary to increase the dose from 30 mJ/cm 2 to 50 mJ/cm 2 to kill viruses. The dose is further increased to 330 mJ/cm 2 to kill mold and protozoan spores. ...
Bio-polybutylene succinate (PBS) is a biodegradable polymer obtained from renewable feedstock having physical–mechanical properties like traditional low-density polyethylene (LDPE). PBS is employed by many manufacturing sectors, from biomedical to agri-food and cosmetics. Although some studies have already evaluated the resistance of PBS to photodegradation caused by natural outdoor solar exposure (UVA-UVB), a systematic study on the resistance to degradation caused by exposure to UVC rays, which is the subject of this study, has not yet been carried out. PBS was exposed to UVC either neat or filled with 2% carbon black (CB). Mechanical and physical characterization (tensile, hardness, calorimetry, contact angle, morphology, and surface roughness analyses) indicates that the bulk and surface properties of the polymer matrix changes after exposure to UVC radiations, due to a severe degradation. However, the presence of carbon black compensates for the degradation phenomenon. Because UVC rays are used for the sterilization process, necessary in applications such as biomedical, cosmetic, pharmaceutical, food, and other products, a comparison of the protocol used in this paper with the literature’s data has been reported and discussed.
... 32 However, microorganisms do have varying susceptibilities to UV irradiation: for example, cryptosporidium is easily inactivated but viruses are more difficult to inactivate. 48,49 With treatment at high UV fluences, microorganisms are inactivated through the absorption of UV photons by proteins in the outer cell membranes, leading to disruption and consequent death of the cell. 50 At lower fluences, microorganisms can no longer cause infection as the ability to replicate is disrupted. ...
Progress toward universal access to safe drinking water depends on rural water service delivery models that incorporate water safety management. Water supplies of all types have high rates of fecal contamination unless water safety risks are actively managed through water source protection, treatment, distribution, and storage. Recognizing the role of treatment within this broader risk-based framework, this study focuses on the implementation of passive chlorination and ultraviolet (UV) disinfection technologies in rural settings. These technologies can reduce the health risk from microbiological contaminants in drinking water; however, technology-focused treatment interventions have had limited sustainability in rural settings. This study examines the requirements for sustainable implementation of rural water treatment through qualitative content analysis of 26 key informant interviews, representing passive chlorination and UV disinfection projects in rural areas in South America, Africa, and Asia. The analysis is aligned with the RE-AIM framework and delivers insight into 18 principal enablers and barriers to rural water treatment sustainability. Analysis of the interrelationships among these factors identifies leverage points and encourages fit-for-purpose intervention design reinforced by collaboration between facilitating actors through hybrid service delivery models. Further work should prioritize health impact evidence, water quality reporting guidance, and technological capabilities that optimize trade-offs in fit-for-purpose treatment design.
... Additionally, it can be used in the postharvest period to preserve fruits and vegetables and replace agrochemicals and pesticides that may remain as toxic residues in food products [9]. Doses of UV-C have been tested to reduce, inactivate and retard the growth of molds and yeasts, which are food spoilage contaminants [10][11][12][13]. Some authors demonstrated [14] the potential of UV-C irradiation on the increase of some biochemical compounds of food, in support of the activation of compounds with health benefits. ...
The effect of exposure of soft wheat buns to Ultraviolet-C radiation (UV-C, 253.7 nm) was studied as an alternative to conventional treatments to control fungal spoilage and prolong shelf life. To identify the most suitable operating conditions, the study included preliminary tests on the permeability of films to UV-C irradiation, and on treatment antifungal efficacy on target microorganisms (Penicillium digitatum and Saccharomycopsis fibuligera) in Petri dishes. A 125 µm T9250B film (Cryovac® Sealed Air S.r.l), commercially available for long-life bread treated with ethanol and conditioned in a modified atmosphere, was selected to pack buns before the UV-C treatment. The study was carried out along with the observation of the fungal growth of buns artificially inoculated with suspensions of P. digitatum and S. fibuligera, treated under UV-C at a distance of 25 cm between bread and the 15 W UV-C source, in comparison to untreated buns used as control. Estimation of fungal growth as well as sensory evaluation was made 2, 4, 7, 10 and 14 days after the treatment. UV-C treated buns showed a noticeable reduction of fungal spoilage and kept a tender texture for up to two weeks after packaging. UV-C treatment represents a good opportunity for the bakery industry, reducing costs and ensuring a prolonged shelf life of a commercial product, respecting the health and hedonistic expectations of the customers.
... Furthermore, the fluences employed here are greater than those which would be used clinically. Previous work has established that far-UVC radiation is an effective antibacterial agent at fluences below 100 mJ/cm 2 [40,41]. It will be important to investigate whether low fluences of far-UVC radiation induce collagen cross-link formation [34,35,37], as increased ECM cross-linking is associated with tissue fibrosis and impaired wound healing [42,43]. ...
For more than 100 years, germicidal lamps emitting 254 nm ultraviolet (UV) radiation have been used for drinking-water disinfection and surface sterilization. However, due to the carcinogenic nature of 254 nm UV, these lamps have been unable to be used for clinical procedures such as wound or surgical site sterilization. Recently, technical advances have facilitated a new generation of germicidal lamp whose emissions centre at 222 nm. These novel 222 nm lamps have commensurate antimicrobial properties to 254 nm lamps while producing few short- or long-term health effects in humans upon external skin exposure. However, to realize the full clinical potential of 222 nm UV, its safety upon internal tissue exposure must also be considered. Type I collagen is the most abundant structural protein in the body, where it self-assembles into fibrils which play a crucial role in connective tissue structure and function. In this work, we investigate the effect of 222 nm UV radiation on type I collagen fibrils in vitro. We show that collagen’s response to irradiation with 222 nm UV is fluence-dependent, ranging from no detectable fibril damage at low fluences to complete fibril degradation and polypeptide chain scission at high fluences. However, we also show that fibril degradation is significantly attenuated by increasing collagen sample thickness. Given the low fluence threshold for bacterial inactivation and the macroscopic thickness of collagenous tissues in vivo, our results suggest a range of 222 nm UV fluences which may inactivate pathogenic bacteria without causing significant damage to fibrillar collagen. This presents an initial step toward the validation of 222 nm UV radiation for internal tissue disinfection.
... These studies assist in explaining the mechanisms of BL 405 viral inactivation and provide evidence that its efficacy is impacted by environmental conditions (dew point), prolonged time exposure, and surface type. The viricidal k values reported for this work were significantly lower than the viricidal k values for the MS2 bacteriophage with UV 254 [19,31]; this was due to the different inactivation mechanisms associated with these wavelengths. ...
The increased prevalence of multidrug-resistant organisms (MDROs), healthcare associated infections (HAIs), and the recent COVID-19 pandemic has caused the photoinactivation industry to explore alternative wavelengths. Blue light (BL405) has gained significant interest as it is much less harmful to the skin and eyes than traditional germicidal wavelengths; therefore, in theory, it can be used continuously with human exposure. At present, the viricidal effects of BL405 are largely unknown as the literature predominately addresses bacterial disinfection performed with this wavelength. This work provides novel findings to the industry, reporting on the virucidal effects of BL405 on surfaces. This research utilizes three surfaces: ceramic, PTFE, and stainless steel. The efficacy of BL405 inactivation varied by surface type, which was due to surface characteristics, such as the contact angle, porosity, zeta potential, and reflectivity. Additionally, the effect of the dew point on BL405 inactivation efficacy was determined. This research is the first to study the effects of the dew point on the virucidal effectiveness of BL405 surface inactivation. The effects of the dew point were significant for all surfaces and the control experiments. The high-dew-point conditions (18 °C) yielded higher levels of BL405 inactivation and viral degradation for the experiments and controls, respectively.
... Commercial reactors are validated for certain target pathogens using challenge or substitute microorganisms, some of which coincide with environmental microorganisms, such as E. coli, Cryptosporidium and MS2, one of the phages of one of F-specific coliphage families. The response of these microorganisms to UV radiation (USEPA 2003;Malayeri et al. 2016) is determined based on collimated beam tests (under ideal conditions), with previously cultured microorganisms, well-defined strains, under highly controlled conditions, and in drinking water. Environmental microorganisms show higher UV resistance than cultured ones. ...
