Scum removal system in sewage treatment plant

Abstract

Treatment water quality can be improved to reduce the burden on the natural environment and to contribute to energy conservation.　In this invention, the first scum removal device of a water channel includes a scum scraper and a water injection nozzle for moving scum to the scum pit side at the end of a main body of the water channel, wherein the scum scraper includes a pair of pipes and a pressure fluid supply unit that supplies a pressure fluid to the pipes, and the pipes extend along a flow direction of raw water, have a plurality of openings, and are provided so as to be positioned below the scum. The second scum removal device of a primary sedimentation basin comprises a pipe skimmer, a scum guiding mechanism, and a water injection nozzle for moving the scum to the pipe skimmer side. The third scum removal device of a final sedimentation basin comprises a pipe skimmer and a water injection nozzle for moving the scum to the pipe skimmer side. The water injection nozzle for the final sedimentation basin accelerates the flow on the water surface to move the scum, but the water injection amount therefrom is smaller than that from the water injection nozzle for the water channel, and the water injection nozzle for the final sedimentation basin breaks up the scum with the force of the injected water without causing turbidity in the water.

Description

Scum removal systems in sewage treatment plants

[0001] The present invention relates to a scum removal system for a sewage treatment plant. This application claims priority to Japanese Patent Application No. 2023-149311, filed September 14, 2023, the contents of which are incorporated herein by reference.

[0002] A sewage treatment plant is equipped with a primary sedimentation tank, sometimes called a first sedimentation tank, which sediments and separates sedimentable substances in the sewage received at the plant; a reaction tank, which biologically treats the treated water from the primary sedimentation tank; and a final sedimentation tank, sometimes called a second sedimentation tank, which receives the raw water treated in the reaction tank and sediments and separates activated sludge.

[0003] These two sedimentation tanks are made up of a number of sedimentation tanks arranged side by side, and raw water is distributed and supplied to each sedimentation tank from a single water conveyance conduit (sometimes called an "inlet conduit").

[0004] The raw water received by a sewage treatment plant contains floating substances in addition to settling substances due to the nature of sewage. As a result, scum, which is a collection of floating substances, forms on the water surface of the primary settling tank, final settling tank, and the water conveyance that distributes and supplies raw water to these settling tanks. For this reason, these facilities are equipped with scum removal equipment.

[0005] The present applicant has previously proposed a scum removal device suitable for primary sedimentation tanks, as shown in Patent Document 1 (Japanese Patent No. 3943551), and has a proven track record with this device. This proposed scum removal device is known as "Shuuichi-kun" (registered trademark).

[0006] The proposed scum removal device is configured with a jetting means for jetting fluid (air) upward near the opening of the pipe gap into which the scum flows. When the air is jetted from the jetting means during scum discharge, the scum is induced to be taken in, and the scum flows into the pipe gap one after another. Once the scum starts to flow in, it continues to flow in even if the air jetting is stopped.

[0007] The proposed scum removal device has the excellent advantage of being able to improve the quality of treated water compared to conventional scum removal devices, and of being able to reduce the amount of water required to discharge scum to 1 / 20 to 1 / 30, thereby contributing to energy savings.

[0008] The applicant has also proposed and successfully implemented scum treatment devices suitable for final settling tanks, as shown in Patent Document 2 (Patent No. 4990856) and Patent Document 3 (Patent No. 5443261). The proposed scum removal device is known as "Nichiichi-kun" (registered trademark).

[0009] This scum removal device has a guide plate on the lower edge that forms an opening in the pipe skimmer, which extends a predetermined length upstream of the water flow and maintains a depth such that its tip is located below the scum generated on the water surface when the opening is located above the water surface, and at a predetermined position upstream of the water flow beyond the tip of the guide plate, water is sprayed from a spray nozzle toward the opening when part of the opening is located underwater.

[0010] The proposed scum removal device can generate a water flow with a faster flow rate on the upper surface of the guide plate facing the opening compared to the surrounding area, and can carry the scum along with the fast water flow to the opening in a short time and reliably without flocculating. This prevents deterioration of the quality of the discharged treated water, and reduces the amount of water required for scum discharge, resulting in excellent energy savings.

[0011] Furthermore, the present applicant has proposed a water conduit (sometimes called an inflow conduit) equipped with a scum removal device as shown in Patent Document 4 (Japanese Patent No. 7018552).

[0012] This conduit is equipped with water injection nozzles that are installed above the scum and spray pressurized water to push the scum toward the scum pit, injection nozzles that are installed in the water below the scum and spray pressurized water to push the scum toward the scum pit, and a compressed air injection mechanism that is installed on the inner wall of the conduit and sprays compressed air along the inner wall to remove the scum from the inner wall.

[0013] The proposed conduit has the advantage that pressurized water is sprayed from above and below the scum to push the scum toward the scum pit, and the scum is peeled off from the inner wall of the conduit, allowing the scum to be smoothly discharged into the scum pit.

[0014] JP 2004-202493 A JP 2010-046622 A JP 2011-240271 A WO 2022 / 123652

[0015] As mentioned above, the applicant has proposed and has a track record of scum removal devices suitable for each settling basin and water conveyance conduit, and has also come to the realization that, when viewed from a bird's-eye view of a sewage treatment plant, it is possible to efficiently remove scum generated throughout the entire plant, improving the quality of treated water, and furthermore, if the amount of water used for scum removal can be reduced as much as possible, it will be possible to conserve energy in scum treatment throughout the entire sewage treatment plant.

[0016] Therefore, an object of the present invention is to provide a scum treatment system for a sewage treatment plant that can improve the quality of treated water, reduce the burden on the environment, and contribute to energy conservation.

[0017] In order to achieve the above object, the scum removal system for a sewage treatment plant according to the present invention is a scum removal system for a sewage treatment plant that removes scum from raw water that is treated via a primary sedimentation basin conduit, a group of primary sedimentation basins, a reaction tank, a final sedimentation basin conduit, and a group of final sedimentation basins, and comprises: a first scum removal device provided in the primary sedimentation basin conduit and the final sedimentation basin conduit; a second scum removal device provided in each primary sedimentation basin in the group of primary sedimentation basins; and a third scum removal device provided in each final sedimentation basin in the group of final sedimentation basins; the first scum removal device comprises a scum peeling device including a pair of pipes extending along the direction of flow of the raw water inside both side walls of a conduit main body through which the raw water flows, having a plurality of openings spaced apart in the lengthwise direction and positioned so as to be below the scum, and a pressurized fluid supply unit for supplying pressurized fluid from a pressurized fluid supply source to the pipes; and a water jet nozzle for the conduit that moves the scum toward a scum pit provided at the end of the conduit main body; the second scum removal device comprises a pipe skimmer for a primary sedimentation basin that collects the scum; a scum guide mechanism that collects the scum toward the center in the width direction of the primary sedimentation basin; and a water jet nozzle for the primary sedimentation basin that moves the scum toward the pipe skimmer for the primary sedimentation basin; the third scum removal device comprises a pipe skimmer for a final sedimentation basin that collects the scum; and a water jet nozzle for a final sedimentation basin that moves the scum toward the pipe skimmer for the final sedimentation basin; The water injection nozzle for the final settling tank is set to inject less water than the water injection nozzle for the water conduit.

[0018] In each of the conduits for the primary and final settling tanks, pressurized fluid is ejected from the pipes to remove the floating scum from the side walls of the conduit body and move it toward the center (scum removal device), and then the water jet nozzles for the conduits push it into the scum pit. In the primary and final settling tanks, scum is collected in the respective pipe gaps and discharged.

[0019] In this series of processes, in the primary settling tank, the thick solidified scum is swept into the pipe gap by the force of water sprayed from the water spray nozzles for the primary settling tank.In the final settling tank, the amount of scum is decreasing and the flow rate is slowing, so the water spray from the water spray nozzles for the final settling tank accelerates the surface layer and sends the scum on the water surface into the pipe gap.

[0020] In this case, by reducing the amount of water sprayed from the water spray nozzles for the final settling tank, the scum that has become scarce and floats to the water surface can be sent reliably to the pipe skimmer while still floating on the water surface, without being scattered, suspended in the water, or dissolved by the force of the water spray.

[0021] In this way, scum can be removed smoothly and reliably from the primary sedimentation tank to the final sedimentation tank according to the treatment status, improving the quality of the treated water. This treated water is then discharged into the natural environment, but because the water quality has been improved, the burden on the environment is reduced. In addition, because the amount of water flowing into the pipe gap with the scum is small and the scum can be removed in a short time, the amount of water returned from the pipe gap to the upstream is reduced, which reduces the amount of electricity required and contributes to energy conservation.

