Aeration Plant For Clarifying Sewage And Waste Effluents

Abstract

An apparatus for surface aeration and circulation of liquids, comprising a tank for containing a body of liquid. An aeration rotor is positioned at least partially submerged in the body of liquid in the tank. This rotor rotates about a substantially vertical axis and includes a shaft position on the vertical axis of the rotor. A first wall member is secured centrally to and extends radially outwardly from the shaft and a second wall member extends radially outwardly from the shaft and has a centrally arranged opening therein concentrically disposed about the shaft of the rotor. Partition means secured to and extending between the first and second wall members form a plurality of guide channels defining flow passageways therebetween, with the opening in the second wall member providing a first opening to each of the flow passageways. A second opening is located at the opposite end of each of said flow passageways at the outer edges of the wall members. There is also provided means for feeding air into each flow passageway substantially at a location where the liquid disposed thereat is moving substantially laterally towards the outer edges of said wall members, the opening of the rotor being freely accessible to the liquid circulating in said tank. The second wall member is formed by a surface of revolution about the vertical axis of the rotor whose generatrix forms a continuous curve extending from the periphery of the first opening to the periphery of the second opening, said curve initially converging inwardly towards the axis of the rotor for a minor portion of its length and then diverging outwardly away from the axis of the rotor for a major portion of its length and the outer end of the curve terminating in a substantially horizontal position at the periphery of said second opening and being in close proximity to the level of the liquid in the tank.

Parent Case Text

CROSS-REFERENCE TO RELATED CASES

This application is a continuation-in-part application of my copending U.S. application, Ser. No. 806,767, now abandoned, filed Jan. 31, 1968, which, in turn, is a continuation application of U.S. application, Ser. No. 434,838, now abandoned, filed Feb. 24, 1965, and also a continuation-in-part application of my copending U.S. application, Ser. No. 64,125, now abandoned, filed July 30, 1970, which, in turn, is a continuation application of U.S. application, Ser. No. 593,562, now abandoned, filed Nov. 10, 1966.

Description

BACKGROUND OF THE INVENTION

The present invention relates to a new and improved apparatus and plant for the aeration and circulation of liquids. The invention is particularly, although not exclusively, concerned with the aeration of sewage and waste effluents for the purification or clarification thereof, particularly by activated sludge processes, and employing means for circulating and aerating the liquids to be treated.

The technology in this particular art is familiar with the aeration of sewage by so-called "surface aeration" during which oxygen from the air is introduced by mechanical devices into the liquid to be treated and dissolved therein according to the oxygen absorption characteristics of the liquid. By means of such surface aeration, circulation and mixing zones of the liquid which are lacking in air, are continuously moved towards the aerator and a movement is created within the liquid body itself capable of maintaining in suspension the desired particles as are liable to settle, for instance the activated sludge.

Moreover, devices for the circulation and aeration of liquid into tanks are already known to the art wherein air is introduced into the liquid, either by blowing it through diffusers or by distributing it into the liquid through a hollow shaft and rotating parts located deep below the liquid surface, or by conveying the liquid by rotors and splashing it against faces or surfaces placed above the liquid surfaces. Basic requirements for such equipment are the capability of effecting so-called "oxygen absorption" as well as the mixing and circulation with a minimum of energy requirements and adjustability for wide variations in performance.

There are also known aeration devices which employ brush rolls rotating upon the surface of the water for aerating the waste water and clarifying plants. Furthermore, there have been proposed for aerating water so-called perculating filters from which water trickles down. These known devices have the inherent disadvantage that the intensity of aeration is adjustable only to a limited degree and therefore can be only insufficiently adapted to the prevailing conditions, typically the quantity of the water to be cleaned per unit of time and the degree of contamination or soiling thereof.