Since 2020, there is a new European Regulation (EU, 2020/741) on minimum requirements for water reuse, where routine and validation monitoring requirements (log reductions of indicator microorganisms and reference pathogens) have been established. Many reclamation facilities that are already in operation might have difficulties to comply with these performance targets. Existing disinfection systems must be expanded and upgraded. In the case of UV disinfection systems, fluence requirements must be determined to properly design with a focus on the safety and economic-environmental viability of reclaimed water. This study can be used as a reference to develop fluence-response curves for Clostridium perfringens spores, Escherichia coli, and total and F-specific coliphages, indicator microorganisms referred to in the new European Regulation. Eight UV-LED collimated beam tests were performed. Samples were obtained from filtered effluent of secondary treatment from two wastewater treatment plants (WWTPs) which ranged between 30 and 54%. Results showed UV sensitivity of 33.46 mJ/cm2 log I for C. perfringens spores and 2.86 mJ/cm2 log I for E. coli, both from environmental origin. Coliphages were inactivated below the limit of quantitation. The non-dominance of MS2 phages in environmental F-specific coliphages was observed.
HIGHLIGHTS
Existing reclamation facilities might have difficulties to meet European performance targets.;
They must be properly expanded with a focus on the safety and economic-environmental viability of reclaimed water.;
Fluence requirements for environmental microorganisms must be determined.;
UV sensitivity of 33.46 mJ/cm2 log I for env. C. perfringens spores was shown.;
Non-dominance of env. MS2 phages was observed.;
... However, the dose required in such environments to achieve a specific reduction has not yet been fully determined. According to data collected by Malayeri et al. [86] in 2016, to achieve a bacterial reduction of 3 uLog (99.9% disinfection), doses vary from 1 mJ/cm 2 to 170 mJ/cm 2 . ...
UV disinfection is cost-effective and easy to maintain for decentralized areas. However, to ensure its effectiveness, some parameters need to be considered. In this study, a general search of Web of Science articles was performed to determine the possible influence of these parameters on the reactivation of microorganisms in UV systems; in addition, different search strings were used focusing exclusively on wastewater treatment, UV systems and Advanced Oxidation Processes (AOPs). It was found that in order to maintain low transmittance, it is essential to remove suspended solids and reduce water hardness. It is recommended to control the zeta potential in the range of 0–5 mV to avoid the aggregation of particles and bacteria. Determining the appropriate UV dose is essential to mitigate the reactivation of microorganisms. A minimum dose of 40 mJ/cm2 can contribute to effective disinfection and reduce the likelihood of reactivation. In addition, maintaining a residual chlorine level of at least 0.5 mg/L provides an additional barrier to reactivation. It is also important to optimize the design flow rate of the UV system as recommended for each individual unit. These measures, together with the combination of UV disinfection and chemical or AOPS, can effectively reduce the reactivation.
... A large compilation of 431 studies on the UV dose (fluence) needed to inactivate common pathogens reveals that most pathogens see a 1-log reduction in numbers (90% pathogen inactivation) at UV doses lower than 20 mJ/cm 2 [91,92]. This is equivalent to 20 s of exposure to the UV-C radiation source used in this experiment. ...
During the initial stages of the COVID-19 pandemic, healthcare facilities experienced severe shortages of personal protective equipment (PPE) and other medical supplies. Employing 3D printing to rapidly fabricate functional parts and equipment was one of the emergency solutions used to tackle these shortages. Using ultraviolet light in the UV-C band (wavelengths of 200 nm to 280 nm) might prove useful in sterilizing 3D printed parts, enabling their reusability. Most polymers, however, degrade under UV-C radiation, so it becomes necessary to determine what 3D printing materials can withstand the conditions found during medical equipment sterilization with UV-C. This paper analyzes the effect of accelerated aging through prolonged exposure to UV-C on the mechanical properties of parts 3D printed from a polycarbonate and acrylonitrile butadiene styrene polymer (ABS-PC). Samples 3D printed using a material extrusion process (MEX) went through a 24-h UV-C exposure aging cycle and then were tested versus a control group for changes in tensile strength, compressive strength and some selected material creep characteristics. Testing showed minimal mechanical property degradation following the irradiation procedure, with tensile strength being statistically the same for irradiated parts as those in the control group. Irradiated parts showed small losses in stiffness (5.2%) and compressive strength (6.5%). Scanning electron microscopy (SEM) was employed in order to assess if any changes occurred in the material structure.
... The UV-C dose is typically expressed as a fluence (J/m 2 ), which is the time integral of the UV flux (W/m 2 ) from the UV-C source. Several tabulated lists of the UV-C dose required to reach desired inactivation levels are available [1,3]. ...
The use of mobile ultraviolet-C (UV-C) disinfection devices for the decontamination of surfaces in hospitals and other settings has increased dramatically in recent years. The efficacy of these devices relies on the UV-C dose they deliver to surfaces. This dose is dependent on the room layout, the shadowing, the position of the UV-C source, lamp degradation, humidity and other factors, making it challenging to estimate. Furthermore, since UV-C exposure is regulated, personnel in the room must not be exposed to UV-C doses beyond occupational limits. We proposed a systematic method to monitor the UV-C dose administered to surfaces during a robotic disinfection procedure. This was achieved using a distributed network of wireless UV-C sensors that provide real-time measurements to a robotic platform and operator. These sensors were validated for their linearity and cosine response. To ensure operators could safely remain in the area, a wearable sensor was incorporated to monitor the UV-C exposure of an operator, and it provided an audible warning upon exposure and, if necessary, ceased the UV-C emission from the robot. Enhanced disinfection procedures could then be conducted as items in the room could be rearranged during the procedure to maximise the UV-C fluence delivered to otherwise inaccessible surfaces while allowing UVC disinfection to occur in parallel with traditional cleaning. The system was tested for the terminal disinfection of a hospital ward. During the procedure, the robot was manually positioned in the room by the operator repeatedly, who then used feedback from the sensors to ensure the desired UV-C dose was achieved while also conducting other cleaning tasks. An analysis verified the practicality of this disinfection methodology while highlighting factors which could affect its adoption.
... 6. Other pathogens with lower UV-C susceptibility, especially bacterial spores, may remain active on N95 respirators even if the applied UV-C dose achieves viral inactivation [46][47][48]. 7. Elastic straps may require a secondary decontamination method [9,44]. Application of the appropriate UV-C wavelength and application of the appropriate dose are critical metrics for reproducible UV-C N95 respirator decontamination protocols under crisis-capacity conditions. ...
... The models differ somewhat in their predictions of SARS-CoV-2 inactivation, but they all indicate that the virus is quite sensitive to UV254 irradiation. For perspective, the UV254 inactivation kinetics for SARS-CoV-2 inactivation predicted by these models were also similar to those that have been reported for many vegetative bacterial cells [50], which are generally considered to be easy to inactivate by UV-C irradiation. Coincidentally, the range of inactivation responses predicted by the three models is similar to the range of measured responses provided by the two reports of experimental SARS-CoV-2 inactivation by UV254 irradiation for aqueous suspensions of the virus [21,22]. . ...
... The relationship between dose and the germicidal efficiency is shown in Eq. (1), where H0 is the dose, D is the fraction of microorganisms killed, and K is a rate constant characteristic of the specific microorganism and the wavelength. Malayeri et al. [7] provided a comprehensive collection of the sensitivity of a wide range of microorganisms to UV-C light. For severe acute respiratory syndrome coronavirus (SARS-CoV), two reported measurements of the required dose are available based on clinical studies. ...
... Data on disinfection of E. coli by low pressure (LP) UV lamps were screened from previously reviewed literature (Malayeri et al., 2016). UV fluence responses were modelled for E. coli strains ATCC 11229 and O157:H7 (Fig. S3). ...
