Abstract:
A separation system is disclosed for use with a treatment tank, such as a flotation or decant tank, to separate particles and/or gases from a liquid stream. The system is coupled to a liquid source comprising a suspension solution. The system includes a hydrocyclone system that directs the solution stream through a first chamber or passage in a generally helical fashion along a cylindrical wall where bubbles-to-particle aggregates are formed and chemicals can be mixed and activated. A second chamber encloses the outlet of the hydrocyclone and may take many forms, including a generally concentric or parabolic form, and acts to decelerate the liquid and deliver the liquid to a third chamber from which bubbles escape the liquid. The liquid drops from the third chamber into the treatment tank in a manner which only minimally disturbs the liquid already in the tank.

Description:
RELATED APPLICATION  
       [0001]    This application claims priority from provisional application Ser. No. 60/176,358, filed Jan. 13, 2000. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    The invention relates to liquid conditioning flotation separation components, systems and methods. More particularly, the present invention relates to liquid conditioning components, systems and methods that may be retrofit into existing flotation, clarification, and decant tanks to improve the separation of particulate matter from carrier liquid streams.  
           [0003]    Dissolved air flotation (DAF) systems are often used to separate particulate material and gases from solutions such as wastewater. The systems typically employ the general principle that bubbles rising through a solution attach to and carry away particles suspended in the solution. Similarly, gases dissolved in the solution diffuse into the bubbles. As bubbles reach the surface of the solution, the attached particles coalesce to form a froth or floc that is easily collected while the entrapped gases within the bubble dissipate into the air. Thus, a DAF must accomplish two main steps when particle removal is the goal: 1) get bubbles to contact and stick to particles (agglomerate), and 2) provide an environment that allows the agglomerations to float to a surface where they collect and can be removed.  
           [0004]    Traditional DAF systems typically introduce small air bubbles into the lower portion of a relatively large tank filled with the usually aqueous liquid to be treated. While such systems work for their intended applications, the processing time and particle/gas removal efficiency typically varies directly with the residence time of the bubbles in the solution. The residence time, in turn, varies directly with turbulence and depth of the bubbles in the solution, and inversely with bubble buoyancy. As a result, traditional DAF systems employ relatively large, deep and costly tanks having correspondingly large “footprints”. The footprints maximize the gas transfer time from the solution into the bubbles. The depth maximizes the probability that particles will contact the bubbles during the residence time available within the tank. Moreover, the relatively large footprints also allow the bubbles sufficient time to float to the surface.  
           [0005]    In an effort to reduce the tank size for a DAF system, one proposal disclosed in U.S. Pat. No. 4,022,696 employs a rotating carriage and floc scoop. The carriage directs an inlet solution substantially horizontally along a flow path to increase the path length for bubble travel, and correspondingly increases the residence time. Unfortunately, while the tank size reduction is alleged as an advantage, the problem with performance tied to residence time still remains. This is due in part to turbulence created by the rotating carriage and scoop.  
           [0006]    Another proposal, disclosed in U.S. Pat. No. 5,538,631, seeks to address the turbulence problem by incorporating a plurality of spaced apart and vertically arrayed baffles. The baffles include respective vanes angularly disposed to re-direct the flow of liquid from an inlet positioned at the bottom of the tank. Liquid flowing through the tank deflects upwardly as it traverses the vanes, allegedly reducing the extent and intensity of turbulence generated near the inlet to the tank.  
           [0007]    While this proposal alleges to reduce the turbulence and thereby the bubble residence time, the redirected liquid still appears to affect bubbles rising in other areas of the tank, and influences the residence time of such bubbles. Moreover, the proposal fails to solve the basic problem of DAF performance being dependent on bubble residence time.  
           [0008]    In an effort to overcome the limitations in conventional DAF systems, those skilled in the art have devised air-sparged hydrocyclones (ASH) as a substitute for DAF systems. One form of air sparged hydrocyclone is disclosed by Miller in U.S. Pat. No. 4,279,743. The device typically utilizes a combination of centrifugal force and air sparging to remove particles from a liquid stream. The stream is fed under pressure into a cylindrical chamber having an inlet configured to direct the liquid stream into a generally helical path along a porous wall. The angular momentum of the liquid generates a radially directed centrifugal force that varies directly with the liquid velocity and indirectly with the radius of the helical path. The porous wall is contained within a gas plenum having gas pressurized to permeate the porous wall and overcome the opposing centrifugal force acting on the liquid.  
