Liquid mixing apparatus and sludge thickening system

Abstract

To provide a liquid mixing device and sludge thickening system that can effectively agitate and mix liquids such as sludge with chemicals such as polymer flocculants with a simple configuration. [Solution] The sludge thickening system 1-1 comprises a coagulation and mixing tank 80 to which sludge generated at a wastewater treatment plant is supplied by a sludge supply pipe 20, and a thickening device 90 for solid-liquid separation of the coagulated sludge coagulated in the coagulation and mixing tank 80. A coagulant supply pipe 60 for supplying a coagulant is connected in the middle of the sludge supply pipe 20, and the point of connection is designated as the coagulant injection point B1. A branch pipe section A11 is provided in the sludge supply pipe 20 downstream of the coagulant injection point B1, where it branches into two. The branch pipe A15 on the side of the branch pipe section A1 that bends at a right angle is connected to the coagulation and mixing tank 80 as the sludge supply pipe 20, and the other branch pipe A13 is closed to form a fluid stirring and mixing section A133.

Description

Technical Field

[0001] The present invention relates to a liquid mixing device and a sludge concentration system suitable for mixing a liquid such as sludge generated in a sewage treatment plant or the like with a chemical such as a polymer flocculant.

Background Art

[0002] Conventionally, for example, in a sewage treatment plant or the like, a sludge concentration system is used to concentrate the sludge discharged from the sewage treatment plant. As a sludge concentration system, for example, in Patent Document 1, after injecting a first polymer flocculant from a first chemical injection means (70) into the sludge transferred from a sludge storage tank (10) by a transfer pump (20), it is mixed and stirred by a first flocculation device (40) and introduced into a second flocculation device (80), and in the second flocculation device (80), while injecting a second polymer flocculant from a second chemical injection means (90) and stirring, a flocculation flock is formed, and then in a sludge dehydrator (100), a sludge flocculation dehydration device (1-1) that separates the flocculated sludge into a dewatered cake and a filtrate is disclosed.

[0003] In the sludge flocculation dehydration device (1-1) of Cited Document 1, since the first polymer flocculant is directly injected (line injection) into the pipe for transferring sludge from the sludge storage tank (10) to the first flocculation device (40), stirring and mixing of the sludge and the polymer flocculant are performed in advance in the pipe before being introduced into the first flocculation device (40). However, sufficient stirring and mixing could not be achieved only by the stirring and mixing by the line injection. If the stirring and mixing of the sludge and the polymer flocculant in the pipe by the line injection can be performed more effectively, the flocculation reaction in the subsequent flocculation device will also become more suitable.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The present invention has been made in view of the above-mentioned points, and its objective is to provide a liquid mixing device and a sludge thickening system that can effectively agitate and mix a liquid such as sludge with a chemical such as a polymer flocculant with a simple configuration. [Means for solving the problem]

[0006] The present invention relates to a liquid mixing device that mixes a liquid with a chemical by adding a chemical to a liquid supply pipe through which a liquid flows, characterized in that a chemical supply pipe for supplying the chemical is connected in the middle of the liquid supply pipe, the point of connection is designated as the chemical injection point, a branch pipe section is provided in the liquid supply pipe downstream of the chemical injection point that branches into two, the more bent branch pipe of the branch pipe section is designated as the liquid supply pipe through which the liquid flows, and the other branch pipe is closed to form a fluid stirring and mixing section. According to the present invention, a liquid stirring and mixing section (closed area) can be formed with a simple configuration that involves providing a branched pipe section. In this closed section of the liquid stirring and mixing area, the liquid and chemicals reverse and flow backward, disrupting the flow and allowing for effective stirring and mixing of the liquid and chemicals. In other words, according to the present invention, the stirring and mixing action between the liquid and the chemical, which occurs when the chemical is injected into the liquid supply piping, can be greatly enhanced by simply providing a branched pipe section and closing one end of it.

[0007] In addition to the above features, the present invention is characterized in that the liquid is sludge generated at a wastewater treatment plant, and the chemical is a coagulant that coagulates the sludge. According to the present invention, sludge and a flocculant can be effectively stirred and mixed in a liquid supply pipe, and for example, coarse flocs can be effectively formed in a subsequent process.

