Abstract:
In a wastewater treatment plant a clarifier is fitted with piping and a pump to withdraw settled sludge from the bottom of the tank upwardly through the tank&#39;s center column and radially out from the clarifier via an exit pipe above the liquid level. The exit pipe can be supported on a fixed walkway. At the bottom end of the central tower is a manifold device for collecting settled sludge, including an annular preferably cylindrical wall, a central pipe hub and at least one pipe branch extending from an opening in the cylindrical wall radially inwardly to the central hub. Sludge is drawn up through a vertical sludge return pipe by a pump located preferably above the tank&#39;s liquid level, drawing sludge into pipe branches of the manifold device and through the hub to the sludge return pipe, then out through the exit pipe.

Description:
BACKGROUND OF THE INVENTION 
     This invention concerns wastewater treatment, and in particular a modification of the manner in which settled sludge is withdrawn from the bottom of a clarifier tank. 
     In a conventional wastewater treatment plant, wastewater is fed into one or more clarifier tanks, where solids are settled to the bottom of the tank, gathered toward the center of the sloping tank bottom by the rake arms of a rotating rake, then discharged out of the tank through a bottom exit pipe installed beneath the concrete floor surface. This type of installation can present problems, such as corrosion, clogging or failure of a pipe beneath the surface, lack of such an exit pipe in a tank to be converted to a clarifier tank, servicing of the pipe, need for increase in outflow capacity, etc. Replacement of such an underground pipe is difficult and very costly. 
     U.S. Pat. No. 5,340,485 showed a somewhat different system for collection of settled sludge from the floor of a clarifier. The patent shows a collection tube positioned radially outwardly from the center column, for drawing the sludge to an elevated position initially, then into the center column and down through an exit pipe. The withdrawal pipe in that system was located beneath the flow of the clarifier. A pump was positioned to withdraw the sludge. In one embodiment the sludge is drawn up almost to the liquid level in the tank, to a sludge collection box, into the center column and a vertical discharge pipe, then back down below the clarifier floor to an exit pipe. The patent also shows, in  FIG. 5 , a manifold device for use where the sludge enters the vertical discharge pipe, and a device similar to that manifold device can be used in the current invention, although in a different way. 
     It is an object of the invention to withdraw settled sludge from the floor of a clarifier into the center column of the clarifier and then upwardly and radially out from the clarifier without underground pipes, including retrofitting existing floor-effluent clarifiers to eject the settled sludge upwardly and outwardly. These and other objects, advantages and features of the invention will be apparent from the following description of a preferred embodiment, considered along with the accompanying drawings. 
     SUMMARY OF THE INVENTION 
     In the clarifier system of the invention, a clarifier tank is built with or retrofitted with piping and a pump to withdraw settled sludge from the bottom of the tank upwardly through the tank&#39;s center column and radially out from that column via an exit pipe which can be secured to a fixed walkway, or other means. 
     At the bottom end of the central tower, and preferably supporting the central tower, is a special manifold device similar to what is shown in U.S. Pat. No. 5,340,485, but installed in a different way and for a different purpose. In the invention the special manifold device, with one or more side branch pipes extending from a central hub outwardly to and through a peripheral wall, is positioned upside down relative to the &#39;485 patent, with an effluent end of the hub oriented upwardly. Three branch pipes, of relatively large diameter and preferably at equal angular intervals, may be provided. The special manifold device, which has sometimes been known as a CMD in its previous uses, can be installed directly down against a foundation or pedestal at the tank bottom, such pedestal being sufficient to support the central column of the clarifier. The special manifold device or CMD preferably is substantially open from top to bottom, within the space defined by the peripheral wall (which typically is cylindrical but could be a polygonal shape if desired), interrupted only by the central hub and pipe branches extending radially through that space. The open upper end of the hub receives settled sludge that has been collected through the pipe branches, and the sludge is drawn upwardly through a vertical RSS (return settled sludge) pipe connected in sealed relationship with (or integral with) the central hub. 
     At the top of the central column the RSS pipe turns outwardly, i.e. is connected to an essentially horizontal exit pipe to carry the RSS outwardly away from the tank. A sludge withdrawal pump preferably is located on the exit pipe outside the tank, although it could be other locations along that pipe. 
     If needed the hub and the connected vertical RSS pipe can be off-center in the special manifold device, in order to properly pass through the drive assembly up near the top of the column. The location of the RSS pipe within the column will depend on size of the RSS pipe and the configuration of the drive assembly through which it must pass. 
     At the bottom of the tank the special manifold device or CMD has its radial openings in communication with the wastewater in the tank, and particularly with the settled sludge at the bottom of the tank. A larger-diameter, conventionally used sludge shield often is included in the tank, this large manifold simply being a large cylinder closed at its top and with side openings, to assure that sludge is collected from locations spaced outwardly from the center column. This is to assure that clarified water, typically present immediately around the center column above the bottom, will not be drawn out along with sludge. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a top plan view, with portions broken away, showing a clarifier which includes the system of the invention. 
         FIG. 2  is a side elevation view showing the clarifier tank and system. 
