GB2164641A - Method and apparatus for the biological treatment of sewage - Google Patents

Abstract

A compact sewage treatment is given by a secondary settling basin 23 disposed within an activator basin 1. A portion of the sludge separated by a cyclone (9) within the settling basin is aerated 13, mixed at 19 with liquid separated within the activator basin, and also aerated and recycled to the activator basin. This mixed flow is at least partially degasified at 16 before recycling into the activator basin, and again aerated, if required. <IMAGE>

Description

SPECIFICATION Method and apparatus for the biological treatment of sewage The present invention pertains to a method and apparatus for the biological, and also chemical treatment of sewage utilizing aeration, with aeration basins, activator basins in which the sewage is separated into liquid and concentrated sludge, secondary settling basins, and means for collecting the settling sludge, all concentrically disposed within an outer basin.

Apparatus for biological treatment of sewage is known comprising a number of stages, with an activator stage for separating liquid from sludge and at least one secondary settling stage for the sludge to settle. Such apparatus has the disadvantage of requiring a large amount of floor space. Compact sewage treatment flocculation plants are known (FR-A 1,081,214), in which interaction with a flocculator takes place in a central basin, while secondary settling action occurs in a surrounding annular basin. Additionally, a two-stage treatment power plant is known (CH-A 462,273), in which treatment of sewage is achieved through precipitation.

It is an object of the present invention to provide an improved method and apparatus for treatment of sewage.

It is also an object of the present invention to provide for more compact, space-saving treatment of sewage.

It is another object of present invention to provide for improved relation and disposition of various sewage-treatment stages with respect to one another.

It is a further object of the present invention to provide for more uniform loading and reaction during sewage treatment.

It is still another object of the present invention to provide for reduction of overall volume of sewage to be treated, while maintaining the same flow rate thereof.

It is still a further object of the present invention to provide a new and improved method and apparatus for treating sewage, in which both the activator basin for separating sewage liquid from sludge and the secondary settling basin are disposed in a single container.

It is also a further object of the present invention to provide a new and improved method and apparatus for treating sewage, in which aeration of the flowing sewage takes place above the activator basin for separating sewage liquid from sludge by circulation of the sewage content of the activator basin, and the secondary settling basin functions according to present classification systems or according to fluidized bed filtration.

These and other objects are attained by the present invention which provides a method for the treatment of sewage to separate clear liquid from sewage sludge, said method comprising the steps of separating a flow of sludge from the sewage into a first flow constituting a major sludge portion to be further treated, and a second flow constituting excess sludge, aerating the first flow, directing the thus-aerated first flow into an activator basin arranged concentrically in an outer basin, the activator basin having a conically-shaped basin concentrically arranged therein, separating liquid from the aerated first flow in the activator basin to form a more concentrated sludge in the activator basin, aerating the thus-separated liquid and mixing the same with additional first flow of sludge for further treatment, directing the more concentrated sludge from the activator basin to the conically-shaped basin concentrically arranged therein and subjecting the same to settling therein, thereby forming clear liquid and further concentrated sludge, separating the thus-formed clear liquid, and removing the thus-formed further concentration sludge.

The present invention also provides an apparatus for treating sewage to separate clear liquid from sewage sludge, comprising an activator basin for separating liquid from a first flow of sludge thereinto, to form a more concentrated sludge therewithin, a conically-shaped insert concentrically disposed within the activator basin, a settling basin concentrically disposed within said conicallyshaped insert such that the more concentrated sludge is directed into the settling basin where the more concentrated sludge is subjected to settling action, directing means for directing the settled sludge out of the settling basin, separating means for dividing the sludge drawn through the directing means into additional first flow of sludge constituting a major portion of sludge to be further treated, and a second flow constituting excess sludge, valve means for regulating the first and second sludge flows and disposed within one of the first and second sludge flows, aerating means for aerate ing the first flow of sludge, and mixing means for mixing the liquid separated within the activator basin with the first flow of sludge.

In the method according to the present invention, the further concentrated sludge from the conically-shaped basin (i.e. a secondary settling basin) is collected at a central location therefrom, and preferably device such as a centrifugal separator, in which the sludge is separated into a first flow for further treatment, and a second flow which constitutes excess sludge and is channelled off.

The first flow of sludge, i.e. the return flow of sludge, is then aerated before being directed to the ring-shaped activator basin. Liquid sewage withdrawn from the activator basin, which may be optionally mixed together with fresh sewage feed, is then mixed with the aerated return flow of sludge from the separation device. This mixture is then passed to the activator basin, where, after retention therein to separate out the sewage liquid, the concentrated sludge is directed into the conicallyshaped, secondary settling basin.

