CA1099037A

CA1099037A - Process and apparatus for sewage purification by activated sludge technique

Info

Publication number: CA1099037A
Application number: CA318,258A
Authority: CA
Inventors: August Schreiber
Original assignee: Individual
Current assignee: Individual
Priority date: 1977-12-23
Filing date: 1978-12-20
Publication date: 1981-04-07
Also published as: FR2412501A1; NL7812371A; DK580578A; FR2412501B1; DE2757860A1; BE872996A

Abstract

Title of the Invention PROCESS AND APPARATUS FOR SEWAGE PURIFICATIOIN BY ACTIVATED SLUDGE
TECHNIQUE

ABSTRACT OF THE DISCLOSURE
A sewage treatment facility includes a round reaction tank, a round aeration tank which encompasses the reaction tank, a final clarification tank and a sludge return station. The crude sewage is passed in part to the reaction tank and in part to the aeration tank, the partially purified contents of the reaction tank are caused to flow into the aeration tank via an overflow wall, the contents of the aeration tank flow, for the most part, to the final clarification tank, the activated sludge separated from the purified water in the final clarification tank is recirculated to the sludge return station, and part of the activated sludge is passed from the sludge return station to the reaction tank and part to the aeration tank. A small amount of the contents of the aeration tank is passed to the sludge return tank and from there to the reaction tank. A bridge rotating over the tanks includes downwardly extending aerators for aerating the contents in both tanks.

Description

~99~37 BACKGROU~D OF THE I~VE~TION
. . ~
FIELD OF THE Il~VE~TION
The present invention relates to both a process and an apparatus for the purification of sewage by means of an activated sludge technique. More particularly, it relates to a sewage purification system wherein crude sewage is treated in both a reaction tank and an aeration tank, and then is passed on to a final clarification tank, and to a system wherein activated sludge from the final clarification tank is returned to a sludge return station for ultimate recirculation to one of the earlier treatment tanks.
THE PRIOR ART
Biological sewage treatment plants which include a biological treat~ent stage, a final clarification tank and a lS return installation for activated sludge ~l to be returned from the final clarification tank to the biologic21 treatment stage are already known. Such plants normally have one or two treatment stages, and when two stages are used in succession, two final clarification tanks will be needed.
At the same time, however, most of the pollution associated with the sewage is digested in the first stage - the second stage digesting only the small remainder. Thus, in prior art treatment plants when the first stage is overloaded the degree of purification of effluent striven for will unfortunately not be achieved in the second stage.

, 1~99~37 As compared to the foregoing, one-stage sewage treatment plants with large treatment zones and mixed-through clari~ication tanks are more reliable in operation because sewage loading shocks are prevented and the operation of the treatment systems is simpler.
A somewhat different two-stage sewage treatment system is known in which a round preliminary clarification tank is encompassed by a circularly-shaped aeration tank, e.g., as described in the publication entitled l~schreiber Gegenstrom Rundbecken" (counter flow circular tank). This system, however, has not proven to be entirely satisfactory in attaining the desired objectives.
It is an ob~ect of the present invention to provide a two-stage purification system wherein an effective degree of sewage purification can be achieved without overloading, -~
wherein the second final clarification tank thought to be necessary in conventional prior art two-stage facilities can be eliminated, wherein input load shocks can be handled, and wherein construction costs and energy consumption costs are low. In other words, a system wherein the desired effluent quality can be achieved when utilizing a given sewage supply, e.g., as in the prior art, but with a smaller treatment area and with the consumption of less energy, or, when the same treatment area and energy consumption as the prior art is used, a purer effluent will be produced.

