Note: Descriptions are shown in the official language in which they were submitted.
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Patent Application of
Isin KAYA
for
TITLE: APPARATUS AND PROCESS FOR TREATMENT OF WASTEWATER
AND BIOLOGICAL NUTRIENT REMOVAL IN ACTIVATED SLUDGE SYSTEMS
BACKGROUND - FIELD OF THE INVENTION
This invention pertains generally to an apparatus and process for the
treatment
of wastewater and biological nutrient removal in activated sludge systems. The
apparatus facilitates universal equipment providing substantially steady
agitation
while accommodating alternating process conditions (such as anaerobic, anoxic,
aerobic, and oxic conditions) in a reactor.
BACKGROUND - PRIOR-ART
Municipal and industrial wastewaters contain significant quantities of
phosphorus
and nitrogen, and the removal of these nutrients has become an important facet
of wastewater treatment. In a wastewater treatment plant, phosphorus and
nitrogen can be removed by both biological and physical chemical means.
Biological means of nutrient removal are generally preferred, as they result
in
lower waste sludge production, produce a sludge that is more amenable to land
application, and have the public perception that biological processes are more
"environmentally friendly" than chemical processes. Processes using biological
mechanisms for phosphorus and nitrogen removal are generally referred to as
biological nutrient removal, or BNR, processes.
Biological nitrogen removal in the activated sludge process takes place in two
sequential reactions - nitrification and denitrification. Nitrification is the
biological
oxidation of ammonia to nitrate and nitrite by two specialized groups of
autotrophic bacteria that takes place under aerobic conditions.
Denitrification is
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the biological reduction of nitrate and nitrite to nitrogen gas that takes
place
under anoxic conditions. During the 1960s, North American research focused on
the development of two- and three-stage processes for nitrogen removal, with
separate stages for carbon removal, nitrification, and denitrification. Each
stage
had the prerequisite conditions required to sustain its biological reaction
followed
by a set of clarifiers. Researchers in Europe, meanwhile, developed single
sludge systems in which all of these reactions take place simultaneously in a
single process in which the sludge is sequentially subjected to anoxic and
aerobic conditions. Recent examples of single sludge applications are SHARON
(Single reactor system for High activity Ammonium Removal Over Nitrite) and
ANAMMOX (ANoxic AMMonium OXidation).
Some of the technologies focused on satisfying high oxygen requirement per
unit
volume and therefore targeted to hold more biological activated sludge in
activated sludge reactors. For example, UNOX system developed in the 1960s
used high purity oxygen (HPO) as an alternative to air provided by surface
aerators and upgraded existing aerobic reactors by simply altering the same
infrastructure and covering aeration tanks. In the 1970s, open-tank HPO
systems
were developed such as the BOC VITOX system by British Oxygen Company,
eliminated the confined space limitations and exhaust-gas troubles of the UNOX
system and also made possible to have deeper aeration tanks in resulting
footprint reduction and capital cost savings.
In the late 1980s, by incorporating an engineered plastic media to activated
sludge system Moving Bed Bio-Reactor (MBBR) systems were developed and
combined suspended-growth and attached-growth advantages into one system.
By adding a recycle activated sludge line to the MBBR system, integration of
suspended-growth and attached-growth was further enhanced and was referred
to as Integrated Fixed-film Activated Sludge (IFAS). In the 1990s, the
Membrane
Bioreactor (MBR) was developed as a robust solid-separation mechanism, and
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integrated into activated sludge systems to meet more stringent suspended
solids and phosphorus effluent targets.
MBR, MBBR, and IFAS systems are often called hybrid systems. Most of the
hybrid systems' performances rely on aeration method they use. In most
existing
aeration devices, rate of hydraulic-mixing and degree of aeration are
simultaneously dependent on each other as, for example, in surface aerators
and
air-blowing diffused aeration systems (such as those disclosed in U.S. patent
U.S. patent 6,372,140). When more air is required, more mixing is
inadvertently
and unnecessarily provided.
Excessive mixing energy and agitation in activated sludge system can cause
adverse effects on system performance, such as a pin-floc problem in
suspended-growth systems or excessive bio-film sloughing-off in attached-
growth systems, which in turn can lead to sedimentation and solids separation
problems.
MBR, MBBR and IFAS systems are examples of wastewater treatment systems
that are the most vulnerable to the problem of excessive agitation. All of
those
systems often use diffused aeration and therefore their efficiency relies on
that
particular aeration method's pros and cons. For example, MBR systems rely on
micro-filtration taking place in an activated sludge reactor with high level
of
suspended solids, and therefore usually require a high degree of agitation in
the
aeration reactor to keep the membranes' surfaces clean and reduce their reject
time. However, excessive agitation has adverse effects on the treatment
performance mentioned above. Some of the MBBR and IFAS systems rely on
the development of bio-film on small, lightweight, rigid plastic floatable
carrier
elements that fill the aeration basin and are kept agitated by means of
diffused
aeration. Homogeneous mixing of MBBR and IFAS plastic floating media has
been a challenging issue since the mixing of floating media by means of
diffused
aeration is more challenging then mixing of settling solids. (Conventional
activated sludge systems do not contain artificially added floating media and
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therefore are relatively less vulnerable to this problem.) Excessive agitation
is
definitely a serious problem and limiting the theoretically expected actual
performance of MBR, MBBR and IFAS systems.
There are commercially available aeration systems that provide an independent
aeration-rate with respect to the hydraulic-mixing-rate, such as BOC VITOX,
MTSJETS and another system disclosed in patent WO/2001/002308. However,
due to their potential high energy requirements (for air blowers or oxygen-
generators in addition to liquid recirculation pumps), as well as their
complexity in
installation, operation, and maintenance, they may not be the best solutions
for
every single scenario. Most of those systems using jet ejectors suffer from a
number of disadvantages, for example:
(a) they are usually horizontally submersed into the liquid adjacent to the
bottom of a typically 4 to 6 meters deep reactor. They use high-velocity
coherent jets which are adapted to overcome water pressure at the
bottom of the reactor, consequently providing high liquid flux and
relatively much more energy to entrain desired quantities of
atmospheric air. Thus, they are often adapted to feed forced air
provided by air blowers which also require additional energy. Despite
the optimization efforts the energy utilization per unit volume is still
considered high
(b) none of them can control entraining gas flow at single nozzle level, the
control mechanisms are usually outside and centralized to provide
uniform air flowrate to every nozzle. This arrangement is potentially a
disadvantage for adjusting aeration levels in a plug-flow reactor.
