Chemical apparatus and process disinfecting – deodorizing – preser – Process disinfecting – preserving – deodorizing – or sterilizing – Using direct contact with electrical or electromagnetic...
Reexamination Certificate
2000-07-31
2002-09-10
Thornton, Krisanne (Department: 1744)
Chemical apparatus and process disinfecting, deodorizing, preser
Process disinfecting, preserving, deodorizing, or sterilizing
Using direct contact with electrical or electromagnetic...
C250S458100, C210S748080
Reexamination Certificate
active
06447720
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates generally to a system and method for ultraviolet disinfection and, more particularly, to a system and method for ultraviolet disinfection of fluids.
(2) Description of the Prior Art
It is well known in the art to use ultraviolet light (UV) for the disinfection treatment of water. Ultraviolet light, at the germicidal wavelength of 253.7 nanometers, alters the genetic (DNA) material in cells so that bacteria, viruses, molds, algae and other microorganisms can no longer reproduce. The microorganisms are considered dead, and the risk of disease from them is eliminated. As the water flows past the UV lamps in UV disinfection systems, the microorganisms are exposed to a lethal dose of UV energy. UV dose is measured as the product of UV light intensity times the exposure time within the UV lamp array. Microbiologists have determined the effective dose of UV energy to be approximately about 34,000 microwatt-seconds/cm2 needed to destroy pathogens as well as indicator organisms found in wastewater. Typical prior art disinfection systems and devices emit UV light at approximately 254 nm, which penetrates the outer cell membrane of microorganisms, passes through the cell body, reaches the DNA and alters the genetic material of the microorganism, destroying it without chemicals by rendering it unable to reproduce.
Ultraviolet light is classified into three wavelength ranges: UV-C, from 200 nanometers (nm) to 280 nm; UV-B, from 280 nm to 315 nm; and UV-A, from 315 nm to 400 nm. Generally, UV light, and in particular, UV-C light is “germicidal,” i.e., it deactivates the DNA of bacteria, viruses and other pathogens and thus destroys their ability to multiply and cause disease, effectively resulting in sterilization of the microorganisms. Specifically, UV “C” light causes damage to the nucleic acid of microorganisms by forming covalent bonds between certain adjacent bases in the DNA. The formation of these bonds prevents the DNA from being “unzipped” for replication, and the organism is unable to reproduce. In fact, when the organism tries to replicate, it dies. UV light with a wavelength of approximately between about 250 to about 260 nm provides the highest germicidal effectiveness. While susceptibility to UV light varies, exposure to UV energy for about 20 milliwatt-seconds/cm
2
is adequate to deactivate 99 percent of the pathogens. Exposure to pathogens does not always cause disease, whether drinking contaminated water could produce disease depends on ingested and the health (nutritional and immunological) status of the person drinking the water. After studying certain variables, including the species and number of pathogens, the World Health Organization (WHO) has determined a standard of performance that must be met by acceptable water disinfection systems. The standard requires that an acceptable water disinfection system must be able to process contaminated water with 100,000 CFUs (colony forming units) of
e
-
coli
per 100 ml of water and produce outlet water with less than one CFU per 100 ml.
Generally, UV disinfection is a safe and reliable means for disinfecting drinking water for daily use, particularly given its relatively rapid, inexpensive, non-taste and odorless resultant treated water. UV light is a World Health Organization-approved method of disinfecting drinking water (Guidelines for Drinking Water Quality, vol. 1, World Health Organization, Geneva, Switzerland, 1993, p. 135). However, UV disinfection is not generally recommended for long-term storage of water.
Ultraviolet light has a proven track record of killing bacteria and viruses found in municipal wastewater. In addition, environmental concerns over the use of chemical disinfectants, coupled with improvements in ultraviolet-lighting technology, have led to the development of UV systems that treat spent metalworking fluids in the industrialized world; disinfect drinking water in developing countries; and clean aquaculture water, ballast water, and hospital air everywhere. Typically, chlorine gas or liquid is injected by a high-speed inductor directly into wastewater to kill bacteria before the water is discharged. According to industry experts, the main advantage of using UV instead of standard disinfection techniques is elimination of the transport and use of chlorine possible with the UV light-based system.
Used properly, ultraviolet light effectively destroys bacteria, viruses and other microorganisms in water and wastewater, without using chemicals. By doing away with chemical treatment, many other problems are also eliminated. There is no longer any need to worry about operator safety or the requirement for buildings for storage and handling of dangerous solutions and gases. Costly liability insurance premiums are significantly reduced. Testing of effluent for chlorine residual is no longer necessary, and toxicity problems associated with chlorine use are eliminated. Another factor leading municipalities to reconsider chlorination is its increased cost due to the national Uniform Fire Code adopted in 1993, which specifies expensive requirements for double containment of stored chlorine and chemical scrubbers in case of leaks.
Prior art applications of UV light used for disinfection of water include private drinking water supplies, municipal drinking water treatment plants, industrial product and process waters, and commercial applications, and wastewater treatment in primary, secondary, and tertiary treatment process for industrial, commercial and municipal wastewater treatment applications.
While UV purification is well suited for many residential, commercial, industrial and municipal water and wastewater treatment applications, considerations of the water quality and about the desired or required effluent purity impact the system design and performance. Prior art UV disinfectant systems work best when the water temperature is between about 35 and about 110 degrees Fahrenheit, since extreme cold or heat will interfere with the UV system performance.
The UV light source used in prior art are typically low pressure mercury lamps, which can effectively clean water of dangerous and illness-causing viruses and bacteria, including intestinal protozoa such as Cryptosporidium, Giardia, and
E.coli,
provided that the proper number and configuration of lamps are included in the system. All known prior art systems calculate, design and configure the proper number and arrangement or positioning of lamps as set forth and described by formulas developed and published by Dr. George Tchobanoglous, presently of University of California at Davis.
Dr. George Tchobanoglous, professor emeritus of civil and environmental engineering at the University of California, Davis and former chairperson on a committee of academic, industrial, and environmental consultants who drafted guidelines on UV disinfection for California in 1994, is perhaps the leading authority on UV water disinfectant systems and methods used in the prior art. His formulas for predicting the minimum required number of UV lamps and configuration of same are based on a key component of positioning the UV lamps within the water to be treated, and more particularly, requiring a lamp centerline-to-centerline distance of not more than three (3) inches to ensure effective disinfectant UV dosage for any influent system and flow rate; these formulas referred to as “point source summation”.
Traditional low-pressure UV systems found in the prior art are used for low flow water disinfection or smaller projects with air and surface applications. The low pressure UV lamp treats between 10 and 180 gallons per minute of fluid using up to 12 lamps at a time. As flows increase or higher UV doses are required, the multiple low-pressure lamp concept becomes complex and cumbersome. The medium pressure UV lamp offers a solution to maintain simplicity and cost effectiveness in meeting the higher flow and higher dose challenge. A single medium pressure UV lamp can treat up to 2,300 gallons per minute o
Garrett Kurt Anthony
Hauck James Pierre
Horton, III Isaac B.
Mathis Ronald Floyd
Riser Andrew P.
Glasgow Law Firm PLLC
Remotelight, Inc.
Thornton Krisanne
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