CA1217583A - Pumpless clarifier apparatus and process for operation thereof in combination with a draft tube circulator/aerator - Google Patents
Pumpless clarifier apparatus and process for operation thereof in combination with a draft tube circulator/aeratorInfo
- Publication number
- CA1217583A CA1217583A CA000438754A CA438754A CA1217583A CA 1217583 A CA1217583 A CA 1217583A CA 000438754 A CA000438754 A CA 000438754A CA 438754 A CA438754 A CA 438754A CA 1217583 A CA1217583 A CA 1217583A
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- Prior art keywords
- clarifier
- channel
- liquor
- mixed liquor
- barrier
- Prior art date
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
- Y02W10/00—Technologies for wastewater treatment
- Y02W10/10—Biological treatment of water, waste water, or sewage
Abstract
ABSTRACT OF THE DISCLOSURE
An integral clarifier is provided that operates without a pump by deriving the clarifier feed stream and its accompanying pump head from the flow being pumped through the draft tube of a draft tube circulator/aerator assembly in a complete mix system or in a basin oxidation ditch. The clarifier feed stream is delivered to the clarifier with this pump head substantially intact to create a differential hydraulic head between the surface of the clarified liquor within the clarifier and the surface of the mixed liquor within the complete mix tank or within the endless channel of the barrier oxidation ditch. The clarifier may be located in any suitable place but is preferably alongside the complete mix tank or alongside the discharge channel of the barrier oxidation ditch, within the discharge channel so that its upstream side forms the barrier, or surrounded by the endless channel, particularly if the clarifier and the ditch are circular in shape.
An integral clarifier is provided that operates without a pump by deriving the clarifier feed stream and its accompanying pump head from the flow being pumped through the draft tube of a draft tube circulator/aerator assembly in a complete mix system or in a basin oxidation ditch. The clarifier feed stream is delivered to the clarifier with this pump head substantially intact to create a differential hydraulic head between the surface of the clarified liquor within the clarifier and the surface of the mixed liquor within the complete mix tank or within the endless channel of the barrier oxidation ditch. The clarifier may be located in any suitable place but is preferably alongside the complete mix tank or alongside the discharge channel of the barrier oxidation ditch, within the discharge channel so that its upstream side forms the barrier, or surrounded by the endless channel, particularly if the clarifier and the ditch are circular in shape.
Description
B GROUND OF THE INVENTION
Field of the Invention This invention relates to waste water treatment. The invention especially relates to methods and apparatuses for clarifying mixed liquor in activated sludge processes that are I
12~'~5~`3 conducted in oxidation ditches of racetrack or loop channel configuration or in conventional complete mix tanks.
Review of the Prior Art Oxidation ditches for continuous aerobic treatment of liquid waste waters have been used since the early 1950's. They were developed in Holland by or. If A. Pasveer, as a variation of the activated sludge process, and were patented in Dutch Patent No. 87,500 and British Patent No. 796,438.
artier oxidation ditches have been operating since 1977, primarily for treating municipal and poultry processing waste waters. Barrier oxidation ditches are described in US.
Patent No. 4,260,486 of John H. Reid. A barrier oxidation ditch comprises an endless channel, a barrier disposed athwart the channel, a vertically mounted pump having an impeller with-in a draft tube which it vertically mounted at the upstream side of the barrier, a J-shaped discharge duct which is flow-connected to the draft tube and is mounted below the bottom of the channel and below the barrier to provide a discharge on the downstream side thereof, and an aeration means which includes a spurge disposed beneath the impeller, and, if needed, diffusers which are removably mounted so that they introduce additional diffused air at about the bottom of the discharge duct. This barrier oxidation ditch, which pumps all of the circulating mixed liquor past the barrier, is herein described as a total barrier oxidation ditch.
It has further been ascertained that the barrier oxidation ditch of US. Patent 4,260,486 creates a differential hydraulic head that is readily measurable when the flow is being pumped through one or more draft tubes and discharge ducts, thereby indicating that there exists a dammed-up moment ~2~'75&3 tug in the mixed liquor which is approaching the barrier. It is important to release the energy contained in the dammed-up momentum.
An improved barrier oxidation ditch is disclosed in US. Patent No. 4,278,547 of John H. Reid. this ditch come proses a barrier having adjustable sized openings and/or gate-ways there through for conserving the momentum of the mixed liquor, a pump means for pumping most of the liquor past the barrier, and an aeration means for aerating the pumped liquor and for selectively aerating the induced-flow liquor passing through the openings so that there is no back mixing of aerated liquor and can be relatively little heterogeneous aeration when the aerated pumped liquor is blended downstream of the barrier, with the induced-flow liquor. This barrier oxidation ditch, which pumps a portion of the circulating mixed liquor past the barrier and provides openings for the remainder to move through the barrier, is herein described as a partial barrier oxidation ditch.
One of the major benefits of the barrier oxidation ditch of US. Patent 4,260,486 is that the spurge in the down-draft tube provides for introducing diffused air to the mixed liquor at a shallow depth, thereby forming an air-liquor mix-lure, and then for pumping this mixture downwardly with its impeller into the discharge duct to a sub-channel oxygen-trans-for depth, at the lowest portion of the discharge duct, that is well below the channel bottom. This oxygen-transfer depth increases the driving force for transferring oxygen molecules across the films at the gas- liquid interfaces, of the air bubbles. Other additional benefits of great practical import lance are: (1) the energy required for downwardly pumping the ~7~`3 air-liquor mixture is considerably less than the energy required for downwardly pumping the liquor alone and for spear-lately compressing air to the hydraulic pressure existing at the oxygen-transfer depth; and I a very high level of turbulence is provided in the oxygen-transfer zone, measured by brake horsepower/1000 ft.3.
For any aeration system used in transferring oxygen to a particular waste water, sewage, or mixed liquor, its oxygen transfer efficiency is a function of five major parameters:
bubble size, bubble retention time, driving force across the air-liquid interface for the dissolved oxygen, hydrostatic pressure, and degree of turbulence in the oxygen-transfer zone.
However, the adjustable gateways through the barrier of US. Patent 4,278,547 allow the induced-flow portion of the mixed liquor to pass through the barrier and be aerated at a depth above the channel bottom instead of at the sub-channel depth that is available within a discharge duct, thereby losing at least some of the advantages of retention time, driving force hydrostatic pressure, and possibly even turbulence.
US. Patent 4,455,232 of John H. Reid accordingly discloses a barrier Ed circulator/aerator in the endless channel of a barrier oxidation ditch which provides a directly pumped flow of mixed liquor into a central liquor inlet zone and an induced flow of mixed liquor into a surrounding liquor inlet zone at the inlet of a deep oxygen contact duct which passes beneath the barrier to the discharge channel on the downstream side thereof. It further provides mixing of diffused air with the directly pumped flow and/or the induced flow and then moving the combined air-liquor flows into the deepest portion of the contact duct where point-source pressurized aeration of both flows occurs. Eddy jet diffusers are preferably used for aerating the induced flow. Oxygen transfer efficiencies are obtained that are 1.6 to 2.2 times as great per brake horse-power per hour as that attainable by 100% pumping of the mixed liquor in a total barrier oxidation ditch, as disclosed in US. Patent 4,260,486.
Jo i - pa -~Z~75~33 This improved barrier oxidation ditch, however, compels 1~0% of the flow, both pumped and induced, to change direction 90 while moving downwardly and then to change direction 135 while moving beneath the barrier and upwardly. As is well known in hydraulic theory, such 225 of direction changing causes significant energy consumption. It would be desirable to provide a means for passing the liquor from the intake channel to the disk charge channel with minimum directional change.
When the air-liquor mixture has reached the lowest portion of the discharge duct, there is also very little time TV
able for oxygen transfer from bubble to liquor across -the films of the liquor-gas interface before the liquor/air mixture begins to rise. Ye, it is at this point in passage from the intake channel to the discharge channel that transfer efficiency is highest because of maximum hydrostatic pressure. Another factor of importance is that the microorganisms are in an oxygen-starved condition and avidly utilize the oxygen as fast as it transfers across the liquor-air films into the bulk liquor, so that the bulk liquor cannot become saturated if the LOSS content is reasonably high. An unusually large proportion of the oxygen in the bubbles is accordingly able to transfer across the films into the bulk liquor. It would accordingly be desirable to prolong the bubble retention time at the maximum depth.
However, simply lengthening the discharge duct, such as by thick-eying the barrier, tends to waste the available land area.
An elongated clarifier is described in US. Patent 3,788,477 of Love, for use alongside complete-mix tanks. As described in this patent, flow of sludge from the sloping bottom of the clarifier into the adjacent mixing basin is limited by flow control plates and is picked up inside the mixing basin by`
So the downward and inward flow of mixed liquor along -the sides and bottom of the mixing basin. Use of sludge return pumps can thereby be avoided.
This clarifier was installed alongside the discharge channel in several barrier oxidation ditches during 1979 and 1980.
However, in a barrier oxidation ditch, the flow is translational, not towardly as in the mixing basin of a complete-mix system. It was consequently discovered that the sludge did not adequately slide out into the discharge channel of a barrier oxidation ditch but had to be pumped out of the clarifier because the turbulent translational flow in the discharge channel created a positive pressure that interfered with automatic discharge of the sludge.
To about 1979, a brochure entitled "Lightning Treatment System" was published by Mixing equipment Co., Rochester, New York, which schematically showed the integral clarifier of US. Patent 3,788,477 disposed downstream of the circulator/aerator in a barrier oxidation ditch and also aligned transversely to the channel so that its upstream side formed the barrier and its down-stream or discharge side was athwart the channel and immediately upstream of the terminus of the discharge duct. Moreover, the length of the clarifier, as illustrated, was shorter than its width and was, in fact, the same as the width of the channel.
However, such an integral clarifier would, in most cases, be far too small to be combined with a barrier oxidation ditch.
If the size of the clarifier were to be increased by extending the discharge side or outer baffle to a location far down the discharge channel and past the end of the discharge duct, there would be such a pool of violently agitated air moving beneath the clarifier and boiling up past the sludge discharge space of the clarifier that its operation would be impossible. In addition to this discharging 12~5~3 difficulty, the bottom of this sideways-extended clarifier would have such a slight slope that settled sludge would not slide downwardly toward the discharge space, whereby its operation would be unsuccessful for this reason as well.
As disclosed in US. Patent 4,303,516 o-f Stencil e-t at, a rectangularly shaped clarifier is mounted in one or both chant nets of an oxidation ditch which has a Mechanical aerator at one end, as taught in US. Patent 3,510,110 of Klein. This clarifier has the same depth as the channel depth, but the channel bottom is excavated beneath the bottom of the clarifier to provide a sub-merged passage for the mixed liquor. The floor of the clarifier slopes toward the channel sidewall in one embodiment and term-notes in a stilling plate that is spaced upwardly from the sidewall to provide a sludge discharge space there between. In another embodiment, the floor is horizontally disposed as spaced-apart rectangular plates having rectangular ports there between which are athwart the channel, each rectangular port having a shallowly inclined plate along its upstream edge and a steeply inclined plate along its downstream edge. The velocity of the flowing waste water is increased as it passes beneath the plates so that sludge is drawn from the clarifier through the ports.
This Stencil et at clarifier might perform well if disposed.ln the return channel, opposite the barrier of a barrier oxidation ditch, or in its intake channel, but if disposed in its discharge channel and close to the barrier, the up rushing air from the discharge duct would enter the clarifier through the discharge ports of either embodiment and disastrously interfere with its operation.
SLY
Clarified liquor is typically and generally removed from clarifiers in activated sludge processes by gravity flow. Scum is almost invariably pumped from the scum trough. Settled sludge is removed from the clarifier and recycled to the activated sludge aeration basin by gravity flow fulled by pumping, by siphon flow followed by pumping, or by direct pumping. The mixed liquor must be pumped from the aeration basin into the clarifier to create a differential hydraulic head between the surface of the clarified liquor and the surface of the mixed liquor if gravity slow ox siphon flow are to operate without -the necessity for pumping the return sludge. Less liquid must be pumped, however, if the mixed liquor flows in by gravity and the sludge is returned by pump to the activated sludge treatment apparatus.
Pumped flow from the aeration basin to the clarifier is cons-quaintly unusual because it requires more power and because the forces generated by a high-speed pumping impeller tend to shear biological floes, causing sludge settle ability to be reduced.
