Abstract:
A ballasted sequencing batch reactor system for treating wastewater including one or more sequencing batch reactors. A weighting agent impregnation subsystem is configured to mix biological flocs and weighting agent to form weighted biological flocs. A weighting agent recovery subsystem is configured to recover weighting agent from the weighted biological flocs and reintroduce the recovered weighting agent to the weighting agent impregnation subsystem.

Description:
RELATED APPLICATIONS 
       [0001]    This application is a continuation-in-part of U.S. patent application Ser. No. 12/584,545, filed Sep. 8, 2009, which is a continuation-in-part of U.S. patent application Ser. No. 12/008,216, filed Jan. 9, 2008, now U.S. Pat. No. 7,695,623, issued Apr. 13, 2010, which claims benefit of and priority to U.S. Provisional Application Ser. No. 60/879,373, filed Jan. 9, 2007, and U.S. Provisional Application Ser. No. 60/994,553, filed Sep. 20, 2007, all of which are incorporated by reference herein. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates to a ballasted sequencing batch reactor (SBR) system and method for treating wastewater. 
       BACKGROUND OF THE INVENTION 
       [0003]    SBR systems are used to treat wastewater. A typical conventional SBR system includes one or more SBRs which contain a large population of microorganisms that ingest contaminants in the influent wastewater to form biological flocs and treat the wastewater. SBR systems typically use four phases to treat wastewater: fill, react, settle, and decant. During the fill phase, the SBR is filled with the influent wastewater and may be aerated, mixed without aeration, or not mixed and not aerated. The react phase involves adding oxygen, mixing, or a combination thereof, to provide treatment by converting biochemical oxygen demand (BOD) to microorganisms to form biological flocs. During the settle phase, the biological flocs formed in the previous phases are allowed settle to the bottom of the SBR to form settled sludge. The decant phase involves slowly decanting the clear water from the settled sludge to provide a treated effluent. 
         [0004]    However, during the settling phase of a typical conventional SBR system, the biological flocs are only marginally heavier than water and therefore settle very slowly. Moreover, the solids separation in the settle phase may be unreliable due to many types of settling problems that are caused by: overgrowth of filamentous organisms, viscous bulking caused by the overgrowth of either zoogleal organisms or exocellular polysaccharide material, pin floc, straggler floc, and the like. This may limit the capacity of a conventional SBR system and can compromise the quality of the treated effluent. 
       BRIEF SUMMARY OF THE INVENTION 
       [0005]    This invention features a ballasted sequencing batch reactor system for treating wastewater including one or more sequencing batch reactors. A weighting agent impregnation subsystem is configured to mix biological flocs and weighting agent to form weighted biological flocs. A weighting agent recovery subsystem is configured to recover weighting agent from the weighted biological flocs and reintroduce the recovered weighting agent to the weighting agent impregnation subsystem. 
         [0006]    In one embodiment, the system may include a sludge storage tank configured to receive settled sludge from the one or more sequencing batch reactors, store the settled sludge therein, and regulate the flow of settled sludge to weighting agent recovery subsystem. The weighting agent recovery subsystem may include a separator subsystem for separating the weighting agent from the weighted biological flocs. The separator subsystem may include a shear mill. The separator subsystem may include a centrifugal separator. The separator subsystem may include an ultrasonic separator. The separator subsystem may include a shear mill and a wet drum magnetic separator. The separator subsystem may include a shear mill and a centrifugal separator. The separator subsystem may include an ultrasonic separator and a wet drum magnetic separator. The separator subsystem may include an ultrasonic separator and a centrifugal separator. The shear mill may include rotor and a stator, wherein the rotor and/or the stator include slots sized as to optimize separation of weighting agent from the weighted biological flocs. The weighting agent impregnation subsystem may include an impregnation tank and at least one mixer. The capacity of the system may be increased by reducing the duration of a settle phase. The one or more sequencing batch reactors may be configured to decant clear effluent from settled sludge to provide a treated effluent. The weighted biological flocs may enhance the quality of the treated effluent by reducing the concentration of suspended solids and related contaminants therein. The system may include a wasting subsystem for wasting settled sludge from the weighting agent recovery subsystem to control a population of microorganisms in a mixed liquor in the one or more sequencing batch reactors. The capacity of the system may be increased by increasing the concentration of the mixed liquor in the one or more sequencing