Patent Publication Number: US-2023136410-A1

Title: Wastewater filters and wastewater filtration systems specifically adapted for their use

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to wastewater treatment, and, more particularly, to filters and associated wastewater filtration systems for use in removing suspended solids from wastewater. 
     BACKGROUND OF THE INVENTION 
     Modern wastewater treatment involves three stages, namely, primary, secondary, and tertiary treatment. Primary treatment generally involves temporary retention of the wastewater in a basin to allow heavy solids to settle to the bottom while oil, grease, and lighter solids float to the surface. Settled and floating substances are removed and the remaining liquid is subjected to secondary treatment. The secondary treatment stage degrades the biological content of the wastewater. The majority of municipal wastewater treatment plants treat the settled wastewater using aerobic biological processes to remove dissolved and suspended biological matter. Biological treated waters flow to a secondary sedimentation stage for clarification. Tertiary treatment involves final treatment stages that raise the effluent quality prior to discharge to the receiving environment. 
     Tertiary filters may utilize porous media filters, such as woven fabric, knitted fabric, gauze, mesh, penetrable membranes, etc. However, over time filtered particles accumulate on the filter media to a level that degrades the effectiveness of the filter. A cleaning process (i.e., a “backwashing” process) is required to restore filter effectiveness by cleaning the filter media. 
     Systems intended to periodically clean the filter media by removal of accumulated solids typically utilize a vacuum pump to create suction for vacuum heads to remove captured solids from the media. Nevertheless, these suction-based designs may suffer from several disadvantages. Turbidity spikes may be experienced during and after a suction-based backwashing process due to the “overcleaning” of the external surfaces of the filters. Perhaps somewhat counterintuitively, accumulated solids on a filter can actually help to raise filtration efficiency when present at low to moderate levels. As a result, overcleaning the surfaces of a filter can reduce filtration efficiency. In addition, the application of an external suction force on the outer surface of a filter may reduce the internal pressure in the filter, artificially increasing the flow of wastewater through the filter to a level that can also reduce filtration efficiency. The vacuum cleaning heads, moreover, take up a great deal of space, thereby limiting the number of filters area per tank. In addition, such systems require substantial energy consumption to power the vacuum cleaning system. 
     Accordingly, there exists a need for improved tertiary media filtration systems with backwashing capabilities that avoid the limitations and disadvantages set forth above. 
     SUMMARY OF THE INVENTION 
     Embodiments of the present invention address the above-identified needs by providing filters and associated wastewater filtration systems that address the above-identified deficiencies. These filters and systems are specifically designed to allow the filters to be cleaned in situ without creating turbidity spikes or otherwise adversely affecting filtration efficiency. 
     Aspects of the invention are directed to an apparatus comprising: a peripheral frame, a first filter media sheet, a second filter media sheet, a plurality of first angled fins, a plurality of second angled fins, and a filtered water outlet. The first filter media sheet is attached to the peripheral frame. The second filter media sheet is attached to the peripheral frame in spaced face-to-face relation to the first filter media sheet such that the peripheral frame, the first filter media sheet, and the second filter media sheet combine to define a filter interior volume. So configured, the first filter media sheet has a first exterior media surface facing away from the filter interior volume and a first interior media surface facing towards the filter interior volume, while the second filter media sheet has a second exterior media surface facing away from the filter interior volume and a second interior media surface facing towards the filter interior volume. The plurality of first angled fins are attached to the peripheral frame external to the filter interior volume and project away from the first exterior media surface at an oblique angle. Likewise, the plurality of second angled fins are attached to the peripheral frame external to the filter interior volume and project away from the second exterior media surface at an oblique angle. The filtered water outlet is in fluid communication with the filter interior volume. 