In the case where sewage has an especially high biological or chemical oxygen requirement, the method of the present invention may be modified in such manner that the activator basin is disposed discrete sections, with intermixing and especially aeration of the first flow of sludge, liquid is separated from the activator basin and any fresh sew age food occurring in the first such section of the activator basin. Additional aeration of the combined sewage flow may take place at the transition of the first section into the second section of the activator basin, with any degasification that is required being carried out in the second section of the activator basin. Finally, the degasified sewage flow is directed by way of a flow-off conduit into a centrally sedimentation channel, and into the secondary settling basin.

In the apparatus according to the present invention, a conically-shaped or truncated cone-shaped insert (i.e. in the shape of a funnel) is centrically disposed within a cylindrically-shaped activator basin. The point or base surface of the coneshaped insert may be disposed at or above the bottom of the activator basin, with a substantially cylindrical, secondary settling basin disposed within the conically-shaped insert. Means for directing the settled sludge out of the settling basin is disposed within the conically-shaped insert.

Such directing means may comprise a base sludge reamer and/or a central sludge pit, into which a suction pipe of a sludge pump extends.

The suction pipe is connected with a pressure conduit, which is in turn connected to means for dividing the sludge drawn through said directing means into an additional first flow of sludge, and a second flow of excess sludge. The separation means may be a centrifugal separator for example.

Additionally, valve means such as a control valve is provided in the underflow (i.e. in the first or second flows of sludge), with means for aerating the first flow of sludge also being provided. Such aerating means may constitute an aerator annularly disposed about the activator basin. Additional features of the present invention are described in more detail below.

An embodiment of the present invention will now be described in more detail with reference to the accompanying drawings, in which: Figure 1 is a side sectional view of a sewage treatment apparatus operating in accordance with the method of the invention; Figure 2 is a top sectional view along line Il-Il of Figure 1; Figure 3 is a side sectional view, similar to Figure 1, of a sewage treatment apparatus and method according to another embodiment of the present invention; and Figure 4 is a sectional view, similar to Figure 2, of the embodiment of Figure 3.

Referring to the drawings, a cylindrical basin 1 is illustrated in Figure 1, in which a truncated, conically-shaped insert 2 is disposed in the form of a funnel, whereby the larger diameter of the funnel 2 (i.e. the greater base surface) is provided in the area of the liquid level as illustrated. The smaller base surface of the funnel is disposed at or just above the bottom of the basin 1. The arrangement of the truncated portion of the conical insert 2 above the bottom of the basin 1 facilitates the easy insertion of a base sludge reamer 18 at the bottom of an activator basin 3, creating an annular area whereby the driving gear of the base sludge reamer 18 is directed through a secondary settling basin 23 formed within the truncated cone-shaped insert 2.

This secondary settling basin 23 also contains a base sludge reamer 4 which conveys sludge precipitated within the settling basins 23 into a centrally-disposed sludge pit 5. The deposited sludge is evacuated from the sludge pit 5 through a suction or evacuating pipe 6 by means of a sludge pump 7. The precipitated sludge is thus raised above the liquid level of the secondary settling basin 23. The conical insert 2 is suspended from a bridge 17 above the bottom of the basin 1, so that the base sludge reamer 18 disposed in the activator basin 3 can be coupled to a drive of the base sludge reamer 4 disposed in the secondary settling basin 23.

A pressure conduit 8 is engaged with the evacuation pipe 6 above the sludge pump 7, and is also engaged with a separation device 9. The precipitated sludge mass is divided within the separation device 9 into two partial flows, an overflow 10 and an underflow 11. This separation device 9 is preferably a centrifugal separator such as a cyclone.

When the centrifugal separator is a cyclone, it has been found that the more critical bacterial colonies are located in the underflow 11, while the number of inactive, dead bacteria in the overflow 10 is generally greater. Therefore, a regulating valve 12 is disposed in the underflow 11, by means of which the quantity of the sludge flowing through the underflow or the overflow can be regulated.

The sludge drained off through the overflow 10 is removed as excess sludge, while the sludge flowing through the underflow 11 is then conveyed to an aerator 13 where it absorbs atmospheric oxygen by flowing past aeration openings and becoming saturated or supersaturated with oxygen. This saturated sludge is then introduced into a mixing vessel 19, where it is mixed with sewage liquid removed from the circular activator basin 3. This liquid flowing from the circular activator basin 3 has also been aerated in a similar apparatus.

