WO1993022021A1

WO1993022021A1 - Device for removing undesirable substances from a fluid

Info

Publication number: WO1993022021A1
Application number: PCT/US1993/004130
Authority: WO
Inventors: Bernard F. Silverwater
Original assignee: Pall Corporation
Priority date: 1992-04-30
Filing date: 1993-04-30
Publication date: 1993-11-11
Also published as: EP0597062A1; JPH06508065A; CA2110515A1

Abstract

The disclosure describes a device (1) including a housing (11, 12) having an inlet (2) and an outlet (3) and defining a flow path for a liquid between the inlet (2) and the outlet (3). The flow path extends through a purification bed (17) which operates to remove substantial quantities of dissolved substances from the liquid. The purification bed (17) may include a plurality of separators (5) which act to increase the velocity of liquid flow through the purification bed (17). A filter may be located in and around the periphery of the housing (14, 15) and downstream from the purification bed. The filter (14, 15) is preferably pleated and has an absolute pore rating no greater than about 0.8 νm to remove many microbiological organisms from the liquid. The disclosure further describes a method for manufacturing the device.

Description

DEVICE FOR REMOVING UNDESIRABLE SUBSTANCES FROM A FLUID

The present invention relates to devices and method for removing undesirable substances from a fluid. In particular it relates to devices and methods for removing a broad spectrum of undesirable substances from a liquid.

Liquids, such as water, may contain many different kinds of undesirable substances including, for example, particulates, dissolved minerals and other chemical substances, and microbiological organisms such as pathogenic bacteria and species of legionella and/or mycoplasma. In a variety of circumstances, these substances must be removed before the liquid can be used. For example, in certain circumstances, it is desirable to increase the amount of moisture in the air. This process is commonly known as humidification and may be performed by a device called a humidifier. If impure water is utilized in the humidification process, it may clog the humidifier. It might even harm people who breath the humidified air. Therefore, the water should be purified before it is discharged into the air by the humidification process.

Ideally, a device for removing this broad spectrum of contaminants would comprise a single, small, lightweight, self-contained device rather than a complex multi-component and/or multistage system to remove the various contaminants. Such a device would not only be more reliable than a complex system, but it would also be less expensive and more compact. Certain humidification applications, such as for use on board an airplane. require a highly compact, light weight device having high reliability and long service life.

Accordingly, the present invention provides a device for removing undesirable substances from a liquid, the device comprising a housing having a side wall, an inlet, and an outlet and defining a liquid flow path between the inlet and the outlet; a purification bed disposed in the housing in the liquid flow path and including a purification material; and a filter disposed in and substantially around the periphery of the housing between the side wall of the housing and the purification bed, the filter having an absolute pore rating no greater than about 0.8 micrometers and being located in the liquid flow path downstream from the purification bed to remove microbiological organisms.

The present invention also provides a device for removing undesirable substances from a liquid, the device comprising a housing having an inlet and an outlet and defining a liquid flow path between the inlet and the outlet; and a purification bed disposed in the housing in the liquid flow path and including particles of a purification material and a plurality of separators dividing the purification material into a plurality of sections, each of the separators having a flow opening permitting liquid to flow from one purification section to another, the separators and flow openings being arranged to lengthen the low path through the purification bed and thereby increase the velocity of the liquid flowing through the bed, wherein the purification bed includes a first region comprising activated carbon and a second region comprising ion exchange resins, the ion exchange resins being downstream in the liquid flow path from the activated carbon.

The present invention further provides a device for removing undesirable substances from a liquid, the device comprising the housing having an inlet and an outlet and defining a liquid flow path between the and the outlet; and a purification bed disposed in the housing in the liquid flow path and including particles of a purification material and a plurality of separators interference fit within the housing dividing the purification material into a- plurality of sections, each of the separators having a flow opening permitting liquid to flow from one purification section to another, the separators and flow openings being arranged for lengthening the flow path and for permitting a uniform distribution of flow through the purification bed. The present invention additionally provides a method for manufacturing a device for removing undesirable substances from a liquid, the method comprising placing a first layer of a first purification material into a housing; and pressing a first interference fit separator plate into the housing until the separator plate contacts and compresses the first purification material.