[0022] In the scum removal system for a sewage treatment plant according to the present invention, the pipe skimmer for the final sedimentation tank may be provided with a scum guide plate that is positioned below the water surface in front of the opening for receiving the scum and that guides the scum while causing it to flow.

[0023] The scum is placed on a scum guide plate just before the opening of the pipe gap and guided to the opening of the pipe gap while flowing. In order to remove small amounts of scum, the scum guide plate guides the raw water so that it scoops up a thin layer of the surface layer. In addition, because the scum guide plate is located near the water surface, the scum can be reliably guided to the pipe gap without being affected by rising currents from below. This ensures that scum is removed reliably.

[0024] In the scum removal system for a sewage treatment plant according to the present invention, the scum guide mechanism comprises a front wall plate arranged below the opening for receiving the scum in the pipe skimmer for the primary sedimentation tank; and a pair of guide plates arranged so that the spacing between them gradually increases towards the upstream side from which raw water flows from both ends of the front wall plate; and preferably, fluid ejection pipes are provided near the front wall plate and the guide plates for ejecting pressurized fluid that rises from the lower ends of the front wall plate and the guide plates along the surfaces of the front wall plate and the guide plates on the side from which raw water flows.

[0025] The scum flowing through the settling tank can be collected in the center by a pair of guide plates and guided to the scum intake opening. In this case, the pressurized fluid ejected from the fluid ejection pipes provided near the guide plates can guide the scum away from the guide plates without causing it to adhere to the guide plates.

[0026] Furthermore, by ejecting pressurized fluid from a fluid ejection pipe provided near the front wall, the scum can be lifted from below and guided into the scum intake opening, thereby reducing the amount of scum left behind and allowing it to be smoothly and reliably taken into the scum intake opening.

[0027] The pressure fluid is preferably compressed air. The bubbling phenomenon can effectively separate the scum from the wall surface, and also generate buoyancy in the scum, allowing it to be effectively guided to the opening (scum intake port).

[0028] In the scum removal system for a sewage treatment plant according to the present invention, the pipe skimmer for the final sedimentation tank has a pipe material arranged along the width direction of the final sedimentation tank and a rotation mechanism for rotating the pipe material around its axis, the pipe material having an upstream scum intake port formed on the upstream side and a downstream scum intake port formed on the downstream side at circumferential intervals, and the rotation mechanism rotates the pipe material in one direction to position the upstream scum intake port at the water surface, and rotates the pipe material in the direction opposite to the one direction to position the downstream scum intake port at the water surface.

[0029] This allows scum flowing in from the upstream side to be taken in through the upstream scum intake port. If scum does not enter the upstream scum intake port and flows downstream, or if scum rises to the surface on the downstream side, the pipe gap can be reversed to remove the downstream scum from the downstream scum intake port.

[0030] In the scum removal system for a sewage treatment plant according to the present invention, it is preferable that a plurality of the pressure fluid supply units are provided and connected to a plurality of locations on the pipe, respectively.

[0031] Since the pressurized fluid is supplied to a plurality of locations in the pipe, the pressurized fluid can be supplied evenly to the long pipe.

[0032] The scum removal system for a sewage treatment plant of the present invention can efficiently remove scum using first to third scum removal devices installed in the primary sedimentation basin conduit, the group of primary sedimentation basins, the final sedimentation basin conduit, and the group of final sedimentation basins according to their respective conditions, improving the quality of treated water and reducing the environmental impact when the water is discharged into the natural environment. Furthermore, because the amount of water flowing into the pipe gap with the scum is small and the scum can be removed in a short time, the amount of water returned from the pipe gap to the upstream is reduced, thereby reducing the associated power consumption, achieving energy savings and reducing the cost of scum treatment at the sewage treatment plant.

[0033] 1 is a plan view showing a schematic configuration of the entire sewage treatment plant to which a scum removal system according to an embodiment of the present invention is applied. FIG. 1 is a plan view showing a primary sedimentation basin conduit and a portion of the primary sedimentation basin connected to the conduit. FIG. 2 is a cross-sectional view taken along line X1-X1 of FIG. 2, showing a state in which a movable gate is closed. FIG. 3 is a partial cross-sectional view taken along line X1-X1 of FIG. 2, showing a state in which a movable gate is open. The pressurized fluid supply unit is omitted. FIG. 1 is an enlarged plan view showing a main portion of a scum removal device incorporated in the primary sedimentation basin conduit of FIG. 2. FIG. 5 is a partial enlarged view of a pipe and a discharge port member taken along line X2-X2 of FIG. 5. FIG. 16 is a plan view showing a portion of a primary sedimentation basin equipped with a second scum removal device. FIG. 7 is a cross-sectional view taken along line X3-X3 of FIG. 7. FIG. 8 is an enlarged view of the vicinity of the pipe skimmer of FIG. 8. FIG. 10A is a cross-sectional view (FIG. 10B) and a plan view (FIG. 10B) of a water injection nozzle. FIG. 11 is a plan view showing a third scum removal device in a final sedimentation basin. FIG. 12 is a schematic view showing a rotation mechanism of the pipe skimmer of FIG. 11. 13A is a cross-sectional view showing the posture of the pipe gap when scum is not taken in, when scum is taken in on the upstream side, and when scum is taken in on the downstream side.

[0034] 1 is a plan view showing the schematic configuration of a sewage treatment plant to which a scum removal system according to one embodiment of the present invention is applied, and shows the flow of water from the inflow of raw sewage water (hereinafter sometimes simply referred to as "raw water") indicated by arrow a in the lower left of the drawing to the outflow of treated water indicated by arrow b in the center of the right side.

[0035] In this sewage treatment plant, similar to well-known sewage treatment plants, treatment facilities are provided from upstream to downstream of the flow of raw water (sewage): a primary sedimentation basin conduit A, a group of primary sedimentation basins B, a reaction tank C, a final sedimentation basin conduit D, and a group of final sedimentation basins E. Of these facilities, each of facilities A, B, D, and E, except for reaction tank C, is provided with a scum removal device. Each facility will be described below with reference to Figure 2 and subsequent drawings.

[0036] (Primary Sedimentation Basin Conduit A) Primary sedimentation basin conduit A (sometimes called an inlet conduit; hereinafter, sometimes simply referred to as conduit A) comprises a conduit main body 2 and a scum pit 3 connected to this conduit main body 2. This conduit main body 2 is a long waterway with an open top, and is configured so that raw water consisting of sewage is supplied from one longitudinal end (the right end in the example shown in Figure 2) (see arrow a).

[0037] The scum pit 3 is provided at the end of the water conduit body 2 in the direction of flow of raw water (the left end in the example shown in Figure 2), and part of the wall forming the scum pit 3 is shared with the wall forming the end of the water conduit body 2. The height of the upper wall surface 3a of this shared wall is set to be slightly lower than the water surface in the water conduit body 2 (see Figure 3).

[0038] A movable gate 4 is provided on the wall on which the upper wall surface 3a is provided, on the side of the water conduit main body 2, so that the flow of raw water from the water conduit main body 2 into the scum pit 3 can be controlled.

[0039] This movable gate 4 is composed of a gate plate 4a and a drive mechanism 4b, and is closed as shown in Figure 3 when scum S is not being discharged from the water conduit main body 2 into the scum pit 3, and is opened as shown in Figure 4 when scum S is being discharged from the water conduit main body 2 into the scum pit 3.

[0040] Therefore, when the movable gate 4 is opened as shown in FIG. 4, the surface water of the water conduit body 2, i.e., the raw water containing scum S, can be discharged into the scum pit 3.

[0041] The width of the gate plate 4a is slightly smaller than the channel width of the water conduit main body 2, and its height is determined to be sufficiently greater than the difference between the position of the upper wall surface 3a and the water surface position within the water conduit main body 2. The drive mechanism 4b is configured to be able to move the gate plate 4a up and down, and employs a well-known up and down movement mechanism such as a system consisting of a screw rod and rotating nut, a rack and pinion system, or a hydraulic cylinder.

[0042] When scum S is not to be discharged, the drive mechanism 4b raises the gate plate 4a so that the upper end position of the gate plate 4a is sufficiently higher than the water surface position in the water conduit main body 2, as shown in Figure 3, thereby blocking off communication between the scum pit 3 and the water conduit main body 2.

[0043] When the scum S is to be discharged, the drive mechanism 4b lowers the gate plate 4a so that the upper end of the gate plate 4a is below the water surface in the conduit body 2 and slightly below the bottom surface of the scum layer S that has formed in the conduit body 2, as shown in Figure 4, thereby establishing communication between the scum pit 3 and the conduit body 2.

