Note: Descriptions are shown in the official language in which they were submitted.
~ ;i883
Background of the Invention
The invention relates broadly to the treatment o~ water
by aeration. The aeration txeatment o water has been used to ,
treat waste water within lagoons and to upgrade'the'quality of ~ ~"
natural bodies of water, such as lakes.
In the majority o~ pxior design critexia evaluations ~or
aerated lagoons, focus has been placed almost entirely on the
satisfaction of waste biochemical oxygen demand (~OD). That is,
the amount o~ supplemental aexation or oxygen which was to be
supplied to a lagoon was caIculated by the amount which the
waste strength exceeded the oxygen available from photosyntheses
and atmospheric aeration. The mixing O:e the waste water to main-
tain solids in suspension while aerating the body of water was
i~nored until recently. In an article entitled "How To Design
Aerated Lagoon Systems to Meet 1977 E~luent 5tandards-Soluble ,~,,;," ~,
Substrate Removal Relationships" by Sam C. White and Linvil G.
Rich at pages 82-83 of WATER AND SEW~GE WORKS, April 1976, mixing
was included as a design parameter for an aerated lagoon. ;
Waste water treatment aeration systèms generally utilize
either dif~used aîr aerators or mechanical aerators. A diffused
air type aeratox introduces air or pure oxygen into water via ~-
submerged ~orced diffusers or nozzles. Mechanical type aerators
generally agitate the water so as to promote solution of air
from the atmosphere into the water. These conventional aerators
are designed prim~rily from the standpoint of introducin~ a cer- ;~
tain amount of oxygen into the water being txeated. The mixing ~' '
of the water and the introduced oxygen has not been a design
criteria and, hence, conventional Prlox aerator systems have
~nef~icient mixin~ capabilities~ For example, in a one acre
,
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aerated pond for treating dome~tic waste. wa.ter, a pond which has ~ `
a depth of ten feet and a 3:1 side wall slope:and a volume of ~.
432,000 cubic feet, conventional aerator sizing procedures would
require approximately 200-400 horsepower of sur~ace area capacity
or over 1,000 horsepower ~or a di~fused alr system~ Such high
power systems result in the oxygen requirement of the pond being
satisfied fourfold, while probably not causing a complete mixing
of the pond so as to assure scouring velocities of 0.5 ~eet per
second throughout the pond~
Mechanical sur~ace aerators also exhibit an additional
problem in that they ha~e separate and genera].ly conflicting mix~
ing vectors. That is, the force vectors from the aerators cannot
generally be managed or manipulated and, hence, with closely spac-
ed aerators, mixin~ vectors tend to cancel out. `
Another problem with most conventlonal aerator systems
is that their oxygen transfer is ef~ectively limited by their
inability to Properly mix the waste. .Most conventional aerator
systems tend to have a very limited core of influence, that is,
the conventional aerators cause a high dissolved oxygen concentra~
tion close to the units themsel~es because of the inability of the . ~:
units to mix. Thus, such conventional systems tend to create a ::
condition of oxygen oversaturation instea`d of under saturation,
which would promote oxy~en trans~er. Many con~entional aerators ~ :~
are tested in small tanks and the test measured oxygen transfer :
rate at zero DO is then reported as a standard for comparision. .
This standard, however, iS not accurate in field apPlications
since ln field applicatlons, the dissolved oxygen is required in
a ~uch larger volume. In field installations, the conventional ~
~ :
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~gL35~ 3
., .,~ .
. units tend to overaerate the nearby region and, thereby, to .
effectively work agains;t themselves. The di.ssolved oxygen is not
effectively reaching outlying regions.
; Other problems also arise due to the fai.lure of the prior
art aeration syætems to adequately mix the waste water being treated.
Without adequate mi~i.ng, for example, when 0.5 ps horizontal velo~
city is not attained, aerated lagoons may develop adverse conditions
that effect performance:such as hydrauli.c short circuiting and/or .
sludge solids build-up. ~s waste water enter~ an uhmixed lagoon, a
certain fraction of waste.may move directly to the outlet without
adequate time Q i.nteracti.on with other lagoon contents for adequate .
treatment. If the pond is completely stagnate,in1uent velocity
' e~ects or momentum may set up such a "short circuit" current and ~:
i this: prohlem may be. exasperated by thermal stratification effects.