batch reactors by reducing the amount of settled sludge wasted by a wasting subsystem. The capacity of the system may be increased by reducing the duration of a react phase. The amount of settled sludge wasted by the wasting subsystem may be reduced to increase the concentration of mixed liquor suspended solids for enhancing nitrification and/or de-nitrification of ammonia in the mixed liquid. Nitrification may be enhanced by increasing the amount of dissolved oxygen introduced into the one or more sequencing batch reactors. A coagulant may be added to the one or more sequencing batch reactors for removing phosphorus by precipitation and/or coagulation. A flocculant may be added to the one or more sequencing batch reactors for enhancing settling and thickening of the weighted biological flocs and for providing agglomeration of non-impregnated biological flocs and/or partially impregnated biological flocs with weighted biological flocs. The weighting agent impregnation subsystem may include a venturi mixer/eductor. A majority of the weighting agent may have a particle size less than about 100 μm. A majority of the weighting agent may have a particle size less than about 40 μm. A majority of the weighting agent may have a particle size less than about 20 μm. The weighting agent may include magnetite. The system may include a mixer disposed in each of the one or more sequencing batch reactors for maintaining the suspended solids or the mixed liquor in suspension. 
         [0007]    This invention also features a method for treating wastewater using one or more sequencing batch reactors, the method including the steps of: a) receiving influent wastewater in the one or more sequencing batch reactors, b) forming biological flocs in the one or more sequencing batch reactors, c) impregnating weighting agent into the biological flocs to form weighted biological flocs, and d) recovering weighting agent from the weighted biological flocs to reintroduce the weighting agent to step c). 
         [0008]    In one embodiment, the method may include the step of separating the weighting agent from the weighted biological flocs. The method may include the step of collecting the weighting agent and recycling the weighting agent to step c). The method may include the step of providing weighting agent in which the majority of the weighting agent has a particle size less than about 100 μm. The method may include the step of providing weighting agent in which the majority of the weighting agent has a particle size less than about 40 μm. The method may include the step of providing weighting agent in which the majority of the weighting agent has a particle size less than about 20 μm. The method may include the step of introducing dissolved oxygen to a population of microorganisms to promote growth of biological flocs in a mixed liquor defined by a concentration of mixed liquor suspended solids. The method may include the step of introducing a flocculant to the mixed liquor to enhance settling and thickening of the weighted biological flocs and to establish agglomeration of non-impregnated biological flocs and/or partially impregnated biological flocs with the weighted biological flocs. The method may include the step of separating and collecting the weighted biological flocs from the mixed liquor in the one or more sequencing batch reactors to provide a secondary effluent and a settled sludge. The method may include the step of recycling the majority of the settled sludge to step b). The method may include the step of decanting the clean effluent from the settled sludge in the one or more sequencing batch reactors to provide a treated effluent. The method may include the step of wasting the remaining settled sludge using a wasting subsystem to control the population of the microorganisms in the mixed liquor. The method may include the step of increasing the capacity of the system by reducing the duration of a settle phase. The method may include the step of enhancing the quality of the treated effluent by reducing suspended solids and related contaminants therein. The method may include the step of wasting settled sludge from the weighting agent recovery subsystem to control a population of microorganisms in a mixed liquor in the one or more sequencing batch reactors. The method may include the step of increasing the capacity of the system by increasing the concentration of the mixed liquor in the one or more sequencing batch reactors by reducing the amount of settled sludge wasted by a wasting subsystem. The method may include the step of increasing the capacity of the system by reducing the duration of a react phase. The method may include the step of reducing the amount of settled sludge wasted by the wasting subsystem to increase the concentration of mixed liquor suspended solids which enhances nitrification and/or de-nitrification of ammonia in the mixed liquid. The method may include the step of enhancing nitrification by increasing the amount of dissolved oxygen introduced into the one or more sequencing batch reactors. The weighting agent may be impregnated into the biological flocs in step b) by mixing the mixed liquor and the biological flocs at a predetermined energy level. 
