Time dose reciprocity in UV disinfection of water

1998 ◽  
Vol 38 (12) ◽  
pp. 145-150 ◽  
Author(s):  
R. Sommer ◽  
T. Haider ◽  
A. Cabaj ◽  
W. Pribil ◽  
M. Lhotsky
Keyword(s):  
Uv Irradiation ◽  
Uv Light ◽  
Water Disinfection ◽  
High Dose ◽  
E Coli ◽  
Dose Rates ◽  
Test Organisms ◽  
Irradiation Apparatus ◽  
Uv Dose ◽  
Time Dose

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.

scholarly journals Demonstration and evaluation of germicidal UV-LEDs for point-of-use water disinfection

2010 ◽  
Vol 8 (3) ◽  
pp. 479-486 ◽  
Author(s):  
Christie Chatterley ◽  
Karl Linden
Keyword(s):  
Uv Irradiation ◽  
Uv Light ◽  
Low Pressure ◽  
Water Disinfection ◽  
Light Emitting ◽  
E Coli ◽  
Point Of Use ◽  
One Year ◽  
Uv Lamps ◽  
Uv Leds

Ultraviolet (UV) irradiation is a common disinfection option for water treatment in the developed world. There are a few systems installed in developing countries for point-of-use treatment, but the low-pressure mercury lamps currently used as the UV irradiation source have a number of sustainability issues including a fragile envelope, a lifetime of approximately one year, and they contain mercury. UV light emitting diodes (LEDs) may offer solutions to many of the sustainability issues presented by current UV systems. LEDs are small, efficient, have long lifetimes, and do not contain mercury. Germicidal UV LEDs emitting at 265 nm were evaluated for inactivation of E. coli in water and compared to conventional low-pressure UV lamps. Both systems provided an equivalent level of treatment. A UV-LED prototype was developed and evaluated as a proof-of-concept of this technology for a point-of-use disinfection option, and the economics of UV-LEDs were evaluated.

Comparison of three laboratory devices for UV-inactivation of microorganisms

1995 ◽  
Vol 31 (5-6) ◽  
pp. 147-156 ◽  
Author(s):  
R. Sommer ◽  
A. Cabaj ◽  
D. Schoenen ◽  
J. Gebel ◽  
A. Kolch ◽  
...  
Keyword(s):  
Uv Irradiation ◽  
Uv Light ◽  
Collaborative Study ◽  
Test Organism ◽  
Dose Measurement ◽  
Technical Problems ◽  
Log Reduction ◽  
Freeze Dried ◽  
Test Organisms ◽  
Uv Dose

UV inactivation experiments of microorganisms have been performed and published by various workers for decades. Resulting data even of the same species of microorganisms may show important differences in UV-susceptibility. The reasons for these varying results could be found either in different biological conditions like culturing methods for preparing the test organisms or in technical problems regarding UV-irradiation equipment and dose measurement. Therefore three groups working on UV inactivation performed a collaborative study to find out which influences could be responsible for varying results in laboratory UV experiments. Each working group had developed a laboratory UV irradiation apparatus, which differed in technical construction and method for UV dose measurement. For our study we used as a test organism spores of Bacillus subtilis ATCC 6633 which were cultured in large quantity, freeze-dried and stored for all following experiments. Thereby we established controlled biological conditions. The first series of experiments in 1992 showed that differences in inactivation curves did occur, related especially to dose distribution in irradiation vessels, in irradiation geometry and in partial shadowing of UV light. Subsequently the irradiation procedure and methods for dose measurement were improved resulting in consistent, reproducible and comparable results. The equation of the regression curve was: log (N/N0) = −0.013 D + 0.18. A 2 log reduction would require a dose of 169 ± 11 J/m2, a 3 log reduction 241 ± 9 J/m2, respectively (level of significance: a = 0.05). In recent years bioassay methods have been suggested in order to evaluate UV-disinfection plants. Therefore it will be of increasing public health interest to ensure the quality of laboratory UV irradiation devices used for calibration of test-organisms for these bioassays.