           [0009]    In operation, the Miller ASH receives and discharges the rapidly circulating solution while the air permeates through the porous wall. Air bubbles that emit from the wall are sheared into the liquid stream by the rapidly moving liquid flow. Micro-bubbles formed from the shearing action combine with the particles or gases in the solution and float them toward the center of the cylinder as a froth in a vortex. In this way, the step of bubble-particle agglomeration is accomplished in less than a second inside the hydrocyclone before the stream reaches a downstream tank. The centrally located froth vortex is then captured and exited through a vortex finder disposed at the upper end of the cylinder while the remaining solution exits the bottom of the cylinder. However, the ASH creates and does not neutralize turbulence, which slows the rise of the bubble-particle agglomerations. In addition, the ASH does not have the ability to use existing tankage to effect separation rapidly. In summary, the ASH cannot deposit conditioned water into existing tankage in a manner that does not introduce turbulence that slows bubble rise.  
           [0010]    Waste and process water treatment frequently involves adding polymers to the stream. Polymers are long chain molecules. This aspect makes them effective at joining with contaminants in the stream to ferry them out. Unfortunately, the long molecular chain nature of polymer molecules results in molecular damage under established mixing methods. In particular, the molecules are broken when subject to stresses such as shear. Damaged molecules do not function as well, necessitating increases in dosage. As dosage increases, polymer usage, and hence cost, are increased. A way is needed to add polymers to liquid streams without damaging the polymers.  
           [0011]    In addition, polymer molecule charges tend to be “self-satisfying”, which means that positive charges at one site tend to pair with negative charges elsewhere along the length. This causes the molecule to twist into a knot. In this coiled form, the charge sites of the polymer molecule are much less available for connecting with contaminants in the stream and the polymer is less effective, again necessitating higher dosing. Established methods for uncoiling polymers include pH adjustment. A non-chemical method to accomplish the same thing would reduce or obviate the need for chemicals.  
           [0012]    Existing DAF systems require mixing tanks for polymers, surfactants, and other substances that are used to create flocs. They also require a high pressure, compressed air system for adding air to the tank. The mixing tanks and compressed air systems are bulky, and compressed air systems tend to be maintenance-, energy-, noise- and leak-intensive.  
           [0013]    Existing conditioning tanks, for example, flotation, clarification, and decant tanks, are not designed for use with ASH devices or other liquid cyclones. Consequently, the advantages of the ASH and fluid cyclones in general are not harvested. Instead, compressed air systems are used to create bubble-particle aggregates, separate mixing tanks are used for additives, including additives that are made less effective by shear forces present in established types of mixers. In addition, the established mixing methods do not uncoil polymeric additives, leaving charge sites unavailable to contaminants in the stream. Thus, in order to incorporate the advantages of a fluid cyclone, an interface designed to receive fluid from the source of the stream, add and mix additives to the stream, and deliver fluid ready for flotation from the cyclone device is required.  
           [0014]    Accordingly, there is a need for an economical flotation separation system which unites liquid cyclone technology with conventional conditioning tanks for the purpose of enhancing flotation and particulate separation in those conventional tanks. Moreover, a need exists for a flotation separation system which can be efficiently attached and plumbed into existing conditioning tanks. The flotation separation system of the instant invention satisfies these needs and provides other related advantages.  
         SUMMARY OF THE INVENTION  
         [0015]    The liquid conditioning system of the present invention provides an efficient and cost-effective way of treating solutions by maximizing particle-bubble contact upstream of the conventional conditioning tanks and converting an existing treatment tank to a separation chamber. The system is designed for simple attachment to existing conditioning tanks, and increases throughput and speed of treatment.  