Siphon flow has been used in clarifiers for many years.
US. Patent 3,494,462 describes a "partial siphon", operating within a circular clarifier having bottom scrapers, in which an air space is maintained above the liquid which is fed into the siphon from the rising pipe to the down pipe, whereby the settled sludge may be perfectly evacuated, especially when the siphon functions as a flow regulator.
A sludge removal system for a clarifier, formed as a rectangular tank and utilizing a plurality of siphons, is desk cried in US. Patent No. 3,333,704. The siphons are supported on a floating carriage. Each siphon comprises a depending pipe of inverted T-form having a horizontally disposed inlet lower branch, a horizontal pipe which is flow connected to the depending pipe, and a U-tube which is flow connected to the horizontal pipe and moves back and forth through a siphon outlet along one long side of the clarifier as the carriage is pulled back and forth within the tank.
Draft tube circulator/aerators have been employed in complete mix basins for several years. Often referred to as a submerged -turbine aerator of the axial flow type, a draft tune circulator/aerator has an up flow or downfall impeller which no-tales within a draft tube beneath an intake funnel or within the funnel itself. This impeller rotates at 90-100 rum so that it is a low-speed pump and causes little damage to biological floes.
The draft tube usually extends from several feet below the sun-face of the liquor to several feet above the bottom of the basin.
An aerating device termed an air spurge is disposed below the impeller and provides fine bubbles as the fast-flowing liquor shears the outgoing streams of air.
A pertinent characteristic of both the Love and the Stencil et at clarifiers is that they are integral clarifiers relying upon flowing currents of mixed liquor, which are rest pectively within an adjacent complete mix tank or oxidation ditch channel, for removing their settled sludges without using a sludge pump for this purpose. Such integral operation is possible because both clarifiers have openings in or near their bottoms which freely allow their sludges to move there through. The very practical disadvantage of bottom connections forming such combined systems is that the clarifier and the complete mix tank or the clarifier and the oxidation ditch must be drained together if any repairs are needed to either unit of the combined system. For example, an oxidation ditch having an average volume of 750,000 gallons would be operated in combination with a clarifier of 12~7~3 about 25,000 gallons; having to drain the clarifier for repairs would consequently create an enormous additional burden with respect to the oxidation ditch. Therefore, an integral clarifier that has sealed boundary surfaces is needed so that either unit can be drained separately.
~75~
STATEMENT OF THE INVENTION
A clarifier which is continuously operable without a pump in combination with a barrier oxidation ditch having an endless channel; a circulator/aerator assembly which is disk posed within the channel; an air spurge assembly; a down draft tube within which the assemblies are mounted; a discharge duct which is flow connected to the downdraft tube; and a barrier which is sealable disposed athwart the channel. The clarifier comprises a clarifier feed system which comprises means for intercepting a clarifier feed stream of mixed liquor as a portion of the flow being pumped past the barrier and for selectively receiving the pump head of at least the feed stream;
and means for conveying the feed stream, while substantially conserving the pump head, from the barrier oxidation ditch to the clarifier, whereby the surface of clarified liquor in the clarifier is continuously maintained at a higher level than the surface of liquor in the endless channel of the barrier oxidation ditch to create a differential hydraulic head there-between. The clarifier also comprises outlet means for disk charging clarified liquor from the clarifier; sludge recycle means for returning settled sludge from the clarifier to the endless channel; and means for sealable isolating the contents of the clarifier from the mixed liquor in the endless channel.
Another aspect of the invention comprises a process for continuously clarifying a portion of mixed liquor being aerobically treated in a barrier oxidation ditch by gravity settling the portion in a clarifier to produce clarified liquor and settled sludge without utilizing a pump for mixed liquor feed to the clarifier, clarified liquor outflow from the clarifier, or sludge return from the clarifier to the ditch.
The oxidation ditch comprises an endless channel containing the mixed liquor which is moving in circuit flow there through, a barrier sealable disposed athwart the endless channel to form an intake channel and a discharge channel, and a circulator/
aerator for aerating and pumping the mixed liquor from the intake channel to the discharge channel at high velocity. The process comprises locating at least one intake line for mixed liquor feed to the clarifier where the high velocity is available;
disposing the intake line so that high velocity liquor is intercepted and the pump head of the high velocity liquor is selectively received; and transferring the mixed liquor feed to the clarifier while conserving the pump head so that the surface of clarified liquor within the clarifier is higher than the surface of the mixed liquor within the endless channel, the contents of the clarifier being sealable isolated from the contents of the endless channel.
A further aspect of the present invention comprises a pimples clarifier which is sealable isolated from an activated sludge aeration basin, containing mixed liquor and having a circulator/aerator assembly which is operably mounted there-within and which pumps a flow of mixed liquor downwardly at high velocity within a draft tube. The pimples clarifier receives a portion of the mixed liquor from the draft tube and separates the portion into clarified liquor and settled sludge.
In addition, the pimples clarifier obtains energy for returning the settled sludge to the aeration basin, without use of a pump therefore from means for intercepting and receiving the portion in the form of the downwardly pumped mixed liquor and the associated pump head thereof within the draft tube; and means for conveying the feed stream and at least most of the pump head to the clarifier so that a differential hydraulic head is created within the clarifier, between the surface of clarified liquor within the clarifier and the surface of the mixed liquor within the aeration basin.
7S~83 BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a plan view of a barrier oxidation ditch comprising a rectangularly shaped clarifier which forms its barrier and is disposed in the upper part of its discharge channel. A liquor/air feed mixture is forced into intake pipes below the impeller and fed to the clarifier under sufficient positive pressure to maintain a differential hydraulic head between the level of liquor in the clarifier and in the return channel.
Figure 2 is a sectional elevation Al view of the same barrier oxidation ditch, looking in the direction of the arrows
Field of the Invention This invention relates to waste water treatment. The invention especially relates to methods and apparatuses for clarifying mixed liquor in activated sludge processes that are I
12~'~5~`3 conducted in oxidation ditches of racetrack or loop channel configuration or in conventional complete mix tanks.
Review of the Prior Art Oxidation ditches for continuous aerobic treatment of liquid waste waters have been used since the early 1950's. They were developed in Holland by or. If A. Pasveer, as a variation of the activated sludge process, and were patented in Dutch Patent No. 87,500 and British Patent No. 796,438.
artier oxidation ditches have been operating since 1977, primarily for treating municipal and poultry processing waste waters. Barrier oxidation ditches are described in US.
Patent No. 4,260,486 of John H. Reid. A barrier oxidation ditch comprises an endless channel, a barrier disposed athwart the channel, a vertically mounted pump having an impeller with-in a draft tube which it vertically mounted at the upstream side of the barrier, a J-shaped discharge duct which is flow-connected to the draft tube and is mounted below the bottom of the channel and below the barrier to provide a discharge on the downstream side thereof, and an aeration means which includes a spurge disposed beneath the impeller, and, if needed, diffusers which are removably mounted so that they introduce additional diffused air at about the bottom of the discharge duct. This barrier oxidation ditch, which pumps all of the circulating mixed liquor past the barrier, is herein described as a total barrier oxidation ditch.
It has further been ascertained that the barrier oxidation ditch of US. Patent 4,260,486 creates a differential hydraulic head that is readily measurable when the flow is being pumped through one or more draft tubes and discharge ducts, thereby indicating that there exists a dammed-up moment ~2~'75&3 tug in the mixed liquor which is approaching the barrier. It is important to release the energy contained in the dammed-up momentum.
An improved barrier oxidation ditch is disclosed in US. Patent No. 4,278,547 of John H. Reid. this ditch come proses a barrier having adjustable sized openings and/or gate-ways there through for conserving the momentum of the mixed liquor, a pump means for pumping most of the liquor past the barrier, and an aeration means for aerating the pumped liquor and for selectively aerating the induced-flow liquor passing through the openings so that there is no back mixing of aerated liquor and can be relatively little heterogeneous aeration when the aerated pumped liquor is blended downstream of the barrier, with the induced-flow liquor. This barrier oxidation ditch, which pumps a portion of the circulating mixed liquor past the barrier and provides openings for the remainder to move through the barrier, is herein described as a partial barrier oxidation ditch.
One of the major benefits of the barrier oxidation ditch of US. Patent 4,260,486 is that the spurge in the down-draft tube provides for introducing diffused air to the mixed liquor at a shallow depth, thereby forming an air-liquor mix-lure, and then for pumping this mixture downwardly with its impeller into the discharge duct to a sub-channel oxygen-trans-for depth, at the lowest portion of the discharge duct, that is well below the channel bottom. This oxygen-transfer depth increases the driving force for transferring oxygen molecules across the films at the gas- liquid interfaces, of the air bubbles. Other additional benefits of great practical import lance are: (1) the energy required for downwardly pumping the ~7~`3 air-liquor mixture is considerably less than the energy required for downwardly pumping the liquor alone and for spear-lately compressing air to the hydraulic pressure existing at the oxygen-transfer depth; and I a very high level of turbulence is provided in the oxygen-transfer zone, measured by brake horsepower/1000 ft.3.
For any aeration system used in transferring oxygen to a particular waste water, sewage, or mixed liquor, its oxygen transfer efficiency is a function of five major parameters:
bubble size, bubble retention time, driving force across the air-liquid interface for the dissolved oxygen, hydrostatic pressure, and degree of turbulence in the oxygen-transfer zone.
However, the adjustable gateways through the barrier of US. Patent 4,278,547 allow the induced-flow portion of the mixed liquor to pass through the barrier and be aerated at a depth above the channel bottom instead of at the sub-channel depth that is available within a discharge duct, thereby losing at least some of the advantages of retention time, driving force hydrostatic pressure, and possibly even turbulence.
US. Patent 4,455,232 of John H. Reid accordingly discloses a barrier Ed circulator/aerator in the endless channel of a barrier oxidation ditch which provides a directly pumped flow of mixed liquor into a central liquor inlet zone and an induced flow of mixed liquor into a surrounding liquor inlet zone at the inlet of a deep oxygen contact duct which passes beneath the barrier to the discharge channel on the downstream side thereof. It further provides mixing of diffused air with the directly pumped flow and/or the induced flow and then moving the combined air-liquor flows into the deepest portion of the contact duct where point-source pressurized aeration of both flows occurs. Eddy jet diffusers are preferably used for aerating the induced flow. Oxygen transfer efficiencies are obtained that are 1.6 to 2.2 times as great per brake horse-power per hour as that attainable by 100% pumping of the mixed liquor in a total barrier oxidation ditch, as disclosed in US. Patent 4,260,486.
Jo i - pa -~Z~75~33 This improved barrier oxidation ditch, however, compels 1~0% of the flow, both pumped and induced, to change direction 90 while moving downwardly and then to change direction 135 while moving beneath the barrier and upwardly. As is well known in hydraulic theory, such 225 of direction changing causes significant energy consumption. It would be desirable to provide a means for passing the liquor from the intake channel to the disk charge channel with minimum directional change.
When the air-liquor mixture has reached the lowest portion of the discharge duct, there is also very little time TV
able for oxygen transfer from bubble to liquor across -the films of the liquor-gas interface before the liquor/air mixture begins to rise. Ye, it is at this point in passage from the intake channel to the discharge channel that transfer efficiency is highest because of maximum hydrostatic pressure. Another factor of importance is that the microorganisms are in an oxygen-starved condition and avidly utilize the oxygen as fast as it transfers across the liquor-air films into the bulk liquor, so that the bulk liquor cannot become saturated if the LOSS content is reasonably high. An unusually large proportion of the oxygen in the bubbles is accordingly able to transfer across the films into the bulk liquor. It would accordingly be desirable to prolong the bubble retention time at the maximum depth.
However, simply lengthening the discharge duct, such as by thick-eying the barrier, tends to waste the available land area.
An elongated clarifier is described in US. Patent 3,788,477 of Love, for use alongside complete-mix tanks. As described in this patent, flow of sludge from the sloping bottom of the clarifier into the adjacent mixing basin is limited by flow control plates and is picked up inside the mixing basin by`
So the downward and inward flow of mixed liquor along -the sides and bottom of the mixing basin. Use of sludge return pumps can thereby be avoided.
This clarifier was installed alongside the discharge channel in several barrier oxidation ditches during 1979 and 1980.