Modeling of Escherichia coli Inactivation by UV Irradiation at Different pH Values in Apple Cider

2004 ◽  
Vol 67 (6) ◽  
pp. 1153-1156 ◽  
Author(s):  
A. QUINTERO-RAMOS ◽  
J. J. CHUREY ◽  
P. HARTMAN ◽  
J. BARNARD ◽  
R. W. WOROBO
Keyword(s):  
Escherichia Coli ◽  
Uv Irradiation ◽  
Uv Light ◽  
Reduction Factor ◽  
Attractive Alternative ◽  
Bacterial Populations ◽  
Apple Cider ◽  
E Coli ◽  
Log Reduction ◽  
Uv Dose

This study examined the effects and interactions of UV light dose (1,800 to 20,331 μJ/cm2) and apple cider pH (2.99 to 4.41) on the inactivation of Escherichia coli ATCC 25922, a surrogate for E. coli O157:H7. A predictive model was developed to relate the log reduction factor of E. coli ATCC 25922 to the UV dose. Bacterial populations for treated and untreated samples were enumerated with the use of nonselective media. The results revealed that UV dose was highly significant in the inactivation of E. coli, whereas pH showed no significant effect at higher UV doses. Doses of 6,500 μJ/cm2 or more were sufficient to achieve a greater than 5-log reduction of E. coli. Experimental inactivation data were fitted adequately by a logistic regression model. UV irradiation is an attractive alternative to conventional methods for reducing bacteria in unpasteurized apple cider.

Inactivation of recalcitrant protozoan oocysts and bacterial endospores in drinking water using high-intensity pulsed UV light irradiation

2012 ◽  
Vol 12 (4) ◽  
pp. 513-522 ◽  
Author(s):  
J. C. Hayes ◽  
M. Garvey ◽  
A. M. Fogarty ◽  
E. Clifford ◽  
N. J. Rowan
Keyword(s):  
High Intensity ◽  
Uv Light ◽  
Waste Water Treatment ◽  
Scale Up ◽  
Clear Trend ◽  
E Coli ◽  
Log Reduction ◽  
Bacterial Endospores ◽  
Pulsed Uv Light ◽  
Uv Dose

This constitutes the first study to compare the use of high-intensity pulsed UV light (PUV) irradiation for the novel destruction of harmful protozoan (Cryptosporidium parvum Iowa isolate) oocysts and bacterial (Clostridium perfringens ATCC 13124 and Bacillus cereus ATCC 11178) endospores in artificially-spiked water where these organisms are resistant to conventional chlorination. Experimental results revealed that all three test organisms in their dormant recalcitrant state required extended levels of pulsing to achieve significant reductions in numbers compared to other similarly PUV-treated Escherichia coli ATCC 25922 that is a non-spore forming indicator of faecal pollution in water. 120 pulses at 900 V or 16.2 J per pulse (equivalent to a UV dose of 8.39 μJ cm−2) were required to achieve ca. 2 log C. perfringens spore numbers, whereas a similar level of PUV irradiation reduced both C. parvum oocysts and B. cereus endospores by ca. 5 log orders. A comparative ca. 5 log reduction of E. coli cell numbers was achieved after only 25 pulses at 900 V (equivalent to a UV dose of 1.74 μJ cm−2). A clear trend emerged where the order of resistance to PUV-irradiation observed was C. perfringens endospores > C. parvum oocysts, B. cereus endospores > E. coli cells. This study suggests disinfection kinetic data for the more resistant C. perfringens endospores can be used as a measure of estimating disinfection efficacy of PUV treatments for C. parvum oocysts in water, avoiding the need to use complex animal or cell culture infectivity models that are only available in specialised laboratories with highly trained technicians. This study will inform future studies exploring scale-up of PUV at waste-water treatment plants.