           [0016]    To realize the advantages above, the invention, in its concentric form, comprises a liquid conditioning system that includes a hydrocyclone defining a cylindrical treatment environment. The cylindrical environment forms a passage or chamber defined by a cylindrical inner wall with an accelerator head at its upstream inlet end and an outlet at its lower downstream end. The accelerator head is coupled to a solution source for receiving a liquid stream and directing it through the passage in a generally helical fashion along the cylindrical inner wall. The head includes a vent to gas, such as atmospheric air. The system further includes a second chamber concentrically disposed about the hydrocyclone, and which is in liquid communication with the lower end of the hydrocyclone. Thus, the helically flowing liquid is received in the second chamber, which redirects the flow upwards and opens to the surface of a third chamber. Large entrained bubbles, which would create turbulence in the downstream quiescent zone if allowed to remain entrained in the stream, escape from the surface of the third chamber, which is open to atmosphere. From the third chamber, the stream flows downward through a passage that penetrates the surface of liquid in an existing treatment tank. Thus, the liquid entry is submerged. The system can be attached externally to an existing treatment tank or submersed directly into the same.  
           [0017]    In yet another form, the unit fits on the side of an existing treatment tank. This embodiment is referred to in this application as the “Parabolic Second Chamber Embodiment”. The upwardly opening second chamber of the invention is rectangular and contains a substantially parabolic or otherwise curved wall to direct liquid flow with minimal turbulence from the hydrocyclone outlet upward to the third chamber. This embodiment includes an energy dissipation sloped ramp, pocket and a false floor within the tank to reduce existing tank depth (which reduces hydrostatic pressure and bubble rise time), and a flexible baffle to divide the existing treatment tank into a turbulent zone and a quiescent zone.  
           [0018]    In an embodiment in which one or more liquid additives are added to the stream, the invention includes one or more inlets for injecting one or more chemicals additives, for example, a liquid polymer, into the liquid stream to be treated. The inlets are preferably disposed in the accelerator head. For liquid polymers, the preferable location for the inlets is in the accelerator head at least 180 degrees downstream from the inlet of the liquid to be treated along the path of the liquid.  
           [0019]    In a group of embodiments in which one or more gases, including atmospheric air, are added to the stream, the hydrocyclone is designed to inject gas into the solution passing through the vessel. The hydrocyclone may include an inlet in its accelerator head, which may introduce gas into the liquid solution as the liquid solution passes through it. Alternatively, the hydrocyclone could be gas-sparged using a porous tube or the like through which gas is sparged into the liquid to be treated as it passes through the hydrocyclone.  
           [0020]    In yet another form, bubbles are induced into the liquid to be treated by partially starving the hydrocyclone of air or other gas. Small bubbles needed for flotation are induced by partially closing the vent in the head of the hydrocyclone. The result is closing of the helical flow of liquid into a vortex. The air in the space above the vortex (upstream) is at pressure lower than atmospheric pressure. Exposure of the liquid to be treated to pressures below atmospheric induces small bubbles to form from gas already dissolved in the liquid. Thus, bubbles needed for flotation are created without gas-sparging, which obviates the need for a regulated pressurized source of gas (e.g. air blower), a gas plenum, and a porous tube. In addition, more bubbles are created in this partially air-starved mode than would be present in the prior art wherein the hydrocyclone is vented to the atmosphere.  
           [0021]    In yet another form, the liquid to be treated is subjected to very low pressures. The vent in the head of the hydrocyclone is either absent or closed to atmosphere, which closes the helical flow into a vortex. Bubbles are created from gas already dissolved in the water coming into contact with the near-vacuum area inside the vortex formed by the liquid. As in the induced air embodiment above, no gas sparging is used, obviating the need for a regulated pressurized source of gas (e.g. air blower), a gas plenum, and a porous tube. In addition, more bubbles are created in this partially air-starved mode than would be present in the prior art wherein the hydrocyclone is vented to the atmosphere or other gas source.  
           [0022]    Thus, the present invention in one illustrative embodiment is directed to a system for receiving liquid from a liquid source and separating particulate matter from the liquid, including a hydrocyclone in communication with the liquid source, the hydrocyclone being configured to pass the liquid therethrough in a generally helical manner, the hydrocyclone further including means to inject liquid or gaseous additives, the hydrocyclone further including an outlet; a second chamber disposed about the hydrocyclone and in liquid communication with the outlet of the hydrocyclone, the secondary chamber including an open upper end; a third chamber above the second, the third chamber including an outlet directed downward to the treatment tank. 
       
    
    
       [0023]    Other features and advantages of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings, which illustrate, byway of example, the principles of the invention.  
