Liquid purification or separation – Filter – Material
Reexamination Certificate
2000-07-31
2003-05-20
Fortuna, Ana (Department: 1723)
Liquid purification or separation
Filter
Material
C210S500370, C210S490000, C210S321770, C210S321860, C210S263000, C210S502100, C210S508000, C210S644000
Reexamination Certificate
active
06565749
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to filters for removing microorganisms from liquid, methods for removing microorganisms from liquid, and methods for manufacturing filters. In particular, the invention relates to filter technology for the removal of bacteria and viruses from drinking water under conditions encountered in faucet mounted filters and pour through filters.
BACKGROUND OF THE INVENTION
Many filter designs are available for removing contaminants from drinking water. Exemplary designs are described by U.S. Pat. Nos. 5,709,794 to Emmons, et al.; 5,536,394 to Lund, et al.; 5,525,214 to Hembree; 5,106,500 to Hembree, et al.; and 5,268,093 to Hembree, et al. which were originally assigned to Recovery Engineering, Inc.
Several filter designs utilizing membrane technology have been proposed for removing submicron size microorganisms. For example, U.S. Pat. No. 5,017,292 to DiLeo, et al. describes a composite membrane including a porous membrane substrate, a surface skin having ultrafiltration separation properties, and an intermediate porous zone having an average pore size smaller than that of the substrate.
Chemical forces can be used to adhere microbials to solid surfaces. See Bitton and Marshall, “Adsorption of Micro organisms to Surfaces,” John Wiley & Sons, New York, pages 1-57 and by Gerba C.P., “Applied and Theoretical Aspects of Virus Adsorption to Surfaces,” Adv. Appl. Microbiol., vol. 30, pages 133-168 (1984). According to their discussion, charge interaction can be considered a major cause of interaction between virus and adsorbent surfaces. Most viruses have coats composed of protein polypeptides containing amino acids such as glutamic acid, aspartic acid, histidine and tyrosine. These amino acids contain carboxyl and amino groups which, upon ionization, give the viral capsid an electrical charge.
Based on the theory of charge interaction as means of removing micro organisms from the water, positively charged ion exchange resins have been utilized for bacteria adsorption by Daniels, “Developments In Industrial Microbiology”, Vol. 13; Proceedings of the twenty-eighth General Meeting of the Society for Industrial Microbiology, pages 211-243 (1972). The fundamental framework of these ion exchange resins is an elastic three dimensional hydrocarbon network comprising ionizable groups, either cationic or anionic, chemically bonded to the backbone of a hydrocarbon framework. The network is normally fixed, insoluble in common solvents and chemically inert. The ionizable functional groups attached to the matrix carry active ions with counter-ions which can be exchanged by the other counter-ions existed in water. Typical examples of commercially available ion exchange resins are the poly styrene cross-linked with divinyl benzene (DVB), and the methacrylate copolymerized with DVB. In the case of polystyrene, a three dimensional network is formed first, and the functional groups are then introduced into benzene rings through chloromethylation. Since those ionizable groups are highly hydrophilic, the more the existence of those groups in resin structure, the more the resin will swell to restrict the flow of water. The resistance to flow exhibited by these resins in controlled by the degree of cross-linking usually in the range of 2 to 12% as discussed by K. Dorfner, “Ion Exchangers” Ann Arbor Science Publishers, Inc., pages 16-35, New York (1962). With a low degree of cross-linking, the hydrocarbon network is more easily stretched, the swelling is large, and the resin exchanges small ions rapidly and even permits relatively large ions to undergo exchange. Conversely, as the cross-linking is increased to make the structure more rigid for high liquid flow, the hydrocarbon matrix is less resilient, the pores in the resin network are narrowed, the exchange process is slower, and the exchanger resin increases its tendency to exclude large ions from entering the structure. The ion exchange resins made by cross-linking the functional group carrying polymers have been successfully applied for the removal of both organic and inorganic ions in Angstrom size range but they are normally unsuitable for the relatively large sized micro-organisms. Also, the matrix swells and the flow resistance increases due to the pore narrowing.
U.S. Pat. No. 4,361,486 to Hou, et al., describes a filter which can be used for removing soluble iron and manganese from an aqueous fluid, and for removing and inactivating microorganisms from fluids. The filter includes an amount of particulate including magnesium peroxide or calcium peroxide immobilized on a substantially inert porous matrix. The filter media can be provided with an electropositive potential by modifying the surface of the particulate or inert porous matrix with a surface modifying agent. Hou, et al., “Capture of Latex Beads, Bacteria, Endotoxin, and Viruses by Charge-Modified Filters,” Appl. Environ. Microbiol., vol. 40, no. 5, pages 892-896, November 1980, reports the use of electropositive filters in removing microorganisms and other negatively charged particles from water. Charge modified filters are disclosed by U.S. Pat. Nos. 4,305,782 and 4,473,474 Ostreicher, et al.
U.S. Pat. No. 4,352,884 to Nakashima, et al. discloses a carrier for bioactive materials comprised of a substrate coated with a copolymer. The substrate may be one of various materials, including inorganic nature such as glass, activated carbon, silica, and alumina as well as organic polymers such as polystyrene, polyethylene, polyvinyl chloride, nylon, polyester, polymethyl methacrylate, and naturally occurring high polymers such as cellulose. The copolymer can be an acrylate or methacrylate monomer and a copolymerizable unsaturated carboxylic acid or unsaturated amine.
U.S. Pat. No. 3,898,188 to Rembawn, et al. and U.S. Pat. No. 3,784,649 to Buckman, et al. describe the polymerization of a dihalide and a ditertiary amine to form poly-quaternary ammonium resin. These polymers have found utility as flocculants in the clarification of water supplies. The materials are also known to exhibit germicidal action or as an effective bactericidal and fungicidal agents.
Preston, D. R., et al., “Removal of Viruses from Tapwater by Fiberglass Filters Modified with a Combination of Cationic Polymers,” Wat. Sci. Tech. Vol. 21, No. 3, pp 93-98 (1989) describes the development of an electropositive filter capable of adsorbing enteroviruses from water at pH 5 to 9. This article reports that electronegative fiberglass filters can be converted to electropositive filters by soaking the filters in an aqueous solution of a cationic polymer and allowing the treated filters to air dry. The cationic polymers polyethylenimine and Nalco cationic polymer 7111 can be used to produce a filter which can recover enteroviruses from environmental waters.
Faucet-mounted drinking water filters are described by U.S. Pat. No. 5,525,214. In general, faucet-mounted drinking filters include a filtration media for removing chemical and mineral contaminants as well as larger microorganisms. Common filter media include carbon, which is often in the form of a porous block. Additional contaminants, such as lead, can be removed with the addition of selective adsorbents. In addition, the filtration media commonly used in faucet-mounted drinking water filters have been combined with microfilters for the removal of small microorganisms and particles. The microfiltration is usually accomplished as a result of the fine porosity of the carbon block, or with the use of a second filter, including a hollow fiber membrane material.
SUMMARY OF THE INVENTION
A filter for removing microorganisms from a liquid is provided by the invention. The filter includes a microorganism filtration media including a substrate having a reactive surface and a polymer covalently bonded to the reactive surface of the substrate. The polymer includes a plurality of cationic groups for attracting microorganisms in a liquid. The filtration media exhibits an MS-2 virus removal coefficient in water of greater than 10 ml/g-sec.
The polymer whi
Bretl Donald S.
Hembree Richard D.
Hou Kenneth C.
Alexander Richard L.
Fortuna Ana
Roof Carl J.
The Procter & Gamble & Company
Vago James C.
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