US3620512A

US3620512A - Aerating apparatus

Info

Publication number: US3620512A
Authority: US
Inventors: Josef Muskat; Dieter Klump; Jurgen Sieckmann
Original assignee: Passavant Werke AG and Co KG
Current assignee: Aqseptence Group GmbH
Priority date: 1969-04-03
Filing date: 1970-03-25
Publication date: 1971-11-16
Anticipated expiration: 1988-11-16
Also published as: CA922310A; AT295424B; AT307335B

Abstract

Aerating apparatus for aerating liquids such as sewage sludges, is improved by providing a rotor which moves in a path on the surface of the liquid and which moves the liquid in a direction at an angle of between 90* and 180* with respect to the path of motion of the frame. Alternatively, a device of this type is improved by providing a rotor which moves in a path on the surface of the liquid the rotor axis of which is inclined at an angle of up to 90* with respect to the horizontal.

Description

United States Patent Josef Muskat:

Dieter Klump;.1urgen Sieckmann. all of Mlchelbach, Germany Mar. 25, 1970 Nov. 16. 1971 Passavant-Werke [72] Inventors [21 App]. No [22] Filed [45] Patented [73] Assignee Hutte. Germany [32] Priority Apr. 3, 1969 [33] Germany [31] P19174620 [54] AERATING APPARATUS 16 Claims, 12 Drawing Figs.

[52] U.S.C1..... 261/92, 261/91.261/120,210/242 [51] lnt.Cl n B0lf7/l0, B01f7/18 [50] Field ofSearch. 261/91,)2.

l References Cited UNITED STATES PATENTS 3,208,734 9/1965 Wood et a1 261/91 3,320,160 5/1967 Welles. Jr. et al... 2611120 3.322.410 5/1967 Ahlenius 261/92 3,462,132 8/1969 Kaelin 261/91 3,548,770 12/1970 Boutros 261/91 3.561.738 2/1971 Galeano 210/242 Primary Examiner-Tim R. Miles Assistant ExaminerSteven H. Markovitz Attorney-Larson. Taylor & Hinds ABSTRACT: Aerating apparatus for aerating liquids such as sewage sludges, is improved by providing a rotor which moves in a path on the surface of the liquid and which moves the liquid in a direction at an angle of between 90 and 180 with respect to the path of motion of the frame. Alternatively. a device of this type is improved by providing a rotor which moves in a path on the surface of the liquid the rotor axis of which is inclined at an angle of up to 90 with respect to the horizontal.

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INV ENTORS MUS KLU JOS EF KAT DIETER MP JURGEN SIECKMANN BY fir; @12 6- ATTOR N EYS INVENTORS JOSEF MUSKAT DIETER KLUMP JURGEN SIECKMANN ATTOR N BY 5 PATENTEUuuv us I97! 3. 620,5 1 2 snmuurs FIG. 8

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INVENTORS JOSEF MUSKAT DIETER KLUMP JURGEN SIECKMANN AERATING APPARATUS BACKGROUND OF THE INVENTION This invention relates to equipment for the surface aeration of liquids particularly in waste water treatment.

Surface aerators are utilized in biological sewage treatment for the introduction of atmospheric oxygen into waste water to increase the biological action of the micro-organisms decomposing the polluted matter. The following two types are commonly used: rotors with horizontal axis and rotors with vertical axis. These differ in operation particularly in view of the horizontal and vertical flow patterns they generate in the water. In smaller tanks, particularly when using rotors with horizontal axis, it is possible to agitate and aerate the entire tank volume if necessary. This, however, is not economical where larger liquid surfaces are concerned. Therefore, a different method has been applied by supporting a rotor or rotors on a traveling carrying structure, for instance a bridge, spanning the tank and to provide this carrying structure with a drive, so it can be moved across the tank and the rotor progressively reaches any area of the tank. This, however, involves expensive piers or pilings to support and drive the carrying structure. Nontraveling rotors, i.e. stationary rotors, in particular, turbines, are commonly supported on pontoons so they maintain the same submergence depth at any liquid level variation.