       BRIEF DESCRIPTION OF THE DRAWINGS  
       [0024]    The accompanying drawings illustrate the invention. In such drawings:  
         [0025]    [0025]FIG. 1 is a vertical cross-sectional view of a Concentric embodiment of the present invention;  
         [0026]    [0026]FIG. 2A is a top plan view of the system of FIG. 1 through cross-section A-A;  
         [0027]    [0027]FIG. 2B is a top plan view of the system of FIG. 1 through cross-section B-B;  
         [0028]    [0028]FIG. 3 is a cross-sectional view of a Parabolic Second Chamber embodiment of the present invention;  
         [0029]    [0029]FIG. 4 is a top plan view of the Parabolic Second Chamber embodiment of FIG. 3;  
         [0030]    [0030]FIG. 5 is a cross-sectional view of an adjustable ramp system of the Parabolic Second Chamber embodiment of FIG. 3;  
         [0031]    [0031]FIG. 6A is a cross-sectional view of a hydrocylone portion of the system under typical gas-sparging; and  
         [0032]    [0032]FIG. 6B is a cross-sectional view of the hydrocylone portion of the system when subjected to reduced pressure. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0033]    Referring now to the FIGURES a liquid conditioning system of the present invention, generally designated by the reference number  10  in FIGS. 1 and 2, and by the reference number  12  in FIGS.  3 - 5 , is shown. The system is designed to condition water or other liquids and to deliver conditioned liquid to virtually any form of existing or new liquid treatment tank  14 , such as a flotation, clarification, or decant tank, where the conditioned liquid may settle and bubble-particulate aggregates  16  in the liquid may rise to the top of the tank  14  and be removed from the top of the tank  14  in any well known manner.  
         [0034]    The systems  10  and  12  include, generally, a hydrocyclone  18  to receive liquid  20  from a liquid source and create a bubble-rich environment for a high incidence of bubble-particle collisions and gas transfer from the liquid to the bubbles. Liquid to be treated  20  is provided to the system by any suitable pump. The liquid  20  enters the system  10  or  12  at accelerator  22 . The hydrocyclone  18  has a cylindrical inner wall  24  which creates a passage or chamber with an outlet  26 .  
         [0035]    The accelerator  22 , frequently a Kreb&#39;s head, accelerates the flow of the liquid  20  into the hydrocyclone  18 . The liquid  20  is preferably delivered to the hydrocyclone  18  through an inlet  28  in the accelerator  22 . The accelerator  22  has a cylindrical interior. The inlet  28  has a rectangular cross section and is arranged to deliver the liquid  20  in a generally tangential direction relative to the inner wall  30  of accelerator  22  and at a relatively high speed. As is well known, such delivery causes the liquid  20  to flow in the above-described helical manner  32  through the hydrocyclone  18 . During the liquid stream&#39;s passage through the hydrocyclone  18 , bubbles attach to particles and the first step of flotation separation is completed.  
       A. Concentric Embodiment  
       [0036]    Referring now to FIGS. 1 and 2, the system  10  includes a second chamber  34  which encloses the outlet  26  of the hydrocyclone  18  in a generally concentric manner and which is in liquid communication with the outlet  26 . The outlet  26  of the hydrocyclone  18  opens into the bottom of the second chamber  34  which receives liquid  20  that now contains bubble-particle aggregates  16 . The second chamber  34  opens upwardly at a top portion thereof into outlet area  36 , and directs the liquid upwardly to a third chamber  38  positioned above the second chamber  34  and disposed in a generally concentric relation about the outlet  36  of the second chamber  34 . The third chamber  38  is generally open to the atmosphere. Alternatively, third chamber  38  can be closed to the atmosphere and ducted to a gas gathering system if gas in the liquid is to be harvested or treated. In the third chamber  38 , large bubbles  40  escape the stream and so are not carried into the existing treatment tank  14  downstream where they would create turbulence and thereby interfere with the rise of bubble-particle aggregates  16 .  
         [0037]    The stream descends from third chamber  38  through an area  42  defining an outlet which surrounds second chamber  34  and passes downward through the free surface of the liquid  44  in the existing treatment tank  14 . As it passes through area  42 , the liquid stream makes a submerged entry into the body of the existing treatment tank  14 . Preferably, the area  42  is elevated with respect to the bottom of tank  14  so that the bubble-particulates have a relatively short travel path to the free liquid  44  surface, minimizing the time needed to place the particles at the surface where they can be skimmed off.  