     Additional aspects of the invention are directed to an apparatus comprising: a wastewater treatment tank, wastewater in the wastewater treatment tank, and a filter cartage mounted in the wastewater treatment tank and submersed in the wastewater. The filter cartridge comprises: a peripheral frame, a first filter media sheet, a second filter media sheet, a plurality of first angled fins, a plurality of second angled fins, and a filtered water outlet. The first filter media sheet is attached to the peripheral frame. The second filter media sheet is attached to the peripheral frame in spaced face-to-face relation to the first filter media sheet such that the peripheral frame, the first filter media sheet, and the second filter media sheet combine to define a filter interior volume. So configured, the first filter media sheet has a first exterior media surface facing away from the filter interior volume and a first interior media surface facing towards the filter interior volume, while the second filter media sheet has a second exterior media surface facing away from the filter interior volume and a second interior media surface facing towards the filter interior volume. The plurality of first angled fins are attached to the peripheral frame external to the filter interior volume and project away from the first exterior media surface at an oblique angle. Likewise, the plurality of second angled fins are attached to the peripheral frame external to the filter interior volume and project away from the second exterior media surface at an oblique angle. The filtered water outlet is in fluid communication with the filter interior volume. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings where: 
         FIG.  1    shows a perspective view of a filter cartridge in accordance with an illustrative embodiment of the invention; 
         FIG.  2    shows an exploded perspective view of the  FIG.  1    filter cartridge; 
         FIG.  3    shows an elevational view of the  FIG.  1    filter cartridge; 
         FIG.  4    shows a sectional view of the  FIG.  1    filter cartridge along the cleave plane indicated in  FIG.  3   ; 
         FIGS.  5  and  6    show sectional views of the  FIG.  1    filter cartridge in the respective regions indicated in  FIG.  4   ; 
         FIG.  7    shows a sectional view of the  FIG.  1    filter cartridge along the cleave plane indicated in  FIG.  3   ; 
         FIG.  8    shows an elevational view of a peripheral frame, a filtered water outlet, and a purging fluid inlet in the  FIG.  1    filter cartridge; 
         FIGS.  9 - 12    show sectional views of the  FIG.  8    elements along the respective cleave planes indicated in  FIG.  8   ; 
         FIG.  13    shows a partially-broken elevational view of the  FIG.  8    peripheral frame in the region indicated in  FIG.  8   ; 
         FIG.  14    shows an elevational view of the  FIG.  1    filter cartridge during filtering; 
         FIG.  15    shows a sectional view of the  FIG.  1    filter cartridge during filtering along the cleave plane indicated in  FIG.  14   ; 
         FIG.  16    shows a sectional view of the  FIG.  1    filter cartridge during filtering in the region indicated in  FIG.  15   ; 
         FIG.  17    shows a partially-broken elevational view of the  FIG.  1    filter cartridge during filtering in the region indicated in  FIG.  14   ; 
         FIG.  18    shows a partially-broken elevational view of the  FIG.  1    filter cartridge  100  during purging; 
         FIG.  19    shows a sectional view of the  FIG.  1    filter cartridge during purging along the cleave plane indicated in  FIG.  18   ; 
         FIG.  20    shows a partially-broken elevational view of the  FIG.  1    filter cartridge during purging in the region indicated in  FIG.  18   ; 
         FIG.  21    shows a sectional view of the  FIG.  1    filter cartridge during purging in the region indicated in  FIG.  19   ; 
         FIG.  22    shows a partially-broken elevational view of the  FIG.  1    filter cartridge during purging in the region indicated in  FIG.  18   ; 
         FIG.  23    shows an elevational view of a spray panel in accordance with an illustrative embodiment of the invention; 
         FIG.  24    shows an exploded perspective view of the  FIG.  23    spray panel; 
         FIG.  25    shows an elevational view of the  FIG.  23    spray panel in the region indicated in  FIG.  23   ; 
         FIG.  26    shows an exploded perspective view of a wastewater filtration system in accordance with an illustrative embodiment of the invention without wastewater present; 
         FIG.  27    shows another perspective view of the  FIG.  26    wastewater filtration system without wastewater present; 
         FIGS.  28  and  29    show sectional views of the  FIG.  26    wastewater filtration system without wastewater present along the respective cleave planes indicated in  FIG.  27   ; 
         FIG.  30    shows a partially-broken sectional view of the  FIG.  26    wastewater filtration system during filtering along the same cleave plane as  FIG.  28   ; 
         FIG.  31    shows a sectional view of the  FIG.  26    wastewater filtration system during filtering in the region indicated in  FIG.  30   ; 
         FIG.  32    shows a sectional view of the  FIG.  26    wastewater filtration system during filtering along the cleave plane indicated in  FIG.  30   ; 
         FIG.  33    shows a sectional view of the  FIG.  26    wastewater filtration system during external cleaning along the same cleave plane as  FIG.  32   ; 
         FIG.  34    shows a sectional view of the  FIG.  26    wastewater filtration system during external cleaning in the region indicated in  FIG.  33   ; and 
         FIG.  35    shows a sectional view of a modified filtration system in accordance with another illustrative embodiment of the invention during filtration along the same cleave plane as  FIG.  32   . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention will be described with reference to illustrative embodiments. For this reason, numerous modifications can be made to these embodiments and the results will still come within the scope of the invention. No limitations with respect to the specific embodiments described herein are intended or should be inferred. 
     As used herein and in the appended claims, a first element is “attached” to a second element if the first element is physically connected to the second element directly or through one or more solid (i.e., not liquid or gas) intermediate elements. Moreover, a first element “overlies” a second element if the first element is covering at least a portion of the second element and is in direct contact with the second element. “Proximate means” within twelve inches. An object is mounted at an “oblique angle with respect to the Earth” if it is mounted so as to be neither parallel to, nor at a right angle to, the local gravitational field lines of the Earth. 
     Aspects of a filter cartridge  100  (a form of apparatus) in accordance with an illustrative embodiment of the invention are now described. The filter cartridge  100  may be used in the tertiary filtration of wastewater, that is, in the final or near-final treatment of the wastewater to raise the water quality prior to discharge to the receiving environment. In a given application, for example, the filter cartridge  100  will see incoming wastewater with a water quality of about 60 parts-per-million of total suspended solids (ppm TSS). The filter cartridge  100  may be used to help achieve a water quality of, as just an example, less than 5 ppm TSS. 
