Abstract:
A filter unit for use in a casing disposed in a septic tank comprising a plurality of stacked filter plates. The individual filter plate is preferably substantially “D” shaped in circumference and has a substantially cone-shaped floor, tapering upward. The filter plates are preferably stacked in a superposed, spaced-apart manner with a particular diameter in relationship to the inner diameter of the case. The filter plates are preferably inserted into the filter case to define a seal horizontally around the bottom opening in the case, thereby allowing wastewater to enter into the filter plates to begin the filtering process. Solids preferably flow upward into the filter plates, where they are separated by size with a predetermined gap in the stacked filter plates.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims priority under 35 USC §119(e) to U.S. Provisional patent application Ser. No. 60/723,645, entitled: WASTEWATER TREATMENT SYSTEM EFFLUENT FILTER, filed Oct. 4, 2005, the entire content of which is incorporated herein.  
       FIELD OF THE INVENTION  
       [0002]     The present invention is directed to filter devices for filtering liquids containing particulate matters such as wastewater. More specifically, the present invention is directed to a self-contained filter unit for use in a filter housing adapted to be mounted at the outlet of a septic tank or similar device.  
       DESCRIPTION OF PRIOR ART  
       [0003]     A septic tank is the first component in a private wastewater system. It is typically a large, underground, watertight container that typically ranges in size from 1,000- to 1,500-gallon capacity. In addition to the overall physical size, tanks also vary according to the internal configuration based upon whether the tank is a single or double compartment container. The number of bedrooms in a house usually determines the actual size of the septic tank.  
         [0004]     Raw water flows from the kitchen, bathrooms and laundry room into the tank, where the solids are separated from the liquid. The heavier solids settle to the bottom of the tank, where bacteria gradually decompose them. However, some of the solids will remain, forming a sludge layer that will eventually have to be pumped out.  
         [0005]     The lighter solids, such as fats, oils and greases, will flow to the top and gradually thicken forming a scum layer. This scum layer will also eventually have to be pumped out. The liquid waste, which is in between the scum layer and the sludge layer, typically goes to the drain field.  
         [0006]     The last component in the system is the drain field. The soil below the drain field is the final disposal area for the liquid waste, commonly referred to as effluent. The drain field will last indefinitely unless it is forced to handle large particles, which will cause it to clog. Once the system becomes clogged, effluent will either rise to the surface above the drain field or back up into the home.  
         [0007]     An effluent filter protects the drain field by keeping large particles in the tank while allowing the effluent to flow to the drain field. The drain field is the most expensive part of the septic system, costing thousands of dollars to repair or replace.  
         [0008]     A typical septic tank comprises three layers: 1) a solids layer at the bottom of the tank; 2) a scum layer comprising oils, lipids and other dispersed particles at the top of the tank; and 3) a clear zone in between these layers. Typically, the filter unit is positioned in the clear zone of the tank. As wastewater enters the tank, a large amount of sediment is pulled from the water to the bottom of the tank through gravitational forces. The remaining wastewater enters into the bottom of the filter, where it is filtered to remove sediment of varying sizes. The wastewater then exits the tank and enters the drain field. Several factors determine how often a filter will require maintenance. Two primary factors are the number of people living in the house and the amount of water used. In addition, personal needs and individual habits can inhibit the normal function of a septic tank. Garbage disposals, anti-bacterial soaps and detergents, pharmaceutical medicines and disposing unwanted material into the tank can all place additional stress on the filter.  
         [0009]     Therefore, it is important to select a filter that requires minimum maintenance without clogging, plugging or requiring constant cleaning.  
         [0010]     The prior art is replete with filters designed to resolve the problems described above. U.S. Pat. No. 3,951,818 to Bosnjak describes a filter unit for use in a housing, where the filter unit comprises inclined lamellar structures that are superposed and spaced apart. U.S. Pat. No. 4,402,829 to Cordua describes a filter unit for use in a filter housing comprising superposed and spaced-apart inclined lamellar structures. U.S. Pat. No. 4,707,259 to Doucet describes a filter unit for use in a filter housing comprising superposed and spaced-apart inclined lamellar structures. U.S. Pat. No. 4,448,689 to von Nordenskjold describes a filtration apparatus comprising two series of filter plates separated by a central intake channel. The filter plates are superposed and spaced apart, inclined plates. U.S. Pat. No. 3,515,280 to Parker describes a filter apparatus comprising at least two stacks of spaced-apart, superposed lamellar structures. Each plate appears to be angled upwardly.  
