Abstract:
A filter media support system that reduces media clogging and head loss in granular filtration systems by providing a layered porous plate. The porous plate can have multiple layers of fine sized and coarse sized pores. The porous plate is positioned between the media and the filter bottom. The filter media support system is securely anchored to the infrastructure of the underdrain system thereby inhibiting media penetration of the filter bottom and avoiding seal failures. The infrastructure can be air lateral piping fitted beneath the underdrain blocks of the support system. The anchors can be secured to pipe clamps circumscribing the air laterals.

Description:
CROSS REFERENCES TO RELATED CASES  
       [0001]    This is a continuation of U.S. Provisional Patent Application, Ser. No. 60/017,052 filed Apr. 26, 1996, now abandoned, International Application No. PCT/US97/06800, filed Apr. 24, 1997 and U.S. patent application Ser. No. 09/176,147, now U.S. Pat. No. ______. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates to a fluid treatment media support system for granular filters. More specifically the invention relates to a fluid treatment media support system using a porous plate, a layered porosity pattern in the porous plate, and an anchoring system for the porous plate. The fluid treatment media supported by the system of this invention can be a filtration media or other media such as an ion exchange resin.  
         BACKGROUND OF THE INVENTION  
         [0003]    Water, wastewater and industrial liquid granular filtration units typically have a filter media support system that separates the filter media from the underdrain system and filter bottom. The underdrain system is the primary support for the filter media, and also serves to collect the filtrate and provide for the uniform distribution of air and water during the backwash of the filter system.  
           [0004]    Underdrain systems are often made of concrete blocks having spaces to allow for piping, such as air laterals, that are part of the backwash air distribution system. A precast concrete, plastic-jacketed underdrain block is disclosed in U.S. Pat. No. 4,923,606. Nozzle-less type underdrain systems with large openings for the passage of the filtrate and the backwash water are preferred because they do not plug as easily as nozzle type underdrains. Because the openings in nozzle-less underdrains are larger than the size of the individual grains of the media, however, it is necessary to use a media support system between the underdrains and the media.  
           [0005]    A media support system serves several purposes that are conflicting. For example, very fine media, such as 0.1 to 0.5 mm sand, may be used in potable water type filters. Consequently, a very fine media support is needed to separate this media from the underdrain system and filter bottom and prevent plugging and loss of filter media. Plugging of the underdrain system filter bottom causes a loss of the filtering capacities of the bed and downtime of the filter system. However, large or coarse-pore media support is necessary to promote the formation of larger air bubbles which are desired because they wash a filter better than fine bubbles of air. Jung &amp; Savage,  Deep Bed Filtration, Journal American WaterWorks Association , February, 1974, pp. 73-78.  
           [0006]    Two types of media support systems have been in common use: (1) support gravel beds comprised of graded gravel placed between the filter media and the filter bottom (or underdrain system) and (2) uniformly porous plates that are anchored to the side walls of the filter or to the underdrain blocks.  
           [0007]    When layered gravel beds are used for media support systems, the bed of gravel is usually 12 to 18 inches in height with several layers of varying size gravel. The layers of gravel adjacent to the media and filter bottom are usually coarse and the intermediate layer or layers smaller or finer in size. The finer intermediate gravel layer inhibits the penetration of the media to the underdrain blocks. The coarser gravel in the top or cap layer, however, inhibits plugging of the fine gravel layer. If the finer media penetrates the gravel layers during filtration, it accumulates in the cap layer and is then washed out during the backwash cycle of the filtration process.  
           [0008]    U.S. Pat. No. 1,787,689 to Montgomery and U.S. Pat. No. 1,891,061 to Friend et al., for example, disclose a water treating tank containing zeolite water softeners. The gravel beds of the tanks are arranged in an hourglass configuration with layers of coarser and finer gravels.  
           [0009]    Gravel layers have several disadvantages including difficulty in installation, the need for deeper filter boxes to allow for the depth of the gravel and higher costs. Also, the gradation of the gravel layers tends to be disturbed during the filtration and backwashing processes and downtime may be required to restore the desired gradation.  
           [0010]    Porous plates have been used to replace gravel layers. Porous plates are typically manufactured from sintered plastics. Plastic porous plates, however, are usually buoyant and need to be secured in some way to prevent lifting, especially during the backwash cycle. Prior art methods of securing the porous plate include a combination of screwing and caulking or grouting the plate to the underdrain blocks as disclosed in U.S. Pat. No. 5,149,427 to Brown, or bolting the plate to the underdrain blocks.  