SUMMARY OF THE INVENTION

Hence, from what has been stated above it should be apparent that this particular technology is still in need of aeration plants for clarifying sewage and waste effluents which are not associated with the aforementioned drawbacks and limitations of the prior art proposals. It is therefore a primary object of the present invention to provide a new and improved aeration plant for clarifying sewage and waste effluents which is not associated with the aforementioned drawbacks and limitations of the heretofore known constructions of aeration plants and effectively and reliably fulfills the existing need in the art.

Yet a further significant object of the present invention relates to an aeration plant for clarifying sewage and waste effluents in a highly efficient and economical fashion, wherein the aeration rotor is constructed in the manner promoting intensive circulation of the liquid throughout the basin.

Still a further significant object of this invention relates to a novel construction of apparatus for the circulation and aeration of liquid in tanks or the like, especially for the treatment of sewage, employing a rotor construction having means for effectively infeeding the air into the guide channels for the liquid so as to promote intensive admixture therewith.

Yet a further noteworthy object of the present invention relates to apparatus for the circulation and aeration of liquids in tanks or the like incorporating a rotor or impeller wheel having specially designed guide channels for the liquid undergoing treatment promoting more efficient operation and circulation of the liquid through the tank.

And another object of this invention relates to a new and improved apparatus for the aeration and circulation of liquids in a tank wherein the rotor or impeller wheel operates without the use of a draft tube or equivalent type of structure so that the rotor itself directly imparts to the liquid within the tank an intense rotational movement distributed throughout the entire body of the tank, to thus cause such liquid to flow in a continuous spiral or rotational path.

Now, in order to implement these and still further objects of the invention, which will become more readily apparent as the description proceeds, the general constructional manifestation of apparatus for aerating and circulating liquid in a tank or the like, for instance for the treatment of sewage, as contemplated by this invention comprises a rotor or impeller wheel which, during use, is at least partially submerged in the liquid and rotates about a substantially vertical axis. This rotor is provided about its circumferential extent with a plurality of upwardly and outwardly directed guide channels through which the liquid enters from the underside of the rotor and from which it is discharged laterally or substantially horizontally by the centrifugal action prevailing during rotor rotation. According to the invention there is also provided means for the introduction of air into the guide channels for the liquid. The means for introducing the air into the guide channels of the rotor preferably incorporates air inlets opening into the guide channels in the vicinity of the location of the rotor guide channels where such are shaped to direct the liquid laterally or substantially horizontally. The liquid departs from the rotor generally in the form of a spray or the like promoting oxygen absorption, this absorption of oxygen being increased by the introduction of air into the rotor itself.

Conveniently, the rotor impeller or impeller wheel incorporating the plurality of guide channels for the liquid may be constituted by radial blades or paddles and two spaced disk-like wall members located in superimposed fashion, and which are curved in a vertial plane and carry such blades or paddles. The guide channels are disposed in such a manner that the liquid, which enters vertically upwards into the guide channel inlets arranged around the rotor axis, is deflected outwards through an angle of approximately 90.degree., departing from the upper part of the rotor in a substantially horizontal direction through the guide channel outlets. The channel outlets are disposed about the periphery of greatest diameter of the rotor compared with the diameter at which the channel inlets are located. The upper curved disk, that is to say that disk-like wall member disposed closer to the axis of rotation of the rotor, may be provided at the region of the rotor axis or along its deflecting curvature and at each guide channel with an outlet portion of an air inlet or duct means communicating with atmosphere. Moreover, such guide channels of the rotor structure may be conveniently connected to the atmosphere by a duct or tube concentric with the rotor axis and which communicates with the guide channels of the rotor through an annular space.

According to a further aspect of this development the rotor itself is not associated with any draft tube or equivalent structure, as such has been heretofore proposed by certain prior art aeration plant constructions, exemplified for instance by U.S. Pat. Nos. 2,054,395 and 2,120,786. Importantly, then, when the rotor of this development is submerged in the tank it is not enclosed with any tube or similar structure so that, as it rotates, it directly imparts to the liquid within the tank a rotational movement which is distributed throughout the entire body of the tank, causing the liquid to flow in a continuous rotational path. This motion in addition to the motion provided by the flow of the liquid outwardly from the channel outlets and into the liquid level of the tank in substantially horizontal direction promotes an extremely effective flow path for the liquid within the tank. Circulation is therefore unimpeded and highly effective.