In the case of certain sewage, especially chemical sewage, the more vigorous bacteria colonies are found in the overflow 10. Therefore, in this situation, it is the overflow 10 that is aerated, and the underflow 11 is drained off as excess sludge. Since the sewage liquid from the activator basin 3 and the sludge have different oxygen requirements, as well as different reaction times, the present apparatus allows for optimal gasification to take place.

The intermixed liquid-sludge flow is now cancelled to a circular area 16 in which a partial degasification takes place by enlargement of the free surface thereof. A reaction time for degasification may be set and determined from the existing statistical settling time.

After suitable gasification, the mixture of liquidsludge is once again aerated by a syphon 20 and conveyed to the actual activator basin 3. The lower opening of the syphon 20 is in the form of a laterally extending arm 21 (see Figure 2) so that the liquid therein is subjected to rotary motion in the circular area of the activator basin 3. As a result of this, intermixing is enhanced on the one hand, preventing sedimentation of the sludge therein, and on the other hand, a longer settling or reaction time is achieved. The surface water within the activator basin 3 is collected by way of a duct 14' and conveyed through a conduit 22 to a cental sink channel 15 within the secondary settling basin 23, where the actual separation of sludge and clear water (liquid) takes place.The sink conduit 15 forms a ring slot 30 within the settling basin 23 as illustrated in Figure 1, with the clear liquid level rising above the ring slot 30 to the upper portion of the settling basin 23, and over into the channel 14'. The clear water is collected in and drained off through the duct 14' the clear water conduit 24.

The conduits 14' and 14' are preferably formed as a double conduit 14, with the middie separating wall therebetween extending above the liquid level as illustrated. An infeed 25 of fresh sewage liquid expediently takes place through a standpipe 26 of circulating liquid from the activator basin 3, or by way of a similar device directly into the mixing vessel 19 which is designed as a common rising conduit for both the aerated sludge and the aerated sewage liquid from the activator basin 3.

As illustrated in Figure 2, the number of aeration components or recycling conduits is, for example, arranged in three-fold symmetry. In actual practice, the number of required parallel conduits may be conveniently determined by any number of factors, such as economic considerations. Thus, in Figures 3 and 4 a five-fold symmetry is selected, e.g. for a somewhat simplified construction of components in another embodiment of the present invention.

Figure 3 in contrast to Figure 1 illustrates mixing vessels 19 separately disposed away from the basin 1. These mixing vessels 19 each have an overflow channel 27 from which the intermixed liquid and sludge flows through radially-disposed channels 28 with respect to the cylindrical basin 1, or by way of syphons with repeated aeration, into the circular activator basin 3. The truncated conical insert 2 of Figure 1 has been replaced by a conical, funnel-shaped insert 2' which is formed with such a pitch that no sludge will adhere to the walls of the insert, and the sludge precipitated within the settling chamber 23 is directed through the suction pipe 6' by the sludge pump 7.

In this embodiment, the suction pipe 6' is, for practical purposes formed as the central sludge pit.

The activator basin 3 also has a conical base, with openings 25 disposed thereat for the suctioning off of liquid from within the activator basin 3 that is required for aeration. The openings 29 are arranged in the region of the tip of the conicallyshaped bottom of the activator basin 3, as best seen in Figure 3. This design eliminates the need for base sludge reamers in this particular embodiment, thus achieving simplification of the overall construction of sewage treatment apparatus. In this situation, a rate control or cutoff device may naturally be provided. However, it is not absolutely necessary to provide a channel 14' as illustrated in Figure 1, since the conduit 22 can be led directly from the activator basin 3 to the sink conduit 15 in which the actual separation of sludge and liquid ensues within the settling basin 23.

The clear liquid within the settling basin 23 then rises through a ring slot 30 into the upper portion of the settling basin 23, flowing over a dividing wall 31 into the channel 14" from which the clear liquid is drained off through the conduit 24. The clear liquid drainoff can, as indicated in the figures, ensure by way of a conduit 24 disposed through the activator basin 3. However, if emptying of the activator basin 3 is desired, then the clear water drainoff ensues by way of a syphon connected to the reamer bridge 17 which diverts the clear water from the channel 14" into a gutter-shaped clear water conduit (not shown).

As seen from the broken line representation in Figure 4, the openings 29 for the sewage liquid from the activator basin 23 which is to be aerated, are located above a circular area 32 which is connected by way of a conduit 33 with a circulation pump 34 directing flow through a riser pipe or pipes to the aeration component. The present invention is not limited to circular basins, but can also be analogously applied with respect to rectangularly-shaped basins.

