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Patent: 6,565,803 issued May 20, 2003 and assigned
to Calgon Carbon Corporation: 1. A method for the prevention of infection from cryptosporidium oocysts found in drinking water comprising irradiating said water with continuous ultraviolet light having predominant wavelength bands that falls within about 200 nanometers to about 300 nanometers with a dose of from about 1 mJ/cm2 to about 175 mJ/cm2. 2. A method as set forth in claim 1 wherein said dose is from about 3.5 mJ/cm2 to about 175 mJ/cm2. 3. A method as set forth in claim 1 or 2 wherein said ultraviolet light substantially comprises a wavelength of about 254 nanometers. 4. A method as set forth in claim 1 or 2 wherein said ultraviolet light is produced by one of a low pressure mercury lamp or a medium pressure mercury lamp. 5. A method as set forth in claim 4 wherein said ultraviolet light is produced by a low pressure mercury lamp. 6. A method as set forth in claim 4 wherein said ultraviolet light is produced by a medium pressure mercury lamp. 7. A method for the prevention of replication of cryptosporidium oocysts or giardia cysts in drinking water treatment comprising irradiating said water with a continuous source of light having predominant wavelength bands that falls within about 200 nm to about 300 nm and a dose of from about 1 mJ/cm2 to about 175 mJ/cm2. 8. A method as set forth in claim 7 wherein said dose is from about 3.5 mJ/cm2 to about 175 mJ/cm2. 9. A method as set forth in claim 7 or 8 wherein said light substantially comprises a wavelength of about 254 nanometers. 10. A method as set forth in claim 7 or 8 wherein said light is produced by one of a low pressure lamp or a medium pressure lamp. 11. A method as set forth in claim 10 wherein said light is produced by a low pressure lamp. 12. A method as set forth in claim 10 wherein said light is produced by a medium pressure lamp. 13. A method of treating drinking water containing contaminants including cryptosporidium comprising exposing said water to a continuous broad band of ultraviolet radiation with a dose of about 1.0 mJ/cm2 to about 175 mJ/cm2, wherein said exposing step is the sole process for rendering cryptosporidium in said drinking water noninfectious. 14. A method as set forth in claim 13 wherein said dose is from about 3.5 mJ/cm2 to about 175 mJ/cm2. Summary of the invention: ”Generally it has been discovered that it is not necessary to "kill" pathogens, such as Cryptosporidium parvum or Giardia muris with ultraviolet light in order to prevent infection; one need only apply enough ultraviolet light to prevent the organism from "replicating". The method of the present invention prevents replication (cell mitosis) by inactivating the DNA to prevent infection. The UV doses required to prevent replication are orders of magnitude lower than required to "kill" the oocysts. This means that the cost of UV treatment to prevent infection by Cryptosporidium oocysts will be markedly lower. ”It has been found that when biological organisms are exposed to ultraviolet light (UV) in the range of 200-300 nm, the UV can be absorbed by DNA, RNA, and proteins. Absorption by proteins can lead to rupture of cell walls and death of the organism. Absorption by DNA or RNA (specifically by thymine bases) is known to cause inactivation of the DNA or RNA double helix strands through the formation of thymine dimers. If enough of these dimers are created in DNA, the DNA replication process is disrupted and hence, in mitosis, the cell cannot replicate. Cells that cannot replicate cannot infect. The present invention utilizes UV doses substantially lower (to achieve the state of hindered replication) by orders of magnitude than those required to cause oocyst death. ”The present invention preferably utilizes a broad band (200-300 nm) medium-pressure mercury UV lamp to achieve the disinfection. In another embodiment of the invention, a low-pressure mercury (essentially monochromatic) UV lamp can be used. The dose required with a medium-pressure lamp was measured to be 11 mJ/cm2 to achieve better than 5.9 log disinfection. From this it can be inferred that a dose of 7 mJ/cm2 will achieve better than 4 log disinfection (99.99%) and 3.6 mJ/cm2 will achieve better than 2 log disinfection (99%). For low pressure lamps a dose of 8 and 16 mJ/cm2 was required to achieve 4.1 and 4.3 log disinfection, respectively. Thus, the dose levels of UV are significantly lower than those used before resulting in significantly lower power levels needed to achieve the results. It has been found that inactivation of Cryptosporidium and similar organisms such as Giardia occurs at dosages from about 1 mJ/cm2. Accordingly, the method provides a substantial improvement in the cost effectiveness of UV for the disinfection of contaminated drinking water as regards to Cryptosporidium oocysts and Giardia cysts that may be present. Other advantages will become apparent from a perusal of the following detailed description of a presently preferred embodiment of the invention.”
1. A method for the prevention of cryptosporidium oocysts comprising irradiating water with a continuous broad band of ultraviolet light in doses of from about 10 mJ/cm2 to about 175 mJ/cm2. 2. A method as set forth in claim 1 wherein said broad band is a frequency of 200 to 300 nm using an UV lamp. 3. A method as set forth in claim 1 or 2 wherein said dose is about 20 mJ/cm2 to about 30 mJ/cm2. 4. A method as set forth in claim 1 wherein said broad band is a frequency of 200 to 300 nm using a medium pressure UV lamp. Summary of the invention: “Generally it has been discovered that it is not necessary to "kill" or "inactivate" pathogens, such as Cryptosporidium parvum or Giardia muris with ultraviolet light in order to prevent infection; one need only apply enough ultraviolet light to prevent the organism from "replicating". The method of the present invention prevents replication (cell mitosis) by cross-linking the DNA to prevent infection. The UV doses required to prevent replication are orders of magnitude lower than required to "kill" or "inactivate" the oocysts. This means that the cost of UV treatment to prevent infection by Cryptosporidium oocysts will be markedly lower. ”It has been found that when biological organisms are exposed to ultraviolet light (UV) in the range of 200-300 nm, the UV can be absorbed by DNA, RNA and proteins. Absorption by proteins can lead to rupture of cell walls and death of the organism. Absorption by DNA or RNA (specifically by thymine bases) is known to cause cross-linking of the DNA or RNA double helix strands through the formation of thymine dimers. If enough of these cross links are created in DNA, it cannot separate into two strands and hence in mitosis, the cell cannot replicate. Cells that cannot replicate cannot infect. The present invention utilizes UV doses substantially lower to achieve the state of hindered replication are much lower (by orders of magnitude) than those required to cause cell oocyst destruction. ”The present invention utilizes a broadband (200-300 nm) medium pressure UV lamp to achieve the prevention. Medium pressure UV lamps provide a continuous ultraviolet spectrum. Medium pressure mercury lamps contain mercury vapor pressure of about 1000 Hg when they are energized (low pressure mercury lamps contain mercury vapor pressure of about 0.001 to about 10 mm Hg when they are energized). A. M. Braun, M. T. Maurette, and E. Oliveros; Photochemical Technology; pp. 109-114; John Wiley & Sons; 1991. The dose required can be as low as 10 mJ/cm2. Doses over 30 mJ/cm2 provide more than 4.5 logs removal measured by mouse infectivity. Thus, the dose levels are significantly lower than used before resulting in significantly lower power levels needed to achieve the results. Accordingly, the method provides a substantial increase in the cost effectiveness of UV reduction in cryptosporidium oocysts infection in drinking water. Other advantages will become apparent from a perusal of the following detailed description of a presently preferred embodiment of the invention.” |
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