Abstract:
A diffuser assembly with a buoyancy vessel and a chamber for buoyantly raising the diffuser assembly for maintenance work. The diffuser assembly has a support structure, diffusers connected to the frame, and a buoyancy vessel positioned on the frame, capable of alternating between a state of buoyancy or ballast.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    None. 
       FIELD OF THE INVENTION 
       [0002]    This invention relates generally to the treatment of liquid, such as wastewater, by diffusion of air or another gas, and more specifically to the diffusion of air into wastewater for aeration and mixing. The invention deals in particular with an improved diffuser assembly or multi-diffuser module that may be raised individually and separately from other modules. This invention also relates to a method for raising and lowering an individual aerator module for inspection, maintenance or repair, without disturbing the remainder of the modules in a grid structure in a large wastewater treatment basin. 
       BACKGROUND OF THE INVENTION 
       [0003]    In the treatment of wastewater, it is known in the industry to use aeration equipment in order to aerate and mix the wastewater. This aeration equipment may be positioned generally at the bottom of the wastewater basin at an intermediate level in the basin, or allowed to float on the surface of the wastewater reservoir. It is common to use submerged diffusers capable of discharging air into the treatment basin. An example of a particularly effective diffuser is a flexible membrane diffuser. U.S. Pat. No. 5,846,412 issued to Tharp provides an example of an air diffuser and mounting arrangement for use in a water treatment system. 
         [0004]    One arrangement for aerating and mixing large wastewater basins makes use of a large number of diffusers contained in separate multi-diffuser modules in a grid pattern throughout the basin. The aeration equipment typically includes a large capacity gas supply source for supplying air to the diffusers. Each individual diffuser is connected to the main air supply conduit via a branch conduit with the diffusers appropriately located throughout the basin to provide thorough mixing and aeration. 
         [0005]    When many individual diffusers are positioned in a grid pattern to aerate a large wastewater treatment reservoir, general maintenance and repair become problematic. Locating and retrieving an individual diffuser module is difficult for a variety of reasons. Mechanical retrieval can be expensive and cumbersome, requiring massive cranes to pull each module up from the bottom of the basin. Modules may be located in the center portion or a far-side portion of the basin where they cannot be accessed at all by a crane. In large basins, many modules are inaccessible even to cranes with lengthy booms. 
         [0006]    After the repair or maintenance is completed, the individual modules must be placed back in position on the bottom surface of the basin, again with a crane. In order to position the module in the proper orientation on the bottom surface of the basin, the module should not appreciably tip or roll during its descent, which might result in the structure landing improperly on its side or planing sideways during descent. Likewise, if a module is removed from a diffuser grid structure, it should be carefully repositioned within the pattern of the grid. The module should be lowered steadily over its position within the grid, preferably with the module being maintained substantially horizontal as it descends. 
         [0007]    In some applications, the main air supply pipes or laterals float on the surface with large diffuser modules suspended from them above the bottom of the basin. The modules are typically suspended on a plurality of flexible air supply lines attached to the floating air laterals. Retrieval of these large diffuser modules in this type of system presents the same types of problems as with bottom mounted modules. 
       SUMMARY OF THE INVENTION 
       [0008]    The present invention is directed to a diffuser assembly with a buoyancy vessel arrangement that is capable of providing individual raising, surface retrieval and lowering of the diffuser assembly separately from other diffuser assemblies in a grid for maintenance or repair of the individual diffusers. 
         [0009]    In accordance with one embodiment of the invention, a diffuser assembly or module for use in a wastewater basin is provided where the diffuser assembly includes a frame; a plurality of diffusers positioned on the frame, and a buoyancy vessel (or vessels) positioned over or as part of the frame and including an air inlet conduit and a flow control. The diffuser assembly can be part of a diffuser grid structure where air supply conduits are positioned generally in a grid pattern throughout the bottom of the wastewater treatment basin. Each diffuser assembly may be connected to the main supply conduit by an air supply conduit which is preferably flexible but which may be rigid or semi-rigid. The flotation chamber of the buoyancy vessel is preferably positioned at the level of the diffusers or partially above the diffuser assembly and is operable to provide buoyancy to raise and lower each diffuser assembly in the desired substantially horizontal orientation when diffuser maintenance is necessary, or alternatively, it may provide ballast (when filled with liquid) to lower the unit back to its operating position in the wastewater treatment basin. In order to raise a diffuser assembly, an air control valve can be operated to apply air through an air line to the flotation chamber. The entering gas will displace liquid out of the buoyancy vessel through a buoyancy vessel opening. The buoyancy vessel opening, in one embodiment, is at the end of a down turned elbow, with the opening being positioned below the lowest portion of the buoyancy vessel when the vessel is in a substantially horizontal orientation. This configuration selectively prevents air from escaping the chamber, effectively providing a non-mechanical seal without requiring any mechanical valves or elements to close the opening. 
