CA1145073A - Advanced means for biological treatment of water - Google Patents

Abstract

ABSTRACT

The invention disclosed relates to an apparatus for use in the advanced biological treatment of waste water or sewage. The apparatus described includes a conically shaped aeration chamber wherein the sewage is subjected to activated sludge and a plurality of settling chambers through which the sewage is passed. The treated water is removed from the settling chambers and sludge is re-cycled back into the aeration chamber by means of an aerator.

Description

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MEANS FOR ADVANCED WATER TREATM~NT
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Technical Field 5 ~ My invention relates to water treatment devices and particularly to physicochemical and biological methods of sewage treatment devices. In the advanced - ;~
waste water treatment process of phosphorous removal using two steps of lime reaction tanks suspended solids settled down in the first step lime reaction tank are collected and pushed back into reaction and flocculation zone by rake arms~and solids settled down in the second step lime reaction tank are pumped back into the first ¦ step tank by separate pumps. On the other hand, it is essential in the biological process of sewage treat-ment to have high concentration of the activated sludge and high intensity of turbulence in the aeration chamber so more sewage can be treated per same volume `
of an aeration tank. But the higher concentration of ~ 20 the activated sludge, the greater amount of suspended ~"
¦ solids is carried out from the activated sludge -~
settling tank. And it is required quite often to ~r~
provide for the second step settling tank to decrease ~i suspended solids in the effluent. In this case an ;`
additional pump and pipe lines will be required to recycle suspended solids settled in the second step ` settling tank back into the aeration tank. It is essential in both cases to eliminate some of the equip-ment for solids recirculation and consequently to decrease expenditures.
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-2 Background Art .
The prior art, U.S. Patent ~o. 3,246,7~2, provided for two settling chambers. Although sludge return from the first settling chamber is produced by the action of an aerator, sludge return from the second settling chamber is produced by using a separate pump. In case a third settling chamber is

3 needed, an additional pump will be required. So this , 10 prior art is not as energy-efficient as my invention.
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~ Disclosure of Invention ~ ~ .
In accordance with the present invention, I provide a waste water treatment apparatus consisting of a mixing or aeration chamber where mixing or aerat- ~ -ing means is mounted, and a plurality of settling chambers adjacent to the aeration chamber and which work in series. My improved waste water treatment apparatus possesses the advantage that suspended `
solids settled down in each of the serially operated settling chambers are returned back into the aeration ~
chamber by the action of the single aerator. The latter feature is of particular advantage and is a distinct . 25 improvement over certain prior art apparati because it eliminates special recycling pumps for each settling chamber, and consequently reduced capital ' and operating expenses. Another advantage of my apparatus is that its mixing (or aeration) chamber has a horizontal sectional area which increases in size from the bottom to the top, thereby greatly increasing turbulence in the aeration chamber. The higher turbulence, the higher biological activity of the' sludge and higher concentration of the sludge can be maintained in the aeration chamber. This shape of ~1 .
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the aeration chamber effects a high degree of waste and sludge mixing in the aeration chamber with minimum `' power consumption.
, Brief Description of_Drawings :
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The details of my invention will be described ;
in connection with the accompanying drawings, in , which Figure 1 is a schematic vertical sectional view showing a first embodiment of the invention with ¦
` two settling chambers and improved shape of the j aeration chamber; Figure 2 is a schematic top plan view of the first embodiment; Figure 3 is a schematic vertical sectional view showing a second embodiment of the invention with two settling chambers working in series; Figure 4 is a schematic top plan Yiew of the second embodiment; Figure 5 is a schematic -top plan view showing a third embodiment of the inven- ~¦
tion with three settling chambers, two of which are working in parallel and one is in series with those two; Figure 6 is a schematic vertical sectional view showing a fourth embodiment of the invention ~ -with an air-diffuser as an aerator. ~, : ;
Best Mode for Carrying Out the Invention ' In accordance with the first embodiment of the i;`
invention (Figures 1 and 2), the device of generally trapezoidal configuration includes housing 1 with number of septums which create inside of the housing 1 aeration chamber 2 and two settling chambers 3 and 4.
The housing element is bounded by a pair of side walls 5 and 6, end walls 7 and 8 and a bottom wall 9.
A support (not shown) mounts an aerating element 10, ~ :~

