CA1148673A - Ring channel aeration apparatus and method - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

In a ring channel aeration system,circulation is provided by one or more hydraulic jumps while the major portion of the energy consumed in aeration is allocated to the release of oxidative process gas through horizontally non-propulsive bubble release means having an oxygen transfer efficiency of at least about 6. The hydraulic jump(s) may be powered by discharge of gas (e.g. the same gas used for aeration) through gas discharge means, in which case the system of gas discharge means and bubble release means may have an overall oxygen transfer efficiency of at least about 6. The invention has advantages of flexibility and resultant energy savings as compared to single device circulation/aeration systems, in that excessive energy need not be consumed in aeration to obtain the requisite circu-lation and vice versa.

Description

RING CHANNEL AERATION APPAR~TUS AND METIIOD

BACKGROUND OF THE IN~ENTION
The present invention relates to ring-channel aeration systems and in particular to ring channel aeration systems having separate means for applying mixing energy and aeration gas to waste water.
One widely known form of ring channel aeration system, known as the "oxidation ditch", is used to perform an extended aeration process and is generally a long narrow continuous typically oval or circular channel containing an aerating device. Oxidation ditches with brush- and paddle-wheel type aerators have enjoyed considerable commercial use both in Europe and the United States.
Design specifications for oxidation ditches with capacities in the range of O.lO to 2.0 million gallons per day have been published by the U. S. Environmental Protection Agency. Such ditches are regarded as providing stable pro-cessing with proper sludge management, production of high quality effluent and predictable process behavior. Among the disadvantages of oxidation ditches which have been dis-cussed in the literature are icing of aerator supports, the need for a crane to remove equipment for major maintenance, frequency of maintenance on drive units, the requirements for good operator skills and routine monitoring, the possible need for provision for nitrification oxygen and p~ control, ., and th~ applicability of only one type of aeration device.
However, oxidation ditches have long been known in which circulation and aeration have been provided by means which bubble air into the waste water in the ditch rrom a source beneath the water surface. For example, see U. S.
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~B~7~3 , Patents 1,6~3,273, 3,336,016, 3,485,750 and 3,88~,812.
U. S. Patents 3,~95,712 and 3,947,358 disclose oxidation ditches having both stationa-ry and moveable aeration means positioned beneath the surface of the waste water, the moveable aeration means serving to keep at least a portion of the contents of the ditch in motion. The latter patent teaches that it is unfavorable to provide an oxidation ditch with circulation means comprising transverse partitions having through-flow openings, in that such partitions considerably reduce the through-flow cross-section of the ditch and represent throttle zones, which have rendered known installations unsuitable ~or the treatment of large quantities of sewage.
In contrast with the foregoing it has been suggested in U. S. Patent 3,846,292 to provide an oxidation ditch whose liquid flow path is free fron obstructions to flow other than are unavoidably presented by certain ejectors submerged in the water, and to e~ploy said ejectors as the sole means ~or aeration and movement of the liquid. Such installations are said to be particularly efficient in terms of reduced horsepower requirements. However, it has been suggested in the literature that ejectors have a poorer oxygen transfer efficiency than other known diffusers, such as for example ceramic dome fine bubble diffusers.
Questions as to the oxygen transfer efficiency and operating costs of existing oxidation ditch systems, as well as continuously rising costs for energy, have created a need for further improvements which offer higher efficiency. The present invention lS directed to this need.

' ~B673 SU~ARY OF THE INVENTION

The ~oregoing object may be attained by providing a ring channel aerator with hydraulic jump means located in said channel. The hydraulic jump means extends between inner and outer wall means defining the channel and is oriented generally transversely of the flow path along which the waste-water circulates in the channel. ~he jump means is adapted to induce an upward and forward rolling motion in the waste water as it passes through and out of the jump. Only a minor portion of the length o~ the flow path, measured along the centerline o~ the channel, is occupied by the jump means. Along the remainder o~ the flow path is positioned horizontally non-propulsive bubble release means having an oxygen transfer efficiency of at least about 6 for bubbling oxidative process gas into the waste water.
The above apparatus is useful in a variety o~ ;
processes, including an energy-saving method which is also considered to be part of the present invention. In this flexible and economic technique, a particularly advantageous balance is maintained between the energy consumed in circu-lation and the total energy used in circulation and aeration.
According to-the method of the invention, horizontal circula-tion is induced by imparting energy to the waste water within a minor portion o~ the length o~ a horizontal circulation path in a ring-channel aerator. Along the remainder o~
said path, oxidatLve process gas is bubbled into the waste water through horizontally non-propulsive bubble release means having an oxygen transfer efficiency of at l~ast about six. In this method the circulation rate praf~ably is at least about 1 foot per second averaged over the trans-verse cross-section of the channel. Circulation is induced by causing upward and ~orward rolling motion of the waste water as it passes through and exits at least one propulsion zone or zones, such as for instance the hydraulic ~ump means mentioned above~ The propulsion zone or zones are located in and extend transversel~ of the horizontal flow path, around which the waste-water circulates in the channel, but said propulsion zone or zones occupy only a minor portion of the length of said flow path, measured along the centerline of the channel. A ratio in the range of about 0.01 to about 0.35, more pre~erably about 0.02 to about 0.25 and most preferably about 0.03 to about 0.2 is maintained between ; the horsepower consumed in inducing said circulation and the total of said horsepower plus the adiabatic horsepower consumed in non-propulsive bubbling of process gas into the waste-water. When the energy used to induce circulation is transmitted to the waste-water by discharge of gas into the t ' propulsion zone(s), this energy is also e~pressed in adiabatic horsepower for purposes of the above ratio.
In the accompanying drawings, referred to below, and in the following description of preferred embodiments may be found illustrations of how the foregoing apparatus and method may be embodied and used.

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L~ 7 3 sRIEF DESCRIPTION OF ~HE DRAWINGS
Figure 1 ls a plan view of a ring channel aerator according to the invention with parts broken out and omitted, Figure 2 is a sectional view taken along section line

2-2 of Figure 1, Figure 3 is a sectional view taken along section line

3-3 of Figure ~, Figure 4 is a sectional view taken along section line

4-4 of Figure 3, Figure 5 is a sectional view taken along section line

5-5 of Figure ~, Figure 6 is a plan view, similar to Figura 1, of an alternate form of ring channel aerator according to the invention, having different bubble release means, Figure 7 is a schematic diagram of a pair of co-located ring channel aerators according to the invention, showing motors, compressors, and their connections to hydraulic jumps and horizon-tally non propulsive bubble release means in the respective aerators.
Figure ~ is a schematic diagram showing three co-located ring channel aerators according to the invention along with their common sludge and effluent handling facilities, Figure 9 is a plan view, in part similar to Figure 6, of sti~l another alternate form of ring channel aerator having the bubble release means positioned at spaced intervals along the flow path.
Figure 10 is a partial sectional view taken along section line 10-10 of Figure 9, :
Figure 11 is a partial sectional view taken along sec-tion line 11-11 of Figure 10, with portions foreshortened, and Figure 12 is a sectional view taken along section line 12-12 of Figure 11 including a full view of subject matter ore-shortened in Figure 11.

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f DESCRIPTION OF T~IE PREFERRED EMBODIMENTS

Figures 1 and 2 disclose a pre~erred ~or~ of ring channel aerator lO which may if desired be combined for pur~
poses of convenience with an optional clarifier to be described - 5 in greater detail below. The ring channel aerator comprisesinner and outer walls which may be o~ any appropriate shape so as to define a liquid circulation circuit o~ circular, oval (racetrack), elliptical, serpentine or other shape as viewed in plan view. Said walls may also be of vertical, sloping, curved or other suitable configuration as viewed in ~ransverse cross-section. ~owever, in the presen-t embodiment the inner and outer walls 11 and 12 are circular as viewed in plan view (Figure 1) and vertical in transverse cross-section (~igure 2). A bottom wall is optional, such as for instance if the inner and outer walls slope to an intersection with one another, but the channel is preferably ~`
provided with a bottom wall 13, connected to inner and outer walls 11 and 12. The bottom wall is substantially horizontal for convenient mounting of diffusers, to be described in greater detail below.
Walls 11, 12 and 13 define an elongated flow path which may in general have any appropriate width, length to width ratio, depth and internal configuration useful for ring channel aerators. While the width of the channel may vary around the circuit, the inner and outer walls in this embodiment are equidistant throughout the circuit or channel which they define. According to the presently pre~erred mode of practicing the invention, the ratio o~ the flow path length measured along the center line cf the channel, relative to the average width of the channel measured throughout the height of its transverse cross section at and below the normal operating water level, is at least about 5.
For e~ample, the ratio of flo~ path length to channel width, measured as indicated above, may be in the range o~
about 5 to about l~ and more pre~erably about 8 to about lO.
The depth of the channel may be varied at dif~erent locations around the flow path, but the channel is most conveniently arranged to have a uniform depth throughout.
Ring channel aerators are known which have channel depths as shallow as 3 feet and it will be possible to practice the invention in these shallow channels. But ~or the most part the invention will be employed in channels whose a~erage depth, measured from the bottom of the channel to its normal operating water line, is at least about 5 feet. ~or example, depths of about 5 to about 20 feet may be employed. The invention can be operated with particular advantage in channels having a depth of about 10 to about 20 feet, with about 12 to about 15 feet in depth being considered optimum.
In general it will be seen that the walls ll~ 12 and 13 define a continuous substantially closed course for liquid circulation such as is common to the extended aeration activated sludge type of oxidation ditch. Although not essen-tial, it is preferable that the ring channel be substantially free of obstructions to flow other than the hydraulic jump means to be discussed below.
The aerator may have one or more inlets and outlets of any appropriate configuration and location. In the present embodiment, the aerator is provided with waste-water inlet 16 which may be connected to a source of waste-water (not shown) which ma~ for instance include a bar screen or comminutor ~olloweù by an aerated grit chamber with clarl~ier -; - 8 -..