A further aspect of this invention contemplates forming the lower and outer wall member of the rotor by a surface of revolution about the vertical axis of the rotor, the generatrix of which forms a continuous curve extending from the periphery of the inlet openings at the lower end of the rotor to the periphery of the outlets of the guide channels. This curve initially converges inwardly towards the axis of the rotor for a minor portion of its length and then diverges outwardly away from the axis of the rotor for a major portion of its length, and the outer end of the curve terminates in a substantially horizontal position at the periphery of the outlets of the guide channels and is in close proximity to the level of the liquid in the tank. It has been found that such construction of rotor provides for an extremely efficient operation and improved throughput.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood and objects other than those set forth above, will become apparent when consideration is given to the following detailed description thereof. Such description makes reference to the annexed drawings wherein the same reference characters have been generally employed for the same elements throughout the various embodiments disclosed and wherein:

FIG. 1 is a fragmentary pictorial view of the aeration tank in operation and employing an aeration rotor designed according to the teachings of the invention;

FIG. 2 is a vertical sectional view through the aeration tank depicted in FIG. 1 and depicting details of the equipment for the circulation and aeration of the liquid contained therein;

FIG. 3 is a vertical sectional view through a modified form of aeration impeller or rotor embodying teachings of this invention;

FIG. 4 is a fragmentary vertical sectional view through another embodiment of aeration rotor or impeller wheel as contemplated by this invention;

FIG. 5 is a top plan view of the rotor or impeller wheel depicted in FIG. 4, part of the upper disk-like wall member being removed to reveal internal structure thereof; and

FIG. 6 is a vertical sectional view through a modified form of aeration plant designed according to the teachings of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Describing now the drawings, the exemplary embodiment of apparatus for the aeration and circulation of liquids, particularly sewage, as depicted Between FIGS. 1 and 2 will be seen to comprise a tank or basin 10 bounded by sidewalls 12 and having a floor or bottom portion 14. Tank 10 may be of any desired cross-section, for instance rectangular or cylindrical by way of example. Between the floor 14 and the sidewalls 12 of the tank 10 there is provided a sloping floor portion 16. Further, a bridge 18 will be seen to extend between two opposite sidewalls 12 of tank 10. Bridge 18 carries a suitable electric motor 20 positioned such that its vertically extending drive shaft 22 passes through such bridge 18 and into the confines of the tank 10. The lower end of the motor shaft 22 carries a turbine-like impeller wheel 24, sometimes hereinafter conveniently simply referred to as "rotor". At this point it is also to be mentioned that the electric motor 20 may be advantageously a standard reversible motor so that rotor 24 can be selectively driven in the one or the other rotational direction. This is true for all of the embodiments of rotor constructions disclosed herein.

Continuing, it will be recognized by referring to FIG. 2 in particular, that on the tank floor 14 and preferably at its central region there is arranged a hollow flow-cone 26. This flow-cone 26 has a length of pipe 28 extending axially from its apex. The center line of this pipe or conduit 28 substantially coincides with the axis of rotation of the rotor 24. Radial guide vanes 30 extend vertically from the surface of the flow-cone 26 up to the free end of the pipe or conduit 28. While in the exemplary embodiment four such guide vanes 30 are contemplated it should of course be apparent that a greater or smaller number could also be employed. Apart from the above structure, the tank 10 is also provided with a material infeed or inlet conduit 32 and an outfeed or discharge conduit 34 at the sidewalls 12 thereof.