[0008] The present invention relates to a sludge thickening system comprising a coagulation and mixing tank to which sludge generated at a wastewater treatment plant is supplied via a sludge supply pipe, and a thickening device for separating the coagulated sludge coagulated in the coagulation and mixing tank into solid and liquid components, characterized in that a coagulant supply pipe for supplying a coagulant is connected in the middle of the sludge supply pipe, the point of connection is designated as the coagulant injection point, a branch pipe section is provided in the sludge supply pipe downstream of the coagulant injection point that branches into two, the more bent branch pipe of the branch pipe section is connected to the coagulation and mixing tank as the sludge supply pipe, and the other branch pipe is closed to form a fluid stirring and mixing section. Wastewater treatment plants include sewage treatment plants, water treatment plants, human waste treatment plants, and industrial wastewater treatment plants. According to the present invention, a liquid stirring and mixing section (closed area) can be formed with a simple configuration that involves providing a branched pipe section. In this closed section of the liquid stirring and mixing section, the sludge and coagulant reverse and backflow, disrupting the flow and promoting the coagulation reaction. This promotes the formation and coarsening of coagulated flocs that are coagulated in the coagulation mixing tank, and improves the concentration performance in the concentration device (improving the concentrated sludge concentration and SS recovery rate). Furthermore, it is possible to reduce the coagulant injection rate and to miniaturize the coagulation mixing tank. In other words, according to the present invention, the stirring and mixing action between sludge and coagulant, which occurs when a coagulant is injected into the sludge supply piping, can be further greatly enhanced simply by providing a branch pipe section with a simple structure.

[0009] In addition to the above features, the present invention is characterized in that the distance from the coagulant injection point of the sludge supply piping to the branch pipe section is 2m or more, and the distance from the branch pipe section to the coagulation mixing tank is 0.5m or more. According to the present invention, by ensuring sufficient distance from the coagulant injection point to the branching point of the sludge supply piping, and from the branching point to the coagulation mixing tank, it is possible to secure sufficient reaction time for the sludge and coagulant solution within the sludge supply piping, thereby promoting the coagulation reaction.

[0010] In addition to the above features, the present invention is characterized in that the wastewater treatment plant is a sewage treatment plant. Among wastewater treatment plants, sewage treatment plants generate a large amount of unconcentrated sludge, and therefore require a particularly large coagulation and mixing tank capacity to ensure sufficient time for the coagulation reaction. For this reason, applying the present invention to a sewage treatment plant can effectively reduce the capacity of the coagulation and mixing tank. In other words, the present invention offers a particularly significant effect in miniaturizing the coagulation and mixing tank.

[0011] In addition to the above features, the present invention is characterized in that the concentration device is a gravity filtration type concentration device. Gravity filtration concentrators include elliptical plate type filtration concentrators and belt type filtration concentrators. An elliptical plate type filtration and concentration device is a concentration machine that has a structure in which multiple rotating elliptical plates (elliptical cylinders) are arranged so that their respective axes of rotation are parallel, and solid matter (sludge) dropped onto these rotating elliptical plates is transported by the rotation of each elliptical plate, while at the same time the separated liquid is dropped between the rotating elliptical plates by gravity, thereby separating the liquid. A belt-type filtration and thickening device is a thickening machine that concentrates sludge by introducing it onto a belt and filtering it through gravity via the belt. Gravity filtration concentrators perform solid-liquid separation by gravity, so it is more effective if the coagulated flocs are soft and coarse due to their moisture content. According to the present invention, the coarsening of coagulated flocs can be performed more reliably, and therefore the present invention is particularly suitable for use in gravity filtration concentrators among concentrators. [Effects of the Invention]

[0012] According to the present invention, a simple configuration consisting of a branched pipe section allows for effective stirring and mixing of liquids such as sludge and chemicals such as coagulants. [Brief explanation of the drawing]

[0013] [Figure 1] This is a schematic diagram of the sludge thickening system 1-1. [Figure 2]This diagram shows the piping configuration of the sludge supply pipe 20 from the coagulant injection point B1 to the coagulation mixing tank 80. [Figure 3] This is an enlarged cross-sectional view of branch pipe section A1. [Figure 4] This figure shows experimental results of the coagulation state when the coagulant injection point is changed or when a conventional piping structure is used. [Modes for carrying out the invention]