           [0011]    U.S. Pat. No. 4,882,053 to Ferri discloses a porous plate used in a filter system without underdrain blocks; the porous plate is attached by a retaining angle secured to each wall of the filter box. The retaining angle holds the plate in place and a seal is made by a sealant bead applied between the side walls and the porous plates.  
           [0012]    Problems arise with the above-referenced methods of anchoring the porous plates. Small irregularities in the floor of the filter, the underdrain blocks and the plates can cause seal failures between the plates. Seal failure allows media to penetrate the media support system, causes a progressive failure of the filter underdrain and then of the filter system itself. The underdrains, effluent piping, and clearwell may become plugged with media and the filter bottom may collapse due to excessive pressures which develop during backwash.  
           [0013]    U.S. Pat. Nos. 5,149,427 and 5,232,592 to Brown disclose a cap for filter underdrain blocks comprising a porous, planar body. The body of the cap is said to be adapted to support a fine grain filter media without the media penetrating therethrough. The pores in the cap body are approximately 700-800 microns in size.  
           [0014]    U.S. Pat. No. 4,882,053 to Ferri, mentioned above, discloses a support or drain plate for filter media comprising porous heat-fusible polyethylene in a traveling bridge filter. The porous drain plates have narrow heat fused, non-porous bands extending vertically through the plates. These bands provide rigidity to the plates said to decrease bowing and subsequent channeling of water during backwash experienced with lap joints. However, the non-porous bands would tend to reduce permeability during filtration and increase head loss.  
           [0015]    U.S. Pat. No. 667,005 to Davis discloses a filter bottom for a granular bed that includes three sheets or layers of wire cloth. The upper layer and lower layer are coarse with the intermediate layer being a fine mesh. U.S. Pat. 2,267,918 to Hildabolt discloses a porous article formed from metal powders and having plural layers of different porosity. U.S. Pat. No. 5,468,273 to Pevzner et al. discloses a nickel-based filter material having three strata of different porosity used for removing contaminants from air.  
         SUMMARY OF THE INVENTION  
         [0016]    The filter media support system of the present invention is a barrier between the media of a filter and its underdrain system. The filter media support system reduces media clogging and head loss by providing a layered porous plate having multiple layers of fine sized and coarse sized pores to restrain media grains and waste solids from entering and damaging the underdrain system. The filter media support system further provides an anchor for securely anchoring the porous plate to the infrastructure of the filter bottom, thereby inhibiting media penetration to the filter bottom and avoiding seal failures.  
           [0017]    In one aspect, the present invention provides a system for supporting granular filter media above a filter bottom. The system has a porous plate which is placed over the filter bottom to support the filter media. The porous plate includes adjacent layers of different porosity. Preferably, the porous plate includes a relatively coarse pore size layer adjacent to the filter bottom, and a relatively fine pore size layer above the coarse pore size layer. If desired, the porous plate can also include a relatively coarse pore size layer above the fine pore size layer. The coarse layer preferably has a pore size of from 500 to 5000 microns, and the fine layer preferably from 150 to 1500 microns.  
           [0018]    The porous plate is preferably supported on a layer of underdrain blocks on the filter bottom. The porous plate preferably has a larger horizontal dimension than that of the individual underdrain blocks. In this manner, a plurality of underdrain blocks support the porous plate. The porous plate can be anchored to air laterals beneath the underdrain blocks, or other infrastructure. The porous plate preferably comprises sintered polyethylene, although it could also be made from ceramics, metals, polymers and the like. The porous plate preferably includes lap joints between adjacent sections.  
           [0019]    In another aspect, the present invention provides a filter which has upright walls defining at least one compartment housing granular filter media supported above a filter bottom on the porous plate with the layers of different porosity just described.  
           [0020]    In a further aspect, the present invention provides a filter system for supporting granular filter media above a filter bottom which has a layer of underdrain blocks placed over infrastructure of the filter bottom. A porous plate is placed over the underdrain blocks to support the filter media. Anchors extend from the porous plate through the layer of underdrain blocks to secure the porous plate to the infrastructure. The infrastructure can include a plurality of air laterals running beneath the underdrain blocks, and the anchors are preferably secured to the air laterals. The underdrain blocks are preferably arranged end-to-end in rows over the air laterals and the porous plate preferably has a larger horizontal dimension than the individual underdrain blocks. In this manner, the porous plate covers a plurality of the underdrain blocks, and the anchors can extend between adjacent ends of the blocks.  
