Note: Descriptions are shown in the official language in which they were submitted.
Desçription
Biolo~ical Purification of Waste Waters ;
.,
Technical Field
The invention relates to the area of advanced
biological treatment of waste waters.
The invention also relates to a device for the
execution of such a treatment~
Backqround Art
United States Patent No. 4,287,062 issued Septem-
ber 1, 1981 to von Nordenskiold describes a biologicalprocess using several floating aerator chains spaced
apart with respect to each other and moving back and ~ ;
forth which produces a wide-area and uniform aeration
and mixing of the waste water containing activated
sludge. These plants are characterized, in particu-
lar, by the fact that a controlled low loaded acti-
vated sludge process can be carried out preferably in -~
earthen basins and without total mechanical m~ing of
the basin content, i.e., a very wide variety of living -
conditions for the activated sludge in the basin can
be controlled at any time with a comparatively small
expenditure of energy.
In the known activated sludge plant the air is
introduced into the basin simultaneoùsly through all
available bottom aerators for aeration and mixing so
that the air is equally distributed along the length
of the basin. The movement of the chains accom~
plishes, among other things, that the activated sludge
does not settlP at any point of the basin long enough
to be damaged.
The bottom aerators, extending as far as the
bottom, which pass over the bottom of the tank with a
reciprocating movement in the case of the known plant,
pick up th~e activated sludge, circulate it, and also ~-~
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tear it away from the bottom locally by means of the
ascending stream of air and water, and thereby also
prevent any settled part of the activated sludge from
becoming anaerobic by remaining on the bottom suffi-
ciently long to develop negative effects.
Despite the comparatively low specific mixing
energy expenditure of this system, it may happen dur-
ing periods of low load, such as, for example, during
night hours, on weekends, etc., that more energy is
consumed for the mixing than would actually be neces-
sary or even desirable for the oxygen supply. This
leads to undesirable oxygen potentials in the basin,
l.e., to an undesired effect on process steps requir-
ing specific oxygen potentials. As used herein, the
term "oxidation potential" means the ability of the
waste water and its components to perform oxidating or -
reducing processes.
Waste water treatment plants which are equipped
with fixed installed bottom aerators or which use
nozzle-like mixing devices belong to the group "high
;~ loaded plants" which generally operate at a minimum
energy level of 10-15 watts/m3 basin volume. They
also require a horizontal well-constructed basin floor ;~
so that the aerators which are su-)ported by the floor `
25 will remain at the same horizontal level which is a `~
requirement for an even introduction of air into the
basin. There have been several attempts to operate
such plants with intermittent airflow through the
fixed aerators. Early attempts are described in
British Patents Nos. 1141 of 1915 to Jones and 9989 of `~
1915 to Naylor, and a later attempt is described in
the published European Patent Application of
Strassler, No. 0145647. Intermittent operation in
such plants is accompanied by various problems. For ;~
example, most fixed installed aerators are prone to
plugging, especially when they are operated intermit~
tently. Nhen pluggage occurs, then the whole basin ~-
has to be emptied to facilitate effective cleaning of;~
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the aerators. Thus, this leads to undesired downtime
for the plant and high extra maintenance. In addition
to the sludge which settles on the aerators when they
are shut off, there is also sludge which settles
around them. This sludge is difficult to resuspend
and part of it remains on the floor and will die,
which destroys the whole activated sludge process.
There are several specialized types of plants
known to carry out processes which require specific
oxygen potentials, e.q., nitrification, denitrifica-
tion and phosphorus removal. It is known, for exam-
ple, to operate a separate denitrification basin up-
stream as well as downstream of the aeration basin in
an activated sludge plant. It is also known to have
several basins connected in series so that the condi-
tions in each basin can be controlled to permit each
of the desired processes to be carried out.
It is also known that such processes can be car-
ried out in circular or oval basins where the waste
water is circulated and where, depending on oxygen
supply, zones with different oxygen potential are
established. To keep the activated sludge in suspen-
sion in this latter type of plant, the water must be
circulated at a velocity of at least 0.3 meters per
second with the help of mixing or pumping devices.
Disclosure of Invention ~;
The purpose of the present invention is to pro-
vide a method and an apparatus to carry out the method
which, at any time and under varying input demands,
will produce not only secondary treatment but also
carry out, in an optimum way in the same basin, pro-
cesses which require specific oxygen potential speci-
fically applicable activated sludge plants operating
at low pollution load using earthen basins.