lt is an object of this invention to provide an apparatus for surface aeration applicable in liquid in any type of basin whether in walled or simply excavated lagoons, natural ponds or lakes, river branches, etc. not requiring any preparatory work in particular any engineering or piling, or the like; a simple design suitable for maintenance-free, continuous operation. An apparatus of the said type is particularly intended to increase the biological self-purification of natural waters receiving a heavy pollution load from domestic or industrial waste water sources and/or to convert existing bodies of water into waste water treatment plants without the requirement of any engineering and constructional work.

BRIEF SUMMARY OF THE INVENTION The foregoing and other objects which will be apparent to those skilled in the art are achieved according to the present invention by providing apparatus for surface aeration of a body of liquid comprising in combination a frame adapted to be floated in the liquid, a bladed aeration rotor rotatably mounted in said frame and having blades at least partially extending into the liquid, means for rotating the rotor, means secured to said frame for guiding liquid moved by said rotor into a horizontal flow, guide means secured to said frame to guide the frame for motion in a predetermined path on the liquid surface, and means secured to said frame for directing at least a portion ofsaid horizontal flow at an angle of between l80 and 90 with respect to the direction of motion of said frame in said predetermined path. In an alternative embodiment, these objects are achieved by providing apparatus for surface aeration of a body of liquid comprising in combination a frame adapted to be floated in a liquid, a bladed aeration rotor rotatably mounted in said frame with its axis of rotation inclined at an angle of up to 90 with respect to the horizontal and having radial blades extending into the liquid, means for rotating the rotor, and guide means secured to said frame to guide the frame for motion in a predetermined path on the liquid surface.

DETAILED DESCRIPTION There follows a detailed description of a preferred embodiment of the invention, together with accompanying drawings. However, it is to be understood that the detailed description and accompanying drawings are provided solely for the purpose of illustrating a preferred embodiment and that the invention is capable of numerous modifications and variations apparent to those skilled in the art without departing from the spirit and scope of the invention.

FIG. 1 is a diagrammatic plan view of a cylindrical tank incorporating an aerating device according to the present invention;

FIG. 2 is a diagrammatic plan view of a rectilinear tank in-- corporating an alternative aerating device;

FIG. 3 is a diagrammatic plan view of an aerating rotor having a horizontal rotor axis;

FIG. 4 is a diagrammatic plan view of an alternative aerating rotor having a horizontal rotor axis;

FIG. 5 is a diagrammatic plan view of the rotor of FIG. 4;

FIG. 6 is a diagrammatic plan view of an aerating rotor having a rotor axis inclined at an angle of 90 with respect to the horizontal;

FIG. 7 is a diagrammatic elevation of an aerating rotor having a rotor axis inclined at an acute angle with respect to the horizontal;

FIG. 8 is a diagrammatic elevation, partly in section of a rotor for nonhorizontal orientation;

FIG. 9 is a diagrammatic top view of the rotor of FIG. 8;

FIG. 10, is a diagrammatic elevation of an alternative rotor for nonhorizontal orientation;

FIG. 11 is a diagrammatic plan view of a rotor-clarifier tank combination according to the invention; and

FIG. 12 is a diagrammatic elevation of the device of FIG. 1 l.

In apparatus according to the invention, the aeration rotor is float mounted in a frame and guided by guiding elements along a predetermined path of travel, and driven by the reaction of the directed current the rotor generates in the water. This type of surface aerator moves as a self-propelled watercraft over the water surface and, except for anchoring of its guide elements, requires no stationary supports, shoreline supports or the like. Thus, biological waste water treatment by forced oxygen transfer is feasible in those cases where conventional-type sewage treatment plants cannot be built for technical or financial reasons.