to dewater the grit. In this particular pre~erred embodi-ment sewage inlet 16 is closelY adjacent and upstream o~
hydraulic jump means to be described hereinafter. A re~urn sludge inlet, e.g. measuring weir 18, is closely adjacent to and upstream of said jump means and delivers sludge to the channel. This inlet is also preferably located ~ust upstream of the a~orementioned hydraulic jump. In this embodiment the effluent outlet is a trans~er pipe 17, located more nearly u~stream than downstream o~ waste-water inlet 16. Pipe 17 is pre~erably located a short distance upstream of the inlet and weir, and provided to withdraw mixed liquor ~rom the channel.
The optional clari~ier may be of any conventional type,~but certain economies can be attained i~ the wall o~
clarifier tank 22 is de~ined by the aerator inner wall 11.
Tn this embodiment, the clarifier has the usual stilling v well 23, scum trough 24, scum ba~ M e 25, sur~ace skimmer 26, e~luent launder 27, and sludge collector drive 28~ The clari-fier includes a suitable sludge air li~t and sludge divider (not shown) for sending recovered sludge back to the aerator lO via weir 18, and/or to appropriate sludge holding or disposal facilities via waste sludge line 29. Clari~ied water ; from the clarifier may be carried by a conduit (not shown) to a receiving body of water or to suitable post treatment ~acilities.
bridge 30 (portions removed in Figure 1), equipped with handrail 31 (Figure 2), extends along a dia-meter line of the apparatus ~rom one side of outer wall 12 to the other, 3nd in so doing bridges across the aerating channel lO and the clari~ier tank 22. This bridge provides _ g --~8~3 support for the sludge collector drive 28 and a means of access by which an operator may supervise the operation of the unit The apparatus of the invention includes a hydraulic jump means. In general the hydraulic jump means is located in the channel 10, extending between inner and outer wall means 11 and 12,generally traversely of the flow path~ and may be any device which is capable of inducing upward and forward rolling motion in the wastewater as it passes -through and out of the jump. Such device should occupy only a minor portion (e.g. less than half) of the length of the circulation flow path measured along the centerline of the channel, and preferably occupies about20~ (or 10~) or Iess of said length thus the jump means should be capable of inducing the requi-site motion within the indicated portion of the flow path length.
In general, the preferr~d mode of operation for the jump means is to establish upward flow in the jump while positively urging said flow in a forward (i.e. downstream) direction as the flow departs the jump. The forward flow-` ing waste water is discharged from the jump as a stream. It is preferred but not essential that this stream include ; the upper surface of the waste water downstream of the jump. Again, although not absolutely essential, it is definitely pre-ferred that the jump means direct the out-- going stream in-to a zone of abruptly increased cross-section - immediately downstream of said jump. Such abrupt increase is of assistance in inducing a forward roll in the waste-water.

When sufficient ene~gy is imparted -to the waste water in the jllmp, it can ~orm a wave in the waste-water as it exits the jump, and may even form a continuation of the rolling motion well downstream o~ the zone. With proper design of channel and jump geometry one may create forward-rolling eddy currents that roll forward, downward, rearward and upward, downstreamof the jump, thereby extend-ing retention of bubbles of oxidative process gas. In certain situations the rolling motion-generated by the lC jump may also assist in flocculation of suspended solids in the waste-water.
The structure of a particularly preferred form of hydraulic jump means may be described as a substantially upright chimney member extendi~ng for substantially the entire ; 15 depth of the channel betwee~ its bottom and t~e normal operàting water line of the channel~ This chimney has an upstream inlet in , the lower half of the channel depth and a downstream outlet in the upper half of the channel depth. The d~wnstream end of the chimney may be connected to, or at least partly defined by, a member defin-ing the abrupt change in cross-section referred to above. Said, member preferably defines a sufficiently abrupt change i~ cross-section from the chimney outlet to the full cross section of the channel downstream thereof for causing water which exits the chimney outlet to whirl or roll about a generally horizontal axis transverse to the flow path.
A structure of the above type which is particularly preferred is disclosed in Figures 1 through 5. In the first two of these figures the hydraulic jumps 36 (of which there are two in this embodiment) are shown along with the rest of the components of the ring channel aerator,, being shown from overhead in Figure 1 and from upstream on the left side of Figure 2. The jump alone is shown in enlarged sections in the next three figures, being shown in longitudinal cross-section in Figure 3~ transverse cross-section in Figure 4 and horizontal cross-section in Figure 5.
In the embodiment of Figures 1-5 -the substantially upright chimne~ member 37 extends through the entire depth of the channel between bottom wall 13 and the normal operating water line 38 of the channel 10. The chimney is defined in part by an upstream upper water baffle 39 and a downstream lower water ba~le 4O and by portions o~ inner and outer channel walls 11 and 12, as well as by channel bottom wall 13.
As will be recognized by persons skilled in the art, the upstream water baffle 39 may have a variety of shapes, sizes and positions. ~owever, in the present embodiment this baffle is combined with or part of a "Y" wall 41 which, as viewed in the longitudinal cross-section of Figure 3, includes a first limb 42 inclined rearwardly and upwardly, thus providing a transition surface for smoothly directing surface water downwardly along the upstream face of upstream water baffle 39 towards upstream inlet 43 whose upper portion is defined by a lower edge 44 of baffle 39. Although it is particularly convenient for -the upstream baffle to be combined with or part of a "Y" wall as sho~m and to extend well above the water line, one may actually employ any desired form of upstream water baffle that projects downward from an 2S elevation at or above the water line par~way to the bottom of ; the channel, ancl that is associated with an upstream inlet lying generally beneath, below or generally at the foot of said baffle. The elevation of the top and bottom of inlet 43 may be varied but it is believed that the optimum placement for the bottom of the inlet is at substantially the same ele-vation as the bottom of the channel.

"Y" wall L~l of this embodiment also includes a second limb 47 inclined forwardl~ and in the downstream direction from the downstream face of water baffle 39.
Although not essen-tial, the inclined surface provided by limb 47 is of assistance in positively urging the flow of water rising in the chimney 37 in a forward direction.
Generally upright extensions 48 and ~9 on "~" wall limbs 42 and 47 respectively may support a grating (not shown) providing a continuation of bridge 3O by means of which an operator may walk across the jump. Beneath such grating and in the space between limbs 42 and 47 and extensions 48, 49 may be mounted sup~ply pipes 50 and 51 for feeding gas to a gas discharge means (when such is provided to power the hydraulic jump) and to horizontally non-propulsive gas release means (to be discussed in greater detail below).
Downstream lower water baffle 40 may be embodied in a wide variety of shapes, sizes and positions as will be recognized by those skilled in the art. In -the present embodiment the downstream lower water baffle projects upward partway to the surface from an elevation at (including near) the bottom of the channel.
As shown in this embodiment, baffle 4O includes an upwardly and downstream-directed inclined surface 55 which is of assistance in smoothly directing water received through inlet 43 in an upward direction into the chimney space between baffles 39 and 40. Baffle 4O has an upper -~ edge 56 which defines the bottom of a downstream outlet 57.
The bottom of this outlet and its top (if it has one) ma~
be varied in shape and position; however it is preferred that the top of the outlet, 1I such is provided, should be at ..

or above the water line so that the forward ~lowing stream of waste-water discharged from the jump may include the upper surface of the waste water which flows in the downstream direction as it departs the jump. Thus, outlet 57 should e~tend from beneath the water to an elevation at or above the normal operating water-line of the channel.
The wide divergance of the downstream face of baffle 40 from the direction of flow through outlet 57 ~e.g. by an angle of about 45 or more) provides the abrupt change in cross-section referred to above. As explained above, if the water is caused to depart outlet 57 with sufficient energy there can be a whirling or rolling of the water about a gen-erally horizontal axis downstream of baffle 40. A ~orwardly and downstream-inclined surface 58 on baffle 40 is of assistance in smoothly directing the lower portion of any such whirling or rolling currents upwardly along the downstream face of baffle 40, wherein such currents may join with additional waste-water departing outlet 57 for entrain-ing bubbles and flocculating suspended solids as indicated above.
` 20 Although the chimney as shown is defined by sub-stantially vertical wall means it will be apparent that the chimney may be tilted forwardly or rearwardly so long as it is substantially upright.
Depending on the length of the flow path, one may provide one or any number of jumps at spaced locations aIong such path. In general, it is desireable that the jumps be equally spaced along the path, but this is not essential.
Because of its configuration, the hydraulic jump accelerates the flow of` water which passes through it.

- - , ~8~'73 This is accomplished in part by propulsion means (to be clescribed in greater detail below) and in part by a reduction of the cross-section of the chimney as compared to the portions o~ the channel which are upstream and downstream of the jump.
In general, the inlet, chimney, and outlet respectively have cross-sections, measured normal to the direction o~ flow, in the range of about 0.2 to about 0.5 of the transverse cross-sectional area of the channel at and below its normal operating water line, averaged along the entire length of said flow ln path. Preferred and particularly preferred ranges for the foregoing ratio of cross-sections are about 0.25 to about 0.~ and about 0.3 to about 0.37, with a ratio of about 1/3 being considered optimum. It is also considered beneficial that the inlet chimney and outlet all have similar cross sections measured normal to the direction of flow, and tha~t the chimney have substantially the same cross-section throughout. ~`
It is also beneficial if the inlet, the interior of the chimney and the outlet are all of substantially the same width as those portions of the channel which are closely adjacent to and both upstream and downstream of the chimney.
In accordance with the invention the hydraulic jump means is provided with an upward propulsion means which ` may be in a wide variety of types, shapes and sizes and ; positions~ Preferably the upward propulsion means is positionedfor distributing energy into the waste-water across substan-tially the entire width of the chimney. Such energy is utilized for causing the upward and forward rolling action to occur. With sufficient uniformity of distribution, the upward and forward rolling motion of the water may occur across su~stantially the entire width of the chimney, 86~3 but it shoulcl be noted that perfect uniformity is not necessarily essential or desireable. For example, in a ring channel aerator in which the waste-water following the outer wall must traverse a greater distance per circuit that~ the water which follows the inner wall, it can be beneficial to cause a relatively higher flow rate in the waste-water adjacent the outer wall as compared to that adjacent the inner wall. This may for instance be accomplished by providing the upward propulsion means with means for imparting energy to the waste-water at a higher rate adjacent the outer wall than adjacent to the inner T.~all .
In general, it is considered that the upward pro-pulsion means will be most effective for causing the desired upward and forward rolling motion if sùch means is positioned for imparting the major portion of the energy to that half of the water in the chimney which flows nearest the upstream water baffle 39. ~lore preferably, the major portion of the energy is imparted to that third of the water which flows nearest baffle 39.
While the upward propulsion means may accomplish the foregoing when positioned within the chimney 37 and/or in one or more locations outside the chimney or in the chimney walls (from which locations thepropulsion means may direct energy into the chimney), the preferred location for the upward propulsion means is within the longitudinal space between the upstream and downstream water baffles.
A variety of devices may be provided by persons skilled in the art which are useable as upward propulsion means, including mechanical impellers and the like. But a considerable advantage in convenience and/or efficiency may : . - , ~ .
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'73 be attained by employing a gas discharge means positioned in the chimney Eor inducing the motion described, the gas discharge means being preferably positioned for distributing bubbIes across the width of the chimney for causing said upward and forward rolling motion. A suitable example of such gas discharge means is shown in Figures 1-5. It should be understood however that a wide variety of gas discharge means may be employed including, without limitation, the horizontally non-propulsive bubble release means descrlbed hereinafter, lG whether of the fine bubble type or not.
The gas discharge means disclosed in Figures 1-5 is mounted in such manner that the major portion of the gas dis-charged thereby is introduced to that half or preferably that third of the water in the chimney which flows nearest the lS upstream upper water baffle. The gas discharge means may be of any configuration and may be mounted in any suitable loca tion to accomplish the foregoing; however as shown in Figures 3-5 there are advantages of convenience and conservation of materials involved in positioning the gàs discharge means on the upper water baffle.
Referring now to Figures 3-5, the gas aischarge means includes a conduit arrangement having a horizontal leg 64 connected to supply pipe 50 and extending through control valve 65 and "Y" wall extension 49 to a single vertical downcomer pipe 66 feeding into the center of a horizontal manifold pipe 67 extending transversely of the water flow path in chimney 37, generally parallel to the downstream face of baffle 39. A plurality o~ diffusers 68 of the general type disclosed in U. ';. Patent 3,424,443 to Paul M. Thayer are dis-tributed at spacea intervals across the manifold and chimney~