[0044] The scum pit 3 is provided with a scum discharge device 10 for discharging accumulated scum from the scum pit 3.

[0045] Of a pair of side walls 5 extending in the longitudinal direction of the long channel that forms the water conduit body 2, a plurality of primary sedimentation tanks 6, which correspond to the group of primary sedimentation tanks B of the sewage treatment plant, are arranged side by side on the outside of one of the side walls 5 (the upper side wall in Figure 2).

[0046] A portion of the peripheral wall of each primary sedimentation basin 6 is shared with the side wall 5 of the conduit main body 2. An inlet 7 and an opening / closing gate 8 leading to each primary sedimentation basin 6 are provided midway along the depth of the side wall 5. Therefore, the inside of the conduit main body 2 communicates with the inside of the primary sedimentation basin 6 via the inlet 7. Therefore, when the opening / closing gate 8 of the inlet 7 is open, the raw water in the conduit main body 2 flows into the primary sedimentation basin 6, and the raw water that has flowed in can flow within the primary sedimentation basin 6 in a direction away from the side wall 5 (see arrow c in Figure 2 ).

[0047] In the example shown in FIG. 2, the primary sedimentation basin 6 is provided adjacent to the outside of one of the side walls 5 of the water conveyance conduit body 2, but it may be provided adjacent to the outside of both side walls 5.

[0048] (Scum Remover 20) Scum S contained in the flowing raw water adheres to the side walls 5, 5 of the conduit body 2, so a scum remover 20 is provided to remove this scum S from the side walls 5, 5. A pair of pipes 9, 9 constituting part of the scum remover 20 are provided inside both side walls 5 of the conduit body 2, extending in the direction of the flow of the raw water and parallel to each side wall 5. These pipes 9, 9 are made of well-known pipe material such as steel or synthetic resin, and as shown in Figure 6, a number of discharge outlet members 21 are provided in a row at predetermined intervals along their length.

[0049] The outlet members 21 are made of synthetic resin such as fluororesin, and are formed in a cup-like (bowl-like, bell-like, etc.) outer shape with an opening 22 at the bottom. These outlet members 21 are fixed to the pipe 9 with their internal spaces communicating with the inside of the pipe 9, and the opening 22 is positioned vertically downward.

[0050] These pipes 9 are installed so as to be located below the scum layer S that is generated within the conduit main body 2. For example, if scum S accumulates due to operation of the conduit A and grows to a thickness of, say, approximately 10 cm, and the scum S is to be discharged from the conduit main body 2 into the scum pit 3, the pipes 9 are installed so as to be slightly below 10 cm from the water surface. The installation position of the pipes 9 varies depending on the sewage treatment plant in which the conduit main body 2 is installed, but in any case, they are determined to be located below the scum S that is generated.

[0051] The scum removing device 20 includes the above-mentioned pipes 9 and a pressurized fluid supply unit 23 that supplies compressed air, pressurized water, or gas-liquid mixed pressurized water to the pipes 9. Here, an example of compressed air is shown as the pressurized fluid.

[0052] The pipe 9 is installed along the length of the conduit body 2 (along the direction of flow of raw water), and is divided into a plurality of regions S1 to S3 of predetermined lengths along the length, and a pressurized fluid supply unit 23 is provided for each of the divided regions S1 to S3. Therefore, a plurality of pressurized fluid supply units 23 are provided within one conduit body 2.

[0053] (Pressure fluid supply unit 23) In the example shown in Fig. 2, the system is divided into three regions S1 to S3, and therefore three pressure fluid supply units 23 are provided (however, the pressure fluid supply units 23 are not shown in Fig. 4). Each pressure fluid supply unit 23 is connected to a pressure fluid pipe 24 that supplies pressure fluid from a pressure supply source. This pressure fluid pipe 24 is provided with branch pipes 25 that supply pressure fluid to each of the pressure fluid supply units 23. Each branch pipe 25 is provided with a flow rate adjustment valve 26 for controlling the flow rate to the respective pressure fluid supply unit 23.

[0054] As shown in FIG. 5, the pressurized fluid supply section 23 is configured to form a loop in plan view, with a pair of long pipe sections 27, 27 arranged parallel to each of the pair of pipes 9, 9, and a pair of short pipe sections 28, 28 connected to both ends of the long pipe sections 27, 27.

[0055] A central connecting pipe 29 that connects the long pipe sections 27, 27 is connected to the approximate center of each of the long pipe sections 27, 27. Each branch pipe 25 of the pressure fluid supply section 23 is connected to the central position of this central connecting pipe 29 in the longitudinal direction.

[0056] A plurality of connecting pipes 30 are provided at predetermined intervals between the long pipe sections 27, 27 of the pressure fluid supply section 23, connecting each of the long pipe sections 27, 27 to the pipes 9, 9. Therefore, the pressure fluid from the pressure fluid supply source is supplied from the pressure fluid piping 24 through each branch pipe 25 to each pressure fluid supply section 23, and is supplied from each pressure fluid supply section 23 to the pipe 9 through each connecting pipe 30.

[0057] Each pressurized fluid supply section 23, together with the pressurized fluid piping 24 and branch pipes 25, etc., is provided above the water surface of the water conduit body 2. Although it is possible to place these underwater, it is preferable to place them above the water surface because this would hinder the flow of raw water. In Figure 2 etc., the pipes 9, etc. are shown with dashed lines, which indicate that they are provided underwater.

[0058] In the scum remover 20 configured as described above, when pressurized fluid (compressed air) is supplied from each pressurized fluid supply unit 23 into the pipes 9, 9, the pressurized fluid is released as bubbles into the raw water from the downward openings 22 of each discharge outlet member 21 (see FIG. 6 ). The released bubbles then rise along the inner surface of the side wall 5, and can remove scum adhering to the side wall 5.

[0059] In place of the pipe 9 and the discharge member 21, a pipe made of an elastic material such as natural rubber or synthetic rubber with a number of slits (long, thin openings) spaced apart along its length, or a steel pipe with a number of holes (openings) spaced apart along its length, can also be used.

[0060] (Water jet nozzles 11 for the conduit) A plurality of water jet nozzles for the conduit (hereinafter referred to as above-water nozzles) 11 are provided above the water in the conduit main body 2. These above-water nozzles 11 are provided slightly above the water surface in the conduit main body 2, at a plurality of locations so as to divide the length of the conduit main body 2 in the direction of water flow at predetermined intervals, and a plurality of nozzles are provided across the width of the conduit main body 2 (see Figure 2).

[0061] Water at a predetermined pressure is supplied to each above-water nozzle 11 via a pressurized water supply pipe 12. The water supplied to the above-water nozzles 11 can be treated water from a sewage treatment plant.

[0062] The above-water nozzles 11 are obliquely provided so that their tip openings face further downward downstream of the water flow in the water conduit main body 2. Therefore, when pressurized water is sprayed from each above-water nozzle 11, the jetted water is supplied downstream against the scum S that has formed in a layer on the water surface of the water conduit main body 2, and this promotes the flow of scum S that tries to flow toward the scum pit 3 (see Figures 3 and 4).

[0063] For ease of explanation, the scum S that has grown in a layer of a certain thickness on the water surface may be referred to as a "scum layer S."

[0064] (Water Jet Nozzles 13 for Conduit) The conduit body 2 is also provided with a plurality of water jet nozzles (hereinafter referred to as submerged nozzles) 13 for the conduit underwater.

[0065] A plurality of these submersible nozzles 13 are provided in the water slightly below the water surface in the conduit main body 2, at predetermined intervals in the direction of water flow in the conduit main body 2. A plurality of submersible nozzles 13 (two in the example shown in Figure 2) are also provided at predetermined intervals in the direction perpendicular to the direction of water flow in the conduit main body 2, i.e., across the width of the waterway. However, there are cases where the submersible nozzles 13 are not provided.

[0066] Water at a predetermined pressure is supplied to the submerged nozzle 13 via a pressurized water supply pipe 14. When pressurized water is supplied from the pressurized water supply pipe 14, the submerged nozzle 13 sprays the pressurized water from an opening facing the scum pit 3, thereby promoting the flow of scum S that is flowing toward the scum pit 3 (see Figure 4). Treated water from a sewage treatment plant can be used as the water supplied to the submerged nozzle 13.

[0067] In the following description, the water jet nozzle 11 installed above water will be referred to as an above-water nozzle, and the water jet nozzle 13 installed underwater will be referred to as an underwater nozzle.

[0068] In the primary sedimentation basin conduit A, the first scum removal device 35 comprises a scum pit 3 with a movable gate 4, a scum peeling device 20, an above-water nozzle 11, an underwater nozzle 13, etc. (Figs. 2 and 3).