       FIG.  1    shows a perspective view of the filter cartridge  100 ,  FIG.  2    shows an exploded perspective view of the filter cartridge  100 , and  FIG.  3    shows an elevational view of the filter cartridge  100 . Externally, it can be discerned that the filter cartridge  100  comprises: a peripheral frame  105 , a first filter media sheet  110 , a second filter media sheet  115 , a first fin assembly  120 , a second fin assembly  125 , a first inner mesh  130 , a second inner mesh  135 , a first cartridge gasket  140 , a second cartridge gasket  145 , internal baffles  150 , a filtered water outlet  155 , a purging fluid inlet  160 , a handle  165 , first screws  170 , and second screws  175 . The peripheral frame comprises a first member  180 , a second member  185 , a third member  190 , and a fourth member  195  arranged as a rectangle (i.e., a form of quadrilateral). When assembled, the first fin assembly  120  overlies the first filter media sheet  110 , which overlies the first inner mesh  130 . These first elements are mounted to one face of the peripheral frame  105  via the first cartridge gasket  140  and the first screws  170 . At the same time, the second fin assembly  125  overlies the second filter media sheet  115 , which overlies the second inner mesh  135 , and these second elements are mounted to a second, opposite face of the peripheral frame  105  via the second cartridge gasket  145  and the second screws  175 . The second elements are thereby in a spaced face-to-face relation to the first elements on opposite sides of the peripheral frame  105 . In this manner, the peripheral frame  105 , the first filter media sheet  110 , and the second filter media sheet  115  combine to define a filter interior volume  200 . The internal baffles  150  span between the first inner mesh  130  and the second inner mesh  135  inside the filter interior volume  200 . 
     Additional details of the filter cartridge  100  are shown in  FIGS.  4 - 13   , where:  FIG.  4    shows a sectional view of the filter cartridge  100  along the cleave plane indicated in  FIG.  3   ;  FIGS.  5  and  6    show sectional views of the filter cartridge  100  in the respective regions indicated in  FIG.  4   ;  FIG.  7    shows a sectional view of the filter cartridge  100  along the cleave plane indicated in  FIG.  3   ;  FIG.  8    shows an elevational view of the peripheral frame  105 , the filtered water outlet  155 , and the purging fluid inlet  160  in the filter cartridge  100 ;  FIGS.  9 - 12    show sectional views of the  FIG.  8    elements along the respective cleave planes indicated in  FIG.  8   ; and  FIG.  13    shows a partially-broken elevational view of the peripheral frame  105  in the region indicated in  FIG.  8   . 
     It will be noted that the first member  180 , the second member  185 , the third member  190 , and the fourth member  195  are formed of hollow square-tubular tubes with end plugs placed as necessary to isolate the interiors of the members  180 ,  185 ,  190 ,  195  from the outside environment. The fourth member  195  defines purging fluid openings  205  that provide fluid communication between an interior of the fourth member  195  (hereinafter, the fourth member interior volume  210 ) and the filter interior volume  200 . In the present illustrative embodiment, the purging fluid openings  205  are in the form of numerous holes in the fourth member  195  that face the filter interior volume  200 . Likewise, the first member  180  defines filtered water openings  215  that provide fluid communication between an interior of the first member  180  (hereinafter, the first member interior volume  220 ) and the filter interior volume  200 . Here, however, the filtered water openings  215  are in the form of elongate slots in the first member  180  that face the filter interior volume  200 . 
     The filtered water outlet  155  projects laterally from the first member  180  and is in fluid communication with the first member interior volume  220 . Given the presence of the filtered water openings  215 , the filtered water outlet  155  is also, by extension, in fluidic communication with the filter interior volume  200 . The purging fluid inlet  160 , in contrast, projects from the first member  180  at a right angle to the filtered water outlet  155 . The purging fluid inlet  160  passes through an interior of the second member  185  (hereinafter, the second member interior volume  230 ) and terminates in the fourth member interior volume  210 . With the purging fluid openings  205  in the fourth member  195 , the purging fluid inlet  160  is also in fluidic communication with the filter interior volume  200 . 
     The first filter media sheet  110  defines a first exterior media surface  235  facing away from the filter interior volume  200  and a first interior media surface  240  facing towards the filter interior volume  200 . Likewise, the second filter media sheet  115  defines a second exterior media surface  245  facing away from the filter interior volume  200  and a second interior media surface  250  facing towards the filter interior volume  200 . The first inner mesh  130  overlies the first interior media surface  240 , while the second inner mesh  135  overlies the second interior media surface  250 . The internal baffles  150  are attached to the first inner mesh  130  and the second inner mesh  135  and span therebetween in the filter interior volume  200 . In the present embodiment, there are gaps between the internal baffles  150  of a given row, and the internal baffles  150  are staggered row-to-row. This arrangement causes the internal baffles  150  to interfere somewhat with any fluids (liquids or gases) travelling from the fourth member  195  towards the first member  180 , which will be beneficial when purging the filter cartridge  100 , as detailed below. 
