JP7660474B2 - Oxidation ditch and method for repairing oxidation ditch - Google Patents

Description

The technology disclosed here relates to oxidation ditches and methods for repairing oxidation ditches.

Patent Document 1 discloses an oxidation ditch. The oxidation ditch is a sewage treatment facility that includes a tank for storing the liquid to be treated, which is made up of wastewater and activated sludge, and an aeration and stirring device. A partition wall is installed in the tank to form an endless circulation flow path in the tank. The aeration and stirring device aerates the liquid to be treated and forms an agitated flow of the liquid to be treated along the circulation flow path. The aeration and stirring device is, for example, a horizontal axis device. Figure 6 of Patent Document 1 discloses a configuration in which two flow paths are separated by a partition wall, and a horizontal axis aeration and stirring device is installed in each of two adjacent straight flow paths. In the oxidation ditch disclosed in Patent Document 1, a straightening wall that is arc-shaped in plan view is provided in the arc flow path. The straightening wall straightens the flow of the liquid to be treated so that the liquid to be treated smoothly rotates in the arc flow path.

Here, the horizontal axis aeration and mixing device has a cylindrical rotor that is installed near the water surface. This can lead to problems such as insufficient mixing at the bottom of the tank or fibrous foreign matter becoming entangled in the rotor. For this reason, in recent years, vertical axis aeration and mixing devices, which have better mixing performance than horizontal axis aeration and mixing devices, have been used in oxidation ditches.

For example, Patent Document 2 discloses an oxidation ditch equipped with a vertical-axis aeration and mixing device. The vertical-axis aeration and mixing device is installed in an arc-shaped flow path. In the arc-shaped flow path, the flow direction of the liquid to be treated is changed by 180°. The vertical-axis aeration and mixing device installed in the arc-shaped flow path can efficiently impart the kinetic energy of the rotor rotating around a vertical axis to the liquid to be treated. In other words, it is preferable to install the vertical-axis aeration device in the arc-shaped flow path in the circulation flow path.

When replacing a horizontal aeration/agitation device installed in an existing oxidation ditch due to deterioration, there is a demand to install a vertical aeration/agitation device with superior agitation performance. However, while a vertical aeration/agitation device is preferably installed in an arc-shaped flow path, as mentioned above, the arc-shaped flow path of the existing water tank is provided with an arc-shaped flow straightening wall. In order to install a vertical aeration/agitation device in the arc-shaped flow path, the existing flow straightening wall must be removed.

For example, Patent Document 3 discloses an oxidation ditch in which a vertical-axis aeration and mixing device is installed in a straight flow path. If a vertical-axis aeration and mixing device is installed in a straight flow path, there is no need to modify the arc flow path. However, the rotation of the rotor of the vertical-axis aeration and mixing device generates a flow not only downstream but also upstream of the straight flow path. Therefore, in the oxidation ditch described in Patent Document 3, a guide plate is installed around the rotor of the vertical-axis aeration and mixing device installed in the straight flow path. The guide plate has a roughly arc shape in a plan view, and is configured to guide the flow generated upstream by the rotation of the rotor to the downstream side.

Japanese Patent Application Publication No. 11-104685 Japanese Patent Application Publication No. 11-169883 Patent No. 5839439

The rotor of the aeration mixer installed in the oxidation ditch has a diameter of more than 2 m. The roughly arc-shaped guide plate installed around the rotor is even larger, and the structure of the guide plate is also complex. Furthermore, the guide plate installed in the water tank must be durable, so it is made of stainless steel, for example. A large stainless steel guide plate is a very expensive part.

Furthermore, when installing a vertical-axis aeration/agitation device in a straight flow path, a vertical-axis aeration/agitation device and guide plate must be installed in each of at least two straight flow paths in the circulation flow path. This not only increases the cost of the parts, but also makes the installation work for the aeration/agitation device and guide plate complicated.

The technology disclosed here provides a simple oxidation ditch configuration using a vertical shaft aeration and mixing device, and also provides a method for easily renovating existing oxidation ditches.

The inventors of the present application have completed the technology disclosed herein by noting that in an oxidation ditch, the two adjacent straight flow paths separated by a partition wall have opposite flow directions.