         [0038]    The system  10  may be disposed within the existing treatment tank  14  such that the hydrocyclone  18 , second chamber  34 , and third chamber  38  components are deployed inside the walls of treatment tank  14 . Alternatively, the system  10  may be otherwise connected to the tank  14  for liquid communication between the system  10  and the tank  14 .  
       B. Parabolic Second Chamber Embodiment  
       [0039]    Referring now to FIGS.  3 - 5 , a Parabolic Second Chamber Embodiment is disclosed. For this embodiment, attached to the bottom of the upwardly opening second chamber  34  is a substantially curved wall such as the illustrated parabolic wall  46 . It is to be understood that the parabolic wall  46  can also be designed to form the second chamber  34 . The open end of the substantially parabolic wall  46  faces generally horizontally toward the upwardly directed outlet  36  of the second chamber  34  so as to direct the flow smoothly from the hydrocyclone  18  out of the upwardly opening second chamber  34 . By smoothing the corners of second chamber  34 , the substantially parabolic wall  46  reduces shear forces on the bubble-particle and polymer-particle aggregates  16  and minimizes their breakage. The substantially parabolic wall  46  extends upward from the floor of the upwardly opening second chamber  34  around the outside of the bottom of hydrocyclone  18 . The wall  46  wraps closely, preferably within an inch, from the outside of the hydrocyclone  18  outlet  26 . The bottom of the hydrocyclone  18  is preferably between  1  and  5  inches above the bottom of the upwardly opening second chamber  34 .  
         [0040]    Referring to FIG. 3, the top of the substantially parabolic wall  46  joins the upper surface  48  of the upwardly opening second chamber  34 . At the corner  50  where the top surface  48  of second chamber  34  turns upward to form an adjacent wall  52  of third chamber  38 , the substantially parabolic wall  46  continues to the far wall  54  of second chamber  34  to at least partially define the outlet  36  of the second chamber  34 .  
         [0041]    With continuing reference to FIGS. 3 and 4, liquid flows through area  36  upward to the third chamber  38 . As in the third chamber  38  of the Concentric Embodiment, large bubbles  40  escape the liquid stream  20 . The liquid flows across the third chamber  38  to a vertical chute  56  which directs the liquid down into the existing treatment tank  14 . The chute  56  preferably has a narrow rectangular horizontal cross-section. The short axis of the rectangle is preferably between  1 / 4  and  1  inch in length; the exact distance increased with liquid flow rate. Further, this distance can be varied depending on the embodiment. The chute  56  passes through the liquid surface of the existing treatment tank  14  and the liquid  20  flows by gravity into the treatment tank  14 . The chute  56  essentially hooks over the side of the existing treatment tank  14  (e.g. DAF tank) but other means of attachment are possible. Thus, this embodiment is well suited for retrofitting existing DAF or other treatment tanks  14 .  
         [0042]    With reference now to FIGS. 3 and 5, an entry ramp  58  is mounted against the wall  60  of the existing treatment tank  14  and under chute  56 . The entry ramp  58  may include hinges  62   a  and  62   b  which allow the angle and height of the entry ramp  58  relative to the treatment tank  14  wall  60  to be adjusted. In addition, the length of ramp  58  is adjustable using a joint  64  wherein two sections of the ramp  58  slide past one another.  
         [0043]    This embodiment may include a false floor  66  which is horizontally oriented above the bottom of existing treatment tank  14 . The false floor  66  serves to reduce the bubble rise distance to the surface of the liquid (which reduces the amount of time needed to float particles out). A hinge  62   c  between a pocket  68  and the false floor  66  allow the false floor  66  to be maintained in a substantially level orientation. Together, the hinges  62   a ,  62   b  and  62   c  are used to adjust the positions of ramp  58 , pocket  68  and false floor  66  to smoothly channel liquid from the chute  56  into the energy dissipating pocket  68 , avoid existing skimmer paddles and the like within the existing treatment tank  14 , and to obtain the proper depth of the liquid relative to the established liquid height within the tank  14 . FIG. 5 shows two positions of the ramp  58 , pocket  68  and floor  66 ; the dashed representations of these structures show a sample second position.  