. Another prohlem is a s.ludge blanket build-up. Under mixed lagoons,
;' cells may develop aerobi.c-anaerobic regions analogous to a fac.ul-
tative ~ond. ~naerobic ~ludge deposits found in undermixed lagoons ~:
may produce noxious odors such as H2S and/or NH3 gase~
. These gases may carry a high concentration of ox~dizable
organi.c material (~..e.,BOD) into the water. Finally, the release
of these gas.es to~ether with:the CH4 and N2 may contribute to float-
ing solids and a tendency to "belch" these into the lagoon or .;
ceIl outlet. This mas~ of material may be transported into sub- -
sequent txeatme.nt ceIls or out as a final e1uent.
51udge. deposits deposited in a lagoon must be regarded
as lo~t ~xom control. Anaerobic digestion may :occur when tempera-
.. tures pexmit, wi.th. the. result that perormance may become ~easonal~
The ~y~tem i`s e~e.cti.ve.ly out of operational control, when
effluent ~uspended ~olids- in BOD concentrations become a function ~:
a ~:
~ ~L35i~83
of such factors. Such a system cannot reliably assure the degree
of performance needed to meet the ordered quality standards of
today.
The method in accordance with the present invention over-
!' .,
comes the above defic.iencies of conventional systems by both aera-
~, ting a body of water and causing mixing of the aerated water at
efficient power levels.
SUMMAR~ OF THE INVENTION .
The present i.nventi,on.relates to a method for treating :~
, 10 water. The method compxises:the steps of:
aexati,ng a bounded body of water wi.th a plurality of ~ ~
propeller-type aerators, each aerator having a hollow tube ~;:
.~ wi.th.opposite.ends,~ longitudinal axis extending between ';
,1 the. ends, and a propeller adjacent one of the ends;
placing e.ach of the aerators in the bvunded body of
" ~atex with. the propeller and tuhe end adjacent thereto
.1 below the'top s.urface Qf the water and with the longitu~
dinal ax~s of each'aeratox disposed at an angle below
' the, hori,zontal;
',' 20 drii,vi,ng the' aerators to create individual ci.rculating ,~
flo~ patterns around each'of the aerators;
~ mi~ing the water by axranging the aerators in a
; d,i`~positi~on to link the indivi,dual flow patterns created
adjacent aerators to one another to ~orm a larger closed
ve~all flo,~ pattern; :-
iniecting Qxygen from ambient ai.r th.rough the tube
into the ~ody of ~atex adjacent th.e propeIler at a rate
gxeater than 1 pound of oxygen per horsepow.er-hour;
inducing by me.an~ of the: pxopellers of the aerators
' 30 the'closed ovexall flo~ pattern at an average linear
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velocity in a ~ener~lly horizontal directi~n through a
cross section to flow at a rate o~ at least 0,25 feet
per second.
In the preferred embodiment, the method of the present
method includes the steps of injecting oxy~en at a rate ~reater
than 2.0 pounds of oxygen per horsepower~hour; and of inducin~
the closed ov`erall flow pattern at a linear velocity greater than
0.5 feet per second by driving -the propellers of the aerators
in the bounded body of water at less than0.1 horsepower per
.~ .
thousand cubic feet of water ln the bounded body of water. The
injection of the oxygen and the inducement of the flow pattern
at the above low horsepower rates results in e~ficient treatment
of waste water and an efficient reduction of effluent is biological
oxygen demand (BOD). It is believed that the efficient treatment ;~
, of waste water is due to the capability of both indu~ing the flow
pattern to maintain solids in suspension and the iniection of
oxygen both at efficient power ratings.
The o~erall flow pattern within a bounded body of water ;; ;
is attained by linking the circulating flow patterns of adjacent
. .
aerators together. In one embodiment, a sin~le series or set
of aerators is arranged in a single closed overall path. In ;
another embodiment a second set of aerators is arranged adjacent
to the ~irst set to create a second closed flow pattern within
the body of water. In another embodiment, a second set of aerators
forms a closed flow pattern within the closed flow pattern formed
b~ a first set of aerators.
