HK1089713B - Filter media with enhanced microbiological interception capability - Google Patents

Description

Filter media with improved microbiological interception capability

The present invention relates to a composite filter medium having a pH-changing material, in which microbial contaminants can be more effectively captured by using the composite filter medium or a filter system employing the composite filter medium.

Summary of The Invention

In a first aspect, the present invention is directed to a composite filter media comprising a positively charged media and a pH altering material, wherein the pH altering material alters the pH of the influent such that microbial contaminants present in the influent maintain a negative charge and the positively charged media maintain a positive charge and provide increased interception of the microbial contaminants. A pH altering material is employed to alter the pH of the influent to less than about 10.5, and more preferably from about 7 to about 9. Preferably, the pH altering material comprises an inorganic carbonate.

The positively charged medium may comprise a solid composite block, and the pH altering material is a flat sheet structure wrapped around the positively charged medium. The positively charged medium may also be mixed with a pH altering material and a binder and extruded to form a solid composite unit.

The pH altering material may comprise a flat plate structure located upstream of the positively charged medium. The pH changing material may be periodically regenerated. The composite filter media of the present invention may further comprise an adsorbent for removing charge-reducing contaminants from the positively charged media upstream.

In another aspect, the present invention relates to a composite filter media comprising: a charged medium capable of providing an enhanced microbiological contaminant interception capability; a pH-changing layer located upstream of the charged medium; and media for removing charge-reducing contaminants located upstream of the charged media. The charged medium can be mixed with an adhesive and fused to a substrate on which the charged layer is formed, wherein the charged layer and the pH changing layer are spirally wound such that the pH changing layer is exposed to the influent before the influent contacts the charged layer. The pH altering layer may also be fused to the second surface of the substrate.

In yet another aspect, the present invention relates to a composite filter media comprising: an active particle treated with a positively charged microbiological interception agent; a binder; a pH-altering material, wherein the active particles, binder, and pH-altering material are mixed and extruded into a solid composite unit; and a material for removing charge-reducing contaminants from upstream of the solid composite unit.

In yet another aspect, the present invention relates to a composite filter media comprising: an active particle treated with a positively charged microbiological interception agent; a binder; wherein the active particles and binder are mixed and extruded into a solid composite unit; and a pH-altering material having a flat sheet structure wound around the solid composite unit; and a material for removing charge-reducing contaminants from upstream of the solid composite unit. The material for removing the charge-reducing contaminant may be incorporated into a flat plate structure having a pH-altering material.

In a further aspect, the present invention relates to a method for removing microbial contaminants in a fluid, the method comprising the steps of: altering the pH of the influent by providing a pH altering material upstream of the charged filter media such that the microbial contaminants remain negatively charged; and obtaining at least about a 4 log reduction in microbial contamination when the fluid is processed through the charged filter media. The method can further comprise the step of removing charge-reducing contaminants from the influent in conjunction with the step of altering the pH of the influent.

In a still further aspect, the present invention relates to a filtration system comprising: a composite filter media having positively charged media and a pH altering material, wherein the pH altering material raises the pH of a fluid being treated by the filter system sufficiently to a pH above the isoelectric point of a target organism present within the fluid to cause the target organism to be negatively charged and the positively charged media to maintain a positive charge to provide a substantial electrical attraction between the target organism and the surface of the positively charged media.

Brief Description of Drawings

The features of the invention believed to be novel and the elements characteristic of the invention are set forth with particularity in the appended claims. The figures are for illustration purposes only and are not drawn to scale. The invention itself, however, both as to organization and method of operation, may best be understood by reference to the following description of a preferred embodiment when read in conjunction with the accompanying drawings in which:

fig. 1A and 1B are cross-sectional views of composite filter media of the present invention.

Detailed description of the preferred embodiments

In describing preferred embodiments of the present invention, reference is made herein to FIGS. 1A and 1B of the drawings in which like numerals refer to like features of the invention. The features of the present invention are not necessarily shown to scale in the drawings.

Definition of

The following terms in singular or plural shall have the meanings specified below.

As used herein, "absorbent" refers to any material that is capable of absorbing impurities primarily by drawing them into its internal structure.

As used herein, "adsorbent" refers to any material that is capable of adsorbing impurities by primarily physical adsorption to its surface.

As used herein, "adsorbent filter media" or "adsorbent prefilter media" shall refer to filter media prepared with an adsorbent, such as activated carbon. An example of an adsorptive filter media is PLEKX, commercially available from Orange, Connecticut, KX Industries, L.P^®。

As used herein, "adhesive" shall mean a material used in principle to hold other materials together.

As used herein, "charged media" shall mean a filter media having a positive or negative charge, depending on the material used to make the filter media, or a filter media that can be chemically treated to provide a charge on at least a portion of the surface of the filter media.

As used herein, "composite filter media" shall mean filter media that combines prefilters, adsorbent prefilter media, charged media for improved microbiological interception, and the pH altering materials of the present invention into a single composite structure. In some embodiments, the prefilter may not be present, or its function may be assumed by the adsorbent prefilter medium. A pH altering material may also be incorporated into the adsorbent prefilter medium.

As used herein, "contaminant reduction" shall mean the reduction of impurities in a fluid by chemically or biologically intercepting, removing or inactivating the impurities in the fluid in order to render the fluid safer for human use, for example, or more useful for industrial applications.