         FIG. 3  is a more detailed elevation view showing a portion of the clarifier and illustrating the system of the invention. 
         FIG. 4  is a detailed elevation view showing, partially in cross section, the bottom center portion of the clarifier tank with equipment according to the invention. 
         FIG. 4A  is a detail view in perspective showing a special manifold device of the invention, known as an RMD (reverse manifold device). 
         FIG. 5  is another detail view at the bottom center of the tank, showing the bottom of the center column and the important components of the invention. 
         FIG. 6  is a detail section elevation view showing a fixed walkway of the clarifier tank system. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIG. 1  shows, in a fragmentary top plan view, a clarifier  10  that includes a tank  12 , a center column  14 , a fixed platform  16 , a fixed walkway  18  for service access to equipment via the platform  16 , and rotational apparatus including rake arms  20  and  22  and a feedwell  24  which extends down approximately from the liquid level in the tank about four to six feet, sometimes more. The tank apparatus includes a drive unit for rotating the rotatable components, the drive unit not being clearly seen in the drawing, but typically located at the top of the center column  14  and connected to a driving cage that extends down to the rake arms. Above the rake arms are skimmer blades, not clearly seen in  FIG. 1 . Feedwell supports are shown at  26 , supporting the feedwell from the rake arms  20 ,  22  below and from stub arms  28  below. 
       FIG. 1  also shows an RSS exit pipe  30  which is included in the clarifier system according to the invention. The RSS exit pipe  30  is supported, preferably suspended from, the walkway  18 , and comes out of the center column  14  as indicated. 
       FIG. 2  shows the system in side elevation view, better illustrating the RSS exit pipe  30  and its relationship to the walkway  18  and the center column  14  from which it emerges. The pipe  30  extends up from the interior of the center column and, in this embodiment, bends out and down to the straight section shown leading generally radially out from the clarifier. A pump is indicated at  32 , just outside the clarifier. This pump, which draws sludge up from the bottom of the clarifier, could be at other locations along the RSS pipe  30 . 
       FIG. 2  also shows a wastewater influent pipe at  34 , shown partially behind the RSS exit pipe  30 . As indicated by a direction arrow, the influent pipe  34  directs wastewater into a cordoned space near the surface, defined by the feedwell  24 . An energy dissipating inland (EDI) can be included at the outlet of the influent pipe  34 . 
       FIG. 2  also shows spiral wiper blades  36  extending to the tank floor from the rake arms. Skimmer blades  38  are shown at the top of the rotating apparatus, rotatable with the rake arms  20 ,  22  and the feedwell  24 . 
       FIG. 3  shows the clarifier system in greater detail, but with a portion of the left side not shown. In  FIGS. 3 and 4  a wastewater influent pipe  40  is shown entering the center column or influent column  14  from beneath, for a system wherein this influent pipe is embedded in the concrete bottom of the tank. In this case the center column or influent column carries the influent up to the feedwell  24 , the influent exiting the influent column through exit ports  42 , preferably into an energy dissipating inlet (EDI)  44 . This influent equipment is conventional, the embedded pipe  40  being an alternative to the above-liquid influent pipe  34  shown in  FIG. 2 . 
       FIG. 3  shows the sludge exit pipe  30  at a different location on the walkway than  FIGS. 1 and 2 . 
     With the invention, sludge accumulated at the bottom of the tank  12  and gathered toward the center along the sloping bottom by the rakes is fed up through a vertical RSS pipe  50  which is indicated as being within the center column or influent column  14 . This can be, for example, a 24 inch pipe contained within a much larger center column which might be 48 inches outside diameter. The withdrawn RSS enters a special manifold device indicated at  52  in  FIG. 3 , the sludge entering essentially radially inwardly through openings in the periphery of the manifold device  52  and then up through the vertical RSS pipe  50 . In another use such a manifold device has been called a CMD or collection manifold device. Here it can be called an RMD or reverse manifold device. The manifold device  52 , as further described below, does not block flow of influent wastewater if the wastewater is delivered through a subterranean influent pipe such as shown at  40 . The inflowing wastewater can flow through the manifold device  52 , isolated from the exiting RSS, and up through the influent column  50 . 
     In  FIG. 4  the CMD or RMD or manifold device  52  is shown connected at the bottom of the center column  14 .  FIG. 4A  schematically shows the special manifold device  52  in one preferred form prior to incorporation into the system of the invention. The manifold device  52  or CMD has an annular vertical wall  54 , preferably cylindrical but which could also be another shape, such as polygonal, and a center hub  56  with a solid bottom as seen in this schematic view. The center hub  56  may not be at center, but can be off-center within the outer ring or wall  54  so as to allow the outflow RSS pipe  50  ( FIGS. 3 and 4 ) to be off-center when needed so as to pass through the drive unit with adequate clearance. As  FIG. 4A  shows, the hub  56  is connected by at least one, and preferably two or three, pipe branches  58  that are open to the interior of the center hub and connect to holes  60  in the outer ring or peripheral wall  54 . These pipe branches  58  provide conduits for inflow of settled sludge, inwardly toward the interior of the central hub  56  and then upwardly into the vertical RSS pipe  50  indicated in  FIGS. 3 and 4 . In  FIG. 4  one of the branch pipe holes  60  is seen, and the central hub  56  is indicated in dashed lines, off-center in this particular implementation. 