This purpose is accomplished by providing a
method of biological treatment using a series of aera-
tor chains distributed over the basin surface area
~4~ ~33~J~
generally perpendicularly to the direction of flow of
waste water through the basin and supporting bottom
aerators from the chains so that they are located in
the vicinity of the basin floor. In operation, each
of the aerator chains moves back and forth so that the
bottom aerators suspended from it move across the
basin floor periodically to aerate and mix the waste
water and the activated sludge. At any time only some
of the aerator chains are supplied with the full
amount of air (l.e., are "fully loaded") while the air
supply to the other chains is more or less throttled
so that there is complete mixing of the waste water ;
and the activated sludge only in the area of the fully -~
loaded chains, and the full supply of air is varied -
among the chains so that different chains are fully
loaded during specific time periods, preferably in a -
way so as to establish a pattern of migrating waves.
The method according to the invention using the
moving on- and off-air loading of the moving aerator
chains thus creates one or several migrating zones of
intensive aeration passing through the basin separated
by zones between the intensive aerated ones in which
the aeration is much weaker or absent. The weaker
zones, of course, migrate in the same way as the in~
tensive aeration zones. Thus, the zones migrate con-
tinuously through the basin and certain reactions ~ ~
which take place because of conditions maintained in ~ -
the migrating zones will be carried out repeatedly
until the process is completed. For example, succes~
30 sive nitrification and denitrification of waste water ~;
can be accomplished with high efficiency by migrating
zones of which some have nitrifying conditions and
other have denitrifying conditions. Thus, the waste ~-
l water passing through the basin is subjected to both
¦ 35 the conditions required for both processes in succes~
! sion a number of times.
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Combining the movement of the bottom aerators
with the periodic variations in loading of air flow
through the aerator chains creates large advantages.
Among these advantages are, for example, that simul-
taneous nitrification and denitrification of the wastewater in the basin can be accomplished with a maximum
oxygen level as low as 0.3 mg/l. This increases the
stability of the operation of the plant and ensures,
for example, that the oxygen potential quickly can
reach denitrification levels when the next zone ar-
rives. The creation of these migrating zones and the
special processes which therefore become possible can
be accomplished in the same basin without mechanical
mixers in spite of the very low oxygen concentrations. - `
15The action of the aerator chains causes mixing of
the waste water in a vertical direction and affects a
clearly defined horizontal area. This results, under
correct circumstances, in well defined narrow zones
which can be made to move as desired through the com-
plete basin. Under the correct circumstances gener~
ally associated with the low energy input made possi-
ble by the invention, there is very little mixing in
the horizontal direction between the zones, which
keeps the zones well defined. The waste water travels
in the direction transverse to the zones from the
inlet to the outlet of the basin. -
The movement of the bottom aerators cleans the
aerators from the point of view that sludge which has
settled on the aerator while it was standing still is
flushed off the aerator by the movement. Therefore,
in spite of the fact that the aerators are shut off
from time to time, they will not become plugged.
According to the invention, there is a combined
effect resulting from using moving aerator chains
supporting bottom aerators for both aeration and mix-
ing and on the other hand operating only some of the
aerator chains with a full air load. Selecting the
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time intervals for the migration of the zones and
selecting the air flow rates makes it possible to vary
the process conditions.
A plant which is operated in the way described
can always be adjusted to operate in an optimum way
for the process. For example, variations during times ~-~
of low load which may occur due to incomplete sewer
systems of growing communities, during night hours and
during vacation times, can be accommodated by varying ~-~
the number of chains supplied with a full air flow at
any time.
The method according to the invention also allows
controlled partial settling of activated sludge which
is accompanied by almost no oxygen supply. As long as
lS the time when the sludge is not supplied with oxygen
is within certain limits, the activated sludge will
not be negatively affected but, on the contrary, is
caused to perform an even more effective treatment and
nutrient removal. Since the moving bottom aerators
sweep over the basin floor periodically, it is assured
that all parts of the basin floor are swept within a
certain period of time. As as result, any partly
. . ~. .
settled sludge in any area of the basin floor will be
lifted into full suspension and included in the mixed
waste water. The sludge, therefore, will not die off
in any area of the basin floor, which is contrary to
~; what happens in a basin with fixed aerators. Another
noteworthy advantage compared to plants with fixed ~`
bottom aerators is that the method according to the
invention permits reactions which demand low oxygen
potential in the same basin as reactions which demand -~
high oxygen potential. This is not possible for
plants which only use fixed bottom aerators (that is, ,~ `
without mechanical mixers) as such plants normally
operate with much higher energy input to promote mix~
ing, which results in higher oxygen potential than
that requi.red for the low oxygen reactions.