[0069] A sewage treatment method including the scum discharge operation in the water conduit A having the above-mentioned configuration will be described.

[0070] Raw water (sewage) is supplied to the conduit body 2 and distributed to each primary sedimentation basin 6 through the inlets 7. Sedimentation and separation is then carried out in each primary sedimentation basin 6. At this time, scum S gradually forms on the water surface of the conduit body 2. Figures 3 and 4 show this state.

[0071] When the scum layer S has formed in the water conduit body 2 to a certain extent and its thickness has reached a predetermined value (for example, 10 cm), pressurized water is supplied to the submerged nozzle 13 and the above-water nozzle 11, which breaks up part of the scum layer S and pushes it downstream. In addition, compressed air is supplied to the pipe 9. This starts the discharge of the scum S into the scum pit 3.

[0072] When pressurized water is supplied to the submerged nozzle 13, the pressurized water is sprayed from the submerged nozzle 13 so that the scum S flows toward the scum pit 3. The tip of the submerged nozzle 13 is formed slightly upward, which acts to lift the scum S slightly out of the water, causing the scum S to move. At the same time, pressurized water is also sprayed from the above-water nozzle 11 so that the scum S flows toward the scum pit 3.

[0073] When the operation of discharging the scum S into the scum pit 3 begins, compressed air is also ejected from the pipe 9, and the compressed air peels off the scum S adhering to the side wall 5, so that the scum S is discharged more smoothly and quickly into the scum pit 3. Figures 3 and 4 show this state.

[0074] The ejection of compressed air from the pipe 9 will now be further explained.

[0075] The pipes 9, 9 are supplied with air from the respective pressurized fluid supply units 23 via connecting pipes 30. Because these pressurized fluid supply units 23 are formed in a loop, the pressure inside them is maintained at a substantially uniform level. This allows compressed air of a substantially uniform pressure to be supplied to the pipes 9 corresponding to each pressurized fluid supply unit 23, and as a result, compressed air of a substantially uniform pressure is ejected from the openings 22 of all the discharge port members 21. This means that scum S adhering to the side walls 5 corresponding to each long pipe portion 27 of the pressurized fluid supply unit 23 can be effectively removed.

[0076] Moreover, the amount of compressed air supplied from the pressurized fluid pipe 24 to each pressurized fluid supply section 23 through each branch pipe 25 can be adjusted by each flow control valve 26. Therefore, by increasing the amount of compressed air supplied to a portion of the plurality of pressurized fluid supply sections 23 where scum S is likely to accumulate and has a high adhesive force in the conduit main body 2, such as the pressurized fluid supply section 23 provided at the end of the flow in the conduit main body 2, scum S can be more effectively removed from that portion.

[0077] Therefore, the supply flow rate of the pressurized fluid to each pressurized fluid supply section 23 can be individually controlled by the flow rate control valve 26, and the pressurized fluid can be supplied appropriately depending on the scum adhesion state, etc., and the scum can be effectively removed.

[0078] Although a plurality of pressure fluid supply units 23 are provided in a separate state, they may be connected to each other.

[0079] When most of the scum S has been discharged from the water conduit body 2 into the scum pit 3, the supply of pressurized water to the submerged nozzles 13 and the above-water nozzles 11 is stopped, and the supply of compressed air to the pipe 9 is also stopped. This completes the operation of discharging the scum S into the scum pit 3.

[0080] Although the above-mentioned operation of discharging the scum S into the scum pit 3 uses the submerged nozzle 13 and the above-water nozzle 11, it is also possible to use either one of them. The choice of whether to use one or both of them is determined by the properties and amount of the scum S to be generated.

[0081] (Primary sedimentation tank group B) As shown in Figures 1 and 2, the primary sedimentation tank group B is configured such that multiple primary sedimentation tanks 6 are installed in parallel, and as described above, sewage received at the sewage treatment plant is received into the primary sedimentation tank group B (each primary sedimentation tank 6) via the primary sedimentation tank water conduit A.

[0082] 7 shows the downstream portion of one primary sedimentation tank 6. As the sewage received in the primary sedimentation tank 6 moves from one side (upstream side: left side in the illustrated example) of the tank 6 to the other side (downstream side: right side in the illustrated example), i.e., during the flow indicated by arrow d in the figure, sedimentable substances contained in the sewage settle and are separated.

[0083] The sedimentary material (sludge) that settles to the bottom of the primary sedimentation tank 6 is collected in a pit located at the bottom of one side of the primary sedimentation tank 6 by a sludge collector (not shown), and then sent to a sludge treatment facility via a sludge discharge pipe 15 (see Figure 1) for treatment.

[0084] The raw water contains floating substances in addition to sedimentary substances, and scum S, which is a collection of floating substances, is generated on the water surface of the sedimentation tank 1. Therefore, in the primary sedimentation tank 6, the aforementioned settling substances are separated, and the scum S is removed by the second scum removal device 60.

[0085] The treated water from which the precipitated matter and floating matter (scum S) have been removed is received in an overflow trough 52 provided on the other side (downstream side) of the primary sedimentation tank 6. The treated water received in the overflow trough 52 is taken out as shown by the arrow e in Figure 7 and sent to a reaction tank (aeration tank) C where it is subjected to biological treatment.

[0086] The second scum removal device 60 is installed downstream of the flow of raw water in the primary sedimentation tank 6 and upstream of the overflow trough 52. This second scum removal device 60 is provided with a pipe skimmer 61 (for the primary sedimentation tank) for taking in scum. The pipe skimmer 61 includes a pipe 62 having a scum intake port 63 and a rotation mechanism 55 for rotating the pipe 62.

[0087] The pipe skimmer 61 is installed so that the pipe material 62 blocks the water surface flow. That is, the pipe material 62 is installed horizontally across the width of the primary sedimentation tank 6 (the direction crossing the flow), and a slit-shaped opening (scum intake port 63) is provided in the peripheral wall along the longitudinal direction. One longitudinal end of the pipe material 62 watertightly penetrates one side wall 6a of the primary sedimentation tank 6 and is rotatably supported, while the other end is rotatably supported on the other side wall 6b of the primary sedimentation tank 6. The end of the pipe material 62 that penetrates the side wall 6a is located in the scum pit 54 provided outside the side wall 6a.

[0088] A rotation mechanism 55 including a motor is provided on the upper surface of the other side wall 6b of the primary sedimentation tank 6, where the other end of the pipe 62 is provided. This rotation mechanism 55 is configured to rotate the pipe 62 back and forth around its axis at a predetermined angle.

[0089] The pipe 62 is supported so that the scum intake port 63, which is provided in the longitudinal direction, is positioned above the water surface as a normal position, as shown in Figures 7 and 8. When the time comes to remove scum, the rotating mechanism 55 rotates as shown by arrow f in Figure 9 (counterclockwise in Figure 9) so that the water surface is positioned at approximately the middle of the width of the scum intake port 63 (the width along the circumferential direction of the pipe 62).

[0090] As a result, the scum S on the water surface flows from the front of the pipe material 62 toward the scum intake port 63, drops into the pipe material 62 from the scum intake port 63, and then passes through the inside of the pipe material 62 and is sent to the scum pit 54. The position of the scum intake port 63 at this time is the scum intake position, and the position where the scum intake port 63 is located above the water surface is the non-intake position.

[0091] The rotation mechanism 55 may be configured to rotate the pipe material 62 manually without using a motor or the like.

[0092] The scum S discharged into the scum pit 54 is removed from the scum pit 54 as shown by arrow g (FIG. 7) and sent to a scum treatment facility (not shown) equipped with a dehydrator and other equipment for treatment. The water from which the scum S has been removed is returned upstream and mixed with the raw water for further treatment.

[0093] When scum removal is complete, the pipe 62 is rotated in the direction opposite to the arrow f (Fig. 9), i.e., clockwise in Figs. 8 and 9, so that the scum intake port 63 is positioned above the water surface as shown in Fig. 8 (see also the two-dot chain line in Fig. 9). Such rotation control of the rotation mechanism 55 is performed by a programmable controller (not shown) that controls the entire primary sedimentation tank 6, including the second scum remover 60.

[0094] 7, the pipe material 62 is formed to be longer than the width of the primary sedimentation tank 6 and is arranged so as to cross the water flow direction of the primary sedimentation tank 6. The scum intake port 63 provided in the longitudinal direction thereof is formed to be shorter than the width of the primary sedimentation tank 6, and both ends in the longitudinal direction are spaced a predetermined distance from the inner surfaces of the side walls 6a, 6b of the primary sedimentation tank 6.