         [0009]    The subject invention, however, in other embodiments, need not achieve all these objectives and the claims hereof should not be limited to structures or methods capable of achieving these objectives. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0010]    Other objects, features and advantages will occur to those skilled in the art from the following description of a preferred embodiment and the accompanying drawings, in which: 
           [0011]      FIG. 1  is a schematic block diagram of one embodiment of the SBR system for treating wastewater in accordance with this invention; 
           [0012]      FIG. 2  is a microscopic view showing one example of weighting agent impregnated in biological flocs using the weighting agent impregnation system shown in  FIG. 1 ; 
           [0013]      FIG. 3  is a schematic block diagram showing another embodiment of the SBR system for treating wastewater of this invention; 
           [0014]      FIG. 4  is a schematic side-view of another embodiment of the impregnation subsystem shown in  FIGS. 1 and 3 ; 
           [0015]      FIG. 5A  is a schematic side-view of one embodiment of the separator shown in  FIGS. 1 and 3 ; 
           [0016]      FIG. 5B  is a schematic top view showing one example of slots in the rotor and stator of the shear mill shown in  FIG. 5A ; 
           [0017]      FIG. 5C  is a three-dimensional view of one embodiment of the shear mill in  FIG. 5A ; 
           [0018]      FIG. 6  is a three-dimensional front-view of another embodiment of the separator shown in  FIGS. 1 and 3 ; and 
           [0019]      FIG. 7  is a three-dimensional front-view of yet another embodiment of the separator shown in  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0020]    Aside from the preferred embodiment or embodiments disclosed below, this invention is capable of other embodiments and of being practiced or being carried out in various ways. Thus, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of components set forth in the following description or illustrated in the drawings. If only one embodiment is described herein, the claims hereof are not to be limited to that embodiment. Moreover, the claims hereof are not to be read restrictively unless there is clear and convincing evidence manifesting a certain exclusion, restriction, or disclaimer. 
         [0021]    There is shown in  FIG. 1 , one embodiment of SBR system  10  for treating wastewater of this invention. System  10  includes at least one SBR  12  which receives a flow of influent wastewater  14  by line  16 . SBR  12  preferably introduces air bubbles  18  by line  20  exposed to ambient air  22 . Air bubbles  18  introduce dissolved oxygen to a population of microorganisms in SBR  12  to promote growth of biological flocs  23  in mixed liquor  24 . Mixed liquor  24  as used herein means a combination of influent wastewater  14  and biological flocs  23 . 
         [0022]    System  10  also includes weighting agent impregnation subsystem  26  which, in one embodiment, includes impregnation tank  28  and mixer  30  which receives mixed liquor  24  from SBR  12  by line  32 . In one embodiment, impregnation tank  28  preferably receives virgin weighting agent  33 , e.g., from feed hopper  34  by line  36 , and/or recycled weighting agent  38  from weighting agent recovery subsystem  74  (discussed below). Weighting agent impregnation subsystem  26  mixes mixed liquor  24  or settled sludge received by line  77  and virgin weighting agent  33  and/or the recycled weighting agent  38  in impregnation tank  28  to impregnate the weighting agent into biological flocs  23  suspended in mixed liquor  24  or settled sludge by line  77  via sludge storage tank  88  and line  76  and/or via lines  76  and  81  to form weighted biological flocs. Mixer  30  utilizes a mixing energy which is sufficient to impregnate the weighting agent into biological flocs suspended in a mixed liquor to form weighted biological flocs.  FIG. 2  shows one example of weighting agent  33 ,  38  impregnated into biological flocs  23  to form weighted biological flocs  25 . The weighted biological flocs impregnated with the weighting agent are then sent back to SBR  12 ,  FIG. 1 , by line  37 . 
         [0023]    The weighting agent may be magnetite, or any similar type weighting agent or magnetically separable inorganic material known to those skilled in the art which increases the density of the biological flocs. In one example, the majority of the weighting agent particles may have a size less than about 100 μm. In other examples, the majority of the weighting agent particles may have a size less than about 40 μm, or, the majority of the weighting agent may have a particle size less than about 20 μm. 