As used herein, "fiber" shall mean a solid characterized by a high aspect ratio, e.g., several hundred to 1. Any discussion of fibers includes whiskers.

As used herein, "filter media" shall mean a material that undergoes fluid filtration.

As used herein, "fluid" shall mean liquid, gas or a combination thereof.

As used herein, "forming" shall mean converting a loose, unstructured substance into a cohesive, uniform structure. For example, converting loose fibers into paper.

As used herein, "intercept" or "interception" refers to interfering with or preventing passage through to effect a change, removal, inactivation, or effect.

As used herein, "log reduction value" or "LRV" shall mean the usual log value of the number of organisms in the influent divided by the number of organisms in the effluent of the filter.

As used herein, "membrane" shall mean a thin porous medium in which the structure is a single continuous solid phase having a continuous pore structure.

As used herein, "microorganism" shall mean any living organism that may be suspended within a fluid, including but not limited to bacteria, viruses, fungi, protozoa, and reproductive forms thereof, including cysts or spores.

As used herein, "PFU" shall mean a plaque (plaque) forming unit.

As used herein, "pH-altering material" shall mean a material that can raise or lower the pH of an influent in contact with such pH-altering material to a desired pH range. The pH altering material may provide an influent buffering effect in contact with the pH altering material.

As used herein, "sheet" shall mean a substantially two-dimensional structure having a length and width substantially greater than its thickness.

As used herein, "whiskers" shall mean filaments having a limited aspect ratio and intermediates having an aspect ratio between particles and fibers. Any discussion of fibers includes whiskers.

Composite filter media

The present invention provides a composite filter media comprising a charged media and a pH altering material that alters the pH of an influent to maintain microbial contaminants present in the influent at a first charge that is opposite the charge of the charged media having a second charge. For example, the pH altering material may raise the pH of the influent to less than about 10, preferably from about 7 to about 9. In this pH range, i.e. a pH range above the isoelectric point of some microbial organisms, such organisms are negatively charged. Within this same pH range, the charge on the filter media can be arranged to be strongly positive, with the isoelectric point of the filter media being greater than about 9, and preferably greater than about 10, so that there is significant electrical attraction between the target organism and the surface of the filter media.

In most non-potable water sources, most microbial contaminants are negatively charged at a pH of about 6 to about 8. While microbial contaminants maintain a negative charge, they can be easily intercepted using electrokinetic methods with positively charged filter media. However, with positively charged filter media, positively charged microorganisms will have greatly reduced capture capacity. Poliovirus has an isoelectric point at a pH of about 7, so poliovirus has a negative charge only at alkaline pH. Thus, it is advantageously ensured that any filter is operated in a pH range in which the target microorganism is negatively charged and the filter medium remains positively charged, i.e. in a pH range between the isoelectric points of the microorganism and the filter medium. The composite filter media of the present invention will change the pH of the influent to a pH of less than about 10 so that microbial contaminants within the influent are sufficiently negatively charged so that a positively charged filter media can effectively capture those contaminants. Depending on the fluid to be filtered, the charged filter media used in combination with the pH altering material of the buffered influent will provide a more effective reduction of microbial contaminants.

Charged medium

The charged media of the composite filter media of the present invention can be any charged media known to those skilled in the art. Such charged media may include membranes, solid composite filter media such as extruded carbon blocks, nanofiber filter media, and the like. The charge on the charged medium can be obtained by chemical treatment of the material used for the preparation of the medium or by using a material having a natural charge.

To provide significant microbiological interception, the composite filter media must have a sufficiently tight pore structure, or microporous structure, to provide a short diffusion distance from the fluid to the surface of the filter media. The charge provided by the charged media helps to electrokinetically intercept microbial contaminants, while the tight pore structure provides a short diffusion path and thus provides the motive force for rapid diffusion of contaminants from the flowing fluid onto the surface of the composite filter media. The tight pore structure also provides an additional direct mechanical barrier to microbial contamination. Since interception of very small particles, i.e. particles significantly smaller than the pores of the filter medium, is mainly a diffusion function, there is a direct relationship between the log reduction of many small virus particles and the contact time of the influent within the filter medium, rather than depending on the thickness of the filter medium.

Preferred charged media are disclosed in pending patent application U.S. application Ser. No.10/286695 directed to nanofiber or membrane filter media and 10/290803 directed to solid composite element filter media, wherein both types of filter media have a microporous structure to enhance interception of microorganisms. The microporous structure is treated with a microbiological interception enhancing agent capable of generating a positive charge on at least a portion of the surface of the microporous structure. Cationic metal complexes are formed on at least a portion of the surface of at least some of the fibers or membranes by treating the fibers or membranes with a cationic compound, followed by precipitation of the metal with an anion associated with a cationic surface treatment agent. In a solid composite element filter media, active particles of a microporous structure are chemically treated with a microbiological interception enhancing agent capable of generating a positive charge on the surface of the active particles. Likewise, the cationic metal complex can be formed on at least a portion of the surface of the active particle by treating the active particle with a cationic compound, followed by precipitation of the metal with an anion associated with a cationic surface treatment agent. The chemical treatment produces a strong positive charge on the treated surface, as measured using streaming potential analysis, and this positive charge is retained at a pH below about 10.5.

pH-changing material

Preferably, the pH altering material comprises a slowly dissolving alkaline material that raises the pH of the influent to less than about 10.5, preferably from about 7 to about 9, to substantially negatively charge all microbial contaminants present in the influent. Useful alkaline materials are inorganic carbonates such as magnesium carbonate, sodium bicarbonate and calcium carbonate, limestone, of which calcium carbonate is most preferred. By changing the pH of the influent to a pH greater than the highest isoelectric point of the human enterovirus, substantially all microbial contaminants of interest remain negatively charged, and thus the positively charged medium can more preferably intercept the microbial contaminants.