scholarly journals Functional Properties of Borrelia burgdorferi recA

2004 ◽  
Vol 186 (8) ◽  
pp. 2275-2280 ◽  
Author(s):  
Dionysios Liveris ◽  
Vishwaroop Mulay ◽  
Ira Schwartz
Keyword(s):  
Gene Expression ◽  
Borrelia Burgdorferi ◽  
Uv Irradiation ◽  
Reca Protein ◽  
Primary Role ◽  
Rapid Loss ◽  
E Coli ◽  
Uv Dose ◽  
Null Mutants

ABSTRACT Functions of the Borrelia burgdorferi RecA protein were investigated in Escherichia coli recA null mutants. Complementation with B. burgdorferi recA increased survival of E. coli recA mutants by 3 orders of magnitude at a UV dose of 2,000 μJ/cm2. The viability at this UV dose was about 10% that provided by the homologous recA gene. Expression of B. burgdorferi recA resulted in survival of E. coli at levels of mitomycin C that were lethal to noncomplemented hosts. B. burgdorferi RecA was as effective as E. coli RecA in mediating homologous recombination in E. coli. Furthermore, E. coli λ phage lysogens complemented with B. burgdorferi recA produced phage even in the absence of UV irradiation. The level of phage induction was 55-fold higher than the level in cells complemented with the homologous recA gene, suggesting that B. burgdorferi RecA may possess an enhanced coprotease activity. This study indicates that B. burgdorferi RecA mediates the same functions in E. coli as the homologous E. coli protein mediates. However, the rapid loss of viability and the absence of induction in recA expression after UV irradiation in B. burgdorferi suggest that recA is not involved in the repair of UV-induced damage in B. burgdorferi. The primary role of RecA in B. burgdorferi is likely to be a role in some aspect of recombination.

UV disinfection of wastewater effluents for unrestricted irrigation

2006 ◽  
Vol 54 (3) ◽  
pp. 83-88 ◽  
Author(s):  
A.M. Nasser ◽  
H. Paulman ◽  
O. Sela ◽  
T. Ktaitzer ◽  
H. Cikurel ◽  
...  
Keyword(s):  
Uv Irradiation ◽  
Wastewater Reuse ◽  
High Rate ◽  
Uv Disinfection ◽  
Secondary Effluent ◽  
E Coli ◽  
Uv Dose ◽  
Inactivation Efficiency ◽  
Transmission Of Disease

Wastewater reuse in arid regions is important for the production of a water resource to be utilised for non-potable purposes and to prevent the environmental transmission of disease-causing agents. This study was conducted to evaluate the effect of water quality on the comparative disinfection efficiency of viruses, bacteria and spores by UV irradiation. Furthermore, the microbial quality of effluent produced by coagulation, high rate filtration (HRF) and either UV irradiation or chlorination was determined. Using low pressure collimated beam, a UV dose of 80 mWs/cm2 was needed to achieve a 3-log10 inactivation of either rotavirus SA-11 or coliphage MS2, whereas over 5-log10 inactivation of E. coli was reached with a dose of only 20 mWs/cm2. B. subtilis inactivation was found to be linear up to a dose of 40 mWs/cm2 and then a tailing up to a UV dose of 120 mWs/cm2 was observed. It is worth noting that effluent turbidity of <5 NTU did not influence the inactivation efficiency of UV irradiation. Operation of a pilot plant to treat secondary effluent by coagulation, HRF and UV disinfection at a UV dose of 80 mWs/cm2 resulted in the production of high quality effluent in compliance with the Israel standards for unrestricted irrigation (<10 CFU/100 mL faecal coliform and turbidity of <5 NTU). Sulphite reducing clostridia (SRC) were found to be more resistant than coliphages and F coliform for UV irradiation. The results of this study indicated that UV disinfection is suitable for the production of effluents for unrestricted irrigation of food crops.

