Note: Descriptions are shown in the official language in which they were submitted.
~4~ tiO
METHOD & APPARAT~lS FOR AERATING AND MIXI NG WASTE WATER
.
This invention relates generally to the treatment of waste
water and deals more particularly with improvements in the
application of ultra fine air bubbles to municipal and
industrial waste water.
s
Various types of aeration and mixing devices have been
used to treat municipal and industrial waste water,
including mechanical devices which function as surface
aerators. Surface aerators are active only at the surface
of the waste water and do not effectively treat remote
areas of the lagoon or basin. Due to the localized nature
of surface aeration and inability to mix to the bottom in
deep tanks or basins, there is a lack of uniform
distribution of eneryy throughout the waste water and a
corresponding lack of thorough mixing of the air with
the liquid. surface aerators are also generally low in
efficiency and high in energy consumption, and they are
characterized by frequent mechanical problems. In
addition, surface aeration systems are laclcing in
flexibility and are difficult ancl expensive to
maintain in good oL~eratiny condition.
Aeration systems known as draft tube systems utilize a
series of aeration tubes which extend vertically in the
waste water basin. The tubes act as draft tubes, and
air is applied internally to create air lift pumpage and
aeration of pumped liquid. The draft tube systems
dispense the air fairly widely throughout the basin but
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are plagued by high energy requirements. Furthermore, the
draft tube system does not stand up well when subjected to
prolonged use in the field.
Fine bubble technology is used in a third type of
aeration system. In the fine bubble system, small air
bubbles are generated and applied to the waste water. The
fine bubbles have been generated by mechanical devices
such as eductors which draw gas into the liquid by liquid
pumpage. Rapidly rotating turbines and pumps have
also been used to break up a stream of compressed air into
fine air bubbles at the air release point of the system.
~nother type of fine bubble aeration device that has been
used to great advantage is an aeration unit having a 1 to
1 1/2 inch thick porous diffuser plate of ceramic or
sintered metal through which compressed air is forced.
The aerator is sub-merged at or near the bottom of the
waste water treatment basin, and the compressed air that
passes through the small pores of the diffuser plate is
released in the form of fine air bubbles which rise
through the waste water to provide aeration. The diffuser
plate aerator is generally more efficient in oxygen
transfer than the other types of aerators that have bsen
used, and it dispsnses the air bubbles more thoroughly
throughout the waste water. The eEfective aeration
that is achieved by the fins bubble systsm is due
primarily to the relatively large areas of surface contact
between the smalL air bubbles and the liquid.
Conventional fine bubble aeration systems are designed
to maximize residence time of the compressed air bubbles
in the liquid in order to maximize the oxygen transfer.
The surface area of the diffuser media is normally
maximized and liquid pumpage is minimiæed. The goal of
the system is to widely dispense the air bubbles
across the basin, cause the bubbles to rise slowly through
the waste water, and minimize directional flow by
minimiziny the intensity of the air flow. For example,
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conventional systems operate at an air flow rate of 0-4
cfm per square foot of diffuser media. Most common rates
are 1 to 1.5 CFM per square foot.
Even though the approach taken by conventional systems
maximizes the oxygen transfer of the air that is pumped
through the diffuser media, there are no significant
surface aeration effects since the slow rise rate of the
bubble does not create appreciable turbulence at the
surface. The non-directional effect resulting fr~l
the wide dispension and low rate of air flow lead to
mixing problems and inefficiencies, particularly in low
F/M systems where the F/M ratio is less than about .2
XBOD/~MLSS. In high rate activated sludge systems having
a higher F/M ratio, existing fine bubble systems
function in an efficient and satisfactory manner for the
most part. However, in low rate activated sludge systems
or in aerated lagoon systems where the F/M ratio is
extremely low, the oxygen demand can be satisfied at low
ene~gy levels which do not result in enough mixing to
achieve proper interaction between the food and
microorganisms. Therefore, in order to provide sufficient
mixing to sustain the process, energy must be added beyond
that required for aeration, and the energy requirements
are increased accordingly. Net energy requirements
for the system are substantially greater than the
theoretical energy to dissolve oxygen.