The technology disclosed herein relates to an oxidation ditch, which includes a water tank for storing a liquid to be treated, a partition wall that is installed in the water tank and forms an endless circulation flow path through which the liquid to be treated flows, and an aeration and stirring device that is installed in the circulation flow path and aerates the liquid to be treated and generates a flow of the liquid to be treated along the circulation flow path,
The aeration stirring device is a vertical-axis aeration stirring device having a rotor and a rotation axis extending vertically, and the partition separates a first straight flow path through which the treated liquid flows in a first direction and a second straight flow path which is adjacent to the first straight flow path and through which the treated liquid flows in a second direction opposite to the first direction, and an opening is provided in the partition so as to connect the first straight flow path and the second straight flow path to each other, and the rotor of the aeration stirring device is installed in the opening so as to span both the first straight flow path and the second straight flow path, and generates a water flow in the first direction in the first straight flow path while simultaneously generating a water flow in the second direction in the second straight flow path.

According to this configuration, the oxidation ditch is equipped with a vertical aeration and mixing device. The mixing performance of the vertical aeration and mixing device is relatively high. The efficiency of the oxidation ditch is improved.

The rotor of the vertical aeration and agitation device is installed in the opening of the partition. The opening is provided in the partition separating the first and second straight flow paths so as to connect the first and second straight flow paths. The rotor installed in the opening is installed so as to straddle the first and second straight flow paths. When the rotor rotates, about half of the rotor generates a flow of the liquid to be treated in the first straight flow path, and the other half of the rotor generates a flow of the liquid to be treated in the second straight flow path. Here, in the oxidation ditch, the adjacent first and second straight flow paths have opposite flow directions. A single rotor can generate a water flow in the first direction in the first straight flow path and a water flow in the second direction in the second straight flow path. For example, unlike a conventional oxidation ditch in which a vertical aeration and agitation device is installed in a straight flow path, there is no need to install a large guide plate around the rotor of the aeration and agitation device. This simplifies the structure of the oxidation ditch, as there is no need to install an aeration and mixing device in each of the two straight flow paths. In addition, while conventional aeration and mixing devices have large losses due to the installation of guide plates to significantly change the direction of the flow, the oxidation ditch with the above structure has the advantage of reducing losses because the direction of the flow generated by the aeration and mixing device is not significantly changed.

This oxidation ditch does not install a vertical-axis aeration and mixing device in an arc-shaped flow path, and even if a vertical-axis aeration and mixing device is installed in a straight flow path, no guide plate is required. Therefore, it is relatively easy to renovate an existing oxidation ditch to create this oxidation ditch configuration.

The opening may be formed as a recessed notch from the upper end of the partition, the depth D of the opening from the liquid surface of the treated liquid may be within RD x 0.8 of the rotor diameter, and the length L of the opening may be greater than RD of the rotor diameter and less than RD + 1.0 m.

The opening connects the first straight flow path and the second straight flow path. If the size of the opening is too large compared to the size of the rotor to be placed therein, a backflow may occur in the first straight flow path and/or the second straight flow path as the rotor rotates, or a flow may occur that circulates around the rotor. Therefore, it is preferable that the size of the opening corresponds to the size of the rotor.

By setting the depth D and length L of the opening to the above-mentioned size relative to the rotor diameter RD, backflow in the first straight flow path and/or the second straight flow path can be suppressed, and circulating flow around the rotor can be suppressed. The aeration mixing device can cause the treated liquid to flow along the circulation flow path.

The rotor diameter RD may be set to 50 to 70% of the width W of the first and second straight flow paths.

The size of the rotor is appropriate for the width W of the first straight flow path and the width W of the second straight flow path, so that a single rotor can efficiently generate a flow of the liquid to be treated in each of the first straight flow path and the second straight flow path, and can provide an aeration effect in each of the first straight flow path and the second straight flow path.

In the oxidation ditch, a protective portion is attached to the end face of the opening to suppress wear of the end face.