     The first fin assembly  120  and the second fin assembly  125  are largely identical. The first fin assembly  120  comprises a plurality of first straight fins  255 , which are arranged perpendicular to a plurality of first angled fins  260  to form a grid. The first straight fins  255  project away from the first exterior media surface  235  at a ninety-degree angle. The first angled fins  260  project away from the first exterior media surface  235  at an oblique angle. In one or more nonlimiting embodiments, for example, the first angled fins  260  form an angle of about thirty degrees with the first exterior media surface  235 . The second fin assembly  125  comprises a plurality of second straight fins  265 , which are arranged perpendicular to a plurality of second angled fins  270  to form a grid. Here again, the second straight fins  265  project away from the second exterior media surface  245  at a ninety-degree angle. The second angled fins  270  project away from the second exterior media surface  245  at an oblique angle (e.g., about thirty degrees). 
     In one or more embodiments, the first filter media sheet  110  and the second filter media sheet  115  may be formed of commercially available pile cloth media, which may, as just an example, be about 0.4 inches in thickness when uncompressed. While pile cloth is preferred, any suitable form of woven fabric, knitted fabric, gauze, mesh, penetrable membranes, and the like would also fall within the scope of the invention. The first filter media sheet  110  may be designed to remove solids greater than five micrometers in diameter. The first cartridge gasket  140  and the second cartridge gasket  145  may be formed of an elastomeric material such as rubber. The remainder of the elements of the filter cartridge  100  may be formed of stainless steel or another suitable material (e.g., plastic). Formation of elements may be by conventional forming techniques, which will be familiar to one skilled in the art given the disclosure described herein. 
       FIGS.  14 - 17    show the filter cartridge  100  immersed in wastewater  1000  during active filtering, as may be the condition in a wastewater treatment tank. In these figures:  FIG.  14    shows an elevational view of the filter cartridge  100  during filtering,  FIG.  15    shows a sectional view of the filter cartridge  100  during filtering along the cleave plane indicated in  FIG.  14   ,  FIG.  16    shows a sectional view of the filter cartridge  100  during filtering in the region indicated in  FIG.  15   , and  FIG.  17    shows a partially-broken elevational view of the filter cartridge  100  during filtering in the region indicated in  FIG.  14   . The filtered water outlet  155  is attached a filtered water hose  305  that carries the filtered water away from the filter cartridge  100 . The purging fluid inlet  160  is attached to a purging fluid hose  310  that is attached to a source of purging fluid (described below). 
     With the filter cartridge  100  submerged in the wastewater  1000 , hydrostatic pressure causes some of the wastewater  1000  to penetrate through the first filter media sheet  110  or the second filter media sheet  115  into the filter interior volume  200 . In so doing, this portion of the wastewater  1000  is filtered so that a filtered portion of the wastewater  1000  (hereinafter, the filtered water  1005 ) has a lower solids content than the wastewater  1000  external to the filter interior volume  200 . The filtered water  1005 , in turn, eventually enters the first member interior volume  220  via the filtered water openings  215  and exits the filter cartridge  100  from the filtered water outlet  155  and the filtered water hose  305 . Some of the solids filtered from the wastewater  1000  collect on the first filter media sheet  110 , which are visible as accumulated solids  1010  in  FIGS.  14 - 17   . The filtered water  1005  can then be collected and further treated and/or reintroduced into the receiving environment. 
     It will be noted that the filter cartridge  100  is inclined, that is, it is oriented with the first exterior media surface  235  and the second exterior media surface  245  forming an oblique angle with respect to the Earth. Filtering by the filter cartridge  100  may be enhanced by installing the filter cartridge  100  with such an inclined orientation. When the wastewater  1000  flows over the inclined filter cartridge  100 , solids from the wastewater  1000  tend to settle on the upward-facing surfaces of the filter cartridge  100 . This kind of filtering is sometimes referred to as “lamella settlement” or “lamella separation” (LAMELLA® is a registered trademark of Parkson Corporation (Fort Lauderdale, Fla., USA)). This settling adds to the accumulated solids  1010  on the filter cartridge  100 . Some of the settled solids also slide down the filter cartridge  100  by gravity to the bottom of the wastewater treatment tank. 
     In this manner, the filter cartridge  100  filters the wastewater  1000  by two mechanisms simultaneously. Solids are captured in the first filter media sheet  110  and in the second filter media sheet  115  as the wastewater passes from the outside of the filter cartridge  100  to the interior of the filter cartridge  100 . At the same time, solids from the wastewater settle on the upward-facing inclined face of the filter cartridge  100  as the wastewater passes over the filter cartridge  100 . 
     At a low to moderate level, the accumulated solids  1010  actually act as another membrane and aid with filtering by the filter cartridge  100 . However, eventually, the accumulated solids  1010  grow to a level that slows the rate at which the filtering occurs. Such a condition can be detected by a corresponding slowing of the filtered water exiting the filtered water outlet  155 . If a constant flow of new wastewater is introduced into the wastewater treatment tank during the filtering process, slowed filtering is also indicated by an increase in the level of the wastewater  1000  in the wastewater treatment tank. 