         [0010]    Once the flotation chamber has enough air to make the diffuser assembly buoyant, the diffuser assembly will rise to the surface of the wastewater treatment reservoir with the pressure of the air decreasing during the rise, allowing it to expand and increase the air volume and hence buoyancy. Once the diffuser assembly has reached the surface, it may be moved to the edge of the basin and removed from the basin either by hand or using some type of lift such as a crane. Alternatively, the diffusers can be inspected, repaired or replaced while the unit is in the basin on the surface. Depending on the location of the diffuser assembly relative to the edge of the wastewater treatment basin, it may be desirable to disconnect the air supply from the main air supply conduit. After any maintenance or repairs are conducted, and the operator wishes to return the diffuser assembly to its position in the diffuser grid structure, the diffuser assembly is returned to its previous position on the surface of the wastewater treatment basin. If the air supply has previously been disconnected, it may be reconnected at this time. The operator, in one embodiment, may introduce liquid into the flotation chamber by utilizing the air control valve to bleed air out of the flotation chamber. This causes liquid to re-enter the flotation chamber and act as ballast to sink the unit. 
         [0011]    The orientations of the non buoyant components of the diffuser assembly relative to the buoyant components help ensure the diffuser assembly&#39;s return to the bottom of the wastewater treatment basin floor in a substantially horizontal orientation. In a preferred embodiment, two symmetrical flotation chamber portions extend along the lateral edges of the frame and substantially above the center of gravity of the diffuser assembly. This arrangement of the chamber is particularly effective in reducing the tendency of the diffuser assembly to roll or tip during descent to the basin floor. Also, at least a portion of the flotation chamber may be positioned above the center of mass or center of gravity of the diffuser assembly when buoyant so that the non-buoyant portion is configured to act as a stabilizer or counterpoise, which inhibits rolling or tipping of the unit, particularly during descent into the basin. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0012]    In the accompanying drawings, which form a part of the specification and are to be read in conjunction therewith in which like reference numerals are used to indicate like or similar parts in the various views: 
           [0013]      FIG. 1  is a top plan view of a diffuser module or assembly constructed according to one embodiment of the present invention, with portions broken away for illustrative purposes; 
           [0014]      FIG. 2  is a side elevational view of the diffuser assembly shown in  FIG. 1 ; 
           [0015]      FIG. 3  is a side elevational view of the buoyancy vessel shown in  FIGS. 1 and 2 ; 
           [0016]      FIG. 4  is a top plan view of a plurality of diffuser assemblies arranged in a grid pattern in accordance with one aspect of the invention; 
           [0017]      FIG. 5  is a top plan view of a diffuser module or assembly constructed according to another embodiment of the invention, with portions broken away; and 
           [0018]      FIG. 6  is a side elevational view of the diffuser module or assembly shown in  FIG. 5 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0019]    Referring now to the drawings in more detail and initially to  FIG. 1 , the present invention relates in a preferred embodiment to a diffuser assembly or module  10  for use individually or in a diffuser grid structure containing a number of the modules  10 . The module  10  has a non-buoyant portion  11  and a selective buoyant portion  14 . The non-buoyant portion includes a frame  20  and a diffuser assembly  22  comprising a plurality of individual diffusers  24  arranged parallel to one another. The selective buoyant portion  14  includes a buoyancy vessel  12  having an interior flotation chamber  19 . The frame  20  supports the diffuser assembly  22  and the buoyancy vessel  12 , operably connecting the structures together. In the illustrated embodiment in  FIGS. 1 and 2 , the frame  20  has a generally rectangular shape, although the frame could have any suitable shape and size. As used herein, non-buoyant means the object has a density greater than the liquid it is in and will not float on its own and buoyant means the object will float on its own and has a density (including a chamber and its contents) less than the liquid it is in. 
