FIELD OF THE INVENTION

The present invention relates to rotary filter discs for treating water or wastewater, and more particularly to a system and method for filtering water in which the filtration operates by gravity and employs filters having a nominal cut-off between 0.5 and 8 micrometers.

BACKGROUND

Rotary disc filters are widely known and used to remove suspended solids. Often, rotary disc filters are used in polishing operations. For example, rotary disc filters are used to remove suspended solids from the effluent produced by secondary treatment of wastewater systems. These rotary disc filters typically remove suspended solids 10 μιη or larger, using filter materials with a nominal cut-off of 10 microns and above.

There is a need to remove smaller particles from water during treatment such that effluents contain less suspended solids. Additionally, a rotary disc filter that would remove smaller sized suspended solids would be able to be used in other filtering applications that demand the removal of small particles. Accordingly, there is a need for a rotary disc filter that can filter and remove suspended solids of much smaller sizes, preferably as low as 1 μιη. SUMMARY

Disclosed herein is a method or process for removing suspended particles by a gravity fed disc filter. In one embodiment of the process, water or wastewater (collectively "water") having suspended particles of 1 micron and larger is treated such that the particles 1 micron and larger are removed. The water is directed to a rotary disc filter having one or more rotatable filter discs. The rotatable filters are at least partially contained within a tank. Filter media are employed on each side of the rotatable filter disc. The filter media include openings that are sized to prevent 95% or more of particles that are 1 micron and larger from passing through the filter media. After a water head pressure is established, that head pressure is used to force water through the filter media. As a result, 95% or more of particles sized 1 micron and larger are filtered from the water. The filter media is cleaned by rotating the filter discs holding the filtered media and removing filtered particles therefrom.

In another embodiment, Cryptosporidium and giardia are removed from drinking water. These contaminants are removed via a method of filtering the drinking water with a rotary disc filter. In this embodiment, water containing Cryptosporidium and giardia is directed to a rotary disc filter. The rotary disc filter has at least one rotatable filter disc. The rotatable filter disc is at least partially contained within a tank or basin. Filter media is employed on each side of the rotatable filter disc. The filter media includes openings that permit the water to flow through the filter media. The openings, however, are sized to reject 1 log or more of the Cryptosporidium and giardia in the water. After a water head pressure is established, at least 1 log of the Cryptosporidium and giardia are removed by utilizing the head pressure to force the water through the filter media. The filter media filters the water such that 1 log or more of

Cryptosporidium and giardia are removed from the water. The filter media is cleaned by rotating the rotatable filter disc(s) and removing filtered Cryptosporidium and giardia from the filtered media.

DESCRIPTION OF THE DRAWINGS

Figure 1 is a perspective view of an exemplary disc filter with portions of the structure broken away to better illustrate basic components of the disc filter.

Figure 1 A is a schematic illustration of an end view of the disc filter showing the backwash pump and the drive system for driving the drum and filter disc.

DETAILED DESCRIPTION

The current invention is directed towards methods of removing suspended particles sized 1.0 μιη or larger from water and wastewater. These methods utilize a rotary disc filter. Rotary disc filters are known and widely used to remove large particles. Rotary disc filters are shown and described in patents and other published materials. For example, reference is made to U.S. Patent No. 7,597,805 and U.S. Patent Publication No. 2008/0035584. The disclosures of these two publications are expressly incorporated herein by reference. A complete and unified understanding of disc filters, their structure, and operation can be gained by reviewing these materials.

A brief overview of the structure and operation of a typical disc filter may be beneficial. Figure 1 shows a disc filter indicated generally by the numeral 10. Disc filter 10 includes an outer housing 12. Rotatively mounted in the housing 12 is a drum. Generally, the drum is enclosed, except that it includes an inlet opening and a series of openings formed in the surface thereof for enabling influent to flow from the drum into a series of rotary filter disc, indicated generally by the numeral 14, mounted on the drum. That is, as will be appreciated from subsequent discussions herein, influent is directed into the drum, and from the drum through openings in the surface thereof into the respective rotary filter discs 14.