     A purging (i.e., backwashing) process may then be initiated in the filter cartridge  100  via the purging fluid inlet  160  and the purging fluid hose  310  to help rid the filter cartridge  100  of some portion of the accumulated solids  1010 . The purging is performed with the filter cartridge  100  in situ; the filter cartridge  100  remains submerged in the wastewater  1000  during the purging process. The purging fluid may comprise, for example, clean water or compressed air. Clean water may be sourced from a reservoir via a pump, and compressed air may be generated by an air compressor. The purging fluid is directed into the purging fluid inlet  160  via the purging fluid hose  310 . The purging fluid travels to the fourth member interior volume  210  and exits the fourth member  195  into the filter interior volume  200  from the purging fluid openings  205 . 
     Compressed air is preferred for purging because it does not add additional liquid volume to the wastewater treatment tank. However, the dynamics occurring while purging the filter cartridge  100  with clean water are largely the same as those described herein for compressed air.  FIGS.  18 - 22    show the filter cartridge  100  submerged in the wastewater  1000  during purging by compressed air. In these figures:  FIG.  18    shows a partially-broken elevational view of the filter cartridge  100  during purging,  FIG.  19    shows a sectional view of the filter cartridge  100  during purging along the cleave plane indicated in  FIG.  18   ,  FIG.  20    shows a partially-broken elevational view of the filter cartridge  100  during purging in the region indicated in  FIG.  18   ,  FIG.  21    shows a sectional view of the filter cartridge  100  during purging in the region indicated in  FIG.  19   , and  FIG.  22    shows a partially-broken elevational view of the filter cartridge  100  during purging in the region indicated in  FIG.  18   . 
     After leaving the purging fluid openings  205 , air bubbles  315  begin to rise in the filter interior volume  200  towards the first member  180 . The presence of the compressed air inside the filter interior volume  200  affects the filter cartridge  100  in several ways. Because of the internal baffles  150 , the air bubbles  315  cannot proceed straight through the filter interior volume  200 , but, instead, take a tortuous path through the filter interior volume  200 . This tortuous path and the corresponding turbulence tend to distribute the air bubbles  315  evenly throughout the filter interior volume  200 , and, as the air bubbles  315  collide with the internal baffles  150 , they also produce vibration, which is transferred to the first filter media sheet  110  and the second filter media sheet  115 . Simultaneously, some of the air bubbles  315  escape the filter cartridge  100  by penetrating the first filter media sheet  110  and the second filter media sheet  115  into the surrounding wastewater  1000 . Lastly, the higher pressure of the compressed air in the filter interior volume  200  versus that external to the filter cartridge  100  causes the first filter media sheet  110  and second filter media sheet  115  to deflect outward (i.e., bow or balloon) somewhat. 
     The purging fluid introduced into the purging fluid inlet  160 , whether it be compressed air or clean water, thereby cleans the accumulated solids  1010  from the first filter media sheet  110  and the second filter media sheet  115  via at least three mechanisms. The purging fluid produces vibrations that knock off the accumulated solids  1010 . The purging fluid penetrates the first filter media sheet  110  and the second filter media sheet  115  in the outward direction, again, forcing the accumulated solids  1010  off of the filter media sheets  110 ,  115 . Lastly, the purging fluid causes the first filter media sheet  110  and the second filter media sheet  115  to deflect outward somewhat with the resultant effect of helping to dislodge the accumulated solids  1010  from the filter media sheets  110 ,  115 . 
     Purging of the filter cartridge  100  in this manner may be performed at various levels of intensity. While the external hydrostatic pressure acting on the filter cartridge  100  would depend on depth, in one or more illustrative embodiments, the external hydrostatic pressure may be about 17-19 pounds-per-square-inch (psi). Accordingly, internal pressure within the filter interior volume  200  during a lower-intensity clean may be set to achieve an internal pressure of about 25 psi (i.e., 6-8 psi higher than the external hydrostatic pressure). The lower-intensity purging may be purposefully designed to leave some of the accumulated solids  1010  on the filter cartridge  100 , allowing that remaining portion to aid with filtering and avoiding turbidity spikes. A higher-intensity purging might utilize an internal pressure closer to about 35 psi (i.e., 16-18 psi higher than the external hydrostatic pressure). If so desired, lower-intensity purging could be performed more often than a higher-intensity purging, with the higher intensity purging occurring, as just one example, once every 3-4 purging cycles. Purging may occur, for example, every two hours, and the purging itself may require about one minute for completion. These numbers are, of course, just by way of example and not intended to limit the scope of the invention. 