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: i which may be of conventional type including a prime mover ll and a rotating shaft 12 mo~unting an impeller ` "
13. A concentric air passage 14 has a lower end 15 adjacent to the impeller 13, so that with rotation .. ~

5 of the impeller~ air is mixed into the treaked water in a well known manner. First, second and third pairs of septums 16, 17 and 18 respectively,`
interconnect an aeration chamber 2 with a pair of ~. :
settling chambers 3 and 4. The septums 17 are sloped outwardly and terminate above the end walls 7 and 8 -and form lower ports l9 and 20 through which activated sludge settled in the chambers 3 and 4 is recycled or inducted into the aeration chamber 2 under ¦ action of the impeller 13. An effluent trough 21 communicates with an effluent pipe 22 for discharge of treated water. Sewage inflow pipe 23 is positioned as shown in Figure l at the lower part o~ the aera-tion chamber, such that sewage will be immediately subjected to the action of air bubbles 24 formed by the impeller. Sewage enters the aeration chamber 2 ~ ~;
and moves upwards, then flows through the passageways ;
between septums 16 and 17 into the settling chambers from which it is discharged. Activated sludge settles`
in the settling chambers because of its density, t and collects at the bottom of the settling chambers, from where it is drawn back into the aeration chamber by suction produced by the circulating water. Re-ferring to Figure l, pressure at ports l9 and 20 is the same because the water is moving at the same velocity in those two areas, inasmuch as they are equi-distant from the aerator. Ak any such area where~such ~ ;i ~ a port or conduit exists, the higher the velocity, .~ of the water, the lower pressure at the port and hence the greater suction effect. Therefore, if the aerator lO is not symmetrically placed but is closer ~9 ' , ' '. , ;`~; i ``~.t ;.

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~5-to settling chamber 4, a greater water velocity will be produced in the area of port 19 than at port 20;
therefore, pressure at port 19 wil~ be lower than at 20 and consequently there will be greater suction effect at port 19 than at port 20. In this arrange-ment of the impeller, settling chambers will work in series (settling c~lamber 3 as first step and ~ settling chamber 4 as second step). From a considera-¦ tion of Figures 1 and 2 it will be apparent that only a single impeller is necessary to create the circula-tion which draws recycling sludge from both settling chambers which are working in parallel. Having the septums 17 slope outwards creates a cross-sectional area which increases toward the top of the aeration chamber 2, thereby producing greater turbulence in the waste water than turbulence in aeration chambers of the prior art. The net result is increased capacity of one aeration chamber to treat sewage, ~i - coupled with a lower requirement for power which must be delivered by the aerator, to make total operating expenses lower than the same in the prior art. , In Figures 3 and 4 is the second embodiment of the invention in which is shown another way of putting two settling chambers in serial operation and recycling sludge back into aeration chamber from both of them and yet using only one aerator. This enables a major portion of' the activated sludge to be removed in ~' ` the first step settling chamber and the remaining ~;
sludge to be removed in the second step settling chamber downstream, with resultant higher efficiency of sludge recovery.
As best seen in F'igures 3 and 4, the second step settling chamber 25 is interconnected by conduit' sections 26, 27 and 28 to the first step settling chamber 29. The chamber 25 is bounded by a pair of `' f .~ :