[0014] Embodiments of the present invention will be described in detail below with reference to the drawings. Figure 1 is a schematic diagram of a sludge thickening system 1-1 according to one embodiment of the present invention. In this example, the case of a sewage treatment plant to which the sludge thickening system 1-1 is applied will be described. As shown in the figure, the sludge thickening system 1-1 includes a raw sludge storage tank 10 for temporarily storing sludge generated at a sewage treatment plant, a sludge supply pump 30 for transferring the sludge stored in the raw sludge storage tank 10 to the coagulation and mixing tank 80 described below via a sludge supply pipe 20, a sludge flow meter 40 for measuring the flow rate of sludge transferred through the sludge supply pipe 20 by the sludge supply pump 30, a sludge concentration meter 45 for measuring the concentration of sludge transferred through the sludge supply pipe 20 by the sludge supply pump 30, and a coagulant dissolving tank 50 for temporarily storing a coagulant solution (also called a polymer coagulant solution, polymer solution, or chemical). The system comprises a coagulant supply pump (polymer supply pump) 70 that injects the coagulant solution stored in the coagulant dissolving tank 50 into the middle of the sludge supply pipe 20 via the coagulant supply pipe 60; a coagulant flow meter (polymer flow meter) 75 that measures the flow rate of the coagulant being transported through the coagulant supply pipe 60 by the coagulant supply pump 70; a coagulation mixing tank 80 that is connected to the sludge supply pipe 20 and receives the sludge and coagulant mixed in the sludge supply pipe 20, further mixes and coagulates them; and a concentration device 90 that introduces the coagulated sludge, whose formation and enlargement of coagulated flocs have been promoted in the coagulation mixing tank 80, and concentrates it (solid-liquid separation).

[0015] And in this sludge thickening system 1-1, a branch pipe portion A1 is provided at a position on the downstream side by a predetermined dimension from the flocculant injection point B1 which is the connection point connecting the flocculant supply pipe 60 of the sludge supply pipe 20.

[0016] The raw sludge storage tank 10 is a water tank that stores, as raw sludge, for example, primary sedimentation sludge (raw sludge) obtained by solid-liquid separation in the first sedimentation tank of a sewage treatment plant, excess sludge obtained by solid-liquid separation in the final sedimentation tank, or mixed sludge thereof.

[0017] The flocculant dissolution tank 50 is a water tank for dissolving a polymer flocculant as a flocculant. Examples of the polymer flocculant include an anionic polymer flocculant, a nonionic polymer flocculant, a cationic polymer flocculant, and an amphoteric polymer flocculant.

[0018] The flocculation mixing tank 80 is a device that promotes the generation and enlargement of flocculation flocs by stirring the raw sludge to which the flocculant is added, and is configured by installing a stirrer that is rotationally driven by a motor in the flocculation mixing tank 80.

[0019] The thickening device 90 is preferably a gravity filtration type thickening device that separates the flocculation flocs input from the flocculation mixing tank 80 by gravity and thickens the sludge to a predetermined concentration. In this example, an elliptical plate type filtration thickening device is used. The elliptical plate type filtration thickening device is installed by arranging a plurality of rotating elliptical plates (elliptical columns) in a belt shape such that each rotation axis is parallel, and while transporting the solids (sludge) dropped on these rotating elliptical plates by the rotation of each elliptical plate, at the same time, the separation liquid is dropped by gravity from between the rotating elliptical plates to separate the liquid component. The solids transported on the elliptical plates are carried out as thickened sludge, and the separated liquid component (separation liquid) is collected at the lower part of the thickening device 90 and discharged.

[0020] Figure 2 shows the piping configuration of the sludge supply piping 20 from the coagulant injection point B1 to the coagulation mixing tank 80, and Figure 3 is an enlarged cross-sectional view of the branch pipe section A1. Note that the piping portion in Figure 2 excluding the coagulation mixing tank 80 constitutes the liquid mixing device of the present invention. As shown in these figures, the branch pipe section A1 is located in the middle of the sludge supply piping 20 downstream of the coagulant injection point B1. The branch pipe section A1 constitutes a part of the sludge supply piping 20.