     The first fin assembly  120  with its first straight fins  255  and first angled fins  260 , as well as the second fin assembly  125  with its second straight fins  265  and second angled fins  270 , perform several functions in the filter cartridge  100  both during active filtration and purging. During filtration, the first angled fins  260  and the second angled fins  270  with their angled orientations deflect settling solids away from the filter cartridge  100 . While purging, the first angled fins  260  and the second angled fins  270  also trap purging fluid leaving the filter cartridge  100  so that the purging fluid remains near the first filter media sheet  110  and the second filter media sheet  115  longer, helping to scour these filter media sheets  110 ,  115  of the accumulated solids  1010 . The first straight fins  255 , the first angled fins  260 , the second straight fins  265 , and the second angled fins  270  also prevent the first filter media sheet  110  and second filter media sheet  115  from deflecting (i.e., bowing or ballooning) too much during purging by restricting the deflection to small squares on the first filter media sheet  110  and the second filter media sheet  115 . Lastly, the first fin assembly  120  and the second fin assembly  125  in combination with the internal baffles  150  provide additional strength and rigidity to the filter cartridge  100 . 
     In addition to the purging process, the filter cartridge  100  may be cleaned externally by placing them in close proximity to spray panels. The spray panels are designed to receive purging fluid and to emit that purging fluid so that it impinges on the outside of the filter cartridge  100 . The impinging fluid aids in externally cleaning the first exterior media surface  235  and the second exterior media surface  245  of the first filter media sheet  110  and the second filter media sheet  115 . 
     Aspects of a spray panel  400  in accordance with an illustrative embodiment are shown in  FIGS.  23 - 25   , with:  FIG.  23    showing an elevational view of the spray panel  400 ,  FIG.  24    showing an exploded perspective view of the spray panel  400 , and  FIG.  25    showing an elevational view of the spray panel  400  in the region indicated in  FIG.  23   . The spray panel  400  has physical dimensions very similar to the filter cartridge  100 . The spray panel  400  comprises: a spray panel frame  405 , a first spray plate  410 , a second spray plate  415 , a spray panel handle  420 , and a spray panel input  425 . The spray panel frame  405  is similar to the peripheral frame  105  of the filter cartridge  100  but does not contain a filtered water outlet like the filtered water outlet  155  in the peripheral frame  105  since the spray panel  400  does not perform a filtering function. The first spray plate  410  and the second spray plate  415  are attached to the spray panel frame  405  in spaced face-to-face relation so that the spray panel frame  405 , the first spray plate  410 , and the second spray plate  415  combine to define an interior volume within the spray panel  400  (hereinafter, the spray panel interior volume  430 ). At the same time, in a manner similar to the purging fluid inlet  160  in the filter cartridge  100 , the spray panel input  425  travels through the spray panel frame  405  and empties into an interior of the bottommost member of the spray panel frame  405 . Spray panel holes  440  in the bottommost member allow the purging fluid from the interior of the bottommost member to enter the spray panel interior volume  430 . The spray panel input  425  is thereby in fluid communication with the spray panel interior volume  430 . 
     A given spray panel  400  can be configured to emit purging fluid from one face or from both faces depending on whether that given spray panel  400  is disposed between two filter cartridges  100  or only neighbors a single filter cartridge  100 . Accordingly, three iterations of the spray panel  400  are intended, as indicated in  FIG.  24   : one where the first spray plate  410  is perforated and the second spray plate  415  is blank, one where the first spray plate  410  is blank and the second spray plate  415  is perforated, and one where both the first spray plate  410  and the second spray plate  415  are perforated. Once in the spray panel interior volume  430 , the purging fluid exits the first spray plate  410  and/or the the second spray plate  415  through these perforations. 
     It is contemplated that a plurality of filter cartridges  100  and a plurality of spray panels  400  may be implemented in a given wastewater filtration system so as to achieve the necessary filtering velocity and cleaning efficiency.  FIGS.  26 - 29    show aspects of a wastewater filtration system  500  (a form of apparatus) comprising a plurality of filter cartridges  100  and a plurality of spray panels  400 , in accordance with an illustrative embodiment of the invention.  FIG.  26    shows an exploded perspective view of the wastewater filtration system  500  without wastewater present,  FIG.  27    shows another perspective view of the wastewater filtration system  500  without wastewater present, and  FIGS.  28  and  29    show sectional views of the wastewater filtration system  500  without wastewater present along the respective cleave planes indicated in  FIG.  27   . 
     In addition to the filter cartridges  100  and the spray panels  400 , the wastewater filtration system  500  comprises: a wastewater treatment tank  515 , a wastewater input pipe  525 , wastewater input barriers  530 , a wastewater overflow barrier  535 , a wastewater overflow pipe  540 , a sludge removal pipe  545 , a sludge removal valve  550 , a clean water trough  555 , clean water transfer hoses/pipes  560 , a clean water output pipe  565 , purging fluid hoses  570 , purging fluid manifolds  575 , a purging fluid source  580 , and purging fluid source lines  585 . Wastewater enters the wastewater treatment tank  515  through the wastewater input pipe  525 , where the wastewater is directed toward the bottom of the wastewater treatment tank  515  via the wastewater input barriers  530 . There, the wastewater is filtered by the filter cartridges  100 . If the wastewater in the wastewater treatment tank  515  gets to a level above the wastewater overflow barrier  535 , it is removed from the wastewater treatment tank  515  via the wastewater overflow pipe  540  to avoid overflows. A sludge removal pipe  545  with upward-oriented holes is positioned in the bottom of the wastewater treatment tank  515  and allows sludge to periodically be removed from the bottom of the wastewater treatment tank  515  via the sludge removal valve  550 . 
