Note: Descriptions are shown in the official language in which they were submitted.
~ ~5976
SPECIFICATION
FIELD OF INVENTION
This invention relates to a simplified high rate mixed-
fluidized bed Anoxic-Aerobic Activated Sludge Treatment System
capable of simultaneous biological removal of carbonaceous,
ni-trogenous and phosphorous compounds and suspended solids from
municipal and industrial waste waters without the use of chemicals
and without the use of the traditional secondary clarifiers. It
has -for its object a provision of a simplified process apparakus
not requiring compressors, mixers, piping, pumps, sludge scrapers
and clarifiers and providing optimum Anoxic-Aerobic Activated
Sludge Process conditions with reliable maintenance free operation
at reduced capital and operating costs. The apparatus of this
invention meets all process requirements along with reduced con-
sumption of energy in mixing, aeration and recirculation of the
reactor mixed liquor between the Anoxic and Aerobic stages in a
single reaction tank and is suitable for use in designing the
standardized waste water treatment packaged plants as well as
in designing the large municipal and industrial waste water
treatment facilities.
BACKGROUND TO T~E INVENTION
In a review of the most advanced technology for kreatment
of waste waters, Barth, E.H. et al. (International Nutrient Control
Technology for Municipal Effluents, Jour. WPCF. V.53, No.12, 1981)
outlined the various process flowsheets and process parameters
currently used in removing the carbonaceous, nitrogenous and
phosphorous compounds from municipal waste waters.
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It was reported there that removal of carbonaceous and nit-
rogenous compounds and phosphorus has been achieved in large
scale commercial plants using a single Activated sludge system
comprising an anoxic stage r an aerobic stage and a clarifier
in which the sludge age is maintained by withdrawing the excess
sludge from the clarifier. Further, i-t was shown by Beer, C.
et al. (Activated Sludge Systems Using Nitrate Respiration -
Design Considerations, Jour. WPCF., 5ept. pg. 2120, 1978) that
the denitrification rate when using the waste water carbonaceous
material as energy source in nitrate respiration is considerably
higher than that achieved with endogenous nitrate respiration
and that the Activated Sludge System in which an Anoxic stage
is followed by an Aerobic stage produces significantly less
excess sludge, uses significantly less oxygen and removes sig-
nificantly less alkalinity from the processed waste water thanthe Activated Sludge System in which an Aerobic stage is
followed by an Anoxic stage.
~ince in an Anoxic-~erobic Activated Sludge Process de-
composition of the organic nitrogen and the nitrification of
the ~mmonia nitrogen to nitrate takes place in the second -
Aerobic stage while denitrification of the nitrate nitrogen
to nitrogen gas takes place in the first - Anoxic stage, to
achie~e efficient removal of nitrogen the Anoxic - Aero~ic
Activated Sludge Process requires an extremely high recircu-
lation of the reactor mixed liquor between the two reaction
stages. Depending on the concentration of total nitrogen in
the incoming waste water and on the required low concentration
of the total nitrogen in the effluent, the desired mixed
liquor to feed recirculation ratio usually varies in the range
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between 10 to 50. Such high recirculation rates are impossible
to achieve in current waste water treatment facili-ties in which
recirculation of the mixed liquor and sludge between the two
reaction stages is maintained by mechanical pumps. As a result
the concentration of nitrogenous compounds in the effluents
from current Anoxic-Aerobic Activated Sludge Systems is undesir-
ably high.
