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UV Rate Constants
Abstract
Microbial susceptibility to ultraviolet light varies widely between species of microbes. Bacteria, viruses, and fungal spores respond to UV exposure at rates defined in terms of UV rate constants. Other parameters used to define UV susceptibility include the Z value or Z
eff (same as UV rate constant), the inactivation cross-section, the D
90 (UV dose to inactivate 90%), and variations of the D
90 (i.e. D
99, D
99.9 etc.). The classic lethal hit dose, D
37 or lethe, does not follow the same convention, and refers to a 37% survival dose (e–1), or 63.2% inactivation (Fraenkel-Conrat and Wagner 1981, Hollaender 1955, Casarett 1968, Wells 1940).
... The effect of reflector material on measured UVC dose was evaluated, where dose is defined as the product of exposure time and UV irradiance between 230 and 280 nm, in-keeping with Bolton's definition 'the total radiant power incident from all upward directions on an infinitesimal element of surface of area δA, containing the point under consideration divided by δA' (Bolton & Linden, 2003). The first-order decay rate constant (k) was calculated using (Kowalski, 2009): ...
There is strong evidence that SARS-CoV-2 is spread predominantly by airborne transmission, with high viral loads released into the air as respiratory droplets and aerosols from the infected subject. The spread and persistence of SARS-CoV-2 in diverse indoor environments reinforces the urgent need to supplement distancing and PPE based approaches with effective engineering measures for microbial decontamination – thereby addressing the significant risk posed by aerosols. We hypothesized that a portable, single-pass UVC air treatment device (air flow 1254 L/min) could effectively inactivate bioaerosols containing bacterial and viral indicator organisms, and coronavirus without reliance on filtration technology, at reasonable scale. Robust experiments demonstrated UVC dose dependent inactivation of Staphylococcus aureus (UV rate constant (k) = 0.098 m²/J) and bacteriophage MS2, with up to 6-log MS2 reduction achieved in a single pass through the system (k = 0.119 m²/J). The inclusion of a PTFE diffuse reflector increased the effective UVC dose by up to 34% in comparison to a standard Al foil reflector (with identical lamp output), resulting in significant additional pathogen inactivation (1-log S. aureus and MS2, p < 0.001). Complete inactivation of bovine coronavirus bioaerosols was demonstrated through tissue culture infectivity (2.4-log reduction) and RT-qPCR analysis – confirming single pass UVC treatment to effectively deactivate coronavirus to the limit of detection of the culture-based method. Scenario-based modelling was used to investigate the reduction in risk of airborne person to person transmission based upon a single infected subject within the small room. Use of the system providing 5 air changes per hour was shown to significantly reduce airborne viral load and maintain low numbers of RNA copies when the infected subject remained in the room, reducing the risk of airborne pathogen transmission to other room users. We conclude that the application of single-pass UVC systems (without reliance on HEPA filtration) could play a critical role in reducing the risk of airborne pathogen transfer, including SARS-CoV2, in locations where adequate fresh air ventilation cannot be implemented.
... The dimer inhibits the formation of new DNA or RNA chains in the process of cell replication, resulting in the inactivation or inability to replicate in organisms affected by UVR (Bolton and Linden, 2003). The impact of UVR on plant physiology is concomitant with physical size, molecular weight of DNA or RNA, content of pyrimidine and purine bases, and the presence of chromophores (Kowalski, 2009a). Amino acids that may contribute to photoreactivity in DNA involving cross-linking with proteins include cysteine, cystine, tyrosine, serine, methionine, lysine, arginine, histidine, tryptophan, and phenylalanine (Kowalski, 2009b). ...
... Overall, Btk spores were approximately an order of magnitude more susceptible to all three combination modes of UV irradiation and gaseous iodine on MCE filters compared to A. fumigatus spores. The findings are consistent with other studies, which report that the fungal spores can be more resistant than bacterial spores (American Air and Water, 2018;Kowalski, 2009). ...