     In the illustrative wastewater filtration system  500 , the filter cartridges  100  and the spray panels  400  are removably mounted in racks in the wastewater treatment tank  515  to form two side-by-side banks of filter cartridges  100  and spray panels  400 . This separation into two side-by-side banks allows the widths of the filter cartridges  100  and the spray panels  400  to be reduced. If the filter cartridges  100  and the spray panels  400  were, instead, the full-size width of a tank, they could be prohibitively heavy, particularly when wet. In each bank, the filter cartridges  100  and the spray panels  400  alternate such that each filter cartridge  100  is positioned between, and in close proximity to, two spray panels  400 . The distance between a given filter cartridge  100  and a neighboring spray panel  400  in a given bank may be, for example, about two inches. The racks hold the filter cartridges  100  and the spray panels  400  such that they are oriented at an oblique angle with respect to the Earth. 
     The clean water trough  555  surrounds one end of the wastewater treatment tank  515  of the wastewater filtration system  500 . Filtered water from the filtered water outlets  155  of each of the filter cartridges  100  flows into the clean water trough  555  via the clean water transfer hoses/pipes  560 . The clean water transfer hoses/pipes  560  penetrate the sidewalls of the wastewater treatment tank  515 . Once in the clean water trough  555 , the filtered water is collected via the clean water output pipe  565 . The filtered water in the clean water trough  555  may also be used as a source of clean water for purging, if so desired. The purging fluid inlets  160  of each of the filter cartridges  100 , as well as each of the spray panel inputs  425  of each of the spray panels  400 , are attached via the purging fluid hoses  570  to the purging fluid manifolds  575 . The purging fluid manifolds  575  are connected to the purging fluid source  580  via purging fluid source lines  585 . 
       FIGS.  30 - 32    show aspects of the wastewater filtration system  500  during active filtering of wastewater  2000 , with:  FIG.  30    showing a partially-broken sectional view of the wastewater filtration system  500  during filtering along the same cleave plane as  FIG.  28   ,  FIG.  31    showing a sectional view of the wastewater filtration system  500  during filtering in the region indicated in  FIG.  30   , and  FIG.  32    showing a sectional view of the wastewater filtration system  500  during filtering along the cleave plane indicated in  FIG.  30   . The wastewater  2000  is preferably introduced into the wastewater treatment tank  515  at a rate that creates a largely quiescent flow across the wastewater treatment tank  515 . This gentle flow allows the pressure across all of the filter cartridges  100  to be equal, stops the filter cartridges  100  from being exposed to rushing wastewater  2000 , and allows settling solids to settle to the bottom of the wastewater treatment tank  515 . Water filtered by the filter cartridges  100  (hereinafter, filtered water  2005 ) leaves the filter cartridges  100  via their filtered water outlets  155  and enters the clean water trough  555  via the clean water transfer hoses/pipes  560 . Eventually, the filtered water  2005  is collected via the clean water output pipe  565 . Notably, the respective rate at which filtered water  2005  is produced by each of the filter cartridges  100  in the wastewater filtration system  500  can be individually determined by simply observing the rate at which filtered water  2005  exits each of the filtered water outlets  155 . By extension, the respective state of the accumulated solids  2010  on each of the filter cartridges  100  can be individually monitored. A filter cartridge  100  with a slow filtration rate may be removed from the wastewater filtration system  500  and serviced without stopping production by the other filter cartridges  100  in the wastewater filtration system  500 . 
       FIGS.  33  and  34    show aspects of the wastewater filtration system  500  during external cleaning of the filter cartridges  100  by the spray panels  400 .  FIG.  33    shows a sectional view of the wastewater filtration system  500  during external cleaning along the same cleave plane as  FIG.  32   , while  FIG.  34    shows a sectional view of the wastewater filtration system  500  during external cleaning in the region indicated in  FIG.  33   . The external cleaning of filter cartridges  100  by the spray panels  400  and the internal purging of the filter cartridges  100  may occur separately or simultaneously. In  FIGS.  33  and  34   , only the dynamics of cleaning by the spray panels  400  are shown since the dynamics of purging the filter cartridges  100  were described in detail above. As was the case for purging the filter cartridge  100 , the purging fluid used by the spray panels  400  may comprise clean water or compressed air. Compressed air is somewhat preferred and that is what is shown in  FIGS.  33  and  34   . 
     During the external cleaning, air bubbles  590  leaving the spray panels  400  impinge on the filter cartridges  100 , acting to knock off accumulated solids  2010  from the filter cartridges  100 . As was the case when purging the filter cartridge  100 , the angled fins  260 ,  270  aid with cleaning. While external cleaning, the angled fins  260 ,  270  trap the air bubbles  590  so that the air bubbles  590  remain near the first filter media sheet  110  and the second filter media sheet  115  longer, helping to scour these filter media sheets  110 ,  115  of the accumulated solids  2010 . At the same time, the angled fins  260 ,  270  deflect settling solids away from the filter cartridges  100 . 