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Brief Descri~tion of Drawin~s
Further objects and advantages of the invention
will be apparent from a reading of the following de-
scription in conjunction with the accompanying draw-
ings, in which:
Fig. 1 is a schematic top view illustrating the
arrangement of a representative waste water treatment
basin arranged according to the invention showing the
range of motion of the moving aerator chains and their
areas of influence;
Fig. 2 is an enlarged fragmentary view illustrat-
ing a bottom aerator suspended from a chain of the
type shown in Fig. l;
Figs. 3a, 3b and 3c are schematic diagrams show-
ing a waste water treatment basin and illustrating thewave motion of successive high and low aeration zones
through the basin in accordance with the invention;
Fig. 4 is a schematic diagram showing a typical
valve arrangement for controlling the supply of air to
1~ 20 chains of aerators in a waste water treatment basin in
~ accordance with the invention;
: Fiy. 5 is a cross-sectional view showing the
~:: structure of one form of control device for control- : :
ling the flow of air to an aerator chain; and
Fig. 6 is a schematic diagram illustrating the ~:
arrangement of a representative control system for
: operating a waste water treatment basin in accordance ~
~ with the method of the invention. ~`
1:: " .. ~:
I Best ~ode for Carryina Out the Invention
l 30 The load of the individual moving aerator chains
¦ in a waste water treatment basin of the type shown in ::
the drawings can be optimally adapted according to
~ requirements and can be carried out, for example, in
¦ such a way that, at a specific point in time, at least ~ :
¦ 35 two aerator chains, separated by at least one less
loaded aerator chain or a chain without any air load,
l are fully loaded and that then, after specific time
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intervals in each case, the next adjacent aerator
chains in the same direction are loaded. If, for
example, eight aerator chains are arranged side by
side in a basin, then the operation may be started
with a full load of air to the first and fifth aerator
chains, while all other aerator chains are loaded only
weakly or not at all. After a certain period of time,
the second and sixth aerator chains are then ully
loaded with air, while the other aerator chains, par~
ticularly the first and fifth, are then switched over
to partial air loading or are completely switched off.
This continues until finally the fourth and eighth
aerator chains are fully loaded to create intensively
aerated regions in the zones influenced by them. Af- ' -
ter this, the cycle starts again with the first and
fourth aerator chains, etc.
Depending on the number of moving aerator chains
present, the dimensions of the basin, the pollution
load, or especially in the case of particularly heavy ~;~
sludge, it is also possible, for example, to always
fully load two adjacent aerator chains (an aerator- ;
chain pair) at any point in time, and also another
aerator-chain pair that is separated from the first
aerator-chain pair by several weakly loaded aerator
chains or chains without any air load. The migrating
movement of the aerated zones which is superimposed on
the movement of the individual moving aerator chains
is then produced by switching off one aerator chain on
` one side of each pair and additionally switching on an
aerator chain adjacent to the still fully aerated
aerator chain on the other side.
It is also possible to load only a partial region -~
of the basin in a migrating manner in order to operate
the other parts with continuous load, either perma~
nently or temporarily. It is also possible to load
individual parts of the basin with different rates of
migration or different intensities. This might be
desirable, for example, if it is required to fully mix
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the waste water at the inlet region of the basin,
either permanently or intermittently, while the re-
maind~r of the basin is subject to a migrating wave
air load. If, on the other hand, it is desired to
provide uniform oxygen potential near or in the outlet
end of the basin, then the aerators in that region
will be subjected to permanent or temporary continuous
load, whereas, on the other hand, the remainder of the
basin i5 subject to one or more migrating waves of
aeration zones.
It is clear to one skilled in the art that the
novel metAod using the moving aerator chains and the
superimposed migrating aeration zones may be applied
in ways other than in the examples just described, and
that, especially with respect to the biological pro-
cess conditions, it provides an enormous advance in
the direction of operational capacities, adaptation
and fine control, resulting in completely new process
conditions in a waste water basin, which were impos-
sible to achieve with the previous technique using
; fixed bottom aerators. This means that, with an as-
sured supply of good and potent activated sludge
available, there are new types of process methods
possible which can only be accomplished with the
plants described herein which are operating at a low
energy level.
The time interval at which the moving aerator -
chains are loaded, and thus the migration velocity
with which the intensive aeration regions migrate -
through the basin, is preferably controlled as a func-
tion of the oxygen potential, the load, and the sludge
data. However, the migration velocity of the waves
must, as a minimum, always be high enough so that
activated sludge particles which settle on the bottom
do not die off and are not damaged. In this way it is
also possible to achieve an optimal adaptation to the
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particular sludge index, which indicates how heavy the
sludge is, and the required minimum energy, which is
dependent on this, can be supplied in each case.
It is also advantageous to control the number of
fully loaded moving aerator chains as a function of
the oxygen potential, the pollution load, and the
sludge data of the waste watler and sludge comprising
the mixed liquor in the basin. The frequency of full
load of the aerator chains, if, for example, it is
controlled as a function of the pollution load, can
then always be adjusted to the required oxygen demand
in ~n optimal manner, with the smallest energy expen-
diture. It has been found that, in most cases, a wave
migration velocity for which each aeration chain is
fully loaded approximately one to ten times per hour
is sufficient.