Exposure to viable bacterial and fungal spores re-aerosolized from air handling filters may create a major health risk. Assessing and controlling this exposure have been of interest to the bio-defense and indoor air quality communities. Methods are being developed for inactivating stress-resistant viable microorganisms collected on ventilation filters. Here we investigated the inactivation of spores of Bacillus thuringiensis var. kurstaki (Btk), a recognized simulant for B. antracis, and Aspergillus fumigatus, a common opportunistic pathogen used as an indicator for indoor air quality. The viability change was measured on filters treated with ultraviolet (UV) irradiation and gaseous iodine. The spores were collected on high-efficiency particulate air (HEPA) and non-HEPA filters, both flattened for testing purposes to represent “surface” filters. A mixed cellulose ester (MCE) membrane filter was also tested as a reference. Additionally, a commercial HEPA unit with a deep-bed (non-flattened) filter was tested. Combined treatments of Btk spores with UV and iodine on MCE filter produced a synergistic inactivation effect. No similar synergy was observed for A. fumigatus. For spores collected on an MCE filter, the inactivation effect was about an order of magnitude greater for Btk compared to A. fumigatus. The filter type was found to be an important factor affecting the inactivation of Btk spores while it was not as influential for A. fumigatus. Overall, the combined effect of UV irradiation and gaseous iodine on viable bacterial and fungal spores collected on flat filters was found to be potent. The benefit of either simultaneous or sequential treatment was much lower for Btk spores embedded inside the deep-bed (non-flattened) HEPA filter, but for A. fumigatus the inactivation on flattened and non-flattened HEPA filters was comparable. For both species, applying UV first and gaseous iodine second produced significantly higher inactivation than when applying them simultaneously or in an opposite sequence.
Existing researches shown that the ultraviolet light at wavelength of 254 nm could inactivate the COVID-19. The parabolic reflector, a key component of the upper-room ultraviolet germicidal irradiation (UVGI) device, plays a vital role in the collimation and restraint of ultraviolet light. This study aims to simulate the collimation effect of four types of parabolic reflectors. They were divided into two categories to compare and analyze the uniformity of irradiance according to the exiting widths and overall heights. The results show that better parallel light can be obtained by placing the lamp at the focal point of the reflector. Increasing the overall height of the reflector can improve the distribution of the irradiation. The improved compound parabolic reflector (d) has higher efficient average value of light constraint and irradiance spatial distribution compared to the other types of reflectors.KeywordsIndoor environmentUV sterilizationReflectorRay-tracingSimulation
In response to the COVID-19 pandemic, healthcare facilities have purchased more ultraviolet-C (UVC) disinfection devices than in previous years. This article discusses the safety and efficacy of UVC disinfection in healthcare settings.
Faced with a global pandemic such as the one triggered by the SARS-CoV-2 virus, the medical supply chain has been highly demanded. An item in which this manifested itself more clearly, are the N95 masks, designed to be disposable items, in many cases they have had to be reused. In these emergency conditions, it was necessary to apply an effective and safe method that can be used locally. Here a device for disinfection by ultraviolet C light was developed that allows irradiating N95 masks with a known and reproducible dose. Thus being able to apply a safe and effective disinfection method according to existing information. The use of a common model of UV-C lamps and simple construction of the device allows it to be built at low cost and with widely available materials. The effectiveness of the device was demonstrated against an enveloped RNA virus, characteristics shared with the virus that causes COVID19, being capable of reducing the viral load by 4 orders of magnitude.
The global health-threatening crisis from the COVID-19 pandemic, caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), highlights the scientific and engineering potentials of applying ultraviolet (UV) disinfection technologies for biocontaminated air and surfaces as the major media for disease transmission. Nowadays, various environmental public settings worldwide, from hospitals and health care facilities to shopping malls and airports, are considering implementation of UV disinfection devices for disinfection of frequently touched surfaces and circulating air streams. Moreover, the general public utilizes UV sterilization devices for various surfaces, from doorknobs and keypads to personal protective equipment, or air purification devices with an integrated UV disinfection technology. However, limited understanding of critical UV disinfection aspects can lead to improper use of this promising technology. In this work, fundamentals of UV disinfection phenomena are addressed; furthermore, the essential parameters and protocols to guarantee the efficacy of the UV sterilization process in a human-safe manner are systematically elaborated. In addition, the latest updates from the open literature on UV dose requirements for incremental log removal of SARS-CoV-2 are reviewed remarking the advancements and existing knowledge gaps. This study, along with the provided illustrations, will play an essential role in the design and fabrication of effective, reliable, and safe UV disinfection systems applicable to preventing viral contagion in the current COVID-19 pandemic, as well as potential future epidemics.