         [0024]    System  10  also includes weighting agent recovery subsystem  74  which receives settled sludge from bottom  39  of SBR  12  by line  76  typically after the settle and decant phases are complete. Weighting agent recovery subsystem  74  preferably includes separator  78  which recovers the weighting agent from the weighted biological flocs in the settled sludge in line  76  and reintroduces (recycles) the weighting agent to weighting agent impregnation subsystem  26  by line  79 . Weighting agent recovery subsystem  74  may include recovery subsystem  83 , discussed below. 
         [0025]    In one embodiment, system  10  includes sludge storage tank  88  which stores settled sludge output from SBR  12  by line  76  typically after the decant phase is complete. 
         [0026]    In one exemplary operation of SBR system  10 , SBR  12  is filled with influent wastewater  14  via line  16  and seeded with a large population of microorganisms that ingest contaminants in influent wastewater  14  to form biological flocs  23 . During a fill phase, dissolved oxygen via air bubbles  18  may be introduced to mixed liquor  24  to promote growth of biological flocs  23 . Once filled, system  10  undergoes a react phase. During the fill and/or react phases, weighting agent impregnation subsystem  26  receives the mixed liquor by line  32 , or settled sludge by line  77  via sludge storage tank  88  and line  76  and/or via lines  76  and  81 , and impregnates the biological flocs therein with virgin weighting agent  33  and/or recycled weighting agent  38  using mixer  30 . The mixed liquor or settled sludge having weighted biological flocs is then sent back to SBR  12  by line  37 . The react phase is followed by the settling phase where the weighted biological flocs settle to bottom  39  of SBR  12  to form settled sludge. The times for the fill, react, settle, and decant phases vary as known by those skilled in the art. Then, the clear effluent is decanted by line  52  to provide treated effluent  50 . During or after the decant phase, some of the settled sludge at bottom  39  of SBR  12  may be sent to sludge storage tank  88  via line  76 . Sludge storage tank  88  stores sludge from SBR  12  and regulates the flow thereof to weighting agent recovery subsystem  74 . Weighting agent recovery subsystem  74  then recovers the weighting agent from the weighted biological flocs as discussed above and recycles the weighting agent to weighting agent impregnation subsystem  26  as recovered weighting agent  38 . 
         [0027]    Because the weighted biological flocs in SBR  12  have a greater specific gravity than non-impregnated biological flocs, they settle faster than non-impregnated biological flocs utilized in a typical conventional SBR system. Thus, the time needed for the settling phase of system  10  is reduced. This alleviates settling problems associated with a conventional SBR system, such as overgrowth of filamentous organisms, viscous bulking caused by the overgrowth of either zoogleal organisms or exocellular polysaccharide material, pin floc, straggler floc, and the like. The result is the capacity of system  10  to treat wastewater may be increased while providing high quality treated effluent  50 . Because the time needed in the settling phase is reduced, system  10  may also allow more time for the react phase, which further increases the quality of treated effluent  50 . The weighted biological flocs also enhance the quality of the treated effluent by reducing the concentration of suspended solids and related contaminants therein. The weighted biological flocs also facilitate higher mixed liquor suspended solids (MLSS) concentrations. Operating at higher MLSS concentrations provides additional advantages, including additional increased treatment capacity, enhanced nitrogen removal, enhanced phosphorus removal, and the like. Moreover, because weighting agent recovery subsystem  74  recovers and recycles the weighting agent, the operational costs of system  10  are significantly reduced. 
         [0028]    System  10 ′,  FIG. 3 , where like parts have been given like numbers, includes at least two SBRs  12 ′ and  12 ″. In this example, SBR  12 ′ is filled with influent wastewater  14  by line  16  by opening valve  62  and closing valve  64 . Once SBR  12 ′ is filled, valve  62  is closed and valve  64  is open. SBR  12 ″ is then similarly filled with influent wastewater  14 . Thus, system  10 ′ allows a continuous flow of influent wastewater  14  to either SBR  12 ′ or SBR  12 ″ for continuous operation. System  10  is not limited to two SBRs, as any number of SBRs may be utilized to accommodate the flow rate of influent wastewater  14 . In one example, after SBR  12 ′ is filled and SBR  12 ″ is in the fill phase, SBR  12 ′ undergoes the react, settle, and decant phases. Similarly, when SBR  12 ′ is in the fill phase, SBR  12 ″ typically undergoes the react, settle, and decant phases. 