[0095] The second scum removal device 60 has this pipe gap 61, and a front wall plate 70 and a pair of guide plates 80 that serve as a scum guide mechanism for collecting scum S toward the center of the width direction of the primary sedimentation tank 6. The front wall plate 70 and the guide plates 80 are provided in front of (upstream of) the pipe material 62, that is, on the side from which raw water approaches the pipe material 62 (the left side of the pipe material 62 in the illustrated example).

[0096] The front wall plate 70 is made of a steel or synthetic resin plate and has a long, narrow rectangular shape when viewed from the direction of raw water flow. The long sides of the rectangular front wall plate 70 are slightly longer than the length of the scum inlet 63, and the short sides are positioned along the depth direction of the primary sedimentation tank 6. As shown in Figure 9, the upper end of the front wall plate 70 is positioned below the lower end of the scum inlet 63 when the pipe member 62 rotates and a portion of the scum inlet 63 is submerged (the lower end of the scum inlet 63 at the scum inlet position). The lower end of the front wall plate 70 extends below the lower end of the pipe member 62.

[0097] One longitudinal end of the front wall plate 70 (widthwise of the sedimentation tank 1) is fixed to the inner surface of one side wall 6a of the sedimentation tank 1 using a support member 71, and the other end is fixed to the inner surface of the other side wall 6b of the sedimentation tank 1 using another support member 71. When fixing both ends of the front wall plate 70, the rear surface (downstream surface) of the front wall plate 70, i.e., the surface opposite the direction of raw water flow, is carefully positioned close to the pipe material 62 without interfering with the rotation of the pipe material 62, and the upper edge of the front wall plate 70 is positioned below the lower end of the scum intake port 63 when facing upstream. However, the upper edge of the front wall plate 70 may be positioned at approximately the same height as the lower end of the scum intake port 63 of the pipe material 62 at the scum intake position.

[0098] A fluid ejection pipe 72 extending across the width of the sedimentation basin 1 is attached using a U-bolt or the like near the bottom edge of the front side (upstream side) of the front wall panel 70, i.e., near the bottom edge on the side from which the raw water flows. This fluid ejection pipe 72 is made of a steel or synthetic resin pipe material, and has a number of discharge port members 73 arranged in a row at predetermined intervals along its length.

[0099] The discharge outlet members 73 are made of synthetic resin such as fluororesin, and have a cup-like (bowl-like, bell-like, etc.) outer shape with an opening 74 at the bottom. These discharge outlet members 73 are fixed to the fluid ejection pipes 72 with their internal spaces communicating with the inside of the fluid ejection pipes 72, and the openings 74 are arranged facing vertically downward.

[0100] One longitudinal end of the fluid ejection pipe 72 is closed, and the other end is connected to a fluid supply pipe 76 via a flow rate adjustment valve 75. The fluid supply pipe 76 is provided with an on-off valve 77 such as a gate valve.

[0101] 7 to 9 show an example in which a front wall plate 70 is provided, but this front wall plate 70 is not necessarily required as a scum guide mechanism, and there are cases in which the front wall plate 70 is not provided. However, providing the front wall plate 70 is preferable because it creates a wall below the pipe gap 61.

[0102] Even when the front wall plate 70 is not provided, it is preferable to provide a fluid ejection pipe 72 having an ejection port member 73 for ejecting pressurized fluid.

[0103] The pair of guide plates 80 have the same shape. These guide plates 80 are also made of steel or synthetic resin plate material, similar to the front wall plate 70. These guide plates 80 are rectangular, with their short sides aligned along the depth direction within the sedimentation tank 1. In some cases, these guide plates 80 are not provided.

[0104] The width of the short side of each guide plate 80 (the dimension along the depth direction of the sedimentation tank 1) is approximately twice as large as the length of the short side (width; the dimension along the depth direction of the sedimentation tank 1) of the front wall plate 70. When both guide plates 80 are installed in the sedimentation tank 1, the position of their upper edges is higher than the top surface of the scum S, and the position of their lower edges is approximately equal to the position of the lower edge of the front wall plate 70 (see Figures 8 and 9).

[0105] Fluid ejection pipes 79 each having a plurality of ejection port members 78 are attached by U-bolts or the like to the lower edges of the front (upstream) sides of these guide plates 80. The fluid ejection pipes 79 provided on both guide plates 80 are connected to a fluid supply pipe 76 via a flow control valve 75, similar to the fluid ejection pipe 72 of the front wall plate 70.

[0106] The piping of the fluid ejection pipe 79 on the side wall 6b is shown only partway for convenience of drawing, and is connected to the piping shown at the top of the drawing at the position indicated by the symbol "Q" in FIG.

[0107] The specific longitudinal dimensions (dimensions of the long sides) of these guide plates 80 will be described later, but both guide plates 80 are fixed using support members 82 so that one longitudinal end abuts against each end of the front wall plate 70 (the upper and lower ends in FIG. 7 ) and the other longitudinal end abuts against the inner surfaces of the side walls 6 a, 6 b of the settling basin 1. When fixing them, they are carefully attached so that the position of the upper edge is higher than the position of the top surface of the scum S and the position of the lower edge is approximately equal to the position of the lower edge of the front wall plate 70.

[0108] The length of the pair of guide plates 80 is determined by the angle θ at which they are attached to the inner surfaces of both side walls 6a, 6b of the primary sedimentation tank 6. In the example of Figure 7, they are attached at an angle of approximately 15° to the inner surfaces of each side wall 6a, 6b, and are arranged so that the distance between the pair of guide plates 80 gradually increases toward the upstream side.

[0109] The purpose of setting the mounting angle θ on the pair of guide plates 80 is to gradually collect the flowing scum S toward the center of the flow, thereby increasing the concentration of scum S and obtaining scum S with a low moisture content. To increase this concentration, it is possible to shorten the length (dimension along the width direction of the primary sedimentation tank 6) of the scum intake port 63 and front wall plate 70 provided on the pipe material 62, but if the mounting angle θ is increased, the guide plates 80 themselves will increase the resistance to the flow of scum S. Therefore, the installation angle θ is appropriately determined based on the properties of the raw water received in the sedimentation tank 1, the amount of scum S generated, etc.

[0110] The pair of guide plates 80 are provided with fluid ejection pipes 79 and water ejection nozzles 90, 91, which will be described later, so that the installation angle θ of the guide plates 80 can be increased to some extent.

[0111] When the mounting angle θ of the pair of guide plates 80 approaches 0°, they become nearly parallel to both side walls 6a, 6b of the primary settling tank 6, and the effect of the guide plates 80 on accumulating scum S is reduced. However, the resistance to the scum S decreases, and the speed at which the scum S moves increases. In addition, since the pair of guide plates 80 are provided with the fluid ejection pipes 79 and water ejection nozzles 90, 91 (described later), the time required to discharge the scum S is shortened, and therefore the amount of water required for discharge is reduced.

[0112] 10A and 10B are provided above the water surface near the second scum removal device 60, which includes the front wall plate 70 and a pair of guide plates 80. A water injection nozzle (above water nozzle) 90, 91 (for the primary sedimentation tank) is provided above the water, and a water injection nozzle (underwater nozzle) 92 (for the primary sedimentation tank) is provided underwater. As shown in FIG. 7, a plurality of water injection nozzles 90 (five in the illustrated example) are provided at predetermined intervals in the direction across the sedimentation tank 1 (crossing the flow direction) in the area between the pair of guide plates 80. Similarly to the water injection nozzle 90, a plurality of water injection nozzles 91, 92 (six in total in the illustrated example) are provided slightly upstream of the installation position of the water injection nozzle 90 (outside the space between the pair of guide plates 80 in the illustrated example).

[0113] Each of the injection nozzles 90, 91, 92 is configured to have a slit 93 that ejects water substantially parallel to the water surface, and a flow straightening piece 94 that protrudes from the top of the slit 93 and holds the stratified water flow ejected from the slit 93. The injection nozzle 90 (above-water nozzle) disposed in the region between both guide plates 80 is provided at approximately the water surface position, and is installed so that the stratified water flow ejected from the slit 93 is directed toward the second scum removal device 60 (pipe skimmer 61).

[0114] Upstream of the area between the guide plates 80, three above-water nozzles 91 positioned slightly above the water surface and three underwater nozzles 92 positioned slightly below the water surface are alternately arranged. The above-water nozzles 91 are tilted slightly downward to spray water diagonally from above toward the water surface. The underwater nozzles 92 are tilted slightly upward to spray water from underwater toward the water surface. In Figures 7 and 8, the above-water nozzles 90 and 91 are shown by solid lines, and the underwater nozzles 92 are shown by dashed lines.