A mathematical model is presented for the ultraviolet susceptibility of microbes based on evaluation of complete genomes. The genomes of 49 animal viruses and bacteriophages, and 33 bacteria, were analyzed using base-counting software to establish the frequencies of potential dimers. A total of 71 data sets represented 27 ssRNA viruses, while 77 data sets represented 22 dsDNA viruses, and 64 data sets represented the bacteria. UV susceptibility (D 90) was correlated with the genomic model and produced R 2 values of 79%, 87%, and 70% for RNA viruses, DNA viruses and bacteria respectively. Predictions of UV susceptibility are provided for dozens of microbes important to human health.
Mathematical models of the response of populations of microorganisms exposed to ultraviolet
germicidal irradiation (UVGI) are developed that include two-stage response curves and shoulder
effects. Models are used to develop a C++ computer program that is capable of predicting the
performance of UVGI air disinfection systems. The algorithms are based on models for 1) the
intensity field of UVGI lamps, 2) the intensity field due to UVGI reflective enclosures, and 3) the
kill rate of microorganisms to UVGI exposure as they pass through the modeled intensity field.
The validity of the UVGI lamp model is established by comparison with lamp photosensor data.
The validity of the overall predictive model is established by comparison of predictions with
laboratory bioassays for two species of airborne pathogens – Serratia marcescens and Bacillus
subtilis. First stage rate constants, second stage rate constants, and the defining shoulder
parameters are determined for Aspergillus niger and Rhizopus nigricans based on bioassay data,
and it is shown how predictions using only single stage rate constants can deviate significantly
from predictions using the complete survival curve. A dimensional analysis of UVGI systems
identifies nine dimensionless parameters responsible for determining the effectiveness of any
rectangular UVGI system. A factorial analysis of the dimensionless parameters based on data
output by the program identifies the most critical parameters and the inter-relationships that
determine UVGI system effectiveness. Response surfaces are generated using program output to
illustrate the inter-relationships of the dimensionless parameters. The optimum values of the
dimensionless parameters are summarized that result in optimized performance. Economic
optimization is demonstrated by a series of examples that calculate life cycle costs, and principles
of economic optimization are summarized. Conclusions are presented that will produce more
energy-efficient and effective designs and a proposed model for improved UVGI systems is
presented.
The effects of ultraviolet (UV) irradiation on the viability of the waterborne triactinomyxon stages of Myxobolus cerebralis were evaluated by vital staining and the infectivity for juvenile rainbow trout Oncorhynchus mykiss. A dose of 1300 mWs cm-2 was required to inactivate 100% of the triactinomyxons held under a static collimated beam of UV as determined by vital staining. Juvenile rainbow trout were protected from infections with M. cerebralis when exposed to 14,000 or 1400 triactinomyxon spores per fish that had been treated with the collimating beam apparatus (1300 mWs cm-2). Among all fish receiving UV-treated triactinomyxons, none had clinical signs of whirling disease, or evidence of microscopic lesions or spores of M. cerebralis after 5 mo at water temperatures of 15 degrees C. In contrast, 100% of the fish receiving the higher dose of untreated triactinomyxons developed clinical signs of whirling disease and both microscopic signs of infection and spores were detected in all of the high and low dose trout receiving untreated triactinomyxon exposures. Two additional trials evaluated the Cryptosporidium Inactivation Device (CID) for its ability to treat flow-through 15 degrees C well water to which triactinomyxons were added over a 2 wk period. CID treatments of a cumulative dose exceeding 64,000 triactinomyxons per fish protected juvenile rainbow from infections with M. cerebralis. Rainbow trout controls receiving the same number of untreated triactinomyxons developed both microscopic lesions and cranial spore concentrations up to 10(4.6) per 1/2 head, although no signs of clinical whirling disease were observed. UV (126 mWs cm-2, collimated beam apparatus) was also effective in killing Flavobacterium psychrophilum, the agent causing salmonid bacterial coldwater disease, as demonstrated by the inability of bacterial cells to grow on artificial media following UV treatment.
