Chemical apparatus and process disinfecting – deodorizing – preser – Process disinfecting – preserving – deodorizing – or sterilizing – Using direct contact with electrical or electromagnetic...
Reexamination Certificate
2001-11-02
2004-05-04
Thornton, Krisanne (Department: 1744)
Chemical apparatus and process disinfecting, deodorizing, preser
Process disinfecting, preserving, deodorizing, or sterilizing
Using direct contact with electrical or electromagnetic...
C250S455110, C422S022000, C422S120000, C422S121000, C422S186300
Reexamination Certificate
active
06730265
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 air and other gases.
(2) Description of the Prior Art
It is well known in the art to use ultraviolet light (UV) for the disinfection treatment of air. 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 air 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 read correctly, and the organism is neither able 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 to about 34 milliwatt-seconds/cm
2
is adequate to deactivate approximately 99 percent of the pathogens.
Additionally, UV light can catalyze a variety of other chemical reactions, and the use of UV light with any one or combination of the plethora of available chemical catalyst generates numerous possible catalytic combinations that can be used to degrade organic particulate matter. A class of these photocatalyst, termed UV-activated dielectric semiconductors, includes Titanium Oxide; TiO2 (photo activation wavelength; not more than 388 nm), Tungsten Oxide; WO2 (photo activation wavelength; not more than 388 nm), Zinc Oxide; ZnO (photo activation wavelength; not more than 388 nm), Zinc Sulfide; ZnS (photo activation wavelength; not more than 344 nm) and Tin Oxide; SnO2 (photo activation wavelength; not more than 326 nm). In addition to these catalysts, other catalysts, such as PtTiO
2
, are known.
In prior art air purification systems, particles, including, for example, household and atmospheric dust, lint, animal dander, food particles, tobacco smoke, aerosols, pollen, plant spores, and the like are removed from the air stream by filtration, trapping, electrostatic precipitation, and other means of arrest. Chemical compounds are removed by activated charcoal filtration. Additionally, particle and chemical compounds can be degraded by UV irradiation, or by oxidation by photocatalysts such as TiO
2
.
While such conventional air cleaners are quite effective in arresting dust and other particles, if the filters or plates are not cleaned regularly to remove the deposited particles, there may be potential for microbial growth on the particles on the filters or collector plates. If microbial growth is present and is not removed through regular thorough cleaning, there is the possibility that bioaerosols such as fungal spores, bacteria and other allergens may be re-entrained into the air stream and circulated back into the occupied enclosure.
Several prior art inventions have used UV irradiation of the particle-arresting apparatus or the gas stream itself to sterilize resident microorganisms. These inventions, as described in U.S. Pat. No. 5,997,619, Dec. 7, 1999; Knuth, et al.; U.S. Pat. No. 5,925,320; Jul. 20, 1999; Jones; U.S. Pat. No. 5,833,740; Nov. 10, 1998; Brais; U.S. Pat. No. 6,053,968; Apr. 25, 2000; Miller. Although these prior art may have been adequate in arresting particulate matter and chemical compounds and inactivating microorganisms, they could not degrade them and thus needed frequent periodic maintenance to clean or replace the arresting devices.
It has now been found possible to degrade the particulate matter and other compounds by incorporating TiO2 or other photocatalyst in the arresting device and irradiating the TiO2 with UV light. The TiO2 catalyzes the breakdown of chemical molecules, both in arrested particles and in the vicinity of the arresting device. For example, U.S. Pat. Nos. 5,933,702; 5,919,422; and 5,835,840 use filters or supports charged or impregnated with TiO2, and by fitting these filters into ventilation systems in which they are also irradiated by a source of ultraviolet rays when they are not themselves exposed to a natural source of UV. Additionally, filters comprised of TiO2 may also be treated with undecylenic derivatives to aid in the decomposition of compounds. For example, Caupin et al. (U.S. Pat. No. 6,071,472) teach that the functioning of filters comprised of TiO2 and undecylenic derivatives proves to be surprisingly effective from the point of view of air quality and, in parallel, a very substantial increase in the lifetime of the filter is observed, the gradual soiling of which appears to be due essentially only to the retention of inorganic particles. However, this and the other prior art require a UV light source devoted to the device, and in no way teach that the UV light may be supplied by a fiber optic transmission line or similar using optical components to focus and control the light input.
U.S. Pat. No. 6,051,194 generally relates to a fixed bed photocatalytic reactor system that employs optical fibers as a means of remote light transmission to and support for a photocatalyst coating. The reactor enables batch treatment or continuous flow applications, e.g., for the destruction of gas or aqueous phase waste effluents contaminated with hydrocarbons or heavy metals. The reactor utilizes one or more optical fibers or rods stiffened or under tension to form non-flexible rod-like components that are positionally secured with respect to a reactor vessel and are spaced apart with respect to each other at a miniscule distance, preferentially 1.5 mm. It is critical to have stiffened, tensioned, or rod-like fibers without flexibility in order to establish and maintain the spaced-apart configuration. The fibers have a non-catalytic portion and a catalytic portion, wherein the catalytic portion comprises a TiO.sub.2 photocatalyst coating on the exposed fibers. Photocatalytic reactions are carried out by using the noncatalytic portion of the fibers to transmit light, e.g., UV, from a light source to the catalytic portion. Because of the efficiency of the fibers in light delivery to the catalytic portion of the coating, the light source may be located a relatively long distance from the catalytic portion of the fibers.
Such a reactor is not particularly well-suited for microfiltration of gas streams, as a filter in this fashion would need to be woven from a single or few fibers. If a multitude of transmission lines were used, these would have to be connected
Glasgow Law Firm PLLC
Remote Light, Inc.
Thornton Krisanne
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