Coagulation and sedimentation apparatus, water treatment apparatus and coagulation and sedimentation method

Abstract

To efficiently form a sludge blanket while enhancing the sludge concentration in a coagulation sedimentation device.SOLUTION: In a coagulation sedimentation device 5, processing object water including a coagulant and floc is supplied, the floc is coarsened by the coagulant and a sludge blanket is generated. The coagulation sedimentation device 5 comprises: a sludge blanket part 5A in which the sludge blanket is formed; a processing object water supply port 52 which is located in a lower part of the sludge blanket part 5A; a concentrated sludge take-out part 61 which is located in a lower part of the coagulation sedimentation device 5 and takes out the sedimented concentrated sludge; and a sludge take-out part 64 which is located in an upper part of the sludge blanket part 5A, substantially consecutively takes out the sludge included in the sludge blanket and re-circulates the sludge to the supply port 52.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a coagulating sedimentation device, a water treatment device including the same, and a coagulating sedimentation method. [Background technology]

[0002] Sludge blanket-type coagulation sedimentation devices that produce a sludge blanket are widely used in water treatment, wastewater treatment, and other applications. Water to be treated, containing a coagulant and flocs, is supplied to the coagulation sedimentation device. The supply inlet for the water to be treated is located at the bottom of the coagulation sedimentation device, and the water to be treated flows upward through the device. A sludge blanket, consisting of coarsened flocs, is formed inside the device. As the water to be treated passes through the sludge blanket, suspended matter and coagulated flocs in the water are captured by the sludge blanket, and the water to be treated is filtered. The thickened sludge that settles at the bottom of the coagulation sedimentation device is periodically discharged.

[0003] Patent Document 1 discloses a coagulation sedimentation device that discharges part of the sludge and recirculates the remainder. The sludge serves as the nucleus for flocs, efficiently generating them. Patent Document 2 discloses a coagulation sedimentation device that removes part of the sludge fed to the coagulation sedimentation device below the sludge blanket and recirculates it. The thickened sludge is discharged from the bottom of the coagulation sedimentation device. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-119061 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-181975 Summary of the Invention [Problem to be solved by the invention]

[0005] To maintain a stable sludge blanket, it is preferable to continuously circulate the sludge. However, the coagulation and settling device disclosed in Patent Document 1 discharges a portion of the sludge extracted for circulation, making it difficult to increase the concentration of the sludge. Low sludge concentration increases the amount of sludge, potentially increasing the cost of sludge treatment. In other words, the technology described in Patent Document 1 makes it difficult to achieve both stable sludge blanket formation and high sludge concentration. The coagulation and settling device disclosed in Patent Document 2 has separate discharge sections for thickened sludge and for sludge recirculation, making it easy to increase the concentration of the sludge. However, unreacted coagulant that should be used for floc formation in the sludge blanket is returned to the previous stage, preventing efficient floc formation within the sludge blanket.

[0006] An object of the present invention is to provide a coagulation and settling apparatus that can efficiently form a sludge blanket while increasing the concentration of waste sludge. [Means for solving the problem]

[0007] In the coagulating sedimentation apparatus of the present invention, water to be treated containing a coagulant and flocs is supplied, and the flocs are coarsened by the coagulant to produce a sludge blanket. The coagulating sedimentation apparatus has a sludge blanket section where the sludge blanket is formed, a supply inlet for water to be treated located below the sludge blanket section, a thickened sludge removal section located below the coagulating sedimentation apparatus for removing settled thickened sludge, and a sludge removal section located above the sludge blanket section for substantially continuously removing sludge contained in the sludge blanket and recirculating it to the supply inlet. The ratio of the time that sludge recirculation is stopped to the time that sludge recirculation is on is 20% or less. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a coagulation and settling apparatus that can efficiently form a sludge blanket while increasing the concentration of waste sludge. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic configuration diagram of a water treatment device according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram of a coagulation sedimentation device of the water treatment device shown in FIG. [Figure 3] FIG. 3 is a schematic configuration diagram of a water treatment device according to a modified example of the first embodiment of the present invention. [Figure 4] FIG. 4 is a schematic configuration diagram of a coagulation sedimentation device according to a second embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description, "above" and "below" mean above or below a certain zone or structure, and "top" and "bottom" mean the upper or lower part of a certain zone or structure itself, particularly the part above or below the center in the height direction.