Conventional fine bubble systems for activated sludge
applications are also characterized by high initial
costs and high operating costs. The aerators are arranged
closely together and a large number of aerators is
required to adequately treat a large basin. Lengthy rigid
pipe air lines are necessary to hold the aerators, along
with a large number of connecting devices for joining
the aerators (diffusers) to the air lines. The diffuser
units can bec~ne clogged so severely from build up of
deposits that application of chemicals such as
~Z47'~
hydrochloric acid is required to clear them. The aerator
devices which are submeryed at the bottom of the basin are
inaccessible and difficult to service. The porous
diffuser media are often ceramic or sintered metal plates
S which have rough texture surfaces that offer little
resistance to biological growth tending to clog their
pores. The diffuser plates are nonmally thick enough (1
to 1 1/2 inchs) that the pores present tortuous paths
which are easily clogged by debris in the air supply,
again blocking the diffuser and reducing the
effectiveness of the aeration.
Fine bubble systems have not been applied to aerated
lagoons. To employ the fine bubble system requires rigid
air piping, strict elevation control of lagoon bottom,
elevation control of air line, and strict elevation
control for diffuser units. Costs to provide these
features have been prohibitive because of the very large
areas in lagoons. Air flow rates for fine bubble air
systems are so low per unit that massive piping
systems would be required.
Fine bubble aeration systems traditionally require
considerable maintenance, Lagoons are not usually
contructed in parallel to allow units to be removed
from service for maintenance. Also, lagoons are so large
that dewatering for maintenance is not practical. Since
fine bubble systems are fixed in place and cannot be
serviced or removed from the lagoon wit~ut dewatering,
fine bubble aeration has not been a viable treatment
option even though substantial energy savings would be
possible. The fsar of operating and maintaining fixed in
place fine bubble systems has effectively prevented their
application to lagoons.
The present invention provides an improved method and
apparatus for treating waste water using fine bubble
technology. In accordance with the invention, a series of
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improved aeration devices is arranged in a prede-termined pattern
on the bottom of a basin or lagoon.
It is an important object of the invention to provde a
method and apparatus for effectively aerating and mixing waste
water in a manner to minimize the energy consumption. The needs
of the biological process are adequately met while achieving
substantial energy savings which become even more significant
in view of expected increases in energy costs in the future.
Another object of the invention is to provide a method and
apparatus of the character described which minimizes damage to
biological colonies or floc in the waste water treatment basin.
According to one aspect of the invention there is
provided apparatus for aerating waste water in a basin, said
apparatus comprising: a main supply pipe for receiving air under
pressure; a plurality of branch pipes each communicating with
said main supply pipe to receive air therefrom, each branch pipe
extending generally along the bottom of the basin and each branch
pipe being a plastic pipe subject to longitudinal expansion and
contraction in response to temperature changes in the waste water;
a plurality of aerators for each branch pipe, each aerator being
adapted to release a plurality of fine air bubbles when air is
supplied to the aerator and each aerato:r beinc~ provided with
ballast to hold the aerator down on the bottom of the basin; a
flexible conduit connecting each aerator with the corresponding
branch line to provide communication between the branch lines and
the corresponding aerators, thereby applying air to the aerators
for release of air bubbles therefrom to effect aeration of the
waste water, wherein each flexible conduit has a length at least
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as great as the distance between the corresponding branch pipe
and the surface of the waste water to permit each aerator to be
raised to the surface of the waste water whil.e the corresponding
branch pipe remains on the bottom of the basin and connected to the
flexible conduit; a flexible line for each aerator connected there-
with at one end and having an opposite end disposed at the surface
of the waste water; a float for each line connected with said
opposite end thereof, said floats floating on the surface of the
waste water to maintain said lines accessible from the surface for
lifting of the aerators to the surface of the waste water; and
at least one hold down bracket for each branch pipe provided with
ballast to hold the bracket down on the bottom of the basin, said
bracket having means for holding down the branch pipe while
permitting the branch pipe to longitudinally expand and contract,
whereby said brackets accommodate thermally induced expansion
and contraction of the branch pipes and said flexible conduits
allow the aerators to remain stationary as the branch pipes expand
and contract.