When the rotor installed inside the opening rotates, the liquid to be treated collides violently with the end face of the opening when the blade tips of the rotor face the end face of the opening. To prevent wear on the end face, a protective part may be attached to the end face of the opening. The protective part may be, for example, a metal protective plate. This protective part can prevent wear on the end face of the opening.

In another oxidation ditch, a straightening section is attached to at least one of the upstream and downstream sections of the opening from the rotor, and the straightening section straightens out a flow that is generated by the rotation of the rotor and that obstructs the flow in the first or second direction, or a flow that intersects the partition, into a flow that runs along the partition .

The rotor of the vertical aeration mixer generates a swirling flow. Because the rotor spans the first and second straight flow paths, the flows generated on the upstream and downstream sides of the rotor in the first or second straight flow paths do not flow along the partition wall. For example, the flows may cross the partition wall or obstruct the flow in the first or second direction.

Therefore, a straightening plate is attached to at least one of the upstream and downstream portions of the rotor in the opening, and the straightening plate straightens the flow that obstructs the flow in the first or second direction, or the flow that crosses the partition, into a flow along the partition. This improves the efficiency of the aeration mixing device. Since the function of guiding the upstream flow to the downstream in the first straight flow path or the second straight flow path, as in the conventional guide plate, is not required, the straightening plate can be made small, unlike the conventional guide plate. The straightening plate is a relatively inexpensive part, and can be easily attached to the opening.

A protective part for preventing wear on the end face of the opening may be attached, and the straightening part and the protective part may be integrated.

By integrating the straightening section and the protective section, installation into the opening becomes easier.

The rotor may have an odd number of blades.

When the rotor blades pass through the opening from the first straight flow path to the second straight flow path, or from the second straight flow path to the first straight flow path, the tips of the blades face the end face of the opening, causing an impact to be applied to the rotor. Here, if the rotor has an even number of blades, the two blades on either side of the rotation axis are arranged in a straight line, so that the two blades face the end face of the opening at the same time. As a result, an impact is applied to the rotor from each side.

On the other hand, if the rotor has an odd number of blades, the two blades on either side of the rotating shaft are not arranged in a straight line. Each blade faces the edge of the opening, one at a time. This helps to reduce the impact on the rotor.

Even if the number of blades is an even number, the tips of the blades can be prevented from facing both end faces of the opening at the same time by slightly shifting the center of the rotor from the straight line connecting both end faces of the opening in a plan view.

The technology disclosed herein also relates to a method for repairing an existing oxidation ditch, which comprises removing an aeration and stirring device installed in a circulation flow path, removing a part of a partition wall separating a first straight flow path and a second straight flow path constituting the circulation flow path to provide an opening through which the first straight flow path and the second straight flow path communicate with each other, arranging a rotor of the aeration and stirring device having a vertical axis in the opening so that the rotor straddles both the first straight flow path and the second straight flow path , and attaching a protective part to an end face of the opening to suppress wear of the end face .
According to this renovation method, an existing oxidation ditch can be renovated to the oxidation ditch having the above-mentioned configuration, that is, a vertical aeration/agitation device is installed, and aeration and water flow generation in each of the two straight flow paths are realized by one aeration/agitation device.

Another renovation method involves removing the aeration stirring device installed in the circulation flow path and removing a portion of the partition separating the first and second straight flow paths that constitute the circulation flow path to provide an opening through which the first and second straight flow paths communicate with each other, placing the rotor of the aeration stirring device on the vertical axis in the opening so that the rotor spans both the first and second straight flow paths, and attaching a straightening unit to at least one of the upstream and downstream portions of the rotor in the opening, which straightens out a flow that obstructs the flow in the first or second direction, or a flow that intersects the partition, generated by the rotation of the rotor, into a flow along the partition .

The oxidation ditch described above has a simple structure. Furthermore, the method for repairing the oxidation ditch described above can easily repair an existing oxidation ditch.

FIG. 1 is a diagram illustrating the configuration of an oxidation ditch. The left diagram in FIG. 2 is a part of a vertical cross-sectional view of the oxidation ditch, and the right diagram is a horizontal cross-sectional view of the oxidation ditch. FIG. 3 is a perspective view illustrating a rotor of the aeration stirring device. FIG. 4 is a comparison of flow between a conventional oxidation ditch and the oxidation ditch disclosed herein. 5A and 5B are diagrams showing examples of configurations in which a protective section and a rectifying section are attached to an opening portion.