Ultraviolet disinfection is a promising solution for decentralized drinking water systems such as communal water taps. A potential health risk is enzymatic photorepair of pathogens after UV disinfection, which can result in regrowth of pathogens. Even though photorepair is a known issue, no formal risk assessments have been conducted for photorepair after UV disinfection in drinking water. The main objective was to construct a quantitative microbial risk assessment (QMRA) of photorepair after UV disinfection of drinking water in a decentralized system. UV disinfection and photorepair kinetics for E. coli were modelled using reproducible fluence-based determinations. Impacts of water collection patterns, and wavelength-dependent water container material transmittance, sunlight intensity, and photorepair enzyme absorbance were quantified. After UV disinfection by 16 or 40 mJ/cm2 of < 5-log microorganisms per L, risk of infection did not exceed 1-in-10,000 under conditions permitting E. coli photorepair. Risk from photorepair was less than 1-in-10,000 for photorepair light exposure < 0.75 h throughout the day for UV fluence 16 mJ/cm2 or greater. UV disinfection followed by solar disinfection surpassing photoreactivation during storage reduced risk below 1-in-10,000 for photorepair light exposure > 2.5 h between modelled times of 9 AM - 3 PM. The model can be expanded to other pathogens as UV fluence and photorepair fluence response kinetics become available, and this QMRA can be used to inform the placement of community water access points to reduce risk of photorepair and ensure adequate shelf life of UV disinfected water under safe storage conditions.
... Depending on the exposure time, the UV-C dose (total energy received) defines the inactivation efficiency (percentage of inactivated particles of the pathogen). The relations between dose and efficiency of inactivation for different airborne pathogens could be evaluated by the publications of IUVA [11] and the University of Milan [12]. The Authors of this paper, in cooperation with the company Light Progress [13], have realised a calculation code that designs the UV-C sanitation section of an air system through the consequential solving of radiation and motion fields. ...
In this work, a numerical code for the evaluation of air sanitation efficiency of UV-C devices placed in air systems (HVAC and MV) is presented. The code can design the sanitation section, giving the necessary UV-C power to achieve a predefined target of sanitation for a certain airborne pathogen. The code, through a three-dimensional discretisation of the channel geometry, first evaluates the radiation field (direct and reflected irradiance) and then calculates the UV-C dose received by the pathogen. The hypothesis of rectilinear trajectories of the pathogen particles is verified through a CFD analysis. A case study is also presented to show the operating mode of the code.
... In addition, the body of knowledge is vast regarding water UV disinfection data for E. coli and MS-2 bacteriophage. The behavior of these surrogates has been studied by many researchers; therefore, we can confidently make comparisons between the dose response behavior observed with water data versus with FFRs (16). ...
Research suggests degradation of FFR materials at high UV doses is important. There appears to be a peak inactivation dose at approximately 1,500 mJ/cm ² . The subsequent dose increases appear to have the reverse effect on inactivation values; these trends have shown true with both the N95 and KN95-Purism respirators.
... UV-C disinfection has been used for several decades to inactivate different infectious agents, including fungi, bacteria, and viruses, both from contaminated liquids and surfaces. [5][6][7] Although the primary mode of action for UV inactivation is considered to be genome damaging through the formation of pyrimidine dimers [8][9][10] different mechanisms have been described. These include protein oxidation, destruction of the capsid protein, and crosslinking of viral genome-protein. ...
Surface residing SARS‐CoV‐2 is efficiently inactivated by UV‐C irradiation. This raises the question whether UV‐C‐based technologies are also suitable to decontaminate SARS‐CoV‐2‐ containing aerosols and which doses are needed to achieve inactivation. Here, we designed a test bench to generate aerosolized SARS‐CoV‐2 and exposed the aerosols to a defined UV‐C dose. Our results demonstrate that the exposure of aerosolized SARS‐CoV‐2 with a low average dose in the order of 0.42–0.51 mJ/cm2 UV‐C at 254 nm resulted in more than 99.9% reduction in viral titers. Altogether, UV‐C‐based decontamination of aerosols seems highly effective to achieve a significant reduction in SARS‐CoV‐2 infectivity.
... The slope of the best-fit line was used to determine D 10 -values for both MS2 and T7. The D 10 -value for MS2 and T7 was determined to be 21.92 6 0.55 and 2.22 6 0.05 mJ cm À2 , respectively, which is in agreement with previously reported D 10 -values for these phages (20,43,47), indicating that the UV-C doses received by these phage suspensions were indeed accurate. This relationship was used to verify the UV fluence delivered in subsequent irradiations of Cronobacter spp. ...
A study was undertaken to model the UV-C inactivation kinetics and determine the fluences required for the incremental inactivation of several strains of Cronobacter spp. suspended in clear phosphate-buffered saline (PBS). In total, 13 strains of Cronobacter spp. were individually suspended in PBS and treated with UV-C doses of 0, 2, 4, 6, 8, and 10 mJ cm−2 with a collimated beam device emitting UV-C at 253.7 nm. The log reduction from each treatment was identified using the plate count method and plotted against the UV-C dose and then curve fitted using several mathematical models. The UV-C dose required for incremental inactivation of each isolate was determined using both linear and nonlinear regression. For the 13 strains tested, a UV-C dose of 10 mJ cm−2 inactivated between 3.66 ± 0.101 and 5.04 ± 0.465 log CFU mL−1. The survival behavior of all strains was best fitted to the Weibull+tail model, with correlation coefficients between 97.17 and 99.71%, and was used to determine the fluences required for incremental inactivation. The UV-C fluences needed to inactivate 1 log (D10-value) of Cronobacter spp. in buffer were between 3.53 and 5.50 mJ cm−2, whereas a fluence greater than 6.57 mJ cm−2 was required to achieve a 4-log inactivation. A clear understanding of the UV-C dose-response of several strains of Cronobacter spp. lays the foundation to design effective UV-based disinfection systems.
HIGHLIGHTS
... Outside the hospital and clinic environment, accommodation facilities and hotels also have the presence of RNA viruses on table and door surfaces [5]. Viral RNA has also been found on various surfaces in households with people infected with SARS-CoV-2 [6]. The World Health Organization has issued guidance and recommendations on cleaning and disinfection in areas where SARS-CoV-2 infection may occur. ...
N95 disposable respirator masks are of particular importance to the Covid-19 pandemic. The high cost and limited supply of N95 disposable respirators promote research and safe and effective methods of reusing medical masks. The CDC of USA has announced that ultraviolet (UVC) irradiation inactivates SARS-CoV-2, virus, and other microorganisms known to culture on N95, as well as the results affecting mask fit and filterability. In this study, we analyze and evaluate the pathogen inactivation mechanism and the performance of respirators after treatment and perfect the method of ultraviolet irradiation (UVC) to help inactivate of SARS-CoV-2. At the same time, the research team successfully designed, fabricated and tested a semi-automatic system with UVC capacity 0.15 mW/cm2 at 220 nm that inactivated SARS-CoV-2 (3 log reduction) substances analogues of viruses, and other microorganisms grown on N95. The research results aim to commercialize the system technology (1) to inactivate the SARS-CoV-2 virus through the our application of UVC irradiation at the appropriate wavelength and effective dose, and (2) maintain the suitability and N95 filter rate.KeywordsSARS-CoV-2Ultraviolet irradiationN95 respirator masks
Severe acute respiratory syndrome (SARS) is a newly emerging infectious disease caused by a novel coronavirus, SARS-coronavirus (SARS-CoV). The SARS-CoV spike (S) protein is composed of two subunits; the S1 subunit contains a receptor-binding domain that engages with the host cell receptor angiotensin-converting enzyme 2 and the S2 subunit mediates fusion between the viral and host cell membranes. The S protein plays key parts in the induction of neutralizing-antibody and T-cell responses, as well as protective immunity, during infection with SARS-CoV. In this Review, we highlight recent advances in the development of vaccines 1 and therapeutics based on the S proteinA direct approach to limit airborne viral transmissions is to inactivate them within a short time of their production. Germicidal ultraviolet light, typically at 254nm, is efective in this context but, used directly, can be a health hazard to skin and eyes. By contrast, far-UVC light (207-222nm) efciently kills pathogens potentially without harm to exposed human tissues. We previously demonstrated that 222-nm far-UVC light efciently kills airborne infuenza virus and we extend those studies to explore far-UVC efcacy against airborne human coronaviruses alpha HCoV-229E and beta HCoV-OC43. Low doses of 1.7 and 1.2 mJ/cm2 inactivated 99.9% of aerosolized coronavirus 229E and OC43, respectively. As all human coronaviruses have similar genomic sizes, far-UVC light would be expected to show similar inactivation efciency against other human coronaviruses including SARS-CoV-2. Based on the beta-HCoV-OC43 results, continuous far-UVC exposure in occupied public locations at the current regulatory exposure limit (~3 mJ/cm2/hour) would result in ~90% viral inactivation in ~8minutes, 95% in ~11minutes, 99% in ~16minutes and 99.9% inactivation in ~25minutes. Thus while staying within current regulatory dose limits, low-dose-rate far-UVC exposure can potentially safely provide a major reduction in the ambient level of airborne coronaviruses in occupied public locations.With nearly every country combating the 2019 novel coronavirus(COVID-19), there is a need to understand how local environmental conditions may modify transmission. To date, quantifying seasonality of the disease has been limited by scarce data and the difficulty of isolating climatological variables from other drivers of transmission in observational studies. We combine a spatially resolved dataset of confirmed COVID-19 cases, composed of 3,235 regions across 173 countries, with local environmental conditions and a statistical approach developed to quantify causal effects of environmental conditions in observational data settings. We find that ultraviolet (UV) radiation has a statistically significant effect on daily COVID-19 growth rates: a SD increase in UV lowers the daily growth rate of COVID-19 cases by 1 % point over the subsequent 2.5 weeks, relative to an average in-sample growth rate of 13.2%. The time pattern of lagged effects peaks 9 to 11 d after UV exposure, consistent with the combined timescale of incubation, testing, and reporting. Cumulative effects of temperature and humidity are not statistically significant. Simulations illustrate how seasonal changes in UV have influenced regional patterns of COVID-19 growth rates from January to June, indicating that UV has a substantially smaller effect on the spread of the disease than social distancing policies. Furthermore, total COVID-19 seasonality has indeterminate sign for most regions during this period due to uncertain effects of other environmental variables. Our findings indicate UV exposure influences COVID-19 cases, but a comprehensive understanding of seasonality awaits further analysis.
