WO2007076019A2

WO2007076019A2 - Filter media and apparatus for water filtration

Info

Publication number: WO2007076019A2
Application number: PCT/US2006/049041
Authority: WO
Inventors: Donald D. Ricketts
Original assignee: Wastewater Technology, Inc.
Priority date: 2005-12-23
Filing date: 2006-12-21
Publication date: 2007-07-05
Also published as: WO2007076019A3

Abstract

A filter media that can be employed in the field of water filtration includes a rigid backing layer and a flexible face layer and a fibrous component between the rigid and face layers.

Description

FILTER MEDIA AND APPARATUS FOR WATER FILTRATION

BACKGROUND OF THE INVENTION Field of the Invention

This invention relates to novel filter media that can advantageously be employed in the field of water filtration. The filter media can be engineered to capture particles smaller than 5 microns, yet are easily backwashed to release captured particles. Methods of manufacturing the filter media and apparatus and methods of using the filter media of the invention are also disclosed.

Description of the Related Art

Filtering water, such as wastewater before discharge to the environment by means of a tertiary filter, is well known as described in copending application, U.S. Application No. 11/066,274 filed February 28, 2005, now published as U.S. Publication No. 2005-0139557 Al.

A tertiary filter has previously been employed in filtering treated wastewater before discharge to the environment to filter particles on the order of 5-10 microns and larger from the treated wastewater. Such filters have heretofore employed a filter cloth of matted fibers, known simply as a "felt" as the means for capturing particles. One illustration of such a material is shown in U.S. Patent 5,374,360.

Although a filter cloth can capture solids entrained by filtering treated wastewater, in that patent the patentee recognized that it was difficult to dislodge captured particles from the filter cloth by mere backwashing of the filter cloth material. Patentee surmized that the combination of a high pressure liquid spray from the downstream side of the filter cloth, in combination with backwashing, could be used to dislodge the captured particles from the filter cloth thereby extending the useful life of the filter cloth. However, such an approach required installation of additional apparatus to deliver the high pressure liquid spray resulting not only in increased capital costs but also the additional energy costs of running a high pressure pump.

The prior art attempted to improve the filter cleaning operation by employing a novel filter cloth in which a plurality of fibers are connected to a backing as shown in U.S. Patent No.6, 103, 132. When in the filtering mode, the fibers tend to lay flat forming tortuous paths, some of which reduce in cross-section and some of which "dead-end" the flow of the treated wastewater. As a result, entrained particles in the flow are captured in these tortuous paths by the long pile fibers. According to that patentee, if a suction head is forcibly moved over the surface of the long pile fibers, while maintaining a mechanical retaining action upon the fibers in a flattened state and then abruptly releasing the pile threads to cause them to abruptly straighten within the suction slit in the suction head based in which vacuum is maintained, the individual fibers will, as they abruptly spring upwards, release the captured particles.

While an improvement of the filter cloth or felt preceding that disclosure, the technique employed to backwash the filter was unduly harsh on the long pile threads and the filter material itself. The mechanical retaining action tended to tear fibers from the backing, and even tear the backing itself, thereby degrading the quality of subsequently filtered water. In some cases the loss of fibers and/or tear in the backing requires shutdown of the filtering apparatus, and replacement of the filtering material. In the type of apparatus used in U.S. Patent No. 6,103,132, the tank in which the filter was situated needed to be drained and the filter cloth replaced by at least partially dismantling the filter device in the drained tank. Such a procedure is not only costly but time consuming resulting in the loss of filter capacity. It is therefore an object of the invention to provide novel filter media, apparatus and methods employing the same, and materials of use thereof which avoid the problems of the prior art.

Summary of the Invention

The present invention utilizes a novel filtering media can generally be described as a rigid backing material and a flexible face material between which fibers are situated. The fibers can take several forms, such as a chopped stable fiber batting, or even a plurality of long pile fibers attached to a backing as in the aforementioned U.S. Patent No. 6,103,132.

Brief Description of the Drawings

Fig. 1 is a schematic representation of one embodiment of the filter media according to the invention partially sectioned to illustrate components thereof.

Fig. 2 is a schematic representation in cross section of the use of the filter media according to the invention to filter water to remove entrained solids therein.

Fig. 3 is a schematic representation according to Fig. 2 during which entrained particles are being backwashed into a suction head.