[0115] These water injection nozzles 90 , 91 , 92 are configured so that the injection amount can be appropriately adjusted by a flow rate adjustment valve 95 , and are connected to a water supply pipe 97 equipped with an on-off valve 96 .

[0116] Of the solids that have risen to the surface as scum, those that would settle if no air bubbles were attached can be separated by destroying the air bubbles with water sprayed from above the scum S by the water injection nozzles 91 and by water sprayed from underwater by the water injection nozzles 92. For this reason, the number and arrangement of the above-water nozzles 91 and the underwater nozzles 92 is determined depending on the properties of the scum S on the water surface, etc.

[0117] The operation of removing scum S from the primary sedimentation tank 6 equipped with the second scum removal device 60 having the above-described configuration is carried out as follows.

[0118] As shown in Fig. 9, when a certain amount of scum S accumulates on the water surface and it is time to discharge the scum, the pipe skimmer 61 is rotated from the state shown in Figs. 7 and 8 to the state shown in Fig. 9.

[0119] The on-off valves 77 and 96 are opened simultaneously with or before the rotation of the pipe skimmer 61. Water is sprayed onto the scum layer S from the water spray nozzles 90, 91, and 92 provided at upstream positions, thereby eliminating air bubbles adhering to the solid matter in the scum layer S and causing the solid matter floating to settle and separate, and the water sprayed downstream accelerates the flow of the water surface, washing the scum downstream.

[0120] The scum layer S is then swept away through the gaps between the guide plates 80 and into the scum intake port 63 of the pipe skimmer 61. At this time, compressed air is being ejected as a pressurized fluid from the discharge port member 78 of the fluid ejection pipe 79 on the surface of the guide plate 80, and the bubbling flow reaches the water surface, so that the scum layer S flows away from the surface of the guide plate 80 and is drawn toward the center, and is guided to the scum intake port 63 without adhering to the guide plate 80.

[0121] At the front surface of the front wall plate 70, compressed air is ejected relatively slowly from the fluid ejection pipes 72, and the buoyancy of the air causes the scum S to be lifted and flow into the scum intake port 63. In this way, the scum S is induced to be taken into the scum intake port 63, and thereafter the scum S is continuously flowed into the pipe material 62 of the pipe skimmer 61. Once the inflow of scum S begins, the ejection of air from the fluid ejection pipes 72 at the front wall plate 70 is stopped.

[0122] The ejection of compressed air from the fluid ejection pipe 79 at the guide plate 80 prevents adhesion of scum S to the guide plate 80 and also separates the scum S from the surface of the guide plate 80, facilitating a smooth flow to the scum intake port 63, and therefore continues even after the intake of scum S has begun.

[0123] On the other hand, in the water injection nozzle 90 arranged in the area between the guide plates 80, the flow of scum S is promoted by the sprayed water flow, and the scum S can be quickly discharged toward the pipe material 62 side of the pipe gap 61.

[0124] The scum S taken into the pipe skimmer 61 is discharged into a scum pit 54 and sent to a scum treatment facility for treatment.

[0125] When most of the scum S has been discharged into the pipe skimmer 61, the pipe skimmer 61 (pipe material 62) is rotated to the non-taking-in position shown in Figures 7 and 8, and the on-off valves 77 and 96 are closed. This stops the compressed air from the fluid ejection pipes 72 and 79, and stops the water injection from the water injection nozzles 90, 91, and 92. This completes the series of scum removal operations by the second scum remover 60.

[0126] The second scum removal device 60 having the above-described configuration is configured such that the pipe material 62 of the pipe skimmer 61 is positioned above the water surface so as to block the flow path, and includes a front wall plate 70 equipped with a fluid ejection pipe 72, a pair of guide plates 80, and water injection nozzles 90, 91, 92, so that scum can be removed by operating it for about 7 to 10 minutes, for example, once a week.

[0127] Therefore, since the scum can be discharged in a shorter time, the amount of water that flows into the pipe skimmer 61 along with the scum is reduced, resulting in an extremely advantageous effect of significantly reducing the amount of power consumed to remove the scum and return it to the raw water. Furthermore, although the treated water is discharged into the natural environment, the improved water quality reduces the burden on the environment. Therefore, the second scum removal device 60 configured as described above has the excellent feature of being able to reduce the burden on the natural environment and contribute to further energy savings.

[0128] Furthermore, the second scum removal device 60 having the above-described configuration has the advantage that the main components, the front wall plate 70 equipped with the fluid ejection pipes 72, 79 and the pair of guide plates 80, can be prefabricated in a factory, and can therefore be easily applied to existing sedimentation tanks.

[0129] (Reaction Tank C) The reaction tank C is where the treated water from the primary sedimentation tank group B is biologically treated. ２ The wastewater is treated by advanced treatment methods such as the anaerobic activated sludge process (AO process) or the anaerobic-aerobic activated sludge process (AO process) (see Figure 1). This reactor C receives treated water from the primary settling tanks B, and also receives returned sludge from the final settling tanks E as needed for biological treatment. This is the core treatment facility of the sewage treatment plant, but since scum is not removed in this reactor C, further explanation will be omitted.

[0130] (Final settling tank conduit D) This final settling tank conduit D is configured to receive treated water from the reaction tank C and distribute and supply the treated water as raw water to each of the final settling tanks 100 in the final settling tank group E (see Figure 1). This final settling tank conduit D is equipped with a scum removal device similar to the first scum removal device 35 (see Figure 1) equipped in the primary settling tank conduit A described above with reference to Figures 2 to 4. Since its configuration is substantially the same as that of the first scum removal device 35, further description will be omitted.

[0131] In the scum removal device for the final settling tank conduit D, the above-water nozzles 11 shown in Figures 2 to 4 may be omitted, although they may be provided if necessary depending on the nature of the scum.

[0132] (Final sedimentation tank group E) Figure 11 is a plan view of the downstream portion of one of the final sedimentation tanks 100 in the final sedimentation tank group E. Since each of the final sedimentation tanks 100 in the first sedimentation tank group E has the same configuration, the following explanation will be given using this one final sedimentation tank 100.

[0133] Like well-known sedimentation tanks, the final sedimentation tank 100 allows sedimentable substances contained in the raw water to settle and be separated as the raw water (treated water from reaction tank C) moves from one side of the tank to the other (from left to right as indicated by arrow h in Figure 11). Although not shown, the settleable substances (sludge) that settle to the bottom of the final sedimentation tank 100 are collected in a pit provided at the bottom of one side of the final sedimentation tank 100 by a sludge collector, and then sent as returned sludge via a sludge discharge pipe 101 (see Figure 1) to reaction tank C for use, while the remaining sludge is sent as excess sludge to a sludge treatment facility for treatment.

[0134] The treated water from the final sedimentation tank 100, from which sedimentable substances have been separated and scum removed by a third scum removal device 105 (described in detail below), is received in an overflow trough 102 provided on the other side of the final sedimentation tank 100. The treated water received in the overflow trough 102 is taken out as shown by arrow i in Figure 11, disinfected, and then released.

[0135] The third scum removal device 105 provided in this final settling tank 100 is configured to include a pipe skimmer 106 for the final settling tank and a water injection nozzle 107.

[0136] The pipe skimmer 106 comprises a pipe 108 made of steel or synthetic resin and a rotation mechanism 112 for rotating the pipe 108. The pipe 108 has two openings (scum intake ports) 109, 110 extending in the longitudinal direction and is provided so as to block the surface flow of raw water in the final sedimentation tank 100. That is, one longitudinal end of the pipe 108 watertightly penetrates one side wall 100a of the final sedimentation tank 100 (the upper side wall in FIG. 11 ) and is provided rotatably, and the other end is provided rotatably on the other side wall 100b of the final sedimentation tank 100.

[0137] The end of the pipe material 108 that passes through the side wall 100a is located in a scum pit 111 that is provided on the outside of the side wall 100a. Therefore, the scum in the pipe material 108 can be discharged into the scum pit 111. The scum discharged into the scum pit 111 is taken out as shown by arrow j and sent to a scum treatment facility (not shown) for treatment.

[0138] The openings (upstream scum intake port 109, downstream scum intake port 110) of the pipe material 108 are formed parallel to each other and spaced apart in the circumferential direction of the pipe material 108. Both ends of each opening 109, 110 are located near the side walls 100a, 100b of the final sedimentation tank 100. The length of each opening 109, 110 is approximately equal to the width of the final sedimentation tank 100.