There are various ways of generating the reaction which causes the thrust. Rotors with horizontal axis have a reaction which is normal to the axis and opposite to the horizontal flow of water generated by the rotor and which can be utilized directly for the thrust. According to the present invention, however, the direction of forward motion of the rotor frame is at an angle of less than l to the direction followed by the horizontal flow generated in order to cut down speed and to have the flow, and thereby the aeration efiect, act upon those surface areas not within immediate reach of the rotor. This can be achieved according to the invention by rotating the horizontal rotor axis in a horizontal plane to form an angle with the direction of travel of the frame or by installation of deflecting plates which are adjusted upstream or downstream of the rotor at an angle to the direction of flow. In both cases the angle is preferably adjustable for velocity control.

Rotors with a vertical axis generate a vertically ascending flow and an overall uniform'radial or tangential flow pattern not resulting in directed reaction of a practical magnitude.- I-Iowever, a reaction causing thrust of good magnitude can be achieved by tilting the rotor axis relative to the vertical, or by installing deflecting plates or shutters upstream or downstream of the rotor which interfere with the rotational symmetry of the-flow pattern. Naturally, these various means can be applied in combination.

It is an advantage if the deflecting or shutter plates are constructed as baffles additionally profiled in vertical section, so the horizontal flow generated by the rotor is deflected downwardly whichprolongs the retention time of the air bubbles introduced into the water and the oxygenation efficiency is increased. It is also advantageous if the baffle plates are spaced at such a distance from the rotor as to extend into the zone where the liquid lifted by the rotor action drops back into the nonnal liquid surface.

Deflecting plates, shutter plates and/or baffles are preferably attached to one or severalof the-pontoons used to float the rotor. Particularly where rotors with vertical axes are concerned, the pontoon can have the shape of a circle concentric with the rotor axis and comprising one or several ports for the passage of a directed horizontal flow causing the reaction.

Connecting means of the rotor frame can consist of rotatable tension or compressionproof ties connected to an anchorage which then is the center of a circle described by the traveling rotor frame. In oblong tanks or lagoons the rotor is preferably guided like a ferry by rectilinear guiding means such as a rope or rail, etc.

A rotor with a horizontal axis can be connected to the anchorage or to a guideway by means of connecting elements, in particular, rods of different lengths connected to the frame at the rotor axis ends and preferably length-adjustable, so the desired angle can be easily set between direction of travel and rotor axis. The direction of rotation of the rotor is preferably reversible, either in order to reverse the direction of travel or, in case of successive runs, to alternate the aeration effect on the areas at both sides of the traveling path. Change of traveling direction can also be achieved by changing the angle of the rotor in its frame or by changing the angle of deflecting plates, or both.

For reversal of the drive, in particular at the reversal points of a straight rotor path, it is preferable to provide switch gear such as limit switches, light barriers, signals to receivers for wireless control, etc. changing the sense of rotation of the rotor, or the angle of the rotor or that of the deflecting plates.

If the rotor in its travel describes a closed circle, it is advantageous to connect and drive the rotor in such a way as to direct thehorizontal flow generated by the rotor towards the center of the path. This way it is possible to also aerate the zone encircled by the traveling rotor. Since the connecting means is thus subjected to only tensile stress, it is possible to use flexible elements, such as ropes, as connecting means. In addition, the danger of the flow damaging the shore or embankment is decreased.

As a further development of the invention, the rotor may be connected to sludge-collecting means intended for the removal of scum or bottom sludge. While in the prior art this type of equipment was also attachedto traveling, propelled supports like bridges, may be secured to the rotor frame according'to the invention and may be driven by the reaction of the rotor. Thus, other complicated attachments and driving gear can be omitted. Such collecting means preferably incorporate deflecting and/or baffle plates.