Other and further objects of the invention, toge-ther
with the features of novelty appurtenant thereto, will appear
in the course of the following description~
Figure L is a top pl.an v.iew showi.ng the waste water
aeration and mixing system oE the present inventlon installed
in a concrete basin in a typical activated sludge application;
Figure 2 is a sectional view taken generally along line
2-2 of Figure 1 in the direction of the arrows;
Figure 3 is a fragmentary sectional view on an enlarged
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sca]e taken generally alony line 3-3 of Figure 1 in the
direction of the arrows and showing one of the anchor brackets
included in the system;
Figure 4 is top plan view of the anchor bracket shown
in Figure 3, with the broken lines illustrating the bracket
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released from the aeration pipe;
Fig. 5 is a top plan view on an enlarged scale showing one
of the aeration units included in the system;
Fiy. 6 is a sectional view taken generally along line 6-6
of Fig. 5 in the direction of the arrows;
Fig. 7 is a top plan view showing the aeration system
installed in an earth basin in a typical lagoon
application; and
Fig. 8 is a sectional view taken generally along line 8-8
of Fiy. 7 in the direction of the arrows.
Referring to Figs. 1 and 2, the present invention provides
a method and apparatus for aerating and mixing waste water
contained in a sunken concrete basin generally designated
by numeral 10. The basin 10 has concrete end walls 12,
side walls 14, and a floor 16. The basin 10 may be
used in an activated sludge system having a relatively
high F/M ratio (greater than about 0.05 #BOD/#MLSS).
Numeral L designates the liquid level of the waste water
in the basin. The basin is open to the atmosphere at the
top.
In accordance with the present invention, compressed air
is filtered by central filtration equipment (not shown)
and delivered to a main header pipe l8 having an erld cap
20 on one end. The main suppLy pipe 1~ extends along
the top of one of the end walls 12 of the concrete
basin. Branching away from the main pipe 18 at spaced
apart locations are a plurality of carbon steel branch
pipes 22 which are generally vertical pipes extending down
into the basin 10 from the main pipe 18. Each of the
branch pipes 22 is equipped with a throttling valve 24 for
controlling the flow into the branch pipe. The lower end
of each pipe 22 is located adjacent the floor 16 of the
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basin and is elbowed to extend horizontall~. Each branch
pipe 22 connects at its lower end Wit}l a plastic aeration
pipe 26. Steel to plastlc adaptor connection 28 connect
pipes 22 and 26. The lateral aeration pipes 26 extend
5 horizontally along the floor 16 and are spaced apart
and parallel to one another, as best shown in Fig. 1. The
pipes 26 extend the length of the basin 10 and are
provided with end caps 30.
10 Each lateral aeration pipe 26 is held down adjacent
the floor 16 by a plurality of anchor brackets 32. The
brackets 32 are spaced apart along the length of each pipe
26 at 8-12 feet intervals. The spacing between adiacent
pairs of pipes 26 is preferably in the range of 4-12
15 feet. The brackets 32 are identical to one another.
Referring now to Figs. 3 and 4 in particular, each anchor
bracket 32 includes a conventional concrete block 34
having a central transverse web 36 separating the hollow
20 interior of the block into spaced apart openings 38.
A stainless steel pipe hanger 40 includes a pair of
vertical bracket arms 42 which are connected at their
lower ends by a horizontal bight portion 44 of the
hanger. The bracket arms 42 are spaced apart a distance
25 greater than the diameter of the lateral aeration pipe
26. Arms 42 extend upwardly through the openings 38 in
the concrete block on oppos ite sides of web 36. The bight
portion 44 underlies web 36 and angles between the lower
ends of the bracket arms 42. The openings 38 in the
30 concrete block are f illed with concrete 46 which acts
as ballast. The bracket arms 42 are embedded in the
concrete 46 to secure the pipe hanger in place.