         [0011]     U.S. Pat. No. 4,710,295 to Zabel describes a prefilter including a plurality of stacked, horizontally-extending, disc-dam units vertically mounted in a housing. Each disc is equipped with finger-shaped appendices defined by a continuous dam-wall that follows a sinuous path. A drawback with this prefilter is that with time, the accumulation of fine particles and the formation of a biological film between the horizontal discs create hydraulic restrictions that favor a detachment of the accumulated matters toward the effluent of the septic tank and ultimately forces cleaning.  
         [0012]     U.S. Pat. No. 6,942,796 to Lacasse et al. describes a filter device for filtering liquids containing particulate matter, specifically wastewater, and specifically for use in a septic tank. The filter comprises a series of superposed inclined discs having an inclined surface.  
         [0013]     However, none of the prior art adequately resolves the problems described above. For instance, a key element to the success of any effluent filter is in the effluent flow pattern for particles that enter the filter unit. A particle small enough to pass through the filter barrier, also called a “weir,” of the filter may be trapped inside the filter until the filter is extracted to be cleaned. Thus, a need exists for an improved effluent filter that addresses these problems. In addition, none of the prior art discloses a filter unit with a series of spaced-apart, superposed, inclined plates having a smooth upper surface, with a serpentine filtration element on the underside of each plate.  
       SUMMARY OF THE INVENTION  
       [0014]     The present invention is directed to a wastewater filter comprising a plurality of stackable filter units. Each of the filter units has a first planar surface and a second planar surface. The second planar surface has a filtering wall extending therefrom to an edge, wherein the second planar surface is designed for stacking alignment with the first planar surface of an adjacent filter unit and wherein the edge forms a filter aperture with the first planar surface of the adjacent filter unit.  
         [0015]     The present invention is further directed to a wastewater filter system comprising a plurality of stackable filter units having a first end and a second end. Each of the filter units includes a first planar surface wherein the first planar surface comprises a smooth inclined surface and a second planar surface having a filtering wall extending therefrom to an edge, wherein the second planar surface is designed for stacking alignment with the first planar surface of a second filter unit and wherein the edge forms a filter aperture with the first planar surface of the second filter unit. The filter system further includes at least one channel opening for receiving unfiltered wastewater effluent, at least one channel opening for receiving filtered wastewater effluent, connecting elements to releasibly connect the stackable filter units together, and at least one channel opening for receiving a handle unit. The first planar surface is preferably conically shaped with an inclined surface wherein the angle of inclination is less the ninety degrees. The filtering wall is a generally serpentine wall extending substantially outwardly from the second planar surface of the filter unit. The filter system preferably includes a series of channel openings for receiving unfiltered wastewater effluent. The filter system also preferably includes a sealing filter at the first end of the filter units. The sealing filter unit is designed for stacking alignment with the first planar surface of an adjacent filter unit and includes a seal for the filtered wastewater effluent channel opening.  
         [0016]     The filter system includes a case for containing the stackable filter units. The case includes a first end which includes a funnel-shaped collar, a second, opposing end which includes an opening to allow wastewater access to the plurality of filter units, a collar adapted to form a sealing engagement with the plurality of filter units, and an outlet for the elimination of filtered wastewater.  
         [0017]     The filter plates are preferably connected in a series of plates in a spaced-apart, superposed manner to form a cartridge of filter plates. Each plate preferably has a smooth top surface and an opposing, bottom surface comprising a series of sinuous filtering weir walls for filtration. Thus, as wastewater enters the cartridge, the filtering weir walls collect all sediment over a certain size and force it back down, either via the smooth top surface of the adjacent plate, or directly back into the tank, yielding a virtually self-cleaning filter cartridge. The term “virtually self-cleaning” connotes a filter requiring far less maintenance than that disclosed in the prior art.  
         [0018]     The filter plates are preferably connected by at least two diametrically opposed support rods. In a preferred version, the rods are connected by a handle. The rods and handle can be of any size suitable for the user&#39;s needs, but in a preferred version, each rod and handle is 0.75 inches (1.91 cm) wide.  