The application of the aeration equipment according to the invention in any type of liquid body, not especially selected for it. may prove to be somewhat inefficient as it will then depend on the shape of the body of water whether zones can be created where the activated sludge particles can settle out and separate themselves from the water and in particular whether this is possible in the discharge area, so the water drawn off is free from suspended solids. Therefore, a further especially advantageous embodiment of the invention, provides near the rotor path a secondary settling tank supported on pontoons and equipped with efi'luent means for clarified water. The bottom of such secondary settling tank can be shaped like a tub. Between the bottom of the tub and the bottom of the tank or pond, inlet ports for the polluted water to enter should be distributed at least over a portion of the circumference of the secondary tank. Such a settling tank, in other words, comprises a peripheral wall surrounding a calm settling zone into which the water to be purified can enter at the tank bottom at the same rate as the clarified liquid leaves the tank via overflow baffles of the like. The secondary tank is preferably rigidly connected to the rotor and participates in its motion. One configuration also provides for a translation motion of the secondary clarifier, i.e., the latter changes its location, the sludge settling in different spots of the tank or lagoon bottom. Thus, it may be possible to dispense with a bottom-scraping mechanism. In another embodiment of the invention, the preferably cylindrical settling tank and the rotor are rotatably supported on a mooring in the tank center. In this case a bottom scraper blade should preferably be rigidly connected to the tank wall. It is a constructional advantage if the pontoons carrying the settling tank or tanks and the rotors are incorporated in the tank wall, and particularly if they consist of a circular ring about the inside or outside of the wall and have a discharge trough in the upper portion and an overflow baffle for the purified water.

It is an essential feature of efficient biological sewage treatment, i.e. an activated sludge process, that at least a certain percentage of the settled sludge is returned into the purification process where the returned sludge particles under the repeated action of the rotor further stimulate the activity of the micro-organisms and serve as settling nuclei for the new activated sludge flocs. In order to impart this feature to this embodiment of the invention to increase purification efficiency, the device preferably includes at least one flow-deflecting plate in the suction area of the rotor in such a way as to extend the suction effect of the rotor into the sludge-settling zone of the secondary clarifier. Thereby part of the settled sludge gets into the suction reach of the rotor and while being aerated is remixed with the liquid to be purified. The suction effect resulting from installation of the deflecting plate preferably extends adjacent to the bottom scraper blade where considerably large quantities of settled sludge are collected in the settling tank.

With reference to FIG. 1, there is shown an aeration tank or lagoon l at least approximating round shape. Two

horizontal aeration rotors

2,2 supported on the ends of their axes on a

frame comprising pontoons

3,3 are operating in this tank. Each rotor has a

drive motor

4,4. Connecting elements 5 in the form of rods or ropes connect the rotors to a stationary mooring 6 in the tank center, so that the rotors describe a circular path around the anchoring point. The left aeration rotor 2 in FIG. 1 has connecting elements 5 of unequal length and thereby is so adjusted that the angle formed by its axis and the radial connection line between its axis center and anchoring 6 is less than Aeration rotor 12 is driven in such a way that it generates a horizontal flow indicated by arrows directed generally towards the tank center, the horizontal flow resulting in a reaction of the rotor in the opposite direction. Due to the angular orientation of the rotor, the reaction is not exactly radial but has a tangential component, therefore the rotor frame is driven by the reaction in a circular path on the surface of the liquid about the anchoring point 6 following the sense of rotation indicated by arrow A. The right aeration rotor 2 in the drawing has its rotor axis normal to the radial connection line between axis center and mooring point 6. This rotor is driven in such a way that the horizontal flow generated by it is directed towards the outside, i.e. towards the tank wall. Within the horizontal flow zone a deflecting plate 7 is attached by means of connecting elements 8, for instance rods, and acts like a rudder deflecting tangentially at least part of the flow. The resulting reaction bearing upon the deflecting plate 7 and thereby on rotor 2' propels rotor 2 as indicated by arrow B in a circle about mooring point 6. Conventional gear (not shown) may be utilized to change the setting angle of the rotor axis of rotor 2 or the angle of the deflecting. plate 7 respectively. 1

It will be understood that the horizontal flow direction of both rotors is not an angle of 180 with respect to the path of motion of the rotor, but is at an angle of between 180 and 90 with respect thereto. Accordingly, the aerated zone extends to areas of the body of liquid remote from the rotor travel path. It is preferred that the angle is between about and l65 to provide a substantial amount of motive reaction and to provide aeration at areas well away from the path of motion of the device.