(c) having submersed jet mixing apparatus approximately 5 meters under
water makes the system vulnerable for any operation and maintenance
concern such as potential nozzle clogging. In that case, the reactor is
required to be emptied or alternatively a professional wastewater diver
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must be hired for the underwater repair work. There are some
retrievable apparatuses also available, but retrieving a 5-meter-wide
and 5-meter-tall nozzle manifold is not a simple maintenance job.
The prior art comprises submersed liquid jet ejectors horizontal or with an
approximate 450 trajectory angle (to horizontal XY-plane) and vertically
plunging
jet ejectors over and above the liquid surface. The following are examples of
technical articles from plunging liquid jet literature and related prior arts
or
patents.
- H. Chanson, R. Manasseh (2003) "Air entrainment processes in a circular
plunging jet: Void Fraction and Acoustic Measurements", Journal of Fluids
Engineering, ASME, September 2003 Vol. 125 pg 910.
- T. Bagatur and N. Sekerdag (2003) "Air-entraintment characteristics in a
plunging water jet system using rectangular nozzles with rounded ends"
ISSN 0378-4738, Water SA Vol. 29 No. 1 January 2003.
- Ito, K. Yamagiwa et al (2000) "Maximum Penetration depth of Air bubbles
entrained by vertical liquid jet", Journal of Chemical Engineering of Japan
Vol 33 pg. 898
- Liu, G., Evans, G.M., (1998). "Gas entrainment and gas holdup in a
confined plunging liquid jet reactor", Proceedings of the 26th Australian
Chemical Eng. Conference, (Chemeca 98), Port Douglas, Australia.
The above technical articles focus on a plunging liquid jet over and outside
the
liquid body where the liquid jet is in contact with the gas above the liquid
surface
in a reactor so that it will usually entrain ambient gas by the impingement at
the
liquid surface (such as disclosed in PCT patent applications, WO/2005/108549
and WO/1992/03218).
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Based on literature and model study results for the present invention, a jet
ejector
can generate a ratio of entrained air to motion water 2 to 4 air per water
(volume/volume) as also disclosed in U.S. patent 4690764. However, dispersing
and effectively dissolving of the entrained gas in an energy-efficient means
still
remains as a challenge for the prior art and this was mentioned above.
The plunging jet mix prior art suffer from a number of disadvantages:
(a) all of the above plunging jet aerators claim and rely on a jet ejector
located over and outside of the liquid to be aerated, therefore air (gas)
entraining is dependent on a high-speed coherent jet impingement on
a liquid surface which can generate a high ratio of entrained air per
liquid flux; however, the more the gas entraining, the less dissolution
efficiency. Therefore, those prior art items often utilize relatively
excessive hydraulic energy deliberately to shear gas bubbles into very
small size to increase bubble penetration depth (energy efficiency
suffers).
(b) despite being not very energy efficient, those prior art items have
another potential problem: coalescence of small bubbles into larger
bubbles due to high concentration of small bubbles and in turn causing
dissolution efficiency and unwanted foaming problems.
(c) even though some of those prior art items disclose a controllable gas
entraining mechanism, most of them are strictly designed for
maximizing gas entrapping by coherent liquid jet impingement and
therefore they are not capable of turning the gas completely off and
accommodating anaerobic mixing conditions
(d) none of those prior art items disclose entraining of any other fluid other
than an oxygen-containing gas or air, therefore they are not designed
to entering any other fluid to accommodate alternating process
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conditions such as anaerobic, anoxic, aerobic, and oxic conditions in a
liquid reactor
(e) none of those prior art items disclose any particular floatable matter
de-stratification mechanism in addition to keeping settleable matter in
suspension. Most of them do not define specific mixing patterns for
energy-efficiency; their focus is strictly on entraining oxygen-containing
gas or air since concomitantly provided mixing is usually chaotic and
very high in both degree and energy utilization
It is an object of the present invention to provide a liquid treatment process
and
apparatus which reduces at least one of the aforementioned disadvantages.
SUMMARY
In accordance with one aspect of the present invention, efficient mixing and
circulation of inputted wastewater into a body of liquid, for micro-organism
reaction and digestion throughout the body of liquid, is achieved by
delivering the
input wastewater or activated sludge in a substantially vertically downward
direction in the body of liquid, through a constricted delivery opening (jet)
disposed a short distance below the surface of the body of liquid. By
suitable,
routine adjustment of the input flow rate, the input liquid can be made to
travel
downwardly to the bottom of the body of liquid initially, and then to move
outwardly and upwardly in a circulating manner, throughout a substantial
portion
of the volume of body of liquid, preferably throughout substantially the
entire
volume thereof. Efficient mixing and maximum utilization of the bacteria
suspended in the body of liquid is thereby approached, whether the digestion
is
conducted aerobically, anaerobically or anoxically. Treated water can be led
off
from a location near the surface of the body of liquid, but displaced a
significant
distance from the input location, to keep the volume of the body of liquid
constant.
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The disposition of the inlet jet for the wastewater just below the surface of
the
body of liquid, and delivery in a downward direction, has a number of other
advantages, besides the establishment of desirable flow circulation patterns,
as
described. When, as is commonly but not invariably the case, it is desired to
supply oxygen-containing fluid such as air to create aerobic fermentation, the
gas
can be supplied along with the input wastewater for dissolution or entrainment
therein, without the use of pumps, compressors, blowers or the like which
would
need to be used if the input wastewater were to be delivered at a deep
location
within the body of water. This represents a significant energy saving, and a
significant reduction in noise associated with operating such equipment (e.g.
blower). The outlet jets are located at a position where they are readily
accessible for cleaning and maintenance purposes, as opposed to deeply within
a large tank of wastewater into which personnel and equipment needs to be
submerged for such purposes. Moreover, the surface splashing of a delivery
system located above the surface of the body of liquid, with its accompanying
noise, mess and lack of control of air entrapment is avoided. Further, the
energy
involved in delivering the wastewater to such a location is minimal, requiring
little
more than gravity feed, as opposed to the heavy duty pumping required for
delivery to a significant depth in a body of liquid.