Now in the embodiment illustrated in FIGS. 1 and 2 the aeration tank may be assumed to constitute, for instance, part of a purification plant and can be inserted between primary and final sedimentation. In such case the infeed or inlet 32 provides for the inflow of sewage from primary sedimentation whereas the activated sludge flows to final sedimentation via the discharge or outflow conduit 34. However, it would be also possible to admit and treat sewage in the aeration tank 10 without primary sedimentation. Furthermore, a return pipe 36 extends from the lower part of the final sedimentation tank (not shown) into the aeration tank 10, terminating inside the hollow cone 26 as best seen by referring to FIG. 2. By means of the return pipe 36 sludge collected during final sedimentation is returned into the aeration tank 10. A drain pipe 38 can be connected with the return pipe 36, this drain pipe extending from the tank bottom or floor 14 of the aeration tank 10 and normally being shut-off by means of a suitable slide valve 40 or other appropriate valve structure or closure. The aforesaid drain pipe 38 is open during stoppages in operation if required in order to empty the contents of the tank through the return pipe 36 and a drain which has not been particularly shown.

Although details of various constructional forms of rotor 24 will be considered more fully in conjunction with the description of FIGS. 3, 4 and 5 in particular, it is thought appropriate at this point to make certain general observations concerning the rotor constructions disclosed herein. Rotor 24 may be advantageously manufactured from a light and preferably plastic material, for example by spray casting techniques. For instance, a wear resistant polyester mixture may be employed to advantage or any other suitable material which is corrosion resistant and unbreakable. Rotor 24 comprises an upper disk-like wall member 42 and a spaced lower disk-like wall member 44. A number of blades or baffles 46 are situated between the upper disk member 42 and lower disk member 44 in order to form a plurality of guide channels 48 defining flow passageways for liquid entering from the lower end 50 of the rotor 24 in a vertical direction into these guide channels 48 arranged circularly about the rotor shaft 22 and specifically peripherally about the body of such rotor. The liquid entering from the lower inlet end 50 of the rotor 24 is deflected through an angle of approximately 90.degree. in the guide channels 48 outwardly and discharges from such guide channels 48 at the outer perimeter of the rotor 24 in a substantially horizontal or lateral direction. It will be seen that the rotor itself is arranged near the level of the liquid 52 in the tank 10 so as to provide for surface aeration and circulation of such liquid.

With the foregoing background in mind attention is now invited to FIG. 3 wherein there is shown in sectional view details of a specific constructional form of rotor 24. Hence it will be seen that rotor 24 is provided with a first disk-like wall member 42 secured centrally to and extending radially outwardly from the rotor shaft 22. There is also provided a second disk-like wall member 44 which likewise extends radially outwardly in spaced relationship from the rotor shaft 22 and has a centrally arranged opening 54 therein concentrically disposed about the rotor shaft 22. This second disk-like wall member 44 is axially spaced below the first disk-like wall member 42. The plurality of generally radially directed baffles or partition walls 46 which extend between the upper disk-like wall member 42 and the lower disk-like wall member 44 serve to form the previously mentioned guide or flow channels 48 which define radial spirally extending laterally enclosed flow passageways. The common inlet opening 54 at the lower disk-like wall member 44 is thus sub-divided into a number of inlets 56, each of which communicates with an associated guide channel 48 in order to feed liquid from each respective individual inlet opening 56 to the associated outlet opening 58 of each such guide channel 48. Furthermore, the bottom end of the driving rotor shaft 22 will be seen to carry a conical deflection member 60 having a pointed end 62 directed towards the center of the inlet opening 54. Moreover, hub member 43 of the rotor 24 is traversed by a plurality of axially directed air inlet ducts or conduits 64, one such air inlet duct 64 being provided for each of the radially extending guide or flow channels 48. The lower end of these air inlet ducts 64 is radially deflected by the conical deflection member 60, so that each air inlet duct 64 radially opens at location 66 into its associated guide channel 48. The point of entry of the air into the liquid stream flowing through the guide channel 48 is advantageously at a location where the liquid stream flows essentially laterally or horizontally towards the discharge or outlet 58 of the relevant flow channel 48.