           [0021]    The upper ends of the anchors are preferably secured to bars positioned over the porous plate which run transversely to the rows of the underdrain blocks. The porous plate can include lap joints parallel to the rows of underdrain blocks. The anchors preferably pass through a bore formed through an overlap of the joint between adjacent porous plate sections. The sides of adjacent underdrain blocks are preferably interconnected by lugs.  
           [0022]    Yet another aspect of the invention is a filter having upright walls defining at least one compartment housing granular filter media supported above a filter bottom which includes a porous plate anchored to the infrastructure of the filter bottom as just described. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0023]    [0023]FIG. 1 is a perspective view, partially cut away, of a section of the filtration system illustrating the filter media support system according to one embodiment of this invention.  
         [0024]    [0024]FIG. 2 is a perspective view of a section of the filtration system illustrating the backwash flow through the filter media support system of FIG. 1.  
         [0025]    [0025]FIG. 3 is a cross-section of the filter media support system of FIG. 1 taken along lines  3 - 3 .  
         [0026]    [0026]FIG. 4 is an enlarged view of a section of FIG. 3.  
         [0027]    [0027]FIG. 5 is a perspective view, partially cut away, of the layered porosity plate according to one embodiment of this invention.  
         [0028]    [0028]FIG. 6 is a cross-section of the filter media support system of FIG. 1 taken along lines  6 - 6 .  
         [0029]    [0029]FIG. 7 is an enlarged view of a section of FIG. 6.  
         [0030]    [0030]FIG. 8 is a plan view of the filter media support system of FIG. 1. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0031]    The filter media support system of this invention is directed to a porous plate, preferably of graded porosity, and a anchor system for securely anchoring a porous plate to the infrastructure of the underdrain system. The media support system of this invention is not a filter in itself and does not perform filter functions. Fitration occurs within the filter media. The media support system of this invention serves two functions: 1) it supports the filtering media and 2) restrains media grains and waste solids from entering the underdrain system where they can cause extensive damage, clogging and headloss. FIG. 1 illustrates a section of a filtration system  10  and a porous plate  20  securely anchored within that system  10 . A filtration system  10  is usually used to filter water, including potable water and wastewater and can also be used for ion exchange or other absorption processes. The filtration system  10  has a filter box  100  containing granular media  90 , such as sand, anthracite, activated carbon, ion exchange resin, or the like, or a combination thereof. Filter influent flows into the filter box  100 , through the media  90  for the removal of suspended solids. During the water treatment process, the filter influent is filtered by the media  90  and than drains through the underdrain system  50  to the bottom of the filter box  102  where it collects in a sump  104 . The porous plate  20  of this invention is a barrier between the filter media and the underdrain to restrain the media and any suspended solids from passing through and damaging the underdrain  50 . Backwash sends any media grains and waste solids that are restained by pores of the porous plate  20  back up into the filtration media  90 .  
         [0032]    During the backwash phase of the filtration cycle, normal downward filtration stops and an upflow of liquid, usually water, and gas, usually compressed air, cleanse the filter system. As seen in FIG. 2, backwash water from backwash pumps (not shown) is pumped into the sump  104  and through the filter system  10 . Backwash air is supplied via headers  110  located on either side of the filter box  100 , and through air laterals  60  into the filter system  10 .  
         [0033]    The porous plate  20  is positioned between the media  90  and the underdrain blocks  40 , thereby supporting and separating the filter media  90  from the underdrain system  50 . As illustrated in FIG. 5, the porous plate  20  has a reverse gradation of coarse and fine pore layers. In a preferred embodiment of the invention, a relatively coarse pore layer  20   c  is adjacent the underdrain blocks  40  and another relatively coarse pore layer  20   a  is adjacent the filter media  90 . A relatively fine pore layer  20   b  lies between the two coarse pored layers  20   a ,  20   c . Varying size pores are beneficial in media support systems. A fine pore layer  20   b  is necessary to separate fine media  90 , 0.1 to 0.5 mm sand for example, from the underdrain system. The fine pore layer  20   b  prevents clogging of the underdrain system  50  and loss of filter media  90 . The coarse pore layer  20   c  of the porous plate  20  promotes the formation of large air bubbles which wash the filter system better than fine air bubbles. Also, if any media penetrates the porous plate  20  during the filtration cycle, it will accumulate in the top coarse pore layer  20   a  and is readily washed out during the backwash cycle.  
         [0034]    In a preferred embodiment, the pore size of the coarse layers  20   a ,  20   c  range from 500 to 5000 microns. The pores in the fine pore layers range from 150 to 1500 microns.  