In a preferred embodiment, baffle plates are provided around the delivery jet
and
at a level shortly below its opening, further to control the flow of liquid
and any
suspended solids within the body of liquid. These baffle plates are suitably
inclined at an acute angle directed downwardly towards the input location.
This
assists in a movement of solids and liquids from the surface of the body of
liquid
near the input location, in a downward direction along with the liquid input.
The
circulating motion of the body of liquid and solids therein is thereby
assisted, and
accumulation of floatable solids at the surface is reduced. Similarly, the
circulation developed in the body of liquid, involving travel of input liquid
to the
bottom, reduces or prevents settling of solids at the bottom of the body of
liquid.
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An important feature underlying the successful operation of further preferred
embodiments of the present invention is entrained gas bubble size control.
When
a gas such as air is being supplied in order to conduct aerobic fermentation
in the
body of liquid, the gas is best provided along with the input liquid, and in
the form
of gas bubbles of a size such that they will circulate throughout
substantially the
whole volume of the body of liquid. In this way, oxygen is available at all
locations
in the body of liquid where the fermentable material encounters the bacteria,
to
lead to the most efficient fermentation. If the gas bubbles are too large,
they will
float to the surface too quickly, and will not circulate throughout the body
of liquid.
Supplying large quantities of air often generates larger air bubbles which
will not
have enough penetration depth into the body of liquid, and will not distribute
properly. Minute gas bubbles, but large enough to be visible, which will
circulate
throughout the body of liquid, are most efficient. The present invention, in a
preferred embodiment, provides for this, along with a simple means for
controlling bubble size and for controlling the amount of gas, e.g. air, which
is
delivered in bubbles of optimum size, from zero supply for anaerobic
fermentation, up through the whole useful range for anoxic and aerobic
fermentation.
For this purpose, the wastewater jet input nozzle described above, for
disposition
a short distance below the surface, is associated with a fluid inlet means
provided in close proximity so that gas such as air from the fluid inlet means
becomes entrained, entrapped or dissolved in the wastewater flowing from the
inlet nozzle. The fluid outlet means may be provided alongside the wastewater
input jet, but preferably surrounds it. The adjustment of the size of the gap
between the fluid outlet means and the wastewater input jet allows for
adjustment
of the gas bubble size. The gas bubbles may be further reduced in size by the
shearing action of their impingement on the edge surfaces of the jets
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Preferably, the fluid outlet jet and the wastewater inlet jet are disposed one
within
the other, e.g. concentrically, and both terminate in downwardly extending
frusto-
conical outlets. Then adjustment of the gap size between them, for bubble size
control, can readily be done by moving one telescopically relative to the
other.
The present invention aims to provide optimum gas entrainment (not maximum)
so as to achieve, in an energy efficient manner, optimum bubble size and gas
transfer rates. Since the fluid entraining mechanism is controllable and can
be
isolated from ambient air, it allows oxygen containing fluid addition when the
optimum air entrainment is exceeded. The present invention allows entraining
not
only oxygen containing fluids but other fluids that are suitable for the
treatment of
wastewater. Examples of such fluids comprise the following: activated sludge,
raw wastewater, biosolids supernatant liquid, high purity oxygen gas, ozone
gas,
hydroxyl-radicals, hydrogen-peroxide, sodium-hypochlorite, chlorine gas,
methanol, aluminum-sulfate, sodium-bisulfate and etc.
Embodiments of the present invention provide apparatus for the treatment of
wastewater and biological nutrient removal in activated sludge systems to
provide steady and adequate but not excessive mixing in a liquid reactor and
effectively de-stratify one or both of solid and fluid layers that may also be
contained in the liquid body, while independently alternating the entraining,
dispersing and dissolving a fluid at atmospheric or higher pressure.
The present invention also provides, in preferred embodiments, a single
apparatus and method to provide steady mixing in a liquid reactor regardless
of
the rate of fluid entrapment, and effectively de-stratify solids and fluid
stratification layers that may be contained in the liquid body, especially
floatable
matter, while controlling the entraining of a fluid at atmospheric pressure,
so that
alternating process conditions can be accommodated in an energy efficient way
by means of a single and universal equipment. For example, one embodiment of
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apparatus of the present invention may use an oxygen-containing gas (such as
atmospheric air) as the fluid to be entrained. By controlling the rate of the
gas
entrainment the following process conditions can be alternately provided in
the
same reactor: when air is off then anaerobic conditions prevail, when air feed
is
at a minimum level then anoxic conditions prevail, when air feed is at an
average
level then aerobic conditions prevail, when air feed is at a maximum level (or
alternatively feeding a high purity oxygen containing fluid) then oxic
conditions
prevail. This type of process flexibility facilitates a unique process
application for
biological nutrient removal in activated sludge systems. One embodiment of the
apparatus of the present invention may be adapted to suit some existing
pumping stations and use pumped liquid energy to mix and provide alternating
conditions mentioned above, to produce an energy efficient process
application.
As a result, the present invention can provide improved biological nutrient
removal efficiency in activated sludge systems comprising MBR, MBBR, and
IFAS systems. The advantages comprise: right and steady degree of agitation
(eliminating adverse affects of excess agitation on biological removal
efficiency),
energy savings, less complexity for installation, process and operation
flexibility,
hassle-free maintenance (by using in-situ cleaning mechanisms and easy access
to the critical equipment), and noise-mitigation (by eliminating any loud
equipment such as air blowers).
BRIEF REFERENCE TO THE DRAWINGS
In the drawings, closely related figures have the same number but different
suffixes.
FIGURE 1 is a diagrammatic sectional view of a liquid-jet-means and liquid-jet-
ejector-means illustrating two embodiments Fig-1(a), and Fig-1(b).