Now in FIGS. 4 and 5 there is shown a further embodiment of rotor 24 again composed of an upper downwardly curved outwardly directed disk-wall member 42 and a lower upwardly curved outwardly directed disk-like wall member 44. Just as was the case for the previously considered embodiments radially extending baffles or partition walls 46 serve to divide the rotor into a number of radially extending laterally enclosed flow passageways formed by the guide or flow channels 48 having an inlet opening 56 and an outlet opening 58 for each such guide channel. Communicating with each guide channel 48 is an air duct 68. Each air duct 68 wil be seen to extend through the body of the upper disk-like wall member 42 and merges with the associated guide channel 48, preferably at the region where the liquid is moving laterally or horizontally towards the outlet 58 thereof. Now in this embodiment the outer annular disk 44 of the rotor 24 is shown in vertical section as forming a portion of an ellipse 70, the major axis 72 of which extends horizontally slightly above the common inlet end or opening 54 for the guide channels 46 and the minor axis 74 of which extends vertically from the rotor outlet or discharge openings 58. Thus the outer disk or disk-like wall member 44 of the rotor forms a portion of an elliptical annulus, the inner diameter 76 of which determines the sectional area of flow slightly above the inlet end of the rotor while the diameter at the outer end of the rotor is substantially equal to the sum of the smallest inlet diameter plus the length of the longer axis of the ellipse 70 formed by the cross-section through the elliptical annulus.

A rotor designed according to the teachings of FIGS. 4 and 5 has given excellent results as to the delivery rate and amount of air sucked-in through the air inlet tubes or ducts 68 and mixed with the liquid expelled through the outlet or discharge openings 58. It should be noted that the lower and outer disk-like wall member 44 of the rotor is formed by a surface or revolution about the vertical axis of the rotor, whose generatrix forms a continuous curve extending from the periphery of the inlet opening at the lower end of the rotor to the periphery of the outlet openings of the guide channels, this curve initially curving inwardly towards the axis of the rotor for a minor portion of its length and then diverging outwardly away from the axis of the rotor for a major portion of its length, the outer end of such curve terminating in a substantially horizontal position at the periphery of the outlets of the guide channels. The rotor 24 is positioned in the tank 10 so that the curve which terminates in substantially horizontal position at the periphery of the rotor outlet openings 58 is in close proximity to the level of the liquid in the tank.

The general arrangement of aeration plant as depicted in FIGS. 1 and 2 can be employed with any of the rotor constructions described heretofore in conjunction with FIGS. 3, 4 and 5. There will not be considered in greater detail the operation of such aeration plant.

When the plant described with reference to FIGS. 1 to 5 is to be started up the aeration tank 10 is filled with sewage through the inlet 32 up to the indicated level of the liquid 52 which is maintained approximately in line with the lower edge 57 of the rotor discharge openings 58, or perhaps a few centimeters above. Drive motor 20 is then switched-on causing the rotor 24 to rotate at about 60 to 80 r.p.m. The liquid inside the guide channels 48 of the rotor 24 will be subjected to centrifugal forces and discharged in radial direction from the upper perimeter of these guide channels. This causes a suction at the inlet or entry 54 to the guide channels 48 drawing more liquid continuously upwards from below into such channels with the centrifugal force first lifting the liquid and then discharging it horizontally outwards. As long as the rotor runs there will, therefore, be a continuous circulation of the liquid contained in the tank 10. Due to the rotation of the partly submerged rotor, the entire content of the tank 10 will gradually obtain a rotational movement, having the same direction of rotation as the rotor but very much slower. This effect is promoted due to the absence of any draft tube or the like at the rotor which allows for unimpeded access of liquid into the rotor and liquid circulation in the tank. With the continuous suction flow into the lower end 54 of the rotor 24 a flow column 59 is set up in the center of the tank in a vertically upward direction and having a diameter essentially corresponding to that of the rotor inlet, as best seen by referring to FIG. 2.