Further it is known that in an Activated sludge Process
the performance of the biochemical reactor, i.e. the reactor
volumetric loading rate depends on the concentration of the
contaminant and on the concentration of mixed liquor volatile
suspended solids (MLVSS) in the reactor. Because of the re-
circulation of the mixed liquor between the two reaction stages
in the Anoxic-Aerobic Activated Sludge Process the concentration
of the contaminant in the two reaction stages is usually very
low and because of use of secondary clariiers the concentration
of MLVSS in the two reaction stages is limited and usually less
than 5,000 mg/lit. As a result the volumetric loading rates
in all existing Anoxic ~erobic Activated Sludge Systems designed
for removal of nutrients are very low and usually less than 0.4
kg/m3 day~
It has been also demonstrated in large commercial plants
that in the Anoxic-~erobic Activated Sludge Pro~ess the removal
of phosphorus is being achieved simultaneously with removal of
nitrogen due to a biological stress imposed on the mixed micro-
bial population while in the Anoxic reaction stage. Since
phosphorus is removed from the processed waste water by assim-
ilation of phosphorus into the cellular material of the micro-
~ 1.55976
organisms the phosphorus removal ef~iciency increases withincreased BOD loadings and with reduced sludge age. The per-
missible sludge age howe~er is effected by the growth rate of
the nitrifiers and by the required removal of the ammonia
nitrogen. Depen~ing on the operating temperature the minimum
sludge age to achieve efficient nitrification may vary in the
ranye from 4 to 10 days and usually is maintained at 7 - 8 days
if simultaneous removal of nitrogen is to be achieved efficiently.
With view to the above discussed Anoxic-Aerobic Activated
Sludge Process variables it then follows that to increase the
overall nitrogen removal efficiency it is necessary to increase
the mixed liquor recirculation rate, to increase the ~erformance
it is necessary to increase the concentration of MLVSS in the two
reaction stages and to increase the removal of phosphorus it is
necessary to operate the system at the minimum permissihle sludge
age.
The Anoxic-Aerobic Activated Sludge Process of my invention
covered by Can. Pat. No. 1 114 528, and 1 116 323 (U.S.Pat.App.
No. 181 r 136 and 268,725) meets all the above discussed process
requirements. Contrary to all current art systems it does not
require a separate clarification stage and as schematically
shown in Fig. 1 it briefly consists of
a) feeding the waste water into the Anoxic stage, recycling
the mixed liquor by a new type mixer-aerator from the Aerobic
stage into the Anoxic stage at the mixed liquor to feed recir-
culation ratio greater than 20, mixing the waste water with
the recycled mixed liquor in the Anoxic stage and contacting
the waste water with MLVSS in the Anoxic stage in the absence
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1~L55976
of dissolved oxygen therein and at concentrations of l~LVSS
greater than 15,000 mg/lit. In the Anoxic stage the soluble
BOD5 is partially used up as energy source in nitrate respir-
ation and in new cell synthesis, NO3--N is gasified and released
due to substrate nitrate respiration by the mixed microbial
population and NH3-N and PO4 are partially assimilated in new
cell synthesis.
b) flowing -the denitrified mixed liquor with the partially
treated waste water from the ~noxic stage into the Aerobic stage,
the Aerobic stage comprising a downflow Aeration zone and an
upflow fluidized bed zone, mixing the anoxic liquor with the
sludge withdrawn from the fluidized bed zone and aerating the
mixture of liquor and sludge by air while continuously recir-
culating the mixture of liquor and sludge in a loop downwardly
through the aeration zone and upwardly through the fluidized
bed zone. In the Aerobic stage the remaining BOD5 and the TKN
are biooxidized by the activated sludge along with new cell
synthesis~ endogenous respiration, assimilation of nitrogen and
phosphorus into new cells and nitrification of the ammonia
nitrogen to nitrate nitrogen.
In addition the recirculated sludge as it moves upward
through the fluidized bed zone flocculates and forms a fluidized
bed which efficiently filters out all suspended solids present
in the processed waste watert leaving a clear effluent collected
above the fluidized bed zone. To maintain the desired sludge
age a portion of the recirculated sludge is withdrawn from the
-fluidized bed zone.