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FIGURE 2 is a diagrammatic sectional view of two further embodiments of liquid-
jet-ejector-means according to the invention, Fig-2(a) and Fig-2(b);
FIGURE 3 is an exploded isometric view of the liquid-jet-ejector-means
embodiment of Fig. 2(a);
FIGURE 4 is an isometric-view of a container as the liquid reactor to receive
liquid jet means and liquid jet ejector means of Figures 1 to 3;
FIGURE 5 is a diagrammatic sectional view of a preferred apparatus
embodiment of the invention, with a bi-directional mixing pattern;
FIGURE 6 is a section-view of a similar apparatus embodiment to that of Fig.
5,
but with a unidirectional mixing pattern;
FIGURE 7 is a diagrammatic isometric view of a set of rectangular reactors
according to Fig. 4, illustrating different mixing patterns and liquid jet
means
arrangements;
FIGURE 8 is a diagrammatic view of a preferred liquid-inlet-routing-control-
means and a liquid-transfer-routing-means according to Figure 5, illustrating
a an
optional and complex arrangements;
FIGURE 9 is a diagrammatic view of one interconnection system of an apparatus
according to an embodiment of the invention;
FIGURE 10 is a diagrammatic view of a preferred embodiment of an overall
process according to a preferred embodiment of the invention;
FIGURE 11 is a perspective view, partially in section, of an apparatus for
conducting preferred process embodiments of the invention.
In the drawings, like reference numerals indicate like parts.
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DETAILED DESCRIPTION
Figure 1(a) is a diagrammatic view, in section, of the preferred embodiment of
the liquid inlet jet means (liquid jet mixer) 40 of the invention,
illustrating the
principle of operation. The jet comprises a vertically downwardly extending
pipe
terminating at its lower extremity in a constricted liquid jet nozzle 48 (or
liquid jet
slot), the outlet 49 being adapted to be disposed a short distance 55 below
the
liquid surface 36 (Fig. 5). Below the outlet 49 is provided a baffle mechanism
80,
comprising plurality of annular plates inclined at acute angles to the liquid
surface
36, and angularly adjustable to provide appropriate flow patterns as the
liquid
from outlet 49 enters the body of liquid. Plurality of baffle plates 82, 86
making up
the baffle mechanism 80 are attached to the lower portion of the liquid inlet
jet
means.
Fig 1(b) is a similar illustration of another embodiment of liquid inlet jet
means,
40A, in which the inlet line to the liquid nozzle 48 includes a fluid
injection
mechanism 115 in the form of a venturi, a fluid feeding control means 71A
through which a fluid such as air (or methanol) can be controllably supplied
to the
wastewater and activated sludge liquid flowing to the liquid jet nozzle 48 via
the
venturi, and a control valve 117 on a flow by-pass line to effectively control
fluid
entraining.
Fig 2(a) and Fig 2 (b) are similar illustrations of further embodiments of
liquid inlet
jet means, but also including controllable fluid inlet means. The embodiment
of
Fig. 2(a) has a fluid inlet means in the form of a sleeve 60 surrounding the
liquid
jet nozzle 48 and separated to leave an annular space therebetween. The sleeve
60 also terminates at its lower extremity in a frusto-conical fluid inlet
nozzle 50 (or
a fluid inlet slot) and its outlet 51, leaving an annular gap 62 between the
sleeve
60 and the liquid jet nozzle 48. By raising and lowering the fluid inlet
nozzle 50 by
use of inter-fitting screw threads 58M and 58F, the size of the gap 62 between
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the nozzles 48 and 50 can be adjusted. Upper extremity of liquid jet ejector
40C
is also made telescopic by use of inter-fitting screw threads 44F and 44M,
(Fig.
2(a) and Fig. 3), so that the submergence depth 55 into the liquid body can be
adjusted. Two separate fluid inlets 63 and 67 are provided in sleeve 60,
communicating with gap 62. Through inlet 63, fluid such as oxygen-containing
fluid is supplied, under flow control of valve 71 and backflow prevention
mechanism (a check valve) 65. This allows for controlled addition of air or
the like
to the incoming wastewater and activated sludge liquid, for controlled
aerobic,
oxic or anoxic fermentation. Through inlet means (a pipe) 67, liquid can be
supplied under control of inlet control valve 72 and backflow prevention
mechanism (a check valve) 65L. This serves as a means for introducing flushing
and cleaning liquid to service the gap 62 and negative pressure reliving
mechanism (64, 66, 68), or for addition of other liquids to assist the
fermentation,
or even as a supplementary, controlled inflow of additional wastewater or
activated sludge.
Fig. 2(b) shows an alternative embodiment, in which the wastewater in the
liquid
jet nozzle 48 surrounds the fluid inlet nozzle 50E, which is in the form of a
tube
41, terminating at its lower end in a frusto-conical tip. An upper chamber 60E
communicates both with the tube 41 via holes 70 in the top-end and with liquid
inlet 67 and fluid inlet 63, as previously described. In both embodiments a
safety
feature 66, 68 is provided to control negative pressures and prevent
cavitation in
sleeve 60 or liquid suck-back into the gap 62. In both embodiments also, it
will be
noted that the outlets 51, 49 project downwardly into the liquid body and
terminate a short distance 55 below the surface.
Figure 3 shows an exploded perspective of the Fig. 2(a) embodiment 40C, with
like reference numerals indicating like parts. Relative vertical positioning
of
screw inter-fitting tubular elements 44F and 44M of the inner sleeve 60
provides
for vertical, telescopic adjustment of the height of the outlet 49 from the
sleeve.
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By raising and lowering the fluid inlet nozzle 50 by use of inter-fitting
screw
threads 58M and 58F, the size of the gap 62 between the nozzles 48 and 50 can
be adjusted. When a gas such as air is supplied through sleeve 60, the size of
this gap and lower peripheral edges 49 and 51 largely control the bubble size
of
the gas entraining with the liquid issuing from liquid jet nozzle 48.
Figure 4 diagrammatically illustrates a rectangular tank 30 of liquid 90
(wastewater and activated sludge as mixed-liquor) with side walls 31, 35, and
containing solids, some of which 92 are floating and others 94 of which are
settling. With no mixing or agitation in the tank 30, stratification results.