However, in a barrier oxidation ditch, the flow is translational, not towardly as in the mixing basin of a complete-mix system. It was consequently discovered that the sludge did not adequately slide out into the discharge channel of a barrier oxidation ditch but had to be pumped out of the clarifier because the turbulent translational flow in the discharge channel created a positive pressure that interfered with automatic discharge of the sludge.
To about 1979, a brochure entitled "Lightning Treatment System" was published by Mixing equipment Co., Rochester, New York, which schematically showed the integral clarifier of US. Patent 3,788,477 disposed downstream of the circulator/aerator in a barrier oxidation ditch and also aligned transversely to the channel so that its upstream side formed the barrier and its down-stream or discharge side was athwart the channel and immediately upstream of the terminus of the discharge duct. Moreover, the length of the clarifier, as illustrated, was shorter than its width and was, in fact, the same as the width of the channel.
However, such an integral clarifier would, in most cases, be far too small to be combined with a barrier oxidation ditch.
If the size of the clarifier were to be increased by extending the discharge side or outer baffle to a location far down the discharge channel and past the end of the discharge duct, there would be such a pool of violently agitated air moving beneath the clarifier and boiling up past the sludge discharge space of the clarifier that its operation would be impossible. In addition to this discharging 12~5~3 difficulty, the bottom of this sideways-extended clarifier would have such a slight slope that settled sludge would not slide downwardly toward the discharge space, whereby its operation would be unsuccessful for this reason as well.
As disclosed in US. Patent 4,303,516 o-f Stencil e-t at, a rectangularly shaped clarifier is mounted in one or both chant nets of an oxidation ditch which has a Mechanical aerator at one end, as taught in US. Patent 3,510,110 of Klein. This clarifier has the same depth as the channel depth, but the channel bottom is excavated beneath the bottom of the clarifier to provide a sub-merged passage for the mixed liquor. The floor of the clarifier slopes toward the channel sidewall in one embodiment and term-notes in a stilling plate that is spaced upwardly from the sidewall to provide a sludge discharge space there between. In another embodiment, the floor is horizontally disposed as spaced-apart rectangular plates having rectangular ports there between which are athwart the channel, each rectangular port having a shallowly inclined plate along its upstream edge and a steeply inclined plate along its downstream edge. The velocity of the flowing waste water is increased as it passes beneath the plates so that sludge is drawn from the clarifier through the ports.
This Stencil et at clarifier might perform well if disposed.ln the return channel, opposite the barrier of a barrier oxidation ditch, or in its intake channel, but if disposed in its discharge channel and close to the barrier, the up rushing air from the discharge duct would enter the clarifier through the discharge ports of either embodiment and disastrously interfere with its operation.
SLY
Clarified liquor is typically and generally removed from clarifiers in activated sludge processes by gravity flow. Scum is almost invariably pumped from the scum trough. Settled sludge is removed from the clarifier and recycled to the activated sludge aeration basin by gravity flow fulled by pumping, by siphon flow followed by pumping, or by direct pumping. The mixed liquor must be pumped from the aeration basin into the clarifier to create a differential hydraulic head between the surface of the clarified liquor and the surface of the mixed liquor if gravity slow ox siphon flow are to operate without -the necessity for pumping the return sludge. Less liquid must be pumped, however, if the mixed liquor flows in by gravity and the sludge is returned by pump to the activated sludge treatment apparatus.
Pumped flow from the aeration basin to the clarifier is cons-quaintly unusual because it requires more power and because the forces generated by a high-speed pumping impeller tend to shear biological floes, causing sludge settle ability to be reduced.
Siphon flow has been used in clarifiers for many years.
US. Patent 3,494,462 describes a "partial siphon", operating within a circular clarifier having bottom scrapers, in which an air space is maintained above the liquid which is fed into the siphon from the rising pipe to the down pipe, whereby the settled sludge may be perfectly evacuated, especially when the siphon functions as a flow regulator.
A sludge removal system for a clarifier, formed as a rectangular tank and utilizing a plurality of siphons, is desk cried in US. Patent No. 3,333,704. The siphons are supported on a floating carriage. Each siphon comprises a depending pipe of inverted T-form having a horizontally disposed inlet lower branch, a horizontal pipe which is flow connected to the depending pipe, and a U-tube which is flow connected to the horizontal pipe and moves back and forth through a siphon outlet along one long side of the clarifier as the carriage is pulled back and forth within the tank.
Draft tube circulator/aerators have been employed in complete mix basins for several years. Often referred to as a submerged -turbine aerator of the axial flow type, a draft tune circulator/aerator has an up flow or downfall impeller which no-tales within a draft tube beneath an intake funnel or within the funnel itself. This impeller rotates at 90-100 rum so that it is a low-speed pump and causes little damage to biological floes.
The draft tube usually extends from several feet below the sun-face of the liquor to several feet above the bottom of the basin.
An aerating device termed an air spurge is disposed below the impeller and provides fine bubbles as the fast-flowing liquor shears the outgoing streams of air.
A pertinent characteristic of both the Love and the Stencil et at clarifiers is that they are integral clarifiers relying upon flowing currents of mixed liquor, which are rest pectively within an adjacent complete mix tank or oxidation ditch channel, for removing their settled sludges without using a sludge pump for this purpose. Such integral operation is possible because both clarifiers have openings in or near their bottoms which freely allow their sludges to move there through. The very practical disadvantage of bottom connections forming such combined systems is that the clarifier and the complete mix tank or the clarifier and the oxidation ditch must be drained together if any repairs are needed to either unit of the combined system. For example, an oxidation ditch having an average volume of 750,000 gallons would be operated in combination with a clarifier of 12~7~3 about 25,000 gallons; having to drain the clarifier for repairs would consequently create an enormous additional burden with respect to the oxidation ditch. Therefore, an integral clarifier that has sealed boundary surfaces is needed so that either unit can be drained separately.
~75~
STATEMENT OF THE INVENTION
A clarifier which is continuously operable without a pump in combination with a barrier oxidation ditch having an endless channel; a circulator/aerator assembly which is disk posed within the channel; an air spurge assembly; a down draft tube within which the assemblies are mounted; a discharge duct which is flow connected to the downdraft tube; and a barrier which is sealable disposed athwart the channel. The clarifier comprises a clarifier feed system which comprises means for intercepting a clarifier feed stream of mixed liquor as a portion of the flow being pumped past the barrier and for selectively receiving the pump head of at least the feed stream;
and means for conveying the feed stream, while substantially conserving the pump head, from the barrier oxidation ditch to the clarifier, whereby the surface of clarified liquor in the clarifier is continuously maintained at a higher level than the surface of liquor in the endless channel of the barrier oxidation ditch to create a differential hydraulic head there-between. The clarifier also comprises outlet means for disk charging clarified liquor from the clarifier; sludge recycle means for returning settled sludge from the clarifier to the endless channel; and means for sealable isolating the contents of the clarifier from the mixed liquor in the endless channel.
Another aspect of the invention comprises a process for continuously clarifying a portion of mixed liquor being aerobically treated in a barrier oxidation ditch by gravity settling the portion in a clarifier to produce clarified liquor and settled sludge without utilizing a pump for mixed liquor feed to the clarifier, clarified liquor outflow from the clarifier, or sludge return from the clarifier to the ditch.
The oxidation ditch comprises an endless channel containing the mixed liquor which is moving in circuit flow there through, a barrier sealable disposed athwart the endless channel to form an intake channel and a discharge channel, and a circulator/
aerator for aerating and pumping the mixed liquor from the intake channel to the discharge channel at high velocity. The process comprises locating at least one intake line for mixed liquor feed to the clarifier where the high velocity is available;
disposing the intake line so that high velocity liquor is intercepted and the pump head of the high velocity liquor is selectively received; and transferring the mixed liquor feed to the clarifier while conserving the pump head so that the surface of clarified liquor within the clarifier is higher than the surface of the mixed liquor within the endless channel, the contents of the clarifier being sealable isolated from the contents of the endless channel.
A further aspect of the present invention comprises a pimples clarifier which is sealable isolated from an activated sludge aeration basin, containing mixed liquor and having a circulator/aerator assembly which is operably mounted there-within and which pumps a flow of mixed liquor downwardly at high velocity within a draft tube. The pimples clarifier receives a portion of the mixed liquor from the draft tube and separates the portion into clarified liquor and settled sludge.
In addition, the pimples clarifier obtains energy for returning the settled sludge to the aeration basin, without use of a pump therefore from means for intercepting and receiving the portion in the form of the downwardly pumped mixed liquor and the associated pump head thereof within the draft tube; and means for conveying the feed stream and at least most of the pump head to the clarifier so that a differential hydraulic head is created within the clarifier, between the surface of clarified liquor within the clarifier and the surface of the mixed liquor within the aeration basin.
7S~83 BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a plan view of a barrier oxidation ditch comprising a rectangularly shaped clarifier which forms its barrier and is disposed in the upper part of its discharge channel. A liquor/air feed mixture is forced into intake pipes below the impeller and fed to the clarifier under sufficient positive pressure to maintain a differential hydraulic head between the level of liquor in the clarifier and in the return channel.
Figure 2 is a sectional elevation Al view of the same barrier oxidation ditch, looking in the direction of the arrows
2-2 in Figure 1, which shows the feeding and discharging devices for the clarifier.
Figure 3 is a partial elevation Al view of a siphon header, looking in the direction of the arrows 3-3 in Figure 2.
Figure 4 is a sectional elevation Al view of a barrier oxidation ditch, having a relatively deep clarifier forming its barrier and occupying the upper portion of its discharge channel.
A feed mixture of liquor and air are guided into an intake tube in the initial portion of its discharge duct and fed into the front edge of the clarifier. The sludge return is also fed into the intake funnel, close to the hub of the impeller.
Figure 5 is a sectional view, looking in the direction of the arrows 5-5 in Figure 4, through the intake tube.
Figure 6 is a plan view of the intake channel, circulator/aerator, clarifier, and terminal portion of the disk charge channel for the barrier oxidation ditch seen in Figure 4, AL_ _ Figure 7 is a sectional view of a portion of the baffler oxidation ditch and the clarifier of Figures 4-6 with a different embodiment of the mixed liquor intake in which an intake tube intercepts well-aerated mixed liquor at the downstream end of the clarifier.
Figure 8 is a plan view of a barrier oxidation ditch and of a rectangular clarifier which is alongside its discharge chant not. The clarifier is fed by intake tubes within the downdraft tube so that it has a positive differential head. Its return sludge is discharged by siphon flow to the discharge channel of the barrier oxidation ditch.
Figure 9 is a plan view of a circular barrier oxidation ditch and a center-feed circular clarifier, in combination.
Figure 10 is a sectional elevation Al view of the ditch and clarifier of Figure 9, looking in the direction of the arrows 10-10 in Figure 9.
Figure 11 is a plan view of a circular barrier oxidation ditch and a pexipheral-feed circular clarifier, in combination.
Figure 12 is a sectional elevation Al view of the clarifier shown in Figure 11, looking in the direction of the arrows 11-11 in Figure 11.
Figure 13 is a plan view of a complete mix tank and of an adjoining integral clarifier.
Figure 14 is a sectional elevation Al view of the come plate mix tank and clarifier of Figure 13.
Figure 15 is a graph showing the effect of siphon head upon clarifier intake flow rate and upon sludge return flow rate.
Figure 16 is a small schematic plan view of a barrier oxidation ditch and of an integral clarifier within its discharge channel in which the various flows, Q, into and out of the ditch and clarifier are identified.
_ I_ ~2~75~3 DESCRIPTION OF TOE PREFERRED EMBODIMENTS
The barrier oxidation ditch 10 seen in Figures 1-3 comprises an endless channel, a circulator/aerator assembly 20, an air spurge assembly 30, a discharge duct 40, and an in-channel clarifier 60. The endless channel is defined by outer side 11 and central partition 13. One straight portion of this endless channel is return channel 19. In the other straight portion of the endless channel, between central partition 13 and one straight side 11, is pimples in-channel clarifier 60. Its upstream wall 61 is also the barrier which separates this portion of the endless channel into an intake channel 16 and a discharge channel 18.
End baffles 15 face each end of central partition 13 in order to guide the pumped mixed liquor around the ends of the endless channel.
Circulator/aerator 20 is mounted in the bottom of intake channel 16 and comprises a motor and reduction gear 21, a shaft 23 which is rigidly connected at its upper end to the reduction gear, an impeller 24 which is rigidly attached to the lower end of shaft 23, a funnel 25 within which impeller 24 rotates, a downdraft tube 26 which is attached to the lower end of funnel 25, a walkway 27 which surrounds motor and reduction gear 21, and vortex-controlling vanes 29 which are attached, top and bottom, respectively, to walkway 27 and funnel 25.