The pH altering material may be incorporated into the composite filter media using methods known in the art. The pH altering material may be incorporated directly into the charged medium. The flat sheet structure incorporating the pH-altering material may be prepared by embedding particles of such pH-altering material within a non-woven fibrous layer or film, with or without an adhesive. The nonwoven fibrous layer or film may also be chemically treated with a microbiological interception enhancing agent that can generate a positive charge on the surface of the fibrous layer or film to form a charged medium. According to Koslow, U.S. Pat. No.5792513, incorporated herein by reference, particulate pH altering materials may be mixed with a binder and fused into a substrate to form a flat sheet structure to form a prefilter upstream of a tape medium. In practicing the method of the 5792513 patent, the nanofiber filter media disclosed in pending U.S. patent application serial No.10/286695 or other charged media can be used as a substrate on which the pH altering material is fused with a binder.

Fig. 1A and 1B are cross-sectional views of a composite filter media 10 of the present invention, the composite filter media 10 including an adsorbent prefilter layer 11 and a microbiological interception layer 19. The composite filter media 10 may be made from the discrete layers shown in fig. 1A. In fig. 1A, a composite filter media 10 has an adsorbent prefilter layer 11 on a charged media 20 having microbiological interception capability. The adsorbent pre-filter 11 comprises an adsorbent support substrate 12. At least a portion of substrate 12 is coated with pH altering material 14, sorbent particles 16, and binder particles 18 fused to each other and to the surface of substrate 12. A coating on sorbent-supported substrate 12 is obtained according to the method described in the' 5792513 patent. The coating is obtained by preparing a mixture of particles of the pH altering material, particles of the adsorbent and particles of the binder, as substantially described in the' 5792513 patent. Preferably, the average particle size of the binder particles is no more than about 80 microns. The mixture is applied to some or all of sorbent-supporting substrate 12 to produce a loose powder coating on the front side. The loose powder coating is heated to at least the softening temperature of the binder particles, but below the melting temperature of the adsorbent support substrate 12 and the particles of the pH altering material, to form softened binder particles 18. Pressure is applied to the mesh substrate 12 causing the softened binder particles 18 to fuse with the pH altering material 14, the sorbent particles 16 and to the sorbent support substrate 12. After or during heating of the powder coating to at least the softening temperature of the binder particles 18, a second substrate 15 may be laminated to the powder coating and bonded to the powder mixture before cooling the softened binder particles. The microbiological interception layer 19 shown in fig. 1A includes a charged medium 20 comprising a plurality of nanofibers 22.

In fig. 1B, a composite filter medium 10 having an adsorbent prefilter layer 11 and a microbiological interception layer 19 can be prepared by using a charged medium 20 as a support substrate on which at least a portion of the surface of the charged medium 20 is coated with a pH changing material 14, adsorbent particles 16, and a binder 18 fused to each other and to the surface of the charged medium 20. A laminated substrate (not shown) may be placed over the powder coating during manufacture in a manner similar to that described above with respect to fig. 1A.

The pH altering material, alone or in combination with other sorbents, may be incorporated in a flat plate configuration into a composite filter media in which the pH altering material is located upstream of the dielectrophoretic in an axial flow device. In a radial flow device, the flat sheet structure may be wrapped around or rolled into a solid filter media core, such as an extruded carbon unit, to contact the influent with the pH altering material prior to contact with the carbon block filter media. Alternatively, in a solid extruded filter media, the pH altering material may be incorporated directly into a mixture of sorbent and/or absorbent, additives and binders to be extruded into, for example, a solid composite unit, according to Koslow, U.S. Pat. No.5019311 (incorporated herein by reference).

Preferably, the pH altering material is incorporated into an adsorbent pre-filtration medium that also contains an adsorbent that removes the reduced charge native organisms. Natural organisms, such as polyanionic humic and fulvic acids, reduce the charge on positively charged media by coating and complexing with positively charged structures, thereby reducing the effectiveness of the filter in removing negatively charged microbial contaminants. By raising the pH of the influent to greater than 7, polyanionic acids such as humic acid are more effectively removed by adsorbents such as activated carbon.

The pH altering material should be present in an amount and form sufficient to alter the pH of the influent to the desired target. Inorganic carbonates in the range of about 10 to about 50 wt%, preferably about 30 wt%, of the pre-filter medium may be used when incorporated into the pre-filter to raise the pH of the influent to less than about 10, preferably about 7 to about 9. The average particle size of the inorganic carbonate is preferably large enough so that it does not readily dissolve when exposed to large volumes of water during the useful life of the composite filter media, and small enough to allow relatively short contact times. The average particle size of the pH altering material is preferably from about-50 to about-150 mesh, more preferably about-100 mesh. The preferred inorganic carbonate is dolomitic limestone with an average particle size of about-100 mesh.

