Patent Description:
Rotary disc filters are designed to filter a liquid, such as water or wastewater, and typically include a drum, a plurality of filter discs secured to the drum, and a backwash system for backwashing filter media forming a part of the filter disc. Liquid to be filtered passes from the drum into the filter disc, which includes the filter media on opposite sides thereof. Liquid in the filter disc flows outwardly through the filter media. In this process, suspended solids in the liquid are captured or retained on the inner surfaces of the filter media. From time-to-time, the filter media is cleaned by a backwashing operation. In the backwashing operation, nozzles disposed exteriorly of the filter disc direct a pressurized backwash through the filter media and into the filter disc. The backwash dislodges the suspended solids retained on the inner surfaces of the filter media. The mixture of backwash and dislodged suspended solids flow by gravity from the filter disc, through openings in the drum, and into a solids trough disposed in the drum.

<CIT>, <CIT>, and <CIT> relate to rotary disc filters and generally describe various conventional features of disc filters. In particular, these references disclose a disc filter for filtering a liquid that comprises a rotary drum for receiving the liquid, and a solids trough that is disposed in the drum that receives a backwash and suspended solids mixture. Moreover, the rotary filter disc includes a series of filter discs where each filter disc comprises a filter frame and filter media on opposite sides of the frame. A drive is provided for rotatively driving the drum and causing the filter disc to rotate with the drum. These rotary disc filters typically are provided with a backwash system for backwashing the filter media, the backwash system including a plurality of nozzles disposed exteriorly of the filter disc and configured to direct backwash through the filter media into the filter disc.

It is challenging, however, to channel all or substantially all of the suspended solids into the solids trough. An accumulation of suspended solids takes place inside the drum and inside the filter disc. Particles of all sizes accumulate in these areas. The reasons for this accumulation are many. A main reason is that <NUM>% of the solids filtered by the filter media do not end up in the solids trough. Some of the solids fall off the media when breaking through the water surface when the drum and filter disc are rotated in a backwashing operation. Other suspended solids fail to reach the solids trough due to a high incoming water speed or a high rotation speed of the filter disc during backwashing. Further, some of the suspended solids captured or retained on the filter media do not end up in the solids trough. All of this tends to result in an inefficient filtering process.

Therefore, there has been and continues to be a need for a rotary disc filter that is designed to more efficiently collect suspended solids and direct them into the solids trough.

Further detailed embodiments are defined in the dependent claims.

The present invention entails a rotary disc filter having backwash guides that are designed to guide a backwash and suspended solids mixture through the filter disc and through openings in the inner periphery of the filter disc after which the backwash and suspended solids pass through openings in the drum and into the solids trough disposed in the drum.

In the present invention, the backwash guides project inwardly from opposite sides of the filter disc and are circumferentially spaced around the filter disc. Backwash guides and the filter media disposed on opposite sides of the filter disc form a series of backwash channels that extend generally between the inner and outer peripheries of the filter disc. Inner end portions of the backwash channels are disposed adjacent openings in the inner periphery of the filter disc. As the filter disc is rotated during the backwashing operation, the backwash channels tend to catch or receive the mixture of backwash and suspended solids and guide the mixture of backwash and suspended solids along the backwash channels and into the openings formed in the inner periphery of the filter disc. Thereafter, the backwash and suspended solids mixture pass through openings in the drum and into the solids trough disposed within the drum.

Other objects and advantages of the present invention will become apparent and obvious from a study of the following description and the accompanying drawings which are merely illustrative of such invention.

With further reference to the drawings and as discussed above, the present invention relates to a rotary disc filter <NUM> that is designed to effectively collect suspended solids in a solids trough <NUM>. This is achieved by a series of backwash guides <NUM> provided in filter discs <NUM> mounted to a rotary drum <NUM>. See <FIG>, <FIG> and <FIG>. Each filter disc <NUM> comprises a filter frame <NUM> and filter segments <NUM> supported in the filter frame. Filter segments <NUM> form filter media disposed on opposite sides of the filter disc <NUM>. Backwash guides <NUM> are spaced inwardly from the filter segments <NUM>. This spacing results in the backwash guides <NUM>, filter frame and the filter segments <NUM> forming backwash channels <NUM> around the interior of the filter disc <NUM>.