         [0035]    The porous plate  20  of this invention may be manufactured from ceramics; metals, particularly sintered metals such as nickel, titanium, stainless steel and the like; and polymers, such as polyethylene, polypropylene or polystyrene; or any suitable material. In a preferred embodiment, the material is a sintered polyethylene. The porous plate  20  can be formed by sintering heat-fusible particles to the desired shape. Other heat-fusible materials may be used such as polypropylene or the above referenced group of materials. The porous plate  20  can include different adjacent layers of different porosity fused integrally together, or the layers can be formed by stacking sheets of different porosity together where each sheet corresponds to a specific porosity layer.  
         [0036]    The length and width of the porous plates  20  may vary according to the size of the underdrain blocks  40  or bottom of filter box  102 . In a preferred embodiment, the porous plate  20  has a larger horizontal area or dimension than the individual underdrain blocks  40  so that the porous plate  20  covers a plurality of underdrain blocks  40 . In another preferred embodiment, the porous plates have widths in multiples of the width of the underdrain blocks  40 . The preferred thickness of the porous plate  20  varies from 1 inch or less to 2 inches or more, depending on the particular application.  
         [0037]    A porous plate  20  manufactured from sintered polymers tends to be buoyant and float. FIGS. 4 and 7 illustrate the improved anchoring of the porous plate  20  of one embodiment of this invention. The porous plate  20  is secured to the infrastructure  60  of the bottom of filter box  102  rather than the side walls  106  of the filter box  100  as done in the prior art media support systems. In one alternative, the porous plate  20  can be anchored to the underdrain blocks  40 . Anchoring the porous plate  20  to the infrastructure  60  improves the seal to prevent lifting and bowing, especially during the backwash cycle. Infrastructure  60  includes but is not limited to air laterals, air headers, floor of filter, sump cover plates, air lateral anchors, piping and support.  
         [0038]    In a preferred embodiment of this invention, the porous plate  20  is anchored to the air lateral piping  60  which supplies the backwash air. The air laterals  60  are run in spaces  42  between block legs  44  of the underdrain blocks  40 . An air lateral  60  can be placed between the legs  44  of every other row of blocks  40 . A preferred underdrain block  40  is described in U.S. Pat. No. 4,923,606 the disclosure of which is hereby incorporated by reference in its entirety. Briefly, as best seen in FIGS. 6 and 7, the underdrain blocks  40  are arranged end-to-end in rows over the air laterals  60 , and the sides of adjacent underdrain blocks  40  are interconnected by lugs  48 . Preferably, the porous plate  20  has a larger horizontal area than the individual blocks  40  so that the porous plate  20  covers a plurality of the underdrain blocks  40 . Anchors  26  extend from the porous plate  20  between adjacent ends of the blocks  40  to the air laterals  60 . An indentation (not shown) is preferably formed in the opposing ends of the adjacent blocks  40  to accommodate the cross-section of the anchors  26 . Alternatively, the anchors  26  could extend directly through an aperture formed in the blocks  40  to an attachment point on the bottom of filter box  102 . In still another alternative, anchors  26  can extend between the lateral sides of the blocks  47  down to the infrastructure.  
         [0039]    Preferably, the upper ends of the anchors  26  are secured to bars  30  positioned over the porous plate  20 . The bars  30  preferably run transversely to the underdrain blocks  40  and help to hold the porous plates securely in place. This inhibits bowing or lifting of the porous plate  20 . Suitable bars  30  are manufactured of a corrosion-resistant metal such as stainless steel and are approximately  2  inches in width and ¼ inch in depth. The preferred anchor  26  is a threaded rod manufactured from a corrosion-resistant metal such as stainless steel. The anchor  26  is secured to the porous plate  20  by a fastener, preferably a nut  27   a  and an oversized washer  27   b . Additional sealants may be used to prevent leakage in the bore through the plate  20  around the rod  26 .  
         [0040]    [0040]FIG. 6 illustrates sections of the porous plate  20  joined together by overlapping the ends of adjacent sections of the porous plate  20  at lap joints  24 . The lap joints  24  run parallel to the rows of underdrain blocks  40 . The anchors  26  pass through the bar  30 , through the porous plate  20  by means of a bore in the lap joints  24  and between the underdrain blocks  40 , and are secured to the air laterals  60 . Preferably, the anchors  26  are secured to the air laterals  60  by pipe clamps  62  circumscribing the air laterals  60  as illustrated in FIGS. 4 and 7. Lateral support angles  76  grouted into the bottom of filter box  102  can provide additional support for the air laterals  60 . As depicted in FIG. 3 support brackets  36  can also be used, if desired, to secure the porous plate  20  to the walls of the filter box  100 .  