In municipal water treatment systems or other on-line treatment processes, the pH of the influent may be changed using perfusion or direct injection or addition of a pH-changing material prior to contacting the influent with a charged medium. Preferably, the pH-altering material is added as an aqueous solution or dispersion.

In some cases, the adjustment of pH can be achieved using a suitable buffer or ion exchange resin that maintains the target pH in the effluent. In the case of ion exchange materials, they can be periodically regenerated using a basic solution.

Filtration system incorporating pH-altering materials

The filtration system of the present invention, which is a pressurized or gravity flow system, can comprise a composite filtration media comprising a charged media having a microporous structure with an average flow path of less than about 2 microns and treated with a microbiological interception agent providing a high positive charge on at least a portion of the surface of the microporous structure, an adsorptive prefilter for removing charge-reducing contaminants, and a pH altering material that increases the influent pH to less than about 10, preferably about 7 to about 9. Preferably, the microporous structure comprises a plurality of nanofibers, membranes, or solid carbon blocks. Where the microporous structure comprises nanofibers or membranes, the pH altering material is preferably incorporated into the adsorption prefilter using the method described in Koslow, U.S. patent No. 5792513. The pH altering material is preferably an inorganic carbonate having an average particle size of from about-50 to about-150 mesh, preferably about-100 mesh, present in an amount of about 30 wt% of the amount of the adsorbent prefilter composition. An adsorption prefilter is located upstream of the charged medium to remove charge-reducing contaminants and increase the pH of the influent before the influent contacts the charged medium. Preferably, the particulate pre-filter is included in the filtration system and is also located upstream of the adsorption pre-filter. Such filters of the present invention have been shown to enhance the interception of microbial contaminants, as shown in the examples below.

Examples

The following examples are provided to illustrate the invention and should not be construed as limiting the scope of the invention.

Micropore sizing studies were performed using an automated capillary Flow Porometer available from Porous Materials, inc. Parameters determined using standard procedures published by equipment manufacturers include mean flow pore size and air (air) permeability. The flow of air was analyzed at variable pressure on both dry and wet filter media. Prior to the wet test, the filter medium was initially immersed in silicone oil for at least 10 minutes while being maintained under high vacuum.

Zeta or streaming potential of various filter media was determined using streaming potential and current measured with a BI-EKA Electro-Kinetic Analyzer obtained from Brookhaven Instruments, Holtsville, New York. The instrument includes an analyzer, a flat-panel measurement cell, electrodes, and a data control system. The analyzer includes a pump to generate the pressure required to move the electrolyte solution (typically 0.0015M potassium chloride) from the reservoir through the measurement cell containing the filter media sample described herein. Sensors measuring temperature, pressure drop, conductivity and pH are arranged outside the cell. According to this method, an electrolyte solution is pumped through the porous material. As the electrolyte solution passes through the sample, charge movement occurs. The resulting "streaming potential and/or current" may be detected by means of electrodes located at each end of the sample. Then, zeta (streaming) potential of the sample was determined by calculation according to the Fairbrother and martin method, which takes into account the conductivity of the electrolyte.

Bacterial challenge of the filter media was performed using a suspension of E.coli (Escherichia coli) of American Type Culture Collection (ATCC) No.11775, and Klebsiella terrestris (Klebsiella terrigena) ATCC No.33527 to evaluate the response to the bacterial challenge. Responses to viral challenges were evaluated using MS-2 phage ATTC No.15597-B1 and PRD-1 ATCCNO.19585-B1. Bacteria and phage were propagated using standard procedures for ATCC, and microorganisms in both the influent and effluent of filters challenged with suspensions of microorganism particles were prepared and quantified using standard microbial procedures well known in the art. Challengers were prepared with RO/DI water unless otherwise stated.

A sheet of a charged medium having a microporous structure was used in the following examples and prepared as described below. Adding 0.90g SHORT STUFF into the blender^®EST-8 binder fibers and 1.0L of reverse osmosis/deionized (RO/DI) water, and the binder was blended for about 30 seconds at the pulse setting. To the binder dispersion was added 27.4g dry weight of lyoce11 fibers as a wet pulp having a 10 wt% canadian standard freeness of about 45, unless otherwise specified. This mixture was blended with an additional 800ml RO/DI water for an additional 15 seconds until the fibers were well dispersed, and 6.0ml MERQUAT was added to the fiber mixture^®100 as a 30% aqueous solution. Blending the fiber with MERQUAT^®100 for about 10 seconds and allowed to stand for at least about 4-6 hours. After about 4-6 hours, the fibers were poured into a standard 8 inch Brit jar fitted with a 100 mesh formed wire and excess water was removed under vacuum to form the resulting pulp sheet. A dilute silver nitrate solution providing 0.45g of silver, 15ml of a 3% stock solution (1.8g in 60ml RO/DI water),it was fully exposed and saturated. The silver nitrate solution was allowed to stand on the pulp sheet for at least about 15 minutes and excess water was removed under vacuum pressure. The silver treated pulp sheet was then shredded into small pieces and placed in WARING^®In a blender, and redispersed in 2.0L of deionized water. Mixing the second part MERQUAT^®6.0ml of 100 solution was added to the dispersion and the mixture was blended for about 2 minutes. The treated fibres were poured into 30.5X 30.5cm²Incorporating 100 mesh forming screens and using non-woven fibres REEMAY^TM2004 layer lined stainless steel FORMAX^®In the paper fixing frame. The deckle was previously filled with approximately 24.0L RO/DI water. 30X 30cm with 60 holes of 2cm diameter²The plate was stirred with stainless steel to tip the fiber mixture up and down (mount) about 8-10 times from top to bottom. Water is removed from the fiber mixture by applying a slight vacuum under the paper frame, causing the fibers to form on the nonwoven fabric. Once most of the water is removed, supplemental dewatering is accomplished using a vacuum pump to remove additional excess moisture and produce a relatively smooth, flat, very thin paper-like sheet. The resulting sheet was separated from the screen and combined with blotter sheets on both the top and bottom sides. The combined sheet was gently rolled with a 2.27kg marble roller to remove excess water and flatten the top surface of the sheet, and the sheet was placed between two fresh and dry blotter sheets and placed in a FORMAX^®From about 10 to about 15 minutes at about 120 ℃ on a sheet dryer. Separating the charged medium from the blotter sheet and directly applying the separated charged medium to a form^®The sheet dryer was heated on each side for about 5 minutes to activate the dried binder fibers. The streaming or zeta potential of a charged medium exhibits a zeta potential of greater than about +20 mV. The average flow path of the charged medium is about 0.35 microns.