In a backwashing operation, the filter discs <NUM> and hence the backwash channels <NUM> are rotated past backwashing nozzles <NUM> that form a part of the backwashing system <NUM> and which are disposed on opposite sides of the filter discs <NUM>. Pressurized backwash from the nozzles <NUM> penetrates the filter segments <NUM> and enters the filter discs <NUM>, and in the process, suspended solids are dislodged from an inner side of the filter segments <NUM>. Backwash that penetrates the filter segments <NUM> does not typically continue in the same direction once inside the filter disc <NUM>. The velocity of the backwash on the inner side of the filter segment <NUM> is relatively low. The backwash which penetrates the filter media tends to run down, by gravity, along the inner sides of the filter media. Expressed in another way, the backwash and suspended solids mixture tends to move by gravity closely adjacent the inner surfaces of the filter segments <NUM>.

Backwash channels <NUM> include open sides that face the direction of rotation of the filter discs <NUM>. As portions of the filter segments <NUM> move towards and past the backwashing nozzles <NUM>, the backwash channels <NUM> tend to catch or scoop the mixture of backwash and suspended solids. Since a substantial portion of the backwash and suspended solids mixture moves adjacent the inner surfaces of the filter segments <NUM>, this facilitates the efficient capture of the mixture. Due to the location of the nozzles <NUM> and the direction of rotation of the filter disc <NUM>, as viewed for example in <FIG>, the backwash and suspended solids mixture tend to move towards and into oncoming backwash channels <NUM>. Once in the backwash channels <NUM>, the backwash and suspended solids mixture is guided inwardly to and through openings 18D formed in the inner periphery 18B of the filter frame <NUM>. From there, the mixture of backwash and suspended solids passes through openings 40A in the drum <NUM> and into the solids trough <NUM> disposed in the drum.

Subsequently, the basic structure and function of the disc filter <NUM> will be described. But first, the focus is on the filter discs <NUM> and the backwash guides <NUM>. <FIG> and <FIG> show a filter disc <NUM> mounted to the rotary drum <NUM>. Drum <NUM> includes an array of openings 40A formed in the surface thereof. Each filter disc <NUM> comprises a filter frame <NUM> and the filter segments <NUM> supported in the filter frame. In the embodiment shown in <FIG>, the filter frame <NUM> comprises a plurality of circumferentially spaced support arms 18A. Support arms 18A extend between an inner periphery 18B and an outer periphery 18C of the filter frame. Inner periphery 18B of the filter frame <NUM> also forms the inner periphery of the filter disc <NUM>. Openings 18D are formed in the inner periphery of the filter disc <NUM>. Openings 18D enable water or liquid to flow from the drum <NUM> into the filter discs <NUM> during the filtering process. They also allow a mixture of backwash and suspended solids to flow from the filter discs <NUM> through openings 40D in the drum <NUM> and into the solids trough <NUM> disposed in the drum.

As noted above, in one embodiment during a backwashing operation, filter discs <NUM> rotates counterclockwise as viewed in <FIG>. Backwash guides <NUM> project from one side of the support arms 18A in the direction of rotation of the filter discs <NUM>. Backwash guides <NUM> can be integrally formed with the filter frame <NUM> and particularly with the support arms 18A attached or fastened to a particular filter frame structure or integrally formed with the filter segment <NUM>.

During a backwashing operation, the nozzles <NUM> are disposed exteriorly of the filter discs <NUM> and direct a pressurized backwash through the filter segments <NUM>. In the process, suspended solids filtered by the filter segments <NUM> and retained on the inner side thereof are dislodged. This results in a mixture of backwash and suspended solids in the filter discs <NUM>. The function of the backwash guides <NUM> and backwash channels <NUM> is to guide the mixture of backwash and suspended solids out of the filter discs <NUM> and into the solids trough <NUM>.

To better illustrate the backwash guides <NUM> and how they facilitate the efficient capture and removal of the backwash and suspended solids mixture, reference is made to <FIG> is a schematic cross-sectional illustration showing a portion of the filter frame <NUM>, filter segments <NUM> and the backwash guides <NUM>. As noted above, filter frame <NUM> includes support arms 18A and they are schematically illustrated in <FIG>. Support arms 18A include an inner portion 18A1, an outer portion 18A2, and a cross portion 18A3. Again, this is a schematic illustration and in one embodiment the transversely aligned support arms 18A shown in <FIG> can be interconnected. In any event, the support arms 18A form back-to-back grooves that receive and hold seals <NUM>. Filter segments <NUM> which include a surrounding frame and filter media are in turn received and held in the seals <NUM>.