Embodiments of the invention offer several advantages. For example, devices and methods embodying the invention remove a broad spectrum of undesirable substances. The purification bed serves to remove many dissolved minerals and other chemical substances and the filter serves to remove many microbiological contaminants such as harmful bacteria and species of legionella and mycoplasma.

Further, devices and methods embodying the invention remove a broad spectrum of undesirable substances from a substantial volume of liquid without fouling. Locating the filter around the periphery of the housing serves to increase the surface area of the filter and generally extends the effective service life of the device. In addition, devices embodying the invention are highly compact and reliable, are easily manufactured, and may be tailored for use with a humidifier. Figure 1 is a cut-away side view of a preferred embodiment of a device constructed in accordance with the present invention;

Figures 2a and 2b are views of two adjacent separator plates of Figure 1; Figures 3a and 3b are views of another embodiment of two adjacent separator plates; and

Figures 4a, 4b, 5a, and 5b are views of still further embodiments of adjacent separator plates. Referring to Figure 1, an exemplary device 1 includes a housing 11 having an inlet 2 for receiving a liquid and an outlet 3 for discharging the liquid. The housing 11 is preferably shaped as a cylinder, although other shapes, such as a parallelepiped, are possible. The housing 11 is preferably fabricated from polypropylene, although it may be fabricated from any sufficiently rigid, impervious material, including other polymers or sheet metal. The housing 11 defines a flow path 18 (shown by arrows) between the inlet 2 and outlet 3 through which the liquid flows. The flow path 18 extends from the inlet 2 through a series of purification mechanisms to the outlet 3.

An inlet filter 4 may be disposed in the flow path 18 immediately following the inlet 2 , at one end of the filter housing 11. The inlet filter 4 preferably rests on a perforated plate which has been forced under pressure along and fitted against an inner wall 8 of the housing 11. The inlet filter 4 may be slightly oversized so it too may be pressure fit within the inner wall 8 and sealed to the inner wall 8 by an interference fit. Alternatively, the inlet filter 4 may be sealed to the inner wall by a sealing compound.

The inlet filter 4 may comprise a high dirt capacity (HDC) depth filter medium formed into a flat, circular pad and sandwiched between upstream and downstream woven screens, e.g., 30 X 30 X .010 screens. The HDC medium may include a mass of woven or non-woven fibers such as a mass of non-woven, synthetic polymeric microfibers (e.g. polypropylene microfibers) . The HDC medium preferably has an effective pore rating of about 2 μ and may have a uniform pore structure or, preferably, a graded pore structure where the size of the pores decreases continuously or stepwise from the upstream to the downstream side of the filter pad.

The inlet filter 4 serves as a prefilter, removing gross particulates from the liquid before the liquid enters a purification bed 17. Consequently, it may have any other suitable configuration. For example, the^' filter pad may be pleated or the filter medium may comprise a porous membrane. An HDC medium is preferred, however, because of the limited surface area available for the prefilter at the end of the housing 1 and the superior dirt capacity and enhanced service life of an HDC depth filter. Further, the effective pore rating of the filter pad may be different from 2 μ as long as it is suitable for removing, over the design life of the device, gross contaminants which might otherwise foul the purification bed 17. In addition, the upstream and downstream screens may instead be any structure which is suitably open- pored or coarse to evenly distribute the liquid over the upstream surface of the filter pad and evenly drain the liquid from the downstream surface of the filter pad. It may have a larger or smaller mesh size or it may comprise a non-woven material.

A purification bed 17 is disposed in the flow path 18 downstream from the inlet filter 4. The purification bed 17 contains at least a single purification material, i.e., a material which removes one or more substances from a fluid. Preferably, the purification bed 17 comprises a plurality of purification materials disposed in respective regions of the purification bed 17. In the illustrated embodiment, the purification bed 17 includes two purification materials respectively disposed in two regions of the bed. The two purification materials are activated carbon and ion exchange resins, the activated carbon being disposed in an upstream region and the ion exchange resins being disposed in a larger downstream region. The activated carbon region removes many chemical substances from the liquid, including trace amounts of chlorine which can interfere with the action of the ion exchange resins. The region of ion exchange resins removes dissolved minerals from the liquid that might otherwise foul a humidifier. In a preferred embodiment, the ion exchange resin comprises a monobed resin such as Amberlite MB-1 available from Rohm & Haas, Inc.