Below, an embodiment of an oxidation ditch and a method for repairing an oxidation ditch will be described with reference to the drawings. The oxidation ditch and the method for repairing an oxidation ditch described here are examples.

(Overall structure of oxidation ditch)
Fig. 1 illustrates an oxidation ditch 1. The oxidation ditch 1 is a facility for treating sewage, and includes a water tank 2 for storing a liquid to be treated, which is composed of wastewater and activated sludge. The water tank 2 illustrated in Fig. 1 has an oval shape in a plan view. The technology disclosed herein can also be applied to a water tank having a horseshoe shape in a plan view.

A partition 3 is installed in the water tank 2. As shown in FIG. 2, the partition 3 stands upright from the bottom of the water tank 2, and thereby the partition 3 divides the water tank 2 into a plurality of flow paths. As shown in FIG. 1, the partition 3 extends straight in the longitudinal direction of the water tank 2 at the center of the water tank 2. A predetermined interval is provided between both ends of the partition 3 and the wall surfaces at both ends of the longitudinal direction of the water tank 2. As a result, the partition 3 forms an endless circulation flow path consisting of a straight flow path and an arc flow path in the water tank 2. More specifically, the partition 3 forms a first straight flow path 31, a second straight flow path 32 adjacent to the first straight flow path 31, and two arc flow paths 33 connecting the ends of the first straight flow path 31 and the second straight flow path 32. The widths W of the first straight flow path 31, the second straight flow path 32, and the arcuate flow path 33 are all the same or substantially the same.

In the first straight flow path 31, the liquid to be treated flows in a first direction. The first direction is from left to right on the paper in FIG. 1 (see the arrow in FIG. 1). In the second straight flow path 32, the liquid to be treated flows in a second direction. The second direction is from right to left on the paper in FIG. 1, which is the opposite direction to the first direction.

A straightening wall 34 is installed in each of the two arcuate flow paths 33. In a plan view, the straightening wall 34 has an arc shape resembling the character "shi" laid on its side. The straightening wall 34 straightens the flow of the treated liquid so that it can swirl smoothly through the arcuate flow paths 33.

The oxidation ditch 1 is equipped with an aeration stirring device 4. As illustrated in FIG. 2, the aeration stirring device 4 has a rotor 41, a rotating shaft 42, and a motor unit 43. As illustrated in FIG. 3, the rotor 41 has a hub 411 and a plurality of blades 412 extending radially from the hub 411. The rotor 41 in FIG. 3 has six blades 412. Each blade 412 has an L-shaped cross section and extends obliquely upward from the base end connected to the hub 411 to the tip (see FIG. 2). The shape of each blade 412 is not limited to the illustrated example.

The motor unit 43 is located above the rotor 41, and the rotating shaft 42 extending vertically connects the output shaft of the motor unit 43 to the hub 411 of the rotor 41. The motor unit 43 is supported by the lid 20 of the water tank 2, and the rotor 41 is disposed near the water surface as shown in FIG. 2. More specifically, most of the blades 412 are located below the water surface, while part of the tip of the blades 412 is located above the water surface. When the motor unit 43 is operating, the rotor 41 rotates around the vertical axis via the rotating shaft 42. When the rotor 41 rotates, the liquid being treated is aerated and a swirling flow is generated, so that the liquid being treated flows along the flow path.

The installation of the aeration stirring device 4 will now be described in detail. The aeration stirring device 4 is installed so as to straddle the first straight flow path 31 and the second straight flow path 32. More specifically, an opening 30 is formed in the partition 3. In the configuration example of FIG. 1, the opening 30 is located in the center of the partition 3 extending in the longitudinal direction. As shown in FIG. 2, the opening 30 is a notch recessed downward from the upper end of the partition 3. The opening 30 connects the first straight flow path 31 and the second straight flow path 32.