In order to prevent v~id flow areas within the center
of an overall flow pattern, one or more aerators can be displaced
out of the overall flow pa-tteXn toward the center of the overall
3 f low pattern. This displacement ~f one or more aerators creates
a sub-flow pattern to avoid a void flow area. ~
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! ,
By injectin$ oxygen at a contrQlled xate and by simultane-
ously controlling the flow and flow patterns of the w~s~e water~
a controlled and e~ficient waste water treatment system can be
maintained. The suspended solids levels in various lagoons and
effluent may be manipulated with proper c~ntrol of the mixing
lagoon by lagoon through a series systeme ~tually~ any form of
seasonal control discharge can be provided for suitable solids
while maintaining a flow-through condition ~or the li~uid~ In
order to implement this strategy with aerator and turbulence ~; ;
(mixing) control, aeration is tapered down during the winter as
temperatures fall. This is appropriate since less oxygen is ;~
required as the rate of exertion of oxygen demand declines with
; temperature and oxygen transfer efficiency is improved with in-
; creasing saturation values for dissolved oxygen.
An additional benefit of this procedure is that solids ;
are allowed preferentially to drop from suspension and the lagoon
provides essentially for solids' storage and holding during
- winter operations. Solids then accumulate~as a thin aerobic
sludge blanket for slow digestion through winter. As noted
above, a reduced level of aeration may be provided during
winter to assure that the lagoon surface remains at least par~
tially open to the atmosphere or, at least, that aerobic con~
ditions prevail throughout the water volumeO Thin sludge layers
held for an extended period under aerobic condition may be
expected to undergo composting and to waste away. ~hen the ~ ;
~` lagoon begins to form again, aeration and turbulence levels may
be restored early and gradually to resuspend solids and to in-
crease treatment wh~le providing for a~ flow proportloned discharg~ -
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of solids as runoff occurs and stream le~els are hi~h.' Thus,
by utilizing the present method, a year round cont~olled system ''
of waste water treatment can be attained at e~icient power levels.
Various advantages and features of novelty whl'ch charac-
terize -the invention are pointed out with particularity in the
claims annexed hereto and formin~ a part hereof~ However, ~or a
better understanding of -the invention, its advantages, and objects
obtained by its use, reference should be had to the drawings
which form a further part hereof, and to the accompanying de-
scriptive ~atter, in which there is illustr~ted and described a
preferred embodiment of the invention.
Brief Description of the Drawin~s
' PIGURE 1 is a side elevational view illustrating a single '~
propeller-type aerator ~or use in the method of the present
invention; ~` `
FIGURE 2a is a plan view diagrammatically illus-trating ~; ~
; the specific placement o~ a number o~ propeIler-type'aerators ~; ;
within a bounded body of water and the overall flow path in- ' ;-
duced by the aerators; ~-
FIGURE 2b is a plan view similar to FIGURE 2a illustra~
ting the specific placement of propeller-type aerators within
a different bounded body of water;
FIGURE 3a is a diagra~ illustrating velocity measurements
taken at various locations within the body of water illustrated
in FIGURE 2a;
FIGURE 3b is a diagram illustrating velocity measurements
taken at various locations within the body of water illustrated
i~ FIGURE 2b;
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. FIGURE 4 i.s a diagrammatic plan view illustrating individ-
ual horizontal circulating flow patterns induced by propeller-type
i aerators and the linking of adjacent circulating flow patterns in
accordance with the method of the present invention; ~ '.'
FIGURE 5 is a diagrammatic plan view illustrating another
arrangement of propeller-type aerators and the resulting adjacent
, overall flow paths; .
; FIGURE 6 is a diagrammatic plan view illustrating an `
arrangement of propeIler-type aerators in encircling overall ~,
~ 10 paths ~herein a subflo~ path.is created by displacing a number of
,,', aerators out of the oYerall flow path;
:, FIGURE 7 is, a diagrammatic plan view illustratiny the :: , placement of a plurality of propeller-type'aerators in a single
: oYerall flow path ~herein a number of aerators are displaced from '~
~ alignment ~i.th the overall flo~ path to create a subflow path.