The upper ends of bracket arms 42 are provided with
35 opposed hooks 48 which curve in opposite directions.
Each hook 48 opens downwardly and is large enough to
closely receive the aeration pipe 26, as shown in Fig.
3. Each hook has an out turned free end 49 which is
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spaced above block 34 a distance greater than lthe diameter
of pipe 26.
Each bracket 32 is applied to the proper aeration pipe 26
5 by initially positioning the block 34 as shown in
broken lines in Fig. 4. In this position, the long axis
of the block is parallel with the axis of the aeration
pipe 26, and the aeration pipe extends between the upper
portions of the bracket arms 42. Block 34 is either
10 rotated through ~0 to the solid line position shown
in Fig. 4, as indicated by the directional arrow. The
free ends 49 of hooks 48 c lear the top of the pipe 26, and
the opposing hooks 48 are aligned directly above the
aeration pipe. When the pipe is thereaEter raised, it
15 fits closely in both of the hooks 48 and is firmly
gripped therein and prevented from floating upwardly away
from the floor 16 of the basin. The concrete ballast 46
and block 34 together have enough weight (approximately 85
lbs.) to anchor bracket 32 down on the floor 16 of the
20 basin. The brackets 32 acc~mmodate thermal expansion
and contraction of the aeration pipes 26 without affecting
the location or operation of the aeration units 50
supplied by the pipes.
25 Each of the lateral aeration pipes 26 supplies
compressed air to a plurality of aeration units 50 which
are identical to one another. A flexible hose 52 directs
the air to each aeration unit 50 from the correspondiny
pipe 26. One end of each hose 52 connects with the
30 aeration unit, and the opposite end oE the hose has a
T connection with the aeration pipe 26. The aeration
units supplied by each pipe 26 are spaced apart at
intervals of 4-12 feet.
35 Each hose 52 has a length at least as great as the
distance between the pipe 26 and the surface of the waste
water. Consequently, each hose is long enough to permit
the associated aeration unit 50 to be raised to the
~ 24t7~tio
surface of the waste water for servicing while the
aeration system remains in operation. This feature
permits the systeln to remain on line while servicing of
the individual aeration units is carried out.
Referring now to Figs. 5 and 6 in particular, the body of
each aeration unit 50 is formed by a thin shell 54. A
flat flange on the periphery of shell 54 provides a stable
base 56 which rests on the floor 16 of the basin. Inside
of the base 56, shell 54 is shaped to provide a
continuous upstanding wall 58 which surrounds a generally
horizontal deck 60. The deck 60 is elevated above base 56
but is lower than a horizontal ledge 62 formed on top of
the wall 58.
The area located below deck 60 and within the wall 58
defines a ballast compartment 64. The ballast compartment
64 is filled with concrete 66 which serves as ballast to
hold the aerator unit down on the floor of the basin. The
concrete 66 fills the interior of wall 58 and has a
flat bottom surface which is coplanar with the base 56.
The area above deck 60 and within the wall 58 provides an
air chamber 68 which receives the compressed air supplied
through the flexible hose 52. The end of hose 52 is
clamped to a plastic inlet fitting 70 by a hose clamp
72. The fitting 70 extends through wall 58, and its end
is threaded at 74 to receive a retainer nut 76 which
secures the inlet fitting to the body of the aerator
unit. Fitting 70 may be equipped with a balancing
valve 78 which can be adjus~.ed to control the flow of air
into the air chamber 68. Fitting 70 may also have a check
valve 80 which permits the flow of air into air chamber 68
but prevents back flow out oE air chamber. The check
valve 80 prevents the entry of water and debris into
the piping when the aeration device is inactive for
extended periods.