The size of the opening 30 is larger than the diameter of the rotor 41. The rotor 41 of the aeration stirring device 4 is installed in the opening 30. As shown in FIG. 1, the rotor 41 spans the first straight flow path 31 and the second straight flow path 32.

As shown in Figure 1, this oxidation ditch 1 is equipped with one aeration and stirring device 4 on a vertical axis. In other words, when one rotor 41 rotates in the clockwise direction in Figure 1, a flow in a first direction is generated in the first straight flow path 31, and at the same time, a flow in a second direction is generated in the second straight flow path 32. Since the number of aeration and stirring devices 4 is small, the configuration of the oxidation ditch 1 is simplified. The installation and maintenance costs of the oxidation ditch 1 are low.

When the rotor 41 rotates, flows are generated in the first straight flow path 31 and the second straight flow path 32 as shown by the dashed arrows in the lower diagram of Figure 1.

Here, a comparison is made between the conventional oxidation ditch and the oxidation ditch 1 disclosed herein with reference to FIG. 4. The left diagram of FIG. 4 illustrates the configuration of the conventional oxidation ditch 10. In the conventional oxidation ditch 10, a rotor 401 of a first aeration stirring device is installed in the first straight flow path 31, and a rotor 402 of a second aeration stirring device is installed in the second straight flow path 32. The rotor 401 generates a flow in a first direction in the first straight flow path 31, and the rotor 402 generates a flow in a second direction in the second straight flow path 32. Each of the rotors 401 and 402 generates a flow in a swirling direction as shown by the dashed arrows in FIG. 4, so that a flow in the opposite direction to the first direction is generated in the first straight flow path 31, and a flow in the opposite direction to the second direction is generated in the second straight flow path 32. Therefore, in the conventional oxidation ditch 10, guide plates 51, 52 that guide the reverse flow to a forward flow are installed in the first straight flow path 31 and the second straight flow path 32. Both of these guide plates 51, 52 have an arc shape in a plan view, and are installed so as to surround the rotors 401, 402. However, in the conventional oxidation ditch 10, the loss of the aeration and stirring devices 401, 402 becomes large due to the change in the flow direction caused by the installation of the guide plates 51, 52.

In contrast, in the oxidation ditch 1 disclosed herein, half of the rotor 41 is located in the first straight flow path 31, and the remaining half of the rotor 41 is located in the second straight flow path 32. The rotation direction of the rotor 41 in the first straight flow path 31 coincides with the flow direction of the liquid to be treated, and the rotation direction of the rotor 41 in the second straight flow path 31 coincides with the flow direction of the liquid to be treated. No reverse flow occurs in the first straight flow path 31, and no reverse flow occurs in the second straight flow path 32 either. Therefore, the large arc-shaped guide plates 51 and 52 required in the conventional oxidation ditch 10 are not necessary. Losses in the aeration and stirring device 4 are reduced.

In addition, in each of the first straight flow passage 31 and the second straight flow passage 32, the flow toward the partition wall 3 on the downstream side of the rotor 41 changes direction when it hits the partition wall 3, and flows along the partition wall 3 toward the downstream of the first straight flow passage 31 or the second straight flow passage 32. In the oxidation ditch 1 of this configuration, the partition wall 3 also has the function of guiding the flow generated by the rotor 41. There is no need to attach a separate guide plate, and an increase in the number of parts can be suppressed.

The oxidation ditch 1 disclosed herein can efficiently generate flow in the circulation flow path using a single aeration and mixing device 4.

In addition, in each of the first straight flow path 31 and the second straight flow path 32, the area near where the aeration stirring device 4 is installed becomes an aerobic zone because aeration is achieved, while the area from the area near the two arcuate flow paths 33 to the upstream side of the aeration stirring device 4 becomes an anaerobic zone where aeration is not achieved. Since the liquid to be treated passes through the aerobic zone, anaerobic zone, aerobic zone, and anaerobic zone in this order, even with only one aeration stirring device 4, a balance between aerobic and anaerobic zones can be maintained throughout the oxidation ditch 1.