I DETAILED DE~SCRIPTION OF THE INVENTION
~.!, Re.ferriny to the dra~ings, there is shown i.n Figure 1 a , ' ;
'~ propeller-type aerator 10 for use'in the method of the present
invention. The' aerator 10 i.s shown disposed ~ithin a li~uid 12
, 20 preferab.ly ~ater or ~aste ~ater. The aerator 10 has an outer
tubular housin~ 14 and an inner tube 16 rotatably carried within
', the outer tubular housing 14. The inner tube 16 ex-tends ~ithin
' the tub.ular housing 14 to a leveI above the top surface of the
:,
uid 12 and is dri.vingly coupled to a motor carried ~lthin a ` ~.
. motor housin~ 18. The, inner tube 16 has at least one hole at its i~
:. upper end abo~e'the top leveI of the li.qui.d 12 for admitting air
into the.'interior of the tube 16. The inner tube 16 extends
. out~ardly ~eyond the lo~er end of the tubular housing 14 and has :.:
'', a prope.Iler 20 ~ixedly attached thereto. A di.ffusion tube 22 is ~'
', 30
::
8~
also attached to the inner tube 16 and has a hollow interior which
communicates with the hollo~ interior of the inner tube 16. ::
~hen the inner tube 14 is rotated by the motor, the .
propeller 20 is also rotated. As the propellex 20 rotates, it
causes a directional, turbulent flow field in the liquid 12. The
reduced pressur~ zone created by this flow downstxeam of the pro-
peller aspirates: or draws air do~n the hollow tube 16 and causes :
air to enter the li.quid through an open end of the diffusion tube
22 as air b.ub~les 24. The air bubbles 24 are thereafter dispersed ' : '
.~ .
by the turbulence caused by the propeller. In this manner, the
' propeIler-type aerator lO aerates while it mixes. As will be ..
: explained more fully hereinafter, aerators 10 can be arranged to
proYide a directional flo~ ~ith the aerators 10 installed to ~:
contri.bute addi.tiYeIy to the uniform mixing patterns involving an .
. entire. bounded body of ~ater. Liquid flow can thus be directed '.
and circulation pattern~ can be developed to assure desired velocity
vectors throughout an entire Yolume of a body of water being .'.~'
:. treated. :
The inner tube'16 has a Iongitudinal axis indicated by :'
line 26. The:aerator 10 i.s supported in the liquid 12 by a ~"
platform or ~oom 28. The aerator 10 is attached to the plat~orm
:~ 28 in any conyentional manner, such as by a bracket 30. The
i~'. aerator 10 is sup~Qrted in.the liquid 12 .such that the longitudinal
axis 26 fo.rma an an~le ~ith:the horizontal ~etween 15 and 25 ~.
~ de~ree~. ~refer~bl~ the angle is set at 22 degrees. In this
.' manner, th~: mi~in~ ene.r~y caused by the rotati.ng propeller tends .
to ~romote ci.xculation and flow over a larger area than is ~-
typical Q~ conve~tional turbine aerators. I.~ the angle is in~
crea~ed past 25 degxees so that the tube 14 ~ecomes more vertical,
to some'degre.e hl.~her oxygen trans~er is obtainea at the expense
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1~35~83
of mixing. As the angle is decreased below 15 degrees to~ard
the horizontal, mixing i.s increased at the expense of oxygen
transfer. It has ~een found that the range of 15 to 25 degrees
for the angle of inclination is an optimum compromise of mixing
and aeration and that the 22 degree angle of :inclination is
preferahle.
The method of the present inventi.on finds its primary
use in aerated lagoons or ponds used as a portion of an overall
waste ~ater treatment process. Aerated lagoons systems can be
10 desi.gned for thxee different leveIs of mixing. LeveIs of mixing :
are generally determi.ned by the degree of pollution in the water
or the BOD requi.rement. For most waste water treatment lagoons
receiYing reIativel~ di.lute domestic wastes, the power required to
satis.fy oxygen demand through:most of the year is markedly less
than requi.red to maintain 501ids in suspension. The lowest.level .
of pow.er input must txansfer s.uffici.ent oxygen to satisfy demand
exerted by the satisfaction of BOD in the waste. Aeration suffici.ent
: to transfer 0.7 to 1.4 pounds of oxygen per pound BOD exerted is
typi.cal. ~n intermedi.ate level of power input must provide for
uni.form oxy~en di.spers.ion throughout a lagoon volume in addition
to mereIy ~upplying a specified quantity of oxy~en. He.nce, addi~
tional pow.er over that required to merely i.nject the oxygen is ~ ;
needed ~o that minimal circulation effects are created to ensure
uniform distribution of oxygen throughout a la~oon volume.
j~ :,. ..