Air spurge assembly 30 comprises an air spurge feed line 31, an air header 33, a spurge ring 35, and spurge fingers 37 from which air emerges to become sheared by the down rushing liquor to form air bubbles.
Discharge duct 40 comprises an upstream wall 41, a bottom 43, a horizontal barrier 45 surrounding downdraft tube 26, _ _ ~217515 3 and a discharge ramp 49. The portion beneath horizontal barrier 45 is a turbulence zone in which intense mixing occurs.
The flow of liquor through the endless channel is thus-treated by translational flow 51 in intake channel 16, flow 53 toward the intake of funnel 25, downward flow 55 from downdraft tube 26, translational flow 56 beneath clarifier 60, upward flow 57 over ramp 49, translational flow 58 in discharge channel 18, and translational return flow 59 in return channel 19.
Clarifier 60 comprises upstream wall 61 which also functions as the barrier in the endless channel, bottom 63 which also functions as the ceiling for the portion of discharge duct I through which translational flow 56 moves, downstream wall 67, clarifier feed system 70, traveling siphon mechanism 80, and clarified liquor withdrawal system 90. The clarified liquor has a surface 66.
Clarifier feed system 70 comprises upwardly curved intakes 71 for a liquor/air mixture within downdraft tube 26, feed lines 73, valves 75, valve handles 77, discharges 78, and an optional transversely disposed baffle 79. Intakes 71 may be equipped with small funnels to decrease entrance losses as the liquor and air move into line 73, but valve handles 77 (controlled by the operator) are the means of establishing a selected flow rate through valves 75 that will create the desired differential hydraulic head 69 that siphon mechanism 80 needs to provide the required sludge return flow rate, according to experience.
Within the endless channel, low liquor level 12, high liquor level 14, and average liquor level 17 within the channel 18 become slightly lower at about the mid-length of return channel 19 and even lower in intake channel 16. However, the decrease in head, from discharge channel 18 to intake channel 16, is slight enough to be ignored for the purposes of this invention.
. Jo , Tao ~Z:~75~3 Traveling bridge siphon mechanism 80 comprises sludge pick-up hydrous for the sludge at the bottom of clarifier 60, sludge siphon and return Lyons, sludge discharge siphons into return channel 19, floating skimmer 84, scum outlet 86, scum trough 87 to receive scum from outlet 86, traveling bridge and motor 88, and rails 89 which mechanism 80 travels longitudinally of clarifier 60. Headers 81 have a plurality of suction holds aye for the inflowinq settled sludge.
Clarified liquor system 90 comprises submerged orifice Decker lines 91, and an effluent rate-of-flow device and valve 93. The clarified liquor then generally flows to a disinfection system, a post-aeration system, and to a final discharge point.
Clarifier 60 is a self-regulating and functioning system Its feed is obtained through liquor intakes 71 which may each be equipped with intake funnels for interrupting down flowing mixed liquor and air bubbles and receiving the pump head thereof for increasing the intake pressure and consequently the flow rate.
The total available pump head is a function of the elevation from intakes 71 to low liquor level (OWL) 12, high liquor level (HOWL) 14, or average liquor level (AWL) 17 plus the pump head generated by the circulator/aerator and the flowing liquor/air mixture.
However, the elevation head is small in comparison to the pump headland the differential hydraulic head between OWL 12 and HOWL
14 can be neglected; i.e., for practical purposes, the pump head upon the liquor/air mixture entering intakes 71 is a constant Because scum outlet 86 and clarified liquor discharge 95 are gravity discharge devices, whereas sludge return 82 is a siphon device, low clarified liquor level 62, high liquor level 64, and average liquor level 66 within clarifier 70 are always higher by a OH 69 than corresponding low mixed liquor level 12, high liquor level 14, and average liquor level 17 within the intake channel, as seen Jo _ _ ~7S~3 in Figure 2. The critical differential hydraulic head for siphon activity affecting sludge discharge siphon 33 is the difference between the liquor level within clarifier 60 and the liquor level within return channel 19 which is always slightly greater than the level 12, 14, 17 within intake channel 16. This critical head is here-inciter identified as the siphon delivery head and is to be understood as represented by ah 69.
When, for example, the liquor level in -the endless channel of barrier oxidation ditch 10 is rising, as from OWL 12 to HOWL 14, OH 69 becomes smaller because the delivery rate through intakes 71, 73, 78 into clarifier 60 is substantially constant.
However, a smaller OH 69 causes the sludge delivery rate to decrease while the scum removal rate and the clarified liquor delivery rate remain substantially constant. The result is that OWL 62 also rises toward HOWL 64 while lagging behind the rise in intake channel 16 so that the sludge return rate through sludge return pipes 83 remains less than normal until HI 64 is reached.
At this level, the sludge return rate rises to the normal value, maintaining HOWL 64 constant until HOWL 14 begins to decrease again.
While HOWL 14 is decreasing toward OWL 12, HOWL 64 is decreasing toward OWL 62 but again lagging behind the fall in intake channel 16 so that the sludge return rate remains greater than normal until the water level again remains stable, such as at AWL 17.
The barrier oxidation ditch shown in Figures uses the pump head of the liquor/air mixture within its draft tube for producing a positive differential hydraulic head within the clarifier and for withdrawing its return sludge by suction as well as by gravity. A siphoning system, such as mechanism 80 in Figures 1-3, is not shown but can be used in the clarifier.
so Ditch 100 comprises sides 101 of its endless channel, a central partition 103, end baffles 105, a circulator/aerator assembly 110, an air spurge assembly 120, a discharge duct 130, and a clarifier 140.
Circulator/aerator assembly 110 comprises a motor/reduoer 111, a shaft 113, a funnel 115, a down-flow draft tube 116, and vanes 119. Air spurge assembly 120 comprises an air spurge feed line 121 and an air header 123. Discharge duct 130 comprises a 90 portion 133 which is flow connected to down-draft tube 116, a horizontal portion 136 beneath clarifier 140, and an ascending portion 138 which is connected to horizontal portion 136 along line 137 and intersects the bottom of discharge channel 108 along line 139, as seen in Figure 6. Portions 136 and 138 are prefer-ably as wide as the channel and clarifier 140.
Clarifier 140 comprises an upstream wall 141 which also functions as the banner across the channel, a horizontally disposed bottom 143, side walls 145, and a downstream wall 147.
The clarified liquor has an average level 146 that creates a H
149 with average mixed liquor level 107. The liquor intake system comprises a liquor inlet duct 151, attached to the inner surface of curved discharge duct 133, which is connected to the vertical flow space between wall 141 and vertically disposed liquor intake baffle 153 at the upstream end of clarifier 140.
Sludge return line 158, from the siphon system which is shown in the drawings or alternatively from a multi-inlet gravity sludge system, is connected to a sludge trough which runs along one side of clarifier 140, as seen in Figure 6. Line 158 is controlled by valve handles 157 from the walkway (also not shown in Figures 3 and 6) before emptying into approximately the center of funnel 115 where the swirling forces generated by the impeller create suction forces on sludge I
outlets 159 which assist in movement of the settled sludge from the bottom portion of clarifier 140.
A conventional clarified liquor outlet or effluent launder 155 is at the far end of clarifier 14~, alongside down-stream wall 147, for discharging the clarified liquor. A scum skimmer is not shown in Figures 4-6.
The flow pattern in barrier oxidation ditch 100 is shown by flow vectors 125 and 126 in intake channel 125, flow vector 127 to represent the downwardly pumped liquor/air mixture from downdraft tube 116, flow vector 128 to represent the liquor/air mixture being discharged from discharge duct 130, and flow vector 129 to represent the aerated mixed liquor in discharge channel 108. The liquor/air mixture entering inlet duct 151 flows into clarifier 140 as shown by flow vector 152. The elan-fled liquor outflow from launder 155 is represented by flow vector 156 in Figure 6.
The mixed liquor intake for a clarifier operated in combination with a barrier oxidation ditch can be located anywhere that high velocity is available from the action of the impeller.
Such high velocity is available from within the intake funnel to the exit end of the discharge duct. However, it is preferred that the mixed liquor be admixed with an oxygen-containing gas, such as air, before it enters the clarifier intake in order to maximize the concentration of dissolved oxygen in the intake liquor to the clarifier. Accordingly, the intake location within the draft tube, as seen in Figure 4, is often preferable.
The terminal location for the liquor intake which is shown in Figure 7 is accordingly highly preferred in many situp-lions because the liquor and the air bubbles have been in contact for almost the entire time that is available within discharge duct _ _ 5l~3 130, yet the aerated liquor is moving at high speed and even accelerating while up rushing over ascending bottom 138. Liquor intake system 160 for clarifier 140' within barrier oxidation ditch 100 comprises at least one intake tube 161 having an intake end 163, a discharge end 164, a control valve 165, and a control handle 167 which is operable from a walkway not shown in the drawings. In flowing liquor is guided and turbulence is minimized within clarifier 140' by optional baffle plate 169. The liquor outlet line is located along the upstream wall.
The alongside-channel embodiment illustrated in Figure 8 has been in operation in several locations except for its liquor intake system. Barrier oxidation ditch 170 comprises sides 171 of its endless channel, a central partition 173, a barrier 174 which is sealable disposed athwart the channel, a pair of end baffles 175, an intake channel 176, a discharge channel 178, a return channel 179, a circulator/aerator assembly 180, and a clarifier 190.
Circulator/aerator assembly 180 comprises a Tory 181, a funnel 185, a downdraft tube 186, and a walkway 187. An air spurge assembly is shown and is to be understood as being of conventional construction.
Clarifier 190 comprises an upstream wall 191, a side wall 195 (the outer side wall is formed by side 171), a downstream wall 197, a traveling bridge sludge siphon mechanism 198, clarified liquor lines 201, a scum trough 202, feed lines 203 for the mixed liquor/air intake mixture, and an intake baffle 209.
Sludge discharge 199 is into discharge channel 178. Control valves 205 are used to set the flow of liquor/air mixture from downdraft tube 186.
/
-- I --75~3 The combination of circular barrier oxidation ditch 210 and circular clarifier 230 which is shown in Figures 9 and 10 permits both to operate with no other power devises than the motors for the impeller and the sludge siphon arm and the blower for the compressed air, because gravity or siphon devices can propel the clarified liquor and sludge A conventional scum trough (not shown in Figures 9 and 10) can be installed on -the surface of clarifier 230 for capturing floating scum or it can be installed along the inner surface of side 213.
Circular barrier oxidation ditch 21n, as seen in Figures 9 and 10, comprises an outer cylindrical side 211, a middle cylindrical side 212, an inner cylindrical or clarifier side 213, a bottom 217, grouted slopes 215, a circulator/aerator assembly 220, and a clarifier 230. Circulator/aerator assembly 220 c~nprises a motor 221, a shaft 223, a funnel 225, a downdraft tube Tao a discharge duct 227 which is flow connected to tube 226, an air supply line 222, and an air header 224.
Clarifier 230 comprises a clarifier feed or intake line 231 for the liquor/air mixture, a feed riser 232, a clarifies center feed well 233, a sludge siphon arm 234, a sludge return line 235, a cylindrical scum baffle 236, an effluent whir trough 237, a clarified liquor discharge line 238, and a bottom 239.
Clarified liquor surface 228 is higher by differential hydraulic head ( OH) 229 than mixed liquor surface 214 in return channel 219. Return channel 219 includes at least the second half of the outer channel and at least the first half of the inner channel.
The sludge discharges from siphon line 235 into return channel 219 where the liquor is in an anoxic state and ready for denitrification.
~7~3 Vector 241 denotes flow into circulator/aerator 220, and vector 242 denotes flow from discharge duct 227 and through discharge channel 218. Vector 243 shows flow through the outer channel, and vector 244 indicates flow from the outer channel to the inner channel. Vector 245 indicates flow through the inner channel.
Vector 246 shows the discharge of the mixture of mixed liquor and air through line 23] and from clarifier feed well 233 into clarifier 230. Vector 247 indicates -the flow of clarified liquor through line 236. Vector 248 shows the intake of settled sludge from the sludge blanket into sludge siphon arm 234 and then into siphon line 235, and vector 249 indicates its flow through line 235 and discharge into return channel 219.