A further very advantageous arrangement of the
procedure provides that the time intervals of full
load and/or the number of fully loaded aerator chains
are controlled automatically as a function of param-
eters important for the required oxygen input, such as ~ -
instantaneous pollution load and sludge quantity. For
the execution of a control loop of this type during ;~
operation, it is possible to measure different param- ~;~
eters that are important for the required oxygen in-
put. Thus, for example, the inlet quantity tm3/hour)
or the inlet temperature T in the basin can be meas-
ured by means of suitable measuring instruments. It ;~
would also be possible, for example, to determine
fluctuations of pH value in the intake or other
strongly oxygen-consuming components by measurement ~ ;;
techniques. It is also possible, for example, to
measure the turbidity of the water. These measured
results can then be transmitted to a central calcula-
tion unit, such as a computer, and can be appropri-
ately evaluated so that the air load of the individual
aerator chains is then carried out automatically as a
function of these measured results, possibly in ac-
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cordance with a waste-water-speci~ic or plant-specific
program. Depending on the measured values obtained,
it is then possible, for example, to introduce more
oxygen locally, for example, in the inlet zone, or the
oxygen input sources can be passed more rapidly
through the basin. All of this permits an individual
and in each case optimal operation of the plant, which
with the specific process conditions selected allows
the achievement of optimum treatment.
Another very advantageous development of the
procedure provides that the quantity of oxygen intro-
duced in each case through the number of fully loaded
moving aerator chains which is less than the total
number of chains may be larger than the oxygen input
that would be supplied to that number of chains if all
the aerator chains were fully loaded. This means that
a larger quantity of air is discharged per aerator ~ -
chain by the process according to the invention as
compared with the quantity of air flowing to each
aerator chain of a plant in which all aerator chains
are operating with the same total air load~ Let us
assume that ten aerator chains are present in a con-
ventional plant, which are all loaded simultaneously.
Then, in contrast to this, in the process according to
the invention, the air load is first reduced to, for
example, a total of 50 percent. However, the air
quantity is not distributed over five aerator chains,
but only, for example, over two chains, so that in
these the air input is significantly increased. In an
extreme case, for example, only one aerator chain is
loaded with this quantity for a short time. This
concentrated air input leads to many advantages. On
the one hand, for example, sludge islands present in a
pond can be locally dispersed in this way.
For example, for a plant with ten moving aerator
chains a tenfold airflow can be supplied to one aera~
tor chain and this concentrated air introduction will
still reach all parts of the floor by the movement of ;
-12-
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the single chain and by alternating the chain which is
actually supplied with the increased airflow to mi-
grate the increased airflow through the basin. On the
other hand, this leads to the fact that the individual
S bottom aerators, because of the high specific air
input taking place from time to time in combination
with the cleansing effect of the movement itself, are
kept free of blockages, because they are continuously
"blown clean" by the increased air discharge and are
subjected to a stronger cleansing effect as the move-
ment becomes very fast. With movirg aerator chains,
this locally increased air input of the individual
aerator chains leads to relatively large amplitudes of
motion and thus to an intensive circulation of the
sludge in the vicinity of the chain.
In the case of extremely intensive settling on
the bottom, for example, after a prolonged power fail-
ure or other shutdown or after an extensive addition
of fecal sludge or the like, it is also possible to
concentrate the total air potential of the plant on a
few rows of moving aerators, so that these are exces-
sively loaded with air. In this case, a very strong
circulation and churning wave migrates through the ~ -
basin which, together with the movement of the indi- ~;
vidual chains, will reach all areas of the floor, and
returns the plant back to its normal state. -
; A representative arrangement for execution of the
activated sludge process according to the invention is
characterized by the fact that, in every air supply
line of a moving aerator chain, there is arranged a
throttle valve controllable by a central control unit,
which, upon command, throttles or blocks the air sup-
ply to the associated air supply line. A throttle
valve associated wlth each air supply line in this way ;
35 makes possible selected operation of the individual ~;
air supply lines of the moving aerator chains and a
blocking or throttling of these lines. This creates
the prerequisite for an individual control, in which -~
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the control can be carried out, for example, by means
of a central control unit, by which both the time
intervals and the number of moving aerator chains
fully loaded at the same time can be variably ad-
justed. The great flexibility thus obtained withrespect to the frequency and quantity in which the air
is introduced makes possible a flexible adaptation to
a very wide variety of loads and an excellent control-
lability in the sense of a wide variety of special
process engineering conditions and variants, particu-
larly of the activated sludge process, with the
smallest possible energy expenditure.
In the apparatus according to the invention, it -
is possible to provide a fine control of the air flow
15 rate in each aerator chain which is beneficial for ~-~
carrying out the special waste water processing treat- -
ment in accordance with the invention. Such fine
control cannot be accomplished using bottom-fixed
aerators because the required constant external pres-
sure of the waste water on the aerators cannot be
assured without expenditure of energy. The reason is -~
that the water level of the waste water in the basin
is always changing, for example, during daytime opera~
tion, and also because the bottom of the basin may be
uneven as a result of earth settling.