Fig. 4 is similar to the cross sectional view of Fig. 2 for the use of another embodiment of filter medium of Fig. 2 and employs a modified suction head incorporating a liquid spray head.

Fig. 5 is a schematic representation of Fig. 4 during operation of backwashing of the filter media to remove external particles. Detailed Description of the Preferred Embodiments

Filtering of water to remove entrained solids by means of dynamic or static filters are generally well known. See for example, U.S. Patents 5,374,360 and 6,103,132, mentioned above, as well as co-pending US. Patent Application Number 11/066,274, published as U.S. Publication No. 2005-0139557 Al.

The problem with the prior art filter materials is that they are difficult to clean to remove the captured solids contained therein.

The prior art attempts at backwashing with or without the use of a concurrent high pressure spray from the downstream side of the filter during the backwashing, is that the fibers of the filter material are subjected to stresses which either damage the fibers by abrasion, cutting, or fatigue, and/or alternatively remove the fibers from the filter material.

The present invention prevents such detriments of the prior art by providing novel filter media.

According to one embodiment of the present invention as shown in Figure 1, the filter media 10 of the invention comprises a rigid backing material 12. The rigid backing material may be formed of metal, such as a screen, perforated plate or other formaminous material but preferably is formed of a polymeric material, such as a plastic which is resistant to the environment in which it is used, e.g., resistant to degradation when immersed in water, resistant to stretching, both during filtering and upon backwashing and is otherwise inert to the other components of the filter media and the water being filtered.

The open, area and the size of the opening in rigid backing material 12 is not critical to the filtering ability of the filter media, but it must cooperate with the other components for structural integrity during the filtering process. The second component of the filtering media is a face wearing surface 14. Preferably face wearing surface 14 is formed of a flexible material. The most preferred material for face wearing surface 14 is a polymeric material formed into a net or screen as illustrated in Figure 1. This polymeric material is preferably formed of a low friction material or may be alternatively formed of a metal or a metal coated with a polymeric low friction material, such as polytetrafiuoroethylene (PTFE). The primary reason that face wearing surface 14 is formed as a flexible material is because in use during the backwashing stage of the filtering process, it preferably enters into the suction head, or alternatively, is drawn near to the suction head, to thereby permit the expansion of the volume of the fibrous component to release entrained particles.

The third component of the filter media is a fibrous material. In the embodiment as shown in Figure 1, a suitable form of fibrous material is a chopped staple fiber batting 13 sandwiched between rigid backing material 12 and face wearing surface 14.

In an alternate embodiment, fiber batting maybe formed from strands of long fibers. These long fibers may be orderly or randomly placed on backing material 12 and looped back upon themselves, e.g., as in carpet fibers. Such a structure can greatly reduce or eliminate the odds of ends of chopped fibers from penetrating face wearing surface 14. Such fibers, in cross-section, may have a shape which is substantially cylindrical, elliptical, or of an alternate shape, such as dual- or tri-lobal, or any other regular or irregular, crimped or crimped shape along its length.

In a preferred embodiment, the long pile fibers of the batting are permanently affixed only to the backing material 12 leaving a free end of the fibers, i.e., either the unfixed end or the middle section when both ends are affixed to the backing material 12. In an alternate embodiment, one end of the fibers is affixed to the backing material, and the opposite end (or a middle section) is affixed to' the face wearing surface 14. For example, the fibers can be joined to the face wearing surface 14 by the same or different method as used to join to the backing material, or the fibers may simply be adhered to the material which defined the openings in the face wearing surface 14. Other embodiments using long pile fibers will be described below. Preferably, the fibers do not limit fluid flow through the face wearing surface 14.

The fiber batting 13 may have antimicrobial, antifungal and/or antibiotic properties in order to control or eliminate growth of unwanted microorganisms on the batting itself. The presence of such microorganisms can impair the filtering and/or damage the batting. The antimicrobial, antifungal and/or antibiotic properties may be achieved by incorporating an antimicrobial, antifungal and/or antibiotic reactive agent into the fibers themselves, such as by impregnation of chemical agents, or inclusion of materials having catalytic antimicrobial properties (e.g., cationic metals, such as copper or silver). Metallic or fibrous strips or elements having such properties, e.g., formed of materials as described in U.S. Patent Nos. 6,482,424 and 5,458,906 and those often used in dentistry, may also be utilized, by being affixed to or incorporated into the structure of the batting.