"PLEKX" according to Koslow, U.S. Pat. No.5792513^®"method for preparing an adsorption prefilter (also known as PLEKX)^®Layers). Both the top and bottom substrates were DuPont with a cutting burr of about 25cm width obtained from E.I. DuPont de Nemours Company, Wilmington, Delaware^®18620 form hydroentangled (hydroentangled) spunlaced nonwovensFabric, unless otherwise indicated. The powder mixture was Grade OL Carbon from Calgon Carbon corporation, Pittsburgh, Pennsylvania with 1 wt% MERQUAT^®100 and 0.5 wt% silver and 22% PAN ground to an average particle size of about 80 x 325 mesh; 14 wt% MICROTHENE available from Equistar Chemicals L.P., Tuscola, Illinois^®FN-510 polyethylene adhesive; and 8 wt% SOLKA-FLOC available from International fiber corporation, North Tonawanda, New York^®1016 purified cellulose treatment. The web speed was about 0.8 m/min. The heated rolls were 10 inches in diameter and heated by hot oil to a temperature of about 232 deg.C (450 deg.F). The nip pressure was about 72 kg/cm. The powder layering (lay-down) and the specific amounts of carbon and pH modifying material are specified in the examples.

Examples 1 and 2: using carbon PLEKX^®Comparative pH study of layer as adsorbent prefilter medium

pH studies of the effluent were performed to determine if PLEKX was present in carbon^®Whether there is a change in the pH of the effluent after the layer contact. Table I below shows the results. The weight of the mat was about 900g/m²。

TABLE I

Example #	PLEKXLayer(s)	pH of the initial influent	Total water volume	pH of the effluent
					1	Calgon-2 layer	RO/DI@5.24	0.5L	8.06
1.0L	8.34
		1.5L	7.14
2.0L	6.34
		2	Calgon-2 layer	Tap water @6.5				5.0L	7.15
10.0L	6.86
					15.0L	6.89
20.0L	7.06
					25.0L	7.03
30.0L	6.83
					35.0L	6.76

In example 1, the pH of the initial influx is completely acidic. Carbon PLEKX^®The layer can raise the pH of the effluent, but it is not possible to maintain a higher pH level. Flowing at 1.5L water through PLEKX^®After layering, the pH dropped below 7. In example 2, carbon-loaded PLEKX at an influent pH of 6.5^®The buffering effect of the prefilter appears to be insufficient.

Examples 3 to 5: using carbon and limestone PLEKX^®Comparative pH study of layer as adsorbent prefilter medium

Various amounts of limestone ("Allydale limestone") obtained from Allydale Corporation were incorporated into carbon PLEKX by reducing the amount of carbon used^®Within the layer. The allydale limestone is an agricultural grade limestone having an average particle size of about-100 mesh. Table II below shows the pH change effect of addition of allydale limestone. The total ply weight was about 900g/m²。

TABLE II

Example #	PLEKXLayer(s)	pH of the initial influent	Total water volume (L)	pH of the effluent
					3	50% limestone-2 layer	Tap water @6.96	0.2	9.85
0.4	9.55
		4	35% limestone-2 layer	Tap water @6.05				0.1	9.61
5	35% limestone-1 layer				Tap water @6.05	0.2	9.82
		0.3	8.35
				5.0		7.58

When the influx is near neutral pH, 50 wt% limestone is added to the PLEKX^®The pH of the effluent is significantly increased and maintained in the layer above 9. Reducing the amount of limestone to 35 wt% and exposing to slightly acidic water (which more closely mimics natural water) also providesThe buffering capacity of the color.

Examples 6 and 7: the use of carbon and limestone PLEKX in the composite filter media of the present invention^®pH study of the layer

Will have a density of about 900g/m²Two-layer carbon/limestone PLEKX of ply weight^®The layers are assembled into a filter housing with a layer of charged media and secured in place with a hot melt adhesive. A 20.0L small-mouth glass vial filled with dechlorinated tap water was attached to the inlet of the filter housing. The pH of the effluent exiting the filter was recorded and the data is shown in table III below.