     It should again be emphasized that the above-described embodiment of the invention are intended to be illustrative only. Other embodiments can use different types and arrangements of elements for implementing the described functionality. These numerous alternative embodiments within the scope of the appended claims will be apparent to one skilled in the art. The spirit and scope of the appended claims should not be limited solely to the description of the preferred embodiments contained herein. 
     For example, while the purging and external cleaning of the filter cartridge  100  can be performed manually in the wastewater filtration system  500 , technology may be utilized to automate these processes. As the filter cartridges  100  become substantially coated with the accumulated solids  2010 , their filtration rate tends to slow and the level of wastewater  2000  in the wastewater treatment tank  515  tends to rise so long as the rate of inflow of the wastewater  2000  into the wastewater treatment tank  515  remains constant. The level of wastewater  2000  in the wastewater treatment tank  515  thereby can become an indicator for the total filtration rate of the filter cartridges  100  in the wastewater filtration system  500 . 
       FIG.  35    shows a sectional view of a modified filtration system  500 ′ in accordance with another illustrative embodiment of the invention during filtration of the wastewater  2000  along the same cleave plane as  FIG.  32   . The modified filtration system  500 ′ includes many of the same elements as the wastewater filtration system  500 , which are labeled with like reference numerals. To aid with automation, the modified filtration system  500 ′ further includes a water level sensor  600  and a controller  605 . The water level sensor  600  acts to measure the level of the wastewater  2000  in the wastewater treatment tank  515  of the modified filtration system  500 ′. The controller  605  reads this water level, and when a predetermined water level is achieved, commands the purging fluid source  580  to send purging fluid to the filter cartridges  100  and to the spray panels  400  so as to activate the purging and external cleaning of the filter cartridges  100 . The controller  605  can activate the purging fluid source  580  for a predetermined amount of time, or, alternatively, may activate the purging fluid source  580  until the water level in the wastewater treatment tank  515  starts to drop or reaches a predetermined water level. The controller  605  may comprise, for example, a programmable logic controller (PLC). 
     In addition, filtering velocity in the wastewater filtration system  500  may be enhanced by the addition of inclined plate settlers or lamella packs in those regions of the wastewater treatment tank  515  not already occupied by the filter cartridges  100  and the spray panels  400 . Viewing the wastewater filtration system  500  in  FIG.  32   , for example, there is space for these additional inclined plates or lamella packs both to the right and left of the filter cartridges  100  and the spray panels  400 , particularly if the added elements are shorter than the filter cartridges  100  and the spray panels  400 . Suitable lamella packs are commercially available from several vendors, including, as just one example, Parkson Corporation (Fort Lauderdale, Fla., USA). 
     If even greater cleaning capability is desired for the filter cartridges  100  in the wastewater filtration system  500 , aeration diffusers may be added to the bottom of the wastewater treatment tank  515 . These aeration diffusers may be plumbed to a source of compressed air and made to expel plumes of air bubbles so that the air bubbles impinge on the filter cartridges  100  to further externally clean the filter cartridges  100 . Suitable aeration diffusers are commercially available from several vendors, including, for example, SSI Aeration, Inc. (Poughkeepsie, N.Y., USA). 
     Lastly, technologies in accordance with aspects of the invention lend themselves to being packaged in cages that can be introduced into existing wastewater treatment tanks. An illustrative cage may comprise, for example, many of the same elements as the wastewater filtration system  500 , namely, racks for holding the filter cartridges  100  and the spray panels  400 , plumbing for the filtered water, plumbing for the purging fluid, etc. The cage may be fitted with lifting posts and may be raised and lowered by, for example, a gantry. 
     Aspects of the invention thereby provide several advantages over prior-art designs. The design of the filter cartridge  100 , for example:
         1. Is robust;   2. Provides a great deal of filtration area per tank volume;   3. May be closely spaced to other filtration cartridges and other filtering elements;   4. May be mounted at an incline to harness lamella settlement as a secondary filtering mechanism;   5. Lends itself to easy placement in, and removal from, a wastewater filtration system without having to halt filtering by other filters in the system;   6. Allows individualized monitoring of filter velocity by having an easily observed and cartridge-specific output of filtered water;   7. Lends itself to various modes of cleaning including internal purging as well as external cleaning by external elements such as spray panels and diffusers;   8. Lends itself to cleaning by modes with low energy consumption and no moving parts to maintain;   9. May be cleaned by a choice of purging fluids such as clean water and compressed air;   10. Lends itself to various intensities of cleaning including those gentle enough to maintain helpful amounts of accumulated solids and avoid turbidity spikes;   11. Lends itself to use in a water filtration system with other types of filters such as inclined plates and/or lamella packs; and   12. Lends itself to incorporation in a wastewater filtration system that only creates a single sludge waste stream to treat.       

     All the features disclosed herein may be replaced by alternative features serving the same, equivalent, or similar purposes, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.