_ 2 ~

~q~99~37 SU~IMARY OF THE I~VENTIO~
According to the present invention, the above objects are achieved when a ~reatment facility like that described in the above-noted publication is constructed to operate as follows:
a part of the input crude sewage to be purified is introduced into the reaction tank along with a part of the activated sludge returned from the final clarification tank (activated sludge which has been settled and concentrated), together with a part of the activated sludge-water mixture from the aeration tank. The streams may be introduced into and mixed with the contents in the reaction tank, either separately or in premixed form, preferably at the bottom of the tank, and the oxygen content of the mixture in the reaction tank is continuously ~ measured and controlled.- Thus, in the reaction tank the noted ;15 stream mixture is aerated, caused to circulate (in part with a rotating action), and thickened. After a sufficient dwell and reaction time in the reaction tank so as to achieve adsorption, paxtial purification and escape of generated gases, the mixture is passed to an aeration tank where it is aerated and further purified, and then fed to a final clarification tank. The obtained purified and de-sludged sewage is fed from the final clarification tank to a receiving water area, whereas a large part of the settled and purified activated sludge is returned to the reaction tank. The smaller part of this obtained activated sludge, together with a part of the crude ~99~37 sewage not initially introduced into the reaction tank, is introduced into the aeration tank.
Preferably the inventive process is carried out in a system constructed such that a round reaction tanX is encompassed S by an outer circular aeration tank. Thus, the process as noted is carried out in a system using an apparatus which includes a reaction tank; an aeration tank; means in the aeration tank to aerate the contents therein; a final clarification tank; a feed line for conveying crude sewage to the system, one branch thereof conveying a large portion of crude feed to the reaction tank and a second branch conveying the remaining smaller portion to the aeration tank; a sludge return apparatus; a line for returning activated sludge from the final clarification tank to the sludge return apparatus; a first branch line extending from the sludge return apparatus to the reaction tank for conveying thereto a large portion of the activated sludge from the final clarification tank; and a second branch line extending from the sludge return apparatus to the aeration tank for conveying thereto the smaller remaining portion of the activated sludge. Means are provided in the reaction tank for aeration, as well as for suspension, rotation, circulation and mi~ing of the tank contents. In addition, an overflow structure is provided between the reaction tank and the aeration tan~.

~L~P99~37 The previously mentioned intermixing of fluid streams with the existing contents in the reaction tank is initially commenced at the bottom of the tank, and the streams are caused to acquire a moderately rotating upward movement during the time spent in the reaction tank.
Due to the noted control of the aeration of the contents in the reaction tank, an increase in sludge concentration in the reaction tank can be achieved. As a result, feed input irregularities (shocks) relating to pollution content and water volume are dealt with, and since the stxeam mixture will be digested therein to a greater than 50% degree, water passing over the overflow structure into the aeration tank will be less polluted. The increased sludge concentration is conditional only on the volume and concentration of stream input from the final clarification tank and on the volume and concentration of stream input of activated sludge-water mixture from the aeration tank.
The noted control of the aeration of the reaction tank contents (and also the contents of the aeration tank) makes possible an alternating throttling and switching off of the aerators in ~he reaction or aeration tanks. As a result, besides achieving an additional part purification, the nit~sgen which has been oxidized to nitrate in the aeration tank may again be decomposed in the reaction tank such that an additional purification effect may also be realized.
This cannot be achieved by a standard one-stage activated ~99~37 sludge installation without a reaction tank. The inventive system allows for not only an improved purification action, but the clari~ication chambers needed can be made smaller. In this manner, it is possible to design activated sludge clarification plants for large, medium and small loads.
The essence of the invention thus includes subdividing the biological stage into two separate biological treatment zones, the first zone treating a very high concentration of sludge and the second zone treating a standard concentration o~ activated sludge, and the method of stream flows (as discussed previously).
With respect to the first point, the inventive system includes two biological aeration tanks, i.e., one round aeration tank having a normal concentration of activated sludge and a round reaction tank which has as high as possible a concentration of activated .
lS sludge.
It is advantageous to have the mechanisms for aeration, circulation and mixing of the tank contents attached to a rotating bridge which spans the diameter of the reaction tank and the aeration tank, with the aerators extending downwardl~
therefrom via air supply pipes to be positioned near the bottom of the pertinent tank. These aerators act in a known manner to aerate the sewage and keep the activated sludge in suspension. In addition, additional mechanisms may also be attached to the rotating bridge which function to intermix and allow gases to escape from the activated sludge-water 1~99~3~