In the longitudinal, rectangular aeration tank 9 illustrated by FIG. 2, the aeration rotor 10 has a horizontal axis supported on a frame including pontoons l1 and can be reciprocated along a straight guide element 12 such as a tightrope. The rotor axis is parallel to the guide element 12, so the horizontal flow generated by the rotor driven by motor 13 is directed normally with respect to the direction of motion of the rotor. Downstream of the rotor, however, deflecting plates 14 are arranged directing part of the flow in longitudinal direction, so the reaction generated drives the rotor along guide element in the direction of arrow C. Limit switches 15 at the ends of the traveling range cooperate with suitable switch elements at the rotor to effect reversal of the traveling direction either by changing the angular position of the deflecting plates 7.

FIG. 3 shows design details of the guide elements of an aeration rotor similar to rotor 2 in FIG. 1. A rotary flange or hub 16 disposed at the mooring point is connected by means of length-adjustable rods 17 to the pontoons 18 supporting the ends of the rotor axis. Screws serve to fix the length of the rods 17 and thereby the angle of the rotor. The pontoons 18 are shaped favorably for the circular movement of the rotor.

The rotor shown in FIGS. 4 and 5 is connected to the hub 19 of the anchoring member 20 by guide elements 21 of equal length, so the rotor axis is normal to the radius. A baffle plate 22 installed downstream the rotor deflects the horizontal flow generated by the rotor towards the bottom and thereby serves to increase the retention time of the air bubbles introduced into the water. The baffle plate 22 seen from above is asymmetrically attached to the rotor, so it deflects the flow in the direction of arrow D and thereby generates the reaction in the direction of rotor motion. In addition, a bottom scraper blade 23 is connected to baffle 22 by means of rods 24. The scraper blade is also driven by the rotor reaction and urges the sludge accumulated on the basin bottom 25 into a sludge trough 26. Column 20 extends from the basin bottom above liquid level 27 and supports hub 19 for the rotor.

The rotor 28 shown in FIG. 6 has a vertical axis and is sup ported by a frame comprising carrying rods 29 and a pontoon 30. The rotor moves as indicated by arrow E sucking in a vertically ascending flow and generating a horizontal flow directed through the gap of a polygonal ring pontoon 30 in the direction of arrow F. The rotor is supported by rods 31 on the hub 32 of anchoring point 33 and is driven by the resulting reaction in a circular motion following the direction indicated by arrow G.

FIG. 7 shows a rotor 34 also having an axis of rotation inclined to the horizontal driven by motor 35. The rotational axis of the rotor is tilted at a certain angle to the vertical, thus creating a component of motion on the surface of the liquid. In this case the float 36 can be a closed ring. In the illustrated configuration, the inner walls of the float are additionally sloped in such a way as to form baffles 37 which downwardly deflect the horizontal flow generated. The rotor is connected to an anchor point by suitable connecting members 38.

Another possibility of creating a feed component with a rotor having a vertical axis is shown in FIGS. 8-10. The rotor 39 with vertical axis as illustrated in FIG. 8 (section) and FIG. 9 (top view) has one half of its circular influent cross section blinded by plate 40. Thus the rotor sucks in the liquid only in one half (left half in the drawings) of its influent cross section and is subject to a resultant unidirectional thrust. The rotor shown in FIG. 10 has one half of its effluent cross section blinded by plate 41 thus the water sucked in over the entire influent area is thrown out only to the left and the thrust on the rotor is directed to the right.

In the embodiment illustrated by FIGS. 11 and 12, the rotor 42 is attached by means of

arms

51,52 to an open cylinder 43 which is supported on a circular pontoon 46. In the center of the cylinder there is a stationary column 47 with a pivot hearing mounted to it. Cylinder 43 is attached to this bearing by means of guy ropes. Rotor 42 is slanted to the tangent of cylinder 27, thus the midvertical on its axis does not run through the turning center 47 of the assembly. On rotation of the rotor in the direction of arrow H, the resulting feed component towards the circumference makes the aeration rotor and cylinder revolve about the turning center 47 in the direction ofarrow I.