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converging walls 30 and 31, an end wall 32, a flat hollow conduit 33, and a wall 34. The lower end of the conduit 33 is positioned at the bottom of the second step settling chamber 25, and terminates at a ! r~
medial level or location 35 of the aeration chamber 36.
Effluent from the chamber 25 flows through a trough 37 feeding an exit pipe 38.
During normal operati~n, the head in the aera-tion chamber 36 is higher than the head in the first :;
step settling chamber 29, and the head in the second step settling chamber 25 is below that of the `~
chamber 29. Thus, as water is introduced into the aeration chamber 36 through a pipe 39 and aeration ;~
takes place, water first travels through the passageway between septums 40, 41 and 42 to the first step settling chamber 29 which operates in a manner similar~
to that in the first embodiment. Then water flows through troughs 26, 27 and 28 to the second step ; j settling chamber 25 where further settling occurs. ` ¦
Effluent from the chamber 25 flows at the top through a trough 37 feeding an exit pipe 38. The ~ j amount of sludge in the effluent from the chamber 25 -is considerably less than that in the chamber 29.
Because of the difference in liquid levels between the chamber 36 and the chamber 25, sludge can be moved back into the aeration chamber from the chamber 25 ¦
by creating at the point 35 a pressure lower than at the point 43. It is accomplished by the fact that ;
two different phenomena are used: in the vicinity of point 43 pressure differential is produced by the circulation of water; while at the point 35 pressure -differential is produced by the motion of the air bubbles rising to the surface. Because the ~elocity of rising air bubbles is higher than the velocity of ~, the clrculating water, it creates lower pressure at , .:
~' , ', ~ 5~73 the point 35 of conduit 33 than at port 43, as was 'explained'in the first embodiment~descrip,tion. That is why a single aerating device 44 for recirculating sludge from both settling chambers is used in this 5~ embodiment. The aerating device 44 can be either a mechanical aerator as shown in Figures 1, 2, 3, 4 and 5 or an air diffuser as in Figure 6.
The third embodiment, illustrated in Figure 5 will be seen to be a combination of the features of the first and second embodiments, in that a pair of first step settling chambers 51 and 52 are dis-posed on either side of the aerating chamber 53, this portion of the third embodiment functioning in exactly the same manner as the first embodiment. In ¦
addition a second step settling chamber is provided which receives the effluent through troughs 45, 46 and 47 from the two first step parallel connected settling chambers. Effluent from the second step settling chamber 49 leaves the treatment unit at the top through a trough 50. Sludge from the second step settling chamber 49 is returned back into aeration . , chamber 53 at the end 55 of conduit 54 in exactly the same manner as the second embodiment. A single impeller aerating device 48 is used to recover sludge from each settling chamber in this embodiment. All three settling chambers 51, 52 and 49 of this emb'odi-ment can work in series if needed by proper arrange-ment of the aerating device 48 as is explained in the first embodiment.
In the fourth embodiment (Figure 6) is shown (for convenience only) an aeration chamber 56 and part of the first step settling chamber 57 and'the second step settling chamber 58. This embodiment differs from the second embodiment in the use of an air diffuser aerator 59 instead of a mechanical .

~9~45~i73 aerator~ The large amount of air tends to rise to the surface of the aeration cham~er at a very rapid rate, creating substantial turbulence to achieve the same hydrodynamic effect as an impeller.
Return of sludge from the settling chambers 57 and 58 back into the aeration chamber 56 is achieved by positioning the air diffuser 59 underneath an upper end 60 of the conduit 61. In this embodiment as well as in the previous ones, no pumps are needed to circulate sludge from the settling chambers back into the aeration chamber.
I wish it to be understood that I do not consider the invention limited to the precise details of structure shown and set forth in this specifica-tion, for obvious modifications will occur to those skilled in the art to which the invention pertains.

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Claims (3)

Claims

1. In a device for the biological treatment of waste water, including a first chamber for the aeration of said water, and the exposure of the same to the effect of activated sludge, said device having at least one second chamber for the settling of said sludge, from which treated water is removed, a wall means separating said first chamber from said second chamber and including an upper passageway for the flow of liquid from the first chamber to the second chamber; and a lower passageway for the flow of sludge from the second chamber to the first chamber, the improvement comprising said first chamber being shaped to include a relatively smaller horizontal sectional area at the lower end thereof, and a relatively larger horizontal sectional area at the upper end thereof; and means for introducing water and air at the lower part of said first chamber, creating a flow of liquid in which the turbulence intensity increases along the way to the top of the first chamber.