The major process differences between the described process
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~1559~B
of my invention and the current art can be su~narized as
foll~ws:
a) the mixed liquor to feed recirculation ratio in the
described process is greater than 20/ while in the current
art systems it is only 2 to 4,
b) the concentration of the ~VSS in the described process
is greater than 15l000 mg/lit, while in the current art systems
it is less than 5,000 mg/lit,
c) the Aerobic stage in the described process comprises a
downflow aeration zone and an upflow fluidized bed zone with
the reactor liquor and sludge continuously recirculating in a
closed loop through the two zones, while the current art syste~s
utilize a completely mixed aeration zone,
d) in the described process suspencled solids are removed
from the processed waste water by filtration in the fluidized
bed within the Aerobic stage, while in the current art systems
suspended solids are removed from the treated waste water by
gravity settling in an additional clarifying stage with the
settled sludge being recirculated from the clarifying stage
into the Anoxic stage.
The described Anoxic-~erobic Acti~ated Sludge Process can
be used either a~ to achieve complete oxidation of volatile
suspended solids associated with less efficient removal of
phosphorus, or b~ for efficient removal of BODs, suspended
solids and nutrients associated with increased production of
excess sludge. Complete oxidation is usuall~ desirable for
"on site" treatment applications where maintenance and excess
sludge are to be minimlzed and where water flow rates are
usually small, while efficient removal of phosphorus with
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maximized production of excess sludge may be desirable for
large waste water flow rates, when the excess sludge may be
recovered for reuse either because of its energy content or
because of the nutrient values of the excess sludge vola-tile
suspended solids. In both situations the Anoxic-Aerobic
Activated Sludge Process of my invention when compared with
current art systems offers considerable savings in capital and
operating costs due to reduction of the required reaction volume,
elimination of the secondary clarifier, elimination of piping and
pumps, elimination of compressors, mixers and aerators, reduction
in consumption of energy used in aerationl mixing and recirculation
of the mixed liquor, reduced maintenance and supervision and
elimination of chemicals such as methanol and lime required by
current art systems in nitrification - denitrification and/or
in removal of phosphorus~ For comparison of the Anoxic-Aerobic
Activated Sludge Process of my invent:ion with the Completely
~ixed Nitifyin~ Activated Sludge Process the major process char-
ac~eristics of the two processes are presented in Table 1.
Durin~ ongoing investigation of ~he above described Anoxic-
Aerobic Activated Sludge Process hydraulics I have found that the
performance of the process apparatus of my invention covered by
the above listed Canadian and U.S. Pat. can be further improve~
by improving the efficiency of mixing of the reactor liquor and
sludge solids -MLVSS in the Anoxic stage.
I have also found that such improved mixing can be achie~ed
without increasing the consumption of energy and along with simp-
lification of the reaction tank r particularly when applied in
large waste water treatment plants when capacity of the plant
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~559~6
may be increased by joining together and in parallel a number
of modular reaction units.
It is therefore the object of the present invention to
provide an improved apparatus for use with the above described
Anoxic-Aerobic Activated Sludge Process of my invention.
More specifically it is the object of the present invention
to provide an apparatus with improved process hydraulics in mix-
ing of the reactor liquor with sludge solids in the Anoxic stageand in recirculation of the reactor liquor and sludge solids be-
tween the Anoxic and Aerobic stages.
It is another object of this invention to provide a simpli-
fied reacticn tank that would be more suitable for use as a modu-
lar reaction unit in designing the large waste water treatment
plants.
It is another object of this invention to provide an appara-
tus with improved hydraulies of the upwardly moving fluidized bedof the floceulated sludge and in withdrawal of the floccula~ed
sludge from the fluidized bed zone.
It is also the object of this invention to provide an appara-
tus with improv~d energy utilization efficiency in mixin~, recir-
cuIating and aerating the reactor mixed liquor and the flocculated
sludge.
Other objects and features of the present invention will be
understood from the following deseription of the apparatus and
claims.
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SUMMARY OF TH~: INVENTIO~
The present invention provldes an improved apparatus for
use with the Anoxic-Aerobic Activated Sludge Process of my in-
vention covered by the above Canadian Patents and U.S. Patent
Applications.