[0011] FIG. 1 shows a schematic configuration of a water treatment device 1 according to a first embodiment of the present invention, and FIG. 2 shows a schematic configuration diagram of a coagulation settling device 5 of the water treatment device 1 shown in FIG. 1. The water treatment device 1 includes a first reaction tank 2, a second reaction tank 3, a coagulation tank 4, a coagulation settling device 5, a metering tank 7, and a regeneration tank 8. The first reaction tank 2, the second reaction tank 3, the coagulation tank 4, and the coagulation settling device 5 are installed on a supply line L1 for water to be treated. With respect to the flow direction of the water to be treated, the second reaction tank 3 is located downstream of the first reaction tank 2, the coagulation tank 4 is located downstream of the second reaction tank 3, and the coagulation settling device 5 is located downstream of the coagulation tank 4. A thickened sludge withdrawal line L2 and a sludge circulation line L3 are connected to the coagulation settling device 5. Thickened sludge that has settled at the bottom of the coagulation settling device 5 is withdrawn from the thickened sludge withdrawal line L2. The sludge circulation line L3 is connected to the second reaction tank 3. The metering tank 7 and the regeneration tank 8 are installed on the sludge circulation line L3. The regeneration tank 8 is located downstream of the metering tank 7 in the direction of sludge circulation. The type of water to be treated is not limited, but the water to be treated in this embodiment is fluorine-containing wastewater discharged from a semiconductor factory or the like.

[0012] The first reaction tank 2 is equipped with a calcium agent supply unit 21 for adding a calcium agent, causing the calcium agent to react with the water to be treated. To agitate the calcium agent and the water to be treated, the first reaction tank 2 is equipped with a motor-driven agitator blade 22. When the water to be treated contains fluorine, it is preferable to use a calcium agent. Ca(OH)2 (slaked lime) or CaCl2 is preferably used as the calcium agent.

[0013] The second reaction tank 3 is equipped with an inorganic flocculant supply unit 31 for adding an inorganic flocculant, causing the inorganic flocculant to react with the water to be treated. The second reaction tank 3 is equipped with a motor-driven agitator blade 32 for stirring the inorganic flocculant and the water to be treated. Examples of inorganic flocculants that can be used include, but are not limited to, aluminum-based flocculants (polyaluminum chloride (PAC), aluminum sulfate (aluminum sulfate), etc.) and iron-based flocculants (polyiron, ferric chloride, etc.). When the water to be treated contains fluorine, it is preferable to use PAC as the inorganic flocculant. A pH adjuster may also be added to adjust the pH of the water to be treated.

[0014] The coagulation tank 4 is equipped with a first organic polymer coagulant supply unit 41 that adds a first organic polymer (polymer) coagulant to the water to be treated, causing the first organic polymer coagulant to react with the water to be treated. The coagulation tank 4 is located between the second reaction tank 3 and the coagulation settling device 5. In order to agitate the first organic polymer coagulant and the water to be treated, the coagulation tank 4 is equipped with a motor-driven agitator blade 42. The first organic polymer coagulant may be cationic, anionic, nonionic, or amphoteric, but a cationic organic polymer coagulant is preferred.

[0015] The water treatment device 1 has a second organic polymer flocculant supply unit 9 (supply line L4) that adds a second organic polymer (polymer) flocculant to the water to be treated. The second organic polymer flocculant may be cationic, anionic, nonionic, or amphoteric, but an anionic organic polymer flocculant is preferred. That is, it is preferable to add the cationic organic polymer flocculant first, followed by the anionic organic polymer flocculant. While a dedicated tank can be provided for adding the second organic polymer flocculant to the water to be treated, this embodiment does not provide a dedicated tank to reduce the number of tanks. For this reason, in this embodiment, the second organic polymer flocculant supply unit 9 is provided at the inlet 51 for the water to be treated of the coagulation / sedimentation device 5. However, the second organic polymer flocculant supply unit 9 may also be provided in the section of the water supply line L1 between the coagulation tank 4 and the coagulation / sedimentation device 5, or more generally, between the coagulation tank 4 and the supply port 52.