Continuing to refer to <FIG>, the backwash guides <NUM> project from one end of the inner portions 18A1. Again, the backwash guides <NUM> project in the direction of rotation of the filter discs <NUM> during backwashing as shown in <FIG> and <FIG>. Note that the backwash guides <NUM> also project inwardly into the filter disc <NUM>. Further, the backwash guides <NUM> are circumferentially spaced around the filter disc <NUM>. Backwash guides <NUM> are arranged in pairs. That is, two backwash guides <NUM> are transversely aligned and disposed across from each other. The backwash guides <NUM> project slightly towards each other. This forms an open space <NUM> between each pair of backwash guides <NUM>. This open space enables water or liquid to pass through the open space when the filter discs <NUM> are rotated.

Backwash guides <NUM> in one embodiment effectively form an elongated edge that extends between the inner and outer peripheries 18B and 18C of the filter frame <NUM>. Further, the backwash guides <NUM>, along with portions of the support arms 18A, seals <NUM> and filter segments <NUM> form the backwash channels <NUM>. During a backwashing operation, the backwash channels <NUM> effectively entrap a mixture of backwash and suspended solids and guide or direct the mixture to openings 18D formed in the inner periphery 18B of the filter frame <NUM>. As noted before, this enables the backwash and suspended solids mixture to pass through the array of openings 40A in the drum <NUM> and into the underlying solids trough <NUM>.

As noted above, during a backwashing operation, the drum <NUM> and the filter discs <NUM> can be rotated. Filter segments <NUM> are rotated to an upper position on the disc filter <NUM> where the nozzles <NUM> are stationed. As the backwash guides <NUM> approach the nozzles <NUM> and move past the nozzles, backwash from the nozzles <NUM> penetrate the filter segments <NUM> and enter the interior of the filter discs <NUM>. When this happens, the backwash and dislodged suspended solids form a mixture. The backwash guides <NUM> tend to urge the backwash and suspended solids mixture into the backwash channels <NUM>. The backwash guides <NUM> and the backwash channels <NUM> tend to catch or scoop the backwash and suspended solids mixture that ends up inside the filter disc <NUM>. Once in the backwash channels <NUM>, the backwash and suspended solids mixture is directed along the channels <NUM>. Inner portions of the backwash channels <NUM> terminate adjacent the openings 18D in the inner periphery 18B of the filter frame or filter disc. Thus, the backwash channels <NUM> effectively guide or direct the backwash and suspended solids mixture into the openings 18D of the filter frame <NUM>. From there, as discussed above, the backwash and suspended solid mixture passes through openings 40A in the drum <NUM> and into the solids trough <NUM>.

In some embodiments, the filter frame <NUM> is modular and is constructed of interchangeable modules. The modules can be constructed of plastic or other suitable materials. With reference to <FIG>, there is shown therein one of the modules <NUM> employed in the filter frame <NUM> shown in <FIG>. In this example, the module <NUM> is constructed of plastic and includes a base <NUM>. Bases <NUM> of the modules form the inner periphery 18B of the filter frame <NUM>. Note that the bases <NUM> are interconnected in back-to-back relationship and secured around and to the drum <NUM>. Each base <NUM> includes openings on opposite sides. These openings form openings 18D in the inner periphery 18B of the filter frame. Extending upwardly from the bases <NUM> are the support arms 18A that has been discussed above. As seen in <FIG>, outer covers <NUM> are interconnected between adjacent modules <NUM>. Thus, the modules <NUM>, along with the outer covers <NUM>, form the filter frame <NUM> shown in <FIG>.

Formed on opposite sides of each module <NUM> is a pair of filter grooves. These filter grooves receive the surrounding frames of respective filter segments <NUM>. A seal can be interposed between the filter segments <NUM> and the filter grooves.