         [0041]    The porous plate  20  of the present invention may be installed in new filtration systems or retrofitted into existing systems. A filter box  100  having side walls  106  and a bottom  102  is constructed conventionally with an infrastructure  50  of air lateral piping  60  across the bottom of filter box  102  and a sump  104  and sump cover plate  105  for collection of filtrate during the filtration process and for the supply of backwash water during backwashing operations. Pipe clamps  62  are placed around the air laterals  60  and anchors  26  secured to the pipe clamps  62 . The underdrain blocks  40  are arranged in rows over the air laterals  60  so that the air laterals  60  lie in spaces  42  between the block legs  44  with an air lateral  60  under every other row of blocks  40 . The blocks  40  are spaced apart to create a gap  45  which provides for air and water flow. The anchors  26  extend upward between the blocks  40 . The beveled configuration of the top of the blocks  40  creates a channel into the gap  45 . The blocks  40  can be interconnected with lugs  48  sized to provide the desired size of gap  45 . Additional sealing can be provided by grouting the perimeter blocks  40  to the filter box  100 . The blocks  40  should be of a weight to resist lifting and shifting, especially during the backwash phase but not so heavy as to prohibit easy handling.  
         [0042]    After the underdrain system is in place, the sections of the porous plate  20  are placed over the rows of blocks  40  and joined by lap joints  24  which run parallel to the blocks  40 . Bores, preferably pre-formed, pass through the upper lips  24   a  and lower lips  24   b  of the adjacent sections of the porous plate  20  for receiving anchors  26  extending upwards from the rows of blocks  40 , thereby improving the seal of the lap joints  24 . A stainless steel bar  30 , running transversely to the blocks  40 , is placed over the lap joints  24 . The anchors are then secured by nuts  27   a  and washers  27   b . Larger sheets of porous plate  20  can be made by further sealing the lap joints  24  by means of mastic, epoxy glues or thermal welding; however, this should be avoided as much as possible to minimize decreasing the permeability of the porous plate  20 . The anchors  26  thus extend through the bar  30 , through the bores in the lap joints  24 , between the underdrain blocks  40  and are secured to pipe clamps  62  circumscribing the air laterals  60 .  
         [0043]    After the filtration media support system is in place, filter media  90  may be installed and operation of the filtration cycle initiated as the filter influent flows into the filter box  100 . Periodically, the filtration process may be stopped so that the filtration system may be backwashed.  
         [0044]    The anchors  26  of the present invention securely hold the porous plate  20  to the air laterals  60 , thereby reducing lifting and bowing that is induced especially by the pressures exerted during the backwash cycle. The graded porosity layers of the plate  20  create larger air bubbles during the backwash cycle which wash the filter system better than fine bubbles, and yet provide fine pores for inhibiting media particles  90  from entering the underdrain system  50  during the filtration cycle.  
       EXAMPLE  
       [0045]    Air spreading tests are performed to observe and record the impact of the reverse-gradient porous plate of this invention on backwash air distribution. During the first test, a 600-700 micron ¾-inch thick porous plate is put in place. Underdrain blocks, specifically 8-inch wide T-blocks are installed in the test column, the column is filled with water up to the overflow weir and backwash air added at a rate of 2.0 CFM/ft 2 . The test is repeated at air rates of 4.0 CFM/ft 2  and 6.0 CFM/ft 2 . A standard is used to measure the size of the air bubbles. The results are photographed and data recorded. An uneven air pattern occurs during the backwash and the air bubbles are relatively small.  
         [0046]    The tests are repeated with the layered porosity porous plate in place at the same three air rates. The porous plate has coarse-pore layers of about ⅜-inch thickness having a pore size of approximately 600 microns and an intermediate fine-pore layer of about ⅜-inch thickness having a pore size of approximately 350 microns. The thickness of the entire plate is about 1⅛ inches. The porous plate produces a more even pattern of air distribution, relatively larger air bubbles, and the pressure drop is comparable to the uniform-porosity plate.  
         [0047]    The foregoing description is illustrative and explanatory of preferred embodiments of the invention, and variations in the size, shape, materials and other details will become apparent to those skilled in the art. It is intended that all such variations and modifications which fall within the scope or spirit of the appended claims be embraced thereby.