The purification material may be loaded into the purification bed 17 in the form of loose particles and then compressed to compact the bed. The size of the particles may vary depending on the type of purification material and the fluid design parameters of the purification bed. For example, in the illustrated embodiment, the activated carbon particles may be in a 12 X 28 mesh range while the particles of the ion exchange resin may be about 0.5 mm in size. Alternatively, the particles of the purification material may be immobilized by any of several well known processes. For example, the particles of the purification material, which expand when they are wet, may be immobilized within a fiber matrix. This and other techniques for immobilizing a purification material are mentioned in United States Patent No. 4,828,698.

It has been found that conventional purification beds suffer from a number of deficiencies that limit their ability to be used in an application requiring low mass flow rates. One problem often encountered is channeling. Channeling is a phenomena in which a slow moving liquid will create and/or follow specific channels through the purification bed and thus only come in contact with a small portion of purification sorbent material. The efficiency and the useful life of the purification bed can be greatly increased by incorporating in the purification bed a series of separators. The separators divide the purification bed into two or more purification sections and lengthen the liquid flow path through the purification bed. Lengthening the flow path increases the velocity of the liquid through the purification bed for a predetermined mass flow rate. In turn, increasing the velocity of the liquid minimizes channeling of the liquid through the purification bed. In addition, the separators are preferably designed to uniformly disperse or distribute the flow of liquid from one purification section to the next through the purification bed.

By minimizing channeling and uniformly distributing the flow, the separators maximize the amount of purification material which contacts the liquid.

The separators may be variously configured to lengthen the flow path through the purification bed. For example, in the illustrated embodiment of Figures 1 and 2, the separators comprise flat plates 5 disposed in parallel within the housing 11 and in parallel with the inlet filter 4. For a cylindrical housing, the separator plates 5 may be generally circular, as shown in Figure 2a, and for a parallelepiped housing, the separator plates 5 may be rectangular. The separator plates 5 are preferably closely and equally spaced within the housing 11, greatly increasing the length of the flow path 18 and, therefore, the velocity of the liquid through the purification bed 17. The purification sections defined by the separator plates 5 comprise a plurality of parallel layers of purification material. Preferably, the activated carbon region of the purification bed 17 includes only the first layer 17a while the ion exchange resin region of the purification bed 17 comprises the remaining layers.

The separator plates 5 are preferably fabricated fro*u sheet metal, although they can be fabricated from many sufficiently rigid, impervious materials, including polymers such as polypropylene. Each separator plate 5 may be relatively thin, e.g., less than about .010 inch, and the outside dimension of each plate 5 may be slightly larger, e.g., by about .020 inch, than the inside dimension at the inner wall 8 of the housing 11. This allows each separator plate 5 to be pressure fit within the housing inner wall 8, establishing an interference fit between the separator plate 5 and the inner wall of the housing 11 and obviating the need for a separate seal. A cylindrical housing with circular separator plates is preferred since this configuration results in a uniform pressure being applied between the inner housing wall and all points along the outer peripheral edge of the separator plates, ensuring a tight seal. Pressure fitting the separator plates 5 within the housing 11 renders the device 1 easy to manufacture, while still preventing channels from forming along the housing inner wall 8 and the separator plates 5. There is no need to provide a seal, e.g., an RTV silicone sealant, between or permanently fix, e.g., by welding, the separator plates 5 and the housing inner wall 8 in order to prevent bypass around the layer of purification material.

The purification bed 17 may be formed by forcing the initial separator plate 5a under pressure along the inner wall 8 of the housing 11 until it is correctly located. The appropriate purification material, e.g., particles of activated carbon , may then be loaded onto the initial separator plate 5a to form the first layer of purification material 17a. The second separator plate 5b may then be forced under pressure along the inner wall 8 of the housing 11 until it contacts and suitably compresses the first layer of purification material 17a. The second layer of purification material, e.g., particles of the ion exchange resin, may then be loaded onto the second separator plate 5b. The process is continued until the entire purification bed 17 is formed.