In such situations, in order to assure equal
pressure in each of the bottom aerators, an independ-
ent compressor would be required, which would be com-
pletely uneconomical. On the other hand, according to
the invention, with bottom aerators suspended a fixed
distance from the top of the water in the basin, the
~`external pressure on all of the aerators is the same. `~-~
This provides an unexpected simple way to permit fine
control of the air supply in each aerator, which is
35 helpful in providing the special waste water proces- ~`
sing treatment in accordance with the invention. ~
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In a specific design of such a system, each air
supply line i5 formed by a hose line and the throttle
valve is designed as a squeeze valve. The squeeze
valve can be charged with air, for example, by means
of a piston operated by compressed air. The individ-
ual squeeze valves can then be controlled, for exam-
pl~, through a central compressed air line and suit-
able valves. By varying the charging with air, the
squeeze valve constricts the cross-section of flow in
the hose line, so that the desired throttling of the
quantity of air supply is achieved in an extremely
simple manner.
The throttle valves toyether with the control -
unit can also be installed in existing plants, so that
plants already in operation can also be converted in a
simple manner to carry out the process according to -
the invention.
It can be advantageous if the air supply to the ~;
not-fully-loaded aerator chains is never shut off
2~ completely so that the possibility of blockage of the
bottom aerators is prevented. If a low load of the
not-fully-loaded aerator chains is maintained, then
the outflowing air bubbles will keep the aerator tubes ~;
free of blockage. For this purpose, it may then be of
25 advantage if a rigid pipe with a small cross-section ;
is installed at the point of action of the squeeze
valve in the interior of the hose line, so that the
squeeze valve in that case, because of the rigid pipe,
never completely blocks a hose line.
The apparatus and process according to the inven-
tion are preferably used for so-called activated
sludge plants, but can also be used for so-called pond ~-
plants, and also for the aeration of lakes or the like
with moving floating aerator chains.
In the accompanying drawings, Fig. 1 is a top
view illustrating a single tank or basin of a waste
water purification plant. A complete plant may in-
clude several basins of this type, as well as addi-
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tional sludge settling and storage basins. The waste
water to be purified is fed into the basin 1 through
inlets 2 and leaves the basin through outlets 3 at the
opposite side of the tank. It can then be conducted
into another activated sludge tank or also into the
sludge settling or storage tank. In addition, sludge ~;
return lines can be provided, with this in each case
depending on the special nature of the plant in which
the process is being carried out. Since the invention
can be used in the same manner for pond plants operat-
ing without sludge return as for activated sludge
plants operating with sludge return, details of the
individual plants have been omitted in the present ~-
embodiment.
In order to be able to purify the waste water, it
is necessary to mix activated sludge with the waste
water essentially in all parts of the basin and to ;
bring the activated sludge into contact with the waste
water with simultaneous availability ~f oxygen as
needed for the process.
For this purpose, eight floating and moving aera-
tor chains 4 through 11 are stretched over the basin `
in the embodiment shown in Fig. 1, each carrying indi~
vidual spaced-apart bottom aerators 12 of the type ;
shown in Fig. 2. The individual aerator chains in
each case comprise flexible hose lines 14, which are
interrupted in the region of each bottom aerator 12.
The connection with the bottom aerators is provided by --
a connecting pipe 16 from the horizontal upper section
15. The two opposite ends of the section 15 are in~
serted into the two hose ends of two adjacent sections
~` of the air supply line 14. At the lower end of the ~-
connecting pipe 16 there is fastened a distributing
pipe 17 parallel to the section 15, which contains `~
3S numerous air openings l9 on its periphery. Through
the air supply line 14 and the connecting pipe 16, the
distributing pipe can be supplied with compressed air,
which then flows out through the air openings 18. In
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this embodiment, a float 13, provided in the region
above each bottom aerator 12, extends along the longi-
tudinal axis of the support and is intended to ensure
the floating support of the bottom aerators 12. The
connections between the hoses and the bottom aerator
are held together with conventional fastening means,
such as, for example, with clamping brackets 19.
In other embodiments (not shown), flexible hose
supply lines can also connect the distributing pipes
17 to the air supply line 14 in each case, instead of
the rigid connecting pipe 16. The use of several
flexible hose supply lines, for example, fastened to
each end of every float 13, leads to an increased
stability, which is of advantage particularly in con~
nection with the process according to the invention
when the individual air input through the individual
moving bottom aerators is greater than in the case of
a uniform input through many bottom aerators. It is
also possible in each case to stretch a support cable
over the tanks in parallel with the air supply line
14, on which cable the air supply line hoses 14 are
then suitably held or fastened.