The liquid which is sucked up into the rotor from below and discharged in a horizontal direction only slightly above the tank liquid level 52 spreads fan-like and in a step-by-step or wave fashion radially over the surface of the tank up to the side walls 12 and hence is deflected downwards, individual particles of the liquid descending to the bottom of the tank 10 with a spiral or screw-like motion 61 caused by the slowly revolving contents of the tank. By means of the sloping tank wall section 16 the liquid between the top edge of the tank and its floor 14 is re-directed towards the center of the tank 10 and the flow-cone 26, thus arriving at the region of suction of the turbulent liquid column 59 and moving axially upwards the rotor inlet. This liquid column is centralised by the flow-cone 26 and guide vanes 30. The guide vanes 30 also serve to slow down the rotational speed of the liquid in the tank so as to maintain an adequate velocity differential between liquid and rotor. In operation, preferably the lower edge 57 of the rotor exit should be situated substantially flush with the liquid level 52 in the tank. However, the height of this edge 57 with respect to the liquid level 52 may slightly vary. The lower edge 57 may be also slightly immersed in the liquid or it may be situated a slight distance above the liquid level.

The liquid sucked up by the rotor 24 and drawn through the guide channels 48 towards the outlets 58 with a high velocity, due to the centrifugal forces, itself causes a suction action, thus drawing air from above the tank level thorugh the air tubes or ducts 64 (FIG. 3) or 68 (IG. 4) into the guide channels 48 for admixture with the passing liquid flow so as to be discharged as a liquid/air mixture from the outlet ends 58 of the rotor guide channels 48.

The breaking up of the liquid conveyed by the rotor into separate streams by means of the guide channels 42 of the rotor 24 and the injector-like air intake inside these channels ensures for an intensive or intimate contact between air and liquid. With the rotor turning in, for instance the direction of the arrow A in FIG. 1, the outlet edge 45 (FIG. 5) of every baffle or partition wall forms a progressive wave on the liquid surface of the tank, intensively mixed with air, but of small height due to the lower edge 57 of the guide channels 48 being only very slightly below the liquid level in the tank. As can be seen from FIG. 1 these turbulent progressive waves travel in a spiral fashion right up to the that of the tank. These progressive waves form the upper layer of the tank liquid onto which the liquid/air mixture is thrown continuously from the rotor guide channels. This ensures thact the liquid surface is roughed-up or continuously disturbed and the contact area between air and water increased, thus improving the diffusion of air or oxygen into the liquid.

As already mentioned, the liquid discharged from the rotor 24 is deflected downwards when reaching the tank walls 12, individual particles of the liquid descending with a screw-like motion down to the tank bottom 14 where they are deflected in a spiral fashion towards the flow-cone 26 only to be drawn with high velocity in an ascending axial direction into the rotor inlet 54 due to its suction effect. Around flow-cone 26 there is, therefore, a region of low pressure which, under suitably applied technical conditions, is sufficient to return into the circulation of the tank a quantity of liquid discharged from the tank through discharge 34. FIG. 2 shows, for example, the return pipe 36 from a final sedimentaion tank entering the hollow flow-cone 26 from below and being connected to tube 28 at the apex of such flow-cone. Due to the prevailing suction effect of the exit of tube 28 caused by the rapidly rising liquid column 59, the sludge which collects at the bottom of the final sedimentation tank is returned and brought again into the circulation of the aeration tank.