More specifically the improved apparatus provides for more
efficient process hydraulics involving mi~ing of -the reactor
liquor with sludge solids in the Anoxic stage, more efficient
recirculation of the reactor liquor and sludge solids between
the two reaction stages and more efficient aeration of the re
actor liquor and sludge solids without increased consumption
of energ~. It also provides improved recirculation of sludge
solids through the aeration zone and fluidized bed zone, provides
a more simple reaction tank more suitable for use as a modular
unit in large waste water treatment plants.
BRIEF DESCRIPTION QF THE DRAWINGS
The forgoing and other objects and advanta~es of the present
invention will becGme apparent from the followin~ detail descrip-
tion which proceeds with reference to the accompanying drawings
where in
Fig. 1 is a simplified schematic diagram of th~ Anoxic~
Aerobic Process of my invention covered by the abo~e listed Cana
dian Patents and U.S. Pat. ~pplications which is being used in
treatment of waste waters with the apparatus of the present in-
vention.
Fig. 2 is a ~ertical view through one prefered embodiment
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i597~
of the apparatus of this invention.
Fig. 3 is a plan view of the prefered embodiment of the
apparatus shown in Fig. 2.
Fig~ 4 is a schematic representation of a large treatment
system comprising a number of modular units of the apparatus
shown in Fig. 2 and Fig. 3 joined into a single reaction tank
of the present invention.
DESCRIPT~ON OF THE PREFERED E~BODIMENTS
Before explaining the present invention in detail it is
-to be understood that the invention is not limited in its appli-
cation to the details of construction and arrangement of parts
illustrated in the accompanying drawings, since the invention
is capable of other embodiments and of bein~ practiced or
carried out in various ways. Also it is to be understood that
the phraseology or terminology employed herein is for the pur-
pose of description and not of limltation.
Reference is made to Fig. 2 and Fig. 3 for an explanation
of one prefered modification of the apparatus of the present
; in~ention. ~s is there shown the apparatus comprises a reaction
tank 10 equipped with two first solid wall partitions 1, la, two
second solid wall partitions 2,2a, inverted funnels 3, 3a, two
25 endless belts 5, 5a, an inlet 7, two outlets 8, 8a equipped with
weirs 9, 9a and one excess sludge withdrawal pipe 18.
The two endless belts 5, 5a each comprise a pair of endless
chains 5.1 joined wi-th a plurality of horizontal pipes 5O2 of a
specific diameter and length dictated by the treatment capacity
~ :~S~7~
of the reaction tank 10. The horizontal pipes 5.2 ha~e their
side ends closed and are permanen~ly attached to t~e endless
chains 5.1 to prevent rotation and change in position of the
plurality of openings 5.3 located on the top and on the bottom
sides of pipes 5.2. The two endless belts 5, 5a are positioned
within the reaction tank 10 with their top portion extending
above the liquid level of the reactor liquor held in reaction
tank 10 and are supported at the top by a pair of rotating
sprockets 5.4, 5.4a mounted on a shaft 5.5, 5.5a rotated b~ a
motor. The hottom portion of endless belts 5, 5a extend near
the bottom of the reaction tank 10 where they are kept in posi-
tion by a pair of leading sprockets 5.6, 5.6a. The two endless
belts may rotate at same or at different speeds, which speed
may vary in the range from 5 to 100 c~/sec, and preferably is
maintained in the range from 15 to 50 cm/sec.
The two solid wall partitions 1, la are positioned inside
the endless ~elts 5, 5a and are attached to the two side walls
of the reaction tank 10 thus separating the reaction tank into
20 a single anoxic zone 11 and two aerobic zones 12, 12a located
on two opposite sides of the anoxic zone 11 and/or at the two
end sides of the reaction tank 10. The anoxic zone 11 is in
communication with the two aerobic zones 12, 12a.via openings
1.1, 1.2 and l.la, 1.2a located in the two solid wall partitions
1, la.