The individual floating aerator chains 4 through ~
ll are stretched loosely over the basin 1, so that, ~;
;25 when charged with air, a reciprocating movement of the
nature of a lateral deflection of the aerator chains
takes place. This lateral deflection is optimally
achieved by full loading of the respective aerator ~P
chains. The floating aerator chains then move the
bottom aerators 12 in a reciprocating movement over
the bottom of the basin, preferably at a very short ;-
distance from the bottom of the basin, for example,
between lO and 30 cm. By means of this reciprocating
movement of the bottom aerators, an oxygen input ef~
35 fective for large regions is achieved, and it is par- ~`
ticularly ensured that the bottom aerators arranged
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near the bottom will again stir up and bring back into
circulation any activated sludge that has settled or
partly settled on the bottom of the basin.
Figs. 3a through 3c provide a schematic represen-
tation of the plant in operation, in a cross-section
through the basin shown in Elig. 1. At a first point
in time, a situation such as shown in Fig. 3a is ob-
tained. At this point in time, as indicated schemati-
cally by the solid circulation arrows 20, the aerator
chains 4, 5, 8 and 9 are fully loaded with air. At
this point in time, therefore, full aeration is being
carried out in only selectecl spaced zones of the
basin, while in other spaced zones, in which the aera-
tor chains 6, 7, 10 and 11 are operating, only an
insignificant oxygen input and a slight flow are tak-
ing place (broken lines).
After a certain time interval, which depends, for
example, on the pollution load of the plant, the
~; fourth and eighth aerator chains are switched off and
the sixth and tenth aerator chains are switched on
;~ instead as shown in Fig~ 3b. The aerator chains 5 and
9 remain fully loaded with air, as before. As a re~
sult of this displacement to the right, the zones in -
which an intensive oxygen input takes place thus mi-
grate to the right in the figure. At a later point in
time, as shown in Fig. 3c, the fifth and ninth aerator
chains are then switched off and the seventh and
eleventh aerator chains are switched on. In the il~
lustrated embodiment, two spaced-apart aerator-chain
30 pairs are thus always loaded in each case. The "~
` switching-on of a new aerator chain in each case takes
place in the same direction in each aerator-chain pair ~;
which, in the case illustrated, is an aerator chain
located to the right of an aerator-chain pair.
In this manner a zone of high oxygen input and/or
high mixing passes as a migratory wave through the
tank, in t:he illustrated example from left to right. ~ -
After the plant has been operated for a time in the ~
... .. . , ... . . . .,... ... .. . ....... " ~ , .
~ 18- ~33~
manner shown in Fig. 3c, the mode of operation shown
in Fig. 3a is then again started, etc. It is impor-
tant for all different conditions that this migrating
wave i5 superimposed and modulated on the moving aera-
tor chains. Only on the basis of the fundamentaleffect of the moving floating bottom aerators - espe-
cially regarding the activated sludge - can the speci-
fically described effects be efficiently accomplished.
It is clear that, depending on the load of the
plant or on the desired process-engineering effect,
the switching-on and -off of the aerator chains can
take place at different time intervals. It is also
clear that, instead of the simultaneous loading of two
pairs of aerator chains, it is possible in each case ;
to load only two individual aerator chains, for exam-
ple, first the aerator chains 4 and 8, ther. the aera-
~ tor chains 5 and 9, then the aerator chains 6 and 10,
; and finally the aerator chains 7 and 11.
In the case of plants operating with fewer aera-
tor chains, for example, with only three aeratorchains, it may also be sufficient to fully load only
one aerator chain in each case with compressed air.
It is also clear that whole sections of the tank can
be loaded with a different rhythm from other sections
or in a fixed manner.
The arrangement for controlling the selected air
loading of the chains is shown schematically in
Fig. 4. A central control unit 21 is provided, which
selectively controls a series of squeeze valves 22
associated with the individual aerator chains 4
! throughill. The squeeze valves in each case act on
the ends of the hose lines 4 through 11 and reduce
their transmission cross-section when actuated. The
unthrottled valves then in each case aerate the hose
lines with the full power that the compressed-air
supply source 23 makes available. The squeeze valves
:` -19-
~ 33~6 :.
22 can, for example, be controlled electrically or can
be charged and actuated with compressed air provided
from a central compressed~air control station.