The performance of two conventional monochromatic ultraviolet-C (UV-C) low pressure mercury (LPM) sources (single and multiple lamps) was measured and compared with three emerging UV sources: a monochromatic KrCl* excimer lamp and UV-LEDs, and a polychromatic pulsed light (UV-C PL) lamp. Fluence-based kinetic parameters and electrical energy per order (EE0) of the UV sources was determined for the inactivation of E. coli bacteria, the reduction of deoxynivalenol (DON) mycotoxin, and F. graminearum spore growth to assess feasibility for various processing targets. The impact on E. coli photoreactivation and dark repair was also assessed. Each of the five UV sources excelled in certain applications while not being feasible for others. The UV-C PL lamp was the most effective for E. coli inactivation, requiring the lowest fluence of 1.4 mJ/cm2 for 5-log10 reduction. The KrCl* excimer lamp was the most effective for preventing subsequent photoreactivation. The UV-LEDs and LPM lamp were equally effective for reducing fungal spore growth requiring 77.0 and 90.1 mJ/cm2 to achieve 90% reduction, respectively. The KrCl* excimer and UV-C PL lamps were the most effective at reducing DON contamination requiring 1250 and 500 mJ/cm2 to achieve 90% reduction, respectively. The evaluation of EE0 showed that the conventional LPM source with multiple lamps had approximately 2–3-fold better electrical efficiency for the reduction of all three tested targets due to its high wall plug efficiency compared to the next best UV-C PL lamp. This indicates that energy efficiency of emerging UV sources needs to be improved in further development.
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Keywords
Pulsed lightUV-LEDsDeoxynivalenolFusariumPhotoreactivationE. coliElectrical efficiency
1. Introduction
Ultraviolet-C (UV-C) light (200–280 nm) has shown to be lethal to most bacteria, viruses, protozoa, fungi and algae (Hijnen et al., 2006). Its use as a disinfection technology for water, air and surfaces has been extensively explored and applied in commercial settings (Koutchma, 2019; Tchonkouang et al., 2023). It has gained traction due to its non-invasive, nonthermal, nonionizing, chemical-free and relatively inexpensive nature compared to other methods such as thermal processing and high-pressure processing. The most common source of artificial UV-C light is the low-pressure mercury (LPM) lamp which emits a monochromatic signal at 253.7 nm. LPM lamps remain the industry standard for UV disinfection due to their high wall plug efficiency up to 30–40% (WPE) and relatively low cost (Koutchma, 2023). However, their implementation in food facilities and processing systems has been slow due to their fragile and bulky nature and the fact that they contain glass and toxic mercury. For this reason, emerging UV light sources such as UV light emitting diodes (UV-LEDs), krypton chloride (KrCl*) excimer lamps and pulsed light (PL) lamps have gained attention from both the research and manufacturing communities.
A commercially available UVLED flow-through device, operating at 40 mJ/cm2, was examined for biofilm control on irrigation pipe material fed by wastewater effluent. Biofouling was monitored through total coliform counts, crystal violet (CV) staining, and ATP analyses. A UV fluence of 40 mJ/cm2 at 280 nm retarded biofilm formation; however, complete biofilm prevention by UV treatment was not achieved despite a high inactivation of planktonic cells. After 5 days of the study, the total coliform and CV biofilm quantification assays between the UV-treated and control bioreactor coupons were not statistically different. The total coliform counts indicated a stable biofilm cell concentration was reached; the CV assay showed biofilm biomass accumulation with time. The ATP results revealed higher coupon ATP on the UV-treated coupons than the control coupons by day 5. The results provoke an interesting discussion surrounding the contribution of viable cells, represented by total coliforms, and extracellular polymeric substance (EPS) to total biofilm biomass. This study also highlighted a need for further investigation into the relationship between ATP responses and complex UV-stress responses of diverse microbial communities as opposed to pure bacteria cultures.
Light now has many applications in life and plays a vital role in therapeutic and protective fields. In the recent era, many light sources are considered for prevention, sterilization, and curing , especially with artificial lamps. Since the coronavirus pandemic appeared in 2019, the world has been interested in sterilization by light rays from a physical and applied point of view. In this work, the authors focus on definite spectral bands and their direct effects on the current COVID-19 pandemic for a prevention spreading purpose. According to the light use results, until now, the most useful method for decontamination against COVID-19 is ultraviolet C. The other spectral bands like UVA, UVB, and violet-blue show that they have a more negligible effect on the deactivation of the COVID-19 virus. The UVA and UVB help increase vitamin D in the human body, reflecting positively on the immunity system and increasing the recovery rate. The violet-blue band is helpful in decontamination against bacteria microorganisms. As for the IR band, the studies are still recent, and until now, there is no recommendation to use this band in sterilization against this pandemic. Studies continued on UV utilization b ecause the world urgently needs industrial and domestic disinfection systems and sterilization. The other bands have another substantial practical effect on health improvement so any people can survive and overcome different diseases.
Introduction: Coxiella burnetii is a zoonotic Gram-negative obligate intracellular bacterial pathogen and the causative agent of query (Q) fever in humans. Contamination of milk by C. burnetii , as a consequence of livestock infection, is a significant public health concern. Effective methods to inactivate C. burnetii in milk are a critical aspect of food safety. Implementation of non-thermal UV-C processing technologies in the dairy industry can effectively preserve the sensory and nutritional quality of raw milk products while ensuring their safety, making them a viable alternative to traditional high-temperature short-time (HTST) pasteurization methods.
Methods: Optical light attenuation factors, such as the absorption, scattering, and reflection by skim milk (SM) were evaluated using a spectrophotometer. SM inoculated with an avirulent strain of C. burnetii was irradiated using a collimated beam device equipped with a low-pressure UV-C 254 nm lamp at doses from 0 to 12 mJ/cm ² . Optical properties were considered for the evaluation of the delivered UV-C dose. The pasteurization treatment was conducted using a lab scale HTST pasteurizer (72°C/15 s). The verification studies were conducted using Escherichia coli ATCC 25922 inoculated in a phosphate buffer (transparent fluid) and humic acid (opaque fluid). Salmonella enterica serovar Muenchen ATCC BAA 1674 inoculated in SM was tested for its suitability as a surrogate for C. burnetii , a bacterium that requires specialized equipment and expertise for experimentation.