To direct fluid through the purification sections, each separator has one or more openings. The separators and their openings may be arranged to direct fluid through the purification bed in a variety of ways but they are preferably arranged to direct fluid sequentially through all of the purification sections. This maximizes the length of the flow path through the purification bed and the velocity of the liquid through each purification section. In the embodiment illustrated in Figures 1 and 2, the openings in the separator plate 5 are holes 7 located along one edge of the plate 5. The separator plates 5 are arranged in the purification bed 17 so that the holes 7 in each successive plate alternate from one side of the bed 17 to the other side, i.e., one offset by 180° from one plate 5 to the next. In the rectangular separator plates 5 shown in Figure 2b, the flow holes 7 allow for the most uniform distribution of flow through the purification material disposed in each layer. Each flow hole 7 in one separator plate 5 is an equal distance from a corresponding flow hole 7 in an adjacent separator plate 5. Additionally, only a single type of separator plate 5 needs to be manufactured, since by inverting the separator plate 5 the flow holes 7 can be alternated from one side to the other.

Other arrangements of the separators and openings are of course possible. A peripheral separator plate has flow holes disposed about the periphery of the plate, and a center separator plate has a flow hole disposed in the center of the plate. The peripheral and center separator plates may be alternately disposed throughout the purification bed in planes parallel to the inlet filter. The flow path extends from the center of the center plate in opposite directions out to the periphery of the adjacent peripheral separator plate, axially through the flow holes in the peripheral separator plate, then in opposite directions in to the center of the next center separator plate, axially through the flow holes 7 in the center separator plate, etc. In this manner, not only is the liquid velocity increased sufficiently to prevent channeling, but the placement of the flow holes ensures a uniform distribution of the flow of liquid through the maximum amount of sorbent material.

The device can be adapted to either a cylindrical or a parallelepiped filter housing. Figure 3a shows a first circular separator plate with a plurality of outer peripheral flow holes and a second circular separator plate with a center flow hole adapted for a cylindrical filter housing 11. The plurality of outer peripheral flow holes are preferably all the same size and equally spaced from one another and from the center hole in an adjacent separator plate. This arrangement allows for uniform flow through all of the purification material disposed in each layer. In addition, the plurality of peripheral flow holes ensures that all of the purification material will come in contact with the liquid and helps ensure a uniform flow of liquid throughout each layer. In this configuration, liquid flows axially through the center hole of one plate and radially outward through a purification layer to the plurality of peripheral flow holes of the next plate. The liquid then flows axially through the peripheral flow holes into the next layer and then radially inward through the purification layer to the center hole of the next plate. In this manner, a uniform flow of liquid is achieved throughout each purification layer.

Figure 3b shows a pair of separator plates specifically adapted for use in a parallelepiped filter housing 11. Figure 3b discloses a first separator plate having a row of center holes preferably disposed along the center line of the separator plate, and a second separator plate having a plurality of peripheral flow holes preferably disposed along opposed edges of the plate. The peripheral flow holes are preferably all the same size and equally spaced from one another and from the center line of the plate. In this configuration, liquid flows axially through the row of center holes of one plate and outward through a purification layer in opposite directions to the plurality of peripheral flow holes aligned along the two side edges of the next plate. The liquid then flows axially through the peripheral flow holes on both side walls into the next layer and then inward through the purification layer in opposite directions to the next row of center holes in the next plate. In this manner, a uniform flow of liquid is achieved throughout each purification layer.

The separator plates may be disposed within the housing at right angles to the inlet filter. The third embodiment can also be adapted to either a cylindrical or parallelepiped filter housing. For the cylindrical housing, the separators may comprise nested, right-circular cylinders disposed coaxially within the housing perpendicular to the inlet filter and capped by opposed circular plates. The separators may be disposed at equal or unequal distances along the radius of the housing. The purification sorbent sections would then comprise right circular cylinders of purification material disposed between adjacent separators. Flow openings may be provided in the separators and in the opposed caps to direct the flow of liquid axially in one direction through one purification section and then axially in the opposite direction through an adjacent section. Further, the liquid may pass sequentially from the center purification section to the outer purification section or vice versa.