A specific embodiment of a squeeze valve 22, such
as can be used in connection with the invention, is
illustrated in Fig. 5. The squeeze valve 22 consists
essentially of a tubular rubber collar 34, having an
internal diameter corresponding approximately to the
external diameter of the hose line 4, so that the
10 collar can be pushed conveniently over the hose line ~ -
4. A ring flange 32 is fastened over the rubber col-
lar 34 in such a way that a continuous compressed-air
space 35 is formed. The flange 32 has a compressed~
air connection 33. After the flange 32 has thus been
15 placed over the rubber collar 34 in a sealing manner, ;~
a pressure P can be produced in the space 35 by sup~
plying compressed air through the compressed-air con-
nection 33, which causes the rubber collar 34 to move
in the direction of the drawn-in arrows P, which leads
to a squeezing together of the hose 4. In the inte-
rior of the hose line 4 a pipe 36 is supported by
means of spacers not shown, permitting a minimal pas- ;~
sage of air even when the hose line 4 has been com-
pressed into the extreme squeezed position, such as is
25 shown by the broken lines in Fig. 5. ~ `
Depending on the magnitude of the pressure pro- ;~
duced in the space 35, different transmission cross- ~ -~
sections of the hose lines can be adjusted. -i;`
~ig. 6 is a schematic drawing illustrating a
30 plant that can be operated by the method according to ~;
the invention. In Fig. 6 the basin l has individual
aerator chains 4 to 9 distributed over the basin in
the same manner described with respect to Figs. 1-4
and a squeeze valve 22, which can have the structure
shown in Fig. 5, is associated with both ends of each
moving aerator chain.
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On the discharge side of the basin 1 there is a
sludge collecting pipe 24 leading to the outlet 3.
Activated sludge can be transported from the sludge
collecting pipe 24 through the return line R to the
inlet side 2 as required, in order to seed the incom-
ing waste water with activated sludge in the inlet
region 2.
The individual moving aerator chains 4 through 9
are connected to each other by means of a compressed
air conduit 25 and the individual squeeze valves.
Dl~erent air compressors 23a through 23e are con-
nected to the conduits 25. These air compressors
ensure the desired air pressure and, for this purpose,
are supplied with the power required for operation of
the compressors from a power supply 37 through a line
26, the connecting lines to the air compressors 23c,
23d and 23e having been omitted for greater clarity.
The control of the plant is carried out by a control
unit 21, which contains a computer 21a a~d a distribu-
tor unit 21b, which, depending on the switching com-
mands received from the computer 21a, can control each
individual valve 22 by means of individual lines 30,
~; only two of which are shown. However, separate air
pressure lines of this type lead to each squeeze valve
22, in order to be able to switch the individual
squeeze valves 22 separately.
; Different measuring probe~ 27, 28, 28a and 28b
are also located in the tank. For example, the oxygen
potential at different positions in the basin can be
measured continuously with the measuring probes 27 and
28a, whereas, for example, the turbidity of the water
is determined with the measuring probe 28. Similar
~ probes can be located at other positions in the basin.
! ~ The measuring probe 28b, which is located in the inlet
2, measures the quantity of waste water fed in.
All of the signals provided by these probes are
transmitted to the computer 21a and are processed in
~ such a way as to determine the required air supply to
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-21- 1 ?3 3 ~ f3
each chain. The computer then transmits the corre-
sponding signals through the command line 38 to the
distributor unit 21b, which then individually charges
the valves 22 with compressed air in accordance with
the signals.
The plant can naturally also be operated accord-
ing to fixed programs by means of the computer.
It has been found that, with the process accord-
ing to the invention or the device according to the
invention, it is also possibLe, in particular, to
operate pure activated sludge plants with an extren,ely
small amount of energy as compared with other plants
of this type, in which case the advantages of the
invention come into effect, in particular, in the case
15 of plants with low pollution loads. By means of the -
migrating aeration zones or "oxidation waves" accord-
ing to the invention and superimposing them on the
movemen~s of the individual aerator chains, it is
possible to achieve a high flexibility and adaptation
to a very wide variety of load values and process
situations, in which the plant can always be operated ;~
economically. Typical migration speeds of the oxida-
tion waves, which ensure an oxygen input in the ratio
of 3:1 or even 10:1 with respect to the more weakly ~ -
aerated or unaerated regions, are approximately 0.01
to 0.06 meter per second. The specific air input in
the intensively aerated regions can have values of Q.3 , ~ -
to 1 m3 of air per m3 of water per hour, while in the ~
.
weakly aerated regions, as mentioned, the aeration can i
30 be lower by a factor of 3 to 10. ~-
It has been found that the sludge, once it has ;;
been mixed with the waste water, sinks only extremely
slowly (typical rates of descent have values of 0.0005
to 0.003 meter per second) so it will take a rela-
tively long time before it would settle on the bottom.
Thus, if the bottom region of each zone is agitated by
the corresponding bottom aerators with a frequency of
approximately one to ten times per hour, with inten-
:
f -22~
~ 3 ~
sive oxygen input, this i5 sufficient to keep the
activated sludge potent, even though anoxic and some-
times anaerobic zones are formed. The plant can
nevertheless be operated, in particular, as a regu-
lated, easily controllable activated sludge plant,
~ith the great advantage of flexible processing method
and improved treatment and at the same time, the en-
ergy expended for mixing is far below 3 watts/m3 -
which is the lowest value for mixing with moving aera-
tor chains with continuous and equal air flow - which
is especially surprising considering that~ for surface
aerators and fixed installed bottom aerators, a value
of approximately 10 watts/m3 is needed for mixing
alone.