[0139] A rotation mechanism 112 including a motor is provided on the upper surface of the other side wall 100b of the final settling tank 100. This rotation mechanism 112 is configured to rotate the pipe 108 back and forth within a predetermined rotation angle by vertically driving a drive rod 114 connected to an arm 113 protruding from one end of the pipe 108. Note that the rotation mechanism 112 may be configured so that the pipe 108 is rotated back and forth manually without a motor or the like.

[0140] A scum guide plate (guide plate) 115 is provided on one side wall of the pipe material 108. This scum guide plate 115 is a guide plate made of steel or synthetic resin and has a rectangular planar shape, and is provided so as to extend a predetermined distance upstream (to the left in the illustrated example) from the position of the lower side that forms one opening 109 of the pipe skimmer 106 (an opening located upstream of the final sedimentation tank 100; an upstream scum intake port).

[0141] That is, one end side (the right side in the drawing) of this scum guide plate 115, which corresponds to the base of the scum guide plate 115, is joined to the lower side of the opening 109, and extends at an angle with respect to the radial direction of the pipe material 108. The guide plate 115 is curved so that the other end side, i.e., the tip portion 115a of the scum guide plate 115, is convex on the upper surface.

[0142] Due to this shape, when the tip 115a of the scum guide plate 115 protrudes above the water surface (FIG. 13A), the flow of scum S is blocked by the scum guide plate 115. When the tip 115a of the scum guide plate 115 is placed in the water (FIG. 13B), the surface (top surface) of the scum guide plate 115 is positioned at a downward slope from the upstream side toward the opening 109, so that the scum S flowing from the upstream side can be placed on the surface of the scum guide plate 115 and flowed down the downward slope, and taken into the opening 109.

[0143] As shown in Figure 13A, the opening (downstream scum intake port) 110 is arranged next to the opening 109 downstream when the opening 109 is positioned above the water surface. As described above, when the tip of the scum guide plate 115 is blocking the entry of scum S (Figure 13A), and when scum is being taken in by the upstream opening 109 (Figure 13B), the opening 110 is set in a positional relationship in which it is located above the water surface. When the pipe material 108 is rotated in the opposite direction (clockwise in Figures 13A to 13C) from the direction when taking in scum upstream, the lower edge of the opening 110 is arranged downstream and below the water surface.

[0144] Therefore, when the pipe 108 is rotated counterclockwise from the state shown in Figure 13A, the tip 115a of the scum guide plate 115 is placed in the water as shown in Figure 13B, and the scum S is guided into the opening 109 by passing over the surface (upper surface) of the scum guide plate 115. When the pipe 108 is rotated clockwise from the state shown in Figure 13A, a part of the opening 110 is placed in the water as shown in Figure 13C, making it possible to take in the scum floating on the downstream side of the pipe 108 into the opening 110. In this state shown in Figure 13C, the upstream scum guide plate 115 protrudes significantly above the water surface.

[0145] The rotation of the pipe material 108 by the rotation mechanism 112 is controlled by a programmable controller (not shown) that controls the entire final settling tank 100 including the third scum removal device 105.

[0146] The water injection nozzle 107 is placed underwater and sprays pressurized water toward the water surface where the scum S has risen to the surface, creating a current of water from underwater that sweeps the rising scum downstream. The water injection nozzle 107 has a flat cylindrical tip 121 that is wider than it is tall, and a valve body 123 that is provided inside the cylindrical tip 121 and that can open and close an opening 122 in the cylindrical tip 121.

[0147] This valve body 123 has its base end supported by a shaft 124 within the cylindrical tip portion 121 so as to be freely rotatable, and rotates up and down between a position where it abuts against the underside of the upper wall 121a of the cylindrical tip portion 121, forming an opening 122 between the underside of the valve body 123 and the lower wall 121b of the cylindrical tip portion 121, as shown in Figure 14A, and a position where it abuts against the upper surface of the lower wall 121b of the cylindrical tip portion 121, closing the opening 122, as shown in Figure 14B.

[0148] Valve element 123 has a weight that causes it to rotate downward under its own weight when pressurized water is not supplied, thereby closing opening 122, and when pressurized water is supplied, causes it to rotate upward under the pressure of the pressurized water, thereby opening opening 122. In addition, a rising plate 124a is integrally formed at the tip of valve element 123, which closes gap 130 that occurs between the upper surface of valve element 123 and upper wall 121a of cylindrical tip portion 121 when opening 122 is closed as shown in Figure 14B.

[0149] By providing this rising plate 124a, when the opening 122 is closed as shown in Figure 14B, the space above the valve body 123 (gap 130) is also closed by the rising plate 124a, thereby preventing scum and the like from entering the interior and causing clogging, and allowing the valve body 123 to operate smoothly.

[0150] A plurality of water injection nozzles 107 (five in the illustrated example) are provided in the water near the water surface at a predetermined distance upstream from the tip of the scum guide plate 115, at predetermined intervals in a direction perpendicular to the flow in the final sedimentation tank 100. Each water injection nozzle 107 is connected to a water supply pipe 126 equipped with a flow control valve 125 midway, and pressurized water is supplied thereto.

[0151] The direction of injection of pressurized water from each water injection nozzle 107 is determined to be toward the pipe material 108 (from the upstream side to the downstream side). Therefore, when pressurized water is injected from each water injection nozzle 107, the flow rate of the surface water in the final sedimentation tank 100 is increased, and the scum S floating on the surface of the surface water can be sent toward the pipe material 108.

[0152] As already mentioned, in the final settling basin group E, little scum is generated because most of the scum S has been removed in the primary settling basin conduit A, the primary settling basin group B, and the final settling basin conduit D. Therefore, unlike the primary settling basin conduit A, etc., where scum adheres to the walls or sticks together, the scum is dispersed and floating on the water surface.

[0153] For this reason, the amount of water sprayed (spray pressure) from the water spray nozzle 107 is set to be less than the amount of water sprayed (spray pressure) from the submersible nozzles 13, 92, etc., provided on the primary sedimentation tank conduit A, the primary sedimentation tank group B, and the final sedimentation tank conduit D, etc., so that the scum S is not destroyed or scattered by the water spray, causing it to become cloudy or dissolve in the treated water.

[0154] In addition, in Figure 11, similar to the water conduit A, etc., a fluid ejection pipe 132 having a discharge port member 131 is provided inside the side walls 100a, 100b, and compressed air is ejected from underwater so that scum near the side walls 100a, 100b can be moved to the center, but if there is only a small amount of scum, the fluid ejection pipe 132 may be omitted.

[0155] Additionally, above the scum guide plate 115, there are provided a plurality of water spray nozzles 127 that spray water toward the scum guide plate 115. These water spray nozzles 127 are well-known cleaning water spray nozzles that can separate and flush away contaminants that are lightly attached to objects, and are connected to a water supply pipe 129 that has a flow rate adjustment valve 128 midway through.

[0156] Next, the scum removal operation in the third scum removing device 105 having the above-described configuration will be described.

[0157] Final settling tank 100 is performing settling treatment, and openings 109, 110 of pipe skimmer 106 are positioned above the water surface as shown in Figure 13A. Upstream of opening 109, tip 115a of scum guide plate 115 protrudes above the water surface, blocking scum S. A thin film of scum S is generated on the water surface upstream of scum guide plate 115.

[0158] When the formation of scum S reaches a certain area, the pipe material 108 of the pipe skimmer 106 is rotated by the rotating mechanism 112. As a result, the scum guide plate 115 is submerged as shown in Figure 13B, a part of the upstream opening 109 is positioned underwater, and pressurized water is sprayed from each water spray nozzle 107.

[0159] The pressurized water sprayed from each water injection nozzle 107 is directed toward the opening 109 of the pipe material 108, and the flow of raw water, which has a slow flow rate due to the final sedimentation tank 100, is accelerated only at the surface by the water injection from the water injection nozzles 107, and the scum floating on the water surface is efficiently sent to the opening 109 of the pipe material 108.

[0160] In this case, the amount of water sprayed from the water spray nozzle 107 is small and is sprayed relatively slowly, so the scum S floats on the water surface or remains in the form of a thin film and moves with the current, and is taken into the pipe material 108 through the opening 109 and discharged into the scum pit 111.

[0161] At this time, the scum guide plate 115 is positioned near the water surface on the upstream side of the pipe material 108, so the scum can be efficiently guided to the opening 109 without being affected by an upward current from below. Therefore, the pipe skimmer 106 can remove scum in a short time, for example, by operating it once a day for about 5 to 7 minutes. The scum S discharged into the scum pit 111 is sent to a scum treatment facility for treatment.

[0162] After the scum S has been removed, the treated water flows into the overflow trough 102 downstream of the pipe skimmer 106, is extracted from the overflow trough 102 as shown by the arrow i in Figure 11, is disinfected, and then is released.