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In order to maintain manifold 67 in a fixed posit-tion against the force of the waste-water flowing up the chimney 37, it may be necessary to provide suitable struc-tural supports (not shown) which will be readily designed fabricated and installed by persons skilled in the art. But it may in certain circumstances be more desireable from the standpoint of reduced construction cost (for structural supports) and convenience (by providing the flexibility of being able to temporarily remove some but not all of the diffusers), if each pair of diffusers is provided wlth its own downcomer. Thus, such arrangement could be preferred over that shown in the drawings in certain circumstances.
The diffusers are arranged in this embodiment so that they cover not more than about 25~ of the lineal dis-tance from one side of the interior of the chimney to theother side thereof. This tends to minimize the amount of interference that will occur between diffuser structure and the flow of water up the chimney. In this connection the use of concentrated bubble diffusers is particularly advan-tageous.
Commercially available forms of diffusers shown inthe above mentioned Thayer patent have an oxidative gas dis-charge rate in the range of about 0.05 to about 0.5 SCFM per square inch and more preferably about 0.1 to about 0.3 SCFM
per square inch.
In general, the gas discharge means is advantageously positioned with its gas discharge outlets at a level of sub-mergance equal to at least half the depth of the upstream upper water baffle 39, measured downward from the normal operating water line of the channel. It is presently considered that the optimum elevation for the gas discharge outlets is at about the same elevation as the lower edge 44 of the chimney upstream inlet 43.

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In general the horizontally non-propulsive bubble release means applicable to -the invention are generally efficient aerators, but are not necessarily useful for foster-ing a net horizontal circulation of waste water around the channel. The invention contemplates the use of bubble release means having the characteristic that one or more of them, collectively, are unable to produce a net horizontal velocity of 0.3 feet per second in waste water in a ring channel, averaged over a longitudinal cross section of said channel which passes through the bubble release means in question.
A particularly preferred bubble release means produces no substantial net horizontal velocity measured in the above manner. On the other hand it should be noted that some of the applicable bubble release means may provide good localized mixing of the waste water (e.g. in the vicinity of the bubble release means), but not necessarily so. For example, it is contemplated to employ in the invention bubble release means capable of emitting oxidative gas in a form and amount sufficient for satisfying the aeration requirements for treat-ment to a 90% removal of BOD5 and suspended solids at aretention time in the range of about 18 to 24 hoursf but insufficient to mix the waste water adequately to prevent sedimentation.
Examples of useful bubble release means include fine bubble ceramic porous plate type diffusers, such being commercially available from Water Pollution Control Corporation of Milwaukee, Wisconsin and from others, as well as flexible plastic tubing type diffusers, which are commercially avail-able from several sources (e.g. Lasaire tubing a product of Lagoon Aeration Corporation of r~ilwaukee, Wisconsin). At ; least some of the commercially available tubing products release fine bubbles as defined herein.

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While the horizontally non-propulsive bubble release means is positioned along that portion of the flow path which remains after deduction of the portion occupied by the hydraulic jump means, this does not necessarily imply that the bubble release means extends along the entire remaining flow path, or that it covers the entire remaining flo~r area of the channel. It will not always be necessary to aerate throughout the flow path in order to maintain the waste water in an aerobic condition; and there may be certain circumstances, such as for instance when it is desired to practice nitrification, when anaerobic conditions may be desired. In that event, certain portions of the flow path outside the hydraulic jump means may not be aerated.
Also, a given zone may be rendered anaerobic in a number of ways, such as for instance by introducing raw sewage and or sludge having a high oxygen demand at the beginning of such zone. In general however the bubble release means will occupy at least about 40%, more preferably at least about 60%, and still more preferably at least about 90% of the length of the flow path measured along the centerline of said channel. It is considered optimum to have the bubble release means occupy substantially the entire flow path outside the -~ hydraulic jump means.
The degree of occupancy of the flow path, just men-tioned, is not necessarily equivalent to the degree of coverage of the available floor area in the channel. For example, the channel may have a flat bottom with the outer walls having a sloped configuration; in which case floor area coverage may not be equivalent to flow path occupancy. But in general it ; 30 is desireable that the bubble release means be distributed ` over at least about 40%, more preferably at least about 60%
and still more preferably about 90% of the floor area of the channel, while distribution of the bubble release means over substantially the entire substantially horizontal floor area outside the hydraulic jump means is considered optimum.
Considerable flexibility of construction and operation may be attained when employing bubble release means which comprises plural arrays of diffusers with each such array comprising a plurality of diffusers having a common supply conduit. For example, when the diffusers are apertured tubing type diffusers, they may be laid in seg-mented circular patterns which generally follow and extend along the flow path as illustrated in Figure 1. When the diffusers are ceramic plate diffusers -they may be arranged in arrays which include generally radially disposed supply conduits and horizontal headers arranged generally perpendicular to said supply conduits, with the ceramic plate type diffusers being arranged at spaced locations along the headers as shown in Figure 6. Such arrays may be spaced about or closely spaced to distribute oxidative process gas over substantially the entire area of the floor of the channel outside the hydraulic jump means.
For additional details of preferred embodiments of the bubble release means, attention is drawn to Figures 1-3.
These disclose the use of the above mentioned Lasaire tubing.
In the figures, as best shown by Figure 1, the tubing is arranged in four separate arrays with individual air supplies each including tubing laid in the form of segments of a circle generally along the flow path around the channel. The four arrays indicated by reference numerals 74-77 terminate at the hydraulic jumps and at the 6 and 12 o'clock positions on the drawing; note that portions of arrays 74-76 ar~ broken out in Figure 1. The following description of arrays 76 and 77 is analgous to arrays 74 and 75.
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~ - 21 -Figures 1-3 show that arrays 76 and 77 have oxida-tive process gas supply conduits including horlzont~l legs 78 extending through individual control valves 79 and "Y" wall limb extensions 48 to downcomer pipes 80 and horizontal feeds 81, connected to manifolds 82. The horizontal legs 78, control valves 79 and downcomer 80 are all visible in Figure 1, but only one of each is visible in Figure 3, being hidden behind the one member of each pair which is visible in the figure.
The tubing 83 is attached at equally, radially spaced points along manifolds 82 and is arranged in the circular pattern referred to above. The foregoing illustrates how at least some of the arrays can have separately controllable gas supplies connected to their supply conduits. By appropriate setting of valves 79 one may adjust certain of the arrays 74-77 to higher or lower gas rates per unit area of channel flow.
Certain of the control valves 79 may also be closed to prevent release of gas from a portion of said arrays while other arrays are in operation.
An alternate form of bubble release means is dis-closed in Figure 6, which is generally similar to Figure 1, but employs ceramic plate type diffusers instead of ~he flexi-ble aeration tubing described above. The embodiment of Figure

6 includes the same channel,hydraulic jump arrangements, clari-fier, sewage inlet, sludge inlet and mixed liquor outlet shown in Figure 1. ~nstead of the oxidative process gas supply condui~s 51, manifolds 82, tubing 83 and other associated conduits disclosed in Figures 1-3, the Figure 6 embodiment includes a supply manifold (not shown) whlch is connected to a source of oxidative process gas, such as air, and which may run around the base of inner wall 11 above or below bottom wall 13. To this manifold are connected a plurality of generally radially disposed horizontal supply conduits 8~. Horizontal 8~7~

headers 89 are connected to said supply conduits at equally spaced intervals and arranged generally perpendicular thereto.
Ceramic plate type diffusers 90 are arranged at spaced locations along each oE said headers. It should be understood that each of the arrays includes the ceramic plate type diffusers 90, even though the diffusers are drawn in on only one of the arrays shown in the drawings. While these diffusers are spaced apart and therefore do not physically cover all of the area of the floor of the channel, they are distributed over substantially the entire floor area, so that they can supply gas to substantially all of the w~ste water in the channel.
In accordance with the invention, advantages of flexibility and savings in power may be realized through the 1~ feature of separate power means for the hydraulic jump means and bubble release means. According to a first aspect of this feature of the invention, it is preferred that the ring channel aerator comprise a first power means connected to the hydraulic jump means. This is for supplying energy to 20 the jump and for inducing the upward and forward rolling motion referred to above. A separate, second power means is connected to the horizontally non-propulsive bubble release means. This is for supplying energy to the bubble release - means to bubble oxidative process gas into the waste water.
~-5 According to a second aspect of this feature of the invention, it is preferred that the first and second power means be separately con-trollable. In this fashion the volume of oxidative process gas released through the horizontally non-propulsive bubble release means may be reduced or increased in response to reductions and increases in the oxygen demand of the waste water. Because of the use~of separate power means, as above described, such reduction or increase does not require corresponding reduction or increase in the energy supplied . .
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through the hydraulic jump means for circulation. According~o still another aspect o~ this feature of the invention, it is preferred that the energy supply capacity of the second power means, as installed in the system, be larger than that of the first power means. More specifically, the capacity of the second power means may be sufficiently large in relation to the energy supply capacity of the first power means, for causing the second power means to supply the major portion of the total energy supplied by the first and second power means, both for inducing the upward and forward rolling motion of the waste water and for discharging oxidative process gas through the bubble release means. According to still ~ another aspect of this feature of the invention, the hydraulic ;~ jump means may comprise gas discharge means for inducing the waste water motion described above. In connection with any of the foregoing four aspects, either or both of the power means may be a compressor (including without limitation centrifugal blowers and positive displacement types) and a motor (including without limitation electric motors and internal combustion engines of all types), the respective power means being appro-priately connected to the respective gas discharge means and bubble release means.
A particularly preferred embodiment of the foregoing is disclosed in Figure 7. In the figure, the first power means 94 includes moto:r 95 having a controller 96 and connected via shaft 97 with compres~or 98 having inlet 99 and outlet 100.
The controller 9~ may be set manually or automatically, such as by means of a liquid level and/or liquid velocity sensing means or the like in the channel. The compressor 98 may be a single compressor or a battery of compressors, may be arranged to draw process gas from atmosphere or elsewhere, and may have conventional inlet filters, water traps and other associated equipment (not shown).