<FIG> depicts one way in which the backwash guides <NUM> can be incorporated into the modules <NUM>. Note that a pair of backwash guides <NUM> extends along a leading side of the support arms 18A of the modules <NUM>. In particular, each backwashing guide <NUM> is integrally formed with a portion of the support arms 18A and projects slightly inwardly therefrom in the manner illustrated in <FIG>. Therefore, on the leading side of each support arm 18A there is provided a pair of backwash guides <NUM> that extend over a substantial length of the support arms 18A. Note that these backwash guides <NUM>, in conjunction with the modules <NUM> and the filter segments <NUM>, also form a pair of backwash channels <NUM> on leading sides of the support arms. Backwash channels <NUM> include inner terminal ends that terminate adjacent the openings in the bases <NUM>. Thus as described above, during a backwashing operation backwash channels <NUM> function to guide and direct a mixture of backwash and suspended solids to the openings formed in the bases <NUM> of the modules <NUM>. And like discussed above, the openings in the bases <NUM> are aligned with openings 40A of the drum <NUM> and hence the backwash and suspended solids mixture passing from the openings in the bases <NUM> flows through the openings 40A into the underlying solids trough <NUM>.

The volume and dimensions of the backwash channels <NUM> can vary. This is especially the case because the width of the filter disc <NUM> varies from one disc filter to another. <FIG> uses L, H and ϕ to denote dimensions and an angle relative to the backwash guides <NUM>. Again, the length of L and H, as well as the angle ϕ, will vary. However, in exemplary embodiments, L would typically be <NUM>-<NUM>, H <NUM>-<NUM>, and ϕ <NUM>°-<NUM>°.

<FIG> illustrates how the backwash guides <NUM> and the backwash channels <NUM> facilitate the recovery of the backwash and suspended solids mixture and how they guide and direct the mixture into the solids trough <NUM>. The flow of the backwash and suspended solids mixture is shown by heavy dotted lines and arrows in <FIG> does not show the backwash channels <NUM>. The dotted lines and arrows are meant to simply represent the flow of the backwash and suspended solids mixture through the respective filter discs <NUM>. Note also in <FIG> where the flow of the mixture passes through openings 18D in the inner periphery of the filter frame and from there through the array of openings 40A formed in the drum and then into the underlying solids trough <NUM>.

The filter discs <NUM>, drum <NUM>, along with the backwash guides <NUM> and the backwash channels <NUM> are incorporated into a disc filter <NUM>. It may be beneficial to briefly review the basic design of an exemplary disc filter. The disc filter <NUM>, shown in <FIG> and <FIG>, includes a housing. Some rotary disc filters (a second type) are not provided with a substantial housing structure. These disc filters are often referred to as frame-type disc filters as they are designed to be installed in a pre-formed concrete basin. There is yet a third type or version of a disc filter which includes a half tank or frame with a bottom and sides and which only reaches to about the center of the drum of the disc filter.

In any event, either type of disc filter is provided with a frame structure for supporting various components that make up the disc filter. In this regard, the drum <NUM> is rotatively mounted on the frame structure of the disc filter. Generally the drum <NUM> is closed except that it includes an inlet opening and the array of openings 40A discussed above. The filter discs <NUM> are secured to the drum <NUM> and rotatable therewith during a backwashing operation. During the filtering of water or liquid, influent water or liquid is directed into the inlet of the drum <NUM> and from the drum into the filter discs <NUM> secured on the drum. The number of filter discs <NUM> secured to the drum can vary. A water holding area is defined inside each filter discs <NUM> for receiving and holding water or liquid to be filtered by the disc filter <NUM>. Head pressure associated with the influent liquid or water is effective to cause the water or liquid to flow outwardly from the filter discs <NUM> and through the filter segments <NUM>. Water exiting the filter discs <NUM> is filtered water or filtrate. As discussed above, this results in suspended solids in the water or liquid being captured or retained on the inner surfaces of the filter segments <NUM>.

Filtered water or liquid exiting the filter discs <NUM> is collected in a holding chamber that underlies the filter discs. This holding chamber or area includes an outlet that enables the filtered water or liquid to be discharged from the disc filter <NUM>.

During the backwashing operation, it is necessary for the drum <NUM> and the filter discs <NUM> mounted thereon to rotate. Disc filter <NUM> is provided with a drive system for rotatively driving the drum <NUM> and the filter discs <NUM>. In the case of the embodiment illustrated in <FIG> and <FIG>, mounted to a panel or wall structure about the back portion of the disc filter <NUM> is a drum motor <NUM> that is operative to drive a sprocket or sheave connected to a shaft on which the drum <NUM> is mounted. Various means can be operatively interconnected between the drum motor <NUM> and the sprocket or sheave for rotating the drum <NUM>. In one example, a chain drive is utilized to drive a sprocket secured to the shaft that rotates the drum <NUM>. Various other types of drive systems can be utilized to rotate the drum and the filter discs <NUM>. In some cases, for example, there may be a direct drive on the drum shaft from a gear motor.