During operation of the plant the rotor 24 for all embodiments can be run in either direction, as generally indicated by the double-headed arrows B and C in FIG. 5. Normally the rotor will be run in the direction of arrow C, the liquid leaving the guide channels 42 of the rotor in the direction of arrow D. With this rotation the baffles or partition walls 46 at the exit from the rotor 24 will be of slightly backwards curvature, opposite to the direction of rotation. The exit edges 45 of the baffles generating only a small amount of turbulence in the liquid discharged from the channels 48 and spreading the liquid/air mixture gently over the tank surface to complete its circulation by descending to the tank bottom in a gradual screw motion, and then being deflected by the flow-cone to return to the rotor as a quickly rising liquid column.

With the rotor running in direction of the arrow B the baffles or partition walls 46 will be slightly curved in their direction of rotation, thus exerting a higher pressure onto the liquid being discharged, i.e. they provide an extra push. The turbulence in the liquid discharged will be increased due to the tearing action by the exit edges 45 of the baffles in the direction of arrow E, thus creating an additional air or oxygen supply into the liquid discharged.

By reversing the rotation of the rotor it is also possible to change the aeration capacity for the tank. As stated, the rotor runs normally in the direction of the arrow C in FIG. 5. Should, for any reason whatsoever there be a temporary increase in sludge content of the aeration tank requiring a higher oxygen demand, the direction of rotation of the rotor can be simply reversed by means of the reversible drive motor 20 to thus run in the direction of the arrow B. The oxygen intake will then be increased corresponding to the greater sludge content without requiring a great deal of extra motor power. Requirements for varying the aeration capacity can also be met by changing the r.p.m. of the rotor or by changing the depth of immersion of edge 57 of the guide channel outlets (FIG. 1 or 3) into the tank liquid. With rotors made and installed according to FIGS. 1 to 5 best efficiencies were obtained at 70 to 72 r.p.m. and 2 - 2.5 centimeters depth of immersion.

Finally, in FIG. 6 there is shown a vertical sectional view through an aeration plant, wherein generally the same reference characters have been again conveniently used as were employed for the general arrangement of aeration plant as disclosed in FIGS. 1 to 5 heretofore. It will be seen that rotor 24, which may be any of the types heretofore disclosed, is suspended such that the lower edge 57 of the rotor discharge or outlet openings 58 is in close proximity to the level of the liquid in the tank 10. A guide cone 80 is placed on the bottom or floor 14 of the tank 10 in axial alignment wth the rotor 24 and is provided with radial guide vanes 82 which extend helically upwards about the guide cone 80. The guide vanes 82 redirect the liquid, approaching the cone in radial or spiral fashion along the bottom of the tank, in a gradually upward direction towards the inlet end 54 of the rotor 24. The upper ends 84 of the vanes 82 extend in a substantially axial direction and upwardly to within a short distance below the lower inlet opening 54 and the inlet openings to the guide channels 48 of the rotor. The upper ends of the upper portions 84 of the vanes 82 act to brake the spiral movement of the liquid in the central portion of the aeration tank, so that in the suction zone immediately below the rotor 24 the liquid does not have any rotary motion but moves upwardly in axial direction only due to the suction effect of the rotor. The efficiency of the rotor is thus increased.

In all of the embodiments herein disclosed it should be noted that the rotor is at least partially submerged in the tank and is not enlcosed with any draft tube or similar structure so that, as the rotor rotates, it can impart directly to the liquid within the tank a circulatory movement which is distributed throughout the entire body of the tank causing the liquid to flow in a continuous rotational path, as indicated for instance by the arrows 86 of FIG. 6. Hence the combination of the motion imparted to the liquid within the tank by the rotational movement of the rotor and also the added motion provided by the flow of the liquid outwardly from the outlets through the rotor horizontally into the liquid level of the tank afford the requisite flow path of the liquid within the tank. Owing to this advantageous arrangement and construction of the various embodiments of rotor as contemplated by the invention there is no need for a draft tube or a propeller to assist the rotor in the flow of the liquid within the tank. It should thus be apparent that there is provided an extremely efficiently operating aeration plant which also is relatively simple in design and construction and because of the lesser number of components required in relation to other prior art systems is not as susceptible to breakdown and malfunction, nor does it require extensive maintenance and servicing.