The two second solid wall partitions 2, 2a each are posit-
ioned in parallel with first solid wall partitions 1, la and
alongside the endless ~elts 5, 5a and are attached to the two
side walls of the reaction tank 10. The top ends o~ the two
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1 ~55976
second solid wall partitions 2, 2a extend above the liquid
level of the reaction tank 10 and the bottom ends extend dia-
gonally into the aerobic zones 12, 12a to form between partitions
1 and 2 and la and 2a the downflow aeration zones 12.1 and 12.1a
and to form between partitions 2 and 2a the end side walls of
the reaction tank 10 the upflow fluidized bed zones 12.2 and
12.2a. The fluidized bed zones 12.2, 12.2a are in communication
with their respective aeration zones 12.1 and 12.la via a number
of inverted funnels 3, 3a located at the top of the fluidized
bed zones 12.2, 12.2a and via openings 2.1 and 2.la formed be-
tween the bottom of partitions 2 and 2a and the bottom of the
aeration tank 10.
Clear well zones 13, 13a are formed in the two aerobic
zones 12, 12a above the two fluidized bed zones 12.2, 12.2a for
withdrawal of the effluent via weirs 9, ~a and exits 8, ~a.
Openings 2.2, 2.2a located in solid wall partitions 2, 2a are
provided for skimming of the floating solids from the clear well
zones 13, 13a into the aeration zones 12.1, 12.la and pipe 18 is
provided for withdrawal of the excess sludge from the fluidized
bed zone 12.2.
::
Referring to the system's hydraulics, when endless belts
5, 5a rotate in the direction shown by arrows ~0 they perform
the following functions:
a~ First, the pipes 5.2 act as propellers in maintaining
a double loop lla, llb rotation of the reactor liquor in the
anoxic zone 11 as shown by arrow 21. Since there are no re-
sistances in the path of the rotating reactor liquor, accept the
tangentially located side wall of the feed inlet trench 7a
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1~5~j~7~
diverting the rotating liquor downwardly in the centre of the
anoxic zone 11, the energy used in maintaining the double loop
rotation of the reactor li~uor in the anoxic zone 11 is minimal.
Because of the inherent momentum the path of the solid parti-
cles is different from the path of the rotating liquid with thesolid particles penitrating from the right rotating loop lla
into left rotating loop llb and the solids from the left side
rotating loop llb penitrating into the right side rotating loop
lla as shown by arrows 22, thus improving the ef~iciency of
mixing and contacting the sludge solids with the reactor liquor
rotating in two hydraulic loops in the anoxic zone 11 without
increasing the consumption of energy above that used in mixing
of the content of the anoxic zone in a single rotating hydrau-
lic loop of the apparatus of my invention described in my above
5 listed patents.
b) Second, when pipes 5.2 are moving downwardly through
throats 19, l9a, each space formed between two neighboring
pipes and the chain links of chains 5.1 forms a cavity 5.7
which when moving at the given speed of the belts 5, 5a through
0 the throats 19, l~a pumps out the liquid from the throat down-
wardly into the aeration zones 12.1, 12.la. secause of this
pumping effect of cavities 5O7 the liquid level in the throats
19, 19a drops below the liquid level maintained in clear wells
13, 13a resulting in a gravity flow of the sludge from the top
of the fluidized bed zones 12.2, 12.2a via funnels 3, 3a into
the throats 19, 19a and from there down through the aeration
zones 12.1 and 12.1a and back into the fluidized bed zones 12.2,
12.2a forming the sludge recirculation loop maintained in the
aerobic zones 12, 12a to improve the efficiency of transfer of
the air oxygen to microorganisms and to improve floccuIationof sludge solids in the fluidized bed zones and to improve
~ ~ ~i5976
filtration of suspended solids from the processed waste water
flowing through the fluidized flocculated sludge into the clear
well zones and out of reaction tank 10. In addition a contin-
uous small stream of the clari~ied effluent via openings 2.2,
2.2a from clear well zones 13, 13a into the throats 19, 19a
is maintained to assure skimming of the floating solids from
the clear well zones 13, 13a into the aeration zones 12.1,
12.la. Several funnels 3, 3a may be used in each fluidized
bed zones to achieve more even redistribution and withdrawal
of sludge solids from fluidized bed zones 12.2, 12.2a.