Returning to the backwash system <NUM> discussed above, the system comprises a backwash pump <NUM>, a manifold <NUM> that extends along a side portion of the disc filter <NUM>, and a series of feed tubes <NUM> connected to the manifold <NUM> and projecting inwardly therefrom. Feed tubes <NUM>, sometimes referred to as inner pipes, project from the manifold <NUM> into areas between respective filter discs <NUM>. Secured to the feed tubes <NUM> are a series of nozzle holders or nozzle bars <NUM>. Nozzles <NUM> are mounted on the nozzle bars <NUM>. In a preferred embodiment, the backwash pump <NUM> forms a part of the disc filter. In other embodiments, pressurized backwash can be provided from a source other than a backwash pump that forms a part of the disc filter <NUM>.

Manifold <NUM> can be rigidly mounted or rotatively mounted along one side of the disc filter <NUM>. In some cases, manifold <NUM> is operatively connected to a drive (not shown) that can be indirectly driven from the drum motor <NUM>. In any event, the manifold <NUM>, during a cleaning operation, can oscillate back and forth, which results in the nozzles <NUM> sweeping back and forth between the filter discs <NUM> so as to backwash particular areas of the filter segments <NUM> disposed on opposite sides of the filter discs <NUM>. In other cases, the manifold <NUM> is rigidly mounted and does not oscillate back and forth during the backwashing operation.

There are many advantages to the backwash guides <NUM>. They assure that a larger percentage of the backwash and suspended solids mixture end up in the solids trough <NUM>. One measure of the effectiveness of the backwash guides <NUM> can be appreciated from examining what is referred to herein as "separation speed of suspended solids" (mg separated suspended solids/s). In order to determine the separation speed of suspended solids, the first step is to measure the flow of the backwash and suspended solids mixture being discharged by the disc filter <NUM>. Secondly, a sample of the flow of the backwash and suspended solids mixture is taken and a total suspended solids (TSS) test is carried out which gives the concentration of suspended solids (mg/L) of the backwash and suspended solids mixture. The separation speed of the suspended solids is defined as the product of the flow and the suspended solids concentration. The employment of the backwash guides <NUM> will, in most cases, increase the separation speed of the suspended solids.

Claim 1:
A rotary disc filter (<NUM>) for filtering a liquid comprising:
a rotary drum (<NUM>) for receiving the liquid and having a plurality of openings formed in a surface thereof;
a solids trough (<NUM>) disposed in the drum and configured to receive a backwash and suspended solids mixture;
one or more filter discs (<NUM>) secured to the drum and configured to receive liquid from the drum and filter the liquid as the liquid flows outwardly from the filter disc through filter media forming a part of the filter disc;
wherein the filter disc comprises a filter frame (<NUM>) that supports the filter media on opposite sides thereof;
the filter disc including a plurality of openings (18D) formed in an inner periphery of the filter disc;
a drive for rotatively driving the drum and causing the filter disc to rotate with the drum;
a backwash system for backwashing the filter media and including a plurality of nozzles (<NUM>) disposed exteriorly of the filter disc and configured to direct the backwash through the filter media and into the filter disc where the backwash dislodges suspended solids from the filter media and a backwash and suspended solids mixture is formed;
a plurality of backwash guides (<NUM>) secured to or integrally formed with the filter frame and projecting inwardly from the filter frame into the filter disc, the backwash guides projecting inwardly from opposite sides of the filter disc into the interior of the filter disc and including elongated edges that angle inwardly with respect to the filter media;
the backwash guides and a portion of the filter disc form a series of backwash channels (<NUM>) that extend through the filter disc;
wherein the backwash channels extend generally toward the openings in the inner perimeter of the filter disc; and
wherein in a backwashing operation, the backwash channels are configured to receive at least a portion of the backwash and suspended solids mixture and to direct the backwash and the suspended solids to the openings in the inner perimeter of the filter disc where the backwash and suspended solids pass through the openings in the drum and into the solids trough.