The circular barrier oxidation ditch shown in Figures 11 and 12 is built around a circular clarifier having a sludge return system which is operated by gravity flow instead of by siphon flow, as in Figures 9 and 10. Barrier oxidation ditch aye in Figures 11 and 12 is exactly like ditch 210 in Figures 9 and 10, and its parts, vectors, and the like bear the same numbers. The only significant difference is that circulator/
aerator assembly aye comprises a longer draft tube aye than draft tube 220 as seen in Figure 10 so that its funnel aye is higher than funnel 225 in Figure 10.
Moreover, clarifier 250 of Figures 11 and 12 is very similar to clarifier 230 of Figures 9 and 10 except that it has a peripheral feed system, in contrast to the central feed system of clarifier 230, and a gravity return system for its settled sludge. Both clarifiers 230, 250 also have a peripheral effluent trough for collecting the clarified liquor.
-- I --5~3 Clarifier 250 comprises a pair o-f very short clarifier intake or feed lines 251, a peripheral in fluent trough 252, a center post 253, a revolvable sludge siphon arm 25~, a motor aye for driving arm 254 which is mounted atop post 253, a sludge return line 255, a scum baffle 256, a peripheral effluent trough 257, an effluent discharge line 258, and a bottom 259.
Pipes 251 lead from draft tube aye to and through wall 213 and into the bottom of inhalant trough 252 which has closely spaced outlet holes or parts aye in its bottom through-out its circular length, as seen in Figure 11. Vector 265 accordingly indicates the flow of a mixed liquor/air mixture through lines 251 into trough 252, and flow arrow 266 indicates downward flow from the plurality of ports aye. Vector 267 indicates the flow of clarified liquor through line 258. Vector 268 indicates the flow of settled sludge through siphon arm 254 and then through and out of line 255.
The clarified liquor has a surface 228 which is higher by differential head aye than surface 214 of the translational flowing mixed liquor in return channel 219. This differential head can be designated as Ha, the head needed for gravity or siphon operation of clarifier 250.
Figures 13 and 14 show a complete mix tank 270 and a clarifier 290 in adjoining relationship. Clarifier 290 is operable without a pump by using a portion of the pump heads available from two of its circulator/aerator assemblies 290 for creating a differential hydraulic head between the surface of its clarified liquor and the surface of the agitated mixed liquor in tank 270.
: I
Jo ~Z~S83 Complete mix tank 270 yin figures 13 and 14 comprises an outer wall 271, end walls 272, a bottom 273, and a plurality of draft tube circulator/aerator assemblies 280. Each circulator, aerator assembly 280 comprises a motor/gear reducer 281, a shaft 283, a funnel 284, a draft tube 285 which is flow connected to funnel 284, and an impeller 286 which rotates within draft tube 285 and is attached to the lower end of shaft 283.
Vector 275 shows the flow of liquor into funnel 284, and vector 276 indicates the downward discharge of liquor and air from draft tube 285. the mixed liquor has a generally turbulent surface 276.
Clarifier 290, adjoining complete mix tank 270 in Figures 13 and 14, comprises an outer wall 291, end walls 292, a bottom 293, a common wall 294 with tank 270, a scum baffle 295 near wall 291, an effluent overflow trough 296 adjacent wall 291, a scum trough 237 near wall 294, and an in fluent baffle 298 which is near wall 294 and supports trough 297. The clarified liquor has a surface 299 which is higher than surface 279 by differential head (I Ho which is visible but not labeled in Figure 14.
Mixed liquor and its associated pump head are fed through intake lines 301 and valves with handles 302 to and through wall 294 to discharge into the stilling space provided by infinity baffle 298. Floating skimmer 303 collects scum which is passed through scum pipe 308 to scum trough 2970 Siphon sludge pickup header 304, which is moved back and forth by motor 307 on traveling bridge pickup mechanism 306, removes sludge from bottom 293. The sludge is then siphoned through line 305 into tank 270.
-~2g--lZ17S~3 The following design example refers to the combination of the clarifier and the barrier oxidation ditch shown in Figures 1 and 2:
DESIGN EXAMPLE
A. SEMITONES
1. Average Daily Flow = 1.0 Million Gallons per Day (MUD);
Minimum 3 Hour Flow = 0.33 MUD;
Peak 3 Hour Flow = 2.0 MUD
2. In fluent BUD = 206 Mel = 1720 pounds of biochemical oxygen demand per day (#Budded)
Figure 3 is a partial elevation Al view of a siphon header, looking in the direction of the arrows 3-3 in Figure 2.
Figure 4 is a sectional elevation Al view of a barrier oxidation ditch, having a relatively deep clarifier forming its barrier and occupying the upper portion of its discharge channel.
A feed mixture of liquor and air are guided into an intake tube in the initial portion of its discharge duct and fed into the front edge of the clarifier. The sludge return is also fed into the intake funnel, close to the hub of the impeller.
Figure 5 is a sectional view, looking in the direction of the arrows 5-5 in Figure 4, through the intake tube.
Figure 6 is a plan view of the intake channel, circulator/aerator, clarifier, and terminal portion of the disk charge channel for the barrier oxidation ditch seen in Figure 4, AL_ _ Figure 7 is a sectional view of a portion of the baffler oxidation ditch and the clarifier of Figures 4-6 with a different embodiment of the mixed liquor intake in which an intake tube intercepts well-aerated mixed liquor at the downstream end of the clarifier.
Figure 8 is a plan view of a barrier oxidation ditch and of a rectangular clarifier which is alongside its discharge chant not. The clarifier is fed by intake tubes within the downdraft tube so that it has a positive differential head. Its return sludge is discharged by siphon flow to the discharge channel of the barrier oxidation ditch.
Figure 9 is a plan view of a circular barrier oxidation ditch and a center-feed circular clarifier, in combination.
Figure 10 is a sectional elevation Al view of the ditch and clarifier of Figure 9, looking in the direction of the arrows 10-10 in Figure 9.
Figure 11 is a plan view of a circular barrier oxidation ditch and a pexipheral-feed circular clarifier, in combination.
Figure 12 is a sectional elevation Al view of the clarifier shown in Figure 11, looking in the direction of the arrows 11-11 in Figure 11.
Figure 13 is a plan view of a complete mix tank and of an adjoining integral clarifier.
Figure 14 is a sectional elevation Al view of the come plate mix tank and clarifier of Figure 13.
Figure 15 is a graph showing the effect of siphon head upon clarifier intake flow rate and upon sludge return flow rate.
Figure 16 is a small schematic plan view of a barrier oxidation ditch and of an integral clarifier within its discharge channel in which the various flows, Q, into and out of the ditch and clarifier are identified.
_ I_ ~2~75~3 DESCRIPTION OF TOE PREFERRED EMBODIMENTS
The barrier oxidation ditch 10 seen in Figures 1-3 comprises an endless channel, a circulator/aerator assembly 20, an air spurge assembly 30, a discharge duct 40, and an in-channel clarifier 60. The endless channel is defined by outer side 11 and central partition 13. One straight portion of this endless channel is return channel 19. In the other straight portion of the endless channel, between central partition 13 and one straight side 11, is pimples in-channel clarifier 60. Its upstream wall 61 is also the barrier which separates this portion of the endless channel into an intake channel 16 and a discharge channel 18.
End baffles 15 face each end of central partition 13 in order to guide the pumped mixed liquor around the ends of the endless channel.
Circulator/aerator 20 is mounted in the bottom of intake channel 16 and comprises a motor and reduction gear 21, a shaft 23 which is rigidly connected at its upper end to the reduction gear, an impeller 24 which is rigidly attached to the lower end of shaft 23, a funnel 25 within which impeller 24 rotates, a downdraft tube 26 which is attached to the lower end of funnel 25, a walkway 27 which surrounds motor and reduction gear 21, and vortex-controlling vanes 29 which are attached, top and bottom, respectively, to walkway 27 and funnel 25.
Air spurge assembly 30 comprises an air spurge feed line 31, an air header 33, a spurge ring 35, and spurge fingers 37 from which air emerges to become sheared by the down rushing liquor to form air bubbles.
Discharge duct 40 comprises an upstream wall 41, a bottom 43, a horizontal barrier 45 surrounding downdraft tube 26, _ _ ~217515 3 and a discharge ramp 49. The portion beneath horizontal barrier 45 is a turbulence zone in which intense mixing occurs.
The flow of liquor through the endless channel is thus-treated by translational flow 51 in intake channel 16, flow 53 toward the intake of funnel 25, downward flow 55 from downdraft tube 26, translational flow 56 beneath clarifier 60, upward flow 57 over ramp 49, translational flow 58 in discharge channel 18, and translational return flow 59 in return channel 19.
Clarifier 60 comprises upstream wall 61 which also functions as the barrier in the endless channel, bottom 63 which also functions as the ceiling for the portion of discharge duct I through which translational flow 56 moves, downstream wall 67, clarifier feed system 70, traveling siphon mechanism 80, and clarified liquor withdrawal system 90. The clarified liquor has a surface 66.
Clarifier feed system 70 comprises upwardly curved intakes 71 for a liquor/air mixture within downdraft tube 26, feed lines 73, valves 75, valve handles 77, discharges 78, and an optional transversely disposed baffle 79. Intakes 71 may be equipped with small funnels to decrease entrance losses as the liquor and air move into line 73, but valve handles 77 (controlled by the operator) are the means of establishing a selected flow rate through valves 75 that will create the desired differential hydraulic head 69 that siphon mechanism 80 needs to provide the required sludge return flow rate, according to experience.
Within the endless channel, low liquor level 12, high liquor level 14, and average liquor level 17 within the channel 18 become slightly lower at about the mid-length of return channel 19 and even lower in intake channel 16. However, the decrease in head, from discharge channel 18 to intake channel 16, is slight enough to be ignored for the purposes of this invention.
. Jo , Tao ~Z:~75~3 Traveling bridge siphon mechanism 80 comprises sludge pick-up hydrous for the sludge at the bottom of clarifier 60, sludge siphon and return Lyons, sludge discharge siphons into return channel 19, floating skimmer 84, scum outlet 86, scum trough 87 to receive scum from outlet 86, traveling bridge and motor 88, and rails 89 which mechanism 80 travels longitudinally of clarifier 60. Headers 81 have a plurality of suction holds aye for the inflowinq settled sludge.
Clarified liquor system 90 comprises submerged orifice Decker lines 91, and an effluent rate-of-flow device and valve 93. The clarified liquor then generally flows to a disinfection system, a post-aeration system, and to a final discharge point.
Clarifier 60 is a self-regulating and functioning system Its feed is obtained through liquor intakes 71 which may each be equipped with intake funnels for interrupting down flowing mixed liquor and air bubbles and receiving the pump head thereof for increasing the intake pressure and consequently the flow rate.
The total available pump head is a function of the elevation from intakes 71 to low liquor level (OWL) 12, high liquor level (HOWL) 14, or average liquor level (AWL) 17 plus the pump head generated by the circulator/aerator and the flowing liquor/air mixture.
However, the elevation head is small in comparison to the pump headland the differential hydraulic head between OWL 12 and HOWL
14 can be neglected; i.e., for practical purposes, the pump head upon the liquor/air mixture entering intakes 71 is a constant Because scum outlet 86 and clarified liquor discharge 95 are gravity discharge devices, whereas sludge return 82 is a siphon device, low clarified liquor level 62, high liquor level 64, and average liquor level 66 within clarifier 70 are always higher by a OH 69 than corresponding low mixed liquor level 12, high liquor level 14, and average liquor level 17 within the intake channel, as seen Jo _ _ ~7S~3 in Figure 2. The critical differential hydraulic head for siphon activity affecting sludge discharge siphon 33 is the difference between the liquor level within clarifier 60 and the liquor level within return channel 19 which is always slightly greater than the level 12, 14, 17 within intake channel 16. This critical head is here-inciter identified as the siphon delivery head and is to be understood as represented by ah 69.
When, for example, the liquor level in -the endless channel of barrier oxidation ditch 10 is rising, as from OWL 12 to HOWL 14, OH 69 becomes smaller because the delivery rate through intakes 71, 73, 78 into clarifier 60 is substantially constant.
However, a smaller OH 69 causes the sludge delivery rate to decrease while the scum removal rate and the clarified liquor delivery rate remain substantially constant. The result is that OWL 62 also rises toward HOWL 64 while lagging behind the rise in intake channel 16 so that the sludge return rate through sludge return pipes 83 remains less than normal until HI 64 is reached.