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~8~73 The first power means described above is connected via supply pipe 50 with hydraulic jump 36 in two ring channel aerators lOI and lOII via master control valve 69 and indivi-dual control valves I65A, I65B, II65A and II65B for the individual jumps in the two ring channel aerators. With controller 96, master control valve 69 and the individual control valves one may control the pressure in supply pipe 50 and the relative flow to the several jumps. This has a number of possi~le advantages. Yor example, it appears that more power is required to commence circulation in a ring channel aerator than to sustain circulation once the desired ra-te of circulation ; has been attained. Thus, for example, once circulation has been commenced, it may be possible to reduce the air flow to all jumps in a given aerator, or to shut off the supply of~air to one or more of the jumps while maintaining the air rate to the other jump or jumps at the same level, an increased level or possibly even a reduced level. Moreover, the pro-vision or separately controllable air supplies for the jumps within a given aerator afford opportunity for controlling the allocation of the horsepower consumed in circulation, as compared to the total horsepower consumed in circulation and non-propulsive release of oxidative process gas into the waste water.

As is also shown by Figure 7, the embodiment described in the preceding paragraph also includes a second, separate power means 10~ having motor 105, controller 106, shaft 107, , compressor 108, inlet 109 and outlet 110. Here again the controller 106 may be manually or automatically set, such as for instance by means for automatically sensing the oxygen demand of the waste water in the ring channel aerator and converting the oxygen demand to a control signal to which the controller is responsive. As previously noted, the second `:

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8~;~3 power m~ ans ~ay be, and preferably is, sufflciently large in relatior to the energy supply capacity of the first power means, so that it supplies the major portion of the total energy suppliec by the two power means. Thus, the major portion of the ener~y is supplied in this instance to ei~ht arrays of horizontally non-propulsive bubble release means I74-I77, and II74-II77 via supply pipe 111v master air valve 84, branch concuits 112,113 and individual control valves I79At I79B, I79C, I79D, II79A, and II79B, II79C and II79D. In this - 10 fashion the flow of air or other oxidative process gas to the manifold 82 and tubing 83 of the several arrays may be separately controlled. This has a number of advantages. For example, it is of assistance in the allocation of energy consumption between circulation and horizontally non-propul-sive bubbling of oxidative process gas into the circulating ` waste water. Moreover it has been suggested in the literature that de-nitrification may be attained in a ring channel aerator by providing anaerobic zones. Thus, for instance, the ring channel aerators depicted in Figure 7 could be provided with anaerobic zones by reducing or completely shutting off the flow of oxidative process gas to one or more arrays of the bubble release means which are downstream from the inlet(s) (not shown) for the waste water and, if any, for the return sludge. Alternatively, for example, it is possible to direct the greatest part of the air flow to the array or arrays immediately downstream of the inlet(s) for the waste water and return sludge (if any) in order to apportion the release of oxidative gas through the respective arrays in proportion or relation to the progressively reduced oxygen demand of the waste water as it moves further and further from the point of introduction in a given circuit around the channel.
It has been found that when the gas discharge means for the jumps includes one or more concentrated bubble diffusers f--~8~3 and the bubble release means is a means for discharging fine bubbles, the second compressor, connected -to the bubble release means, will usually be operating against a substantially higher back pressure than the first compressor. In general, the difference in back pressures will be at least about 1.3 psi, more commonly about 1.5 psi and preferably at least about 2 psi. As compared with a system in which the total air require-ments for the gas discharge means and bubble release mean~ would be a common compressor or battery of compressors, the compression of the air for the gas discharge means against a lower back pressure can result in considerable savings of energy.
When the hydraulic jump means comprises gas discharge means for inducing upward and forward rolling motion of the waste water, such gas discharge means can contribute to the overall oxygen transfer efficiency of the aerator. According to preferred embodiments of the invention the combined system oxygen transfer efficiency of the gas discharge means and bubble release means can be at least about 6, is more preferably at least about 7 and still more preferably is at least about 8.
In the construction of water trea-tment plants incor-; porating the ring channel aerators of the present invention, one may provide a plurality of co-located aerators having common facilities for treating effluent sludge and water. This is illustrated by Figure 8. As shown in the figure, three co-located ring ch-annel aerators lOIII, lOIV, and lOV are supplied by raw sewage main 118 and branch sewage supply pipes 119, 120 and 121. These aerators include clarifiers 22III, 22IV and 22V, the aerators and the clarifiers being similar to those disclosed in Figures 1-5. The waste sludge lines 29III, 29IV
and 29V of these aerator/clarifier combinations are connected to and feed into common sludge holding tank 122, from which the sludge may be delivered to a processing facility, a land fill or trucks for remote disposal. Effluent water lines -:

lB~73 123III, 123IV and 123V from the respective clarifiers are all connected to, and deliver clarified water from the clarifiers to, a common treatment vessel 124 which may for instance be a post aeration unit, a chlorinator or a combination of post aeration and chlorination facilities or other suitable facilities - for final treatment of the water.
Many variations of the ap;paratus are possible and, with the benefit of the prior description, can be readily formulated by persons skilled in the art without departing from the spirit of the invention. The process of the present inven-tion can also be embodied in a wide variety of ~orms without departing from the spirit of the invention. Some o~ the possible variations are discussed below, it being understood that other variations may be made without departing from the spirit of the invention.
According to the invention, anaerobic conditions may be maintained in a portion of the channel. However, according to a particularly preferred embodiment, aerobic conditions are maintained substantially throughout the channel.
The attributes of the process are such that it is par~
ticularly attractive for ring channel aerators or co-located groups of ring channel aerators having a throughput of waste water in the range of about 0.1 to 2 million gallons of through-put per day, and more preferably about 0.25 to about 1.5 ~` 25 gallons of plant throughput per day.
The process may be used in a wide variety of different types of applications. For example, the process may be employed in the aeration of industrial waste water, which can vary quite widely in oxygen demand, and can also be used in the treatment of domestic sewage. For example, in a domestic sewage applica-tion, the waste water may have an oxygen demand (including that ~.

iS~3 required for nitrification, if any) of about 150 -to about 250 ppm BOD5, and the waste water may be treated with about 1200 to about 2200 pounds of oxygen per million gallons of plant throughput per day. However, the invention is also readily applicable to waste water having an oxygen demand of about 100 to about 300 ppm BOD5 and to oxygen treat~ent of about 800 to about 2500 pounds of oxygen per million gallons o~ plant throughput per day. Even broader ranges of oxygen demand and oxygen treatment are possible and contemplated for use in the invention.
In most instances, the method of the invention will be operated as a multiple pass operation in which oxidative process gas addition, waste water addition~ return sludge addition, if any, and effluent water and sludge withdrawal are balanced to provide a desired degree of treatment in retention times in the range of about 12 to about 36 hours.
One example of a level of treatment attainable in accordance with the invention is a reduction of pollutants in the waste ; water to levels of about 30 ppm BOD5 or less and about 30 ppm suspended solids or less. Another example is removal from the waste water of about 90% of its initial BOD5 and of about 90% of its-initial suspended solids, and conversion to nitrate ion of substantially all of any ammonia which may have been present in t:he waste water~ The process may also be operated in such a manner as to accomplish the foregoing in a retention time in the range of about 15 to about 30 hours and more preferably about 18 to about 24 hours.

. i As notecl above, the waste water may be a mixed liquor of domestic dewage and return sludge. Without any intention of limiting the invention, it should be noted that the amount of return sludge may for example be in the range of about 25% to about 125% by volume of the influent water, and preferably about 40~ to about 100% by volume of the influent wate water.
According to a preferred embodiment of the invention, energy is applied to the waste water in the propulsion zone or zones at the rate of about 0.5 to about 5 adiabatic horsepower per million gallons of daily flow of waste water through the plant. Preferred and particularly preferred values of the fore-going, in terms of adiabatic horsepower per million gallons of daily flow of waste water through the plant, are about 0.8 to about 3.5 and about 1 to about 3.
The circulation rate induced in the waste water by causing the upward and forward rolling motion, as aforesaid, may vary considerably. While a given circulation rate may be selected in relation to the desired retention time, it may also be influenced by suspended solids, if such are present.
Different waste waters may or may not have significant quantities of suspended solids in the waste waters themselves or in the aerated waste waters. In general, domestic sewage and mixed li~uors composed of domestic sewage and return sludge have sufficïent quantities of suspended solids so that the circulation rate should be sufficient for maintaining the majority of the solids in suspension until they are removed from the channel. In view of the foregoing, it has been found that, in general, the circulation rate for domestic sewage, with or ; without return sludgej should average at least about 1 foot ; per second over the transverse cross-section of the channel;
and this same rate should be useful with a variety of other kinds of waste water.
According to one preferred embodiment of the method, sufficient energy is imparted to the waste water in the propul-sion zone or zones to form a wave in the waste water as it exits said zone(s). Preferably the energy is sufficient to form a continuation of the rolling motion downstream of said zone(s) for creating currents in the waste water that roll forward, downward, rearward and upward. Such currents can extend retention of oxidative process gas bubbles and assist in flocculation of suspended solids in the waste water.
As indicated above, it is preferred to induce the upward and forward rolling motion in the channel by discharge of gas in the propulsion zone or zones. Preferably the gas is lQ discharged at the rate of about 2 to about 3 SCFM per foot of side to side width inside of the propulsion zone(s).
In the practice of the method, the rate of flow of gas into the propulsion zone(s) may be varied independently of the rate of flow of oxidative process gas through the bubble release means, and vice versa.
According to the method of the present invention, a specified ratio is maintained between the adiabatic horse-power consumed in inducing circuation and the total of said horsepower plus the adiabatic horsepower consumed in non-propulsive bubbling of process gas into the waste-water.
Preferred and particularly preferred ranges for said ratio are about 0.02 to about 0.25 and about 0.03 to 0.2.
According to a preferred embodiment of the invention, ; the oxidative process gas may be introduced into the channel at a rate of about 10 SCFM or less per thousand cubic feet of liquid volume. Preferably said rate may be about 8 SCFM or less. The liquid volume referred to herein may be the liquid volume of the entire channel; alternatively, the liquid volume may be the volume of liquid above that portion of the floor of the channel over which the bubble release means is distributed.