(More preferred form of oxidation ditch)
The opening 30 formed in the partition 3 is preferably of an appropriate size according to the size of the rotor 41. The opening 30 connects the first straight flow passage 31 and the second straight flow passage 32. If the size of the opening 30 is too large compared to the size of the rotor 41, a backflow may occur in the first straight flow passage 31 and/or the second straight flow passage 32 as the rotor 41 rotates, or a flow that circulates around the rotor 41 may occur.

As shown in the left diagram of FIG. 2, the depth D of the opening 30 from the liquid level WL of the treated liquid is preferably within 0.8 times the diameter RD of the rotor 41. The length L of the opening 30 is preferably greater than the diameter RD of the rotor 41 and is preferably equal to or less than the diameter RD + 1.0 m. This makes it possible to suppress backflow in the first straight flow path 31 and/or the second straight flow path 32, and to suppress circulating flow around the rotor 31. One aeration stirring device 4 can efficiently flow the treated liquid along the circulation flow path.

As shown in the upper diagram of Figure 1, the diameter RD of the rotor 41 is preferably set to 50-70% of the width W of the first straight flow path 31 and the second straight flow path 32. By doing so, a single rotor 41 can efficiently generate a flow of the treated liquid in each of the first straight flow path 31 and the second straight flow path 32, and can provide an aeration effect in each of the first straight flow path 31 and the second straight flow path 32.

When the rotor 41 installed in the opening 30 rotates, the tip of the blade 412 of the rotor 41 faces the end face of the opening 30, and the liquid to be treated collides violently with the end face. In order to suppress wear of the end face, a protective part 51 may be attached to the opening 30, as illustrated in FIG. 5. The protective part 51 may be, for example, a metal protective plate. This protective part 51 can suppress wear of the end face of the opening 30. The protective part 51 may be attached not only to the end face located on the upstream side of the rotor 41 and the end face located on the downstream side of the opening 30, but also to the end face located below the rotor 41.

In order to further improve the efficiency of the aeration and mixing device 4, a small flow straightening unit may be attached to the opening 30. The flow straightening unit straightens the flow that crosses the partition wall 3, which is generated by the rotation of the rotor 41, into a flow that runs along the partition wall 3.

Specifically, as shown in FIG. 5(a), the first flow straightening section 61 may be attached to the edge of the opening 30 on the upstream side of the rotor 41, that is, on the left side of the rotor 41 in the first straight flow path 31. The first flow straightening section 61 has an arcuate surface that follows the outer periphery of the rotor 41, and straightens the flow that is at an angle of 90° with respect to the partition wall 3 and moves away from the partition wall 3 as shown by the dashed arrow in FIG. 5(a) to a flow that is inclined toward the downstream side with respect to the partition wall 3 as shown by the solid arrow. The first flow straightening section 61 also straightens the flow that obstructs the flow in the first or second direction to a flow along the partition wall 3. This improves the efficiency of the aeration and mixing device 4 in the oxidation ditch 1.

A second flow straightening section 62 may also be attached to the edge of the opening 30 downstream of the rotor 41, that is, to the right of the roller 41 in the first straight flow path 31. The second flow straightening section 62 has an inclined surface that connects the outer periphery of the rotor 41 to the partition wall 3, and straightens the flow toward the partition wall 3 to a flow along the partition wall 3, as shown by the solid arrow in FIG. 5(a). The second flow straightening section 62 also straightens the flow that obstructs the flow in the first or second direction to a flow along the partition wall 3. This improves the efficiency of the aeration and mixing device 4 in the oxidation ditch 1.

Here, the first straightening section 61 and the protective section 51 described above may be provided integrally. Also, the second straightening section 62 and the protective section 51 may be provided integrally. By integrating the members, the number of parts can be reduced, making installation to the opening 30 easier.

Also, as shown in FIG. 5(b), in the second straight flow channel 32, the first and second straight flow sections 61 and 62 may be attached to the edge of the opening 30, similar to the first straight flow channel 31. In this case, the first straight flow section 61 and protective section 51 of the first straight flow channel 31 and the second straight flow section 62 of the second straight flow channel 31 may be integrated, and the second straight flow section 62 of the first straight flow channel 31, protective section 51 and the first straight flow section 61 of the second straight flow channel 31 may be integrated.

