Abstract:
In a tank for treating wastewater and including a first plurality of air diffuser elements and a second plurality of air diffuser elements, means for adjusting the relative height of the first diffuser elements with respect to the height of the second diffuser elements in response to changing operating conditions in the tank and changes in the characteristics of the diffusers.

Description:
RELATED APPLICATIONS  
       [0001]     This application claims priority to U.S. Provisional Application No. 60/740,758 filed Nov. 30, 2005. All of the subject matter of that provisional application is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates to wastewater treatment systems and the construction to compensate for headloss migration in a wastewater treatment system using ceramic elements and membrane diffusers.  
       BACKGROUND PRIOR ART  
       [0003]     A conventional wastewater treatment plant typically involves aeration. One type of aeration device is a fine bubble diffuser. The most common types of fine bubble diffusers are ceramic elements and rubber membrane diffusers. In some wastewater treatment systems, the systems specify the use of both ceramic element diffusers and rubber membrane diffusers in the same system. For example, ceramic elements may be installed throughout most of the treatment tanks in the wastewater treatment system and with the use of rubber membrane diffusers installed in the remainder of the system. In such wastewater treatment systems, the rubber membrane diffusers and the ceramic elements are not mounted on any single header but are instead installed on separate grids of headers. However, both sets of grids of headers share the same air supply. In some applications, valves cannot be used to balance the air flow between the grid supporting the ceramic element diffusers and the grid supporting the rubber membrane diffusers.  
         [0004]     It is known from testing that operating the diffusers for long periods of time results in headloss rise or “headloss migration” due to a change in the relative resistance to air flow through the fine bubble diffusers caused primarily by either biofouling and/or changes in water absorption of the diffuser elements.  
         [0005]     In the design of a wastewater system it is difficult to design membrane and ceramic element diffusers to have identical headloss versus air flow curves. Additionally, it is also difficult to maintain the headloss from element to element within manufacturing control limits and to influence or predict the different rates of headloss migration arising as a result of fouling of the diffuser elements and changes in surface properties of the rubber membrane diffusers. It is also difficult to predict the changes over time of the flow volume into the wastewater treatment system and the operating flow rates of wastewater treated by the system as additional demands are placed on the system by growth of a community.  
         [0006]     When two types of diffusers such as ceramic diffusers and rubber membrane diffusers are installed on headers or grids connected to the same air supply system, the less restrictive elements produce higher air flows. Even if balancing orifices are used to compensate for air flow between the header pipes into the diffuser elements, the balancing orifices have a non-linear headloss versus air flow curve, and that non-linear headloss versus air flow curve is significantly different than the headloss/air flow curve of the diffuser elements. Because the headloss/air flow curve of a ceramic diffuser element does not match the headloss/air flow curve of a rubber membrane diffuser, changes in air flow through the headers can only truly be balanced at one flow rate. Additionally, different rates of headloss migration over time complicate the situation further. If the migration rates are significantly different, which is usually the case between ceramic diffusers and rubber membrane diffusers, the balanced flow point will shift with time to a different system flow rate.  
         [0007]     All of these factors prevent the engineer designing a system that may be balanced at initiation of operation of the wastewater treatment system to maintain its balance over the life of the system&#39;s operation.  
       SUMMARY  
       [0008]     The invention involves installing provision to allow headers supporting one type of fine bubble diffuser element to be raised or lowered as needed and whenever an imbalance occurs, relative to headers supporting a second type of diffuser element.  
         [0009]     If the two characteristic headloss/air flow curves of the diffuser elements are such that both share the same shape and slope, but one is shifted higher than the other by an inch of water, then reducing the elevation of the header with the more restrictive membranes by the same amount will compensate for the difference.  
         [0010]     This approach is feasible because the flow imbalance through the diffuser elements is very sensitive to small differences in headloss. Therefore, it does not take much vertical correction in the position of the grid to bring the two types of grid elements into flow balance. Only a few inches of relative submersion difference is normally required to correct for the imbalance. If the characteristic headloss/air flow curves of the two types of elements have the same slope, then the resulting correction in elevation of the diffuser elements will result in substantially balanced flow distribution over a wide range of flow.  
         [0011]     Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]      FIG. 1  is a schematic view of a wastewater treatment system embodying the present invention.  
         [0013]      FIG. 2  is an enlarged cross-section elevation view of a portion of the wastewater treatment system illustrated in  FIG. 1  and showing an elevation adjustment arrangement for a header.  
         [0014]      FIG. 3  is an enlarged illustration of headers shown in  FIG. 1  and with the elevation of the headers adjusted to compensate for headloss migration.  
         [0015]      FIG. 4  is an illustration of an alternative arrangement to facilitate adjustment of the height of the header.  
         [0016]      FIG. 5  is an illustration of another alterative arrangement for adjusting for the height of the header.  
         [0017]      FIG. 6  is another alternative embodiment of an arrangement for adjusting height of a header.  
         [0018]      FIG. 7  is another alternative embodiment of an arrangement for adjusting for the height of a header. 
     
    
     DETAILED DESCRIPTION  
       [0019]     Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms “mounted,” “connected,” “supported,” and “coupled” and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings. Further, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings.  