A particularly preferred form of the invention pro-vides flexible allocation of horsepower consumption between -circulation and aeration and comprises circulation at a rate of at least about one foot per second as described above.
According to this embodiment about 0.5 to about 5 adiabatic horsepower are applied, per million gallons of daily plant throughput, for inducing circulation, while the rate of release of oxidative process gas is varied in response to the BOD of the waste water and independently of the rate of discharge of gas through a gas discharge means which is used for inducing the circulation in a propulsion zone or zones. Simultaneously with the foregoing r the ratio of the foregoing horsepower, relative to the total of said horsepower plus the adiabatic horsepower consumed in non-propulsive bubbling of process gas into the waste water, is maintained in the range of about 0.01 to about 0,3, more preferabl~ about 0.02 to about 0.25 and most preferably about 0.03 to about 0.3.

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~8~3 ADVANTAGES

Provision of a ring channel aera-tor with horizontally non-propulsive bubble release means and hydraulic jump means for inducing circula~ion -- and possibly also flocculation --enables one to separate the major portion of the work involved in the aeration of the waste water from the work of circulatlng the waste water; thus unlike aerating systems combining the functions of aeration and circulation, one need not employ excessive quantities of energy for circulation and/or mixing in order to obtain the requisite degree of aeration and vice - versa.
Where the energy released in the propulsion zone or zones is released by means of a gas discharge means and the bubble release means is a means for releasing ~ine bubbles, the gas for the gas discharge means may be compressed against a lower back pressure than the gas for the bubble release means, resulting in substantial savings of energy.
Where the design of the ring channel aerator is such that it takes less energy to keep the channel contents in motion than to commence circulation, the amount of energy allocated to circulation may be reduced once circulation is established --without affecting or impairing the operation of the bubble release means through which the~oxidative process gas is released.
Separate oontrolability of the consumption of energy in the propulsion zone or zones as opposed to the remainder of the flow path (in which the horizontally non-propulsive bubble release means is operated) makes it possible to operate the plant in different modes to accomplish different results.
- Thus, for example, one may change the waste water (e.g. mixed liquor) from aerobic to anaerobic, and then back to aerobic, , .

;

such as for example might be employed in nitrification/de-nitrification. In systems with multiple hydraulic jumps, it may be possible to obtain some adjustment in the dwell time in the successive portions of the flow path between the jumps, by adjusting the relative rates of energy release in the respective jumps.
The invention makes possible highly efflcient aeration, not only in shallow channels, but also in deeper channels, such as for instance those about 10 to 20 feet deep in which it has been found possible to operate with reduced energy consumption and/or increased oxygen transfer efficiency as compared with ring channel aerators using rotating brushes, rotating paddles or ejectors as the sole circulation and aeration means.

Aeration in an activated sludge sewage treatment plant involves three ~unctions: transfer of oxygen into the liquid - being treated; mixing of the tank contents; and flocculation of the fines to promote better settling in a clarifier. Porous plates, domes and other types of aeration devices all have their particular strengths and weaknesses, but the present invention provides a hydraulic jump which can do the major portion of the mixing and flocculation, while a separate bubble release means does the major part of the work of aeration. The combined result is a particularly efficient attainment of the above-mentioned three functions, as compared to many other aeration devices.
Moreover, when circulation is induced by gas discharge means in the propulsion zone or zones, such gas may be an oxidative gas which adds oxygen to the channel contents. This increases the available oxygen transfer efficiency, as compared to that available from the bubble release means alone.
Other advantages of the invention will be apparent to those skilled in the art from the foregoing disclosure of the invention and from experience with its operation.

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DEFINITIONS
Waste water - water containing domestic sewage, industrial waste or other pollutants which can be ameliorated in or removed from the water by treatment which includes aeration.
Aeration - introducing oxidative gas such as air, oxygen enriched air, oxygen, ozone or other gas capable of providing oxygen for reaction with pollutants in waste water.
Circulation - movement around a circuit in such a way as to repetitively return to and pass by a given point on said circuit.
Ring channel - an open-,or closed-top channel, conduit or other liquid carrying means having wall means which, as viewed in plan view, are laid out in a circular, oval, ellipsoidal, serpentine or other shape for guiding waste water in a circuit during circulation.
Concentrated bubble diffuser - a bubble release device adapted to release oxidative gas into waste water through apertures arrayed in said bubble release device in a group containing a sufficient number of apertures to release oxida-tive gas at the rate of at least about .05 SCFM per square inch of the horizontal projected area of said group.
Fine bubble diffuser - a diffuser which produces an array of bubbles in which those bubbles representing the major portion of the total volume of all bubbles in the array exhibit an average rise rate of about 0.8 foot per second or less while rising in said waste water.
Adiabatic horsepower (EI.P.) - the horsepower consumed in compressing air in a pump (e.g. compressor) and discharging same under water through an air dischargin~ device such as an aerator, as determined in accordance with the formula: Y
.

Q[(Pl ) l]

where Q = volume air rate (SCFM), P2 = pump outlet pressure (psia), and Pl = pump inlet pressure (psia).
Oxygen transfer efficiency (O.T.E.) - the pounds of oxygen absorbed in clear water under standard conditions (20C, zero dissolved oxygen, sea level barometric pressure) per horsepower hour. In determination of the O.T.E. of a complete aerating system, all horsepower consumed by the system for inducing movement of the waste-water and for discharging air into the water is considered, but adiabatic horsepower is used in the calculation for all aerating devices whether employed for non-propulsive bubble release and/or for inducing circulation of the waste water. In determination of the O.T.E. of an aerating device or group of such devices, only the horsepower (adiabatic) consumption of the device or devices is considered.
Horizontally non-propulsive - as applied to one or more bubble release means in a ring channel, signifies that such bubble release means, collectively, are unable to produce a net horizontal velocity as great as 0.3 feet per second in the waste water, averaged over a longitudinal cross section or sections of the channel passing through the bubble release means.
Substantially upright - as applied to the baffle means of a hydraulic jump means, indicates on the average more nearly vertical than horizontal.
In - as applied to gas discharge means, includes within, extending into or on.

Induced - caused, commenced and maintained, or merely maintained.

: ~ ' ,' -' ' . ' .

It has been previously mentioned that, while the horizontally non-propulsive bubble release means is positioned along that portion of the flow path which remains after deduction of the portion occupied by the hydraulic jump means, this does not necessarily imply that the bubble release means extends along the entire remaining flow path, or that it covers the entire remaining floor area of the channel. It will not always be necessary to aerate throughout the flow path in order to main-tain ~he waste-water in an aerobic condition; and there may be certain circumstances, such as for instance when it is desired to practice denitrification, when anaerobic conditions may be desired. Thus, although a given zone may be rendered anaerobic in a number of ways, such as for instance by introducing raw sewage and/or sludge having a high oxygen demand at the beginning of such zone, anaerobic conditions can also be attained by not aerating certain portions of the flow path outside the hydraulic jump means. There can be other reasons for providing bubble ; release means along only a portion of the remainder of said flow path. For example, it may be desired to employ bubble release 20 means mounted on swing units, whereby such bubble release means may be swung up and Out of the channel for servicing. In such circumstances it is beneficial to arrange the-bubble release means in one or more relatively compact arrays. When a sufficient number of bubble release means are arranged in such manner, and the oxygen requirements of the waste-water are not too large, oxygen transfer requirements may be satisfied even though sub-stantial portions of the flow p~th between such arrays are un-occupied. In such case, the ceramic plate type diffusers may for example oCCIlpy as little as about 15 to 20~ of the length of the flow path outside the hydraulic jump means, measured .~ ;

along the center line of the channel. Thus, the invention is not restricted to a particular percentage of occupancy of the remainder of the flow path by the bubble release means. However, it is nevertheless preferred that the bubble release means occupy at least about 40~, more preferably at least about 60~, and still more preferably at least about 90% of the length of the flow path measured along the centerline of said channel. It is considered optimum to have the bubble release means occupy substantially the entire flow path outside the hydraulic jump means.
The degree of occupancy of the flow path, just mentioned, may or may nt be equivalent to the degree of occupancy of the total floor area in the channel. For example, if the channel has a flat bottom with outer walls having a sloped configuration, and if the horizontally projected area of the sloping outer walls is regarded as part of the floor area of the channel, the flow path occupancy will not be equivalent to floor area occupancy.
In such case the above mentioned percentages of occupancy, i,e.
15-20%, 40%, 60~, and 100%, may be based on the horizontal floor area of the channel outside the hydraulic jump means.
As mentioned previously, when the oxygen transfer requirements of the process are not too large, it is possible to meet process oxygen requirements by employing a smaller number of diffusers than are shown in Figure 6, such diffusers being arranged in relatively compact arrays whereby the diffusers are not distributed over substantially the entire floor area, and whereby substantial portions of the flow path outside the hydraulic jump means are ~ot occupied by bubble release means. The fore-going is illustrated by the embodiment of Figure 9 It dis-closes a ring channel aerator which is similar to that of Figure ::
6 in certain respects.