TABLE III

Example #	Composite layer	pH of the initial influent	Total volume (L)	Flow rate (ml/min)	pH of the effluent
						6	Layer 2 PLEKXw/35 wt% limestone + charged medium	Tap water @6.35	0.5	36	8.96
5.0	56	7.34
			10.0	40	6.60
7	Layer 2 PLEKXw/35 wt% limestone + charged medium	RO/DI@4.92							0.5	48	8.85
			RO/DI@4.92	5.0	60	8.65
		RO/DI@4.92					10.0	52	8.20
			RO/DI@4.92	15.0	36	8.10
		RO/DI@4.95					20.0	64	7.95
			RO/DI@4.95	25.0	50	7.83
		RO/DI@4.95					30.0	40	7.76
			RO/DI@4.93	35.0	68	7.96
		RO/DI@4.93					40.0	48	7.80
			RO/DI@4.93	45.0	50	7.74
		RO/DI@5.00					50.0	44	7.84
			RO/DI@5.00	55.0	46	7.66
		RO/DI@5.00					60.0	40	7.15
			RO/DI@4.65	65.0	64	7.55
		RO/DI@4.65					70.0	56	7.49
			RO/DI@4.65	75.0	44	7.44
		RO/DI@4.92					80.0	68	7.74
			RO/DI@4.92	85.0	48	7.79
		RO/DI@4.92					90.0	44	7.72

In example 6, the improvement in pH after exposure to large volumes of water was limited. However, when the flow rate was increased in example 7, the elevated pH level was better maintained, averaging about 7.5. After exposure to 90.0L of low pH water, MS2 (2.06X 10 prepared in RO/DI water) was used⁹) The filter of example 7 was challenged to determine if an acceptable log reduction was possible. For MS2, the filter provided a log reduction of greater than 9.0 after exposure to 90.0L of low pH water.

Example 8: composite filter media of the present invention challenged with MS2

According to the method disclosed in U.S. Pat. No.5792513, a single layer of tape dielectric was used, followed by two layers of PLEKX prepared with Grade OL Carbon from Calgon Carbon Corporation^®Layer, and about 35 wt% of pulverized allydale limestone, the filter housing was assembled. When MERQUAT is adopted^®100, the charging medium used in this example was treated with sodium bromide. Each PLEKX^®Layer from about 800 to about 900g/m²Layering composition of granular materials. A layer of INTERNET^TMThe mesh was placed on the bottom of the filter housing and fixed in place with hot melt adhesive. Firmly attaching a charged medium to the web, followed by two layers of PLEKX^®A material. The entire filter housing was glued together with a hot melt adhesive to prevent any overflow. The actual filtration area was about 2.5 inches by 3.75 inches (6.35cm by 9.53 cm). An 1/4 inch inner diameter hose was secured to the inlet of the filter housing using a hot melt adhesive, and the outlet of the filter housing was open to the direction of fluid flow. A water column pressure of about 4 inches (10.2cm) was maintained at all times. The filter was attached to a small glass jar filled with RO/DI water.

The filter was removed from the small-mouth glass vial and challenged with 250ml of MS2 solution at various time intervals after the appropriate amount of RO/DI water was flowed through the filter. The effluent was collected in a sterilized 250ml Erlenmeyer flask, diluted and plated onto a petri dish according to standard procedures, and left to stand overnight. After each challenge, the filter was reattached to the small glass vial.

TABLE IV reduction of MS2

Flow rate (ml/min)	Water volume (L)	Challenge of MS2 influent	PFUs	LRV
					52	5.5	2.06×10	0	9.31
56	35.5	1.13×10	8.0×10	7.15
					40	74.0	1.00×10	1.80×10	5.74
40	112.0	2.80×10	8.40×10	4.53
					28	141.0	3.70×10	4.80×10	3.88

The filter of example 8 provided an excellent log drop in MS2 even after 4 challenges and exposure to large volumes of water.

Example 9: composite filter media of the present invention challenged with E.coli

The filter housing described in example 8 was challenged with E.coli. As shown in table V below, similarly excellent results were obtained with continued bacterial challenge.

TABLE V reduction of E.coli

Flow rate (ml/min)	Water volume (L)	Challenge with E.coli influx	PFU	LRV
					40	5.0	1.4×10	0	9.14
46	35.0	1.30×10	0	9.11
					40	73.0	1.10×10	0	9.04
40	112.0	1.05×10	0	9.02
					28	141.0	1.10×10	0	9.04
20	168.0	4.00×10	0	9.60
					20	175.0	2.65×10	0	9.42
16	207.0	1.95×10	0	9.29
					14	218.0	3.60×10	2.4×10	7.17
16	225.0	1.10×10	6.00×10	5.26

This example shows that the filter will still provide an acceptable bacteria log reduction value of greater than about 4 log values until the flow rate drops to an unacceptable level.