Results and Discussion: Absorption, reduced scattering coefficient, and the reflectance of SM at 254 nm were measured as 19 ± 0.3/cm, 26 ± 0.5/cm, and 10.6%, respectively. The UV-C results showed a log-linear inactivation of C. burnetii in SM with the UV-C sensitivity (D 10 ) value of 4.1 ± 0.04 mJ/cm ² . The results of HTST pasteurization revealed that C. burnetii was heat-sensitive with a D value of 1.75 min. Salmonella Muenchen showed similar UV inactivation kinetics and is, thereby, suggested as a suitable surrogate to C. burnetii for the pilot-scale UV-C processing studies of SM.
For more than 100 years, germicidal lamps emitting 254 nm ultraviolet (UV) radiation have been used for drinking-water disinfection and surface sterilization. However, due to the carcinogenic nature of 254 nm UV, these lamps have been unable to be used for clinical procedures such as wound or surgical site sterilization. Recently, technical advances have facilitated a new generation of germicidal lamp whose emissions centre at 222 nm. These novel 222 nm lamps have commensurate antimicrobial properties to 254 nm lamps while producing few short- or long-term health effects in humans upon external skin exposure. However, to realize the full clinical potential of 222 nm UV, its safety upon internal tissue exposure must also be considered. Type I collagen is the most abundant structural protein in the body, where it self-assembles into fibrils which play a crucial role in connective tissue structure and function. In this work, we investigate the effect of 222 nm UV radiation on type I collagen fibrils in vitro . We show that collagen’s response to irradiation with 222 nm UV is fluence-dependent, ranging from no detectable fibril damage at low fluences to complete fibril degradation and polypeptide chain scission at high fluences. However, we also show that fibril degradation is significantly attenuated by increasing collagen sample thickness. Given the low fluence threshold for bacterial inactivation and the macroscopic thickness of collagenous tissues in vivo , our results suggest a range of 222 nm UV fluences which may inactivate pathogenic bacteria without causing significant damage to fibrillar collagen. This presents an initial step toward the validation of 222 nm UV radiation for internal tissue disinfection.
This white paper summarizes the key outcomes, topics, and recommendations from the Canada-India Healthcare Summit 2021 Conference, Biotechnology Session, held on May 20–21, 2021. In particular, the authors have focused their attention on topics ranging from research and development into the etiology and treatment of COVID-19 to novel approaches, such as ultraviolet-C disinfection and cell and gene therapy. The paper also deals with important topics around the effects of food distribution and nutrition on COVID-19 and vice versa, as well as key considerations around research and development, innovation, policy, grants, and incentives, and finally, summarizes the ways in which Canada and India, being close allies, have already begun to partner to fight the pandemic (as well as future strategies to continue this excellent progress). We also include key points raised during the summit and summarize them as part of this white paper.
UV disinfection of drinking water and municipal wastewater are the most common applications of UV photoreactors. Although drinking water and municipal wastewater display many differences in their composition, there are important similarities between these media as well. Important similarities also exist among UV disinfection processes that are used to treat drinking water and municipal wastewater. The design and implementation of UV disinfection for these applications is strongly influenced by the regulations that define their applications; common regulatory constraints are reviewed. As with all UV photoreactors, overall process dynamics are strongly influenced by reaction kinetics. Kinetic models to describe UV disinfection are presented, along with information to describe the effects of microbial repair processes. UV disinfection system design is also strongly influenced by hydraulic behavior, including head loss and flow distribution. The physical and chemical phenomena that lead to inorganic fouling of quartz surfaces, a major maintenance issue with these systems, are also discussed. The chapter concludes with a presentation of stochastic methods that have been developed for optimization of UV disinfection system design and operation.
Light now has many applications in life and plays a vital role in therapeutic and protective fields. In the recent era, many light sources are considered for prevention, sterilization, and curing, especially with artificial lamps. Since the coronavirus pandemic appeared in 2019, the world has been interested in sterilization by light rays from a physical and applied point of view. In this work, the authors focus on definite spectral bands and their direct effects on the current COVID-19 pandemic for a prevention spreading purpose. According to the light use results, until now, the most useful method for decontamination against COVID-19 is ultraviolet C. The other spectral bands like UVA, UVB, and violet-blue show that they have a more negligible effect on the deactivation of the COVID-19 virus. The UVA and UVB help increase vitamin D in the human body, reflecting positively on the immunity system and increasing the recovery rate. The violet-blue band is helpful in decontamination against bacteria microorganisms. As for the IR band, the studies are still recent, and until now, there is no recommendation to use this band in sterilization against this pandemic. Studies continued on UV utilization because the world urgently needs industrial and domestic disinfection systems and sterilization. The other bands have another substantial practical effect on health improvement so any people can survive and overcome different diseases.
Previous bench-scale results demonstrated that polychromatic medium-pressure (MP) ultraviolet (UV) disinfection could achieve 4-log adenovirus inactivation at equivalent UV doses well below those required under the Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR). These findings were confirmed and extended to a full-scale UV disinfection reactor using a live adenovirus challenge. The MP UV disinfection system was able to measure > 4-log adenovirus disinfection at an MS2 coliphage reduction equivalent dose (RED) of < 100 mJ/cm2. The highest observed adenovirus-based RED achieved, referenced to a low-pressure (LP) UV dose-response, was 233 mJ/cm2; the validated RED, including relevant validation factors, was equivalent to that required by the LT2ESWTR for 4-log virus inactivation credit. These results proved that required virus disinfection doses can be validated and that MP UV is capable of meeting the 4-log virus disinfection standard in the LT2ESWTR at a measurable and achievable UV dose substantially lower than that of LP UV technology.
Ultraviolet (UV) Light Emitting Diodes (LEDs) emitting at 260 nm were evaluated to determine the inactivation kinetics of bacteria, viruses, and spores compared to low-pressure (LP) UV irradiation. Test microbes were E. coli B, a non-enveloped virus (MS-2), and a bacterial spore (Bacillus atrophaeus). For LP UV, 4-log10 reduction doses were: E. coli B, 6.5 mJ/cm(2); MS-2, 59.3 mJ/cm(2); and B. atrophaeus, 30.0 mJ/cm(2). For UV LEDs, the 4-log10 reduction doses were E. coli B, 6.2 mJ/cm(2); MS-2, 58 mJ/cm(2); and B. atrophaeus, 18.7 mJ/cm(2). Microbial inactivation kinetics of the two UV technologies were not significantly different for E. coli B and MS-2, but were different for B. atrophaeus spores. UV LEDs at 260 nm are at least as effective for inactivating microbes in water as conventional LP UV sources and should undergo further development in treatment systems to disinfect drinking water.
Polychromatic ultraviolet (UV) irradiation is a common method of pathogen inactivation in the water treatment industry. To
improve its disinfection efficacy, more information is necessary on the mechanisms of ultraviolet inactivation on microorganisms
at wavelengths throughout the germicidal UV spectrum, particularly below 240 nm. This work examined UV inactivation of the
bacteriophage MS2, a common surrogate for enteric pathogens, as a function of wavelength. The bacteriophage was exposed to
monochromatic UV irradiation from a tunable laser at wavelengths between 210 nm and 290 nm. To evaluate the mechanisms of
UV inactivation throughout this wavelength range, RT-qPCR (Reverse Transcription quantitative Polymerase Chain Reaction) was
performed to measure genomic damage for comparison with genomic damage at 253.7 nm. The results indicate that the rates of
RNA damage closely mirror the loss of viral infectivity across the germicidal UV spectrum. This demonstrates that genomic
damage is the dominant cause of MS2 inactivation from exposure to germicidal UV irradiation. These findings contrast those
of adenovirus, for which MS2 is used as a viral surrogate when validating polychromatic UV reactors.
Aims:
To investigate the medium-pressure (MP) and low-pressure (LP) Ultraviolet (UV) susceptibility and the repair potential of Enterococcus faecalis (DSM 20478) after UV treatment.