[0016] The water to be treated undergoes the following treatment before being introduced into the internal space (sludge blanket section 5A) of the coagulation sedimentation device 5. The water to be treated is first introduced into the first reaction tank 2. A calcium agent is added to the water to be treated, and the fluorine and calcium react to produce calcium fluoride. Next, the water to be treated is introduced into the second reaction tank 3. An inorganic coagulant is added to the water to be treated, and the water to be treated and the inorganic coagulant are stirred. This causes microflocs to form in the water to be treated. Next, the water to be treated is introduced into the coagulation tank 4. A first organic polymer coagulant is added to the water to be treated, and the microflocs coagulate to form coagulated flocs. Next, a second organic polymer coagulant is added to the water to be treated. The water to be treated that has undergone the above treatment is introduced into the internal space of the coagulation sedimentation device 5 from the supply port 52 of the coagulation sedimentation device.

[0017] The coagulating sedimentation device 5 is a double-cylindrical vessel, with the outer portion of the double cylinder constituting the sludge blanket section 5A and the inner portion of the double cylinder constituting the sludge thickening section 5B. The sludge blanket section 5A and the sludge thickening section 5B are separated by a cylindrical inner wall 53. The sludge blanket section 5A, the sludge thickening section 5B, and the inner wall 53 are concentrically arranged, and the central axis CL of the coagulating sedimentation device 5 coincides with the central axes of the sludge blanket section 5A, the sludge thickening section 5B, and the inner wall 53. Therefore, the sludge blanket section 5A has an annular horizontal cross section, and the sludge thickening section 5B has a circular horizontal cross section. It is possible to arrange the sludge blanket section 5A inside the double cylinder and the sludge thickening section 5B outside the double cylinder, but it is preferable to make the outer portion of the double cylinder the sludge blanket section 5A, which makes it easier to ensure a large volume.

[0018] The coagulating sedimentation device 5 has a rotating shaft 54 ​​that rotates around a central axis CL of the coagulating sedimentation device 5. The rotating shaft 54 ​​is driven to rotate by a motor 55 provided above the coagulating sedimentation device 5. The coagulating sedimentation device 5 is provided with a supply pipe 57 for water to be treated that extends downward inside the coagulating sedimentation device 5. The supply pipe 57 is connected to the rotating shaft 54 ​​and rotates together with the rotating shaft 54 ​​around the central axis CL. Therefore, the rotating shaft 54 ​​and the motor 55 constitute a rotation drive mechanism 56 that rotates the supply pipe 57. The supply pipe 57 has a first portion 57A that has a connecting portion (not shown) with the rotating shaft 54 ​​and extends in the vertical direction so as to cover the rotating shaft 54, a second portion 57B that is connected to the first portion 57A and extends obliquely (i.e., in the vertical and radial directions), and a third portion 57C that is connected to the lower end of the second portion 57B and extends in the vertical direction. The upper end (inlet 51 for water to be treated) of the first section 57A is open, and the water supply line L1 and the second organic polymer flocculant supply line L4 terminate inside the open end. Preferably, multiple second sections 57B are provided; in this embodiment, two second sections 57B are provided at 180-degree intervals. The lower end of the third section 57C is provided with a water supply inlet 52 for water to be treated. The water supply inlet 52 for water to be treated is located inside the coagulation and settling device 5, below the sludge blanket section 5A and below the separation zone 5A2 (described later). A granulating blade 58 is provided on the side of the third section 57C of the supply pipe 57. The granulating blade 58 is a flat plate that protrudes in a direction perpendicular to the third section 57C. The granulating blade 58 agitates the water to be treated as the supply pipe 57 rotates, promoting the reaction between the second organic polymer flocculant and the flocs, and coarsening the flocs. Preferably, the granulating blade 58 is provided in multiple stages in the vertical direction.