Example 10: composite filter media of the present invention challenged with Klebsiella terrestris, PRD-1, and MS2

Three filters were challenged with the three organism cocktails described above. Using PLEKX containing only carbon, not limestone^®The filter prepared from the layers was used for comparison. Each PLEKX containing only carbon^®The layer has a thickness of 600g/m²Two layers were used. Grade TOG carbon from Calgon Corporation was used in comparative Filter A and Grade OL carbon was used in comparative Filter B. The composite filter media of the present invention has a ply weight of 1500g/m²Single carbon limestone PLEKX^®And (3) a layer. One layer of the charged medium prepared using the general process described above was firmly glued to the INTERNET^TMIn a ceramic buchner funnel 6 inches in diameter and 3 inches high on top of the mesh layer. PLEKX^®The layer is glued firmly on top of the charged medium. The outside edges of the buchner funnel were glued to prevent overflow through the system. A small glass vial of dechlorinated tap water was placed on top of the buchner funnels and water flowed through each funnel. The filters were pre-wetted with 500ml of dechlorinated tap water and then challenged with 250ml of a cocktail of three organisms prepared with dechlorinated water. The effluent was collected in a sterilized 250ml Erlenmeyer flask, diluted, and plated onto a petri dish according to standard procedures, and left to stand overnight. After each challenge, dechlorinated water was flowed through each filter.

TABLE VI compositions having Grade TOG carbon LPEKX^®Comparative Filter A of layers

Volume of water (L)	Challenge article	PFUs	LRV
				MS2 challenge
0.5	8.4×10	3.90×10	8.33
				13.0	6.70×10	9.00×10	4.87
PRD-1 challenge
				0.5	2.10×10	0	8.32
8.0	6.00×10	0	8.77
				13.0	7.00×10	2.40×10	3.46
Klebsiella terricola challenge
				0.5	1.15×10	0	9.06
8.0	7.50×10	0	8.87
				13.0	3.00×10	3.50×10	4.93

TABLE VII Grade OL carbon LPEKX^®Comparative filter B of layers

Volume of water (L)	Challenge article	PFUs	LRV
				MS2 challenge
0.5	8.40×10	2.70×10	8.49
				15.0	6.70×10	1.40×10	4.68
PRD-1 challenge
				0.5	2.10×10	0	8.32
8.0	6.00×10	9.00×10	4.82
				15.0	7.00×10	4.10×10	3.23
Klebsiella terricola challenge
				0.5	1.15×10	0	9.06
8.0	7.50×10	6.00×10	6.09
				15.0	3.00×10	3.25×10	3.96

TABLE VIII having Grade OL carbon and limestone LPEKX^®Example 10 of layer

Volume of water (L)	Challenge article	PFUs	LRV
				MS2 challenge
0.5	8.40×10	3.60×10	8.37
				11.0	6.70×10	2.50×10	8.43
32.0	2.02×10	1.98×10	3.01
				PRD-1 challenge
0.5	2.10×10	0	8.32
				5.0	6.00×10	2.00×10	7.48
11.0	7.00×10	3.30×10	7.33
				32.0	9.00×10	1.40×10	2.80
Klebsiella terricola challenge
				0.5	1.15×10	0	9.06
5.0	7.50×10	0	8.87
				11.0	3.00×10	0	8.48
32.0	1.20×10	8.05×10	4.17

The filter of example 10 maintained a greater challenge with a larger test volume than the filters a and B without the pH altering material, limestone.

Example 11: long-term study of the composite filter media of the present invention challenged with Klebsiella terrestris (Kleb), PRD-1, and MS2

Using a layer of charged media prepared according to the general description set forth above, a filter similar to that used in example 10 was assembled and a layer of Grade OL carbon PLEKX with 35 wt% limestone was placed upstream of the charged media^®. The filters were initially wetted with RO/DI water and challenged with a cocktail of three organisms. An additional amount of RO/DI water was passed through the filter prior to subsequent challenge.

TABLE IX EXAMPLE 11

Time (hr)	Total water volume (L)	Challenge (PFU/ml)	LRV
				0	0.25 (initial challenge)	MS2 3.00×10	7.48
PRD 4.40×10	7.64
		Kleb 2.50×10	7.40
72	1.5					MS2 3.00×10	6.48
		PRD 1.20×10	6.08
				Kleb 9.50×10	6.98
		96	4.0			MS2 9.00×10	6.95
PRD 1.30×10	6.11
				Kleb 3.00×10	6.47
120	9.75					MS 29.00×10	6.95
		PRD 1.8×10	6.25
				Kleb 4.50×10	6.65
		144	15.5			MS2 8.00×10	6.90
PRD 1.10×10	6.04
				Kleb 5.00×10	6.70
168	22.0					MS2 7.80×10	6.89
		PRD 2.30×10	6.36
				Kleb 6.00×10	6.78
		192	26.0			MS2 9.00×10	6.95
PRD 6.00×10	6.78
				Kleb 4.00×10	6.60
264	30.0+0.25L humic acid (5ppm)					MS2 3.10×10	6.49
		PRD 2.70×10	6.43
				Kleb 5.50×10	6.74

The filter of example 11 maintained an acceptable reduction in microbial contamination even when the amount of water passing through the filter dropped to an unacceptable flow rate.

Example 12: long-term study of the composite filter media of the present invention challenged with Klebsiella terrestris (Kleb), PRD-1, and MS2

The filter of example 12 was similar to the filter used in example 10. MERQUAT of the first section as described in the general description above^®During the 100 treatment, the nanofibers used in the charged medium were treated with sodium bromide and thus followed the other procedures. The filter is initiallyWetted with RO/DI water and challenged with a cocktail of three organisms. Prior to a subsequent challenge, additional RO/DI water was passed through the filter.