This is
undesirable, since in most instances the solids (especially the floating
solids that
are artificially added to improve process performance in MBBR and IFAS
systems), have substantial amounts of the required fermentation bacteria
adhered to them. These need to be distributed through the body of liquid for
efficient fermentation. For an embodiment adapted to MBBR and IFAS systems,
artificially added floatable solids will not be removed from the tank 30 via
outlets
39 and 39A as the process is conducted continuously.
With reference to accompanying Figure 5, a preferred embodiment of an
apparatus according to the invention shows the container (tank) 30 as liquid
reactor, with inlet liquid jet ejector 40C according to the embodiments
previously
described operating therein. A liquid-inlet-routing-control-means 110 (a
valved
intake or set of flow routing control valves as shown in Figure 8) is adapted
to
draw liquid from a plurality of liquid containers (optionally including the
container
as described below via outlet 39A at the bottom of container 30).
25 A liquid-transfer-routing-control-means 120 (comprised of multi-port flow
control
valves for flow routing and interconnecting pipelines as shown in Figure 8)
connects to and is adapted to transfer liquid into a plurality of liquid
containers,
including the container 30, via a plurality of liquid jet nozzles 48 or liquid
jet
ejector 40C previously described, the jets being disposed just below the
liquid
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surfaces 36 of the respective containers. This plurality of containers aspect
is
further described below, with reference to Figure 7 to Figure 11.
A liquid pump 101, connected to the liquid-inlet-routing-control-means 110 and
the liquid-transfer-routing-control-means 120 transfers liquid from one to the
other.
A fluid injection mechanism (e.g. venturi) 115 is connected to the liquid-
transfer-
routing-control-means 120 via branch piping to a back-flow preventing device
(e.g. a check valve) 65A and a fluid entraining flow control means (e.g. a
control
valve and a solenoid valve) 71A (all off-the-shelf, conventional non-
proprietary
items), and a bypass-line with a flow control valve 117, and to a liquid
distribution
means 150 (e.g. a sparge bar or manifold). The manifold 150 communicates to a
plurality of liquid jet ejector devices 40C that protrude vertically
downwardly,
terminating at their lower ends in a constricted liquid jet nozzle 48 with a
lowermost throttled outlet 49, disposed a short distance below the surface 36
of
the body of liquid 90 in the container 30.
The apparatus also includes a central fluid feeding system disposed generally
above the container and comprising, connected in series by fluid delivery
pipes, a
central fluid feeding control means (e.g. a flow control panel comprising a
valve
and a flow monitoring device) 200, a fluid feeding header or manifold 220, a
plurality of local fluid feeding control means (e.g. a valve) 71, and a back
flow
preventing device 65. This is normally used for supplying controlled amounts
of
oxygen containing fluid for aerobic fermentation, recycled activated sludge
and
nitrate-recycle for anoxic fermentation, methanol for anaerobic fermentation
and
any combination the above fluids to improve biological nutrient removal. A
plurality of fluid output pipes 63 communicates with the interior of a
plurality of
depending annular sleeves 60, one for each liquid jet nozzle 48 (or liquid jet
slot),
arranged concentrically around the vertically downwardly protruding portion of
liquid jet ejector 40C (Fig. 2(a)), to deliver fluid thereto. Sleeve 60
terminates at
its lower end in the frusto-conical fluid inlet nozzle 50 described in
connection
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with Fig. 2(a) and constituting a fluid entraining slot (or nozzle) and
forming a
fluid inlet means. The outlet from the sleeve 60 defines an adjustable contact
gap
62 between the fluid inlet nozzle 50 formed by lower extremity portion 51
(Fig.02(a)) and the throttled liquid outlet 49, and disposed at about the same
level as, in fact slightly lower than, throttled outlet 49 of the liquid inlet
means.
The nozzles (or slots) 50 and 48 are custom designed for each application
defining the liquid flowrate, degree of mixing energy and desired (optimum)
fluid
entraining rate (a optimum bubble size for gas feed). The gap 62 is adjustable
by
means of telescopic positioning mechanism (inter-fitting screw threads) 58F
and
58M. The submergence depth 55 of the liquid nozzle throat 49 into the liquid
body can also be adjusted by means of similar telescopic mechanism (inter-
fitting
screw threads) 44F and 44M, to generate small bubbles when a gas such as air
is fed as the fluid, for the purpose of optimizing the amount of gas
entrapping so
that increasing gas transfer rate into the liquid (wastewater and activated
sludge).
There are at least 4 types of fluid entrapping control which can be used in
embodiments of the invention: custom design liquid jet throat 49 and fluid
outlet
throat 51 of predetermined cross-sectional areas, a gap 62 adjustment
mechanism such as an inter-fitting screw threads 58F and 58M; alternating the
both cross-sectional area of throttled outlets 49 and 51 accommodated by means
of a flexible spout (or slot) shape control mechanism; a local flow control
valve
comprised in control assembly 71; and a central flow control valve comprised
in
global flow control panel 200.
Also provided generally above the container 30 is a central liquid feeding
system
comprising a central control means (a control panel) 230, an interconnecting
pipeline 240 and liquid feeding pipeline (header or manifold) 250. This also
communicates with sleeve 60, via a local inlet control valve 72, a check valve
65L and a negative pressure prevention mechanism 66 adapted to relieve any
excess negative pressure occurrence in tube 60 to prevent possible cavitation
when fluid feeding controls 71 and 72 are both closed, all as described above
with reference to Figure 5. In the event of excess negative pressure, liquid
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(wastewater) is sucked from the container 30 by means of pipeline 68 through
control means 66 (a valve) and connecting pipeline 64 into sleeve 60 and
therefrom recycled back to the container 30 by means of gap 62.
The container 30 also includes an optional second influent mechanism 38 by
which liquid is fed to the container 30, and two effluent mechanisms 39 and
39A,
by which liquid can be removed from the container. The liquid pump 101 is
adapted to draw liquid via a liquid-inlet-routing-control-means 110 and
transfer
liquid to the liquid-transfer-routing-control-means 120. The liquid-inlet-
routing-
control-means 110 (in the form of a valved intake) is provided with an
optional
inlet-routing-means (in the form of multi-port set of valves and depending
pipelines, one embodiment shown in Figure 8) adapted to draw liquid from
plurality of liquid containers including the liquid reactor 30, to be mixed
therein.