Methods and results:
A range of UV doses from 4 to 19 mJ cm(-2) was selected in this study. Photoreactivation and dark repair performance were investigated under fluorescent light or in the dark respectively. The inactivation and repair performance of UV disinfection under a range of salinities (0, 1%, 3%) and temperature (4 and 25 °C) were compared. Results indicated that MP UV exposure resulted in higher inactivation efficiency against E. faecalis than LP UV exposure. For repair potential, LP UV resulted in a greater level of light repair than MP UV. Effect of salinity on the inactivation and repair of E. faecalis was correlated with UV sources, whereas low temperature generally adversely affected the inactivation efficiency and final repair levels after both MP and LP UV exposure.
Conclusions:
Both salinity and temperature demonstrated to play an important role in the inactivation and repair capability when UV light was used to treat ballast water.
Significance and impact of the study:
Considering that UV-treated ballast water is exposed or discharged to marine water environment in many countries with various temperature and salinity conditions, results of this study provide significant implications for the management of public health associated with ballast water treatment and discharge. This article is protected by copyright. All rights reserved.
Organic micro-pollutants in drinking water treatment, including soluble microbial products (SMP) can affect the disinfection process of pathogens. This work studied the effect of sodium alginate (SA), a natural polysaccharide and model SMP, on UV inactivation of coliphage MS2 as an entric virus surrogate. SA could enhance UV inactivation, and the effect might be related to reactive oxygen species (ROS) generated from the SA solution. Calculated by UV dose requirement for a 4 log MS2 inactivation, 50 mg L−1 SA increased the inactivation efficiency by approximately 50%. Scavengers of possible reactive species were applied, and t-BuOH and NaN3 reduced the enhancing effect, indicating the production and contribution of hydroxyl radical and singlet oxygen, respectively. The former was not produced in the absence of SA, while the latter was generated by both the test medium and SA. The overall mechanism of virus disinfection by UV in the presence of SA was proposed to include direct UV damage, singlet oxygen produced from the test medium and SA, and hydroxyl radical from SA.
Practical difficulties of the traditional adenovirus infectivity assay such as intensive labor requirements and longer turnaround period limit the direct use of adenovirus as a testing microorganism for systematic, comprehensive disinfection studies. In this study, we attempted to validate the applicability of integrated cell culture quantitative PCR (ICC-qPCR) as an alternative to the traditional cell culture method with human adenovirus type 2 (HAdV2) in a low-pressure UV disinfection study and to further optimize the procedures of ICC-qPCR for 24-well plate format. The relatively high stability of the hexon gene of HAdV2 was observed after exposure to UV radiation, resulting in a maximum gene copy reduction of 0.5 log10 at 280 mJ cm(-2). Two-day post-inoculation incubation period and a maximum spiking level of 10(5) MPN mL(-1) were selected as optimum conditions of ICC-qPCR with the tested HAdV2. An approximate 1:1 correlation of virus quantities by the traditional and ICC-qPCR cell culture based methods suggested that ICC-qPCR is a satisfactory alternative for practical application in HAdV2 disinfection studies. ICC-qPCR results, coupled with a first-order kinetic model (i.e., the inactivation rate constant of 0.0232 cm(2) mJ(-1)), showed that an UV dose of 172 mJ cm(-2) achieved a 4-log inactivation credit for HAdV2. This estimate is comparable to other studies with HAdV2 and other adenovirus respiratory types. The newly optimized ICC-qPCR shows much promise for further study on its applicability of other slow replicating viruses in disinfection studies.
Disinfection of microbes is of importance to prevent the spread of pathogens and non-indigenous species in the environment. Here we test the applicability of using flow cytometry (FCM) to evaluate inactivation of the phytoplankter Tetraselmis suecica after UV irradiation and labeling with the esterase substrate 5-carboxyfluorescein diacetate acetoxymethyl ester (CFDA-AM). Non-irradiated and UV irradiated samples were analyzed with the plate count technique and FCM for 24days. The numbers of colony forming units were used as a standard to develop a FCM protocol. Our protocol readily distinguishes live and dead cells, but challenges were encountered when determining whether UV damaged cells are dying or repairable. As damaged cells can represent a risk to aquatic organisms and/or humans, this was taken into account when developing the FCM protocol. In spite of the above mentioned challenges we argue that FCM represents an accurate and rapid method to analyze T. suecica samples.
Copyright © 2015 The Authors. Published by Elsevier Ltd.. All rights reserved.
Disinfection of bacterial viruses MS2, Q, and X174 in water was successfully carried out using deep ultraviolet light-emitting diodes (DUV-LEDs) operated at 280nm and 255nm. It was shown that the 280-nm DUV-LEDs are much more suitable than the 255-nm DUV-LEDs for the disinfection of water because, even though the disinfection efficiency of the former DUV-LEDs is only half that of the latter ones, the production of high-power 280-nm DUV-LEDs is much easier than that of the 255-nm ones because the external quantum efficiency of the 280-nm DUV-LEDs is more than ten times that of the 255-nm DUV-LEDs. We propose the use of vertical emitting DUV-LEDs for the design of an efficient DUV-LED disinfection chamber. This disinfection technique using DUV-LEDs will open new avenues for water purification.
The use of Aspergillus niger (A. niger) fungal spores as challenge organism for UV reactor validation studies is attractive due to their high UV-resistance and non-pathogenic nature. However A. niger spores UV dose-response was dependent upon sporulation conditions and did not follow the Bunsen-Roscoe Principle of time-dose reciprocity. Exposure to 8 h of natural sunlight for 10 consecutive days increased UV resistance when compared to spores grown solely in dark conditions. Application of 250 mJ cm(-2) at high irradiance (0.11 mW cm(-2)) resulted in a 2-log inactivation; however, at low irradiance (0.022 mW cm(-2)) a 1-log inactivation was achieved. In addition, surface electron microscopy (SEM) images revealed morphological changes between the control and UV exposed spores in contrast to other well accepted UV calibrated test organisms, which show no morphological difference with UV exposure.
Adenoviruses, the most UV resistant microorganism currently known, are posing concerns in UV treated drinking water. To reduce the risk from adenovirus infection, combination processes of UV and chlorination are attractive. Bacteriophage MS2 and adenovirus 5 (AdV5) were used in this study, and inactivated by low-pressure UV (LPUV) lamp, chlorination, sequential processes (UV-Cl 2 and Cl 2 -UV) and a simultaneous process (UV/Cl 2). MS2 was more resistant against chlorine than AdV5, and CT values for 2 log reduction of MS2 and AdV5 were 0.77 and 0.033 mg-min/L, respectively. However, AdV5 was more resistant to UV than MS2 and required a 101 mJ/cm 2 of fluence for 2 log reduction. Compared to the application of UV or chlorine separately, an increasing trend of MS2 inactivation rate was found in the sequential processes, which was statistically significant (p < 0.05, ANCOVA). The simultaneous process of UV/Cl 2 for MS2 provided about 2.3 times higher inactivation rate than a summation of inactivation rates by the separate application of either chlorine or UV, even at the same UV fluence rate and the same initial chlorine concentration. The combination processes of UV and chlorine, either sequential or simultaneous application, seemed to be more effective than a standalone process in viral inactivation.
Disinfection by low-pressure monochromatic ultraviolet (UVC) radiation (253.7 nm) became an important technique to sanitize drinking water and also wastewater in tertiary treatments. In order to prevent the transmission of waterborne viral diseases, the analysis of the disinfection kinetics and the quantification of infectious viral pathogens and indicators are highly relevant and need to be addressed. The families Adenoviridae and Polyomaviridae comprise human and animal pathogenic viruses that have been also proposed as indicators of fecal contamination in water and as Microbial Source Tracking tools. While it has been previously suggested that dsDNA viruses may be highly resistant to UVC radiation compared to other viruses or bacteria, no information is available on the stability of polyomavirus toward UV irradiation. Here, the inactivation of dsDNA (HAdV2 and JCPyV) and ssRNA (MS2 bacteriophage) viruses was analyzed at increasing UVC fluences. A minor decay of 2-logs was achieved for both infectious JC polyomaviruses (JCPyV) and human adenoviruses 2 (HAdV2) exposed to a UVC fluence of 1,400 J/m2, while a decay of 4-log was observed for MS2 bacteriophages (ssRNA). The present study reveals the high UVC resistance of dsDNA viruses, and the UV fluences needed to efficiently inactivate JCPyV and HAdV2 are predicted. Furthermore, we show that in conjunction with appropriate mathematical models, qPCR data may be used to accurately estimate virus infectivity.