A number of different factors have contributed to an increased awareness of the threat posed by pathogenic microorganisms in indoor and outdoor environments and this in turn has led to renewed interest in ultraviolet germicidal irradiation (UVGI) as a potential control measure. This paper presents the results of a series of experiments carried out to determine the UV susceptibility of aerosolised Serratia marcescens and the effect of increased relative humidity on the UV susceptibility constant. Photoreactivation is a light induced DNA repair mechanism which enables microorganisms to recover from sub-lethal UV doses. Although this is an important issue it is often overlooked and not taken into account when estimating the UV susceptibility of microorganisms. This paper also presents data regarding the photoreactivation potential of Serratia marcescens and the effect that this can have on the UV susceptibility constant. INTRODUCTION In recent years a number of factors have stimulated an increased awareness of the presence of potentially pathogenic bioaerosols in indoor and outdoor environments and the detrimental health effects associated with them (Lin & Li, 2002). One of the main driving forces has been the re-emergence of tuberculosis as a major health concern mainly in the developing world but also more recently in the more developed countries of Europe. The situation has been compounded by the rise in the number of multi-drug resistant strains of Mycobacterium tuberculosis which has made antibiotic treatment of the disease increasingly problematic. There has also been an increase in the number of nosocomial infections (i.e. those acquired in hospital) and in the UK alone it is estimated that 1 in 10 patients will acquire some kind of infection during their stay in hospital (Beggs, 2000). Traditionally it has been thought that the main source of infection in healthcare facilities was person to person contact. However, it is now believed that the airborne transmission route accounts for as much as 10% of all nosocomial infections (Beggs, 2000).
During bioaerosol research microorganisms are frequently aerosolized from phosphate-buffered suspension via air-jet nebulization. Buffer will therefore be present in organism-free droplets (''empties") as solutes in hydrous surface coatings of airborne organisms or as dry surface coatings on organisms. It might be expected that the buffer would influence the resulting aerosol size distribution and that the influence might vary with relative humidity. In this work we examined the effect of various buffer concentrations on the aerosol size distribution of Bacillus subtilis (B. subtilis) and Pseudomonas fluorescens ( P. fluorescens ) at various relative humidities. Microorganism suspensions in distilled deionized water and phosphate-buffered water were prepared and nebulized from a 3-jet Collison nebulizer into a sampling chamber maintained at 10% relative humidity. The aerosol was then conducted to a second chamber to which moist air was added to achieve the target relative humidity. Particle aerodynamic size distributions were measured at 10, 20, 40, 60, 80, and 90% relative humidity. Buffer concentrations used were 0, 2.5, 5, 7.5, and 10%. Phosphate buffer substantially affected the indicated aerodynamic size distribution of both bioaerosols, with greater effect seen for the Gram-positive B. subtilis than for the Gram-negative P. fluorescens . The effects were most pronounced above 80% relative humidity. Further, aerosol size distributions of B. subtilis , but not P. fluorescens , were affected by relative humidity even in the absence of buffer, suggesting a species-related difference in hygroscopic growth. Growth predicted from theory was generally consistent with observed behavior, although uncertainties remain concerning organismand instrument-related influences on measured behavior.
Ultraviolet germicidal irradiation (UVGI) as an engineering control against infectious bioaerosols necessitates a clear understanding of environmental effects on inactivation rates. The response of aerosolized Serratia marcescens, Bacillus subtilis, and Mycobacterium parafortuitum to ultraviolet irradiation was assessed at different relative humidity (RH)levels in a 0.8 m3 completely-mixed chamber. Bioaerosol response was characterized by physical factors including median cell aerodynamic diameter and cell water sorption capacity and by natural decay and UV-induced inactivation rate as determined by direct microscopic counts and standard plate counts. All organisms tested sorbed water from the atmosphere at RH levels between 20% and 95% (up to 70% of dry cell mass at 95% RH); however, no concomitant change in median aerodynamic diameter in this same RH range was observed. Variations in ultraviolet spherical irradiance were minor and not statistically significant in the 20-95% RH range. Cell water sorption and inactivation response was similar for each of the pure cultures tested: when RH exceeded approximately 50%, sorption increased markedly and a sharp concurrent drop in UV-induced inactivation rate was observed.
The Oxford Handbook of Nucleic Acid Structure is a comprehensive reference text on all aspects of nucleic acid sturcture. Particular emphasis is placed on the results from X-ray crystallography and NMR studies, with both methods being given equal weight. The nineteen chapters describe in detail the variety of DNA and RNA structural types discovered to date with all the major 'native' structures being represented. The text progresses systematically through the polymorphs of double helical DNA through to the higher-order organizations of triplexes, quadruplexes, and junctions, then to RNA structures in their various degrees of complexity. Each chapter has been written by authorities in the field who have worked together to provide this comprehensive text on nucleic acid structure. The whole project has been brought together and edited by Professor Stephen Neidle who is Director of the CRC Biomolecular Structure Unit at the Institute of Cancer Research.