. Howeyer, at such.an i.ntermediate leveI, sufficient turhulence is
; not created to mai.ntain solids in suspens.i.on. The highest level
of power i.nput that would reasonably be necessary would provide
for o~gen dispers~l.on as ~ell as minimum s.couring veloci.ties,
such as~ Q.4 to 0.5 feet per second (fpsl. Prior art aeration systems
h.a~e re~uir~ed at l~ast ~ 5 hp/10~:3.o.f wa~er and hl.gher ~ower
`,~!. :
383
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: densities to attain ~uch.flow velocities.
The method of the present invention accompli.shes both ~ ;~
adequate oxygen injection into waste water and mi~ing of the ;~
aerated ~a~te water at ef~icient power levels. The present inven-
tion permits management or control of oxygen injection and mixing
velocities at effi.cient power levels under numerous water pollution :.
- condi.tion~. ~he method includes the steps of providing a plurality ; .~
of propeIler-t~pe aerators where each. aerator has a hollow tube ; ~`
wi.th opposite ends and a longitudinal axis extendi.ng bet~een the
ends and a propeIler adjacent one of the ends. The aerator 10 is
. s.peci.all~ suited for the present method. The aerators are placed ;~
.. in a bounded body of water, such.as a pond or a lagoon, with the ~;
; propeller and tube end adjacent thereto beIo~ the top surface of the ;~ ~:
: water and ~i.th.a longitudinal axis of each.:aera-tor disposed at an
angle beIo~ the horizontal. The water i.s mixed by arranginy and
driving the. aeratars i.n a di~position so that indi.vidual circulating
flow patterns are created around each.of the aerators and the
~ indiyidual flow patterns-link to one another to form a larger
.: closea overall flo~ pattern. That is, the. aerators are arranged ~ .
such.that ~hen:the propellers-of the aerators are driven at suffi-
ciently hi:gh. ~peeds to inject ambient air i.nto the water, indivi- ~
. dual ~low patterns are created around each.of the aerators and ~:
: are linked to~th~r to form a larger closea overall flow pattern. ;~
The individual flo~ patterns and the linki.ng of adjacent
indivi.dual flow-pattern~ is illustrated in Fi.gure 4. Three
aeratoxs laa, 10~, lOc a~e il:lustrated diagrammaticall~ i.n Fig. 4.
Horizontal flo.~ vectors indi.cating a horizontal flow of the water
are sho~n emanati.n~ about each. of the aerators lOa,.lOb, and lOc.
A plurali.ty of forward hbrizontal flow vector~ 32 indicate a ~
~ :
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horizontal flow of fluid forward of the propellar of aerator lOa.
Negative horizontal flow of vectors 34 indicate a horizontal flow
of fluid which i5 drawn toward the propeller of operator lOa from
the area rearward of the propeller. Horizontal flow vectors 36
indicate a diffuse hbrizontal flow of fluid bending backward from
the forward flow indicated bv vectors 32 and interconnecting or
forming a portion of the flow indicated by negative vectors 34.
Similarly numbered flow vectors are indicated about aerators lOb
and lOc. As seen în Figure 4 -the aerators lOa, lOb, and lOc are ~ ,
arranged relati.ve to one another so that at least some of the
flow indi.cated by the negative flow vectors 34 of one of the
aerators. link.s with. at least some of the forward flow vectors 32
of an adjacent aerator. In this manner, an overall horizontal
flow is created in the yeneral direction of the forward flow
vectors 32.
Fi~ure~ 2a and 2~ illustrate a plurality of propeller~
type aerators 10 supported on platforms or booms 28 wi.thin a pair ~
of waste water treatment lagoons in which studies of the present ~ ::
lnventiQn ~ere made. Flow vectors or arrows 4G, 38 indicate a
closed oYerall horizontal flo~ pattern or path.of the waste water.