         [0044]    A baffle  70  divides the tank  14  into a turbulent zone  72  and a quiescent zone  74 . Turbulence of the liquid stream dissipates above the pocket  68  in the turbulent area  72 . In this manner, the liquid from system  20  creates minimal disturbance to the fluid already in the tank  14 . The baffle  70  is preferably comprised of a water impermeable material. In applications where the treatment tank  14  has skimmers that would get caught or be disrupted by a rigid baffle, a flexible baffle  76 , preferably 3 to 7 inches tall, extends above the surface of the fluid and extends beneath its surface to a rigid baffle  78  to which it is attached. The flexible baffle  76  and the rigid baffle  78  act to separate the tank into a turbulent zone  72 , where the kinetic energy from the drop through chute  56  dissipates before the liquid  20  flows into the quiescent zone  74 . Less turbulence allows more rapid rise of the bubble particulate aggregate  16  for the purpose of skimming. In addition, the rigid baffle  78  defines the top of a gap  80  through which the liquid flows into the quiescent zone  74 .  
         [0045]    The false floor  66  may extend underneath part of both the turbulent  72  and quiescent  74  zones. Between the false floor  66  and the rigid baffle  78  the gap  80  directs the flow of the liquid stream  20  into the quiescent zone  74 . The gap  80  is preferably between 3 inches and 8 inches tall depending upon liquid stream throughput. The false floor  66  has a downstream edge  82  that is preferably between 18 inches and 4 feet from the hinge  62   c.    
         [0046]    In either of the above embodiments, to enhance particle separation, a liquid additive, preferably a polymer, may be added to the helical flow in the accelerator  22 . The hydrocyclone  18  includes an inlet  84  which may be used for injecting surface chemistry, such as liquid or solid coagulant agents, flocculent agents, polymer compounds, or chemical catalysts to reduce and reverse the attraction of the particles to the liquid and increase particle-to-particle attractions or liquid-phobic interfaces.  
         [0047]    The additive inlet  84  is preferably disposed in the accelerator head  22  downstream of the upper end of the first cylindrical wall  30 . In the preferred embodiment, the additive inlet  84  is disposed, for polymers, at least 180 degrees of a turn of the liquid stream  20  around the inside of the cylindrical wall  30  downstream from the inlet  28  into the accelerator head  22 . Additive inlet  84  is typically sufficiently downstream of the stream inlet  28  to avoid the inlet  28 -related pressure drop and shear forces that would damage the polymer molecules and render the polymer less effective. The inlet  84  may be perpendicular to the wall  24  of the hydrocyclone  18  or it may be at an acute angle to the flow of the stream inside the hydrocyclone  18 . Alternatively, inlet  84  may be used for liquid chemical injection and located in the top of the accelerator  22 . Injected in these configurations and locations, the liquid additive is swept into the helical flow  32  and mixed with the liquid stream  20  with a minimum of shear force.  
         [0048]    Alternatively, or additionally, a gaseous additive (or additives) may be added into the helical flow inside the hydrocyclone  18 . Gas bubbles such as air, ozone, or chlorine are injected into the liquid  20  by the hydrocyclone  18  through gas inlet  92  or valve  98  and gas inlet  96  of FIG. 6B.  
         [0049]    The hydrocyclone  18  may be in the form of a modified air-sparged hydrocyclone (ASH), as disclosed in U.S. Pat. No. 4,279,743 or other form of liquid cyclone capable of infusing a large quantity of air or gas bubbles into a helically flowing liquid. The disclosure of U.S. Pat. No. 4,279,743 is expressly incorporated herein by reference for these purposes.  
         [0050]    Referring to FIG. 6A, when the hydrocyclone  18  is a gas-sparged hydrocyclone, it typically includes a cylindrical containment vessel having an open ended porous tube  86  formed of a gas-permeable material. The porous tube  86  includes a cylindrical interior wall  24  defining an inner liquid passage with respective inlet and outlet openings. An enlarged cylindrical hollow housing  88  is disposed concentrically around the porous tube  86  to form an annular plenum  90  enclosing the porous tube  86 . The plenum  90  includes a gas inlet  92  coupled to a source of regulated pressurized air or gas. When the hydrocyclone  18  is air-sparged, the source of air is a blower that generates between 2 and 10 psi at the outer surface of the porous tube  86 . The shearing action of the high velocity solution passing by the pores in the interior wall of the porous tube  86  creates bubbles ranging from sub-micron to several hundred microns in size. The head  22  is vented to atmosphere by an opening  94  at between 10 and 25 percent of the diameter of the inner cylindrical wall  24  of the hydrocyclone  18 .  