[0163] In this way, most of the scum S is taken into the opening 109 of the pipe 108, but a small amount may flow downstream of the pipe 108. Therefore, the pipe 108 is rotated from the state shown in Figure 13A in the opposite direction to when taking in the scum S on the upstream side, so that part of the opening 110 located on the downstream side is positioned below the water surface as shown in Figure 13C. This allows the scum S floating on the water surface to flow into the opening 110 and be discharged into the scum pit 111.

[0164] 13A, and, if necessary, spraying of water from the spray nozzle 127 is started to clean the surface of the scum guide plate 115. The water used to clean the guide plate 115 is allowed to flow through the opening 109 into the pipe 108. The surface of the scum guide plate 115 is cleaned by the spraying of water from the spray nozzle 127, which effectively prevents the scum S from adhering to the scum guide plate 115 and interfering with the next scum removal.

[0165] The third scum removal device 105 in the final settling tank group E configured as described above allows the small amount of scum S that is generated to flow relatively slowly, and can capture the scum S in the pipe skimmer 106 in a floating state on the water surface or in a thin film state without clouding the treated water.

[0166] This prevents deterioration of the quality of the discharged treated water, reduces the amount of water required to discharge the scum S, and provides the excellent effect of energy conservation. In other words, the third scum removal device 105 configured as described above has properties that can greatly contribute to so-called eco-friendly measures. Moreover, by providing the scum guide plate 115 with a curved tip, floating scum S can be efficiently flowed toward the opening 109, which also reduces the amount of water flowing into the pipe gap 106. In addition, the upper surface of the scum guide plate 115 is cleaned by spraying water from the spray nozzle 127, preventing any problems with the next scum removal.

[0167] The scum removal system in the sewage treatment plant configured as described above can efficiently remove scum using the first scum removal device 35 installed in the primary sedimentation tank conduit A, the second scum removal device 60 installed in the primary sedimentation tank group B, the scum removal device (similar in configuration to scum removal device 35) installed in the final sedimentation tank conduit D, and the third scum removal device 105 installed in the final sedimentation tank group E, thereby improving the efficiency of scum removal throughout the sewage treatment plant.

[0168] Therefore, the quality of treated water can be improved, the burden on the natural environment can be reduced, and scum removal using pipe gaps can be completed in a short time, reducing the amount of return water that accompanies this, which has the effect of achieving energy savings and significantly reducing the cost of scum treatment at sewage treatment plants.

[0169] The scum removal system for a sewage treatment plant according to the present invention has been described above with reference to the drawings. However, the specific configuration is not limited to the above-described embodiment, and design changes and the like are possible within the scope of the gist of the present invention.

[0170] For example, in the above-described embodiment, the fluid ejection pipes 72 and 79 are provided with the ejection outlet members 73, but the fluid ejection pipes themselves may have small holes formed therein without providing the ejection outlet members 73. However, if the ejection outlet members 73 are provided, the amount of compressed air can be increased. Furthermore, although compressed air is used as the fluid ejected from the fluid ejection pipes 72 and 79, the same effect can be obtained by using a water flow or pressurized water containing air bubbles.

[0171] Scum removal can be performed efficiently using scum removal equipment installed in the primary sedimentation basin conduit, primary sedimentation basin, final sedimentation basin conduit, and final sedimentation basin, depending on the situation. This improves the quality of treated water, reducing the environmental impact when it is released into the natural environment. Furthermore, because the amount of water flowing into the pipe gap with the scum is small and the scum can be removed in a short time, the amount of water returned from the pipe gap to the upstream is reduced, resulting in a reduction in the associated power consumption, energy savings, and reduced scum treatment costs at sewage treatment plants.

[0172] A: Conduit for primary sedimentation basin B: Group of primary sedimentation basins C: Reaction tank D: Conduit for final sedimentation basin E: Group of final sedimentation basins 2: Conduit body 3: Scum bit 4: Movable gate 6: Sedimentation basin (primary sedimentation basin) 7: Inlet 8: Opening / closing gate 9: Pipe 11: (For conduit) Water injection nozzle (above water nozzle) 13: (For conduit) Water injection nozzle (underwater nozzle) 20: Scum remover 21: Discharge member 22: Opening 23: Pressurized fluid supply unit 24: Pressurized fluid piping 35: First scum remover 52: Overflow trough 54: Scum pit 60: Second scum remover 61: (For primary sedimentation basin) Pipe gap 62: Pipe material 63: Scum intake port 70: Front wall panel 72: Fluid ejection pipe 73: Discharge member 74: Opening 78 Discharge outlet member 79 Fluid jet pipe 80 Guide plate 90, 91 (For primary sedimentation tank) Water injection nozzle (above water nozzle) 92 (For primary sedimentation tank) Water injection nozzle (underwater nozzle) 100 Sedimentation tank (final sedimentation tank) 102 Overflow trough 105 Third scum removal device 106 (For final sedimentation tank) Pipe gapper 107 (For final sedimentation tank) Water injection nozzle 108 Pipe material 109 Opening (upstream scum intake port) 110 Opening (downstream scum intake port) 111 Scum pit 112 Rotating mechanism 115 Scum guide plate (guide plate) 123 Valve body 124a Rising plate 127 Sprinkler nozzle

Claims

1. A scum removal system for a sewage treatment plant that removes scum from raw water being treated through a primary sedimentation basin conduit, a group of primary sedimentation basins, a reaction tank, a final sedimentation basin conduit, and a group of final sedimentation basins, comprising: a first scum removal device provided in the primary sedimentation basin conduit and the final sedimentation basin conduit, a second scum removal device provided in each primary sedimentation basin of the group of primary sedimentation basins; and a third scum removal device provided in each final sedimentation basin of the group of final sedimentation basins; the first scum removal device comprises a scum peeling device that extends along the flow direction of the raw water inside both side walls of the conduit main body through which the raw water flows and has a plurality of openings spaced apart in the length direction, the scum peeling device comprising a pair of pipes positioned below the scum, and a pressurized fluid supply unit that supplies pressurized fluid from a pressurized fluid supply source to these pipes; and a water jet nozzle for the conduit that moves the scum to the scum pit side provided at the end of the conduit main body. The second scum removal device comprises: a pipe skimmer for a primary sedimentation tank that collects the scum; a scum guide mechanism that collects the scum toward the center of the width of the primary sedimentation tank; and a water injection nozzle for the primary sedimentation tank that moves the scum toward the pipe skimmer for the primary sedimentation tank; and the third scum removal device comprises: a pipe skimmer for a final sedimentation tank that collects the scum; and a water injection nozzle for a final sedimentation tank that moves the scum toward the pipe skimmer for the final sedimentation tank; and the water injection nozzle for the final sedimentation tank is set to inject less water than the water injection nozzle for the water conduit.

2. A scum removal system for a sewage treatment plant as described in claim 1, characterized in that the pipe skimmer for the final sedimentation tank is equipped with a scum guide plate that is positioned below the water surface in front of the opening for receiving the scum and guides the scum while causing it to flow.

3. A scum removal system for a sewage treatment plant as described in claim 1, wherein the scum guide mechanism comprises: a front wall plate arranged below the opening for receiving the scum of the pipe skimmer for the primary sedimentation tank; and a pair of guide plates arranged so that the distance between them gradually increases toward the upstream side from which raw water flows from both ends of the front wall plate; and a fluid ejection pipe is provided near the front wall plate and the guide plates for ejecting a pressurized fluid that rises from the lower ends of the front wall plate and the guide plates along the surfaces of the front wall plate and the guide plates on the side from which the raw water flows. The scum removal system for a sewage treatment plant as described in claim 1, characterized in that the scum guide mechanism comprises: a front wall plate arranged below the opening for receiving the scum of the pipe skimmer for the primary sedimentation tank; and a pair of guide plates arranged so that the distance between them gradually increases toward the upstream side from which raw water flows from both ends of the front wall plate.

4. A scum removal system for a sewage treatment plant as described in claim 1, wherein the pipe gap for the final sedimentation tank has a pipe material arranged along the width direction of the final sedimentation tank and a rotation mechanism for rotating the pipe material around its axis, the pipe material has an upstream scum inlet formed on the upstream side and a downstream scum inlet formed on the downstream side spaced circumferentially, and the rotation mechanism positions the upstream scum inlet on the water surface by rotating the pipe material in one direction, and positions the downstream scum inlet on the water surface by rotating the pipe material in the direction opposite to the one direction.

5. A scum removal system for a sewage treatment plant as described in claim 1, characterized in that a plurality of the pressurized fluid supply units are provided and connected to a plurality of locations of the pipe, respectively.

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