At this level, the sludge return rate rises to the normal value, maintaining HOWL 64 constant until HOWL 14 begins to decrease again.
While HOWL 14 is decreasing toward OWL 12, HOWL 64 is decreasing toward OWL 62 but again lagging behind the fall in intake channel 16 so that the sludge return rate remains greater than normal until the water level again remains stable, such as at AWL 17.
The barrier oxidation ditch shown in Figures uses the pump head of the liquor/air mixture within its draft tube for producing a positive differential hydraulic head within the clarifier and for withdrawing its return sludge by suction as well as by gravity. A siphoning system, such as mechanism 80 in Figures 1-3, is not shown but can be used in the clarifier.
so Ditch 100 comprises sides 101 of its endless channel, a central partition 103, end baffles 105, a circulator/aerator assembly 110, an air spurge assembly 120, a discharge duct 130, and a clarifier 140.
Circulator/aerator assembly 110 comprises a motor/reduoer 111, a shaft 113, a funnel 115, a down-flow draft tube 116, and vanes 119. Air spurge assembly 120 comprises an air spurge feed line 121 and an air header 123. Discharge duct 130 comprises a 90 portion 133 which is flow connected to down-draft tube 116, a horizontal portion 136 beneath clarifier 140, and an ascending portion 138 which is connected to horizontal portion 136 along line 137 and intersects the bottom of discharge channel 108 along line 139, as seen in Figure 6. Portions 136 and 138 are prefer-ably as wide as the channel and clarifier 140.
Clarifier 140 comprises an upstream wall 141 which also functions as the banner across the channel, a horizontally disposed bottom 143, side walls 145, and a downstream wall 147.
The clarified liquor has an average level 146 that creates a H
149 with average mixed liquor level 107. The liquor intake system comprises a liquor inlet duct 151, attached to the inner surface of curved discharge duct 133, which is connected to the vertical flow space between wall 141 and vertically disposed liquor intake baffle 153 at the upstream end of clarifier 140.
Sludge return line 158, from the siphon system which is shown in the drawings or alternatively from a multi-inlet gravity sludge system, is connected to a sludge trough which runs along one side of clarifier 140, as seen in Figure 6. Line 158 is controlled by valve handles 157 from the walkway (also not shown in Figures 3 and 6) before emptying into approximately the center of funnel 115 where the swirling forces generated by the impeller create suction forces on sludge I
outlets 159 which assist in movement of the settled sludge from the bottom portion of clarifier 140.
A conventional clarified liquor outlet or effluent launder 155 is at the far end of clarifier 14~, alongside down-stream wall 147, for discharging the clarified liquor. A scum skimmer is not shown in Figures 4-6.
The flow pattern in barrier oxidation ditch 100 is shown by flow vectors 125 and 126 in intake channel 125, flow vector 127 to represent the downwardly pumped liquor/air mixture from downdraft tube 116, flow vector 128 to represent the liquor/air mixture being discharged from discharge duct 130, and flow vector 129 to represent the aerated mixed liquor in discharge channel 108. The liquor/air mixture entering inlet duct 151 flows into clarifier 140 as shown by flow vector 152. The elan-fled liquor outflow from launder 155 is represented by flow vector 156 in Figure 6.
The mixed liquor intake for a clarifier operated in combination with a barrier oxidation ditch can be located anywhere that high velocity is available from the action of the impeller.
Such high velocity is available from within the intake funnel to the exit end of the discharge duct. However, it is preferred that the mixed liquor be admixed with an oxygen-containing gas, such as air, before it enters the clarifier intake in order to maximize the concentration of dissolved oxygen in the intake liquor to the clarifier. Accordingly, the intake location within the draft tube, as seen in Figure 4, is often preferable.
The terminal location for the liquor intake which is shown in Figure 7 is accordingly highly preferred in many situp-lions because the liquor and the air bubbles have been in contact for almost the entire time that is available within discharge duct _ _ 5l~3 130, yet the aerated liquor is moving at high speed and even accelerating while up rushing over ascending bottom 138. Liquor intake system 160 for clarifier 140' within barrier oxidation ditch 100 comprises at least one intake tube 161 having an intake end 163, a discharge end 164, a control valve 165, and a control handle 167 which is operable from a walkway not shown in the drawings. In flowing liquor is guided and turbulence is minimized within clarifier 140' by optional baffle plate 169. The liquor outlet line is located along the upstream wall.
The alongside-channel embodiment illustrated in Figure 8 has been in operation in several locations except for its liquor intake system. Barrier oxidation ditch 170 comprises sides 171 of its endless channel, a central partition 173, a barrier 174 which is sealable disposed athwart the channel, a pair of end baffles 175, an intake channel 176, a discharge channel 178, a return channel 179, a circulator/aerator assembly 180, and a clarifier 190.
Circulator/aerator assembly 180 comprises a Tory 181, a funnel 185, a downdraft tube 186, and a walkway 187. An air spurge assembly is shown and is to be understood as being of conventional construction.
Clarifier 190 comprises an upstream wall 191, a side wall 195 (the outer side wall is formed by side 171), a downstream wall 197, a traveling bridge sludge siphon mechanism 198, clarified liquor lines 201, a scum trough 202, feed lines 203 for the mixed liquor/air intake mixture, and an intake baffle 209.
Sludge discharge 199 is into discharge channel 178. Control valves 205 are used to set the flow of liquor/air mixture from downdraft tube 186.
/
-- I --75~3 The combination of circular barrier oxidation ditch 210 and circular clarifier 230 which is shown in Figures 9 and 10 permits both to operate with no other power devises than the motors for the impeller and the sludge siphon arm and the blower for the compressed air, because gravity or siphon devices can propel the clarified liquor and sludge A conventional scum trough (not shown in Figures 9 and 10) can be installed on -the surface of clarifier 230 for capturing floating scum or it can be installed along the inner surface of side 213.
Circular barrier oxidation ditch 21n, as seen in Figures 9 and 10, comprises an outer cylindrical side 211, a middle cylindrical side 212, an inner cylindrical or clarifier side 213, a bottom 217, grouted slopes 215, a circulator/aerator assembly 220, and a clarifier 230. Circulator/aerator assembly 220 c~nprises a motor 221, a shaft 223, a funnel 225, a downdraft tube Tao a discharge duct 227 which is flow connected to tube 226, an air supply line 222, and an air header 224.
Clarifier 230 comprises a clarifier feed or intake line 231 for the liquor/air mixture, a feed riser 232, a clarifies center feed well 233, a sludge siphon arm 234, a sludge return line 235, a cylindrical scum baffle 236, an effluent whir trough 237, a clarified liquor discharge line 238, and a bottom 239.
Clarified liquor surface 228 is higher by differential hydraulic head ( OH) 229 than mixed liquor surface 214 in return channel 219. Return channel 219 includes at least the second half of the outer channel and at least the first half of the inner channel.
The sludge discharges from siphon line 235 into return channel 219 where the liquor is in an anoxic state and ready for denitrification.
~7~3 Vector 241 denotes flow into circulator/aerator 220, and vector 242 denotes flow from discharge duct 227 and through discharge channel 218. Vector 243 shows flow through the outer channel, and vector 244 indicates flow from the outer channel to the inner channel. Vector 245 indicates flow through the inner channel.
Vector 246 shows the discharge of the mixture of mixed liquor and air through line 23] and from clarifier feed well 233 into clarifier 230. Vector 247 indicates -the flow of clarified liquor through line 236. Vector 248 shows the intake of settled sludge from the sludge blanket into sludge siphon arm 234 and then into siphon line 235, and vector 249 indicates its flow through line 235 and discharge into return channel 219.
The circular barrier oxidation ditch shown in Figures 11 and 12 is built around a circular clarifier having a sludge return system which is operated by gravity flow instead of by siphon flow, as in Figures 9 and 10. Barrier oxidation ditch aye in Figures 11 and 12 is exactly like ditch 210 in Figures 9 and 10, and its parts, vectors, and the like bear the same numbers. The only significant difference is that circulator/
aerator assembly aye comprises a longer draft tube aye than draft tube 220 as seen in Figure 10 so that its funnel aye is higher than funnel 225 in Figure 10.
Moreover, clarifier 250 of Figures 11 and 12 is very similar to clarifier 230 of Figures 9 and 10 except that it has a peripheral feed system, in contrast to the central feed system of clarifier 230, and a gravity return system for its settled sludge. Both clarifiers 230, 250 also have a peripheral effluent trough for collecting the clarified liquor.
-- I --5~3 Clarifier 250 comprises a pair o-f very short clarifier intake or feed lines 251, a peripheral in fluent trough 252, a center post 253, a revolvable sludge siphon arm 25~, a motor aye for driving arm 254 which is mounted atop post 253, a sludge return line 255, a scum baffle 256, a peripheral effluent trough 257, an effluent discharge line 258, and a bottom 259.
Pipes 251 lead from draft tube aye to and through wall 213 and into the bottom of inhalant trough 252 which has closely spaced outlet holes or parts aye in its bottom through-out its circular length, as seen in Figure 11. Vector 265 accordingly indicates the flow of a mixed liquor/air mixture through lines 251 into trough 252, and flow arrow 266 indicates downward flow from the plurality of ports aye. Vector 267 indicates the flow of clarified liquor through line 258. Vector 268 indicates the flow of settled sludge through siphon arm 254 and then through and out of line 255.
The clarified liquor has a surface 228 which is higher by differential head aye than surface 214 of the translational flowing mixed liquor in return channel 219. This differential head can be designated as Ha, the head needed for gravity or siphon operation of clarifier 250.
Figures 13 and 14 show a complete mix tank 270 and a clarifier 290 in adjoining relationship. Clarifier 290 is operable without a pump by using a portion of the pump heads available from two of its circulator/aerator assemblies 290 for creating a differential hydraulic head between the surface of its clarified liquor and the surface of the agitated mixed liquor in tank 270.
: I
Jo ~Z~S83 Complete mix tank 270 yin figures 13 and 14 comprises an outer wall 271, end walls 272, a bottom 273, and a plurality of draft tube circulator/aerator assemblies 280. Each circulator, aerator assembly 280 comprises a motor/gear reducer 281, a shaft 283, a funnel 284, a draft tube 285 which is flow connected to funnel 284, and an impeller 286 which rotates within draft tube 285 and is attached to the lower end of shaft 283.
Vector 275 shows the flow of liquor into funnel 284, and vector 276 indicates the downward discharge of liquor and air from draft tube 285. the mixed liquor has a generally turbulent surface 276.
Clarifier 290, adjoining complete mix tank 270 in Figures 13 and 14, comprises an outer wall 291, end walls 292, a bottom 293, a common wall 294 with tank 270, a scum baffle 295 near wall 291, an effluent overflow trough 296 adjacent wall 291, a scum trough 237 near wall 294, and an in fluent baffle 298 which is near wall 294 and supports trough 297. The clarified liquor has a surface 299 which is higher than surface 279 by differential head (I Ho which is visible but not labeled in Figure 14.
Mixed liquor and its associated pump head are fed through intake lines 301 and valves with handles 302 to and through wall 294 to discharge into the stilling space provided by infinity baffle 298. Floating skimmer 303 collects scum which is passed through scum pipe 308 to scum trough 2970 Siphon sludge pickup header 304, which is moved back and forth by motor 307 on traveling bridge pickup mechanism 306, removes sludge from bottom 293. The sludge is then siphoned through line 305 into tank 270.
-~2g--lZ17S~3 The following design example refers to the combination of the clarifier and the barrier oxidation ditch shown in Figures 1 and 2:
DESIGN EXAMPLE
A. SEMITONES
1. Average Daily Flow = 1.0 Million Gallons per Day (MUD);
Minimum 3 Hour Flow = 0.33 MUD;
Peak 3 Hour Flow = 2.0 MUD
2. In fluent BUD = 206 Mel = 1720 pounds of biochemical oxygen demand per day (#Budded)
3. 1.8# Oxygen Supplied/#80D Applied B. OXIDATION DITCH DESIGN
____ .
1 AIR = 1.8 (1720) = 129$2/HR
SWEARER 1.33 for specific process conditions of altitude, U-tube depth, and temperature 20C 172.5#02/HR
Spurge 350 aim of air into Circulator/Aerator (DATA), having a 72-inch diameter draft tube and a 30-HP
motor, which pumps the mixed liquor into a U-tube or discharge duct which has a center-line depth equal to 5 feet deep below the average water level in the oxidation ditch and is approximately 135 feet long and is estimated to produce 50% oxygen transfer efficiency at depth.