mixture. Special mountings may be provided on the rotating bridge to allow for these additional mechanisms, together with the aerators and/or their air supply lines, to be releasable therefrom.
In order to achieve a lower speed of circulation in the reaction tank for the activated sludge-water mixture with respect to the speed of rotation of the bridge, at least one transverse separating wall is located in the aeration tank. This transverse wall is, however, provided with openings to allow for the passage of the aerators, their air supply pipes and their mountings therethrough as the bridge passes thereover.
In order to achieve the greatest possible purification of sewage, the stream of activated sludge which is returned ,~
from the final clarification tank to the aeration tank (that part of the return stream which is not discharged into the reaction tank) is discharged at the surface level of the contents in the aeration tank. In addition, this discharge should occur very closely behind the transverse wall, i.e., very close to the side of the transverse wall opposite the side impinged by the tank contents as a result of circulation generated by the aerators and other mechanisms attached to - the rotary bridge. At this location the activated sludge in the tank which needs oxygen is aerated and then is mixed with the partial stream of input crude sewage. This latter is also discharged at the surface level of the contents ~99~37 in the aeration tank, but at a point which is 15 to 20 (arc measure) behind the transverse separating wall.
The sewage, which is treated in both the reaction tank and the aeration tank, is then fed to the final clarification tank wherein the sludge is caused to settle and the upper level of purified product sewage is fed to a receiving water area.
In the reaction tank the oxygen content is kept so low that no septic formation occurs; however, adsorption and reaction between the contents of the activated sludge-water mixture and the activated sludge from the aeration tank occurs as a result of contact between the activated sludge and the input crude sewage and activated sludge-water mixture entering from the aeration tank. This results in a fairly considerable purification of the input sewage. This sewage, thus pretreated and with less pollution, together with activated sludge which is non-saturated with oxygen, then enters the aeration tank where the greatest part of the remaining pollution is digested by a more intensive aeration, and the developed activated sludge is mineralized.
With the low oxygen content in the reaction tank, a denitrification will occur, even at low temperatures, due to the fact that nitrates formed in the aeration tank as a result of the oxidation of nitrogen-containing compounds will be returned ~o the reaction tank by way of the return feed of activated sludge from the aeration tank.

~99~3~7 It is also advantageous to utilize a measuring probe in the reaction tank, preferably connected to an ro~ating with the bridge, to measure the oxygen level in the contents of the reaction tank. The probe can then be connected via a magnetic valve to control the air feed to ~he aerators such that the o~ygen content will stay within the limits of between 0 and 0.2 mg/l. A measuring probe may also be provided in the aeration tank to control either the air supplied to all the aerators in the aeration tank (the air then being supplied 10 . to the aerators in the reaction tank being throttled or turned off), or else to only half the aerators in the aeration tank (the aerators in the reaction tank then being full~ supplied with air).
Further objects, advantages and features of the invention.
will bw apparent from the arrangement and construction of constituent parts of an embodiment of the sewage treatment apparatus as depicted in the accompanying.drawings and discussed in the following description.
DESCRIPTION OF THE DR~WI~GS
In the drawings, Figure 1 schematically depicts the top view of a sewage treatment system in accordance with the present invention.
Figure 2 depicts a side view of the system in Figure 1 viewed along a line represented by A-B-C-D-E-A in Figure 1.

l~D99037 Figure 3,schematically depicts a vertical sectional view taken through a portion of the bottom of the reaction tank of the inventive system, showing the in-feed line for crude sewage, the in-feed line for activated sludge return from the final clarification tank, and the in-feed line for activated sludge-water mixture returned from the aeration tank.
Figure 4 represents a schematic top view of the li~uid in-feed lines to the reac.tion tank represented in Figure 3.
Figure 5 schematically depicts an overflow structure which is located between and effectively separates the react;on and aeration tanks.
Figure 6 schematically depicts a cut away view of the , overflow structure of Figure 5. ,, ' . ' .' , ~:, . . Figure 7 schematically depicts a top view of the overflow structure of Figures 5 and 6.
DETAILED DESCRIPTIO~ OF I~IE PREFER~ED EMBODIME~TS
As depicted in Figure 1, the inventive treatment system includes an aeration tank 2, a reaction,tank 1, a final clarification tank 3, and a sludge return apparatus 4, the sludge return apparat~s receiving the activated sludge from the final clarification tank 3 via a return line 3, 1. The crude sewage is fed into.the treatment system via line 1, 1.
Each of the tanks 1, 2 and 3 have a rounded configuration when viewed from above, and as can be seen from Figure 1, aeration tank 2 is larger in diameter than, and is positioned to surround, reaction tank 1.