While there is shown and described present preferred embodiments of the invention, it is to be distinctly understood that the invention is not limited thereto but may be otherwise variously embodied and practiced within the scope of the following claims. Accordingly,

Claims

What is claimed is:

1. An apparatus for surface aeration and circulation of liquids, comprising a tank for containing a body of liquid to have a liquid level therein, means disposed within said tank for aerating and circulating the liquid contained therein by drawing liquid upwardly from the tank and directing the liquid in an outward path back into the body of liquid in the tank, said aerating and circulating means comprising an aeration rotor positioned within said tank and arranged to be at least partially submerged in the body of liquid therein, said rotor being arranged to rotate about a substantially vertical axis, said rotor comprising a shaft positioned on the vertical axis of said rotor, a first disk-like wall member secured centrally to and extending radially outwardly from said shaft, a second disk-like wall member extending radially outwardly from said shaft and having a centrally arranged opening therein concentrically disposed about the shaft of said rotor, said second disk-like wall member being spaced below said first disk-like wall member, upright partition means secured to and extending between said first and second disk-like wall members and forming a plurality of guide channels defining flow passageways therebetween, the opening in said second disk-like wall member providing a first opening to each of said flow passageways, a second opening located at the opposite end of each of said flow passageways at the outer edges of said disk-like wall members, means for feeding air into each flow passageway substantially at a location where the liquid disposed thereat is moving substantially laterally towards the outer edges of said disk-like wall members, said opening of the rotor being freely accessible to the liquid circulating in said tank.

2. The apparatus as defined in claim 1, wherein the free accessibility of said opening of the rotor is insured through the absence of any draft tube at the region of such opening of said rotor.

3. The apparatus as defined in claim 2, wherein said second disk-like wall member is formed by a surface of revolution about the vertical axis of said rotor whose generatrix forms a continuous curve extending from the periphery of the first opening to the periphery of the second opening, said curve initially converging inwardly towards the axis of the rotor for a minor portion of its length and then diverging outwardly away from the axis of the rotor for a major portion of its length and the outer end of the curve terminating in a substantially horizontal position at the periphery of said second opening and being in close proximity to the level of the liquid in the tank.

4. The apparatus as defined in claim 1, wherein said partition means comprise substantially radially directed blades, said air feeding means comprising air intake duct means extending through the first disk-like wall member and communicating with said guide channels.

5. The apparatus as defined in claim 4, wherein said air intake duct means communicate with the atmosphere.

6. The apparatus as defined in claim 4, wherein said radially directed blades are radially spirally curved, said opening in said second disk-like wall member defining a common inlet opening at the bottom of the rotor for admitting liquid in axial direction, said second opening at the opposite end of each flow passageway defining individual outlet openings at the periphery of the rotor for discharging such liquid.

7. The apparatus as defined in claim 1, wherein said opening of said second disk-like wall member defines a common inlet opening for admitting liquid in axial direction into the rotor, a deflection member disposed at the region of said common inlet opening, said deflection member being positioned to direct air supplied by said air feeding means into said flow passageways defined by said guide channels.

8. The apparatus as defined in claim 1, further including a guide cone having an apex directed upwardly and placed upon the floor of the tank in substantial axial alignment with the rotor, said guide cone being provided with upwardly directed and radially extending guide vanes.

9. The apparatus as defined in claim 8, wherein said guide vanes on said guide cone extend helically upwards about said guide cone.

10. The apparatus as defined in claim 8, wherein the upper ends of said guide vanes are closely spaced below said opening in said second disk-like wall member.

11. The apparatus as defined in claim 1, wherein said air feeding means comprises a tube arranged substantially concentric about said vertical axis of the rotor and in flow communication with said guide channels.

12. The apparatus as defined in claim 1, wherein said air feeding means comprises an air infeed duct provided for each guide channel at said first disk-like wall member and extending through the body thereof.