We have used integrating-sphere UV spectroscopy to study scattering of radiation from an XeBr exciplex lamp (282 nm) by nanoparticles of a photocatalyst (TiO2) and Escherichia coli CN13 cells. We have demonstrated that we must take into account scattered radiation in calculating the UV doses for disinfection of water in the presence of suspended TiO2 particles. We have established that using the absorption intensities for the water to be disinfected in the dose calculation, obtained without taking into account the intensity of scattering of the radiation, leads to the actual dose exceeding the calculated dose by 5.2% to 69.4%. Total inactivation of the cells (from the absence of colony-forming units (CFU) after incubation of the irradiated aqueous suspension) was achieved at a UV radiation dose of 30 and 40 mJ/cm2 and TiO2 concentration of 0.25 and 0.10 g/L. The optimal concentration of TiO2 in water determined was 0.25 g/L, which corresponds to the maximum concentration of hydroxyl radicals and the rate of their formation.
The microbicidal effect of UV light depends on the dose in both, disinfection processes and natural inactivation by the sunlight in surface water. Deviations of the time dose reciprocity are well known from chemical water disinfection whereas no data are available about this effect in UV inactivation in water. In a previous study we found that the UV inactivation behaviour of yeast strains does not follow the time dose reciprocity, insofar that longer exposure led to higher reduction of cultivable cells. In contrast, an earlier study about E coli B/r claimed a higher inactivation with single exposure compared with fractionated UV irradiation. To investigate this question we selected water-relevant microorganisms and studied their UV inactivation behaviour (253.7nm) by means of a specially designed UV irradiation apparatus (a) under standard irradiation conditions (2W/m2) and (b) with three levels of UV dose rate (2, 0.2 and 0.02W/m2). The test organisms were (i) three E coli strains (ATCC 25922, ATCC 11229 and an isolate from sewage) representing the routinely used faecal indicator, (ii) three bacterial viruses (MS2, ϕX174 and B40-8) proposed as indicators for viral contamination in water and (iii) spores of Bacillus subtilis because of their use as a biodosimeter in prototype testing of commercial UV plants for drinking water disinfection. We found, under standard inactivation conditions, that the E coli strains and phage ϕX174 are most UV susceptible, followed by B40-8 and finally MS2 and bacterial spores. The dose protraction experiments revealed for the E coli strains a higher inactivation with high dose rates compared to low dose rates at the same UV doses (difference of about 1 log10 at 80-100J/m2). The other test organisms did not deviate from the time dose reciprocity in the proven range of dose.
Previous evaluations of the effect of ultraviolet (UV) light on Cryptosporidium parvum oocysts have been limited to a single strain-the Iowa strain. This study investigated the response of five strains of C. parvum to UV. A collimated beam apparatus was used to apply controlled doses of monochromatic (254 nm) UV to oocysts of the Iowa, Moredun, Texas A&M, Maine, and Glasgow strains. Irradiation was measured using a calibrated radiometer and sensor. Inactivation was quantified through animal infectivity by inoculation of cohorts of CD-1 neonatal mice with UV-treated and untreated control oocysts of each strain followed by examination of intestinal sections for infection using hemotoxylin and eosin staining. A UV light dose of 10 mJ/cm(2) achieved at least 4-log(10) inactivation of all strains evaluated. All five strains of C. parvum were shown to be highly susceptible to low levels of UV light.
Recent studies have shown that ultraviolet (UV) radiation reduces the infectivity of Cryptosporidium parvum oocysts and Giardia spp. Cysts. The objective of this work was to further parvum oocysts and G. muris cysts in the presence of suspended examine UV inactivation of C. particulate matter. Naturally occurring particulate matter consisting of a heterogeneous mixture of biological and non-biological particles, mainly in the 5-25 mu m size range, was concentrated from a lake. Different aliquots of this material were mixed with purified oocyst and cyst and the suspensions were exposed to UV fluences of reparations in aqueous suspensions, p 5 and 40 mJ/cm(2) from a medium-pressure mercury arc lamp using a collimated beam apparatus. Parasite inactivation was determined using mouse infectivity assays. Addition of particulate matter was correlated with statistically significant reductions in C. parvum and G. muris inactivation of 0.8 log(10) and 0.4 log(10), respectively, even after the fluence was adjusted for increased absorbance due to the presence of the particles. The corresponding increases in turbidity were 0.3-20 NTU for C. parvum and 7.5-20 NTU for G. muris. The magnitude of the effect was a function of the final suspension turbidity but was independent of fluence. in this the effect of particles on parasite inactivation at turbidity values of less than 10NTU was study, small and difficult to measure, and would likely be unimportant in practice. Although the mechanism for this reduction was not determined, the results suggest that the particulate matter present in natural surface waters may interact with oocysts and cysts and thereby result in a reduction in UV inactivation over and above that attributable to simple absorbance. The effect of turbidity on inactivation measured in this work may not necessarily apply generally since the characteristics of the particles that compose turbidity may differ considerably between water sources.
Biodosimetry, that is the application of microorganisms for the measurement of radiation, is already in wide use in the field of UV disinfection. The measurement of the mean fluence in flow-through systems with a biodosimeter (microorganisms with calibrated UV sensitivity) results in the Reduction Equivalent Fluence (REF). In the case of quasi monochromatic radiation (mercury low pressure lamp, 253.7 nm), the flow pattern of the water through the inhomogeneous radiation field, together with some other parameters, strongly influences the REF but the spectral sensitivity of the biodosimeter plays no role. If microorganisms with shouldered survival curves are used as biodosimeters two parameters (k and d) are necessary to describe their survival curves. In general, both parameters are wavelength dependent and the functions k(λ) and d(λ) must be known if medium pressure mercury lamps are used, which emit polychromatic UV radiation. The knowledge of k(λ) also is necessary for selecting an appropriate UV sensor which controls the function of the UV lamps during the operation of the disinfection plant. In literature many different spectral sensitivity curves were published but they all differ somehow. The functions k(λ) and d(λ) were measured for spores of Bacillus subtilis ATCC 6633 in using quasi-monochromatic UV radiation and the results were tested in using polychromatic UV radiation.
Ultraviolet irradiation is gaining importance as a disinfection procedure for drinking water and in waste water treatment. Since water is one of the main transmission routes of hepatitis A virus the susceptibility of HAV to UV rays is of special interest. MS-2 coliphage resembles HAV in size and structure, is easy to handle, and might therefore serve as indicator organism for the assessment of water quality and for evaluating the quality of water treatment processes. Hepatitis A virus and MS-2 coliphage were suspended in 0.9% sodium chloride solution and were irradiated in a 20-ml quarz cuvette at 254 nm. For a reduction rate of four log units a three times higher UV dose was required with MS-2 than with HAV.
Abstract: A ring-shaped disinfection apparatus has been developed containing twenty ultraviolet-light-emitting diodes (UV-LEDs) with
emission at 285 nm. The apparatus was applied to Escherichia coli, Qβ, MS2, and adenovirus in water. The reduction-equivalent fluence in
the apparatus was determined, based on a modification of the protocol for the bench-scale challenge test by low-pressure (LP) UV lamp
systems (LPUV). All species demonstrated log-linear inactivation profiles versus the fluence, and the inactivation rate constants for E. coli,
Qβ, MS2, and adenovirus were 0.157, 0.037, 0.029, and 0.023 cm2/mJ, respectively. The inactivation rate constant for adenovirus under the
UV-LED exposure (k'UV-LED) was higher than that under a LPUV lamp (k'LPUV), and the ratio of k' UV-LED to k'LPUV, which is approximated as a germicidal factor at 285 nm, was 1.15 for adenovirus. To conclude, this study demonstrated a high potential of the 285 nm UV-LEDs to
inactivate microorganisms in water. The germicidal factor found for adenovirus implies that the 285 nm UV-LED could be a good option to
inactivate adenovirus in water. DOI: 10.1061/(ASCE)EE.1943-7870.0001061. © 2015 American Society of Civil Engineers.