As formed, the chopped staple fiber batting 13 can be made into a compressible mat in which intersections of the fibers are preferably adhered at points of intersection. Such adherence can be achieved by heat, sonic or microwave welding, solvent, or adhesive bonding as well as other conventional bonding techniques known in the art.

However, adherence is a preferred embodiment. As laid down, the longitudinal portion of each fiber is generally aligned with the longitudinal dimension of the resulting mat. hi such a form, the individual fibers will not extend beyond the face wearing surface 14. The type of fiber used in the fiber batting 13 is not critical so long as it is inert to the process fluid being filtered, and is not degraded under the typical process conditions of filtering.

Nor is the initial density of the fiber battering 13 critical, as it is a feature of the invention that fiber batting 13 is designed to be compressible under the conditions of filtering such that it compresses and forms flow channels therethrough that are generally smaller than the flow channels therethrough when the fiber batting 13 is being backwashed.

As shown for example in Figure 2, as the filter media 10 is being used to filter process fluid, such as treated wastewater containing entrained solids, the filter media 10 is in a compressed state, caused by the the fluid flow shown by arrows 15.

However, when backwashed, as illustrated in Figure 3, the fiber batting 13 expands under the effect of the reduced pressure in suction head 16 so as to enlarge the flow channels under the effect of the backwash shown by arrows 17 with the flow channels releasing the solids 18 captured by the fiber batting 13 into suction head 16 to be either removed from the process or recycled to an upstream portion of the water treatment cycle.

As shown in Figures 1 and 2, the suction head 16 is provided with rounded corners 19, 20, 21 and 22 at both the leading and trailing edges of the suction head as well as at the suction head opening so as to reduce stress on the face wearing surface 14 and as surface 14 is preferably of a low friction material, preferably a polymer, or polymer coated metal, with the polymer most preferably being PTFE, nylon, or polyurethane, protecting the fibrous batting 13, there is no likelihood of damaging the fibrous material 13. Such corners may be attached to suction head 16 by any suitable means, including the bolts and nuts 23, 24 as shown in Figures 2-3. It is therefore within the scope of the invention to form the fiber batting 13 of predetermined density and resultant flow channel size such that when compressed, the fiber media will preferably retain particles smaller than 10 microns, e.g., as small as 5 microns, and preferably smaller than 5 microns. Such size retention makes the filter media of the present invention suitable not only for filtering process wastewater for ultimate discharge as surface water, e.g., irrigation, but also for filter water suitable for use as drinking water.

It will be understood by those of ordinary skill in the art that the face material wearing surface 14 must have openings much larger than that of the entrained solids to permit the solids to pass through, not only to prevent clogging of wearing surface 14 by the solids during filtering, but also to permit high throughput of filtered process fluid. The openings in backing material 10 suitably are larger than the solids being captured to permit high flow of treated process water.

The initial density of the fiber batting 13 together with its compressibility under filtering process conditions determines the size of entrained solids that it will capture. In view of this disclosure those skilled in the art will be able to fabricate filter media for a wide variety of filtering specifications, not only for wastewater or drinking water specifications but for other types of fluid processing.

Furthermore, although I have disclosed chopped staple fiber batting 13 as a suitable fibrous media in Figures 1-3, it is to be understood that the invention is also applicable to the use of a filter cloth comprising a plurality of long pile fibers attached to a backing as shown in the aforementioned U.S. Patent No. 6,103,132.

As shown schematically in Figure 4, such a filter cloth may be used provided the free ends (e.g., the ends opposite the backing) of the fibers do not extend beyond face material wearing surface 14. As shown in Figure 4, as the process fluid containing solids is being filtered, the flow of the fluid compresses the filter cloth to collapse the fibers in random manner creating tortuous channels between the fibers to capture the entrained solids.

By the use of a modified suction head 26 (Figures 4-5) having a suction chamber 27 operatively in contact with wearing surface 14, the fibers can be extended to their full lengths thereby opening the tortuous channels previously formed therein to release the captured solids 18 as shown in Figure 5.