         [0051]    Alternatively, a gaseous additive may be added through an inlet  96  in the accelerator  22 . A source of pressurized regulated gas can be attached in any suitable manner at inlet  96  and fed into the less-than-atmospheric pressure area inside the vortex. The inlet  96  would be equipped with a valve  98  suitable for adjusting flow of the gas. For example, CO 2  can be added in this way to reduce the pH of the liquid stream  20 .  
         [0052]    Referring to FIG. 6B, bubbles can be induced from the liquid rather than created only by turbulence. A liquid cyclone  18  can be used without sparging air or a gas through the helical liquid flow  32 . In particular, the hydrocyclone  18  can be starved of air or other gas at the upstream end by partially closing the vent  94  using any suitable valve  98 . The liquid  20  flowing through the hydrocyclone  18  then creates a low pressure area inside the liquid helix  32 , and the helical flow  32  closes into a liquid vortex  100  at the downstream end of the hydrocyclone  18 . The vortex  100  encloses a space not occupied by liquid and the pressure in this area is less than atmospheric pressure. To create bubbles for particle flotation, the system then relies either on bubbles created from air or gas drawn into the system through vent  94  by the partial vacuum associated with the liquid vortex  100  or on the air or gas dissolved in the liquid before it enters the hydrocyclone  18 . In this way, bubbles are induced in the liquid stream. In any case, the relative velocities of particles and bubbles is preferably on the order of approximately one meter per second, which creates a substantial likelihood that bubbles and particles will collide to form an aggregate  16 .  
         [0053]    The vortex of liquid may be closed to form an area of near vacuum. A liquid cyclone  18  can be used without sparging air or a gas through the helical liquid flow. In particular, the helix  32  of the stream flow inside the hydrocyclone  18  is closed into a vortex  100  at the downstream end of the hydrocyclone  18 . This is accomplished by closing to the atmosphere the vent  94  in the accelerator head  22  of the hydrocyclone  18 . The vent  94  is closed using the valve  98 . Alternatively, the hydrocyclone could simply lack a vent  94  and valve  98 . The helical flow away from the head reduces the pressure inside the vortex  100  to pressures closer to vacuum than to atmospheric pressure. Gases such as CO 2  introduced into the interior of the vortex and controlled by a valve at inlet  96  in the accelerator  22  reduce the pH of the liquid without the need for chemical mixing tanks.  
         [0054]    To create bubbles for particle flotation, the system then relies on the near vacuum conditions inside the vortex to create bubbles from air or gas present within the liquid before it enters the hydrocyclone  18 . In any case, the relative velocities of particles and bubbles is preferably on the order of approximately one meter per second, which creates a substantial likelihood that bubbles and particles will collide to form an aggregate  16 .  
         [0055]    It will be understood by those having skill in the art that the system  10  or  12  of the present invention may be used in connection with an existing treatment tank  14 , and can be easily connected to the tank  14  without requiring any puncturing of the existing tank. Alternatively, the system  10  or  12  may be incorporated into an entirely new water treatment system including a new tank  14 .  
         [0056]    Those skilled in the art will appreciate the advantages afforded by the present invention. Of particular significance is the capability of retrofitting existing treatment tanks  14  to become more efficient in removing particulates from a liquid, while at the same time not requiring any modifications to the existing tank  14 . Additionally, by introducing the conditioned liquid to the tank  14  near the surface of the tank, the bubble-particulate composites  16  have a relatively short travel path to the free liquid surface, which minimizes the time needed to place the particles at the surface where they can be skimmed off. Thus, bubble residence time is effectively reduced, the flotation process is faster, and system throughput thereby increases.  
         [0057]    Although several embodiments have been described in detail for purposes of illustration, various modifications may be made without departing from the scope and spirit of the invention. Accordingly, the invention is not to be limited, except as by the appended claims.