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i73 The Figure 9 embodiment provides a channel 10 formed by inner and outer walls 11, 12 and bottom wall 13. These three walls define a flow path for circulation of waste-water under treatment. Optionally inner wall 11 may surround or define a clarifier tank 22 similar to that shown in greater detail in Figures 1 and 2. Channel 10 has a waste-water inle:t 16 in outer walls 12, and a transfer pipe 17 in inner wall 11 communicating with clarifier tank 22. As ln the Figure 6 embodiment there is a bridge 30 which extends across the aerator extending between the right and left sides as viewed in Figure 9, said bridge being provided with handrail 31 (see Figures 3 and 8). When a clarifier 22 is provided, its drive unit 28 may be located on bridge 30 centrally of tank 22. Figure 9 includes a hydraulic jump 36 like those used in Figure 6 and disclosed in greater detail in . Figures 1-5, and said hydraulic jump occupies a relatively small portion of the above mentioned flow path.
Among the dissimilarities of the Figure 6 and 9 embodiments is that the latter includes only one jump 36 instead . of two. Also, in the Figure 9 embodiment bridge 30 has two extensions 32 and 33 extending horizontally perpendicular to the bridge, said extensions appearing to extend upward and downward respectively as viewed in plan view in Figure 9. Whereas the horizontally non-propulsive bubble release means of Figure 6 are secured to the bottom wall 13 of channel 10, said means are suspended from the bridge in three sets of relatively compact arrays 34 in Figure 9. The three respective sets of arrays 34 are suspended, in clockwise order, from bridge extension 33, from the left portion of bridge 30 and from bridge extension 32. Note that a portion of bridge extension 33 is broken out to show that portions of all of said arrays 34 may extend beneath the C ~

'~ ~ `' ~ `. , , 8~73 respective portions of the bridge. Note also that the three sets of arrays 34 are positioned along the remainder of the above mentioned flow path in such a way that significant portions 35 of the length of the flow path outside the hydraulic jump means are not occupied by the bubble release means.
The respective arrays 34 include ceramic plate type diffusers 54 which receive oxidative gas via gas mains (not shown) and tees (not shown) under the respective bridge portions, said tees being connected to elbow fittings 45 secured to the respec-~ive bridge portions and connected to vertical downcomer pipes 46. The latter feed oxidative gas through half-headers 52 (52A, 52B~ and cross-headers 53 (53A-53H) (see Figures 11 and 12) to the diffusers 54. The aforementioned elbow fittings 45, vertical downcomer pipes 46, half-headers 52 and cross-headers 53 may be arranged in a fixed manner whereby the diffusers 54 in said arrays 34 are fixedly secured in a horizontal plane a short distance, e.g. a few inches or feet, above channel bottom wall 13.
However, it is preferred to provide for securing the - 20 arrays, means having the capability of swinging saia arrays up out of channel 10 to a position alongside the respective hridge portions for servicing. A num~er of devices of this type have been described in the prior art, but a preferred example is provided by U.S. Patent 4,294,696 issued October 13, 198I to Paul M. Thayer, for Improved Swing Diffuser. One embodiment of the subject matter of said application, as applied to the present invention, is shown in Figures 9-12 of th`e present disclosure. - ~
As shown in Figures 9-12, and particularly in the larger scale Figures 10-12, a plurality of hollow stanchion ~ F~;

86~73 portions 45A of elbow fittinys 45 are connected to the above-mentioned air mains, tees and bridge or bridge extensions 30, 32, 33. Said fittings also include ho:Llow swing elbow portions 45B
which can pivot about stanchion portions 45A in essentially vertical planes. Downcomer pipes 46 are divided into rigid tubular upper hanger arms 46A and rigid tubular lower hanger arms 46B. Upper hanger arms 46A are attached to elbows 45 so that arms 46A extend downwardly into the channel 10 below water level 38 as illustrated. Conventional hollow knee joints 59 pivotably connect upper arms 46A to lower arms 46B, so that a major portion or all of each lower arm 46B can be folded toward the respective upper arm 46A and the two arms rotated upwardly to a collapsed position at and/or abo-~e bridge extension 33. Although rigid, hollow arms are preferred both to carry the oxidative gas and tG
support the diffuser array, flexible tubing supported by rigid arms may also be used.
At the lower portion of each arm 46B, in this embodi-ment at its lower end, a hollow swing elbow 60 is provided which is pivotably mounted to a hollow header connector 61, so that upper hanger arm 46A and header connector 61 have their longi-tudinal axes in a common vertical plane. A pair of hollow half-headers 52A, 52B are rigidly connected to header connector 61 and extend laterally from the vertical plane of arm 46A and header connector 61. For balance, half-headers 52A, 52B preferably are of equal length. A plurality of cross-headers 53A-53H are mounted on top of half-headers 52A, 52B and preferably at right angles thereto. An array of diffusers for oxidative gas is defined by a further plurality of individual plate diffuser assemblies 54 extending upwardly from half-headers 53A-53H.
Assemblies 54 preferably comprise diffusers of the type ; . .

,.
: ~9 disclosed in Canadian Patent Application Serial No. 345,545, filed February 12, 1980 by Lloyd Ewing, David T. Redmon, Paul M. Thayer, Frank L. Schmit and William H. Roche, for Sewage Aeration System. However, those skilled in the art will appreciate that other types of diffusers could be used without departing from the scope of the present invention.
Conventional header stops or rests (not shown), attached to the channel 10 and/or to supports (not shown) on the outermost cross-headers, can be used to position the apparatus in the orientation shown in Figures 10 and 11. Alter-natively, or in addition, the arrays can be weighted to retain them in their desired, substantially horizontal operating position near the bottom wall 13 of the channel.
A swing diffuser having many of its diffuser assemblies 54 located at a considerable distance from half-headers 52A, 52B can be readily used in the present embodiment, because the array 34 of diffusers can be pivoted to a substantially upright position (not shown) convenient for servicing. Handrails 31 on bridge 30 and its extensions 32,33 may include moveable portions or gates (not shown) to accommodate upward pivoting of elbow 45 and arms 46A, 46B. Using conventional hoists (not shown) arms 46A and 46B are raised to folded position above bridge 30, while lever arm 62 and reach arm 63 cause rotational movement of each diffuser array 34 from its operating position to its servicing position.
Lever arm 62 is rigidly attached to header connector 61 and extends, in the illustrated embodiment, in a plane essentially parallel with the array 34. Of course, arm 62 need not be parallel with the array for the swing diffuser to function as indicated; however, the parallel arrangement is preferred due to i-ts compact geometry. Or, arm 62 may comprise one of cross-headers 53D, 53E, suitably strengthened for the purpose, rather than a separate element as illustrated. Reach arm 63 is pivoted at its lower portion to the outer portion 70 of lever arm 62. The upper portio:n 71 of reach arm 63 is pivoted at a point fixed relative to but movable with upper hanger arm 46A. In the illustrated embodiment, upper end 71 is pivoted at the end of an offset flange 72 rigidly attached to the lower portion of upper hanger arm 46A.

AS indicated above, the arrays 34 of diffusers 54 occupy only a portion of the lëngth of the remainder of the flow path, i.e. that portion which remains after deduction of the portion occupied by the jump 36, which itself occupies only a minor portion of the length of the flow path. Moreover, in the Figure 7 embodiment the arrays 34 occupy only a relatively small portion of the remainder of said flow path, The percentage of said remainder which is occupied by said arrays can be deter-mined on a plan view of the aerator by determining the fraction of said remainder ~hi'ch is covered by the envelope(s) surrounding ~O the area(s) occupied by the diffusers. For example the envelope surrounding the area occupied by the diffusers 54 under the left end of bridge 30 in Figure 9 is indicated by reference lines 73.

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Claims (128)

The embodiments of the invention in which an exclusive property or privilege is claimed, are defined as follows:

1. In a ring channel aerator comprising inner and outer wall means for circulating waste water along a horizontal flow path, the improvement which comprises:
hydraulic jump means located in said channel and extending between said inner and outer wall means generally transversely of said flow path for inducing an upward and forward rolling motion in the waste water as it passes through and out. of said jump, said hydraulic jump means occupying a minor portion of the length of said flow path;
horizontally non-propulsive bubble release means positioned along the remainder of said flow path for bubbling oxidative process gas into the waste water and having and oxygen transfer efficiency of at least about 6;
whereby the major portion of the work involved in the aeration of the waste-water may be performed separately from the work of circulating said waste-water.

2. An apparatus according to claim 1 wherein the ratio of the flow path length measured along the center line of the channel, relative to the average width of the channel measured throughout the height of its transverse cross-section at and below the normal operating water level is at least about 5.

3. An apparatus according to claim 1 wherein the ratio of the flow path length measured along the center line of the channel, relative to the average width of the channel measured throughout the height of its transverse cross-section at and below the normal operating water level is in the range of about 5 to about 15.

4. An apparatus according to claim 1 wherein the ratio of the flow path length measured along the center line of the channel, relative to the average width of the channel measured throughout the height of its transverse cross-section at and below the normal operating water level is in the range of about 8 to about 10.

5. An apparatus according to claim 1 wherein the average depth of said ring channel, measured from the bottom of the channel to its normal operating water line is at least about 5 feet.

6. An apparatus according to claim 1 wherein the average depth of said ring channel, measured from the bottom of the channel to its normal operating water line is in the range of about 5 to about 20 feet.

7. An apparatus according to claim 1 wherein the average depth of said ring channel, measured from the bottom of the channel to its normal operating water line is in the range of about 10 to about 20 feet.

8. An apparatus according to claim 1 wherein the average depth of said ring channel, measured from the bottom of the channel to its normal operating water line is in the range of about 12 to about 15 feet.

9. An apparatus according to claim 1 wherein the ring channel is of uniform depth throughout.

10. An apparatus according to claim 1 wherein said ring channel is substantially free of obstructions to flow other than said hydraulic jump means.

11. An apparatus according to claim 1 wherein said channel is of circular configuration in plan view.

12. An apparatus according to claim 1 wherein said inner and outer walls are both circular when viewed in plan view.

13. An apparatus according to claim 1 wherein said inner and outer walls are substantially equidistant throughout.

14. An apparatus according to claim 1 wherein said inner wall is substantially vertical.

15. An apparatus according to claim 1 wherein said channel is further defined by bottom wall means connected with said inner and outer wall means.

16. An apparatus according to claim 1 wherein said bottom wall means is substantially horizontal.

17. An apparatus according to claim 1 wherein said ring channel includes a waste-water inlet closely adjacent to and upstream of said hydraulic jump means.

18. An apparatus according to claim 1 wherein said ring channel includes a return sludge inlet closedly adjacent to and upstream of said hydraulic jump means.

19. An apparatus according to claim 1 wherein said ring channel includes a waste-water inlet and an effluent outlet which is more nearly upstream of said waste-water inlet than downstream thereof.