         [0019]     The filter unit of the present invention provides many advantages over the prior art. For instance, the case of the present invention is stronger and easier to level in the tank. Further, the case provides improved access to wastewater. The filter plates are virtually self-cleaning, easy to remove from the case for cleaning, easy to re-insert into the case after cleaning and provide an increased amount of surface area for filtration. Further still, the filter plates provide an improved effluent flow pattern. For instance, the prior art filter units trap effluent particles in the filter. In contrast, the present invention provides traps particles and sediments in the filtering weir walls on the bottom side of each plate. This advantageously leaves the top surface of each filter plate smooth and unencumbered, thereby allowing any particulate matter trapped by the filter unit to smoothly slide down the inclined, unencumbered top surface of each plate, out of the filtration unit, and into the bottom of the septic tank.  
         [0020]     In addition, unlike the prior art, the filter unit of the present invention does not include a hollow discharge chamber. Rather, each filter plate preferably comprises a series of openings which simultaneously allow the clean, filtered fluid to continue rising up and eventually out of the filter unit and particulate matter removed from the fluid to drop back down to the tank. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]      FIG. 1  is a perspective view of the filter system of the present invention.  
         [0022]      FIG. 2  is an exploded view of the cartridge portion of the filter unit removed from the filter case.  
         [0023]      FIG. 3  is a perspective view of the filter case viewed from the top side.  
         [0024]      FIG. 4  is a top perspective view of a filter plate of the present invention.  
         [0025]      FIG. 5  is a bottom perspective view of the filter plate of  FIG. 4 .  
         [0026]      FIG. 6  is a top perspective view of the first or top filter plate of the present invention.  
         [0027]      FIG. 7  is a bottom perspective view of the filter plate of  FIG. 6 .  
         [0028]      FIG. 8  is a top perspective view of the last or bottom filter plate of the present invention.  
         [0029]      FIG. 9  is a bottom perspective view of the filter plate of  FIG. 8 .  
         [0030]      FIG. 10  is a perspective view of a carriage of filter plates.  
         [0031]      FIG. 11  is a cross-sectional view of one hub of the filter case taken along lines  11 - 11  of  FIG. 1 .  
         [0032]      FIG. 12  is a cross-sectional view of the cartridge of the present invention taken along lines  12 - 12  of  FIG. 1 .  
         [0033]      FIG. 13  is an enlarged segmental view of a portion of  FIG. 12  at line  13 - 13 .  
         [0034]      FIG. 14  is a enlarged segmental view of a portion of  FIG. 12  taken at line  14 - 14 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0035]     Referring to  FIGS. 1 and 2 , a new and improved effluent filter  10  for use in septic systems is shown. The filter  10  of the present invention preferably comprises a case  12  surrounding at least two and typically a plurality of substantially cone-shaped filter plates  14  combined in a superposed, spaced-apart manner to define a cartridge  15  of filter plates  14 .  
         [0036]     The filter plates  14  are preferably connected via a handle unit  20 . The handle unit  20  includes a generally horizontal hand grip  22  perpendicularly supported by two elongated rods  24  and  26  which extend from an area above the cartridge  15  through each filter plate  14  in a manner which will be described further in this disclosure. Situated at the proximal end of the elongated rods  24  and  25  are matching end caps  25  which assist in the placement and securing of the cartridge  15  in the case  12  as will be described later in the disclosure.  
       The Case  
       [0037]     Referring now to  FIGS. 1, 2  and  3 , the case  12  preferably comprises a substantially hollow, cylindrical structure having an open first top end  30 , a second, opposing, bottom end  32 , a first outer surface  34  and a second inner surface  36 . The case  12  is preferably open at both ends  30  and  32 .  
         [0038]     Preferably, the case  12  is conically-shaped to facilitate the placement of the cartridge  15  in the case  12 . As illustrated in  FIG. 1 , the first end  30  of the case  12  is defmed by a funnel-shaped collar  38  to catch and assist in the initial placement of the cartridge  15  as the cartridge  15  is lowered into the case  12 . The case  12  also tapers slightly from the first end  30  to the second end  32 . For example, the diameter of the case  12  at the second end  32  may be slightly less, e.g., 0.25 inches (0.66 cm) less, than the diameter of the first end  30 . The angular reduction facilitates the placement and removal of the cartridge  15 . While it is within the scope of the present invention to provide a case  12  with straight, i.e., non-tapered walls, the preferred mode is to include a slight tapering as described above.  