         [0029]    System  10 ′ may include sludge storage tank  88 ′ which receives some of the settled sludge from SBR  12 ′ via line  90  and some of the settled sludge from SBR  12 ″ via line  92  during or after the decant phase in each respective SBR  12 ′,  12 ″. 
         [0030]    System  10 ′ also includes weighting agent impregnation subsystem  26 ′ which, in this embodiment, is located downstream from sludge storage tank  88 ′. In this example, impregnation tank  28  and mixer  30  receives settled sludge from sludge storage tank  88 ′ by line  100 . Impregnation tank  28  also preferably receives virgin weighting agent  33 , e.g., from feed hopper  34  by line  36 , and/or recycled weighting agent  38  from weighting agent recovery subsystem  74 . Mixer  30  mixes the settled sludge and virgin weighting agent  33  and/or the recycled weighting agent  38  in impregnation tank  28  to impregnate the weighting agent into the biological flocs suspended in the settled sludge to form weighted biological flocs, similarly as discussed with reference to  FIG. 1 . 
         [0031]    System  10 ′,  FIG. 3 , also includes weighting agent recovery subsystem  74 ′ which receives the sludge from sludge storage tank  88 ′. Weighting agent recovery subsystem  74 ′ preferably includes separator  78 , which in this embodiment, is located downstream from sludge storage tank  88 ′ and upstream from weighting agent impregnation subsystem  26 . Separator  78  recovers the weighting agent from the weighted biological flocs in the settled sludge in line  95  from sludge storage tank  88 ′ and reintroduces (recycles) the recovered weighting agent  38  to weighting agent impregnation subsystem  26  via line  79 . Weighting agent recovery subsystem  74 ′ may include recovery subsystem  83 ,  FIG. 3 , e.g., a wet drum magnetic separator or similar type device, which is typically located downstream from separator  78 . 
         [0032]    In one exemplary operation of system  10 ′, valve  62  is opened and valve  64  is closed to fill SBR  12 ′ (SBR #1) with influent wastewater  14 . Then valve  62  is closed and valve  64  is opened to fill SBR  12 ″ (SBR #2). While SBR  12 ″ is being filled, SBR  12 ′ undergoes the react, settle, and decant phases as discussed above. During or after the decant phase in SBR  12 ′, excess (waste) settled sludge at the bottom of SBR  12 ′ is pumped to sludge storage tank  88 ′ via line  90 . Some of the settled sludge in sludge storage tank  88  may be directed via line  100  to weighting agent impregnation tank  28  of weighting agent impregnation subsystem  26 ′ and some of the sludge in sludge storage tank  88  may be directed to separator  78  via line  95 . Weighting agent impregnation subsystem  26 ′ impregnates virgin weighting agent  33  and/or recovered weighting agent  38  into the biological flocs in the settled sludge in impregnation tank  28  using mixer  30 . 
         [0033]    Weighting agent recovery subsystem  74 ′ then sends the settled sludge having weighted biological flocs therein to line  16  via line  76 . At this point, SBR  12 ″ (SBR #2) has been filled so valve  62  is opened and valve  64  is closed so that the mixture of influent wastewater  14  and the settled sludge having weighted biological flocs therein is directed to fill SBR  12 ′ (SBR #1). At this point, SBR  12 ″ is undergoing the react, settle, and decant phases. Similar, as discussed above, during or after decant phase, some of the settled sludge at the bottom of SBR  12 ″ is pumped to sludge storage tank  88 ′ via line  92 . This settled sludge is processed by weighting agent impregnation subsystem  26 ′ as discussed above to form weighted biological flocs in the settled sludge in impregnation mixing tank  28 . Weighting agent recovery subsystem  74 ′ then directs the settled sludge with the weighted biological flocs therein to line  16 , as discussed above. Valve  62  is closed and valve  64  is open to fill SBR  12 ″ with the mixture of influent wastewater and settled sludge having weighted biological flocs. The process of switching between SBR  12 ′ and SBR  12 ″ continues when ever system  10 ′ is operational. 