The combined performance of UV light and chlorine during reclaimed water disinfection

2008 ◽  
Vol 57 (6) ◽  
pp. 935-940 ◽  
Author(s):  
M. Montemayor ◽  
A. Costan ◽  
F. Lucena ◽  
J. Jofre ◽  
J. Muñoz ◽  
...  
Keyword(s):  
Ultraviolet Light ◽  
Uv Light ◽  
Reclaimed Water ◽  
Microbiological Quality ◽  
Water Disinfection ◽  
Water Reclamation ◽  
E Coli ◽  
Combined Action ◽  
Water Reclamation Plants

The combined effects of disinfectant agents on the microbiological quality of reclaimed water produced by two full-scale water reclamation plants in Catalonia, Spain, were examined in this work. All the disinfectant treatments tested led to the absence, or near absence, of E. coli in 100 mL samples of water, with log reductions of more than 3 log u. Hypochlorite reduced the bacterial concentrations. However, ultraviolet light was more effective than hypochlorite at reducing the concentrations of bacteriophages, viruses and pathogenic protozoa such as Cryptosporidium spp. We conclude that a combination of these two disinfectant agents is effective in protecting public health, as each agent acts to a different degree against the different groups of microorganisms studied. Further studies should investigate the combined action of disinfectant agents at water reclamation plants with ultraviolet light equipment in more favourable working conditions in order to assess their capacity to inactivate microorganisms.

scholarly journals Comparison of indicator bacteria inactivation by the ultraviolet and the ultraviolet/hydrogen peroxide disinfection processes in humic waters

2011 ◽  
Vol 9 (4) ◽  
pp. 659-669 ◽  
Author(s):  
Arzu Teksoy ◽  
Ufuk Alkan ◽  
Sevil Çalışkan Eleren ◽  
Burcu Şengül Topaç ◽  
Fatma Olcay Topaç Şağban ◽  
...  
Keyword(s):  
Hydrogen Peroxide ◽  
Fulvic Acid ◽  
Uv Radiation ◽  
Surface Waters ◽  
Uv Light ◽  
Indicator Bacteria ◽  
E Coli ◽  
Bacteria Inactivation ◽  
Potential Indicator ◽  
Test Organisms

The aim of the present study was to evaluate responses of potential indicator bacteria (i.e. Escherichia coli, Pseudomonas aeruginosa, Bacillus subtilis) to the ultraviolet (UV) radiation and the UV/hydrogen peroxide (H2O2) disinfection processes of surface waters with different qualities in terms of humic content. The UV and the UV/H2O2 processes were applied to waters containing various concentrations of fulvic acid in order to inactivate E. coli, P. aeruginosa and B. subtilis spores. Three fulvic acid (0, 2 and 6 mg l−1) and four H2O2 (0, 10, 25 and 50 mg l−1) concentrations were used. Results showed that the k values of E. coli, P. aeruginosa and B. subtilis spores varied between 2.22 and 4.00, 1.73 and 3.58, and 1.40 and 1.86, respectively, in all test conditions. The sensitivity of the test organisms followed a decreasing order of E. coli > P. aeruginosa > B. subtilis. Results of the study indicated that the blocking effect of fulvic acid for the UV light was diminished by using H2O2 in combination with the UV radiation. Findings of the present study strongly suggested that the UV/H2O2 process was significantly effective on the inactivation of E. coli and P. aeruginosa in humic waters, whereas it induced little or no apparent contribution to the disinfection efficiency of B. subtilis spores.

scholarly journals Determination of Pyrimidine Dimers inEscherichia coli and Cryptosporidium parvum during UV Light Inactivation, Photoreactivation, and Dark Repair

2001 ◽  
Vol 67 (10) ◽  
pp. 4630-4637 ◽  
Author(s):  
Kumiko Oguma ◽  
Hiroyuki Katayama ◽  
Hiroshi Mitani ◽  
Shigemitsu Morita ◽  
Tsuyoshi Hirata ◽  
...  
Keyword(s):  
Uv Irradiation ◽  
Cryptosporidium Parvum ◽  
Genomic Dna ◽  
Uv Light ◽  
Fluorescent Light ◽  
Dark Repair ◽  
E Coli ◽  
Pyrimidine Dimers ◽  
Sensitive Site