         [0039]     As illustrated in  FIGS. 1 and 3 , end  32  is defined by an opening  40  to allow sewage effluent better access to the cartridge  15  and to provide more tolerance for turbulence, preventing any “surges” of effluent from moving the cartridge  15  of filter plates  14  within the case  12 .  
         [0040]     The second end  32  of the case  12  is also defined by a collar  42  which surrounds the opening  40  as illustrated in  FIGS. 1 and 3 . The collar  42  also forms a sealing engagement with the cartridge  15  when the cartridge  15  is in place in the case  12  as will be described later. As illustrated in  FIGS. 1 and 3 , the collar  42  also includes two integrally molded hubs  44  for attaching the cartridge  15  to the case  12 . The hubs  44  are preferably diametrically opposed in the collar  42  along the circumference of the case  12 . The hubs  44  are designed to frictionally engage the end caps  25  of the handle unit  20  in order to releasibly fasten the cartridge  15  to the case  12 . To that end, the hub  44  includes at least one and preferably a series of extended ridges  46  for assistance in releasibly securing the cartridge  15  to the case  12 . The hubs  44  can be of any size, but in a preferred version, accommodate the end caps  25  of the rods  24  and  26 .  
         [0041]     As illustrated in  FIGS. 1, 2  and  3 , the case  12  has a generally D-shaped configuration, including a rounded portion  48  and a flat wall  50 . The flat wall  50  is defined by an outlet  52 , an opening in the flat wall  50  of the case  12 . The outlet  52  is defined by an outlet collar  54  molded to the case  12 . One or more strengthening grids  56  may also be formed on the outlet collar  54  to strengthen the placement of the outlet collar  54  to the flat wall  50  of the case  12 .  
         [0042]     The case  12  may also include a supporting hub  58  located on the flat wall  50  of the case  12  and below the outlet  52 . The purpose of the supporting hub  58  is to align and support the filter unit  10  in the septic tank to maintain the filter  10  in a generally vertical position and to prevent undue angular pressure on the outlet collar  54 , which may cause breakage at the area of the outlet collar  54 . In operation, a spacer rod (not shown) is designed to fit within the opening  59  of the supporting hub  58 . The spacer rod is generally long enough to extend to the inside wall of the septic tank to support the filter  10  in vertical alignment.  
         [0043]     Preferred materials for the case  12  are any durable material, such as plastic or metal. In a preferred version, the case is made from plastic, PVC or any suitable thermoplastic material known to the art.  
         [0044]     Referring now specifically to  FIGS. 2 and 4 - 9 , the filter plates  14  of the present invention are shown. In a preferred version, each filter plate  14  comprises an angled, smooth top surface  60  surrounded by a circumferential ring or collar  62 ; a bottom surface  64  comprising a serpentine series of filtering weir walls or dams  66  protruding substantially outwardly from the bottom surface  64  and ending at dams  68 .  
         [0045]     The filter plates  14  are characterized by a series of triangular openings  70  arranged around the substantially circular circumference of each plate  14 . As illustrated in the drawings, the triangular openings  70  border the collar  62 . However, it is within the scope of the present to place the openings  70  in other locations on the surface  60  of the filter plate  14 . In addition, it is within the scope of the present invention a variety of shapes other than a triangle as long is the openings  70  of the stacked filter plates  14  align to form one or more primary wastewater effluent channels  71  as will be described later in this disclosure.  
         [0046]     The filter plates  14  are also characterized by at least one substantially U-shaped groove  72  on one edge of the plate  14  and cut into the collar  62  of the filter plate  14 . While the groove  72  is illustrated as having a U or scalloped shape, it is within the scope of the present invention for the groove any defined shape as long as it provides open space to form a filtered effluent channel  73  as will be described later in the disclosure.  
         [0047]     The filter plates  14  are also optionally but preferably provided with a substantially V-shaped groove  74  positioned generally diametrically opposite the U- shaped groove  72  and also cut into the collar  62 . While the groove  74  is illustrated as having a V shape, it is within the scope of the present invention for the groove any defined shape as long as it provides open space to form an optional secondary wastewater effluent channel  75  as will be described later in the disclosure.  