For the parallelepiped housing, the separators may comprise flat plates disposed in parallel within the housing perpendicular to the inlet filter and capped by opposed rectangular plates. The purification sections would then comprise layers of purification material disposed between adjacent separator plates. Flow openings may be provided in the separator plates and the opposed caps to direct the flow of liquid in one direction through one purification layer and in the opposite direction through an adjacent purification layer.

In each of these embodiments, the purification bed is sectioned to increase the length of the flow path and therefore to increase, the velocity of the liquid through the bed, minimizing any channeling of the liquid through the bed. At the same time, flow through the purification bed is distributed as uniformly as possible to ensure maximum contact between the liquid and the purification material. Other embodiments are also possible. For example, the flow opening may comprise one or more slots. A slot in the outer periphery of a separator plate 5 may serve the same purpose as a flow hole within the separator plate 5. Alternatively, the separator plates could be fashioned such that the slot extended substantially across the periphery where the flows holes would have been located. Figures 4 and 5 (corresponding respectively to Figures 2 and 3) show the flow holes in the first and second embodiments replaced with one or more extended slots. The embodiments shown in Figures 4 and 5 may eliminate a manufacturing step of drilling holes in the separator plates.

A bed outlet filter 9 may be disposed in the flow path 18 downstream from the purification bed 17, for example, at the opposite end of the housing 11 from the inlet filter 4. The bed outlet filter 9 acts to remove particles picked up by the liquid in the purification bed 17 as well as small particles which passed through the inlet filter 4. The bed outlet filter 9 may be very similar to the inlet filter 4 but preferably has a smaller pore rating, e.g., a 0.5μm effective pore rating. Thus, the bed outlet filter 9 may also comprise an HDC depth filter medium formed into a flat, circular pad and sandwiched between upstream and downstream woven screens. The bed outlet filter 9 is preferably pressure fit within the inner housing wall 8 on top of the final separator. By slightly oversizing the bed outlet filter 9, the filter 9 may be sealed to the inner wall 8 of the housing 11 by an interference fit. A perforated cap may then be fit within the inner housing wall 8 on top of the bed outlet filter 9.

Liquid flowing out of the bed outlet filter 9 may be directed through an end channel 10 toward the outer periphery of the housing 11 and into a peripheral channel 13 along an outer wall 15 of the housing 11. The peripheral channel 13 is preferably disposed about the entire periphery of the device 1. A filter 15 for removing microbiological organisms is disposed within the housing 11 around the periphery of the housing 11. In the illustrated embodiment, the microbiological filter 15 is disposed between the inner and outer walls 8,14 of the housing 11, i.e., between the outer side wall 14 of the housing 11 and the purification bed 17, and is sealed, for example by a sealant such as an RTV silicone compound or any other suitable potting compound between flanges that extend between the inner and outer walls 8,14 of the housing 11. The flanges have openings so that liquid entering the peripheral chamber 13 passes through the microbiological filter 15 into an outlet chamber 16 between the filter 15 and the inner wall 8 and then exits the device 1 through the outlet 3.

The microbiological filter may be variously configured. For example, the filter is preferably pleated, the pleats extending axially. Locating the microbiological filter 15 around the periphery of the housing 11 increases the surface area of the filter and pleating the filter increases the surface area even more. This is an important advantage. The larger surface area of the microbiological filter 15 greatly extends the effective service life of the device 1.

Further, the microbiological filter 15 preferably includes a porous membrane having a pore size which effectively blocks the passage of microbiological organisms. To remove microbiological organisms, the filter 15 most preferably has an absolute pore rating no greater than about 0.8 μm. For example, the porous membrane may comprise a porous nylon or PVDF membrane having an absolute pore rating of about 0.1 μm. The microbiological filter 15 may also include a porous element having a larger pore size than the 0.1 μ porous membrane and located upstream of the porous membrane. This porous element may comprise a second porous membrane having an absolute pore rating of, for example, 0.45 μm or, more preferably, a thin sheet of a fibrous depth filter medium. The depth filter medium may have a uniform pore structure or, more preferably, a graded pore structure wherein the effective pore rating decreases from the upstream side to the downstream side of the sheet. In a preferred embodiment, at least a portion of the filter sheet has an effective pore rating in the range from about 0.55 μm to about 0.35 μm. The porous membrane and the fibrous sheet are preferably formed as an integral composite together with upstream and downstream support and drainage materials and then pleated to orm the microbiological filter 15.