[0019] According to this embodiment, the water to be treated containing a coagulant and flocs is supplied to the sludge blanket section 5A of the coagulating sedimentation device 5, where the flocs are coarsened by the coagulant, producing a sludge blanket in the sludge blanket section 5A. More specifically, the water to be treated supplied to the sludge blanket section 5A forms an upward flow and flows toward the top of the sludge blanket section 5A. During this time, the water to be treated is gently agitated by the granulating blades 58. This causes repeated collisions and rolling of the coagulated flocs, gradually increasing the particle size of the coagulated flocs and forming spherical pellets. The pellets form a sludge blanket (pellet blanket) due to their own weight and the upward flow of the water to be treated supplied from the supply port 52. As a result, the sludge blanket section 5A is divided into a coarsening zone 5A1, i.e., a zone where the reaction between the second organic polymer flocculant and the flocs progresses, causing the flocs to coarsen (grow), and a separation zone 5A2 located above the coarsening zone 5A1, i.e., a zone where the flocs coarsen and form a stable sludge blanket. The coarsening zone 5A1 roughly corresponds to the zone where the granulating blades 58 are provided and the zone below it, and for convenience, the height level of the top of the uppermost granulating blade 58 can be considered to be the boundary between the coarsening zone 5A1 and the separation zone 5A2. The reaction between the second organic polymer flocculant and the flocs is almost complete in the separation zone 5A2.

[0020] In separation zone 5A2, the coarse flocs are mainly used to separate flocs from the water to be treated (to purify the water to be treated). As a result, a relatively clear treated water zone (treated water zone 5C) is formed above separation zone 5A2. A treated water outlet 59 is provided at the top of treated water zone 5C. Treated water outlet 59 is a weir arranged around the outer wall 60 of the coagulating sedimentation device 5. The treated water flows into outlet 59 from a connecting passage (not shown) provided in the outer wall 60 and is discharged to the outside of the coagulating sedimentation device 5 through a treated water outlet line L5 connected to outlet 59.

[0021] Coarse flocs in the separation zone 5A2 flow over the top of the inner wall 53 into the sludge thickening section 5B. Because large flocs flow into the sludge thickening section 5B, the top of the inner wall 53 can be considered the upper end of the separation zone 5A2 or the sludge blanket section 5A. The sludge thickening section 5B collects and thickens some of the coarse flocs in the sludge blanket. The flocs settle inside the sludge thickening section 5B and settle to the bottom, where they are thickened. A thickened sludge removal section 61 is provided at the bottom of the coagulation-sedimentation device 5, more specifically near the bottom of the sludge thickening section 5B, for removing thickened sludge that has settled to the bottom of the coagulation-sedimentation device 5. A thickened sludge removal line L2 is connected to the thickened sludge removal section 61. To prevent the thickened sludge removal line L2 from passing through the sludge blanket section 5A, the lower part of the sludge thickening section 5B protrudes downward from the bottom of the sludge blanket section 5A, and the thickened sludge removal section 61 is provided on the side of this protruding part 62. The rotating shaft 54 ​​extends vertically inside the sludge thickening section 5B. An agitating blade 63 having a structure similar to the granulating blade 58 is provided on the side of the rotating shaft 54 ​​inside the sludge thickening section 5B. The agitating blade 63 agitates the thickened sludge inside the sludge thickening section 5B and prevents the sludge thickening section 5B from clogging with thickened sludge.

[0022] A sludge removal section 64 is provided above the sludge blanket section 5A. The sludge removal section 64 is connected to a sludge circulation line L3 for returning a portion of the sludge to the second reaction tank 3. That is, the sludge contained in the sludge blanket is substantially continuously removed from the sludge removal section 64 and ultimately recycled to the supply port 52. The sludge removal section 64 is located in the separation zone 5A2, i.e., above the uppermost granulation impeller 58 and below the top of the inner wall 53. In particular, it is preferable that the sludge removal section 64 be located below the separation zone 5A2. This is because the sludge concentration is higher in the lower part of the separation zone 5A2 than in the upper part. Furthermore, if the sludge removal section 64 is provided above the separation zone 5A2, not only sludge but also treated water is likely to flow into the sludge removal section 64, making it difficult to efficiently recirculate the sludge.