         [0048]     At least two circular rod channels  76  are positioned on diametrically opposing sides of each plate  14  for receiving rods  24  and  26  of the handle unit  20 . In addition, the filter plate  14  includes a plurality of connecting pins  78 , including a male end  80  and a female end  82 . The connecting pins  78  are used to connect the filter plates  14  together in a superposed, spaced-apart manner to define the cartridge  15  as illustrated in  FIG. 2 .  
         [0049]     Referring to  FIGS. 4 and 5 , the dorsal and ventral views of an individual filter plate  14  are illustrated. In a preferred version, the top surface  60  is generally smooth While the surface of the filter plate may be flat, the preferred filter plate  14  angles upwardly in an inclined direction at an approximate angle up to but not including ninety degrees, preferably an angle between ten and forty degrees, and most preferably between twenty and thirty degrees toward the center  61  of the top surface  60  of the filter plate  14 . However, in alternate versions, this angle may change. Further, while in a preferred version the angle of each plate  14  is identical, in alternate versions, the angles of each filter plate  14  may vary from each other.  
         [0050]     The bottom side  64  of each plate  14  preferably comprises at least one weir wall  66  in contact with the inclined bottom surface  64  of the filter plate  14 . The weir wall is defined by an edge  67 . The weir wall  66  preferably comprises a thin, sinuous or serpentine wall that extends substantially outwardly from the bottom surface  64  of the plate  14 . The weir wall  66  provides a large surface area to further assist in the collection and removal of sediment from the filter unit  10 .  
         [0051]     Reference is now made to  FIGS. 2, 6  and  7 , which illustrate the uppermost seal plate  90 , which has a similar design as the filter plates  14 . However, there are distinctions between the seal plate  90  and the filter plates  14  as the seal plate  90  is designed to act as an upper seal to the cartridge  15  when the cartridge  15  is placed in the case  12 . Like filter plate  14 , the seal plate  90  has a generally circular configuration with a top surface  92 , a bottom surface  94  and a collar  96 . The top surface  92  of the seal plate  90  is preferably angled at an upward slope to the center  93  of the top surface  92 . Additionally, circular channels  76  are provided for the rods  24  and  26  of the handle unit  20 . Because connecting pins  78  are not necessary to apply to the seal plate  90 , as there are no plates above seal plate  90 , the collar  96  includes tabs  98  to receive the male end  80  of the connecting pins  78  from the adjacent filter plate  14 . Unlike filter plate  14 , the seal plate  90  is not equipped with a U-shaped groove  72 . Rather, seal plate  90  includes a squared edge  100  designed to align with the collar  38  at the area of the flat wall  50  in the case  12  to provide a seal at the upper end of the U-shaped channel  73 .  
         [0052]     An additional opening  102  with a snap tab  103  is provided in the seal plate  90 . The opening  102  is situated in alignment with the secondary wastewater effluent channel  75  created by the V-shaped grooves  74  of the successive filter plates  14 . The purpose of opening  102  and the secondary wastewater effluent channel  75  is to receive an optional alarm system (not shown), known to the art, within the filter unit  10 . Reference is made to U.S. Pat. No. 6,841,066 to Nurse, Jr. et al., which is incorporated by reference for its disclosure of an alarm system which can be used in the present invention. The opening  102  includes the snap tab  103  and other mechanisms known to the art to allow the alarm system to be placed in locking engagement within the secondary wastewater effluent channel  75  of the filter unit.  
         [0053]     As illustrated in  FIG. 7 , the bottom surface  94  of seal plate  90  is characterized by a lack of weir walls  66 . Thus, the seal plate  90  rests directly on the top filter plate  14 .  
         [0054]     Reference is now made to  FIGS. 8 and 9 , which illustrate the bottom filter plate  110 , which is designed to be the lowest filter plate in the cartridge  15 . Filter plate  110  is characterized by a top surface  112 , a bottom surface  114 , a collar  115 , triangular openings  70 , which align with the triangular openings  70  of the filter plates  14  and a V-shaped groove  74  which aligns with the V-shaped groove  74  of the filter plates  14 . In addition, there are channel openings  76  for the rods  24  and  26  of the handle unit  20 . Similar to the seal plate  90 , but unlike filter plates  14 , the collar  115  includes a flat edge  116  which serves as the lowermost seal to the channel  73  thereby preventing any of the wastewater effluent from the septic tank to go directly into the channel  73 .  