         [0020]    As shown in  FIGS. 1 and 2 , the diffuser assembly  22  includes a central header pipe  28  providing a supply of air to the diffusers  24 . Air is supplied to header pipe  28  by an air supply conduit  40  which may be equipped with a quick disconnect coupling  44 . The diffusers may be tubular membrane diffusers of the type having rigid tubes  23  that receive flexible membranes  25 . The size and position of the diffusers  24  may be varied to suit the needs of the particular wastewater treatment process. For simplicity, only representative membranes  25  are shown in  FIG. 1 . Other types of diffusers can be employed, including disk diffusers and coarse bubble diffusers. 
         [0021]    The frame of the diffuser assembly includes a series of transverse ballast beams  18  ( FIG. 2 ) positioned below the diffusers  24 . The ballast beams  18  are positioned and sized to provide the ballast required to keep the diffuser module  10  positioned on the bottom of a wastewater basin when operating. The header pipe  28  may be strapped, bolted or otherwise secured on top of the ballast beams  18  at a location extending along the longitudinal axis of the module  10 . The wastewater basin may have an earthen, polymeric, metallic or concrete bottom which may invoke different details in the construction of the module  10 , particularly in the portions adjacent the bottom. 
         [0022]    The buoyancy vessel  12  may take the form of a U-shaped tubular structure that has side portions  12 A,  12 B preferably extending generally along the length of the assembly parallel to the pipe  28  and perpendicular to the diffusers  24 . Coaxial end portions  12 C and  12 D connect with the respective side legs  12 A and  12 B through elbow fittings. The shape and size of the buoyancy vessel  12  and chamber  19  may be selected to fit the size profile and buoyancy needs of the module  10 . The components that are buoyant during lift are sized and positioned to effect the lift and descent of the module  10  in the wastewater reservoir. Lift and descent may be controlled as discussed below. Additionally, the flotation chamber  19  is preferably positioned relative to the remainder of the module  10  so at least some portion of the chamber  12 , and preferably all of it, is located at or above the center of mass (designated CM in  FIG. 2 ) of the non-buoyant portion  11  when the module  10  is in a horizontal orientation. It is not necessary but preferred for the entire body of flotation chamber  19  to be above the non-buoyant portion  11 . This configuration enhances stability and allows the module  10  to descend in a substantially horizontal orientation, which limits planning, rolling or flipping of the module  10  during descent. 
         [0023]    The configuration, size and orientation of the chamber  19  determines the location of the center of lift (designated as CL in  FIG. 2 ), and the center of lift may change as gas flows in or out of the chamber. The center of lift is the general mean point where the lift forces exerted by the air in the chamber  19  may be considered to be focused. The center of lift relative to the center of mass may vary as the chamber  19  varies between ballast and buoyancy, i.e., as the relative amounts of gas and liquid in the chamber  19  changes. 
         [0024]    The buoyancy chamber  19  is in flow communication with gas supply lines such as a pair of flexible air hoses  30  each having a three-way air valve  32 . One of the hoses  30  connects to chamber portion  12 C and the other hose  30  connects with portion  12 D. The portions  12 C and  12 D are preferably isolated so that flow between them is not permitted The buoyancy vessel  12  terminates in one or more flow control sections  33 , each of which may take the form of a down turned elbow  16  presenting a flow control opening  36  communicating between chamber  19  and the exterior to the chamber  19 . The opening  36  may be at the lower end of a spout  34 . The opening  36 , in the illustrated structure can function as an inlet and an outlet for liquid, as will be described. In one embodiment, the elbow  16  forms a generally 90° angle following a bend  35 . 
         [0025]    The opening  36  is shown as positioned below the level of the center of lift CL when the module  10  is relatively horizontal or level, to allow the opening  36  to function as a self-sealing hydraulic seal when air is in the chamber  19 , thereby forming a valve with no mechanical valve elements. It is preferred that the end portion of each side leg  12 A and  12 B of the flotation chamber be equipped with a flow control section  33  and a flow control opening  36 . 
         [0026]    The module  10  is normally located in a wastewater treatment basin submerged either on the basin bottom or suspended from floating air laterals. In either case, when air is supplied through hose  40  to the header pipe  28 , the air is directed into the diffusers  24  and discharged through slits in the membranes  25  into the wastewater in the form of fine bubbles. This effects aeration and mixing of the wastewater with the fine bubbles efficiently transferring air to the liquid. 
         [0027]    If the operator wishes to raise the module  10 , he or she may commence purging liquid from the chamber  19  through the openings  36  by first opening the air valves  32  to allow gas under pressure to enter the chamber  19  through hoses  30 . The following described process will apply to all the embodiments described in this application, but for simplicity this description will only refer to the embodiment shown in  FIGS. 1-3 . In any embodiment, the chamber  19  is generally filled with liquid when the module  10  is in an operating position on the bottom of the wastewater treatment basin. 