2. In a device for the biological treatment of waste water comprising a chamber for the aeration of said waste water and the exposure of said waste water to activated sludge, said aeration chamber having a horizontal sectional area which generally increases in size from a relatively smaller horizontal sectional area at the lower end thereof to a relatively larger horizontal sectional area at,the upper end thereof, said aeration chamber having a waste water inlet in the lower area thereof so that the water moves generally from bottom to top of the aeration chamber, an aerator positioned in the lower part of said aeration chamber to aerate said waste water and cause said waste water to circulate in said aeration chamber, and a plurality of chambers for the settling of said sludge, at least one wall separating each of said settling chambers from said aeration chamber and said settling chambers positioned in approximately the same horizontal plane and surrounding said aeration chamber, a passageway for waste water from the upper part of said aeration chamber to one of said settling chambers providing for a first step of the activated sludge settling and having the water level slightly lower than in the aeration chamber, trough means for conducting effluent from the first step settling chamber to another of said settling chambers providing a second step of sludge settling and having the water level slightly lower than in the first step sludge settling chamber, a conduit for sludge return from the second step sludge settling chamber to the aeration chamber, said conduit having a sludge inlet from the lower part of said second step settling chamber and a sludge outlet into said aeration chamber above said aerator in a zone of rising air bubbles emanating from said aerator, so that the pressure at said sludge outlet aspirates the sludge through the conduit without the use of pumps and is lower than at the port for sludge return from the first step sludge settling chamber, and a port in the lower part of the wall separating the first step settling chamber from the aeration chamber providing for the return of sludge from the said first step settling chamber to the aeration chamber, said port opening into said aeration chamber at a location which will be aspirated by said cir-culation of waste water, and the second step settling chamber having an outlet for removal of treated clarified waste water from the top thereof.

3. A device for the biological treatment of water comprising an aeration chamber for the aeration of said water and the exposure of said water to activated sludge, an aerator positioned in said aeration chamber, a waste water inlet in the lower part of said aeration chamber, a plurality of settling chambers, a first settling chamber provid-ing a first step of sludge sedimentation, a second settling chamber providing a second step of sludge sedimentation, and a third settling chamber for a third step of sludge sedimentation; septum means for separating each of said settling cham-bers from the aeration chamber, a passageway com-municating between said aeration chamber and said first settling chamber, first trough means for conducting effluent from said first settling chamber to said second settling chamber, second trough means for conducting effluent from said second settling chamber to said third settling chamber, a first sludge return port from the first settling chamber into said aeration chamber, said first sludge return port opening into said aeration chamber at a location aspirated by said circula-tion of waste water, a conduit for sludge return from the second settling chamber into said aeration chamber, said sludge return conduit opening into said aeration chamber at a location of lower pressure than the opening location of the first sludge return port, and a second conduit for sludge return from the third settling chamber into the aeration chamber, said second conduit opening into the aeration chamber at a zone of rising air bubbles above said aerator where the pressure is even less than at the openings for said port and said first conduit, said third settling chamber having an outlet for removal of treated clarified waste water, and said second and third chambers posi-tioned in approximately the same horizontal plane whereby settled sludge returns from the settling chambers to the aeration chamber without the use of pumps by the provision of suction effects at each sludge return opening, so as to effect either simultaneous operation in parallel of settling and sludge return from all settling chambers with the pressures at all sludge return openings into the aeration chamber being maintained equal; or so as to effect a step-by-step operation, with every sludge return opening into the aeration chamber in an area of less pressure, and therefore greater suction, than the sludge return opening from the previous step of sedimentation.