         [0055]     When the cartridge  15  is in place in the case  12 , the collar  42  on the case  12  aligns with the collar  116  of the bottom filter plate  110  to form a seal on the filter unit  10  and force the wastewater effluent through the primary wastewater effluent channels  71  and secondary wastewater effluent channel  75 . Thus, the bottom plate  110  creates a seal between the septic tank and the interior of the filter unit  10 , closing off the filter unit  10  from the rest of the septic tank and blocking any wastewater effluent into the cartridge  15  in any other way other than the primary wastewater effluent channels  71  and the secondary wastewater effluent channel  75 .  
         [0056]     As illustrated in  FIG. 9 , the bottom surface  114  of the bottom filter plate  110  is smooth and does not include any weir walls  66 . Like the other filter plates, the bottom filter plate  110  is preferably conically-shaped such that the upper surface  112  and bottom surface  114  are angled toward the center  113  of the top surface of filter  110 . In addition, the bottom filter plate  110  is characterized by a modified connecting pin  118 , which only includes a female end  120  to receive the male end  80  of the adjacent filter plate  14 .  
         [0057]     As shown in  FIGS. 2, 10  and  11 , filter plates  14  are stacked in an accordion-like fashion, one atop another, from the bottom filter plate  110  to the top seal plate  90  to form the cartridge  15 . The number of filter plates  14  forming the cartridge  15  depends upon the needs of the filter unit  10 . While a minimum of two filter plates  14  are necessary to form the cartridge  15 , it is preferable to have a plurality of filter plates  14  as illustrated in the figures. The filter plates  14  are stacked and connected by the placement of female end  82  of the connecting pin  78  of one filter plate  14  on the male end  80  of a connecting pin  78  of the next filter plate  14  above it. The placement of the connecting pins  78  aligns the filter plates  14  to form the cartridge  15  as illustrated in  FIG. 2 .  
         [0058]     As illustrated in  FIGS. 12-14 , the connecting pins  78  play another important role in the filtering action of the filter unit  10 . The height of each connecting pin  78  determines the distance between adjacent filter plates  14 . Thus, the connecting pins  78  must provide a sufficient distance between adjacent filter plates  14  such that a gap  122  is formed between the edge  67  of the filtering weir walls or dams  66  and the top surface  60  of an adjacent filter plate  14  and the top surface  112  of the bottom filter plate  110 , as best illustrated in  FIGS. 13 . The size of the gap  122  determines the size of a particulate which may eventually leave the filter unit  10  through the outlet  52 . For example, the filter plates  14  may be stacked one upon each other such that the edge  67  of the weir wall  66  of one filter plate  14  forms a one-eighth inch (0.32 cm) gap  122 . In this manner, all particulates or sediment in the wastewater effluent larger than one-eighth inch will be trapped by the weir wall  66 , thus preventing larger sediment from flowing out of the filter unit  10 . The gap  122  distance may be adjusted by the height of the connecting pins  78 . It is within the scope of the present invention to adapted the connecting pin length to provide varying gap sizes from one-thirty second inch (0.08 cm) and smaller to one-eighth inch and larger.  
         [0059]     When the filter plates  14  are stacked upon each other in alignment, the following channels are formed:  
         [0060]     1) the alignment of the triangular openings  70  form the primary wastewater effluent channels  71  which extend from the bottom filter plate  110  in the cartridge  15  up to but not passing through the seal plate  90  in the cartridge  15 ;  
         [0061]     2) the alignment of the V-shaped grooves  74  on each successive filter plate form the secondary wastewater effluent channel  75  extending from the bottom filter plate  110  to the seal plate  90 ;  
         [0062]     3) the alignment of the U-shaped grooves  72  on each succeeding filter plates  14  form the U-shaped channel  73  extending from the bottom filter plate  110  to the seal plate  90 ; and  
         [0063]     4) the alignment of the circular channels  76  in each filter plate  14  forms the channels for receiving the rods  24  and  26  of the handle unit  20 .  