Every year around 3.4 million people die from water-related diseases, mainly amoebiasis and diarrhoea caused by bacteria. The assessment of the efficiency of a UV light disinfection process in the inactivation of indicators, pathogen bacteria and amphizoic amoebae in a secondary treated effluent was carried out. Wastewater was irradiated with different doses of UV light using a collimated-beam reactor. Dose-response results showed that a UV dose of 15 mW·s/cm 2 was enough to inactivate FC to the limit established in Mexican legislation (<1,000 MPN/100 ml) for irrigation reuse, as well as reaching a 2 log inactivation for faecal streptococci. Also, the final concentration reached for Salmonella typhi was <10 3 MPN, which is the minimal concentration for a disease response in humans. The isolation from the secondary effluent and the pathogenicity determination of Acanthamoeba were carried out. Amoebae were concentrated to higher concentrations than those of the effluent for irradiation tests. Radiation tests showed that amoebae required higher doses than bacteria for their total inactivation (60 mW·s/cm 2 for a 2 log reduction). Results showed that UV light is an alternative to inactivate high contents of bacteria and amoebae trophozoites, although higher doses were needed for the high concentrations of amoebae used.
After a critical review of the fundamental equations describing photobiological and photochemical processes occurring in a medium exposed to a quasi-collimated monochromatic UV light beam, the analysis in this review is extended to analogous processes driven by polychromatic UV light, such as that emitted by medium pressure mercury-vapor arc lamps. The analysis is based on the Second Law of Photochemistry, namely that all photochemical events must be independent, and the rate of such events must be proportional to the rate of photon absorption. A consistent application of the Second Law of Photochemistry leads to a concept change; hence it is proposed herein to use photon fluence and photon fluence rate, rather than fluence (UV dose) and fluence rate, respectively, in the analysis and interpretation of photobiological and photochemical processes. As a consequence, many equations that have been used in the past must be revised, and some experimental information (e.g., action spectra) needs to be re-analyzed. This article is protected by copyright. All rights reserved.
This article is protected by copyright. All rights reserved.
Ultraviolet (UV) disinfection is being considered for inactivation of pathogens in filtered surface waters across North America. MS2 coliphage is the most commonly used test microbe for UV reactor validation in North America, and the development of UV dose-response data for MS2 at bench scale is an integral part of validation testing. This research evaluated the effect of water quality (e.g., turbidity, particle count, particle size, and absorbance) and sample depth on inactivation of MS2 coliphage in 17 filtered waters. In addition, the inactivation performance of low-pressure (LP) and medium-pressure (MP) lamp types was compared. Results indicated that turbidity, particle count, and absorbance, when factored into the bench-scale dose measurement, did not affect UV inactivation of MS2 coliphage in filtered waters meeting federal regulations. UV light from MP lamps appeared more effective than LP UV for inactivating MS2. These results suggest that water quality should not be considered a major factor in properly designed UV bench-scale tests or in reactor validation challenges that use inactivation kinetics of MS2 coliphage as a dose-measurement tool in filtered surface waters.
Disinfection with UV radiation in the range of 240-290 nm is emerging as an alternative to conventional chemical disinfectants because byproduct formation is negligible with UV radiant exposure of 400 J/m2 (at 253.7 nm) required for a 4 log-reduction of germs and viruses. Prerequisites for disinfection are outlined, and both chemical and UV disinfection are compared. A 4 log-reduction requires a 99.99% homogeneous UV radiant exposure of ≤ 400 J/m2 to all water volume elements passing the UV system and depends on radiation field and flow pattern and cannot be calculated from technical data. Hydraulics may cause severe mismatch between calculation and reality. A performance of 400 J/m2 and a 4 log-reduction has to be verified by biodosimetric testing of prototypes using suspensions of germs with a known UV susceptibility. Safe UV disinfection is ascertained by flow control and monitoring of UV irradiance in W/m2 with standardised UV sensors at defined positions in the UV units. During operation UV irradiance must not fall below a system specific minimum value approved with the biodosimetric test.
Ultraviolet (UV) disinfection is now an accepted technology for inactivation of a variety of waterborne pathogens in wastewater and drinking water. However, the techniques used in much of the previous research aimed at providing information on UV effectiveness have not yet been standardized. Thus in many peer reviewed published literature, it is not clear how the UV irradiations were carried out, nor how the average fluence (or UV dose) given to the microorganisms has been determined. A detailed protocol for the determination of the fluence (UV dose) in a bench scale UV apparatus containing UV lamps emitting either monochromatic or broadband UV light was developed. This protocol includes specifications for the construction of a bench scale UV testing apparatus, methods for determination of the average irradiance in the water, details on UV radiometry, and considerations for microbiological testing. Use of this protocol will aid in standardization of bench scale UV testing and provide increased confidence in data generated during such testing.
UV light emitting diodes (UV-LEDs) with peak emissions at 265, 280 and 310. nm were applied to batch and flow-through water disinfection systems. Inactivation efficiency of Escherichia coli was compared between reactors and among emissions based on the exposure time and fluence. Combined emissions at 265/280, 265/310, 280/310 and 265/280/310. nm were also tested in the flow-through reactor.The time-based inactivation efficiency was highest with the 280nm UV-LED while the fluence-based efficiency was highest with the 265nm UV-LED. In the batch reactor, the UV-LEDs at 265 and 280nm achieved over 4 log inactivation of E. coli at fluences of 10.8 and 13.8mJ/cm2, respectively, while the UV-LED at 310nm required 56.9mJ/cm2 for 0.6 log inactivation. The flow-through reactor showed tailing in the fluence-response curves and resulted in lower inactivation efficiency than the batch reactor, with lower fluence-based inactivation rate constant of 29% for 265nm and 32% for 280nm. Combined emissions were less efficient than the component emissions applied separately, and reduced output power for each UV-LED was observed for combined cases. This study provides key implications for the future application of UV-LEDs to water disinfection systems.
Adenoviruses are water-borne human pathogens with high resistance to UV disinfection. Combination of UV treatment and chlorination could be an effective approach to deal with adenoviruses. In this study, human adenovirus 5 (HAdV-5) was challenged in a bench-scale experiment by separate applications of UV or chlorine and by combined applications of UV and chlorine in either a sequential or simultaneous manner. The treated samples were then propagated in human lung carcinoma epithelial cells to quantify the log inactivation of HAdV-5. When the processes were separate, a fluence of 100 mJ/cm(2) and a CT value of 0.02 mg min/L were required to achieve 2 log inactivation of HAdV-5 by UV disinfection and chlorination, respectively. Interestingly, synergistic effects on the HAdV-5 inactivation rates were found in the sequential process of chlorine followed by UV (Cl2-UV) (p < 0.05, ANCOVA) in comparison to the separate processes or the simultaneous application of UV/Cl2. This implies that a pretreatment with chlorine may increase the sensitivity of the virus to the subsequent UV disinfection. In conclusion, this study suggests that the combined application of UV and chlorine could be an effective measure against adenoviruses as a multi-barrier approach in water disinfection.
Ultraviolet inactivation of enteric pathogenic microorganisms, including Shigella dysenteriae, Salmonella typhimurium, and human rotavirus (HRV-Wa) and somatic coliphages (MS2 and T4), was investigated in different water samples. Significant differences in the sensitivity of the bacteria and viruses to ultraviolet radiation were observed. Viruses were more resistant to ultraviolet disinfection than all the enteric bacteria tested in this study. With the exception of S. typhimurium, which showed flattening and tailing, strong first-order relationships between the logarithm of survival and the ultraviolet dose were observed. While S. dysenteriae and S. typhimurium were found to undergo photoreactivation after ultraviolet exposure, the photoreactivation decreased significantly with higher ultraviolet doses. Moreover, the inactivated bacteria exhibited different photoreactivation rates with different water samples. Combination of a low ultraviolet dose and a low concentration of chlorine not only inhibited the photoreactivation of ultraviolet-damaged bacteria but also effectively inactivated the bacteria.