         [0034]    Similar as discussed above, the weighted biological flocs introduced to mixed liquor  24  in SBRs  12 ′,  12 ″ settle faster to reduce the time needed for their respective settling phases. This increases the capacity system  10 ′ to treat wastewater and alleviates the problems associated with conventional SBR systems discussed above and provides a cleaner treated effluent  50 ′,  50 ″. 
         [0035]    Similar as discussed above, flocculant  62 ,  FIG. 3 , may be added to mixed liquor  24  in SBR  12 ′,  12 ″ to enhance settling and thickening of the weighted biological flocs suspended in mixed liquor  24  in SBR  12  and establishes agglomeration of non-impregnated biological flocs and/or partially impregnated biological flocs with the weighted biological flocs in SBR  12 ′,  12 ″. The weighted biological flocs also provide a cleaner treated effluent, with fewer suspended solids and related contaminants. 
         [0036]    Coagulant  64  may also be added to SBR  12 ′,  12 ″ for removing phosphorus from mixed liquor  24  by precipitation and/or coagulation, as known by those skilled in the art. Mixer  40  and/or air bubbles  18  may be used to maintain biological flocs  23  in suspension in mixed liquor  24  and to mix the flocculant and/or the coagulant with mixed liquor  24  in SBR  12 ′,  12 ″. 
         [0037]    In another embodiment, weighting agent impregnation subsystem  26 ′ may receive mixed liquor  24  directly from SBR  12 ′ or directly from SBR  12 ″. Similar as discussed above with reference to  FIG. 1 , weighting agent impregnation tank  28  mixes mixed liquor  24  and virgin weighting agent  33  and/or recovered weighting agent  38  from separator  78  and/or recovery subsystem  83  to impregnate the weighting agent into biological flocs suspended in the mixed liquor to form weighted biological flocs. The weighted biological flocs are then sent back to SBR  12 ′ or to SBR  12 ″. 
         [0038]    Thus, system  10 ′ can impregnate the biological flocs either by impregnating the biological flocs in the mixed liquor in SBRs  12 ′,  12 ″, or by impregnating the biological flocs in the settled sludge output by SBRs  12 ′,  12 ″, or using a combination of both methods. 
         [0039]    System  10 ,  FIG. 1 , and/or system  10 ′,  FIG. 3 , may also utilize weighting agent impregnation subsystem  26 ″,  FIG. 4 , where like parts have been given like numbers. Weighting agent impregnation subsystem  26 ″ includes venturi mixer/eductor  27  having nozzle  31  and funnel  45  which receives virgin weighting agent  33 , e.g., from tank  34  by line  36 , and/or recycled weighting agent  38  from separator  78  or recovery subsystem  83 ,  FIGS. 1 and 3 . Venturi mixer/eductor  27  preferably receives mixed liquor by line  32 ,  FIG. 1 , or settled sludge by line  77 , or settled sludge by line  100 ,  FIG. 3 . 
         [0040]    In operation, the velocity of mixed liquor in line  32 ,  FIG. 1 , or the settled sludge in line  77 , or line  100 ,  FIG. 3 , is increased through nozzle  31 ,  FIG. 4 . Virgin weighting agent  33  and/or recycled weighting agent  38  in funnel  45  enters nozzle  31  by line  39  and travels downstream to line  37 . The widening of line  37  at  41  induces intimate mixing and entrainment, as shown at  43 . This impregnates the virgin and/or recycled weighting agent into the biological flocs to form weighted biological flocs. The weighted biological flocs are then returned to SBR  12 ,  FIG. 1 , by line  37 , or SBR  12 ′,  12 ″,  FIG. 3 , by lines  76  and  16 . 
