Chemical apparatus and process disinfecting – deodorizing – preser – Process disinfecting – preserving – deodorizing – or sterilizing – Using direct contact with electrical or electromagnetic...
Reexamination Certificate
2000-11-28
2002-06-11
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
06403030
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 waste-containing fluids.
(2) Description of the Prior Art
Mechanism of Action
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 about 200 nanometers (nm) to about 280 nm; UV-B, from about 280 nm to about 315 nm; and UV-A, from about 315 nm to about 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 produce molecules essential for life process, nor is it able to reproduce. In fact, when an organism is unable to produce these essential molecules or is unable 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.
Prior Art
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 teclnology, 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.
Unfortunately, evidence is mounting that organic chemical by products of chemical disinfection, especially byproduct of chlorination such as dioxane, are carcinogens and/or toxins for humans. Therefore, chemical disinfection is not a viable alternative when chemical purity of the fluid is desired and/or required. Additionally, in spite of this toxicological evidence, the EPA has recently been forced to relax restrictions on certain known carcinogenic chlorination by-product, such as chloroform. Additionally, other chemicals, such as the nitrate ion, have been shown to negatively influence the development of children.
In light of the emerging, data concerning the toxicity of organic and inorganic chemicals and the relaxation of water purity regulations, reducing the discharge into the environment of these compounds is of growing concern. However, removal of these compounds requires the use of extremely expensive methods, such as filtration through activated charcoal or similar. Thus, there exists a need for a system that can easily remove or eliminate organic and inorganic compounds from wastewater.
Used properly, ultraviolet light effectively destroys bacteria, viruses and other microorganisms in water and wastewater, without using chemicals. By doing away with 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 arc 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 med
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Thornton Krisanne
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