The liquid-transfer-routing-control-means 120 (in the form of a valved
discharge)
with an optional outlet-routing-means (in the form of multi-port set of valves
and
depending pipelines, one embodiment shown in Figure 8) is adapted to pump
liquid into a plurality of liquid containers including said reactor 30, as
illustrated in
Figure 7 and Figure 10, by means of a plurality of flow distribution manifolds
150
which are adapted to distribute liquid into plurality of liquid jet mix
ejectors 40C of
the type illustrated in Fig. 2(a).
A further outlet pipe 64 leads from the tube 60, via a negative pressure
preventing mechanism (e.g. control valve) 66, into the container 30,
terminating
at its lower end 68 at about the same level as outlet 49, but laterally offset
therefrom. This serves to relieve excess negative pressure to prevent possible
cavitation and back-flow into the sleeve 60 via gap 62, according to good
engineering practice.
Figure 6 illustrates an apparatus according to another embodiment of the
invention. It is similar to Figure 5, except that the plurality of liquid jet
ejectors
40C are disposed to one side of the container 30 instead of centrally. All
other
apparatus items are essentially the same. The delivery of liquid to container
30
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from each liquid jet nozzle 48 is still essentially vertically downward, at a
location
just below the liquid surface. Similar flow patterns are obtained, but to one
side of
the container only. Effective de-stratification is still achieved.
The liquid jet ejectors 40C and 40E (in Figure 2) are adapted to mix a body of
liquid 90 in the reactor 30 that may contain one or both of floatable matter
such
as floatable solids 92 and settleable matter such as settleable solids 94,
effectively to de-stratify floatable-matter-layer by means of a floating-
matter-
routing-baffle-means (baffles) 80 and settleable-solids-layer in the body of
liquid.
This is achieved by vertically downward delivery of liquid just below the
surface
36 of the body of liquid, so that the flow penetrates to the bottom 33 of the
container 30 with a sufficient hydraulic force, resulting in homogeneous
mixing
throughout said reactor 30, while concomitantly achieving in-situ and
controlled
entraining, dispersing or dissolving of a fluid 91 in the body of said liquid
90.
The operation of the process of the present invention, using an apparatus such
as that illustrated in Figure 5 or Figure 6, will be apparent from a
consideration of
the drawings. The liquid pump 101 transfers liquid such as wastewater at a
desired liquid flow-rate and at a certain pressure, thereby providing a steady
agitation rate to a body of liquid 90 contained in the reactor 30. The pumped
liquid is fed through liquid-transfer-routing-control mechanism 120 and
optional
fluid injection mechanism "J" or 115 (in the form of a venturi) to sparge-bar-
manifold 150 and distributed into evenly disposed liquid jet nozzles 48
exposing
said liquid jet nozzles or liquid jet ejectors 40C to the body of said liquid
90 at a
certain vertical submergence level 55 preferably just under the liquid surface
36
to provide constant mixing independently from entraining a fluid or gas,
progressing substantially vertically downward into the body of liquid, and
creating
vertically plunging parallel trajectory jet streams on a line located adjacent
to
liquid surface 36, at the mid-point along the reactor width 36 (liquid surface
and
reactor width are represented by the same number: 36), parallel to side walls
(31
or 35) and lining along the reactor length (37).
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The fluid inlet nozzle 50 is adapted to each liquid jet nozzle 48 to
accommodate
controlled entraining, dispersing and dissolving a fluid 91 into the body of
liquid
90. The contact-gap 62 between liquid jet nozzle 48 and fluid inlet nozzle 50
is
adjusted to control -especially for gas entraining- the rate-of-gas-flow and
gas
bubble size for optimizing gas dissolution and transfer rate.
The optional fluid injection venturi 115 is adapted to accommodate controlled
entraining, dispersing or dissolving a fluid into body of liquid by means of a
control valve 117 on by a pass pipeline. This optional fluid injection means
115 is
used as an alternative fluid inlet for further improvement especially in gas
dissolution and gas transfer rates into the body of liquid.
The kinetic energy of each individual vertically plunging liquid jet
(dependent on
cross-section 49) is adjusted to penetrate a certain thickness of floatable
solids
layer at the liquid surface 36 and to entrain the floatable solids 92 into the
plunging jet stream by means of assistance from the baffle mechanism 80; the
mixture of liquid-solid-gas-fluid is then carried downwards, to reach the
reactor
bottom with an adequate energy to keep settleable solids also in suspension.
The flowing mixture then diverges into two, and produces bi-directional
streams
along the reactor bottom across to the each side walls 31 and 35 (Figure 5).
Then the streams move upwards along the side walls 31 and 35 and reach the
liquid surface 36. Then the streams move along the surface 36 pushing the
floatable solids 94 towards the plurality of liquid jet ejectors 40C induction
area
and finally to converge at the mid point where liquid jet-mix-ejectors are
located,
thus completing a full cycle. When the body of liquid comprises artificially
added
floatable solids 92 (such as in MBBR and IFAS systems), the liquid jets are
designed to provide adequate kinetic energy to carry some of the floatable
solids
vertically downwardly to and along the bottom portion of the container 30,
with
subsequent upward movement of the floatable solids to contribute to the liquid
mixing pattern and efficiency. Minimizing the kinetic energy provided by
liquid
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jets and taking advantage of floating solids to contribute subsequently upward
liquid mixing pattern will significantly reduce energy utilization.
The present invention of apparatus in Figure 5 is shown as including a single
inlet liquid jet mixer 40 arrangement (Figure 1), but it can readily be
adapted to
include a plurality thereof, all feeding into a single container 30 or into a
plurality
of such containers. Figure 7 of the accompanying drawings illustrates three
embodiments in which several inlet jet means feed into a single container 30
In
Fig. 7(a), the arrangement is as shown in more detail in Figure 5, with the
inlet
1o jets located centrally in the container and creating circular flow patterns
in two
sides of the container. In Fig. 7(b), the arrangement is as shown in detail in
Figure 6, with the liquid jet nozzles 48 (as a portion of 40 or 40C) at one
side and
creating a single circulation system in the container. In Fig. 7(c), two sets
of liquid
jet nozzles 48 are provided at opposed sides of the container 30, creating a
flow
pattern similar to that of the Fig. 7(a) arrangement, but in the reverse
directions.