     The CMD or manifold device  52  allows flow of wastewater up through the device, isolated from RSS being removed, as indicated by the arrow in  FIG. 4A .  FIG. 4A  shows that the center hub  56  is closed at its bottom end  62 . The upper end of the manifold device  52  is secured to the bottom end of the center column  14 , which can be by a lip or flange  64  on the manifold device that can be coupled by bolts or welding to a similar flange secured to the bottom end of the center column  14 . Another mounting flange  66  at the bottom side of the CMD or manifold device  52  can be used to secure the CMD down to the tank floor or to a pedestal  68  which would normally receive the bottom end of the center column. 
     The upper end of the hub  56  is secured to the vertical RSS pipe  50  as shown in  FIG. 4 . This can be by welding, securement using a sealing sleeve, or other means. The center hub could be a longer section of pipe if desired, with a coupling, such as a threaded sleeve, to connect it to the bottom of the RSS pipe  50 . 
     In some implementations the manifold device  52  is formed integrally at the bottom end of the center column or influent column  14  ( FIG. 5  can be considered an example of this). The center column is simply of the proper length to bear against the pedestal  68 , and pipe branches  58  are welded to the interior of the center column at holes such as shown at  60 , and to a center hub connectable to a vertical RSS pipe. This can conveniently be done in a new installation, as opposed to a retrofit where the existing center column is saved, although it can be done in either case. The lower end part of the column in this integral installation is considered to have the RMD or reverse manifold device  52 . 
       FIG. 4  also shows an outer manifold or sludge shield  70  as discussed above. The sludge shield  70  is designed to cause settling sludge to accumulate somewhat outwardly from the center of the tank, spaced away from the inlet holes  60  of the CMD or special manifold device  52 . Such sludge shields have been used previously for conventional systems wherein accumulated sludge is directed downwardly through a floor pipe and removed from beneath the floor. This generally keeps clarified water from being discharged with sludge. The shield  70  has a closed top and can be a large-diameter simple cylinder, with large exterior holes as indicated at  72  in  FIG. 4 . As shown in the detailed view of  FIG. 5 , the sludge shield  70 , which may have diameter of seven feet or more in a large clarifier wherein the manifold device  52  is about four or five feet in diameter, is positioned against the tank floor  74  and can have rectangular inlet openings  76 .  FIG. 5  shows a center column  14  with the CMD/RMD or manifold device  52  at its bottom end, and this could be an integral installation such as described above. One of the manifold device intake holes  60  is seen in  FIG. 5 . The manifold device, or the base of the center column  14  in the case of a integral installation, is shown secured down into the concrete pedestal  68  by anchor bolts  78 . 
       FIG. 6  shows a preferred construction for support of influent wastewater and effluent sludge (RSS) pipes which are also seen in  FIGS. 1, 2 and 3 . The walkway  18  has a walkway base structure  80  to which are connected pipe hangers  82  and  84 . The wastewater influent pipe  34 , larger in diameter than the RSS exit pipe  30 , is shown suspended generally centrally from the walkway structure, while the RSS exit pipe  30  is shown suspended from a position to the side of the other pipe, which is also seen in  FIGS. 1 and 2 . The top edge of the tank wall is illustrated in relation to these pipes, at  86 . 
     For installation of the invention in an existing clarifier apparatus, where the center column is to be retained, the base of the center column is disconnected from the floor or pedestal, then raised up and cut to a shorter length as needed to accommodate the RMD to be installed. The RMD is designed and configured to fit the diameter of the center column and with a hub positioned in a proper location for the desired location of the vertical RSS pipe, which has been determined based on a proper location for the RSS pipe to pass through the drive unit above, with adequate clearance. The RSS pipe is lowered into the column from the top and secured at its bottom end to the hub of the RMD. A new attachment flange is welded to the cut column end, and the RMD is secured to the bottom of the column in a sealed connection. Then the RMD is secured down to the floor or pedestal. This could be using the same array of bolts that secured the column, if they are in good condition. 
     For a new clarifier system, or in a situation where an existing center column is to be replaced, the RMD can be built into the bottom of a new center column, as described above with reference to  FIGS. 4 and 5 . Again, the center hub of the RMD is located as needed so that the attached RSS pipe can pass properly through a drive unit above. The column is bolted down to the floor or pedestal in the usual way. Note that a separately-formed RMD could be secured to the bottom of a new center column if desired, but in the case of a new column it is usually preferred to form the RMD as an integral part of the column. Further, it is also possible to form an integral RMD in an existing, reused center column, but this would generally not be preferred because of the more difficult conditions for cutting holes in the column and welding the branch pipes in place. 
     The above described preferred embodiments are intended to illustrate the principles of the invention, but not to limit its scope. Other embodiments and variations to these preferred embodiments will be apparent to those skilled in the art and may be made without departing from the spirit and scope of the invention as defined in the following claims.