c) Third, when belts 5, 5a are moving upwardly in the anoxic
zone 11 and when the pipes 5.2 are located above the liquid
level of the reaction tank 10 at positions 23, 23a the liquid
held in pipes 5.2 is flowing out o~ the pipes into the anoxic
zone 11 via the plurality of openings 5.3 located on the bottom
side of pipes 5.2 while at the same time atmospheric air is
entering into the pipes via the pluxality of openings 5.3
located on the top side of pipes 5.2 until all liquid in pipes
5~2 is replaced with air. When pipes 5.2 are then moving down-
ward into the throats 19, l~a and then into the aeration zones12.1j 12.1a they are filled only with air. ~hen pipes are
submerged into the recirculated reactor liquor and sludge
in the aeration zones 12.1, 12.la the en-trapped air is slowly
released from pipes 5.2 via the plurality of openings 5.3 lo-
cated on the top side of pipes into the downwardly recirculatedliquor and sludge and simultaneously the air released from pipes
5.2 is being replaced with the recirculated liquor and sludge
which liquor and sludge are then transported in pipes 5.2 from
the aeration zones 12.1, 12.la into the anoxic zone 11 where
the liquor and sludge are released from pipes into the anoxic
zone at positions 23, 23a. In this way reactor liquor and
~, .
5~6
sludge are continuously recirculated from aerobic zones 12,
12a into the anoxic zone 11 at a recirculation rate that may
be controlled by controlling the speed of the endless belts
5, 5a. The volume of liquor and sludge pumped by pipes 5.2
from aerobic zones 12, 12a into the anoxic zone 11 is replaced
by the anoxic mixed liquor continuously flowing by gravity
from the anoxic zone 11 into the aerobic zones 12, 12a via
openings 1~1, l.la located in first solid wall partitions 1,
la. In this way recirculation of the reactor liquor and sludge
solids between the aerobic zones 12, 12a and the anoxic zone 11
is achieved at reduced hydraulic resistance and therefore at
reduced consumption of energy.
d) Fourth, the air is being released from pipes 5.2 into
a downwardly recirculated liquor and sludge via the plurality oF
openings 5.3 in form of coarse bubbles which are then dispersed
through out the aeration zones 12.1, 12.la and which bubbles rise
in the aeration zones countercurrently to the downwardly recir-
culated liquor to the top of the aeration zones. At the top and
under the throats 19, l9a the collected air is redispersed and
recycled into the recirculated liquor and sludge by the mechanical
action of pipes 5.2 acting here as propellers and by the kinetic
energy of the recirculated liquor. Since the downflow~velocity
of the recircula-ted liquor and sludge drops due to incrased cross-
sectional area of the aeration zones 12.1, 12.la at the bottom
part of the aeration zones~ the air bubbles are separated from
the recirculated slud~e and stay within the aeration zones. Thus
the air bubbles are not present and therefore they do not disturb
the fluidized bed of the flocculated sludge held in the fluidized
bed zones 12.2~ 12.2a in which the floccuIation of the sludge
solids takes place as the sludge continuously flows u~wardly
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~ ~5~
through the fluidized bed zones back into the aeration zones.
Since sludge is continuously recirculated in a closed loop
downwardly through the aeration zone and upwardly through the
fluidized bed zone the hydrostatic pressure difference between
the aeration zone and the fluidized bed zone is eliminated and
the hydraulic resistances are minimized. Since the upward
velocity of the rising bubbles in a stationary liquid is within
the range from 15 to 45 cm/sec, and because the downward velocity
of the recirculated liquor may be controlled within the same
range, the velocity of the rising bubbles relative to the aeration
zone may be controlled in the range from 0 to about 25 cm/sec.