Table X example 12 (sodium bromide treated nanofiber charging media)

Time (hr)	Total water volume (L)	Challenge (PFU/ml)	LRV
				0	0.25 (initial challenge)	MS2 3.00×10	7.48
PRD 4.40×10	7.64
		Kleb 2.50×10	7.40
72	6.0					MS2 3.00×10	6.48
		PRD 1.20×10	6.08
				Kleb 9.50×10	6.98
		96	11.0			MS2 9.00×10	6.95
PRD 1.30×10	6.11
				Kleb 3.00×10	6.47
120	19.25					MS2 9.00×10	6.95
		PRD 1.8×10	6.25
				Kleb 4.50×10	6.65
		144	29.0			MS2 8.00×10	6.90
PRD 1.10×10	6.04
				Kleb 5.00×10	6.70
168	35.0					MS2 7.80×10	6.89
		PRD 2.30×10	6.36
				Kleb 6.00×10	6.78
		192	39.0			MS2 9.00×10	6.95
PRD 6.00×10	6.78
				Kleb 4.00×10	6.60
264	41.0+0.25L humic acid (5ppm)					MS2 3.10×10	6.49
		PRD 2.70×10	6.43
				Kleb 5.50×10	6.74

In example 12, although the log reduction of the three organisms was exactly the same as in example 11, the volume of water flowing through the filter was significantly greater due to treatment with sodium bromide. Both filters of examples 11 and 12 maintained acceptable antibacterial and antiviral performance.

The composite filter media of the present invention provides improved microbiological contaminant interception capability over extended periods of time, even when challenged with a variety of organisms.

While the invention has been particularly described, in conjunction with a specific preferred embodiment, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art in light of the foregoing description. It is therefore contemplated that the appended claims will embrace any such alternatives, modifications and variations as falling within the true scope and spirit of the present invention.

Claims (23)

1. A composite filter media comprising a positively charged media and a pH altering material, wherein the pH altering material alters the pH of an influent such that microbial contaminants present in the influent remain negatively charged and the positively charged media remain positively charged and provide increased interception of microbial contaminants.

2. The composite filter media of claim 1, wherein the pH altering material is for altering the pH of the influent to less than 10.5.

3. The composite filter media of claim 1, wherein the pH altering material is used to alter the pH of the influent to between 7 and 9.

4. The composite filter media of claim 1, wherein the pH altering material comprises an inorganic carbonate.

5. The composite filter media of claim 4, wherein the inorganic carbonate comprises magnesium carbonate or calcium carbonate.

6. The composite filter media of claim 1, wherein the pH altering material is incorporated into the positively charged media.

7. The composite filter media of claim 1, wherein the positively charged media comprises a solid composite unit and the pH changing material is a flat sheet structure wrapped around the positively charged media.

8. The composite filter media of claim 1, wherein the positively charged media is mixed with the pH changing material and binder and extruded to form a solid composite unit.

9. The composite filter media of claim 1, wherein the pH altering material comprises a flat plate structure located upstream of the positively charged media.

10. The composite filter media of claim 1, further comprising an adsorbent for removing charge-reducing contaminants upstream of the positively charged media.

11. The composite filter media of claim 1, wherein the pH altering material can be periodically regenerated.

12. A composite filter media comprising

A charged medium capable of providing enhanced microbiological contaminant interception capability;

a pH-altering layer located upstream of the charged medium; and

a medium for removing charge-reducing contaminants located upstream of the pH-altering layer.

13. The composite filter media of claim 12, wherein the charged media comprises a flat sheet structure.

14. The composite filter media of claim 12, wherein the charged media is mixed with a binder and fused to a substrate forming a charged layer, the charged layer and the pH changing layer being spirally wound such that the pH changing layer is exposed to an influent before the influent contacts the charged layer.

15. The composite filter media of claim 14, wherein the pH altering layer is fused to the second surface of the substrate.

16. The composite filter media of claim 12, wherein the pH altering material increases the pH of the influent and is suitable for regeneration.

17. A composite filter media comprising:

an active particle treated with a positively charged microbiological interception agent;

a binder;

a pH-altering material, wherein the active particles, the binder, and the pH-altering material are mixed and extruded into a solid composite unit; and

a material for removing charge-reducing contaminants upstream of the solid composite unit.

18. The composite filter media of claim 17, wherein the pH altering material comprises a slow dissolving alkaline material.

19. A composite filter media comprising:

an active particle treated with a positively charged microbiological interception agent;

a binder; wherein the active particles and the binder are mixed and extruded into a solid composite unit; and

a pH-altering material having a flat sheet structure wrapped around the solid composite unit; and

a material for removing charge-reducing contaminants upstream of the solid composite unit.

20. The composite filter media of claim 19, wherein said material for removing charge-reducing contaminants is incorporated into a flat sheet structure having said pH-altering material.

21. A method for removing microbial contaminants from a fluid, the method comprising the steps of:

altering the pH of the influent by providing a pH altering material upstream of the charged filter media such that the microbial contaminants remain negatively charged; and

at least a 4 log reduction in microbial contamination is obtained when the fluid is processed through the charged filter media.

22. The method of claim 21, further comprising the step of removing charge-reducing contaminants from the influent in conjunction with the step of altering the pH of the influent.

23. A filtration system, comprising:

a composite filter media having positively charged media and a pH altering material, wherein the pH altering material raises the pH of a fluid treated by the filter system sufficiently to a pH above the isoelectric point of a target organism present within the fluid to negatively charge the target organism and the positively charged media maintains a positive charge to provide substantial electrical attraction between the target organism and the positively charged media surface.