Figure 8 of the accompanying drawings diagrammatically illustrates one
interconnecting arrangement of a plurality of apparatus as described in Figure
5.
This shows in more detail the liquid-inlet-routing-control-means 110, which is
in
the form of interconnecting pipeline associated controls "C", each feeding
liquid
from selectively one (or more) of set of containers, e.g. anaerobic container
380,
anoxic container 382, aerobic container 386, and solids separator 388, by
means
of pump 101, to the liquid-transfer-routing-control-means 120. This provides
far
feed or recycle of liquid to an additional set of containers e.g. anaerobic
container
390, anoxic container 392, aerobic container 394. Also transferring from
liquid-
transfer-routing-control-means 120 back to containers 380, 382, and 386 can be
arranged. All containers are equipped with inlet arrangements such as liquid
jet
mixer 40 or liquid jet ejector 40A, 40C, or 40E as previously described.
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For these and similar arrangements, a fluid-feeding-system comprising one or
more fluid-flow-control-mechanisms 200 can be adopted, feeding to a manifold
220 with several separate pipelines and valves 71 feeding to different liquid
jet
ejectors 40C, as diagrammatically illustrated in Figure 9. Also included are
the
liquid inlet system 230 for the cleaning, flushing and optional chemical
addition,
and the liquid-transfer-routing-control-means 120 for the inlet of wastewater
or
activated sludge, as described in Figure 6. Each feeds a respective manifold
and
thence to the different liquid jet ejector 40C. Local liquid and fluid feeding
control
systems 71 and 72 can be eliminated for small systems where individual liquid-
jet-ejector 40C flow adjustment is not critical and required.
For one embodiment of the present invention of apparatus 100 as illustrated in
Figure 5, liquid jet mix ejector 40C (in Fig-2(a)) direction is substantially
vertically
downward, with an essential angle of 90 with horizontal XY-plane represented
by liquid surface 36. In other words it is essentially vertical to both
horizontal X-
axes and horizontal Y-axes and those angles depicted by angles 45 and 47 in
Figure 5. Suitable jet penetration angles range between 81 to 99 degrees
with
respect to horizontal-Y-axis (angle 45) and also make an optional angle range
between 81 to 99 degrees with respect to horizontal-X-axis (angle 47),
resulting in optional 10% deviation from 90 -degree-vertical-line to the XY-
horizontal-plane which represents quiescent liquid surface 36.
Liquid jet nozzle (48) exposure in to the body of said liquid (90) is a
certain
vertical submergence level (55) with a general range of 0.001 meter to 1.0
meter, further ranging from 0.04 meter to 0.30 meter, preferably 0.06 meter to
0.15 meter from the surface.
The degree of hydraulic force created by the liquid jet nozzles (48) are
dependent of Reynolds Number, "Re" (a dimensionless fluid flow measure
defined as the ratio of dynamic pressure and shearing stress) with a general
range between 16,000 and 90,000 (observed during model study for the present
invention) however, calculated general range for actual size embodiment "Re"
is
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between 100,000 and 500,000. It will be noted that, there is no optimum "Re"
or
hydraulic agitation energy per unit volume for all scenarios. Optimum "Re" is
calculated by considering many design factors such as tank dimensions (depth,
width, shape), characteristics of body of liquid to be agitated, required
amounts of
fluid (or gas) to be entrained, percent solids content and other key
characteristics
of the body of liquid. Therefore, for specific cases the present invention can
be
designed to have lower or higher "Re" as disclosed above. The higher "Re" the
less energy-efficiency, so the object is to aim low "Re" values as possible
but
high enough "Re" values accommodating the required adequate agitation and
fluid entraining. The liquid jet nozzle (48) jet also has a preferred "mean
cross-
sectional velocity" with a general range tested during the model study between
5.0 m/second and 24 m/second. Again, the higher the jet velocity the less the
energy-efficiency, so the object is to aim low velocities as possible, but
high
enough to provide adequate agitation and fluid entraining requirement for an
individual case.
Liquid-inlet-routing-control-means has an optional routing-control-means (110)
comprising a plurality of pipelines, valves, open/close control mechanisms,
and
screens (one embodiment shown in Figure 8).
Liquid-transfer-routing-control-means (120) has an optional routing control
mechanism comprising a plurality of pipelines, valves, open/close control
mechanisms, pressure and temperature monitoring devices (one embodiment
shown in Figure 8).
The liquid-jet-ejector (40C), liquid-jet-nozzle (48) and fluid-inlet-nozzle(s)
(50,
50A) have cross-sectional shape preferably circular or oval, alternatively a
custom designed geometric shape where a custom designed spout is made up of
a flexible material to alternate its cross-sectional shape and area to control
fluid
entraining rate and gas bubble size created.
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A preferred container for a most energy efficient embodiment of the present
invention is custom designed for individual cases. As a rule of thumb, the
container can be hydraulically idealized by custom Width (W) - Length (L) -
Height (H) ratios to provide ideal hydraulic conditions for substantially
vertical
downward (tumbling) mixing, where those are defined as ratio H/W is between 1
and 3 and the ratio of L/H between 1 to 10. It will be noted that the present
invention will be suited to work in existing containers with a higher or lower
H/W
and L/H ratios than provided above with a potential less energy-efficient
means.
The operation of a preferred embodiment of the process of the invention will
now
be described with reference to Figure 10. A process for the treatment of
wastewater and biological nutrient removal, in particularly for integrated
fixed-film
activated sludge system uses a plurality of the apparatus described above, as
universal equipment to provide adequate mixing required in a set of reactors
310,
320, 330, 340, 350, and 360, followed by a downstream solids separator 370. In
each of the reactors, desired process conditions such as anaerobic, anoxic,
aerobic and oxic (advanced oxidation) can be concomitantly arranged while
agitation is being provided. Alternatively the conditions can be varied or
alternated in one reactor. As depicted in Figure 10, the process includes a
first
step of introducing raw wastewater to an equalization tank or container 300.