When the blades 412 of the rotor 41 pass through the opening 30 from the first straight flow path 31 to the second straight flow path 32, or from the second straight flow path 32 to the first straight flow path 31, the tips of the blades 412 face the end face of the opening 30 and apply an impact to the rotor 41. Here, as shown in FIG. 5(a), if the number of blades 412 on the rotor 41 is even, the two blades 412 on both sides of the rotating shaft 42 are arranged in a straight line, so that the two blades 412 face the end face of the opening 30 at the same time and apply an impact to the rotor 41 from each side.

For example, as shown in FIG. 5(b), the number of blades 412 on the rotor 41 may be an odd number. If the number of blades 412 on the rotor 41 is an odd number, the two blades 412 on either side of the rotation axis are not arranged in a straight line. Therefore, each blade 412 faces the end face of the opening 30. This makes it possible to reduce the impact applied to the rotor 41. Note that the number of blades 412 is not limited to five as shown in the example.

Furthermore, by slightly shifting the center of the rotor 41 from the straight line connecting both end faces of the opening in a plan view, it is possible to prevent the blade tips from facing both end faces of the opening at the same time, even if the number of blades 412 is an even number.

(How to repair an oxidation ditch)
In the oxidation ditch 1 described above, the aeration and stirring devices 4 on the vertical axis are installed in the straight flow paths 31 and 32. A straightening wall 34 is installed in the arcuate flow path 33. Therefore, for example, an existing oxidation ditch in which the aeration and stirring devices on the horizontal axis are installed in the straight flow paths and straightening walls are installed in the arcuate flow paths can be relatively easily modified to the oxidation ditch 1 shown in Figure 1.

Specifically, the method for repairing the oxidation ditch 1 includes the following steps (a) to (c).

(a) Remove the aeration and mixing device installed in the circulation flow path. For example, an old horizontal aeration and mixing device is removed.

(b) By removing a portion of the partition wall 3 separating the first straight flow path 31 and the second straight flow path 32 that constitute the circulation flow path, an opening 30 is provided that allows the first straight flow path 31 and the second straight flow path 32 to communicate with each other. As described above, the opening 30 may be provided in the center of the longitudinal direction of the first straight flow path 31 and the second straight flow path 32, with a size corresponding to the size of the rotor 41.

(c) Then, the rotor 41 of the vertical axis aeration and mixing device 4 is placed in the opening 30 so that the rotor 41 spans both the first straight flow path 31 and the second straight flow path 32.

Unlike the case of installing a vertical-axis aeration and stirring device 4 in an arcuate flow path 33, this renovation method does not require the removal of the installed flow straightening wall 34. In addition, it does not require the installation of a large guide plate, which is necessary when installing a vertical-axis aeration and stirring device in a straight flow path. Although an opening 30 must be formed in the partition wall 3, the renovation cost of the water tank 2 can be reduced.

In addition, since the renovated oxidation ditch 1 has only one aeration and mixing device 4, equipment costs and subsequent maintenance costs can be reduced. In addition, since the single aeration and mixing device 4 efficiently generates aeration and water flow in the circulation flow path, it is expected that operating costs will be lower than before the renovation.

As mentioned above, the oxidation ditch disclosed herein is not limited to oval tanks, but can also be applied to horseshoe-shaped tanks. In this case, multiple aeration and mixing devices 4 may be installed in the tank.

REFERENCE SIGNS LIST 1 Oxidation ditch 2 Water tank 3 Partition wall 30 Opening 31 First straight flow path 32 Second straight flow path 4 Aeration stirring device 41 Rotor 412 Blade 42 Rotating shaft 51 Protective section 61 First flow straightening section 62 Second flow straightening section

Claims (8)