~ ~99C~37 The crude sewage feed line 1,1 is divided into two branch lines 1,2 and 1,3. Branch line 1,2 extends into the reaction tank 1, whereas branch line 1,3 extends to a point within aeration tank 2 Both branch lines are equipped with an indicated locking slide. As can be appreciated from Figures 1, 3 and 4, branch line 1, 2 terminates within a central shaft 1,7 located at the center o~ tank 1, the wall of which includes.apertures 1,71 to allow communication to the insiae of reaction tank 1.
The branch line 1,3 terminates at the surface of the fluid contents within the aeration tank 2.
The return line 3,1 emanating from the final clarification tank 3 communicates with the sludge return apparatus ~, from which two branch l~nes 2,1 and 2,3 return the activated sludge to the treatment tanks: the branch line 2,1 extending along the I5 bottom of tanks 2 and 1 (similarly to branch line 1,2) to terminate within central shaft 1,7, whereas branch line 2,3 terminates at the surface of the contents within the aeration Sim l/o,~ Iy tank 2 (simiarly in this regard to branch line 1,3). Mechanisms 1,4; 1,5; and 1,6 are positioned within xeaction tank 1 for the purpose of selective aeration, as well as for suspension, rotation, circulation and mixing of the contents within the reaction tank. Furthermore, an overflow device 1,8 and 1,9 (see Figure 6) is positioned between the reaction tank 1 and the aeration tank 2. The branch lines 2,1 and 2,3 also have indicated locking slides.

~ 11 --~99~37 As can be appreciated from a review of Figures 1 and 2, a common rotatable bridge 12 is positioned to span across both of reaction tank 1 and aeration tank 2, and connected thereto so as to extend by way of air supply pipes to a point near the bottom of the tanks are the mounted aerators 1,5 and 1,6 (these of course extending to a point near the bottom of reaction - tank 1) and aerators 2,5 and 2,6 (which are positioned to extend to a point near the bottom of aerator tank 2). The various aerators can be releasably attached to the bridge 12. The rotatable bridge 12 is centrally mou~ted on the central shaft 1,7 as well as supported at its extremities by suitable means on the outside wall 6 of aeration tank 2, these means being also capable of driving the bridge so as to be rapidly rotated.
A transverse separating wall 2,7 is positioned within the aeration tank 2; however, it also includes suitable recesses for the passagetherethrough by aerators 2,5 and 2,6, as well as their air supply pipes, when the bridge 12 passes thereover.
The branch line 2,3 is positioned to extend into the acration tank 2 at a point either slightly in front of, or quite closely behind, transverse separating wall 2,7, i.e., with respect to the clockwise rotation by bridge 12 as indicated by arrow 7, whereas the branch line 1,3 extends into the aeration tank at a 15 to 20 arc measure distance behind the transverse separating wall.

~99~137 The devices for the selective aeration of the contents in reaction tank 1 include also a measuriny probe 1,4 which ,~,5p~s~d A is d~e~e~ in the reaction tank for measuring the oxygen level in the oon~ents therein and for control of the intensity of the aeration taking place as a result of the action of aerators I,5 and 1,6. In this latter regard, a magnetic valve (not shown) can be connected in series with the measuring probe 1,4 for appropriate control o the aeration intensity, i.e., of the volume of discharged air per unit of time.
Similarly, the devices for the selective aeration of the contents in aeration tank 2 include a measuring probe 2,4 disposed in the aeration tank for measuring the oxygen level in the contents therein and for control of the intensity of the ~.
aeration taking place as a result of the action of aerators