The cylinder 43 extends almost to the tank bottom 44 and surrounds a calm secondary sedimentation zone 45 where the sludge flocs settle out. The top of the circular pontoon 46 carries an overflow weir 48 through which clarified water leaves the tank. This water is conducted to the corotational center column 47 and from there via a dip pipe connected with a seal to the shore. At the same rate as clear water is leaving the tank, unsedimented water enters through the ring slot between the lower part of the cylinder 43 and the tank bottom 44.

The sense of rotation of the aeration rotor is such that the downstream flow generated by it is outwardly directed, whereas a suction zone is created on the inside. By a suitable deflecting plate 49 the suction zone 50 is downwardly extended into an area where the ring slot is located between the lower part of the cylinder 43 and the tank bottom 44 so that at this point settled sludge is sucked in through the ring slot. Then the aeration rotor 42 thoroughly mixes the sludges with the water to be treated. A bottom scraper blade is provided with its outer end is attached to the cylinder 43 and with its inner end is rotatably supported on center column 47. Driven by the reaction drive of the rotor 42 the blade revolves together with the rotor and the cylinder and urges the settled sludge at the tank bottom towards the outside. The blade is arranged so as to immediately precede the zone of an aeration rotor 42, so the suction zone 50 of the rotor 42 is bound to draw in a certain quantity of sludge accumulated by the rotor.

In order to create a weight balance for the rotor 42 located at one side of the cylinder 27, additional pontoons may be provided, for

instance arms

51, 52 can be constructed as pon' toons. Of course, weight balance can also be achieved by installing a second rotor symmetrically with the rotor 2 on the other side of the cylinder 27.

What is claimed is:

1. Apparatus for surface aeration of a body of liquid comprising in combination:

a frame adapted to be floated in the liquid;

a bladed aeration rotor rotatably mounted in said frame and having blades at least partially extending into the liquid; means for rotating the rotor;

means secured to said frame for guiding liquid moved by said rotor into a horizontal flow;

guide means secured to said frame to guide the frame for motion in a predetermined path on the liquid surface; and means secured to said frame for directing at least a major pOl'tlOl'LOf said horizontal flow at an angle in a horizontal plane of more than and less than with respect to the direction of motion of said frame in said predetermined path.

2. Apparatus according to claim 1 wherein the axis of rotation of said rotor is horizontal.

3. Apparatus according to claim 2 wherein the horizontal axis of said rotor is at an angle of between 90 and 180 with respect to the direction of motion of said frame in said predetermined path.

4. Apparatus according to claim 2 including baffle means secured to said frame extending into the liquid and positioned to deflect liquid motivated by said rotor.

5. Apparatus according to claim 1 wherein the axis of said rotor is inclined at an angle of up to 90 with respect to the horizontal.

6. Apparatus according to claim 5 wherein said directing means comprise baffle means interfering with the rotational symmetry of the flow cross section of said rotor.

7. Apparatus according to claim 1 including second baffle means to direct said horizontal flow downwardly.

8. Apparatus according to claim 1 including a circular pontoon supporting said rotor within the periphery of the pontoon, said pontoon including at least one opening for a horizontal flow of said fluid.

9. Apparatus according to claim 1 wherein said predetermined path is helical.

10. Apparatus according to claim 1 including a secondary clarifier tank defined by a vertical peripheral wall in the liquid and being open at the bottom, said predetermined path being located outside of said wall.

11. Apparatus according to claim 10 wherein said rotor is secured to said wall and wherein said tank is secured for rotation with said rotor about a stationary support.

12. Apparatus according to claim 11 wherein said tank is cylindrical said support being located centrally of said tank,

said tank including means to convey sludge outwardly from said support toward said rotor.