[0021] Branch pipe section A1 is a piping structure that branches the upstream sludge supply pipe 20 into two, and in this example, it is specifically constructed using a T-joint (tee). Branch pipe section A1 is T-shaped and consists of a first branch pipe A11 that connects to the sludge supply pipe 20 on the raw sludge storage tank 10 side, a second branch pipe A13 that extends linearly from the first branch pipe A11, and a third branch pipe A15 that is connected almost perpendicularly to the first and second branch pipes A11 and A13. In other words, it is a piping structure that branches the sludge flowing in from the first branch pipe A11 to the second branch pipe A13 and the third branch pipe A15.

[0022] The tip of the second branch pipe A13 is closed by a closing plate A131, thereby creating a closed area inside the second branch pipe A13, which is a fluid stirring and mixing section A133. The tip of the third branch pipe A15 is connected to the sludge supply pipe 20 on the coagulation and mixing tank 80 side.

[0023] As explained above, the branch pipe section A1 is provided to branch the sludge supply pipe 20 downstream of the coagulant injection point B1 into two. Of the second and third branch pipes A13 and A15 that branch in the branch pipe section A1, the third branch pipe A15, which is bent at a right angle, is used as the sludge supply pipe 20 through which the liquid flows, and the other second branch pipe A13 is closed, thereby configuring the inside of this second branch pipe A13 as a fluid stirring and mixing section A133.

[0024] In this embodiment, as shown in Figure 2, the length of the piping L1 from the coagulant injection point B1 to the tip of the branch pipe section A1 (second branch pipe A13) is 6 m, and the length of the piping L2 from the branch pipe section A1 to the coagulation mixing tank 80 is 2 m. The lengths of the first branch pipe A11, the second branch pipe A13, and the third branch pipe A15 that make up the branch pipe section A1 are each 0.15 m.

[0025] Next, the operation of the sludge thickening system 1-1 will be described. By driving the sludge supply pump 30 shown in Figure 1, sludge (primary sedimentation sludge and excess sludge, or a mixture thereof) is transferred from the raw sludge storage tank 10 to the coagulation and mixing tank 80 via the sludge supply pipe 20. The amount of sludge transferred is measured by the sludge flow meter 40, and the sludge concentration is measured by the sludge concentration meter 45.

[0026] Meanwhile, by driving the coagulant supply pump 70, the coagulant is transferred from the coagulant dissolving tank 50 via the coagulant supply piping 60 and injected into the sludge supply piping 20 at the coagulant injection point B1.

[0027] The sludge and coagulant are effectively mixed within the sludge supply pipe 20 downstream of the coagulant injection point B1 by this line injection, and are then transferred to the branch pipe section A1, where they are further effectively agitated and mixed.

[0028] The state of agitation and mixing of the coagulant-mixed sludge (hereinafter also referred to as "mixed sludge") in branch pipe section A1 is as shown by the arrows in Figure 3, for example. Specifically, the mixed sludge introduced into the first branch pipe A11 from the upstream side travels straight into the second branch pipe A13 (fluid agitation and mixing section A133), reverses and flows backward near the closing plate A131, and moves into the third branch pipe A15 while being strongly mixed (in a turbulent flow) with the newly entering mixed sludge from the first branch pipe A11 side, and is transported downstream. By providing a fluid agitation and mixing section A133 in branch pipe section A1 in this way, the sludge and coagulant can be effectively agitated and mixed.

[0029] Returning to Figure 1, the mixed sludge introduced into the coagulation mixing tank 80 is stirred and mixed by the rotational drive of the agitator inside, promoting the formation and enlargement of coagulated flocs. However, since the sludge and coagulant are thoroughly stirred and mixed in the sludge supply piping 20, including the branch pipe section A1, before being introduced into the coagulation mixing tank 80, the formation and enlargement of the coagulated flocs in the coagulation mixing tank 80 are more effectively promoted. The enlarged coagulated flocs formed at this time are large in diameter but are soft lumps containing a lot of water.

[0030] The mixed sludge, in which the formation and enlargement of flocculated flocs have been promoted, is then introduced into the thickening unit 90, where the solid components (concentrated sludge) and the separated liquid are separated by gravity. The sludge introduced into the thickening unit 90 contains few uncoagulated flocs and is enlarged, resulting in a good concentrated sludge concentration and SS recovery rate.

