Note: Descriptions are shown in the official language in which they were submitted.
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
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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
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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
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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.
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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
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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
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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.
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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.
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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,
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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.
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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,
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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.
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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
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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
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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
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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.
/
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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
24
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
_ _
I 3
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
24
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
7583
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.
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