The increased surface area of the peripheral, pleated filter 15 as well as the varying pore size con igurations have proven highly e fective for removing many microorganisms and particulates while delaying the onset of fouling. Further, the larger surface area allows the filter to have a greatly increased operating life without greatly increasing the size of th-s device 1 since the microbiological filter 15 is located along the periphery of the housing 11. The compact size of the device 1 is highly advantageous for aerospace applications and generally results in lower manufacturing costs.

In operation, the device is intended to purify six pounds of water per hour for up 300 hours or - more where the water has an initial impurity level on the order of 500 parts per million or .5 mg per liter of total dissolved minerals. The device is particularly applicable for use as a water demineralizer which also removes many microbiological organisms from the demineralized effluent water.

Claims

We claim:

1. A device for removing undesirable substances from a liquid, the device comprising: a housing having a side wall, an inlet, and an outlet and defining a liquid flow path between the inlet and the outlet; a purification bed disposed in the housing in the liquid flow path and including a purification material; and a filter disposed in and substantially around the periphery of the housing between the side wall of the housing and the purification bed, the filter having an absolute pore rating no greater than about 0.8 micrometers and being located in the liquid flow path downstream from the purification bed to remove microbiological organisms.

2. The device of claim 1 wherein the filter- is disposed completely around the periphery of the housing.

3. The device of claim 2 wherein the housing is cylindrical and the liquid flows radially through the filter.

4. The device of claim 1 wherein the filter is pleated.

5. The device of claim 1 wherein the filter includes at least first and second porous elements, the first porous element being disposed upstream from the second porous element and having a larger pore rating than the second porous element.

6. The device of claim 5 wherein the first porous element has a pore rating in the range from about 0.55 μm to about 0.35 μ and the second porous element has a pore rating of about 0.1 μm.

7. A device for removing undesirable substances from a liquid, the device comprising: a housing having an inlet and an outlet and de ining a liquid low path between the inlet and the outlet; and a purification bed disposed in the housing in the liquid flow path and including particles of a purification material and a plurality of separators dividing the purification material into a plurality of sections, each of the separators having a flow opening permitting liquid to flow from one purifi- cation section to another, the separators and flow openings being arranged to lengthen the flow path through the purification bed and thereby increase the velocity of the liquid flowing through the bed, wherein the purification bed includes a first region comprising activated carbon and a second region comprising ion exchange resins, the ion exchange resins being downstream in the liquid flow path from the activated carbon.

8. The device of claim 7 wherein the particles of purification material are compressed.

9. The device of claim 7 wherein the particles of purification material are immobilized.

10. The device of claim 7 wherein the separators comprise separator plates which divide the purification material into a plurality of layers, wherein at least one layer of the purifica¬ tion material includes activated carbon and wherein at least one other layer of the purification material includes ion exchange resins.

11. The device of claim 7 wherein the separators comprise separator plates and wherein the separator plates are pressure fit within the housing and form an interference fit with a housing wall.

12. The device of claim 7 further comprising a first filter disposed in the liquid flow path upstream from the purification bed; a second filter disposed in the liquid flow path downstream from the purification bed; and a third filter disposed substantially in and. around the periphery of the housing and in the liquid flow path downstream from the second filter, wherein the third filter is pleated and has an absolute pore rating no greater than about 0.8 μm for removing microbiological organisms.

13. A device for removing undesirable substances from a liquid, the device comprising: a housing having an inlet and an outlet and defining a liquid flow path between the inlet and the outlet; and a purification bed disposed in the housing in the liquid flow path and including particles of a purification material and a plurality of separators interference fit within the housing dividing the purification material into a plurality of sections, each of the separators having a flow opening permitting liquid to flow from one purification section to another, the separators and flow openings being arranged for lengthening the flow path and for permitting a uniform distribution of flow through the purification bed.

14. The device of claim 13 wherein a uniform pressure is exerted between the housing and all points along an outer peripheral edge of each separator.

15. The device of claim 13 wherein each separator comprises a circular separator plate.

16. The device of claim 13 wherein the separators are pressed into the housing and compressed against the purification material.