2,5 and 2,6. As before, a magnetic valve (not shown) can be connected in series with the measuring probe for aeration control.
Both of the measuring probes 1,4 and 2,5 may be advantageously disposed on the rotatable bridge 12.
The overflow structure which is provided between and effectively separates reaction tank l and aeration tank 2 includes a circular wall means 5 which extends vertically to a point above the contents level in the aeration tank 2, but which has distributed around the entire circumference openings l,8 that are positioned at the height of the contents 1~'99~?37 level in the aeration tank 2. As can be seen from FigureS 5 to 7, a groove-shaped sludge rejector 1,9 is positioned within reaction tank 1 in front of the openings 1,8 so as to extend around the inner circumference o~ wall means 5 and acts as sh~ p~ J
a calming chamber lthe sludge rejector is-chaped in the fashion of an annular settling groove). The rejector acts to partially hold back activated sludge from passing through openings 1,8 into reaction tank and altering the concentration of contents therein.
Due to the feeding into reaction tank l of not only crude 0 sewage via the branch line 1,2, but also of concentrated, activated sludge from the final clarification tank 3 via branch line 2,1, as well as the influx of activated sludge-water mixture from aeration tank 2 via return line 2,8, and due to the particular arrangement for such introductions as depicted in Figures 3 and 4 (e.g., the discharge for the line 1, 2 being tangential with respect to the shape of shaft 1,7), a rotating current is produced at the bottom of the tank which is counter-current to the direction of rotation of bridge 12 and to the current inherently produced thereby. The rotating current O within reaction tank 1, i.e. that produced by the rotation of bridge 12, is thus caused to slow down and is also caused to spirally rotate upwardly to the level of openings 1,8 in -wall 5 and finally through them into aeration tank 2. At the same time, sludge rejector 1,9 tend to brake down this rotating movement and acts to decrease the escape of the ,.

sam/

~99~37 activated sludge until the sludge concentration in the reaction tank 1 is considerably greater than the sludge concentration in the aeration tank 2.
The rotating liquid (water) in the aeration tank 2 which is generated by movement of the rapidly rotating bridge 12 is slowed down by the separating wall 2,7, as a result of which a greater relative speed between aerated, activated sludge-water mixture and rotating aerators 2,5 and 2,6 will be achieved.
In this way a greater utilization of oxygen will be accomplished.
While there has been shown and described what is considered to be preferred embodiments of the present inventionr it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the inv~ntion as defined in the appended claims.

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Claims

I CLAIM:

1. In a continuous process for sewage purification by means of an activated sludge technique wherein the crudge sewage is passed through an aeration tank, a reaction tank, a final clarification tank and a sludge return installation, the improvements wherein (a) a part of the crude sewage to be purified is fed to the reaction tank to mix with the contents therein, a part of the concentrated activated sludge produced in the final clarification tank is recirculated to the reaction tank to mix with the contents therein, and a part of the activated sludge-water mixture from the aeration tank is recirculated to the reaction tank to mix with the contents therein, (b) the oxygen level of the mixed contents in the reaction tank is continuously measured and controlled by aeration, rotation, circulation and thickening of the reaction tank contents, (c) after the contents in the reaction tank have been adsorbed and partially purified, and after developed gases have escaped, the mixed contents of the reaction tank are passed to the aeration tank, (d) aerating the mixed contents in the aeration tank for additional purification thereof, (e) passing the purified mixed contents of the aeration tank to the final clarification tank where a purified and de-sludged fraction is formed and a deposited concentrated activated sludge fraction is formed, (f) recirculating the part of the concentrated activated sludge not recirculated to the reaction tank to the aeration tank, and (g) passing the part of the crude sewage not fed to the reaction tank to the aeration tank.

2. The process of Claim 1 wherein the reaction tank is circular and is encompassed within a larger circular reaction tank, and wherein the mixed contents of the reaction tank which are passed to the aeration tank travel in a radial direction with respect to the remaining contents in the reaction tank.

3. The process of Claim 2 wherein the oxygen level in the reaction tank is controlled to a level of no more than 0.2 mg/l.

4. The process of Claim 2 wherein the aeration of the contents in the reaction tank and the aeration tank is achieved by moving aerators through said tanks in a circular fashion.

5. The process of Claim 2 wherein the contents of the reaction tank are passed to the aeration tank via circumferentially disposed openings in the wall of the reaction tank which separates the reaction tank from the aeration tank, said holes being at the level of the contents in the aeration tank.

6. The process of Claim 2 wherein both the crude sewage and the actuated sludge passed to the aeration tank are discharged at the fluid level therein.