[0023] Thus, providing the sludge removal section 64 above the sludge blanket section 5A or in the separation zone 5A2 ensures sufficient reaction time for the second organic polymer flocculant to react with the treated water. That is, because the calcium agent, inorganic flocculant, and first organic polymer flocculant are added in their own tanks, sufficient reaction time is ensured. Therefore, the reaction between the calcium agent and flocculant and the treated water is essentially completed before the second organic polymer flocculant is added. In contrast, since the second organic polymer flocculant is released from the supply port 52 into the internal space of the coagulation-sedimentation device 5 before fully reacting with the treated water, it is desirable to ensure reaction time within the internal space of the coagulation-sedimentation device 5. For example, as described in Patent Document 2, providing the sludge removal section 64 at the bottom of the sludge blanket section 5A would result in the removal of unreacted second organic polymer flocculant, which would not only prevent effective use of the second organic polymer flocculant but also potentially prevent the formation of a good sludge blanket.

[0024] In this embodiment, first, the water to be treated containing the second organic polymer flocculant and flocs is supplied to the coagulation-sedimentation device 5 through the supply port 52 located inside the coagulation-sedimentation device 5. The second organic polymer flocculant (and furthermore, the action of the granulating blades 58) coarsen the flocs, and a stable sludge blanket is produced in the separation zone 5A2 above the supply port 52. The reaction between the second organic polymer flocculant and the water to be treated is almost completed in the coarsening zone 5A1. Therefore, by providing a sludge removal section 64 above the sludge blanket section 5A or in the separation zone 5A2, sufficient time is ensured for the second organic polymer flocculant to react with the water to be treated, enabling the sludge blanket to be efficiently formed.

[0025] The sludge circulation line L3 and the thickened sludge removal line L2 share a portion of their common line LB (shared section), and the common line LB is provided with a sludge transfer pump 10 and a flow meter 11. Specifically, the upstream section L2A of the thickened sludge removal line L2 and the upstream section L3A of the sludge circulation line L3 are provided independently and merge to form a single common line LB, which branches downstream into a downstream section L2C of the thickened sludge removal line L2 and a downstream section L3C of the sludge circulation line L3. This allows sludge recirculation and thickened sludge removal to be performed with a single sludge transfer pump 10, thereby reducing the cost of the water treatment device 1.

[0026] The water treatment device 1 further includes a switching means for switching between the sludge circulation line L3 and the thickened sludge discharge line L2. Specifically, the switching means includes a first valve V1 provided in the upstream portion L2A of the thickened sludge discharge line L2, a second valve V2 provided in the upstream portion L3A of the sludge circulation line L3, a third valve V3 provided in the downstream portion L2C of the thickened sludge discharge line L2, and a fourth valve V4 provided in the downstream portion L3C of the sludge circulation line L3. To stably form a sludge blanket, it is preferable to perform sludge discharge and recirculation substantially continuously. In contrast, it is preferable to perform thickened sludge discharge intermittently when the thickened sludge becomes highly concentrated. Therefore, under normal circumstances, the second valve V2 and the fourth valve V4 are open, and the first valve V1 and the third valve V3 are closed. In contrast, when thickened sludge is being removed, the second valve V2 and the fourth valve V4 are closed, and the first valve V1 and the third valve V3 are opened. Thickened sludge is removed for only a few minutes per hour. Therefore, even if the second valve V2 and the fourth valve V4 are closed and sludge recirculation is stopped during this time, the impact on the stable formation of the sludge blanket can be ignored. Note that the term "substantially continuously" as used above means that the time during which the second valve V2 and the fourth valve V4 are closed is short, and the ratio of the time during which sludge recirculation is stopped to the time during which sludge recirculation is performed is generally 20% or less, preferably 10% or less, and more preferably 5% or less.

[0027] The switching means includes a timer 12 to control the timing of opening and closing the first through fourth valves V1 through V4. The timer 12 can close the second valve V2 and the fourth valve V4 and open the first valve V1 and the third valve V3 at a predetermined time (e.g., 55 minutes after every hour), and then open the second valve V2 and the fourth valve V4 and close the first valve V1 and the third valve V3 at another predetermined time (e.g., 0 minutes after every hour), and repeat this process. Alternatively, the timer 12 can close the second valve V2 and the fourth valve V4 and open the first valve V1 and the third valve V3 after a predetermined time (e.g., 55 minutes), and then open the second valve V2 and the fourth valve V4 and close the first valve V1 and the third valve V3 after another predetermined time (e.g., 5 minutes), and repeat this process. As described above, by controlling the opening and closing timing of the first to fourth valves V1 to V4, the concentration of waste sludge can be increased. Although the sludge transfer pump 10 is always in operation, it is preferable to adjust the flow rate when the first valve V1 and the third valve V3 are open and when the second valve V2 and the fourth valve V4 are open. For this reason, it is preferable to use inverter control for the sludge transfer pump 10.