The
raw wastewater is drawn from the equalization tank or container 300 via
pipeline
152, and transferred into an anoxic reactor 320 or alternatively into an
anaerobic
reactor 310 under control of liquid-flow-control-mechanism (valve) 311F. The
energy of the pumped liquid is used for the mixing in the anoxic reactor 320
while
concomitantly-controlling the entraining (by means of flow control system
322F),
dispersing and dissolving of air at atmospheric pressure or alternatively
another
fluid such as methanol as required for process, using the previously described
jets 40 to maintain desired anoxic conditions in said reactor 320. Delivery of
liquid in each case is substantially vertically downwardly, at a location just
below
the liquid surface as previously described, optionally but preferably using
baffle
plates to create the desired flow patterns.
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In one method, activated sludge is drawn from the underflow of a solid-
separation unit 370 located downstream of the reactors 320, etc., and
transferred
into an anaerobic reactor 310 upstream of the aforementioned anoxic reactor
320, and into another anoxic reactor 350 located upstream of an aerobic
reactor
360. Again, the pumped liquid energy is used for the mixing in the reactors
310
and 350, while concomitantly -controlled- entraining or feeding of raw
wastewater from the pipeline 152 is effected by means of liquid-flow-control-
mechanisms 311 F and 356F into the corresponding liquid jet mix apparatuses
311, 356, which are liquid jet ejectors 40C as previously described.
Activated sludge mixed-liquor may be drawn from an aerobic reactor 360 or 340
in which nitrification (biological oxidation of ammonia to nitrate and nitrite
using
specialized bacteria) taking place, and recycling into a preceding anoxic
reactor
320 or alternatively into a preceding anaerobic reactor 310 (not shown for the
embodiment in Figure 10) for denitrification (biological reduction of nitrate
and
nitrite to nitrogen gas). Again, the pumped liquid energy is preferably used
for the
mixing in the respective anoxic or anaerobic reactor 320 or 310, further
reducing
energy consumption. At the same time, concomitantly -controlled- entraining
and dispersing of returned activated sludge from a header or pipeline 151 or
156
is effected by means of a sludge-flow-control-mechanism 323F into a mixing
apparatus 323 involving a jet of the type 40C previously described.
In another method according to the embodiments of the invention, activated
sludge mixed-liquor is drawn from an aerobic reactor 340 and transferred to an
upstream aerobic reactor 330, again using the pumped liquid energy for the
mixing while concomitantly -controlled- entraining dispersing and dissolving
of an
oxygen containing fluid (such as air, oxygen gas, or hydrogen-peroxide) is
effected to maintain desired aerobic conditions in the aerobic reactor 330 for
mixing and aeration. Recycling of activated sludge mixed-liquor from a
nitrifying
reactor to an upstream aerobic reactor facilitates more robust nitrifiying
bacteria
culture throughout the disclosed process of invention.
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In another method in accordance with the invention, activated sludge mixed-
liquor is drawn from an aerobic reactor 340, 360 and recycled to the same
aerobic reactor 340, 360, using the pumped liquid energy for mixing while
concomitantly -controlled- entraining dispersing and dissolving of an oxygen
containing fluid (such as air, oxygen gas, or hydrogen-peroxide) is conducted
to
maintain desired aerobic conditions in said aerobic reactor 340, 360.
Embodiments of the present invention provide a mixing apparatus with a
capability of entraining, dispersing and dissolving fluids that may be
necessary
for the activated sludge system and biological nutrient removal.
When the present invention is incorporated to entrain an oxygen containing
fluid,
it serves as aeration equipment; therefore it provides a system in which the
degree of mixing and degree of aeration are not dependent each other.
The present invention incorporates an immersed-plunging liquid jet which does
not entrain ambient air due to surface impingement. On the contrary, the
vertical
jet is deliberately created just under liquid surface to provide steady mixing
energy to the liquid body and concomitantly but independently from the rate of
mixing accommodating in-situ and controllable entraining, dispersing and
dissolving a fluid (such as atmospheric air) in the body of liquid contained
in a
reactor. Submersed jets do not create any significant surface impingement and
therefore cause less likely foam problems associated with. The degree of
mixing
provided by the liquid jet is kept relatively constant, while entrained rate
of fluid
(air) is independently adjustable from zero to a maximum value to meet desired
conditions and optimum bubble size for improved gas transfer and dissolution
efficiency. Fluid. (air) entrainment can be turned off completely to provide
mixing
only for anaerobic and anoxic reactors.
One embodiment of this invention not only incorporates steady mixing versus
independently variable aeration in one apparatus, but also facilitates energy
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efficient biological nutrient removal in activated sludge systems and its
improved
versions (often called hybrid systems such as MBR, MBBR and IFAS).
The invention incorporates a vertically plunging jet created just under the
liquid
surface in order to have a steady mixing concomitantly but independently
achieving in-situ and controllable entraining, dispersing and dissolving of
not only
atmospheric air but any other fluids that may be necessary for the process.
One embodiment of this invention has been adapted so that no major equipment,
device, or pipeline has to be totally submerged into a reactor to do either or
both
of mix and aerate. All equipment can be located outside of the liquid reactor,
except the plurality of liquid-jet-ejectors 40C that need to be semi-submerged
or
just submersed under the liquid surface to provide in-situ-controllable fluid
entrainment including atmospheric air. The liquid-jet-ejectors are located at
a
very convenient distance from the liquid surface so that, in case of a
potential
clogging occurrence, they can easily be inspected and cleaned without stopping
the operation. If an ejector ever needs to be serviced outside for
maintenance,
then it can be retrieved individually while the remaining ejectors that are
unplugged can keep running.
The apparatus of the present invention comprises well known components such
as pumps, pipelines, manifolds, valves, fluid-control systems etc. that can be
easily mastered by any ordinary operation technician. There is no major
proprietary equipment other than the custom designed jet-ejectors which can be
cost effectively stored as spare parts. The design of the jet-mixing-apparatus
may be complicated for some cases; however, the final product is relatively
simple, energy-efficient and user friendly to operate and maintain, and
significantly less noisy compared to air compressors or blowers.
Desired air bubbles size (93 in Figure 5) is created by means of plurality of
concentric frusto-conical nozzle arrangement (such as in 40C) and the control
surface at the gap 62 between the nozzles 48 and 50.
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