20. An apparatus according to claim 1 wherein said hydraulic jump means is a substantially upright chimney member extending for substantially the entire depth of said channel between its bottom and the normal operating water line of the channel, said chimney having an upstream inlet in the lower half of the channel depth and a downstream outlet in the upper half of said channel depth, the downstream end of said chimney being defined at least in part by a member defining a sufficiently abrupt change in cross-section from said chimney outlet to the full cross-section of the channel downstream thereof for causing water which exits the chimney outlet to whirl or roll about a generally horizontal axis transverse to said flow path.

21. An apparatus according to claim 20 wherein said chimney is defined by substantially vertical wall means.

22. An apparatus according to claim 20 wherein the bottom of said inlet is at substantially the same ele-vation as the bottom of the channel.

23. An apparatus according to claim 20 wherein said outlet extends from beneath the water surface to an elevation at or above the water surface in said channel.

24. An apparatus according to claim 20 wherein the inlet, chimney and outlet respectively has cross-sections measured normal to the direction of flow in the range of about 0.2 to about 0.5 of the transverse cross-sectional area of the channel at and below its normal operating water line, averaged alone the entire length of said flow path.

25. An apparatus according to claim 20 wherein the inlet, chimney and outlet respectively have cross-sections measured normal to the direction of flow in the range of about 0.25 to about 0.37 of the transverse cross-sectional area of the channel at and below its normal operating water line, averaged along the entire length of said flow path.

26. An apparatus according to claim 20 wherein the inlet, chimney and outlet respectively have cross-sections measured normal to the direction of flow in the range of about 0.3 to about 0.37 of the transverse cross-sectional area of the channel at and below its normal operating water line, averaged along the entire length of said flow path.

27. An apparatus according to claim 20 wherein said inlet, chimney andoutlet are all of similar cross-section measured normal to the direction of flow.

28. An apparatus according to claim 20 wherein said inlet, the interior of the chimney and said outlet are of substantially the same width as those portions of the channel which are closely adjacent to and both upstream and downstream of said chimney.

29. An apparatus according to claim 20 wherein said change in cross-section is sufficiently abrupt to create sufficiently vigorous rolling action for assisting in floc-culation of solids suspended in waste-water.

An apparatus according to claim 20 wherein said change in cross-section is sufficiently abrupt to create sufficiently vigorous rolling action for entraining bubbles of oxidative gas in the rolling water and thereby prolonging their contact therewith.

31. An apparatus according to claim 20 wherein upward propulsion means is positioned in said chimney for imparting energy in an upward direction to the contents of the chimney.

32. An apparatus according to claim 31 wherein said upward propulsion means is positioned for distributing said energy across substantially the entire width of said chimney with sufficient uniformity of distribution for causing said upward and forward rolling action to occur across substantially the entire width of said chimney.

33. An apparatus according to claim 31 wherein said upward propulsion means includes means for imparting energy to said waste-water at a higher rate adjacent said outer wall than adjacent said inner wall for causing a relatively higher flow rate in said waste water adjacent said outer wall as compared to adjacent said inner wall.

34. An apparatus according to claim 31 wherein said chimney is defined at least in part by an upstream upper water baffle and a downstream lower water baffle.

35. An apparatus according to claim 34 wherein said upward propulsion means is positioned for imparting the major portion of said energy to that half of the water in the chimney which flows nearest the upstream upper water baffle.

36. An apparatus according to claim 34 wherein said upward propulsion means is positioned for imparting the major portion of said energy to that third of the water in the chimney which flows nearest the upstream upper water baffle.

37. An apparatus according to claim 34 wherein said upward propulsion means is positioned in the longitudinal space between the upper water baffle and the lower water baffle.

38. An apparatus according to claim 20 wherein gas discharge means is positioned in said chimney for impart-ing upward motion to the contents of the chimney.

39. An apparatus according to claim 38 wherein said gas discharge means is positioned for distributing bubbles across the width of said chimney with sufficient uniformity of distribution for causing said upward and forward rolling action to occur across substantially the entire width of said chimney.

40. An apparatus according to claim 38 wherein said gas discharge means includes means for discharging said gas at a higher rate adjacent said outer wall than adjacent said inner wall for causing a relatively higher flow rate in said waste-water adjacent said outer wall as compared to adjacent said inner wall.

41. An apparatus according to claim 38 wherein said chimney is defined at least in part by an upstream upper water baffle and a downstream lower water baffle.

42. An apparatus according to claim 41 wherein said gas discharge means is positioned for introducing the major portion of said gas to that half of the water in the chimney which flows nearest the upstream upper water baffle.

43. An apparatus according to claim 41 wherein said gas discharge means is positioned for imparting the major portion of said gas to that third of the water in the chimney which flows nearest the upstream upper water baffle.

44. An apparatus according to claim 41 wherein said gas discharge means is positioned on the upper water baffle.

45. An apparatus according to claim 44 wherein the longitudinal position of said gas discharge means is closer to said upper water baffle than to said lower water baffle.

46. An apparatus according to claim 41 wherein said gas discharge means has gas discharge outlets whose level of submergence is equal to at least half the depth of the upper water baffle, measured downward from the normal opera-ting water line of the channel.

47. An apparatus according to claim 41 wherein said gas discharge means is positioned at about the same elevation as the lower edge of the chimney inlet.

48. An apparatus according to claim 38 wherein said gas discharge means is a plurality of gas diffusers distributed at spaced intervals across said chimney.

49. An apparatus according to claim 48 wherein the projected area of said gas diffusers covers not more than about 25% of the lineal distance from side to side of the interior of said chimney.

50. An apparatus according to claim 48 wherein said gas diffusers are concentrated bubble diffusers.

51. An apparatus according to claim 50 wherein said concentrated bubble diffusers have an oxidative gas discharge rate of about .05 to about 0.5 SCFM per square inch.

52. An apparatus according to claim 50 wherein said concentrated bubble diffusers have an oxidative gas discharge rate of about 0.1 to about 0.3 SCFM per square inch.

53. An apparatus according to claim 1 wherein said hydraulic jump means comprises a plurality of hydraulic jumps at spaced locations along said flow path.

54. An apparatus according to claim 53 wherein said plurality of hydraulic jumps is positioned at equally spaced locations along said flow path.

55. An apparatus according to claim 1 wherein said hydraulic jump means occupies about 10% or less of the length of said flow path, measured along the center line of said channel.

56. An apparatus according to claim 1 wherein said bubble release means occupies at least about 40% of the length of the flow path, measured along the center line of said channel.

57. An apparatus according to claim 1 wherein said bubble release means occupies at least about 60% of the length of the flow path, measured along the center line of said channel.

58. An apparatus according to claim 1 wherein said bubble release means occupies at least about 90% of the length of the flow path, measured along the center line of said channel.

59. An apparatus according to claim 1 wherein said bubble release means occupies substantially the entire flow path outside said hydraulic jump means.

60. An apparatus according to claim 1 wherein said bubble release means is distributed over at least about 40%
of the floor area of the channel.

61. An apparatus according to claim 1 wherein said bubble release means is distributed over at least about 60%
of the floor area of the channel.

62. An apparatus according to claim 1 wherein said bubble release means is distributed over at least about 90 of the floor area of the channel.

63. An apparatus according to claim 1 wherein said bubble release means is distributed over substantially the entire area of the floor of said channel outside said hydraulic jump means.

64. An apparatus according to claim 1 wherein said bubble release means comprises plural arrays of diffusers, each such array comprising a plurality of diffusers having a common supply conduit.

65. An apparatus according to claim 64 wherein said diffusers are capable of emitting oxidative process gas in a form and amount sufficient for satisfying the aeration requirements for treatment to a 90% removal of BOD5 and suspended solids at a retention time in the range of about 18 to 24 hours, but insufficient to mix the waste-water adequately to prevent sedimentation.

66. An apparatus according to claim 64 wherein at least some of said arrays have separately controllable oxidative process gas supplies connected to their supply conduits.

67. An apparatus according to claim 66 wherein said separately controllable oxidative process gas supplies include means for adjusting certain of said arrays to higher rates than other arrays in respect to rate of oxidative process gas release, per unit area of channel floor.

68. An apparatus according to claim 66 wherein said separately controllable oxidative process gas supplies include means for preventing release of oxidative process gas from a portion of said arrays while other arrays are in operation.

69. An apparatus according to claim 64 wherein said arrays are closely spaced to cover substantially the entire area of the floor of said channel outside said hydraulic jump means.

70. An apparatus according to claim 64 wherein said bubble release means includes apertured tubing.

71. An apparatus according to claim 64 wherein said bubble release means includes means for discharging fine bubbles.

72. An apparatus according to claim 71 wherein said means for discharging fine bubbles includes ceramic plate diffusers.

73. An apparatus according to claim 71 wherein said means for discharging fine bubbles comprises apertured tubing.

74. An apparatus according to claim 64 wherein said diffusers are apertured tubing type diffusers laid in segmented circular patterns which generally follow and extend along said flow path.

75. An apparatus according to claim 64 wherein said arrays include generally radially disposed horizontal supply conduits, horizontal headers arranged generally perpendicular to said supply conduits, and ceramic plate diffusers arranged at spaced locations along said headers.

76. An apparatus according to claim 1 wherein said apparatus comprises a first power means connected to said hydraulic jump means for supplying energy thereto for inducing said upward and forward rolling motion in said waste-water, and separate second power means connected to said horizontally non-propulsive bubble release means for supplying energy thereto for bubbling oxidative process gas into said waste-water.

77. An apparatus according to claim 76 wherein said first power means comprises a compressor and motor.

78. An apparatus according to claim 76 wherein said second power means comprises a compressor and motor.

79. An apparatus according to claim 76 wherein said first and second power means respectively comprise compressors and motors.

80. An apparatus according to claim 76 wherein said first and second power means are separately controllable whereby the volume of oxidative process gas released through said horizontally non-propulsive bubble release means may be reduced or increased as required by corresponding reductions and increases in the oxygen demand of said waste-water without requiring corresponding reductions or increases in the energy supplied through said hydraulic jump means for circulation.

81. An apparatus according to claim 76 wherein the energy supply capacity of the second power means, as installed in said apparatus, is sufficiently large in relation to the energy supply capacity of said first power means, for causing said second power means to supply the major portion of the total energy supplied by said firs-t and second power means both for inducing said motion and for discharging oxidative process gas through said bubble release means.

82. An apparatus according to claim 81 wherein said first power means comprises a compressor and motor.

83. An apparatus according to claim 81 wherein said second power means comprises a compressor and motor.

84. An apparatus according to claim 81 wherein said first and second power means respectively comprise compressors and motors.