         [0041]    In one design, separator subsystem  78 ,  FIGS. 1 and 3  may be configured as shear mill  112 ,  FIG. 5A , which shears the sludge in line  76 ,  FIG. 1 , or line  95 ,  FIG. 3 , to separate the weighting agent from the weighted biological flocs. Shear mill  112  ideally includes rotor  80  and stator  82 . In operation, the settled sludge in line  76 ,  FIG. 1  or  95 ,  FIG. 3 , enters shear mill  112  and flows in the direction of arrows  180  and enters rotor  80  and then stator  82 . Shear mill  112  is designed such that there is a close tolerance between rotor  80 ,  FIG. 5B  and stator  82 , as shown at  93 . Rotor  80  is preferably driven at high rotational speeds, e.g., greater than about 1,000 r.p.m., to form a mixture of weighting agent and obliterated flocs in area  181 ,  FIG. 5A , of shear mill  112 . The mixture of weighting agent and obliterated flocs exits shear mill  112  by line  79 , as shown by arrows  184 .  FIG. 5C  shows in further detail the structure of one embodiment of shear mill  112 . Preferably, rotor  80 ,  FIGS. 5A-5C , and/or stator  82  includes slots which function as a centrifugal pump to draw the settled sludge from above and below rotor  80  and stator  82 , as shown by paths  182 ,  FIG. 5A , and then hurl the materials off the slot tips at a very high speed to break the weighted biological flocs into the mixture of weighting agent and obliterated flocs. For example, rotor  80 ,  FIG. 5B , may include slots  186 , and stator  82  may include slots  188 . Slots  186  in rotor  80  and/or slots  188  in stator  82  are preferably optimized to increase shear energy to efficiently separate the weighting agent from the weighted biological flocs. The shear developed by rotor  80  and stator  82  depends on the width of slots  186  and  188 , the tolerance between rotor  80  and stator  82 , and the rotor tip speed. The result is shear mill  112  provides a shearing effect which effectively and efficiently separates the weighting agent from the weighted biological flocs to facilitate recovery of the weighting agent. 
         [0042]    In another design, separator subsystem  78 ,  FIGS. 1 and 3 , may be configured as ultrasonic separator  116 ,  FIG. 6 , where like parts have been given like numbers. Ultrasonic separator  116  typically includes one or more ultrasonic transducers, e.g., ultrasonic transducer  262 ,  264 ,  266 ,  268 , and/or  270 , available from Hielscher Ultrasonics GmbH, Stuttgart, Germany, which generates fluctuations of pressure and cavitation in the settled sludge in line  76 ,  FIG. 1  or line  95 ,  FIG. 3 . This results in microturbulences that produce a shearing effect to create a mixture of weighting agent and obliterated flocs to effectively separate the weighting agent from the weighted biological flocs in the settled sludge. The resulting mixture of weighting agent and obliterated flocs exits ultrasonic separator  116  by line  79 . 
         [0043]    In yet another design, separator subsystem  78 ,  FIG. 7 , where like parts have been given like numbers, may be configured as centrifugal separator  118 . Centrifugal separator  114  typically includes cylindrical section  302  located at the top of hydrocyclone  300  and conical base  304  located below section  302 . The settled sludge in line  76 ,  FIG. 1  or line  100 ,  FIG. 3 , is fed tangentially into cylindrical section  302  via port  303 . Smaller exit port  306  (underflow or reject port) is located at the bottom of conical section  304  and larger exit port  308  (overflow or accept port) is located at the top of cylindrical section  302 . 
         [0044]    In operation, the centrifugal force created by the tangential feed of the sludge by port  303  causes the denser weighting agent to be separated from the biological flocs in the settled sludge. The separated weighting agent is expelled against wall  308  of conical section  304  and exits at port  306 . This effectively separates the weighting agent from the weighted biological flocs. The recovered weighting agent  38  exits via port  306  and may be deposited to weighting agent impregnation system  26 ,  26 ′, or  26 ″,  FIGS. 1 ,  3 , and  4 . The less dense biological flocs remain in the sludge and exit via port  308  through tube  310  extending slightly into the body of the center of centrifugal separator  118 . 