         [0028]    As the gas enters the chamber  19 , it displaces liquid in the chamber and purges it through openings  36  in flow control sections  33 . As the gas displaces the liquid in the chamber  19 , the module  10  becomes buoyant and begins to lift off the bottom surface of the wastewater basin, first near the end of the module where the gas is introduced into the chamber  19 , which is opposite openings  36 . While a plurality of openings  36  and flow control sections  33  are shown, the use of only one of each can suffice in some applications. 
         [0029]    As the air enters the chamber  19 , openings  36  act as hydraulic seals to prevent gas from escaping the chamber, so long as the openings  36  remain below the level of the chamber  19 . In a preferred embodiment, the elbow  16  and position of the openings  36  relative to the chamber  19  create this self-sealing feature without the use of mechanical valve elements or moving parts or other mechanical closures or devices. 
         [0030]    The absence of mechanical valves provides for a more trouble free product for use in environments such as wastewater treatment. Mechanical methods to seal the opening could easily become blocked or corroded in the sludge or materials processed by most wastewater treatment works. The absence of mechanical valve obstacles within the flow control section  33  means the present invention offers fewer opportunities for repair problems or malfunction delays. In a less preferred embodiment, the flow control sections  33  could include a mechanical valve upstream from the respective opening  36  for selectively opening and closing the chamber  19  to liquid flow. 
         [0031]    Once the gas has displaced most of the liquid from the buoyancy vessel  12 , the module  10  will rise as a result of its buoyancy and approach the surface of the liquid in the basin. The operator may then retrieve the module by any convenient method, including towing from a boat or removal by crane. The module  10  may be removed for servicing, repair, or replacement of the diffusers  24  or other components. It may also be serviced while at the surface without removal from the basin. The module  10  can be moved to an edge of the basin where it can be lifted or, often more conveniently, tilted and then lifted out of the basin. 
         [0032]    When the operator desires to install the module  10  in the basin following maintenance, he or she can position the module  10  on the surface of the wastewater at the desired location. The operator will then begin to bleed gas from the buoyancy chamber  19  by positioning the three-way valves  32  to allow air to escape from the flotation chamber  19 . As the air escapes the chamber  19  through the conduits  30 , liquid will begin to re-enter the buoyancy vessel through the openings  36 . As the liquid re-enters the buoyancy chamber  19 , the vessel  12  begins to lose buoyancy, causing the module  10  to begin its descent to the bottom of the wastewater basin. 
         [0033]    The center of lift CL of the buoyant portion  14  is generally above the center of mass CM of the non-buoyant portion  11 . The force vector at the center of lift CL is generally in line with and generally above the force vector due to the counterpoise weight of the non-buoyant portion  14 . Also, at least a portion of the chamber  19  is preferably positioned above the center of mass of the non-buoyant portion  11 . For stability, the buoyant portion includes two chamber legs  19 A,  19 B located in sides  12 A,  12 B and each extending along a respective side portion of the module  10 . Additionally, the chamber legs or portions  19 A,  19 B are connected to the separate infeed hoses  30  by vessel portions  12 C,  12 D which also have a respective chamber portion  19 C,  19 D therein each communicating with the chamber portions  19 A,  19 B. The chamber portions  19 C,  19 D are isolated from each other and provide for buoyancy at the end of the module  10  opposite that of the location of the flow control sections  33 . Accordingly, the end of the unit opposite the openings  36  normally rises first and descends last, providing a slight cant or inclination to the module  10 . This can help achieve and maintain a seal in the flow control sections  33  while still substantially preventing planning of the diffuser module, particularly during descent. 
         [0034]    In an alternative embodiment, a single vessel  12  with a single chamber  19  therein may be provided and preferably would be positioned generally along the longitudinal central axis of the module  10 . By proper relative positioning of the center of mass and the center of lift, appropriate ascent and descent may be accomplished. However, two separate chambers spaced apart on opposite sides of the unit is preferred because such a configuration enhances the stability much in the manner of a double pontoon boat. 