The number of rotary filter discs 14 secured on the drum and rotatable therewith can vary. Basically, each rotary filter disc 14 includes a filter frame 16 and filter media 18 secure on opposite sides of each rotary filter disc 14. A holding area, formed by compartments, is defined inside each rotary filter disc 14 for receiving influent to be filtered by the rotary filter disc 14.

As will be discussed later, the disc filter 10 is provided with a drive system for rotatively driving the drum and the rotary filter discs 14 mounted thereon. There is provided a drum motor 64 that is operative to drive a sprocket or sheave (not shown) connected to the drum. Various means can be operatively interconnected between the drum motor 64 and the sprocket for driving the sprocket, and hence the drum. For example, a belt drive can be utilized. Various other types of drive systems can be utilized to rotate the drum and the rotary filter discs 14 mounted thereon.

Continuing to refer to Figure 1 , the disc filter 10 includes an influent inlet 22. Influent inlet 22 leads to an influent holding tank 24. Influent holding tank 24 is disposed adjacent an inlet opening formed in the drum such that influent held within the influent holding tank 24 can flow from the holding tank into the drum. As seen in the drawings, the influent holding tank is disposed on the upstream side of the disc filter 10. Disposed around and generally below the influent holding tank 24 is a bypass tank 30. An outlet 32 enables influent to flow from the bypass tank 30. Note that the influent holding tank 24 includes overflow openings. These overflow openings permit influent overflow to flow from the influent holding tank 24 downwardly into the bypass tank 30. This effectively limits the water level height in the influent holding tank 24.

Disc filter 10 also includes an effluent holding tank or basin 26. Effluent holding tank 26 is disposed about a downstream end portion of the disc filter 10, and as shown in the drawings, extends around at least a lower portion of the rotary filter discs 14. As the influent moves outwardly through the filter media 18, this results in the water being filtered, and it follows that the filtered water constitutes an effluent. It is this effluent that is held within the effluent holding tank or basin 26. There is also provided an effluent outlet associated with the effluent holding tank 26 for directing effluent or filtered water from the disc filter 10.

Therefore, it follows that influent water to be treated or filtered is directed into the influent inlet 22 and into the influent holding tank 24 where the water accumulates to a selected height therein so as to provide a head pressure for effectively causing the water to move from the inner portions of the rotary filter discs 14 outwardly through the filter media 18. Influent held within the holding tank 24 eventually is directed into the drum, and from the drum through openings therein into the interior areas of the rotary filter discs 14. Now, the water within the rotary filter disc moves outwardly through the filter media 18 into the effluent holding tank 26, and eventually out the effluent outlet. Disc filter 10 also includes a backwashing system for periodically cleaning the filter media 18. Generally the backwashing system includes a manifold 40 that extends along a side of the disc filter 10 and is operatively connected to a backwash pump 42 (Figure 1 A) that is operative to direct high pressure wash water through the manifold 40. Extending off the manifold 40 are a series of feed pipes 44 with each feed pipe being connected at its outer end to a nozzle array 46. As seen in the drawings there is a sludge or backwash water outlet 50. Outlet 50 is operatively connected to a trough or a catch structure that extends through the drum and is disposed generally underneath the various nozzle arrays 46. When the backwashing system is in operation, the debris, sludge and wash water fall into the trough or catch structure and through gravity pass from the disc filter 10 through the sludge or backwash water outlet 50. In order to backwash the filter media 18, the drum can be continuously or intermittently rotated such that the filter media or filter panels 18 enter the accumulated effluent in the effluent holding tank 26. It is appreciated that only a bottom portion of the filter media 18 is effective at any one time to filter the influent. From time-to-time the drum and rotary filter discs will be rotated, and when this occurs some portions of the filter media 18 will be rotated to an upper portion and in this position the filter media 18 will not be in a position to filter the effluent.