Wastewater disinfection has grown in popularity in recent years in the UK particularly for reducing faecal coliform levels in effluents impacting on bathing waters not compliant with EC Directive standards. Although disinfectants appear effective against bacterial indicators of faecal pollution, their efficiency against human viruses is still unclear. This has significance both for attainment of compliance with viral standards in the EC Bathing Waters Directive and, potentially, for protection against viruses likely to cause gastroenteritis. This study reports on bench scale disinfection of primary effluent treated with chlorination and secondary effluent treated with UV. Disinfection experiments comprised of wastewater, sterilised by gamma irradiation, seeded with monodispersed laboratory grown bacterial indicators (Escherichia coli and Enterococcus faecalis), human enterovirus (poliovirus) and F+ bacteriophage (MS2) – a potential ‘viral indicator’. Under the experimental conditions used, the inactivation of bacterial indicators was rapid in comparison to the inactivation of F+ bacteriophage which was very poor. Seeded poliovirus was significantly more susceptible to inactivation by chlorine and UV irradiation than F+ bacteriophage but was more resistant than bacterial indicators in both cases. These results indicate that the use of bacterial indicators alone to determine the effect of wastewater disinfection when using chlorination or UV irradiation underestimates human enteric virus inactivation, whereas the use of F+ bacteriophage is likely to give a conservative estimate of virus inactivation.
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.
''Excellent and very timely....It will undoubtedly become a standard reference for the application of circular dichroism (CD) to biomolecules.'' --- Quarterly Review of Biology, March 1997 ''[T]estament to the book's utility is the fact that during the course of my review I had to 'rescue' it from the desks of graduate students on an almost daily basis. In summary, this is a great book.'' --- American Scientist ''Well documented chapters provide a very good insight into the problems surrounding the conformation of biomacromolecules...An indispensible source of information.'' --- Nahrung, 42(2), 1998 Renowned experts present the first state-of-the-art description of circular dichroism spectroscopy (CD). Chapters present in-depth discussions of the history of the field, the theory of CD for application to globular proteins, membrane proteins, peptides, nucleic acids and their interactions, carbohydrates, and instrumentation. Discussions also feature new techniques using synchrotron radiation, vibrational Raman optical activity, and vibrational CD. More than 250 illustrations supplement the text.
The time seems ripe for a critical compendium of that segment of the biological universe we call viruses. Virology, as a science, having passed only recently through its descriptive phase of naming and num bering, has probably reached that stage at which relatively few new truly new-viruses will be discovered. Triggered by the intellectual probes and techniques of molecular biology, genetics, biochemical cytology, and high resolution microscopy and spectroscopy, the field has experienced a genuine information explosion. Few serious attempts have been made to chronicle these events. This comprehensive series, which will comprise some 6000 pages in a total of about 18 volumes, represents a commitment by a large group of active investigators to analyze, digest, and expostulate on the great mass of data relating to viruses, much of which is now amorphous and disjointed, and scattered throughout a wide literature. In this way, we hope to place the entire field in perspective, and to develop an invalua ble reference and sourcebook for researchers and students at all levels. This series is designed as a continuum that can be entered anywhere, but which also provides a logical progression of developing facts and integrated concepts.
This book is a collection of data on the tenacity in the environment of bacteria and some rickettsiae important in medicine and veterinary medicine. These data are of fundamental importance to physicians, veterinarians, epidemiologists and others when, in their practices, they are confronted with epidemics of contagious diseases or outbreaks of foodborne illnesses. At such times prompt answers are often needed to limit the problem, and thus to protect the public's health. Since data needed for such a purpose are widely distributed in the internatio nal scientific literature, the occasional desperate literature search is likely to miss some of the information that is available. This book seeks to fill that void. It lies in the nature of a compilation such as this is that it can never be totally complete. The compilation requires continual up-dating to include new information, and some currently acceptable information may have to be corrected as new data become available. However, most of the information in this compilation will never be out-of-date. The authors are always thankful for suggestions from others. Collection of the data in this book resulted from, first, several decades of studying the literature, and, second, literature searches made by the Institut fUr Dokumentationswesen in Frankfurt a. M. , the Biomedi zinische Datenbank of Hoechst A. G.