         [0035]      FIG. 4  illustrates a plurality of modules  10  positioned in a basin  60  in a grid configuration. A gas supply conduit  61  extends along a portion of the reservoir and preferably along a substantial length of a grid system  60 . The gas supply conduit is provided with a plurality of gas supply branch conduits  62  connected thereto, each also being connected in flow communication with a respective module  10  through one of the valves  32 . The supply conduit  62  connects through valve  32  with both the gas lines  30  and the header pipe  28  so that air can be fed to either the diffusers  24  or the buoyancy vessel  12 . When it is desired to raise a module  10 , air is fed primarily to the chamber  19  with zero to low air flow to the diffusers through appropriate operation of the valving. A respective module  10  of the grid may be raised or lowered for appropriate maintenance or inspection in the manner previously described. 
         [0036]      FIGS. 5 and 6  depict an alternative embodiment of the invention which includes a modified diffuser module  110 . The module  110  is equipped with a diffuser assembly which may be of any desired type, including a plurality of large tube diffusers  123  which may be clustered relatively closely together, individual tube diffusers  124  which may be spaced closer together and may be smaller overall than the diffusers  123 , or a plurality of disk diffusers  126  mounted along the length of supply pipes  126   a.  Diffusers  123  may be equipped with flexible membranes  123   a  which discharge air into the wastewater in the form of fine bubbles. Similarly, diffusers  124  may be equipped with flexible membranes  124   a  through which air is transferred to the wastewater in the form of fine bubbles. The disk diffusers  126  may be of any suitable type, including bodies having their faces equipped with flexible disk membranes through which air in the supply pipes  126   a  is delivered to the wastewater in the form of fine bubbles. 
         [0037]    The diffusers  123 ,  124  and/or  126  are mounted on and receive air from a horizontal header pipe  128  which in turn receives air from a blower (not shown) through an air supply conduit  140  which may be a flexible hose. The header pipe  128  extends along the longitudinal center line of the module  110 . Ballast beams  118  are secured to the header pipe  128  near its opposite ends by suitable straps  131  or other fastening means. 
         [0038]    The module  110  is equipped with a single buoyancy vessel  112  which may be located above the header pipe  128  and arranged to extend above pipe  128  along the longitudinal center line of the diffuser module  110 . The buoyancy vessel  112  may take the form of a pipe having a hollow interior forming a flotation chamber  119  ( FIG. 6 ). One end of vessel  112  may be equipped with a down turned elbow  116  which in turn connects with a short vertical spout  134 . The lower end of the spout  134  is open to provide a flow control opening  136  that functions in substantially the same manner as opening  36 . The buoyancy vessel  112  may be connected with the module  110  in any suitable manner such as being formed as part of a frame that includes the diffuser module and buoyancy vessel  112 . 
         [0039]    Air is supplied to and bled from the buoyancy vessel  112  through an air hose  130  that connects with the vessel  112  at the end opposite the spout  134 . The air hose  130  may be equipped with a valve such as a three-way air valve  132 . The end of the buoyancy vessel  112  adjacent to the connection of the air hose  130  may be provided with a down turned leg  155  that connects with the header pipe  128 . 
         [0040]    The diffuser module  110  may be lifted to the surface by a pair of retrieval cables  157 , each connected with a harness  159 . The two harnesses  159  connect with the two ballast beams  118  near the opposite ends of the beams. 
         [0041]    The embodiment of  FIGS. 5 and 6  functions and operates in substantially the same manner as described for the embodiment of  FIGS. 1-4 . The buoyancy vessel  112  may be supplied with air through the hose  130  in order to effect a buoyant condition of the module  110 , causing it to rise to the surface for maintenance and/or repair. The flow control opening  136  functions as a valve to confine the air in the buoyancy vessel  112  while avoiding the ingress of water due to the air pressure. When the buoyancy vessel  112  is bled of air through the air hose  130 , water enters the flotation chamber  119 , and the module  110  then reverts to a non-buoyant condition in which it descends to the basin floor  113  and remains in place on the floor until it is again made buoyant. 
         [0042]    Thus, there has been shown and described several embodiments of a novel invention. As is evident from the foregoing description, certain aspects of the present invention are not limited by the particular details of the examples illustrated herein, and it is therefore contemplated that other modifications and applications, or equivalents thereof, will occur to those skilled in the art. The terms “having” and “including” and similar terms as used in the foregoing specification are used in the sense of “optional” or “may include” and not as “required”. Many changes, modifications, variations and other uses and applications of the present construction will, however, become apparent to those skilled in the art after considering the specification and the accompanying drawings. All such changes, modifications, variations and other uses and applications which do not depart from the spirit and scope of the invention are deemed to be covered by the invention which is limited only by the claims which follow.