17. The device of claim 13 wherein the flow openings are alternately disposed along opposite sides of consecutive separators.

—18,- The ievice of claim 13 wherein the flow openings are alternately disposed between the center and the outer periphery of consecutive separators.

19. A method of manufacturing a device for removing undesirable substances from a liquid, the method comprising: placing a first layer of a first purification material into a housing; and pressing a first interference fit separator plate into the housing until the separator plate contacts and compresses the first purification material.

20. The method of claim 19 further comprising: placing a second layer of a second purification material into the housing on top of the first plate; and pressing a second interference fit separator plate into the housing until the separator plate contacts and compresses the second purification material.

21. The method recited in claim 20 including placing a third layer of the second purification material into the housing on top of the second plate; pressing a third interference fit separator plate into the filter housing until the separator plate contacts and compresses the second purification material.

22. The method of claim 20 wherein the first purification material includes activated carbon and the second purification material includes ion exchange resins.

23. The method of claim 19 wherein the first interference fit separator plate is circular, the housing is cylindrical, and a uniform pressure is exerted between the housing and all points along an outer periphery of the first separator plate forming an interference fit.

AMENDED CLAIMS

[received by the International Bureau on 31 August 1993 (31.08.93); original claims 19,20 and 23 deleted original claims 1,12,21 and 22 amended; remaining claims unchanged; claims renumbered as claims 1-20

(5 pages)]

1. A device for removing undesirable substances from a liquid, the device comprising: a housing having a side wall, an inner wall, an inlet, and an outlet and defining a liquid flow path between the inlet and the outlet; a purification bed disposed in the housing in the liquid flow path and including a purification material surrounded by the inner wall; and a filter disposed in and substantially around the periphery of the housing between the side wall of the housing and the inner wall, the filter having an absolute pore rating no greater than about 0.8 micrometers and being located in the liquid flow path downstream from the purification bed to remove microbiological organisms.

2. The device of claim 1 wherein the filter is disposed completely around the periphery of the housing.

4. The device of claim 1 wherein the filter is pleated.

6. The device of claim 5 wherein the first porous element has a pore rating in the range from about 0.55 μm to about 0.35 μm and the second porous element has a pore rating of about 0.1 μm.

7. A device for removing undesirable substances from a liquid, the device comprising: a housing having an inlet and an outlet and defining a liquid flow path between the inlet and the outlet; and a purification bed disposed in the housing in the liquid flow path and including particles of a purification material and a plurality of separators dividing the purification material into a plurality of sections, each of the separators having a flow opening permitting liquid to flow from one purifi- cation section to another, the separators and flow openings being arranged to lengthen the flow path through the purification bed and thereby increase the velocity of the liquid flowing through the bed, wherein the purification bed includes a first region comprising activated carbon and a second region comprising ion exchange resins, the ion exchange resins being downstream in the liquid flow path from the activated carbon.

12. The device of claim 7 wherein the housing includes a side wall and an inner wall and wherein the device further comprising: a first filter disposed in the liquid flow path upstream from the purification bed; a second filter disposed in the liquid flow path downstream from the purification bed; and a third filter disposed substantially in and around the periphery of the housing between the sidewall and the inner wall and in the liquid flow path downstream from the second filter, wherein the third filter is pleated and has an absolute pore rating no greater than about 0.8 μm for removing microbiological organisms.

18. The device of claim 13 wherein the flow openings are alternately disposed between the center and the outer periphery of consecutive separators.

19. A method of manufacturing a device for removing undesirable substances from a liquid, the method comprising: placing a first layer of a first purification material into a housing; and pressing a first interference fit separator plate into the housing until the separator plate contacts and compresses the first purification material; placing a second layer of a second purification material into the housing on top of the first plate; and pressing a second interference fit separator plate into the housing until the separator plate contacts and compresses the second purification material; and placing a third layer of the second purification material into the housing on top of the second plate; pressing a third interference fit separator plate into the filter housing until the separator plate contacts and compresses the second purification material.

20. The method of claim 19 wherein placing the first layer includes placing activated carbon into the housing and placing the second and third layers includes placing ion exchange resins into the housing.