85. An apparatus according to claim 76 wherein said hydraulic- jump means comprises gas discharge means for inducing upward and forward rolling motion of said waste water, said first power means being a first compressor and motor connected to said gas discharge means and said second power means being a second separate compressor and motor connected with said horizontally non-propulsive bubble release means.

86. An apparatus according to claim 85 wherein said gas discharge means includes a concentrated bubble diffuser and said bubble release means is a means for dis-charging fine bubbles and said second compressor is connected for operating against a substantially higher back pressure than said first compressor.

87. An apparatus according to claim 86 wherein the difference in back pressures is at least about 1.3 PSI.

88. An apparatus according to claim 86 wherein the difference in back pressures is at least about 1.5 PSI.

89. An apparatus according to claim 86 wherein the difference in back pressures is at least about 2 PSI.

90. An apparatus according to claim 1 wherein said hydraulic jump means comprises gas discharge means for inducing upward and forward rolling motion of said waste-water, and wherein the combined system oxygen transfer efficiency of said gas discharge means and bubble release means is at least about 6.

91. An apparatus according to claim 1 wherein said hydraulic jump means comprises gas discharge means for inducing upward and forward rolling motion of said waste water, and wherein the combined system oxygen transfer efficiency of said gas discharge means and bubble release means is at least about 7.

92. An apparatus according to claim 1 wherein said hydraulic jump means comprises gas discharge means for induc-ing upward and forward rolling motion of said waste water, and wherein the combined system oxygen transfer efficiency of said gas discharge means and bubble release means is at least about 8.

93. An apparatus-according to claim 1 wherein said- inner wall encloses a clarifier, said channel having a return sludge inlet from said clarifier and, upstream of said return sludge inlet, a mixed liquor transfer conduit for transferring mixed liquor from said channel to said clarifier.

94. A plurality of co-located ring channel aerators according to claim 1.

95. An apparatus according to claim 94 wherein said ring channel aerators each enclose a clarifier and the respective clarifiers are connected to a common sludge tank and common liquid post treatment facilities.

96. An apparatus according to claim 94 wherein said ring channel aerators are each provided with gas dis-charge means in their respective hydraulic jump means and wherein said gas discharge means are connected to a common compressor means and said horizontally non-propulsive bubble release means are connected to a separate common compressor means and wherein the respective common compressor means are separately controllable.

97. In a ring channel aerator comprising inner and outer wall means for circulating waste-water along a horizontal flow path, the improvement which comprises:
hydraulic jump means located in said channel and extending between said inner and outer wall means generally transversely of said flow path, said hydraulic jump means including means for establishing upward flow in said jump, for positively urging said flow in a forward direction as it departs said jump, for discharging said forward flowing waste-water from said jump as a stream which includes the upper surface of the waste water downstream of the jump, for directing said stream into a zone of abruptly increased cross-section immediately downstream of the jump and for inducing thereby a forward roll in the waste-water, said hydraulic jump means occupying a minor portion of the length of said flow path;
horizontally non-propulsive bubble release means positioned along the remainder of said flow path for bubbling oxidative process gas into the waste water and having an oxygen transfer efficiency of at least about 6.

98. In a ring channel aerator comprising inner and outer wall means for circulating waste water along a horizontal flow path, the improvement which comprises:
hydraulic jump means located in said channel for inducing an upward and forward rolling motion in the waste water as it passes through and out of said jump, said hydraulic jump means occupying a minor portion of the length of said flow path and comprising:

an upstream upper water barrier and a lower water barrier, said barriers extending between said inner and outer walls and generally transversely of said flow path, an upstream inlet and downstream outlet positioned respectively below and above said up-stream and downstream water barriers, and gas discharge means distributed laterally between said inner and outer walls in the space between said upstream and downstream barriers, said air discharge means being positioned for releasing the major portion of its discharge of gas closer to said upstream barrier than to said downstream barrier; and horizontally non-propulsive bubble release means positioned along the remainder of said flow path for bubbling oxidative process gas into the waste water and having an oxygen transfer efficiency of at least about 6.

99. A method of aerating waste-water undergoing circulation in a ring channel along a horizontal flow path, comprising:
inducing said horizontal circulation by causing upward and forward rolling motion of the waste-water as it passes through and exits at least one propulsion zone, said zone or zones, being located in and extending trans-versely of said flow path, and occupying a minor portion of the length of said flow path, bubbling oxidative process gas into the waste-water along the remainder of said flow path through horizontally non-pr pulsive bubble release means having an oxygen transfer efficiency of at least, about six;
maintaining a ratio in the range of about 0.01 to about 0.35 between the adiabatic horsepower consumed in inducing said circulation and the total of said horsepower plus the adiabatic horsepower consumed in non-propulsive bubbling of process gas into the waste-water.

100. A method in accordance with claim 99 herein sludge is formed and circulated in said channel, and said circulation rate is sufficient for maintaining the majority of said sludge in suspension until it is removed from said channel.

101. A method according to claim 99 wherein said oxidative process gas is air.

102. A method according to claim 99 wherein said waste-water is a mixed liquor of domestic sewage and return sludge.

103. A method according to claim 102 wherein the amount of return sludge is in the range of about 25% to about 125% by volume of the influent waste-water.

104. A method according to claim 102 wherein the amount of return sludge is in the range of about 40% to about 100% by volume of the influent waste-water.

105. A method according to claim 99 wherein said oxidative process gas is introduced at a rate of about 10 SCFM or less per thousand cubic feet of liquid volume in said channel.

106. A method according to claim 99 wherein said oxidative process gas is introduced at a rate of about 8 SCFM or less per thousand cubic feet of liquid volume in said channel.

107. A method according to claim 99 wherein sufficient energy is imparted to said waste water in said pro-pulsion zone(s) to form a wave in the waste-water as it exits said propulsion zone or zones and to form a continua-tion of said rolling motion downstream of said zone(s) for creating currents in said waste-water that roll forward, down-ward, rearward and upward thereby extending retention of gas bubbles and assisting in flocculation of suspended solids in waste-water.

108. A method according to claim 99 wherein energy is applied to said waste-water in said propulsion zone or zones at the rate of about 0.5 to about 5 adiabatic horsepower per million gallons of daily flow of waste-water through said plant.

109. A method according to claim 99 wherein energy is applied to said waste-water in said propulsion zone or zones at the rate of about 0.8 to about 3.5 adiabatic horsepower per million gallons of daily flow of waste-water through said plant.

110. A method according to claim 99 wherein energy is applied to said waste-water in said propulsion zone or zones at the rate of about 1 to about 3 adiabatic horsepower per million gallons of daily flow of waste-water through said plant.

111. A method according to claim 99 wherein said upward and forward rolling motion is induced by discharge of gas in said propulsion zone or zones.

112. A method according to claim 111 wherein said gas is discharged at the rate of about 2 to about 3 SCFM per foot of side to side width inside said propulsion zone or zones.

113. A method according to claim 111 wherein said gas is discharged by at least one concentrated bubble diffuser in said propulsion zone or zones and said oxidative process gas is released through means forproducing fine bubbles.

114. A method according to claim 111 wherein the gas for causing said upward and forward rolling motion and the oxidative process gas are supplied from separate sources.

115. A method according to claim 111 wherein the rate of flow of gas into said propulsion zone or zones is varied independently of the rate of flow of oxidative process gas through said bubble release means.

116. A method according to claim 111 wherein the rate of flow of oxidative process gas through said bubble release means is varied independently of the rate of flow of gas into said propulsion zone or zones.

117. A method according to claim 99 wherein anaerobic conditions are maintained in a portion of said channel.

118. A method according to claim 99 wherein aerobic conditions are maintained substantially throughout said channel.

119. A method according to claim 99 wherein said ratio of horsepower is in the range of about 0.02 to about 0.25.

120. A method according to claim 99 wherein said ratio of horsepower is in the range of about 0.03 to about 0.2.

121. A method according to claim 99 wherein said waste-water has an oxygen demand (including that required for nitrification, if any) of about 100 to about 300 ppm BOD5 and wherein said waste water is treated with about 800 to about 2500 pounds of oxygen per million gallons of plant throughput per day.

122. A method according to claim 121 wherein said oxygen demand is about 150 to about 250 ppm and said oxygen treatment is about 1200 to about 2200 pounds of oxygen per million gallons of plant throughput per day.

123. A method according to claim 99 wherein the throughput of said waste water is in the range of about 0.1 to about 2 million gallons of plant throughput per day.

124. A method according to claim 99 wherein the throughput of said waste-water is in the range of about 0.25 to about 1.5 million gallons of plant throughput per day.

125. A method according to claim 99 wherein said method is a multiple pass operation in which oxidative process gas addition, waste-water addition, return sludge addition, if any, and effluent water and sludge withdrawal are balanced to provide, in a retention time of about 12 to about 36 hours, either (A) a reduction of pollutants in the waste water to levels of about 30 ppm BOD5 or less and about 30 ppm suspended solids or less, or (B) a removal from the waste-water of about 90% of its initial BOD5 and 90% of its initial suspended solids, and conversion to nitrate ion of substan-tially all of any ammonia which may have been present in the influent waste-water.

126. A method according to claim 125 wherein said retention time is in the range of about 15 to about 30 hours.

127. A method according to claim 125 wherein said retention time is in the range of about 18 to about 24 hours.

128. A method of aerating waste-water with flexible allocation of horsepower consumption between circulation and aeration, said method comprising:
inducing circulation of waste-water in a loop channel along a horizontal flow path at a circulation rate which averages at least about one foot per second over the transverse cross-section of said channel, by discharging gas into said waste-water through gas discharge means for causing upward and forward rolling motion of the waste-water as it passes through and exits at least one propulsion zone, said zone or zones, being located in and extending transverse-ly of said flow path, and occupying a minor portion of the length of said flow path, bubbling oxidative process gas into the waste-water along the remainder of said flow path through horizontally non-propulsive bubble release means having an oxygen transfer efficiency of at least about six;
applying about 0.5 to about 5 adiabatic horse-power per million gallons of daily plant throughput for inducing said circulation, while varying the rate of release of oxidative process gas in response to the BOD of the waste-water and independently of the rate of discharge through said gas discharge means, and maintaining the ratio of said horsepower relative to the total of said horsepower plus the adiabatic horsepower consumed in non-propulsive bubbling of process gas in the waste-water in the range of about .01 to about .35.