[0028] The second valve V2 and the fourth valve V4 may be left open when the thickened sludge is being removed. During this time, the recirculated sludge and the removed thickened sludge will mix, but as mentioned above, this is not a major problem because the time that the first valve V1 and the third valve V3 are open is limited. In this case, the second valve V2 and the fourth valve V4 are always open, so control by the timer 12 is not necessary. Alternatively, the second valve V2 and the fourth valve V4 can be eliminated. With this configuration, the sludge contained in the sludge blanket can be continuously removed from the sludge removal section 64.

[0029] The sludge flowing through the sludge circulation line L3 is metered in a metering tank 7 before being introduced into the regeneration tank 8. The metering tank 7 measures the flow rate of the sludge using the principle of a triangular weir. A bypass line L6 branches off from the sludge circulation line L3 upstream of the metering tank 7, and a valve V5 installed in the bypass line L6 is controlled so that a constant flow rate of sludge is introduced into the regeneration tank 8. The bypass line L6 is connected to the coagulation tank 4.

[0030] The regeneration tank 8 is equipped with an alkaline substance supply unit 81 that adds an alkaline substance, such as sodium hydroxide, to the sludge. To agitate the alkaline substance and sludge, the regeneration tank 8 is equipped with a motor-driven agitator blade 82. Adding the alkaline substance to the sludge raises the sludge's pH. This dissolves the insoluble aluminum hydroxide contained in the sludge, releasing adsorbed fluorine as fluoride ions, and regenerating the coagulant. It is desirable to add calcium hydroxide to the regeneration tank 8 and react the released fluorine with the calcium hydroxide to produce calcium fluoride. The regenerated coagulant is returned to the second reaction tank 3 through the sludge circulation line L3, thereby reducing the amount of inorganic coagulant used. In this embodiment, the sludge circulation line L3 connects the sludge discharge unit 64 to the second reaction tank 3. However, the sludge discharge unit 64 may also be connected to the coagulation tank 4, or to both the second reaction tank 3 and the coagulation tank 4. The metering tank 7 and the regeneration tank 8 may be omitted, but if the water to be treated contains fluorine, it is preferable to provide these facilities.

[0031] FIG. 3 shows a schematic configuration of a water treatment device 1 according to a modification of the first embodiment. In this modification, the thickened sludge extraction line L2 and the sludge circulation line L3 are provided completely independently, and the common line LB and switching means of the first embodiment are not provided (although a first valve V1 and a second valve V2 are provided). The thickened sludge extraction line L2 and the sludge circulation line L3 are provided with a first sludge transfer pump 10A / first flow meter 11A and a second sludge transfer pump 10B / second flow meter 11B, respectively. The rest of the configuration is the same as in the first embodiment. In this modification, although the number of sludge transfer pumps is increased, sludge recirculation and thickened sludge extraction can be performed independently, thereby increasing the operational flexibility of the water treatment device 1. Sludge recirculation does not need to be stopped even when thickened sludge is being extracted. Furthermore, the capacities of the first sludge transfer pump 10A and the second sludge transfer pump 10B can be determined according to the flow rates required for sludge recirculation and thickened sludge removal, respectively, which also reduces the cost of the sludge transfer pumps 10A and 10B.

[0032] FIG. 4 shows a schematic configuration of a water treatment device 1 according to a second embodiment. In this embodiment, the coagulating sedimentation device 5 is a single-cylindrical vessel. Only a sludge blanket section 5A is provided at the bottom of the coagulating sedimentation device 5. Thickened sludge settles at the bottom of the sludge blanket section 5A. For this reason, a thickened sludge removal section 61 is provided at the bottom of the sludge blanket section 5A. As in the first embodiment, a sludge blanket is formed in the sludge blanket section 5A. The sludge blanket section 5A includes a coarsening zone 5A1 that coarsens flocs and a separation zone 5A2 located above the coarsening zone 5A1 and separating the coarsened flocs from the water to be treated. A sludge removal section 64 is provided in the separation zone 5A2, preferably below the separation zone 5A2. As in the first embodiment, this embodiment also allows for efficient formation of a sludge blanket while increasing the sludge concentration. [Explanation of symbols]