         [0020]     Illustrated in  FIG. 1  is a wastewater treatment system  10  including an activated sludge tank  12  and a clarifier  14 . Influent wastewater flows through supply  16  into the activated sludge tank  12  wherein the wastewater is treated. The activated sludge tank  12  will include several compartments or zones  18 . The tank  12  further includes a plurality of air diffusers  20  and  22  mounted near the bottom  24  of the tank and intended to diffuse air in the form of small bubbles into the wastewater  26  in the tank  12 . The air diffusers  20  and  22  are mounted on headers  28  and the headers  28  are connected to an air supply pipe  30 .  
         [0021]     One of the headers  28  is shown more particularly in  FIG. 2 . As shown in  FIG. 2 , at least one of the headers  28  includes a horizontally extending pipe  31  supported near the bottom  24  or the floor of the wastewater treatment tank  12 . The horizontally extending pipe  31  supports a plurality of air diffuser elements  20  such that air or other gas can be discharged from the horizontally extending pipe  31  through the diffuser elements  20  and into the wastewater  26  in the form of fine bubbles  34 .  
         [0022]     The diffusers elements  20  can be any type of diffuser element for the type used in wastewater treatment and including ceramic diffusers and rubber membrane diffusers.  
         [0023]     The horizontally extending pipe  31  is connected to an air supply pipe  30  which is in turn connected to a source of air pressure (not shown).  
         [0024]     In the arrangement illustrated in  FIG. 2  the header  28  is connected to the vertically extending air supply pipe  30  by an elbow joint pipe  38 , the elbow joint pipe  38  having an end  40  pivotally connected to the lower end of the vertical pipe  30  and a second end  42  pivotally connected to an end of the pipe  31 . The joined sections of pipe can pivot with respect to one another to permit relative vertical movement of the horizontal pipe  31 .  
         [0025]     The header  28  is also supported by a pair of support links or arms  44 . Each of the support links  44  has one end  46  pivotally connected to a band  48  surrounding and supporting the header  31  and an opposite end  50  pivotally connected or mounted to the floor  24  of the tank  12 . The support links  44  have the same length as the elbow joint pipe  38  and function to maintain the horizontal pipe  31  parallel to the floor  24  in response to relative movement of the pipe  31 .  
         [0026]     A pair of actuators  52  are also provided for effecting vertical movement of the header  28  with respect to the floor  24  of the tank. The actuators  52  each have one end supported by the floor  24  of the tank and an opposite end connected to the header  28  to move the header vertically. The actuators  52  can be a pneumatically actuated piston and cylinder. In other arrangements, the actuators could be a hydraulically actuated piston and cylinder or a screw driven extendable actuator, the screw being driven by an electric motor, mechanical language, by an air motor or hydraulic motor.  
         [0027]     A control  58  is mounted externally to the tank  12  and can be connected through line  60  to the actuators  52  to control operation of the actuators  52  and thus control the relative vertical position of the header  28  in the tank.  
         [0028]     In operation, the control  58  and actuators  52  can be used to change the vertical position of the header  28  in the tank and such that, as shown in  FIG. 3 , the relative vertical height of one header  28  can be changed with respect to the vertical height of another header  28  in the wastewater treatment tank  12 . The head pressure of the wastewater  26  on the surface of the diffusers  22  can thus be changed to achieve a balance of air flow through the two sets of diffusers  20  and  22 . During operation of the two sets of diffusers  20  and  22 , the characteristics of the diffusers may change over time. These changes may be caused by microbial growth on the diffusers or by changes over time in the material characteristics of the diffusers. The operating parameters of the wastewater system may also change over time due to fluctuations in the quantity of wastewater flowing into the wastewater treatment system or changes in the characteristics of the wastewater being treated by the system.  
         [0029]     The control  58  and actuators  52  can be used to maintain balance of the air flow through the different types of diffusers  20  and  22  and accommodate changes in the use of the wastewater system or changes in the flow characteristics of the diffusers over time.  
         [0030]      FIG. 4  illustrates an alternative arrangement for flexibly connecting the horizontal header  31  to the air supply pipe  30 . In the arrangement shown in  FIG. 4 , the vertical pipe  30  supplying air flow to the horizontal header includes a flexible section of pipe  20 , the flexible section of pipe having sufficient flexibility to accommodate several inches of vertical movement of the horizontal header  31  with respect to the bottom of the tank.  
         [0031]      FIG. 5  illustrates another alterative arrangement wherein a flexible section  80  of pipe is provided in the end of the horizontal header  31  where the horizontal header  31  is connected to the air pipe  30  feeding air to the header. The flexible section of pipe  80  accommodates relative vertical adjustment movement of the horizontal header  31  with respect to the air supply pipe  30 .  
         [0032]      FIG. 6  illustrates another arrangement wherein a flexible section of pipe  72  is joined in the air supply pipe  30  to accommodate relative vertical movement of the horizontal header  31 .  
         [0033]      FIG. 7  shows another alternative arrangement wherein an elbow joint  86  is provided between the air supply pipe  30  and the horizontal header  31  to facilitate relative vertical movement of the horizontal header  31  with respect to the supply pipe  30  in the bottom of the wastewater treatment tank.  
         [0034]     Various features and advantages of the invention are set forth in the following claims.