A water tank for storing the liquid to be treated;
a partition wall that is installed in the water tank and forms an endless circulation flow path through which the liquid to be treated flows;
an aeration and stirring device that is installed in the circulation flow path and aerates the liquid to be treated and generates a flow of the liquid to be treated along the circulation flow path;
The aeration and stirring device is a vertical shaft aeration and stirring device having a rotor and a rotation shaft extending vertically,
the partition separates a first straight flow path through which the liquid to be treated flows in a first direction from a second straight flow path that is adjacent to the first straight flow path and through which the liquid to be treated flows in a second direction opposite to the first direction;
an opening is provided in the partition wall so as to connect the first linear flow path and the second linear flow path to each other;
The rotor of the aeration stirring device is installed in the opening so as to span both the first straight flow path and the second straight flow path, and generates a water flow in the first direction in the first straight flow path and a water flow in the second direction in the second straight flow path at the same time ;
An oxidation ditch, wherein a protective portion is attached to an end face of the opening to suppress wear of the end face . A water tank for storing the liquid to be treated;
a partition wall that is installed in the water tank and forms an endless circulation flow path through which the liquid to be treated flows;
an aeration and stirring device that is installed in the circulation flow path and aerates the liquid to be treated and generates a flow of the liquid to be treated along the circulation flow path;
The aeration and stirring device is a vertical shaft aeration and stirring device having a rotor and a rotation shaft extending vertically,
the partition separates a first straight flow path through which the liquid to be treated flows in a first direction from a second straight flow path that is adjacent to the first straight flow path and through which the liquid to be treated flows in a second direction opposite to the first direction;
an opening is provided in the partition wall so as to connect the first linear flow path and the second linear flow path to each other;
The rotor of the aeration stirring device is installed in the opening so as to span both the first straight flow path and the second straight flow path, and generates a water flow in the first direction in the first straight flow path and a water flow in the second direction in the second straight flow path at the same time ;
a flow straightening unit is attached to at least one of a portion of the opening on the upstream side and a portion of the opening on the downstream side of the rotor,
The straightening section straightens a flow that is generated by the rotation of the rotor and that obstructs the flow in the first direction or the second direction, or a flow that intersects the partition wall, into a flow that runs along the partition wall . 3. The oxidation ditch according to claim 2 ,
A protective portion is attached to an end surface of the opening to suppress wear of the end surface,
An oxidation ditch, wherein the flow straightening portion and the protective portion are integrated. The oxidation ditch according to any one of claims 1 to 3 ,
The opening is formed as a recessed notch from an upper end of the partition wall,
a depth D of the opening from the liquid surface of the liquid to be treated is within 0.8 times the diameter RD of the rotor;
An oxidation ditch, wherein the length L of the opening is greater than the diameter RD of the rotor and is equal to or less than the diameter RD + 1.0 m. The oxidation ditch according to any one of claims 1 to 4 ,
An oxidation ditch, wherein a diameter RD of the rotor is set to 50 to 70% of a width W of the first and second straight flow paths. In the oxidation ditch according to any one of claims 1 to 5 ,
The oxidation ditch, wherein the rotor has an odd number of blades. A method for repairing an existing oxidation ditch, comprising the steps of:
The aeration and mixing device installed in the circulation flow path is removed.
removing a part of a partition wall separating a first straight flow path and a second straight flow path constituting the circulation flow path, thereby providing an opening through which the first straight flow path and the second straight flow path communicate with each other;
a rotor of a vertical aeration/agitation device is disposed in the opening so that the rotor spans both the first linear flow path and the second linear flow path;
A method for repairing an oxidation ditch, comprising attaching a protective part to the end face of the opening to suppress wear of the end face . A method for repairing an existing oxidation ditch, comprising the steps of:
The aeration and mixing device installed in the circulation flow path is removed.
removing a part of a partition wall separating a first straight flow path and a second straight flow path constituting the circulation flow path, thereby providing an opening through which the first straight flow path and the second straight flow path communicate with each other;
a rotor of a vertical aeration/agitation device is disposed in the opening so that the rotor spans both the first linear flow path and the second linear flow path;
a flow straightening portion is attached to at least one of a portion of the opening on the upstream side and a portion of the opening on the downstream side of the rotor;
The method for repairing an oxidation ditch, wherein the straightening section straightens a flow that is generated by rotation of the rotor and that obstructs the flow in the first direction or the second direction, or a flow that intersects the partition wall, into a flow that runs along the partition wall .