         [0064]     As illustrated in  FIGS. 2 and 11 , the proximal ends of the rods  24  and  26  of the handle unit  20  are defined by identical end caps  25 . Referring to  FIG. 2 , the elongated rods  24  and  26  pass through the openings  76  in each of the filter plates in the cartridge  15  and extend beyond the lowest filter plate. Once the rods  24  and  26  have extended through the cartridge  15 , the end caps  25  are secured to the proximal ends of the rods  24  and  26  as illustrated in  FIG. 2 . The end caps  25  provide the joint responsibility of securing the filter plates  14  together to form the cartridge  15  and releasibly securing the cartridge  15  to the case  12 .  
         [0065]     Reference is made to  FIG. 11  which shows the end cap  25  with a friction fit ridge  27  designed to frictionally engage the hubs  44  of the case  12  by snap fitting the ridge  27  of the end cap  25  over and beyond the ridge  46  of the hubs  44  to releasibly engage the cartridge  15  to the case  12 . In this manner, the cartridge  15  may be connected to the case  12  without concern for the cartridge  15  dislodging from the case  12  until releasing pressure is applied to the end caps  25  of the handle unit  20 . The extended ridge  46  of each hub  44  may be in the form of a continuous ring around the interior wall of the hub  44  or a series of extended ridges as illustrated in  FIG. 3 .  
         [0066]     The following description of the operation of the filter unit  10  illustrates the unique three-stage filtering system provided by the filter unit  10 . In use, the filter  10  is submerged and affixed in a septic tank (not shown) at a point such that at least the bottom end  32  of the filter unit  10  is positioned below the surface level of the wastewater effluent in the septic system. For purposes of the present invention, the contents of the septic system will generally be referred to as “wastewater effluent.” As can be imagined, wastewater effluent is a fluid or water-based composition generally in liquid form which includes a variety of particulate material of a variety of sizes. A drain pipe (not shown) is connected to the outlet collar  54  of the outlet  52  to allow the filtered effluent exiting from the filter  10  to flow to a drain field. As illustrated in  FIGS. 1 and 12 , the outlet collar may be provide with one or more stops  55  to prevent the drain pipe from entering the filter unit  10  and possibly damaging the cartridge  15  or prohibiting flow to the outlet  52 .  
         [0067]     The first stage: Wastewater effluent in the septic tank containing unwanted particulate matter can only enter the filter unit  10  through the opening  40  in the case  12  and flow upwardly through the cartridge  15  in the direction of the outlet  52 . Because of the configuration of the bottom filter plate  110 , the wastewater effluent must flow through the primary wastewater effluent channels  71  and the secondary wastewater effluent channel  75  in the filter plates  14  and  110  along the flow path identified by lines  120  in  FIGS. 12 and 13 . The composition of the wastewater effluent entering the filter unit  10  is determined by the size of the entrance openings  71   a  and  75   a  of the primary wastewater effluent channels  71  and the secondary wastewater effluent channel  75 . Any particulate matter having a size larger than the entrance openings  71   a  or  75   a  will not pass into the filter unit  10 , which creates the first stage of the filtering system.  
         [0068]     The second stage: As the wastewater effluent moves in an upwardly direction through the primary wastewater effluent channels  71  and the secondary wastewater effluent channel  75 , the sediment in the wastewater is hindered by. the filtering weir walls  66  of each filter plate  14 . If the gap  122  size of the cartridge  15  is one-eighth inch, any particles in the wastewater effluent larger than one-eighth inch cannot pass through the gap  122 . The larger particles therefore must remain in the primary wastewater effluent channels  71  and the secondary wastewater effluent channel  75  and eventually float by gravity pull down the primary wastewater effluent channels  71  and the secondary wastewater effluent channel  75  and out the opening  40  at the bottom end  32  of the filter unit  10 . This forms the second stage of filtration provided by the filter unit  10  whereby all particulates in the wastewater effluent larger than a designated size, one-eighth inch in this example, are prevented from flowing past the primary wastewater effluent channels  71  and the secondary wastewater effluent channel  75  of the cartridge  15 .  
         [0069]     The third stage: With continued reference to  FIGS. 12, 13  and  14 , the wastewater effluent in the primary wastewater effluent channels  71  and the secondary wastewater effluent channel  75  continues to rise only through the primary wastewater effluent channels  71  and the secondary wastewater effluent channel  75 . Only the wastewater effluent with a particulate size less than the designated gap  122  size will then be able to pass through the gap  122  and enter the chamber  124  as shown by the flow path identified by lines  126 .  