The outex set or ci.rcle of aerators 10 creates the overall flow ,~
pattern indi.cated by vectoxs.38. The overall flow pattern indicated
hy vectors 40.is, create.d by an inner set or circle of aerators 10,
The oYexall flo~ pattern indi.cated by vector~ 40 circulates within
the over~ll flo~ pattexn indicated by vectors 38.
Fi~u,res 2a and 2b dia~rammatically represent a plan view ~ .:
of two la~oon~ or ponds that form a portion of a waste water
treat~lent plant ~ithi.n ~hi,ch the present method was utilized~ .
ThR water treatment plant also included a primary sedimentation
unit, a ,roughin~ filter and a clari~ier follo~.ed by a pond or
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~35~3 ` ~
lagoon system having four ponds, which Figs. 2a and 2b,respectively,
illustrate first a~d second ponds of the pond system. Each of these
first two ponds ha~ a surface area of approximately 3/4 of an acre
and a water volume of approximately 275,000 cubic fee. The ponds
are approximately 175 ft. wi,de and 190 ft. long.
' The pond of Fi,g.2a has a plurality of propeller-type ~
aerators 10 installed ~i,th,a total power of 36 hp. The pond repre- ' ~,'
sented by Fig.2b has a plurali-ty of aerators 10 installed with a
. .
combined po~er of 20 hp. The booms 28 extend inwardly from approxi-
mately the'middle of each,side of each,~pond.Each of the outer '
;
;aerators ia dispo~ed approximately 30ft. from a respective side wall ~;-
and each'of the, inner aerators is disposed approximately 60 ft.
from a respective side wall.
; Fi~. 3a illustrate~ a profile or verti,cal section through
~, the pond illustrated in Fi,b.2a along the 195 ft. line passing
" between SE and N~. Flg.3b i,llustrates a similar profile or vertical
, section alang 195 ft. li,ne passing SW to NE in the pond illustrated -', ~'
in Fig.2b. Figs. 3a and 3b specify the veIocity measurements in ;~
., : .
~eet per second ~fps~ taken at various depths within the ponds,along ~' '
the'cross section, when the aerators 10 were'operaking to create
" the overall flow patterns indicated by arrows 38,40. The measured ~'
veloci,ties in Fig.3a result in average linear velocity in a gener~
ally horizontal directian through th,é cross ~ection of the first ' ~,
.,. ~ ~.
pond o~ 0.77 fps and the veIocities measured in Flg.3b result in
average linear veIocity in a ~enerally horizontal direction through ~-
;, a cross section of the second pond o~ 0.58 ~ps. These calculated
average pond YeIocitie~ are also the avera~e velocity of the closed , ,~
overall ~low-patkern in the ponds. Since a total of 36 hp is used
' in the ~ir~t pond and the ~irst pond has a yolume of approximately ~;
,, 30 275,000 cuhic ~eet, the avera~e pond veloci,ty of 0~77 ~ps is
attained, utili,zin~ 0~13 hp per lOOQ cubic ~k. of ~ater. The
second pond also has an approximate volume o~ 275,000 cubic ~eet
.
.~ .
,~ - 14 ~,
L3~8~3
and, hence, an average pond velocity in the second pond of
0.58 fps is attained, utilizing 0~07 hp per 1000 cubic feet of
:
water. The 20 hp utilized in the second pond attained a velocity
sufficient to maintain solids in a complete suspension.
When a 5 horsepower propeller-type aerator is used and
the aerator is disposed approximately 22 degrees below the
horizontal, a horizontal flow sufficient to maintain solicLs in
suspension extends forwardly at least 60 feet and a diffuse flow
field approximately 60 feet wide is formed. ~hen a 2 horsepower
propeller-type aerator is used and is disposed at an angle
approximately 22 degrees below the horizontal, a horizontal
forward flow field sufficient to maintain solids in suspension
extends for~ardly at least 30 feet and a diffuse flow field has
; a width bet~een approximateIy 30 and 40 feet.
It is~ generally -
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recognized, an average pond velocity of 0.50 fps should be
sufficient to maintain solids in suspension within a waste water
treatment facility. The higher power used within the first pond
was utilized because of increased BOD loading to the pond system.