Consequently the contact time of the air bubbles with the liquor
and sludge is extended and the efficiency of transfer of air
oxygen to microorganisms significantly increased when compared
with completely mixed aeration reactors. As a result the energy
used for aeration of the reactor li~uor and for mixing and re-
circulation of the liquor and sludge in the reaction tank of this
invention is utilized more efficiently than that used in surrent
art systems.
e) Fifth, as the reactor liquor and sludge reci~culates
downwardly through aeration zones 12.1, 12.la and upwardly through
fluidized bed zones 12.2, 12.2a the absorbed oxygen is used up ~y
the activated sludge in the fluidized bed in biooxidation of the
remaining BODs, T~N and in nitrification of the ammonia nitrogen
to nitrate nitrogen. Consequently the concentration of the dis-
solved oxygen in the recirculated liquor and sludge entering the
aeration zone may be maintained close to zero mg/lit thus in-
creasing the oxygen transfer rate in the aeration zones~ Further,
with better control of the dissolved oxygen in the fluidized bed
zone and with improved withdrawal of the sludge from the top of
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;5~76
the fluidized bed zone into the aeration zone the ~locculati.on
of the sludge in the ~luidized bed zones of the apparatus of
the present invention is improved and the removal of suspended
solids from the processed waste water is more efficient. Since
the suspended solids present in the waste water are removed
from the treated waste water by the flocculated and fluidized
sludge as the treated waste water is filtered through the flo-
cculated sludge a separate clarifi.cation stage is not needed.
The filtered and/or clarified effluent is collected above the
~luidized bed of sludge b~ weirs 9, 9a located in clear well
zone~ 13, 13a with the effluent continuously flowing out by
gravity via exits 8, 8a. The e~cess sludge can be withdrawn
continuously or periodically from the fluidized bed zone 12.2
via pipe 18 either for further treatment or disposal.
From the above description of the prefered apparatus and
the associated process hydraulics it i.s evident that the ~noxic-
Aerobic Activated Sludge System of the presen-t invention does
not re~uire the traditional secondary clarifier, does not xequire
the traditional compressors and air diffusers and/or surface
aerators for aeration of the reactor liquor, does not require
the traditional mixers to maintain the biolo~ical activity in
the denitrification stages of the treatment in the anoxic zone
11, does not require the traditional pumps and piping for recir-
culation of -the reactor liquor and sludge between the Anoxic and
Aerobic stages, does not require sludge return pumps/ sludge
scrapers and the associated piping as commo~n in all current art
systems.
It is also evident that the described apparatus of t~e
present invention does not use equipment or parts that wou].d
.~
~L ~ 5 ~
require maintenance or parts that can fail.
From the described hydraulics it is also evident that the
efficiency in utilization of energy in recirculation of the
reactor liquor and sludge between the Anoxic and Aerobic stages,
in mixing o~ the reactor liquor and sludge in the Anoxic and
Aerobic stages and in aeration of the reactor liquor and sludge
in the aeration zones is much better than that in current art
systems. It is also evident from the described Anoxic-~erobic
Activated Sludge Process used in the apparatus of the present
invention that the performance offered by the present apparatus
is much higher than that offered by current art systems. It
therefore follows that the capital and operating costs for the
described system may be expected to be much lower than that of
the current art systems.
Reference is now made to Fig. 4 which represents another
embodiment of the apparatus of the present invention in which a
large Anoxic-Aerobic Activated Sludge System is provided by
joining four modular units utilizing the apparatus of the present
in~ention shown in Fig. 2 and 3.