During a backwash cycle, high pressure water is sprayed from the nozzle arrays 46 onto the outer surfaces of the filter media 18 to clean them. This can occur when the drum and rotary filter discs 14 are stationary or being rotated. The water sprayed on from the nozzle arrays 46 impacts the outer surface of the filter media 18, vibrating the filter media and even penetrating the filter media. This causes debris caught on the inner side of the filter media 18 to be dislodged or removed from the inner surface of the filter media 18. This debris and the backwash water fall into the underlying trough extending through the drum. Thereafter the debris and backwash water are channeled out the outlet 50. It is appreciated that while upper portions of the filter media 18 are backwashed and cleaned that the lower submerged portions of the filter media can continue to filter the influent.

The present application focuses on the use of a non-woven media for the disc filter that will affectively remove suspended matter of 1.0 μιη or larger. Filter disc 14 includes filter media 18. Filter media 18 actively filters the feedwater passing through filter disc 14 by preventing suspended particles from passing through filter disc 14. Filter media 18, in a preferred embodiment, has an effective thickness in the range of 100-1300 μιη, and preferably less than 400 μιη, and is configured such that it rejects at least 95% of particles sized 1 μιη and larger.

Filter media 18 includes a non-woven filter material. The non-woven filter material may be comprised of homogeneous or heterogeneous fibers. In a preferred embodiment, the non- woven filter material is a homogeneous non-woven material. The fibers comprising the non- woven filter material may be of various materials. Examples of materials that may comprise the fibers include, but are not limited to, polyolefins, polyesters, nylons, thermoplastic, fluorinated polymers (PVDF, ECTFE), polysulfones, urethanes, natural polymers such as cellulosics and cellulosic derivatives, and combinations thereof.

In one embodiment, a substantial portion of the fibers comprising the non-woven filter media have a diameter between 0.5 μιη and 8.0 μιη. Fibers of larger diameter, however, may be incorporated. In another embodiment, a majority of fibers comprising the non-woven filter media have a diameter between 0.5 μιη and 8.0 μιη.

The fibers comprising the non-woven filter material may be secured together by conventional means. Examples of such means for securing the fibers are well known in the art and include, but are not limited to, ultrasonic pattern bonding, gluing and chemical bonding, thermal bonding, hydroentangling, and meltblown bonding. In constructing the non-woven filter material, the fibers are integrated in such a way as to prevent passage of particles sized 1 μιη or larger. The fibers are further arranged such that the non-woven filter material has a nominal pore size of 1-8 μιη. In one embodiment, the open area of the non-woven filter material is approximately 5-12% of the total surface area of non-woven filter material. It is recognized that in a non-woven filter media, the pores are not conventional in the sense that they do not define a straight or orderly passageway. In a non-woven filter media configuration, the filtrate follows many convoluted, unaligned pathways through the filter media.

In another embodiment, filter media 18 is a composite filter media. In this embodiment, the non-woven filter material is comprised of nanofibers. The nanofibers may have a diameter between 0.1 μιη to 1.0 μιη.

In some embodiments, filter media 18 further includes a backing. Backing may be comprised of woven or non-woven fabric. Backing is positioned such that it provides mechanical strength to non-woven filter material. Backing may be positioned on one or both sides of non-woven filter material. In some embodiments, backing is physically attached to the non-woven filter material.

The above described disc filter 10 may be used remove suspended particles sized 1.0 μιη or larger from water or wastewater. In such a method, the disc filter 10 includes at least one filter disc 14 that is at least partially contained within a tank or basin. There are two types of rotary disc filters: the "inside-out" version and the "outside-in" version. In the "inside-out" version, water is directed into a drum, and then flow out from the drum and through the filter media. In the "outside-in" version, the water flows through the filter media into the compartment in the drum.