As mentioned above, the average pond velocities attained in the ;:
ponds illustrated in Figures 2a and 2b maintained solids totally
; in suspension. It is also within the contemplation of the present
invention to utilize lower flo~ velocities wherein solids may be
only partially suspended. However, the present invention con~
lQ templates an average pond veIocity of greater thanlQ25 fps for the `
purpose of mixing the waste water. In the preferréd embodiment,
an average pond velocity of greater than Q.5 fps is used. An
average pond velocity of yreater than 0.5 fps shbuld be sufficient -~
; to maintain solids in complete suspension~
In the ponds illustrated by Figures 2a and 2b, oxygen
was injected at a rate greater than 2.0 pounds of oxygen per
horsepo~er. The method of the present invention contemplates ~ ~
injectiny oxygen at a rate of at least 1 pound of oxygen per horse- -
power hour and preEera~ly at a rate ~reater than 2 pounds of
oxygen per horsepower hour. In the present method, utilizing
propeller-type aerators as illustrated in Figure 1, oxygen
injection rates exceeding 3 pounds of oxygen per horsepower ~ ~-
hour can be obtained.
While some conventional aerators claim a capability of
injectîn~ oxy~en at the above rate, Applicants are una~are of any
aeration system which can combine both the oxygen injection and
inducement of flow velocîty in accordance wîth the method of the
present in~ention.
Fî~ures 2a and 2b illustrate one form of an overall
flow pattern in accordance with the method of the present invention.
~.
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~.~.35~
The overall flow pattern illustrated in Fi.gs. 2a and 2b includes ::.
': a closed overall flow pattern, illustrated by vectors 40, which
: flows within a closed overall flow pattern indicated by vectors 33.
.~ Fi.g. 5 illus:trate~ an alternate overall flow pattern of water
. wherein tw.o sets of aerator~ 10 are utilized to form a pair of
closed overall flo~ patterns or paths side-by-si.de or adjacent to
one another. The adjacent closed overall flo~ paths are indlcated
by h.orizontal flow vectors 44, 46.
F~g. 6 i.llustrates: an overall flow pattern system similar
to that i.llu~trated in Fi.gs. 2a and 2b wherein an outer closed
overall flo~ path'is indicated by horizont.al flow vectors 50. An
, inner cloaed overall flow path is indicated by horizontal flow :
'~ vectors 52. The'outer flow indicated by vectors 50 is created by
an outer $et of aerators l0 and the inner flow path is created by ~:
. ~ - .
two aeratoxs 10. One or more aerators, two are shown in Fig. 6
and are desi:gnated by the number 54, are displaced out of alignment
.. with the inner flo~ path'toward the center thereof. The aerators - ~:
54 which.'are di.sposed out of the closed overall flow path are
ori.entatea to~ards the:center of the flow path for the purpose of
20 creatin~ a subflow path of ~ater to prevent tha formation of void
;' flow areas in -the center of the pond. The subflow path is indicated
by horizontal flow vectors 56.
Fig. 7 illustrates a variation of aerator orientation simi-
lar to Fig. 6 wherein only a single set of aera-tors 10 is utilized .'~
', to form a closed overall flow path, indicated by horizontal flow :.'.
vector~ 58. A number of aerators, designated by the number 60, in
.
~ Fig. 7 are disposed out of alignment with the close~d overall flow '~
i
to :Eorm a subflow path, indicated by horizontal flow vectors 62,
for the purpose of preventin~ the formation of a void flow path
in the center of the~pond. While four aerators 60 are'shown disposed
out of alignment, it shbuld be understood that any number of
''~ aerators may be ~o disposed.
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Numerous characteristics and advantages of o~ invention
have been set forth in the foregoing description, together with :
details of the structure and function of the invention, and the
novel features thereof are pointed out in the appended claims.
The disclosure, ho~.ever, is illustrative only" and changes may be
made in detail, especially in ma~ters of shape, size, and arrange-
ment of parts, ~ithin the principle of the invention, to the full . :
extent indicated by the broad general meaning of the terms in
;~ ~hich. the appended claims are expressed.
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