By modulating the basic movement of the floating
chains and attached bottom aerators which provide
stirring action from the bottom of the basin with the
described wave-like moving load changes or in part of
the basin with a load pattern fixed to zones, makes
advanced treatment - that is, simultaneous (in one
basin) nitrogen and phosphorus reduction by activated
sludge - possible in a simple and energy-efficient
way. This is something that would never have been
expected in simple earthen basins and which also has
been looked upon as impossible by wide circles of
~ contemporary experts.
; In accordance with the oxygen potential, the detention times in each zone of the basin and the food
supply for microorganisms in the waste water, etc.,
the microorganisms contained in the activated sludge
used in the process will carry out different procèss
reactions. For example, carbonaceous BOD removal and
nitrification are carried out at higher oxygen poten-
tials, carbonaceous BOD removal combined with denitri-
fication occur under conditions which lack dissolved
oxygen but include the presence of nitrites and/or `
nitrates (anoxic conditions) and phosphate removal is
stimulatecl by conditions in which both oxygen, ni-
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~ ' '
-23- ~3~
trates or other oxygen sources are lacking (anaerobic
conditions). For conventional plants, an oxygen level
in the waste water of 2 mg/l or higher is generally
recommended for nitrification.
s If the complete basin is run first in the nitri-
~ication mode, l.e., with an oxygen level throughout
of 2 mg/l or higher, and then in a denitrification ~-
mode under anoxic conditions with a continuous waste
water influent to and effluent from the basin, then
10 some of the waste water influent which enters during ~
the denitrification mode will not be oxidized and ; ,
cannot then be denitrified so that it will pass out of
the basin unaffected by the nitrogen removal process,
that is, with the harmful ammonia remaining in the
15 water. In addition, if all the water is first nitri-
fied, then this reaction will, due to the consumption
of alkalinity, lead to undesirable changes in the pH
value, which affects the process negatively. "
By establishing zones of high and low oxygen
20 potential in accordance with the invention, the influ- !,: ,,~
~; ent waste water must pass through several successive
zones providing alternate oxidizing conditions and `
; denitrifying conditions before any influent reaches
the outlet.Use of the invention with the constant -
25 repetition of the process steps will dramatically in-
crease the overall efficiency of the waste water
treatment process. For example, if a process which,
for some reason, is run at suboptimum conditions, for ~`
example, with a 50% efficiency is carried out twice,
30 then the overall efficiency becomes 75%, and if car-
ried out three times, it becomes 87.5%. Thus, with a ; ;~
plurality of active zones for carrying out successive `~
process conditions repeatedly, the process can be
substantially completed despite a lack of complete
35 efficiency in each of the zones.
~ The comparatively slow intermixing of the zones
; (low horizontal mixing) also assures that all parts of
~' the influent waste water remain in the basin for a
q
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~ 33~ ~13~
time long enough to complete the process, such as one
hour, while the prior art circulating systems de-
scribed previously, in which waste water passes
through a circulatory treatment system in a matter of
minutes will only permit treatment of influent waste
water for a few minutes before the influent reaches
the outlet of the system. This clearly makes the
treatment less complete and ~he effluent quality will
quickly deteriorate even during brief and minor upsets -~
in the process.
Therefore, the key to proper treatment of waste
water in accordance with the invention is to establish
many well-defined zones and change the conditions to
which the waste water is subjected in the zones com-
paratively often so as to ensure that the waste wateris thoroughly treated and, at the same time, to keep
the microorganisms in suspension in the waste water.
In the migrating zones provided in accordance with the
invention, relatively narrow zones can be established
and maintained in a surprisingly well-defined manner
without the use of any mechanical mixers and with
expenditure of a minimum amount of energy. This re-
` sults in excellent treatment and clear, defined pro- ;
cess steps, for example, providing simultaneous nitri-
fication/denitrification in the same basin at surpris-
ingly low oxygen levels (oxygen contents of 0.3 mg/l
;~ or less) and correspondingly low energy consumption.
The repeated change of conditions also stimulates the
bacteria to a higher level of activity. Substantial
phosphate removal is also accomplished in this way.
A typical basin designed to carry out the inven~
tion using, for example, a municipal waste water input ~ -~
of one million gallons per day would typically have a
capacity of 0.75-3 million gallons, and optimally have
a depth of 8-20 feet.
Although the invention has been described herein
with ref~rence to specific embodiments, many modifica-
tions and variations of the invention will be obvious ~
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:- -25- ~3~
to those skilled in the art. Accordingly, all such
variations and modifications are included within the ;.
intended scope of the invention as defined by the ;
following claims.
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