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The top of the air chamber 6~ is covered by a flexible
plastic difiEuser plate 82 which rests on top of ledge 62
at its periphery. Stainless steel anchor bolts 84 which
are embedded in the concrete ballast 66 project upwardly
5 through the periphery of the ;liffuser plate 82. The
periphery of the diffuser plate is held down on ledge 62
by stainless steel straps 86 which also receive the anchor
bolts 84. Stainless steel nuts 88 are threaded onto bolts
84 and are tightened down against the straps 86 in order
10 to secure the diffuser plate 82 in place, Plate 82 is
generally parallel to the deck 60.
The diffuser plate 82 is a -porous plate having a porosity
or void ratio of at least 40%. The diffuser plate has a
lS large number of small pores which are less than 60
microns in diameter and which are about 35 microns in
diameter on average. The thickness of plate 82 is less
than one half inch in order to reduce the length of the
path that is taken by air passing through its pores. At
20 the same time, the plate is thin enough to readily
flex due to abrupt changes in the air pressure. The
flexibility of the plate permits it to flex when the air
supply is interrupted and then resumed, and the periodic
flexing of the E~late dislodges any biological growth that
25 would otherwise tend to build up~ The use oE a thin
plate also reduces the pressure losses during operation,
An eyebolt 90 is embedded in the concrete ballast 66 of
each aeration unit, The eye bolt projects Erom one end of
30 the aerator body, and a flexible rope 92 is tied to
each eye bolt. Each rope 92 has a length yreater than the
depth of the waste water so that it can extend to the
surface with the aerator on the floor 16 of the basin. A
floating rope 94 (Fiy. 2) is tied to the top end of each
35 rope 92 and floats on top of the waste wa ter~ The
aerator units 50 can be raised to the surface for
servicing simply by pulling the corresponding ropes 92.
Each rope 92 is formed from a substance that does not
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deteriorate when exposed to the waste water.
In operation of the aeration system, compressed air is
supplied to the main header pipe 18 and is directed
through the branch pipes 22 to the lateral aeration
pipes 26. The throttling valve 24 permit the flow rates
to the various aeration pipes 26 to be controlled as
desired. Normally, each pipe 26 will receive the same
amount of air, although special distribution patterns are
possible.
The air in the aeration pipes 26 passes through the
flexible hoses 52 to the aeration units 50. The balancing
valves 78 can be adjusted to supply each aeration unit 50
with the desired amount of air. By properly adjusting
the balancing valves 78, the system can be controlled in a
manner to compensate for variations in the elevation of
the basin floor and to preven-t starving of the aeration
units that are far downstream in a system having long
aeration pipes. Normally, the same amount of air is
supplied to each aeration unit, although other
distribution patterns are possible.
The compressed air that is supplied to each aeration unit
50 enters the air chamber 68. The pores in the
diffuser plate 82 provide the only means of egress of air
from the air chamber, and the air passes through the
diffuser plate and is released thereErom in a series of
ultra fine air bubbles. E~ch bubble has a di~neter Less
than 60 microns and 35 [nicrons is the normal bubble
size. The air bubbles rise through the waste water to
provide the desired aeration and mixing action. Due to
the small size of the ultra fine air bubbles, there are
larye areas of surface contact between the air and liquid,
and the transfer of oxygen to the waste water is thus
effectively carried out. Since the aerator units 50 are
at discrete locations, the bubbles are released from a
plurality of discrete locations distributed uniformly on
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the floor of the basin~
The fine bubbles are generated from the aerator units 50
in a highly intense manner. The flow rate of air through
each diffuser plate 82 is between 5 and 50 cfm per
square foot of surface area presented on the diffuser
plate, depending upon the particular application of the
system. The highly intense manner in which the fine air
bubbles are genera-t~ provides agitation and mixing of the
liquid, resulting in a high liquid velocity. The
liquid is thus mixed in a thorough manner and solids are
maintained in suspension without the need to provide added
energy for the purpose of mixing of the waste water.