DATA pumping rate = 166.25 cubic feet per second ifs and time in draft tube = 12.2 seconds.
2. Use Oxidation Ditch with Average X-Section Area = 155 ft.2 for design velocity 166.25/155 1.0726 feet per second (fops)' Go _ _ 3. Ditch Volume = 750,000 gallons for average hydraulic detention time = 18 hours; F/Mv ratio =
owe (3500 Mel = .08#BOD/per pound of mixed liquor volatile suspended solids (#MOVIES) (assuming MLVSS concentration = 3500 Mel
____ .
1 AIR = 1.8 (1720) = 129$2/HR
SWEARER 1.33 for specific process conditions of altitude, U-tube depth, and temperature 20C 172.5#02/HR
Spurge 350 aim of air into Circulator/Aerator (DATA), having a 72-inch diameter draft tube and a 30-HP
motor, which pumps the mixed liquor into a U-tube or discharge duct which has a center-line depth equal to 5 feet deep below the average water level in the oxidation ditch and is approximately 135 feet long and is estimated to produce 50% oxygen transfer efficiency at depth.
DATA pumping rate = 166.25 cubic feet per second ifs and time in draft tube = 12.2 seconds.
2. Use Oxidation Ditch with Average X-Section Area = 155 ft.2 for design velocity 166.25/155 1.0726 feet per second (fops)' Go _ _ 3. Ditch Volume = 750,000 gallons for average hydraulic detention time = 18 hours; F/Mv ratio =
owe (3500 Mel = .08#BOD/per pound of mixed liquor volatile suspended solids (#MOVIES) (assuming MLVSS concentration = 3500 Mel
4. Channel Width = 15.5 feet.
Minimum liquid depth = 10.0 feet.
Average depth = 11.50 feet.
Maximum liquid depth = 13.0 feet.
Effective length = 645 feet.
C. CLARIFIER DESIGN
.
Surface Overflow Area = 15.5 feet (width) x 130 feet (length) = 2015 feet Hydraulic Surface Loading Rate =
1,000,000 gallons per day (god) 496 pd/f5 2 2015 ft.2 Under average conditions:
Depth = 13.0 feet Volume = 26,200 feet Detention time = 4.70 hours Horizontal velocity = 0.46 ft/min.
D. A 30 HP DATA operating in a 72-inch diameter draft tube, drawing 30 (0.90) = 27 bhp, will pump 166.25 ifs at a total head of about 1.07 feet.
E. The head loss occurring at 166.25 ifs from the draft tube inlet past the draft tube air spurge is approximately 0.40 feet, leaving a remaining available pump head at the clarifier feed pipe inlet of 1.07 - 0.40 = 0.67 feet.
F. Clarifier is to use a conventional traveling bridge siphon mechanism with two 8-inch diameter PVC siphon pipes, each with 8-inch PVC bottom pickup pipe with twelve 3-inch diameter sludge intake orifices.
_ Jo _ Lowe G. SIPITON PIPING HEADLESS US FLOW
Two sludge return siphons, each designed for 50~ of average daily flow rate, = 0.50 (1.0) = 0.50 MUD average flow; total sludge return rate _ 100% average designed flow (AD).
Siphon Flow per Total Siphon Total Plant Inflow Siphon Pipe Sludge Flow** Cafe. Headless*
0.50 MUD _ 0.25 MUD 0.50 MUD 0.1252 ft.
1.00 0.50 1.0 0.4530 _ 1.20 0 60 1 2 0.5547 ._. .,.__ ____ ___ ._ . __ __._.. _ ._ __._ 1.50 0 75 1 5 0 963 2.00 1.0 2 0 1.672 __ _ ._ 2.50 1.25 2.5 2.57 . __ _ 3.0 Q 1 50 3.0 3.61 * For 8-inch PVC Siphon Piping as shown ** Designed to equal 100% of plant inflow H. CLARIFIER IN FLUENT FLOW VS. HEADLESS VS. SIPHON HEAD PRODUCED
Clarifier Total Total Plant In fluent Clarifier Cafe. Available Inflow Flow/Pipe In fluent Flow Headless* Siphon Head*
0 50 MUD 0 50 MUD 1 0 MUD 0.0373ft. + 0.6327ft.
_ 1.0 1.0 2.0 0.1255 + 0.5445 _20 1.20 2.4 0.189 + 0.481 1.50 1.50 3.0 0.2750 + 0.3950 _ 2.0 2 0 _ 4 0 0.4854 + 0.1846 2.5 2.5 5.0 0.744 _ 0.074 3 0 3.0 6.0 1.054 - 0.384 * Available Siphon Head = 0.67 - Total Calculated Headless =
head available between higher clarifier water level and lower oxidation ditch liquor level to generate sludge siphon flow. In Figure 15, a descending curve 311 repro--sets the Siphon Head as a function of the Clarifier In fluent Flow, and an ascending curve 313 represents the Siphon Head as a function of the Siphon Flow which equals the Plant Inflow when all of the settled sludge is intended to be returned to the aeration basin.
_ I _ ~L75~
Based on these curves in Figure 15 and referring to the schematic plan view of a barrier oxidation ditch and an in-channel integral clarifier in Figure 16, -the following conclusions can be made:
.
1. Clarifier Inflow Rate = TIC = 1.1(2) = 2.2 MUD when the Clarifier Water Level is +0.50 feet above the Oxidation Ditch Water Level (HO = +0.50 feet) in fluent to Clarifier;
when the Clarifier water level is +0.50 feet above the ditch water level, the total siphon sludge return flow =
OR = 1.1 MUD which is approximately equal to the average daily oxidation ditch in fluent flow rate of 1.0 MUD.
2. If the oxidation ditch inflow rate increases to the 3-hour peak flow rate = 2.0 MUD; assuming TIC remains steady at about 2.2 MUD and OR remains at 1.1 MUD, the oxidation ditch water level will rise as follows:
I + OR = 2-0 + 1.1 = 3.1 GO
while TIC = 2.2 MUD
accumulation rate = +0.90MGD
0 90 (3) = 112,500 gallons accumulated in 3 hours = 37,500 gph accumulated = 5012.7 ft3/hour at this accumulation rate, the level of the mixed liquor in the barrier oxidation ditch will rise at a rate of:
5012.7 (645) (15.5) d 0.50 ft/hr = Ed Therefore, in 15 minutes the a d would be 0.50/4 = 0.125 ft.;
as the ditch liquor level rises, the siphon head = HO
will be reduced to: .
0.50 - 0.125 = 0.3750 ft.
as HO is reduced, the siphon sludge return flow will be reduced from 1.1 MUD to about 0.90 MUD, and, TIC will increase to 3.1 MUD, as shown in Figure 11; then if YE remains steady at 1.0 MUD, the clarifier will accumulate water a-t the rate of:
~;Z17~1~3 3.1 - 0.90 - 1.0 = +1.2 MUD
= +50,000 gallons per hour = + 6683.5 ft3/hr then the clarifier water level will try to rise at a rate of:
6683;5 = +3.31 ft/hr which is a faster wise rate than the oxidation ditch, indicating that the clarifier water level and ditch liquor level will rise together with a differential head --H = 0.50 it + being maintained.
I
3. If the ditch inflow rate decreases to the minimum 3-hour flow = 0.33 MUD, then the ditch water level will try to fall at the following rate:
TIC = 2.2 MUD (assume steady) I = I- 33 MUD
YE = 1.0 MUD (assume steady) OR = 1.1 MUD (assume steady) I + OR = 0 33 + 1.1 = 1.43 MUD
while TIC = 2.2 MUD
loss rate =-0.77 MUD
+ 4289 ft3/hr At this loss rate, the oxidation ditch water level will drop at a rate of:
(645) (15.5) 0.43 ft/hr Ed Therefore, in 15 minutes the d would be 0.1072 ft.; as the ditch level falls, the siphon head, Ha, will try to increase to:
0.50 + 0.1072 = 0.6072 it.
as HO is increased, the siphon sludge return flow will be increased from 1~1 MUD to about 1.22 MUD, and, TIC will increase the same; TIC will decrease to 1.0 MUD; then if YE remains steady, the clarifier will lose water at the rate of:
1.0 - 1.22 - 1.0 = - 1.22 MUD
= - 50833 galore = - 6795 ft3/hr then the clarifier water level will try to drop at a rate of:
(130) (15.5) = 3-37 ft/hr which is a faster drop rate than the oxidation ditch, indicating that the clarifier water level and ditch liquor ._ _ level will also drop together with a differential head =
HO = 0 50 ft. - being maintained.
because it will be readily apparent to those skilled in the waste water treatment art that innumerable variations, modify-cations, applications, and extensions of the examples and principles herein before set forth can be made without departing from the spirit and the scope of the invention, what is herein defined as such scope and is desired to be protected should be measured, and the invention should be limited, only by the following claims.
-- I --
Minimum liquid depth = 10.0 feet.
Average depth = 11.50 feet.
Maximum liquid depth = 13.0 feet.
Effective length = 645 feet.
C. CLARIFIER DESIGN
.
Surface Overflow Area = 15.5 feet (width) x 130 feet (length) = 2015 feet Hydraulic Surface Loading Rate =
1,000,000 gallons per day (god) 496 pd/f5 2 2015 ft.2 Under average conditions:
Depth = 13.0 feet Volume = 26,200 feet Detention time = 4.70 hours Horizontal velocity = 0.46 ft/min.
D. A 30 HP DATA operating in a 72-inch diameter draft tube, drawing 30 (0.90) = 27 bhp, will pump 166.25 ifs at a total head of about 1.07 feet.
E. The head loss occurring at 166.25 ifs from the draft tube inlet past the draft tube air spurge is approximately 0.40 feet, leaving a remaining available pump head at the clarifier feed pipe inlet of 1.07 - 0.40 = 0.67 feet.
F. Clarifier is to use a conventional traveling bridge siphon mechanism with two 8-inch diameter PVC siphon pipes, each with 8-inch PVC bottom pickup pipe with twelve 3-inch diameter sludge intake orifices.
_ Jo _ Lowe G. SIPITON PIPING HEADLESS US FLOW
Two sludge return siphons, each designed for 50~ of average daily flow rate, = 0.50 (1.0) = 0.50 MUD average flow; total sludge return rate _ 100% average designed flow (AD).
Siphon Flow per Total Siphon Total Plant Inflow Siphon Pipe Sludge Flow** Cafe. Headless*
0.50 MUD _ 0.25 MUD 0.50 MUD 0.1252 ft.
1.00 0.50 1.0 0.4530 _ 1.20 0 60 1 2 0.5547 ._. .,.__ ____ ___ ._ . __ __._.. _ ._ __._ 1.50 0 75 1 5 0 963 2.00 1.0 2 0 1.672 __ _ ._ 2.50 1.25 2.5 2.57 . __ _ 3.0 Q 1 50 3.0 3.61 * For 8-inch PVC Siphon Piping as shown ** Designed to equal 100% of plant inflow H. CLARIFIER IN FLUENT FLOW VS. HEADLESS VS. SIPHON HEAD PRODUCED
Clarifier Total Total Plant In fluent Clarifier Cafe. Available Inflow Flow/Pipe In fluent Flow Headless* Siphon Head*
0 50 MUD 0 50 MUD 1 0 MUD 0.0373ft. + 0.6327ft.
_ 1.0 1.0 2.0 0.1255 + 0.5445 _20 1.20 2.4 0.189 + 0.481 1.50 1.50 3.0 0.2750 + 0.3950 _ 2.0 2 0 _ 4 0 0.4854 + 0.1846 2.5 2.5 5.0 0.744 _ 0.074 3 0 3.0 6.0 1.054 - 0.384 * Available Siphon Head = 0.67 - Total Calculated Headless =
head available between higher clarifier water level and lower oxidation ditch liquor level to generate sludge siphon flow. In Figure 15, a descending curve 311 repro--sets the Siphon Head as a function of the Clarifier In fluent Flow, and an ascending curve 313 represents the Siphon Head as a function of the Siphon Flow which equals the Plant Inflow when all of the settled sludge is intended to be returned to the aeration basin.