[0033] 1 Water treatment equipment 2. First Reactor 3 Second Reactor 4 Coagulation tank 5 Coagulation sedimentation device 5A Sludge Blanket Section 5A1 Coarsening Zone 5A2 Separation Zone 5B Sludge thickening section 52 Inlet for treated water 53 Inner wall 56 Rotation drive mechanism 57 Treated water supply pipe 58 Granulating blade 61 Thickened sludge removal section 64 Sludge removal section 9. Second organic polymer flocculant supply section 10, 10A, 10B Sludge transfer pump L2 Thickened sludge removal line L3 Sludge circulation line LB shared line

Claims

1. A coagulation and settling device that receives treatment water containing a coagulant and flocs, coarsens the flocs with the coagulant, and produces a sludge blanket, a sludge blanket section where the sludge blanket is formed; a supply port for the water to be treated located at a lower portion of the sludge blanket section; a thickened sludge removal unit located at a lower portion of the coagulation sedimentation device and removing the settled thickened sludge; a sludge removal section located above the sludge blanket section for substantially continuously removing sludge contained in the sludge blanket and recycling the sludge to the supply inlet; and A coagulation and settling apparatus, wherein the ratio of the time during which the recirculation of the sludge is stopped to the time during which the recirculation of the sludge is performed is 20% or less.

2. a sludge thickening unit having the thickened sludge removal unit and collecting and thickening a portion of the coagulated flocs that have coarsened in the sludge blanket; An inner wall separating the sludge blanket section and the sludge thickening section, 2. The coagulation and sedimentation apparatus according to claim 1, wherein the sludge removal section is located below the top of the inner wall.

3. a supply pipe for the water to be treated extending downward inside the coagulation sedimentation device and having the supply port at its tip; a rotation drive mechanism that rotates the supply pipe; a granulating blade provided on a side surface of the supply pipe for coarsening the flocs; and 3. The flocculating sedimentation apparatus according to claim 2, wherein the sludge removal section is located above the granulating blades.

4. 4. The coagulation and sedimentation apparatus according to claim 1, wherein the sludge blanket unit is formed with a coarsening zone for coarsening the flocs and a separation zone located above the coarsening zone for separating the flocs from the water to be treated, and the sludge removal unit is located in the separation zone.

5. 5. The coagulation and settling apparatus according to claim 4, wherein the sludge removal section is located below the separation zone.

6. The coagulation and sedimentation device according to any one of claims 1 to 5; a reaction tank provided upstream of the coagulation settling device, including a supply unit for an inorganic coagulant, and for reacting the inorganic coagulant with the water to be treated; a coagulation tank provided between the reaction tank and the coagulation settling device, the coagulation tank including a supply unit for a first organic polymer coagulant, and the first organic polymer coagulant reacting with the water to be treated to form the flocs; a sludge circulation line connecting the sludge removal unit to the reaction tank or the coagulation tank; A water treatment device comprising:

7. 7. The water treatment device according to claim 6, further comprising a second organic polymer flocculant supply unit provided between the flocculation tank and the supply port, which adds a second organic polymer flocculant as the flocculant to the water to be treated.

8. a concentrated sludge removal line connected to the concentrated sludge removal unit and having a common line with the sludge circulation line; a sludge transfer pump provided in the common line; a switching means for switching between the sludge circulation line and the thickened sludge removal line; The water treatment device according to claim 6 or 7, comprising:

9. The water treatment device according to claim 6 , wherein the water to be treated contains fluorine.

10. supplying water to be treated containing a flocculant and flocs to a sludge blanket section of a coagulation settling device from a supply port located below the sludge blanket section; coarsening the flocs with the coagulant to form a sludge blanket in the sludge blanket section; removing the settled thickened sludge from a thickened sludge removal section located at the bottom of the coagulation sedimentation device; substantially continuously removing sludge contained in the sludge blanket from a sludge removal section located above the sludge blanket section and recirculating the sludge to the supply port; and A coagulation and sedimentation method, wherein the ratio of the time during which the recirculation of the sludge is stopped to the time during which the recirculation of the sludge is performed is 20% or less.

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