         [0070]     As the wastewater effluent enters the chamber  124 , continuous pressure builds in the chamber  124  requiring the evacuation of the wastewater effluent, which follows the flow path identified by lines  128 , into the filtered effluent channel  73 . However, the swirling action of the wastewater effluent within the chamber  124  also causes the smaller, i.e., less than one-eighth inch, particulates to come into contact with the filtering weir walls  66 , which effectively hinders the particulate motion and impedes the particulate from exiting the chamber  124  through the flow path  128 . The particulates which then remain in the chamber  124  eventually fall by gravity to the top surface  60  of the adjacent filter plate  14  or the top surface  112  of the bottom filter plate  110 . Because of the conical, smooth surface  60  or  112  of the filter plates  14  or  110 , the particulate matter will continue a downward migration toward the direction of the collar  62  of the filter plate  14  and eventually fall into the primary wastewater effluent channels  71  and the secondary wastewater effluent channel  75  and freefall through the opening  40  and out of the filter unit  10 . This forms the third stage filtration process in the filter unit  10  whereby smaller particulate matter may be removed along with the larger particles.  
         [0071]     With each rising filter plate  14  in the cartridge  15 , greater amounts of particulate matter are removed from the wastewater effluent. As the particulate matter is collected by the filtering weir walls  66 , it is directed through the weir wall  66  and down the inclined top surface  60  of the adjacent filter plate  14 . The sediment slides downwardly along the inclined, smooth, top surface  60  of the filter plate  14  and through the openings  70  onto the top surface  60  of the next lower filter plate  14  in the cartridge  15 . When the sediment reaches the lowest filter plate  14  in the cartridge  15 , the sediment exits through the opening  40  at the bottom end  30  of the case  12  and drops back into the septic tank.  
         [0072]     As the wastewater continues rising upwardly through the filter unit  10  toward the outlet  52 , each level of filter plates  14  remove additional quantities of sediment from the wastewater. In turn, the sediment which is hindered by the filtering weir walls  66  extending downwardly from the lower surface  64  of each filter plate  14  drops onto the smooth upper surface  60  of the next lower filter plate  14 . The downward angle of the conical filter plate  14  creates a gravity pull on the sediment causing the sediment to roll or move toward the outer ring  62  of each filter plate  14 . As the flows toward the outer ring  62 , the sediment encounters the triangular openings  70  and free fall toward the opening  40  at the bottom  32  of the filter  10  to exit the filter and drop to the bottom of the septic tank.  
         [0073]     The purpose of the filtered effluent channel  73  is to give volume to any filter effluent to enable the effluent flow up the filter unit  10  to exit through the outlet  52  as illustrated by the flow path designated by lines  130 . As the filtered effluent enters the filtered effluent channel  73 , the filtered effluent rises through the filtered effluent channel  73  and eventually exits through the outlet  52 . Therefore, any filtered effluent and any sediment which reaches the filtered effluent channel  73  will leave the filter  10  along flow paths  128  and  130  through the outlet  52 , thereby exiting completely from the septic tank.  
         [0074]     It is within the scope of the present invention to provide slight modifications to the shape of the filter plates  14  in the cartridge  15  to enable the cartridge  15  to be used in combination with a case having a different shape and size. For example, the flat wall of the filter plates  14  could be eliminated and other arrangements made to create a filtered effluent channel in order to accommodate a round shape case. In addition, the filter plate  14  can have a squared shape. Therefore, it may not be necessary to replace the entire filter unit but simply to retrofit a cartridge  15  of filter plates  14  into the existing case. Further, all existing mound systems or other systems with no filter may be fitted with the filter plates and/or case of the present invention.  
         [0075]     The filter plates  14  may be made of any durable material such as metal or plastic. In a preferred version, the filter plates are made from plastic.  
         [0076]     It is understood that the invention is not confined to the particular construction and arrangement of parts herein illustrated and described, but embraces such modified forms thereof as come within the scope of the claims in any later-filed non-provisional application. Note that further exemplary preferred versions of the invention are described in the appended pages, which are incorporated by reference and constitute a portion of this application.