The rapid rise rate of the air bubbles and the high
liquid velocity creates a large turbulent boil of liquid
at the surface of the waste water above each aerator
unit. ~he turbulant boil results in substantial surface
aeration from atmospheric air above the basin and draws
atmospheric air into the waste water. The intense
application of fine air bubbles at a relatively small
number of locations produces a net oxygen transfer and
mixing rate that is superior to conventional fine bubble
systems when pumped air, dif~usion, and surface aeration
are all taken into account.
The individual aeration units 50 are spaced apart from one
another to a greater extent than in conventionaL fine
bubble systems. ~y releasing air at high rate~ ~rom a
relativeLy smaLl number o~ discrete locations that are
widely spaced, improved liquid circulation patterns are
achieved. The turbulent circulation patterns of the air
bubbles that are released frc~ adjacent aerators impinging
against and overlap and interact with one another to
provide improved mixing and aeration. At the same
time, high pumpage rates of the aerator units distribute
air and energy uniformly throughout the basin 10.
1~4~;t~(3
The method and apparatus of the present invention is
equally well suited for use in relatively low F/~ systems
such as the typical lagoon application shown in Figs. 7
and 8. Numeral 110 generally designates a lagoon having
sloping ends 112, sloping sides 114, and a generally
horizontal bottom 116.
The aeration system for lagoon llQ is for the most part
the same as the system for the concrete basin 10, and the
same reference numerals are used in Figs. 7 and 8 for
components that are identical to those used in the basin
shown in Figs. 1 and 2. The aeration system of the
present invention is installed in the lagoon 110 in
essentially the same manner as in the concrete basin 10
shown in Figs. 1 and 2. However, the lateral aeration
pipes 126 extend across the width of the lagoon 110 and
are spaced apart more widely than in the activated sludged
application. Also, the steel branch pipes 122 which
connect with the main header pipe 118 incline in a manner
to conform generally with the incline of the side
walls 114. The aerator units 150 used in the lagoon
application are identical to the aerators 50 described
previously, although the lagoon aerators 150 are normally
spaced apart from one another at 20-50 foot intervals due
to the low F/M ratio and low oxygen uptake rate of the
waste water in the lagoon.
The aeration system operates in the lagoon application in
the same manner as in the activated sludge appLicatiorl.
The thorough mixing and air distribution throughout
the lagoon makes the process efficient in the dispensed
growth biological system as well as in the activated
sludge application,
The method and apparatus of the present application is
flexible enough to accommodate variations in the system
loading, season of the year, and type of aerobic process
desired. At the same time, the capital cost of the
equipment is relatively low since only a relatively few
1~47~7~0
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aerator units are required. The maintenance requirements
are also reduced due to the ease with which the aerators
can be serviced while the system remains in operation.
Due to its improved efficiency, the energy costs of
operatin~ the system are also reduced. It is a~ain
pointed out that the system can be installed in both new
and existing bioloyical reactors.
When the aeration units are used in an earthen basin or
lagoon, they protect the underlying surface against
erosion. This anti-erosion effect is unnecessary in
concrete basins such as the basin 10. If additional
protection against erosion is desired in an earthen basin,
a flat plastic plate (not shown) can be bolted to the
lS flange or base 56 of each aeration unit. This plate
extends beyond the base 56 to the extent desired, and it
shields the underlying surface against erosion.
Fr~n the foregoiny, it will be seen that this invention is
one well adapted to attain all the ends and objects
hereinabove set forth toyether with other advantayes which
are obvious and which are inherent to the structure.
It will be understood that certain features and
subcombinations are of utility and may be employed
without reference to other features and subcombinations.
This is contemplated by and is within the scope of the
claims.
Since many possible embodi~nents may be made of the
invention without departiny from the scope thereof, it is
to be understood that all matter herein set forth or shown
in the accompanying drawings is to be interpreted as
illustrative and not in a limitiny sense.