13. Apparatus for surface aeration of a body of liquid comprising in combination:

a frame adapted to be floated in a liquid;

a bladed aeration rotor rotatably mounted in said frame with its axis of rotation inclined at an angle of substantially less than 90 with respect to the horizontal and having radial blades extending into the liquid;

means for rotating the rotor; and

guide means secured to said frame to guide the frame for motion in a predetermined path on the liquid surface.

14. Apparatus according to claim 13 including means secured to said frame for guiding liquid moved by said rotor into a horizontal flow.

15. Apparatus according to claim 14 including means secured to said frame to direct at least a portion of said horizontal flow at an angle of between and with respect to the direction of motion of said frame along said predetermined path.

16. Apparatus for surface aeration of a body of liquid comprising in combination:

a frame adapted to be floated in a liquid;

a bladed aeration rotor rotatably mounted in said frame with its axis of rotation inclined at an angle of up to 90 with respect to the horizontal and having radial blades extending into the liquid;

means for rotating the rotor;

guide means secured to said frame to guide the frame for motion in a predetermined path on the liquid surface; and means secured to said frame to direct at least a major portion of said horizontal flow at an angle in a horizontal plane of more than 90 and less than 180 with respect to the direction of motion of said frame along said predetermined path.

Claims

2. Apparatus according to claim 1 wherein the axis of rotation of said rotor is horizontal.
3. Apparatus according to claim 2 wherein the horizontal axis of said rotor is at an angle of between 90* and 180* with respect to the direction of motion of said frame in said predetermined path.
4. Apparatus according to claim 2 including baffle means secured to said frame extending into the liquid and positioned to deflect liquid motivated by said rotor.
5. Apparatus according to claim 1 wherein the axis of said rotor is inclined at an angle of up to 90* with respect to the horizontal.
6. Apparatus according to claim 5 wherein said directing means comprise baffle means interfering with the rotational symmetry of the flow cross section of said rotor.
7. Apparatus according to claim 1 including second baffle means to direct said horizontal flow downwardly.
8. Apparatus according to claim 1 including a circular pontoon supporting said rotor within the periphery of the pontoon, said pontoon including at least one opening for a horizontal flow of said fluid.
9. Apparatus according to claim 1 wherein said predetermined path is helical.
10. Apparatus according to claim 1 including a secondary clarifier tank defined by a vertical peripheral wall in the liquid and being open at the bottom, said predetermined path being located outside of said wall.
11. Apparatus according to claim 10 wherein said rotor is secured to said wall and wherein said tank is secured for rotation with said rotor about a stationary support.
12. Apparatus according to claim 11 wherein said tank is cylindrical said support being located centrally of said tank, said tank including means to convey sludge outwardly from said support toward said rotor.
13. Apparatus for surface aeration of a body of liquid comprising in combination: a frame adapted to be floated in a liquid; a bladed aeration rotor rotatably mounted in said frame with its axis of rotation inclined at an angle of substantially less than 90* with respect to the horizontal and having radial blades extending into the liquid; means for rotating the rotor; and guide means secured to said frame to guide the frame for motion in a predetermined path on the liquid surface.
14. Apparatus according to claim 13 including means secured to said frame for guiding liquid moved by said rotor into a horizontal flow.
15. Apparatus according to claim 14 including means secured to said frame to direct at least a portion of said horizontal flow at an angle of between 90* and 180* with respect to the direction of motion of said frame along said predetermined path.
16. Apparatus for surface aeration of a body of liquid comprising in combination: a frame adapted to be floated in a liquid; a bladed aeration rotor rotatably mounted in said frame with its axis oF rotation inclined at an angle of up to 90* with respect to the horizontal and having radial blades extending into the liquid; means for rotating the rotor; guide means secured to said frame to guide the frame for motion in a predetermined path on the liquid surface; and means secured to said frame to direct at least a major portion of said horizontal flow at an angle in a horizontal plane of more than 90* and less than 180* with respect to the direction of motion of said frame along said predetermined path.