ABSTRACT UV inactivation, photoreactivation, and dark repair ofEscherichia coli and Cryptosporidium parvum were investigated with the endonuclease sensitive site (ESS) assay, which can determine UV-induced pyrimidine dimers in the genomic DNA of microorganisms. In a 99.9% inactivation of E. coli, high correlation was observed between the dose of UV irradiation and the number of pyrimidine dimers induced in the DNA ofE. coli. The colony-forming ability of E. coli also correlated highly with the number of pyrimidine dimers in the DNA, indicating that the ESS assay is comparable to the method conventionally used to measure colony-forming ability. WhenE. coli were exposed to fluorescent light after a 99.9% inactivation by UV irradiation, UV-induced pyrimidine dimers in the DNA were continuously repaired and the colony-forming ability recovered gradually. When kept in darkness after the UV inactivation, however,E. coli showed neither repair of pyrimidine dimers nor recovery of colony-forming ability. When C. parvum were exposed to fluorescent light after UV inactivation, UV-induced pyrimidine dimers in the DNA were continuously repaired, while no recovery of animal infectivity was observed. When kept in darkness after UV inactivation, C. parvum also showed no recovery of infectivity in spite of the repair of pyrimidine dimers. It was suggested, therefore, that the infectivity of C. parvumwould not recover either by photoreactivation or by dark repair even after the repair of pyrimidine dimers in the genomic DNA.

scholarly journals Efficacy of UV Irradiation in Inactivating Cryptosporidiumparvum Oocysts

2002 ◽  
Vol 68 (11) ◽  
pp. 5387-5393 ◽  
Author(s):  
Shigemitsu Morita ◽  
Atsushi Namikoshi ◽  
Tsuyoshi Hirata ◽  
Kumiko Oguma ◽  
Hiroyuki Katayama ◽  
...  
Keyword(s):  
Uv Irradiation ◽  
Fold Increase ◽  
Fluorescent Light ◽  
High Dose ◽  
Dark Repair ◽  
Dose Requirement ◽  
Pyrimidine Dimers ◽  
Sensitive Site ◽  
Effects Of Temperature ◽  
Uv Dose

ABSTRACT To evaluate the effectiveness of UV irradiation in inactivating Cryptosporidium parvum oocysts, the animal infectivities and excystation abilities of oocysts that had been exposed to various UV doses were determined. Infectivity decreased exponentially as the UV dose increased, and the required dose for a 2-log10 reduction in infectivity (99% inactivation) was approximately 1.0 mWs/cm2 at 20°C. However, C. parvum oocysts exhibited high resistance to UV irradiation, requiring an extremely high dose of 230 mWs/cm2 for a 2-log10 reduction in excystation, which was used to assess viability. Moreover, the excystation ability exhibited only slight decreases at UV doses below 100 mWs/cm2. Thus, UV treatment resulted in oocysts that were able to excyst but not infect. The effects of temperature and UV intensity on the UV dose requirement were also studied. The results showed that for every 10°C reduction in water temperature, the increase in the UV irradiation dose required for a 2-log10 reduction in infectivity was only 7%, and for every 10-fold increase in intensity, the dose increase was only 8%. In addition, the potential of oocysts to recover infectivity and to repair UV-induced injury (pyrimidine dimers) in DNA by photoreactivation and dark repair was investigated. There was no recovery in infectivity following treatment by fluorescent-light irradiation or storage in darkness. In contrast, UV-induced pyrimidine dimers in the DNA were apparently repaired by both photoreactivation and dark repair, as determined by endonuclease-sensitive site assay. However, the recovery rate was different in each process. Given these results, the effects of UV irradiation on C. parvum oocysts as determined by animal infectivity can conclusively be considered irreversible.

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