Claims (16)

1. A method for the treatment of sewage to separate clear liquid from sewage sludge, said method comprising the steps of separating a flow of sludge from the sewage into a first flow constituting a major sludge portion to be further treated, and a second flow constituting excess sludge, aerating said first flow, directing the thus-aerated first flow into an activator basin arranged concentrically in an outer basin, the activator basin having a conically-shaped basin concentrically arranged therein, separating liquid from said aerated first flow in the activator basin to form a more concentrated sludge in the activator basin, aerating the thus-separated liquid and mixing the same with additional first flow of sludge for further treatment, directing the more concentrated sludge from the activator basin to the conically-shaped basin concentrically arranged therein and subjecting the same to settling therein, thereby forming clear liquid and further concentrated sludge, separating the thus-formed clear liquid, and removing the thus-formed further concentrated sludge.

2. A method according to Claim 1 comprising the additional step of separating the removed, thus-formed further concentrated sludge into first and second flows thereof.

3. A method according to Claim 2 comprising the additional step of introducing fresh sewage, when necessary, into the thus-separated liquid from the activator basin.

4. A method according to Claim 3, comprising the additional steps of aerating the mixture of thus-separated liquid and additional first flow of sludge from the activator basin, and at least partially degasifying the thus-aerated mixture.

5. A method according to Claim 4, wherein the mixture of separated liquid and additional first flow of sludge is aerated in a first section of the activator basin, and is at least partially degasified in a second section of the activator basin.

6. A method according to Claim 3, wherein the additional first flow of sludge is aerated in a separate conduit and the thus-separated liquid prior to mixing with the same, and the thus-separated liquid and additional first flow of sludge are mixed in a common uptake.

7. Apparatus for treating sewage to separate clear liquid from sewage sludge, comprising an activator basin for separating liquid from a first flow of sludge thereinto, to form a more concentrated sludge therewithin, a conically-shaped insert concentrically disposed within said activator basin, a settling basin concentrically disposed within said conically-shaped insert and connected with the activator basin in a manner such that the more concentrated sludge is directed into said settling basin where the more concentrated sludge is subjected to settling action, directing means for directing the settled sludge out of said settling basin, separating means for dividing the sludge drawn through said directing means into additional first flow of sludge to be further treated, and a second flow of excess sludge, valve means for regulating the first and second sludge flows and disposed within one of the first and second sludge flows, aerating means for the first flow of sludge, mixing means for mixing the liquid separated within said activator basin with the aerated first flow of sludge, and introducing means for introducing the mixture of thus-separated liquid and aerated sludge into said activator basin.

8. The apparatus according to Claim 7, wherein said directing means comprises a base sludge reamer disposed at or near the bottom of said conical insert, a centrally-disposed sludge pit adjacent said base sludge reamer, said pit and reamer disposed in a manner such that the sludge settling within said settling basin falls thereon, a conduit communicating with said sludge pit, and pump means disposed within said conduit for drawing the settling sludge thereinto, said conduit communicating with said separating means.

9. Apparatus according to Claim 7, wherein said separating means is a centrifugal separator.

10. Apparatus according to Claim 7, wherein said conically-shaped insert comprises an extension disposed to form two separate channels, a first one of said channels is in communication with said activator basin and said settling basin, and a second one of said channels is in communication with said settling basin and constituting means for draining clear liquid out of said apparatus, and a sink channel is centrally and concentrically disposed about said conduit and pump means and communicating said first one of said channel with said settling basin.

11. Apparatus according to Claim 7, including an annularly-shaped basin concentrically disposed about at least a portion of said activator basin and communicating with said aerating means to constitute said introducing means.

12. Apparatus according to Claim 7, wherein said separating means is constituted by a narrow outlet of said conically-shaped insert.

13. Apparatus according to Claim 11, including a helically-shaped syphon interconnecting said annularly-disposed basin and said activator basin to constitute part of said introducing means and also constituting second means for aerating the mixed flow of liquid and sludge.

14. Apparatus according to Claim 7, including a bridge connected to an upper part of said conically-shaped insert for suspending the same within said activator basin, and a second base sludge reamer disposed within said activator basin and adapted to be coupled to said first base sludge reamer.

15. A method for the treatment of sewage to separate clear liquid from sewage sludge according to Claim 1 and substantially as hereinbefore described.

16. Apparatus for treating sewage to separate clear liquid from sewage sludge substantially as hereinbefore described with reference to the accompanying drawings.