; As shown schematically in Fig. 4 a single reaction tank 100
is formed by joining four modular units lO to form a single anoxic
zone ll located between eight aerobic zones 12. Each aerobic zone
12 has the same arrangement of parts as those shown in Fig. 2 and
Fig. 3 with two endless belts 5 located in each aerobic zone.
Baffles 30 may be pro~ided :in the anoxic zone 11 to utilize a
small portion of the kinetic energy of the ro-tating reactor liquor
to induce a longitudinal circulation of the rotating liquo~ in the
anoxic zone ll shown by arrows 31 to further improve the mixlng
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~ ~5$576
of the anoxic zone content. ~aste water inlet 7 may be directed
into the waste water distribution channel 7.1 from which waste
water is distributed into the anoxic zone via openings 7.2. The
clarified effluent flows out from each aerobic stage 12 via in-
dividual exits 8 into a common trench 8.1 and the excess sludgemay be withdrawn via pipe 18.
It should be apparent that an efficient apparatus for bio-
logical purification of waste waters can be constructed also by
other modifications of the anoxic and aerobic stages or by modifi-
cation of other parts of the described apparatus. It should be
also apparent that the apparatus of the present inventicn can be
combined with any current art apparatus designed for pretreatment
of the incoming waste water and/or designed for further treatment
o:E the effluent to achieve higher effluent quality.
Having described the prefered embodiments of the present in-
vention it should be apparent to those skilled in the art that
the sa~e permits modification in arrangement and details. I
therefore claim as my invention all such modifications as come
within the -true spirit and scope of the following claims.
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ABLE 1 - Comparison of the Anoxic-Aerobic Systems (A-A-S) vs
Complete Mix Nitrifying Activated Sludge System (N.A.S.S.)
Design Base: Flow = 454 m3/d Domestic Waste Water;
T = 15C; BODs - 300 mg/l; TSS = 250 mg/l;
USS = 200 mg/l; TKN = 50 mg/1,
PO4P = 10 mg/l; Alkalinity = 200 mg/l
COMPLETE COMPLETE COMPLETE
OXIDATION TREATMENT MIX
PROCESS PARAMETER A-A-S A-A-S N.A.S.S.
1. Sludge Age -
Areation Days 16 8.8 8.8
2. Sludge Age -
Denitrification Days 9 6.2
3. Av.BOD in
Effluent mg/l 4.2 5.0 8.0
4. Av.SS in
Effluent mg/l 5.0 5.0 10.0
5. Av.TKN in
Effluent mg/l 0.1 0.3 0.3
6. Av.NO3-N in
Effluent mg/l 1.6 1.2 28.3
7. Av.NH~-N in
Eff~uent mg/l 0.1 0.3 0.3
8. Av.TN in
Effluent mg/l 1.8 1.8 29.0
9. Av.PO4P in
Effluent mg/1 2.6 1.3 6.4
10. Av~ BOD Load
kg BODs/kg VSS day 0.16 0.22 0.20
11. Av. BOD Load
kg BODs/m3 day 1.22 1.67 0.37
12. Design MLSS gr/lit 20.0 20.0 3.0
13. Desi~n 2
Concentration mg/l 1.0 1.0 2.0
14. Oxygen Uptake
kg/kg VSS day 0.2 0.2 0.2
15. Oxygen Uptake kg/m3 day1.44 1.63 0.5
16. Oxygen Uptake kg/day 132.2 110.0 150.0
17. Excess Sludge kg/day 77.1 92.6 104.4
18. Excess Sludge
kg/kg VSS day 0.07 0.11 0.12
1~. Aeration Volumem3 58.2 39.2 301.0
20. Anoxic Volume m3 33.4 28.3
21. Clarifier Volume m3 - - 45.0
22. Total System Volume m3 91.6 67.5 346.0
23. Total HydrauIic
Retention Time hr 4.8 3.6 18.2
24. Sludge Recirculation
Ratio Qs/Q 5 5 0.5
725. Mixed Liquor Recir-
culation Rat~o Ql/Q 30 30
JL