'Comprehensive virology 12' deals with several special groups of viruses showing properties that set them apart from the main virus families. The book comprises 5 chapters, all written by specialists, in which respectively 5 groups of viruses are discussed: in the 1st chapter, the viruses of invertebrates; chapter 2, the viruses of fungi; chapter 3, the cyanophages and viruses of eukaryotic algae; chapter 4, the viruses of fungi capable of replication in bacteria; and chapter 5, a view on lipid-containing bacteriophages. Each chapter has an impressive number of references. An index concludes this 12th volume in a series of 15.
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.
During the past five years my co-workers and I have been making a concerted effort to control the occasional sporadic operating room infection occurring in a case of otherwise clean operation. About 90 per cent of the infections have been caused by Staphylococcus aureus, usually of the hemolytic type. Occasionally there has been a mild infection with Staphylococcus albus and rarely a severe infection with Streptococcus haemolyticus.
Beginning with the cleansing of the skin of the patient, the operating room technic was checked throughout. This survey covered the skin of the operative field, the hands of the operating team, the linen used for draping, sponges, autoclaves, sterile water tanks, hot water sterilizers, oil sterilizers, brushes, instruments, gloves, plain and chromic catgut, needles, silk, scalpels and solutions and powder for the hands and gloves. Cultures of these were uniformly found to be sterile. Freshly laundered doctors', nurses' and orderlies' uniforms and
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.
If secondary infections could be avoided in hospital wards, both the patients and the hospital would be greatly benefited. Until a few years ago, these infections were thought to be carried either by the attendants' hands or by droplets coughed out by the patients. Such droplets travel only a few feet, and sufficient space between the beds would control this mode of spread. However, the work of W. F. Wells and M. W. Wells1 has shown that bacteria in very small particles, or "nuclei," can remain suspended in the air for two or three days, and this strongly suggests that air-borne bacteria may play a part in the spread of disease in the wards.That ultraviolet lamps can be used to kill air-borne bacteria has been demonstrated by several investigators. For example, Hart2 reported that when he operated under a battery of eight tubular ultraviolet lamps, the wounds
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.
This paper supplements reviews of the literature and outlines the development of the technique with particular reference to the disinfection of water supplies. Fundamental principles are discussed and details are given of two small installations.
Full-scale ultraviolet (UV) light and chlorine disinfection systems were operated in parallel using nitrified and partially denitrified tertiary treated wastewater effluent. A UV dose of 75 mW · s/cm2 reduced the concentration of fecal coliforms, enterococci, fecal
streptococci, MS2 bacteriophage, and poliovirus by four logs. A higher dose was needed to reduce the concentration of heterotrophic plate count (HPC) by four logs and to achieve a total coliform value ≤2.2 MPN per 100 mL within a consecutive 7-day period as required by the most restrictive
California Wastewater Reclamation Criteria (CWRC). The cleaning frequency needed to maintain a minimum operational UV dose was assessed by constructing a lamp fouling curve describing reduction in UV intensity as a function of elapsed time since lamp cleaning. Substitution of UV light for
chlorine disinfection eliminated formation of trihalomethanes, reduced formation of aldehydes, and formed a mid-polarity unidentified peak at a bench-scale dose of 2 800 mW·s/cm2 The unidentified UV peak was not detected at a full-scale dose of 188 mW·s/cm2.
No chronic toxicity was observed for the full-scale UV irradiated effluent; a decline in the reproductive rate of Ceriodaphnia dubia was observed for the full-scale chlorinated effluent.
The responses of three species of coliform bacteria (Citrobacter diversus, Citrobacter freundii and Klebsiella pneumoniae) and the bacteriophage (virus) phi X-174 to three wavelengths of UV light (254, 280 and 301 nm) were measured. The values of germicidal efficiency at 280 nm determined for each of the microorganisms were not significantly different. At 301 nm, the values of germicidal efficiency were significantly different, but ail values were too small (< 0.06) to warrant consideration in the modeling of the germicidal intensity delivered by a medium pressure UV system. The data from this study provide some evidence that the values of germicidal efficiency determined for one species of bacteria or virus may be used to represent the relative responses of all bacteria and viruses to medium pressure UV irradiation.