         [0045]    Although as discussed above, separator subsystem  78  may be configured as a shear mill, an ultrasonic separator, or a centrifugal separator, this is not a necessary limitation of this invention. In other designs, separator subsystem  78  may be configured as a tubular bowl, a chamber bowl, an imperforate basket, a disk stack separator, and the like, as known by those skilled in the art. 
         [0046]    In the example above where a separator  78 ,  FIGS. 5A-5C , is configured as shear mill  112  to create the mixture of weighting agent and obliterated biological flocs, a wet drum magnetic separator or centrifugal separator  118 ,  FIG. 7 , may be used to recover the weighting agent therefrom e.g., recycled weighting agent  38 ,  FIGS. 1 and 3 , delivered to weighting agent impregnation subsystem  26  by line  79  and/or recycled weighting agent  38 ,  FIG. 7 , delivered to weighting agent impregnation subsystem  26  via port  306 . 
         [0047]    In the example where separator subsystem  78 ,  FIG. 6 , is configured as an ultrasonic separator  116  to create the mixture of weighting agent and obliterated biological flocs, a wet drum magnetic separator or centrifugal separator  118 ,  FIG. 7 , may be used to recover the weighting agent therefrom, e.g., recycled weighting agent  38 ,  FIGS. 1 and 3 , delivered to weighting agent impregnation subsystem  26  by line  79  and/or recycled weighting agent  38 ,  FIG. 7 , delivered to weighting agent impregnation subsystem  26  via port  306 . 
         [0048]    The result of recovering and recycling the weighting agent as discussed above with reference to  FIGS. 5A-7  significantly reduces the operating costs of wastewater treatment system  10 . 
         [0049]    System  10 ,  10 ′,  FIGS. 1 and 3 , may also include wasting subsystem  85  coupled to separator  78  and/or recovery subsystem  85  which wastes the remaining settled sludge output by separator subsystem  78  and/or recovery subsystem  83  to control the population of the microorganisms in mixed liquor  24  in SBR  12 ,  FIG. 1 , or SBR  12 ′,  12 ″,  FIG. 3 . The capacity of system  10 ,  10 ′,  FIGS. 1 and 3  to process wastewater  14  may be increased by increasing the concentration of the mixed liquor suspended solids (MLSS) in SBR  12 ,  FIG. 1 , or SBR  12 ′,  12 ″,  FIG. 3 , by reducing the amount of settled sludge wasted by wasting subsystem  85 . Increasing the concentration of the MLSS may reduce the duration of the react phase. The amount of settled sludge wasted by wasting subsystem  85  may also be reduced to increase the concentration of MLSS to enhance nitrification and/or de-nitrification of ammonia in mixed liquor  24 . The nitrification process may also be further enhanced by increasing the amount of dissolved oxygen introduced to SBR  12 ,  12 ′,  12 ″ via bubbles  18 . 
         [0050]    Aside from the preferred embodiment or embodiments disclosed below, this invention is capable of other embodiments and of being practiced or being carried out in various ways. Thus, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of components set forth in the following description or illustrated in the drawings. If only one embodiment is described herein, the claims hereof are not to be limited to that embodiment. Moreover, the claims hereof are not to be read restrictively unless there is clear and convincing evidence manifesting a certain exclusion, restriction, or disclaimer. 
         [0051]    Although specific features of the invention are shown in some drawings and not in others, this is for convenience only as each feature may be combined with any or all of the other features in accordance with the invention. The words “including”, “comprising”, “having”, and “with” as used herein are to be interpreted broadly and comprehensively and are not limited to any physical interconnection. Moreover, any embodiments disclosed in the subject application are not to be taken as the only possible embodiments. Other embodiments will occur to those skilled in the art and are within the following claims. 
         [0052]    In addition, any amendment presented during the prosecution of the patent application for this patent is not a disclaimer of any claim element presented in the application as filed: those skilled in the art cannot reasonably be expected to draft a claim that would literally encompass all possible equivalents, many equivalents will be unforeseeable at the time of the amendment and are beyond a fair interpretation of what is to be surrendered (if anything), the rationale underlying the amendment may bear no more than a tangential relation to many equivalents, and/or there are many other reasons the applicant cannot be expected to describe certain insubstantial substitutes for any claim element amended.