Liquid purification or separation – Processes – Chemical treatment
Reexamination Certificate
2000-11-27
2002-10-29
Hoey, Betsey Morrison (Department: 1724)
Liquid purification or separation
Processes
Chemical treatment
C210S501000, C210S504000, C252S175000
Reexamination Certificate
active
06471876
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to filter media with germicidal properties. In particular, the present invention is directed to ceramic, polymeric and glass filter media to which is chemically grafted and bonded a polymerized salt of a polymerizable anionic monomer with a cationic germicide for use in water treatment.
BACKGROUND OF THE INVENTION
For close to a century, microorganism content, e.g., bacteria and viruses, in municipal water supplies has been controlled through the addition of oxidative chemicals such as chlorine. This has proven effective in control of most microorganisms and is readily simple to monitor. For example, a residual capable of being measured is carried throughout the municipal distribution system and periodically monitored to insure that the drinking water supply has been effectively treated. However, these systems are not always reliable or readily available to remote areas. Moreover, when an oxidizing agent is used at the source point, there can be contamination away from the source caused by pipeline problems that could allow the water to be unsafe at the time it arrives at the final point of use. In addition, there are also growing health concerns surrounding some of the compounds formed from the use of oxidative chemicals in the water supply.
To address contamination away from the source, a variety of devices or methods can be utilized to remove, destroy or deactivate microorganisms at the point of use. These include boiling the water, exposing the water to ultraviolet light, use of ozone, addition of chemicals and others. Most, if not all, of the methods used to remove, destroy and/or deactivate microorganisms include the need for external energy or the addition of chemicals to the water.
None of the known methods typically used to remove, destroy and/or deactivate microorganisms at the point of use can be used to remove sediment or turbidity from the source water. Typically, conventional filtration apparatuses are used in combination with a process or apparatus to destroy, deactivate and/or remove microorganisms. The filtration apparatuses are utilized primarily for removing particles in order to reduce turbidity. Examples of typical water filtration media include sand, garnet and anthracite.
In addition to bacteria and viruses present in the source, other microorganisms that can be harmful include protozoan cysts. Removal of harmful cysts is desired and is reflected in the EPA filtration requirements now mandated by the Surface Water Treatment Rule. Since some of these cysts are not destroyed and/or deactivated effectively by the typical chlorine dosages used in municipal application, filtration and the use of chemical coagulants are typically used. The chemical coagulants increase the size of the particles containing the cysts to a point at which they can be removed by conventional filtration. During coagulation, small particles are agglomerated into larger particles by adding the chemical coagulants to the source. Once agglomerates of a desired size are produced, the solution is passed through a filter to filter out the agglomerates.
However, chemical coagulation has several disadvantages. The mechanism for filtering the liquid is by physically straining particles from the feed solution which are larger than can pass through interstices between grains of the media. The media can only remove particles that are larger than the interstices. For example, sand filters can only remove particles greater than about 20 microns in size. Eventually, the particles held by the media seal off the interstices, reducing filtration efficiency. Moreover, chemical coagulation does not necessarily remove or deactivate all of the microorganisms present in the source water. Chemical coagulation is also disadvantageous in view of the cost of the chemicals, the need to regulate the amount of chemicals despite a continuously changing feed stream and in view of a low flow rate. Disposing of chemical sludge waste is another concern
Thus, there is a need for a method and apparatus that could simultaneously filter and disinfect a water supply without the need for external energy or addition of chemicals.
SUMMARY OF THE INVENTION
The present invention is directed to filtration media having germicidal properties for use in filtering particles and simultaneously destroying, removing and/or deactivating microorganisms from a feed liquid passing therethrough. The filtration media comprises ceramic, polymeric and/or glass particles wherein the particles have chemically grafted and covalently bonded thereto in a germicidal effective amount a polymerized salt of a polymerizable anionic monomer and a cationic germicide. The polymerizable anionic monomer and the cationic germicide are present in about a 1:1 molar ratio. The cationic germicide preferably has a minimum inhibitory concentration less than about 1000 ppm (parts per million) for at least one targeted microorganism. Preferably, the cationic germicide is selected from the group consisting of bisguanidines and quaternary ammonium compounds. More preferably, the cationic germicide is selected from the group consisting of zinc pyrithione and diiodomethyl-p-tolylsulfone. The polymerizable anionic monomer is selected from the group consisting of a vinyl and acrylic monomer that preferably includes a carboxyl group or a sulfonyl group. The salt of the polymerizable anionic monomer and the cationic germicide may be copolymerized with at least one polymerizable monomer copolymerizable therewith. The amount of said anionic monomer is from about 10 to about 20 percent of the amount of said at least one other polymerizable monomer.
Preparing the germicidal grafted filter media includes preparing a grafting solution by mixing to a uniform solution a cationic germicide, at least one anionic monomer, a catalyst for initiating polymerization and a graft initiator. Then, the grafting solution is contacted with the filtration media to form a mixture which is then filtered to obtain a filtrate. The filtrate is dried and then cured at an elevated temperature effective to chemically graft and covalently bond to a surface of the media in a germicidal effective amount a polymerized salt of the polymerizable anionic monomer and the cationic germicide. Optionally, at least one other polymerizable monomer co-polymerizable with the anionic monomer and the cationic germicide.
The germicidal filter media is effective for purifying water by flowing source water across the germicidal filter media whereby the filter media removes particles and is in an effective amount for destroying, removing and/or deactivating microorganisms in the water.
Other embodiments of the invention are contemplated to provide particular features and structural variants of the basic elements. The specific embodiments referred to as well as possible variations and the various features and advantages of the invention will become better understood when considered in connection with the detailed description that follows.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
The present invention is generally directed to filter media having antimicrobial properties. In particular, filter media is contacted with a grafting solution wherein a germicide-polymer is grafted onto a surface of the filter media. Advantageously, filters including at least one layer of the germicidal grafted filter media are effective for deactivating, destroying or removing microorganisms from a feed liquid such as water. The filtration media is preferably selected so that a wide range of particle sizes and specific gravities can be attained. Thus, the present invention can advantageously be used in a wide variety of filter applications including its use in single layer, multi layer, upflow or downflow filtration configurations. Moreover, depending on the choice of germicidal grafted onto the filter media, the filter media, in addition to filtering particles, can be tailored to effectively remove, deactivate or destroy targeted bacteria, viruses or cysts present in the source feed liqui
Dragnea Felicia
Hansen Christopher L.
Horowitz Carl
Mason Samuel
Sanduja Mohan L.
Hoey Betsey Morrison
Kinetico Incorporated
Watts, Hoffmann, Fisher & Heinke Co. LPA
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