_ I _ ~L75~
Based on these curves in Figure 15 and referring to the schematic plan view of a barrier oxidation ditch and an in-channel integral clarifier in Figure 16, -the following conclusions can be made:
.
1. Clarifier Inflow Rate = TIC = 1.1(2) = 2.2 MUD when the Clarifier Water Level is +0.50 feet above the Oxidation Ditch Water Level (HO = +0.50 feet) in fluent to Clarifier;
when the Clarifier water level is +0.50 feet above the ditch water level, the total siphon sludge return flow =
OR = 1.1 MUD which is approximately equal to the average daily oxidation ditch in fluent flow rate of 1.0 MUD.
2. If the oxidation ditch inflow rate increases to the 3-hour peak flow rate = 2.0 MUD; assuming TIC remains steady at about 2.2 MUD and OR remains at 1.1 MUD, the oxidation ditch water level will rise as follows:
I + OR = 2-0 + 1.1 = 3.1 GO
while TIC = 2.2 MUD
accumulation rate = +0.90MGD
0 90 (3) = 112,500 gallons accumulated in 3 hours = 37,500 gph accumulated = 5012.7 ft3/hour at this accumulation rate, the level of the mixed liquor in the barrier oxidation ditch will rise at a rate of:
5012.7 (645) (15.5) d 0.50 ft/hr = Ed Therefore, in 15 minutes the a d would be 0.50/4 = 0.125 ft.;
as the ditch liquor level rises, the siphon head = HO
will be reduced to: .
0.50 - 0.125 = 0.3750 ft.
as HO is reduced, the siphon sludge return flow will be reduced from 1.1 MUD to about 0.90 MUD, and, TIC will increase to 3.1 MUD, as shown in Figure 11; then if YE remains steady at 1.0 MUD, the clarifier will accumulate water a-t the rate of:
~;Z17~1~3 3.1 - 0.90 - 1.0 = +1.2 MUD
= +50,000 gallons per hour = + 6683.5 ft3/hr then the clarifier water level will try to rise at a rate of:
6683;5 = +3.31 ft/hr which is a faster wise rate than the oxidation ditch, indicating that the clarifier water level and ditch liquor level will rise together with a differential head --H = 0.50 it + being maintained.
I
3. If the ditch inflow rate decreases to the minimum 3-hour flow = 0.33 MUD, then the ditch water level will try to fall at the following rate:
TIC = 2.2 MUD (assume steady) I = I- 33 MUD
YE = 1.0 MUD (assume steady) OR = 1.1 MUD (assume steady) I + OR = 0 33 + 1.1 = 1.43 MUD
while TIC = 2.2 MUD
loss rate =-0.77 MUD
+ 4289 ft3/hr At this loss rate, the oxidation ditch water level will drop at a rate of:
(645) (15.5) 0.43 ft/hr Ed Therefore, in 15 minutes the d would be 0.1072 ft.; as the ditch level falls, the siphon head, Ha, will try to increase to:
0.50 + 0.1072 = 0.6072 it.
as HO is increased, the siphon sludge return flow will be increased from 1~1 MUD to about 1.22 MUD, and, TIC will increase the same; TIC will decrease to 1.0 MUD; then if YE remains steady, the clarifier will lose water at the rate of:
1.0 - 1.22 - 1.0 = - 1.22 MUD
= - 50833 galore = - 6795 ft3/hr then the clarifier water level will try to drop at a rate of:
(130) (15.5) = 3-37 ft/hr which is a faster drop rate than the oxidation ditch, indicating that the clarifier water level and ditch liquor ._ _ level will also drop together with a differential head =
HO = 0 50 ft. - being maintained.
because it will be readily apparent to those skilled in the waste water treatment art that innumerable variations, modify-cations, applications, and extensions of the examples and principles herein before set forth can be made without departing from the spirit and the scope of the invention, what is herein defined as such scope and is desired to be protected should be measured, and the invention should be limited, only by the following claims.
-- I --
Claims (26)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A clarifier which is continuously operable without a pump in combination with a barrier oxidation ditch having an endless channel, a circulator/aerator assembly which is disposed within said channel, an air sparge assembly, a down-draft tube within which said assemblies are mounted, a discharge duct which is flow connected to said downdraft tube, and a barrier which is sealably disposed athwart said channel, comprising:
A. a clarifier feed system which comprises:
(1) a means for intercepting a clarifier feed stream of mixed liquor as a portion of the flow being pumped past said barrier and for selectively receiving the pump head of at least said feed stream; and (2) a means for conveying said feed stream, while substantially conserving said pump head, from said barrier oxidation ditch to said clarifier, whereby the surface of clarified liquor in said clarifier is continuously maintained at a higher level than the surface of liquor in said endless channel of said barrier oxidation ditch to create a differential hydraulic head therebetween.
B. an outlet means for discharging clarified liquor from said clarifier;
C. a sludge recycle means for returning settled sludge from said clarifier to said endless channel; and D. a means for sealably isolating the contents of said clarifier from said mixed liquor in said endless channel.
A. a clarifier feed system which comprises:
(1) a means for intercepting a clarifier feed stream of mixed liquor as a portion of the flow being pumped past said barrier and for selectively receiving the pump head of at least said feed stream; and (2) a means for conveying said feed stream, while substantially conserving said pump head, from said barrier oxidation ditch to said clarifier, whereby the surface of clarified liquor in said clarifier is continuously maintained at a higher level than the surface of liquor in said endless channel of said barrier oxidation ditch to create a differential hydraulic head therebetween.
B. an outlet means for discharging clarified liquor from said clarifier;
C. a sludge recycle means for returning settled sludge from said clarifier to said endless channel; and D. a means for sealably isolating the contents of said clarifier from said mixed liquor in said endless channel.
2. The clarifier of claim 1, wherein said flow is pumped downwardly by a downflow impeller, as a part of said circulator/aerator assembly, which forces said flow through said downdraft tube.
3. The clarifier of claim 2, wherein said feed stream intercepting and receiving means is an upwardly curved mixed liquor intake line which traverses the wall of said downdraft tube, whereby said intercepting is performed within said down-draft tube.
4. The clarifier of claim 3, wherein said clarifier is rectangular in shape, having a pair of short sides and a pair of long sides.
5. The clarifier of claim 4, wherein said clarifier is disposed within said endless channel and downstream of said barrier.
6. The clarifier of claim 5, wherein said barrier is formed by one of said short sides of said clarifier.
7. The clarifier of claim 6, wherein said discharge duct extends beneath said clarifier and beyond the other of said short sides, whereby said flow is pumped beneath said barrier and said clarifier until said flow emerges within said endless channel and past said other short side.
8. The clarifier of claim 7, wherein said clarifier comprises sludge discharge siphons which discharge sludge into said endless channel without utilizing a pump therefor.
9. The clarifier of claim 3, wherein said clarifier is rectangular in shape and is disposed alongside said endless channel.
10. The clarifier of claim 9, wherein said rectangular clarifier is surrounded by said endless channel.
11. The clarifier of claim 3, wherein said clarifier is circular in shape and is disposed alongside said endless channel.
12. The clarifier of claim 11, wherein said circular clarifier comprises a center-feed well into which said intake line discharges.
13. The clarifier of claim 11, wherein said circular clarifier comprises a peripheral influent trough, and wherein said clarifier intake line extends from said downdraft tube to said trough.
14. The clarifier of claim 13, wherein said clarifier comprises a revolving sludge pick-up arm.
15. The clarifier of claim 11, wherein said circular endless channel comprises an inner channel, an outer channel, and a cross-over therebetween which forms said barrier.
16. The clarifier of claim 2, wherein said discharge duct passes beneath said barrier.
17. The clarifier of claim 16, wherein said feed stream intercepting and receiving means is a mixed liquor intake tube having an intake end which is disposed within said discharge duct, whereby said intercepting is performed within said discharge duct.
18. A process for continuously clarifying a portion of mixed liquor being aerobically treated in a barrier oxidation ditch by gravity settling said portion in a clarifier to produce clarified liquor and settled sludge without utilizing a pump for mixed liquor feed to said clarifier, clarified liquor outflow from said clarifier, or sludge return from said clarifier to said ditch, said barrier oxidation ditch compare-sing an endless channel containing said mixed liquor which is moving in circuit flow there through, a barrier sealable disposed athwart said endless channel to form an intake channel and a discharge channel, and a circulator/aerator for aerating and pumping said mixed liquor from said intake channel to said discharge channel at high velocity, said process comprising:
A. locating at least one intake line for mixed liquor feed to said clarifier where said high velocity is available;
B. disposing said intake line so that said high-velocity liquor is intercepted and the pump head of said high-velocity liquor is selectively received; and C. transferring said mixed liquor feed to said clarifier while conserving said pump head so that the surface of clarified liquor within said clarifier is higher than the surface of said mixed liquor within said endless channel, the contents of said clarifier being sealable isolated from the contents of said endless channel.
A. locating at least one intake line for mixed liquor feed to said clarifier where said high velocity is available;
B. disposing said intake line so that said high-velocity liquor is intercepted and the pump head of said high-velocity liquor is selectively received; and C. transferring said mixed liquor feed to said clarifier while conserving said pump head so that the surface of clarified liquor within said clarifier is higher than the surface of said mixed liquor within said endless channel, the contents of said clarifier being sealable isolated from the contents of said endless channel.
19. The process of claim 18, wherein said aerating and pumping causes a mixture of mixed liquor and air to move downwardly at said high velocity.
20. The process of claim 19, wherein said locating of said intake line is below said aerating and said mixture is intercepted, whereby said mixed liquor feed is aerated when said mixture is transferred to said clarifier.
21. The process of claim 20, wherein said settled sludge is transferred to said endless channel by siphoning.
22. The process of claim 20, wherein said settled sludge is transferred to said endless channel by gravity flow.
23. The process of claim 20, wherein said settled sludge is discharged to said circulator/aerator and is transferred to said endless channel at least partially by suction from passing of said high-velocity liquor.
24. A pumples clarifier which:
A. is sealable isolated from an activated sludge aeration basin, containing mixed liquor and having a circulator/
aerator assembly which is operably mounted there within and which pumps a flow of mixed liquor downwardly at high velocity within a draft tube.
B. receives a portion of said mixed liquor from said draft tube and separates said portion into clarified liquor and settled sludge; and C. obtains energy for returning said settled sludge to said aeration basin, without use of a pump therefor, from:
(1) a means for intercepting and receiving said portion in the form of said downwardly pumped mixed liquor and the associated pump head thereof within said draft tube;
and (2) a means for conveying said feed stream and at least most of said pump head to said clarifier so that a differential hydraulic head is created within said clarifier, between the surface of clarified liquor within said clarifier and the surface of said mixed liquor within said aeration basin.
A. is sealable isolated from an activated sludge aeration basin, containing mixed liquor and having a circulator/
aerator assembly which is operably mounted there within and which pumps a flow of mixed liquor downwardly at high velocity within a draft tube.
B. receives a portion of said mixed liquor from said draft tube and separates said portion into clarified liquor and settled sludge; and C. obtains energy for returning said settled sludge to said aeration basin, without use of a pump therefor, from:
(1) a means for intercepting and receiving said portion in the form of said downwardly pumped mixed liquor and the associated pump head thereof within said draft tube;
and (2) a means for conveying said feed stream and at least most of said pump head to said clarifier so that a differential hydraulic head is created within said clarifier, between the surface of clarified liquor within said clarifier and the surface of said mixed liquor within said aeration basin.
25. The pimples clarifier of claim 24, wherein said aeration basin is a complete mix tank.
26. The pimples clarifier of claim 25, wherein said aeration basin is an oxidation ditch, comprising an endless channel within which said circulator/aerator is operably mounted to provide translational flow of said mixed liquor through said channel.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US433,639 | 1982-10-12 | ||
| US06/433,639 US4512895A (en) | 1977-11-04 | 1982-10-12 | Pumpless clarifier apparatus and process for operation thereof in combination with a draft tube circulator/aerator |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1217583A true CA1217583A (en) | 1987-02-03 |
Family
ID=23720949
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000438754A Expired CA1217583A (en) | 1982-10-12 | 1983-10-11 | Pumpless clarifier apparatus and process for operation thereof in combination with a draft tube circulator/aerator |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1217583A (en) |
-
1983
- 1983-10-11 CA CA000438754A patent/CA1217583A/en not_active Expired
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