7. The process of Claim 2 wherein the amount of crude sewage fed to the reaction tank and the amount of crude sewage fed to the aeration tank are controlled, such that a major amount is fed to the reaction tank.

8. The process of Claim 2 wherein the amount of activated sludge stream passed to the reaction tank and the amount of activated sludge stream passed to the aeration tank from the final clarification tank is controlled, and wherein the stream passed to the reaction tank is discharged at the bottom portion thereof and the stream passed to the aeration tank is discharged at the fluid level therein.

9. The process of Claim 2 wherein the aeration, rotation, circulation and thickening of the contents in the reaction tank is achieved by rotation of means therein extending downwardly from a rotating bridge.

10. The process of Claim 9 wherein a transverse separating wall is positioned in the aeration tank, wherein the activated sludge passed thereto is accomplished at a point close behind the transverse wall, considered with respect to the rotation of the means extending downwardly from the rotating bridge, and wherein the crude sewage fed thereto is accomplished at a point between 15 and 20° arc measure behind the transverse wall.

11. A sewage purification system comprising (a) a reaction tank, an aeration tank, a final clarification tank and a sludge return apparatus, (b) means for supplying a part of a continuous crude sewage stream to said reaction tank and means for supplying the balance of the continuous crude sewage stream to said aeration tank, (c) means for recirculating the activated sludge produced in the final clarification tank to said sludge return apparatus, (d) means for passing a part of the activated sludge from said sludge return apparatus to said reaction tank and means for passing the balance of the activated sludge from said sludge return apparatus to said aeration tank, (e) means for aerating the contents in the reaction tank, (f) means for passing part of the fluid contents of the reaction tank to the aeration tank, (g) means for passing part of the fluid contents of the aeration tank to the final clarification tank, and (h) means for passing part of the fluid contents of the aeration tank to the sludge return apparatus.

12. The system of Claim 11 wherein said reaction tank is round, in horizontal cross section, and wherein said aeration tank is round, in horizontal cross section, said aeration tank being larger than and encompassing said reaction tank.

13. The system of Claim 12 wherein a rotatable bridge is positioned to extend across the diameter of said aeration tank, and wherein means, including aerators, are attached to said bridge to extend downwardly to near the bottoms of both the reaction and aerator tanks to produce aeration, suspension, rotation, circulation and mixing of the contents in each tank.

14. The system of Claim 13 wherein a transverse wall is positioned within the aeration tank, said wall including recesses to allow for passage therethrough of said means attached to said bridge which extend into said aeration tank when said bridge is caused to pass thereover.

15. The system of Claim 14 wherein said means attached to said bridge includes a oxygen level measuring probe extending into said reaction tank, and wherein said measuring probe is connected to control the intensity of aeration in said reaction tank by adjusting the amount of air supplied to the aerators located in said reaction tank.

16. The system of Claim 14 wherein said means attached to said bridge includes an oxygen level measuring probe extending into said aeration tanks, and wherein said measuring probe is connected to control the intensity of aeration in said aeration tank by adjusting the amount of air supplied to the aerators located in said aeration tank.

17. The system of Claim 13 wherein said means for passing a part of the fluid contents from the reaction tank to the aeration tank comprises an overflow wall which is positioned between and defines the reaction tank and the aeration tank.

18. The system of Claim 17 wherein said overflow wall comprises a circular wall which includes circumferentially disposed openingstherein.

19. The system of Claim 18 wherein means forming sludge rejectors are positioned along said circular wall and in the reaction tank side thereof to provide a calming chamber between the contents in the reaction tank and the openings in the circular wall.

20. The system of Claim 12 wherein a central shaft having circumferential openings therein is positioned at the center of the reaction chamber, wherein both said means for feeding crude sewage and said means for supplying activated sludge to said reaction tank have discharge openings within said central shaft, and wherein the discharge opening for said crude sewage is tangentially oriented with respect to the central shaft.

21. The system of Claim 14 wherein said means for supplying activated sludge to said aeration tank has a discharge opening adjacent the back side of said transverse wall therein, and wherein said means for feeding crude sewage to said aeration tank has a discharge opening on the same side of said transverse wall as said discharge opening for said activated sludge supply means, but at a 15 to 20° arc measure back of said transverse wall.