Filter media 18 is employed on each side of rotatable filter disc 14. As discussed above, filter media 18 includes openings that are sized to prevent the passage of at least 95% of particles that are 1 μιη or larger. To remove at least 95% of the particles sized 1 μιη or larger from the water, the water is directed through the filter media 18. To do so, a water or wastewater head pressure sufficient to force water through filter media 18 is developed. The head pressure is then used to force water or waste water through filter media 18. The contaminants that are filtered from the water are then removed by the backwash cleaning system. In some embodiments, to remove the contaminants, filter disc 14 is rotated such that the backwash system may clean filter disc 14 in segments.

Another embodiment of this method may be used to remove Cryptosporidium and giardia from water. Cryptosporidium and giardia are protozoan parasites. Humans who are infected with these parasites may become victims of intestinal conditions that may result in stomach pain, fever, diarrhea, nausea, and vomiting. Cryptosporidium and giardia are commonly found in untreated water. Due to the substantial health concerns related to these parasites, it is important to remove such parasites from water treated for drinking as well as treated industrial wastewater that may be discharged into the environment. Because

Cryptosporidium is also resistant to a number of common disinfectants, to include chlorine- based disinfectants that are used in some water treatment processes, a filtering method for removing these parasites is needed. It has been observed that the disc filter 10 described herein with non-woven filter material that removes 95% of particles sized 1.0 μιη or larger is capable of removing at least 1 log of Cryptosporidium and giardia present in water.

To remove Cryptosporidium and giardia from water, the dirty water is directed to the rotary disc filter 10. The rotary disc filter 10 has at least one rotatable filter disc 14 that is contained in a tank or basin. Filter media 18 is employed on each side of the filter disc 14 and contains openings that permit the water to flow through the filter media 18. The openings are sized such that 1 log or more of the Cryptosporidium and giardia are rejected by filter media 18.

To remove at least 1 log of the Cryptosporidium and giardia in the water, a water head pressure is established in the rotary disc filter 10. The head pressure is used to force the water through filter media 18 located on both sides of rotatable filter disc 14.

The filtered Cryptosporidium and giardia are cleaned from the filter media. In one embodiment, the filter media 18 is cleaned by rotating the filter disc 14 such that the backwash cleaning system is able to clean each segment of filter disc 14.

In one embodiment, the method of the present invention includes filtering

Cryptosporidium and giardia from water by forcing the water through homogeneous non-woven fibers. Here, the non-woven fibers make up the non-woven filter media. The method entails capturing or collecting the Cryptosporidium and giardia on the homogeneous non-woven fibers that make up the non-woven filter media. In another embodiment, the present invention entails filtering Cryptosporidium and giardia from the water by forcing the water due to the head pressure in the disc filter through non-woven fibers where the non-woven fibers make up the non-woven filter media and have a diameter of approximately 0.5 μιη and 8.0 μιη. Still in another embodiment of the present invention, the method entails utilizing a disc filter to filter Cryptosporidium and giardia from the water by forcing the water through non-woven fibers that form the non-woven filter media and wherein the non-woven fibers form pores in the filter media that have a nominal pore size of approximately 1-8 μιη. In yet another embodiment of the present invention, the method entails utilizing a rotary disc filter to filter Cryptosporidium and giardia from water by forcing the water with the Cryptosporidium and giardia therein through non-woven nanofibers that have a diameter of approximately 0.1 μιη and 1.0 μιη, and collecting the Cryptosporidium and giardia on the non-woven nanofibers.

Although the present apparatus and methods have been shown and described in considerable detail with respect to only a few exemplary embodiments thereof, it should be understood by those skilled in the art that it is not intended to limit the apparatus or methods to the embodiments since various modifications, omissions, and additions may be made to the disclosed embodiments without materially departing from the novel teachings and advantages of the apparatus and methods, particularly in light of the foregoing teachings.