The face ends of the long pile fibers may be prevented from extending beyond the wearing surface 14 by attaching the fabric backing of the filter cloth to the rigid backing 10 by any known manner, e.g., mechanical attachment, spot welding, or adhesive. The face ends may be optionally attached to the wearing surface 12 by sonic, thermal or solvent welding, adhesive other mechanism. Alternatively, the free ends of the individual long pile fibers may be melted or welded into clumps distal their attachment to backing, increasing the size of the ends of the fibers and, preventing them from extending beyond wearing surface 14.

As shown in Figures 4-5 suction head 26 is provided with leading and trailing edge 29, 30 which are curved so as not to snag wearing surface 14 or the long pile fibers. Furthermore, interior surfaces 31, 32 are also provided with a curved cross-section so as to not disrupt wearing surface 14.

In this embodiment, a fluid spray head 28 is operatively connected to a conduit 33 for delivering a pressurized fluid to spray head 28 which can be used to assist in mechanical dislodgement of solids 18 or, alternatively, be used to treat the fibers with chemical agents, e.g., fungicide, mildewicide, and/or similar bio-active agents to prolong the effectiveness of the filtering process. Advantageously both bio-active treatment and hydraulic dislodgement can be performed simultaneously or sequentially. My filter media can be used in the filtering apparatus and methods of the prior art, such as the aforementioned U.S. Patents No. 5,374,360 and 6,103,132 or in the apparatus and methods disclosed in my copending application, U.S. Application No. 11/066,274, now published as U.S. Publication No. 2005-0139557 Al, as well as in other filtering processes.

It should be apparent that my invention has utility in both static and dynamic filters as well as in static and dynamic operation of the suction heads. My disclosure here is only exemplary and not by way of limitation. The relative positions of the suction head as being to the left of the filter media is illustrative only and any position to the right, up, down, the direction of movement, the positioning of one or a plurality of suction heads in one or more locations, reciprocating, rotational or stationary suction heads or obvious modifications of the components, and structure of my filter media are all with the scope of my disclosure.

It will be apparent by those of ordinary skill in the art that various modifications of my invention will become apparent without departing from the spirit and scope of my invention.

Claims

I Claim:

1. A filter media comprising: a backing material, said backing material comprising a plurality of openings; a face wearing surface; and a compressible fibrous component between said backing material and said face wearing surface.

2. The filter media of claim 1 , wherein said face wearing surface is formed of a flexible material.

3. The filter media of claim 1, wherein said face wearing surface is in the form of a screen.

4. The filter media of claim 1, wherein said face wearing surface is in the form of a net.

5. The filter media of claim 1 , wherein said compressible fibrous component is formed of a chopped staple fiber batting.

6. The filter media of claim 1 , wherein said compressible fibrous component is formed of long pile fibers affixed to the backing material.

7. The filter media of claim 1 , wherein said backing material is rigid.

8. The filter media of claim 6, wherein said compressible fibrous component is also affixed to said face wearing surface.

9. The filter media of claim 3, wherein said fibrous component is formed of long pile fibers affixed to the backing material and the portions of the fibers distal to said backing material are enlarged so as to not enter openings in said screen.

10. The filter media of claim 9, wherein said compressible fibrous component, when compressed, can capture particles as small as 5 microns.

11. The filter media of claim 1 , wherein said face wearing surface comprises a screen of a polymeric material.

12. The filter media of claim 1, wherein said face wearing surface comprises a screen of a metal.

13. The filter media of claim 1, wherein the compressible fibrous component contains at least one of an antimicrobial, antifungal or antibiotic reactive agent.

14. The filter media of claim 1, wherein the compressible fibrous component contains at least one metal selected from the group consisting of copper and silver.

15. A process of filtering wastewater, said process comprising passing wastewater through a filter media to remove solid particles entrained in said wastewater, wherein the filter media comprises the filter media of claim 1.

16. The process of claim 15, further comprising back washing the filter media by the use of a suction head applied against the face wearing surface of the filter media.

17. The process of claim 16, wherein the fibrous component does not extend beyond the face wearing surface of the filter media when the filter media is subject to suction by the suction head.

18. The process of claim 16, further comprising delivering a pressurized fluid to the filter media during said backwashing step.

19. The process of claim 18, wherein said pressurized fluid comprises a bio-active agent.

20. The use of the filter media of claim 1.