THE purpose of this communication is to describe an investigation of the action of ultra-violet light in destroying micro-organisms. It is hoped to be able to show (1) that ultra-violet light is capable under ordinary conditions of producing hydrogen peroxide; (2) that the destruction of micro-organisms by ultra-violet light is due and is directly proportional to the production of this substance; (3) that the relative susceptibility of different micro-organisms to ultra-violet light is of the same order as their relative susceptibility to hydrogen peroxide as tested in vitro. Further, it is proposed to draw some conclusions as to the mode of action of the fluorescent antiseptics. Evidence by Chemical Tests of the Production of Hydrogen Peroxide by Ultra-Violet Light. There is really no reliable specific test for hydrogen peroxide in minute quantities. The starch-iodide and titaniuim sulphate colour reactions can both be obtained, but are both non-specific and unreliable. The following results were obtained using a water-cooled Kromayer (Quartzlampe Wechselsform), which will hereafter be designated as " the lamp ": Starch-iodide solution in watch-glass-blue colour produced in 4 minutes. Titanium sulphate solution in watch-glass-yellow colour produced in 20 minutes. In each case the lamp was 4 in. from the solution.
A comparative study of the effects of ultraviolet radiation on three Bacillus subtilis phages is presented. Phages φ29, SPP1 and SPO2c12 or their DNAs were irradiated by UVC (254 nm) and quantum yields for inactivation were calculated. For each phage, the purified DNA was found to be more sensitive than the intact virus when assayed in a uvr+ host. The data imply that this is because transfecting DNA is repaired less efficiently than DNA of the intact phage; rather than because of differences in sensitivity to lesion production. Even though φ29 has the smallest target size of the three phages, φ29 and its DNA are the most sensitive. Phages SPO2 and SPP1 code for gene products which complement the repair system of the host. The transfecting DNA of phage SPP1 is extremely sensitive to UV damage when assayed in a uvr− host. This is attributed to the fact that in transfection SPP1 DNA must undergo recombination for productive infection to occur. The recombination process strongly interferes with the repair damaged DNA.
Ultraviolet; UV; UVC; UVGI; HVAC; ductwork; mold; fungus; effectiveness; microbial; dose; irradiance; reflectance; bacillis; aspergillis
This article shows that multiple disinfectants can effectively protect public health and meet emerging US Environmental Protection Agency requirements. The authors demonstrate that adenovirus inactivation can be effectively achieved with the combination of ultraviolet (UV), free chlorine (Cl 2), and conversion to chloramines. Sequential addition of Cl 2 and conversion to chloramines are far more effective than the use of preformed chloramines at achieving adenovirus inactivation. This research was undertaken to show that UV disinfection at typical doses of 40 mJ/cm 2 followed by the sequential addition of chlorine to water containing ammonia ultimately resulting in chloramines could effectively achieve a 4-log adenovirus inactivation. This method will enable water utilities that have difficulty maintaining a free Cl 2 residual to meet the new Long Term 2 Enhanced Surface Water Treatment Rule requirements using UV-Cl 2 chloramines. - LH.
In this paper the possibility of UV-reactor validation based on computational fluid dynamics will be discussed and related to biodosimetry and actinometry. Microbial inactivation depends on the UV-C dose that is described as UV intensity multiplied by exposure time. As a microbe enters a chamber containing UV lamps, it will receive varying irradiance levels from lamps depending on its distance from the lamp and the exposure time will depend on the specific path of the microbe through the reactor. It is necessary for UV-C dose calculation to determine the exposure time of a particular particle (microbe) and the UV intensity as function of position in the irradiation chamber based on the assumed UV-C power emission of the lamp. We can determine UV-C dose of a particular particle as function of position using the powerful software (3D Intensity calculation) supported by computational fluid dynamics. In order to calibrate CFD model, biodosimetric tests with the Bacillus subtillis spore were carried out in the four different reactors, each reactor equipped with 3, 4, 6 and 8 lumps respectively. It was founded that CFD model for UV reactor validation was in excellent agreement with the biodosimetric results. The actinometric tests with free chlorine were also undertaken to verify its possibility as alternative to the biodosimetry and the obtained results showed that the actinometry with free chlorine was a useful tool for determination of the average UV intensity in UV reactor.
It is abundantly evinced by experiments that direct insolation in some way leads to the destruction of spores of Bacillus anthracis , and in so far the results merely confirm what had already been discovered by Downes and Blunt in 1877 and 1878. From the fact that an apparent retardation of the development of the colonies on plates exposed to light was observed several times under circumstances which suggested a direct inhibitory action of even ordinary day-light, the author went further into this particular question with results as startling as they are important, for if the explanation given of the phenomena observed in the following experiments turns out to be the correct one, we stand face to face with the fact that by far the most potent factor in the purification of the air and rivers of bacteria is the sun-light.