[0031] As described above, the present invention allows for effective stirring and mixing of sludge and coagulant through the configuration of the branch pipe section A1. However, the inventors have further discovered that the formation of coagulated flocs can be further improved by making the pipe length L1 from the coagulant injection point B1 to the tip of the branch pipe section A1, as shown in Figure 2, and the pipe length L2 from the branch pipe section A1 to the coagulation mixing tank 80, greater than or equal to a predetermined length. This will be explained below in conjunction with the case of a conventional piping structure.

[0032] Figure 4 shows the coagulation state of the flocculated flocs formed in the coagulation mixing tank 80 and the concentrated sludge concentration (%) and SS recovery rate (%) by the concentrating device 90 when the sludge thickening system 1-1 is operated in each of the following cases: when the coagulant injection point (polymer injection point) shown in Figure 2 is injection point B1, where the pipe length from the tip of branch pipe section A1 (second branch pipe A13) is L1 (L1 = 6 m); when the injection point is B2, located just before connecting to the first branch pipe A11 of the sludge supply pipe 20; and when the conventional piping structure without branch pipe section A1 is used and injection point B1 is used. In this example, the pipe length L2 from branch pipe section A1 to coagulation mixing tank 80 is fixed at 2 m. The conventional piping structure is an L-shaped piping structure without the second branch pipe A13 (i.e., liquid stirring and mixing section A133) of branch pipe section A1.

[0033] As shown in Figure 4, when the coagulant was injected at injection point B1, there were few fine flocs and no uncoagulated flocs; instead, the flocs were large and clustered together. In other words, there were many enlarged coagulated flocs (large flocs that were soft due to high water content). At this time, the concentrated sludge concentration by the concentration device 90 was 5.5%, and the SS recovery rate was 98.1%.

[0034] Next, when the polymer flocculant was injected at injection point B2, although there were slightly more unflocculated flocs compared to the case of injection point B1, the flocs were more cohesive. At this time, the concentrated sludge concentration by the concentration device 90 was 5.1%, and the SS recovery rate was 93.8%.

[0035] Next, when an L-shaped piping structure was adopted, without the liquid stirring and mixing section A133 instead of the branch pipe section A1, and the injection point of the coagulant was set to the injection point B1, the flocs were not clustered together, and a coagulated state was obtained in which many uncoagulated, fine flocs existed.

[0036] As can be seen from these results, even if the coagulant injection point is set to injection point B2, the effect of effective stirring and mixing of sludge and coagulant by the branch pipe section A1 can be obtained. Furthermore, if the coagulant injection point is set to injection point B1, which is located further upstream from branch pipe section A1, it was found that even more effective stirring and mixing of sludge and coagulant can be achieved, and solid-liquid separation can be performed more effectively. It was also found that even if the injection point is set to injection point B1, effective stirring and mixing of sludge and coagulant cannot be obtained unless the branch structure of branch pipe section A1 is used.

[0037] Experiments have confirmed that the effect of positioning the coagulant injection point upstream of branch pipe section A1 becomes particularly noticeable when the pipe length from the tip of branch pipe section A1 exceeds approximately 2m. This effect occurs because positioning the coagulant injection point more than a predetermined length upstream from branch pipe section A1 promotes the stirring and mixing of sludge and coagulant in the sludge supply pipe 20 before it enters branch pipe section A1, and simultaneously extends the coagulation reaction time.

[0038] Furthermore, by making the length L2 of the sludge supply pipe 20 downstream from branch pipe section A1 (towards the coagulation mixing tank 80) longer than a predetermined length, the sludge and coagulant that have been stirred and mixed in branch pipe section A1 can be further stirred and mixed in the sludge supply pipe 20, and at the same time the coagulation reaction time can be extended, which can more effectively promote the formation and enlargement of coagulated flocs in the coagulation mixing tank 80. In order to produce this effective effect, the length L2 of the pipe from branch pipe section A1 to the coagulation mixing tank 80 was set to 2m in the above experimental example, but experiments confirmed that this effect becomes particularly noticeable when the pipe length L2 exceeds about 0.5m.

[0039] Although the sludge supply piping 20 shown in Figures 1 and 2 above is depicted as a straight pipe both upstream and downstream of the branch pipe section A1, the same effect can be achieved even if the sludge supply piping 20 bends one or more times along its length.

[0040] In the above example, the first branch pipe A11 and the second branch pipe A13, which constitute the branch pipe section A1, are connected in a straight line, and the third branch pipe A15 is connected perpendicularly to the first and second branch pipes A11 and A13, thereby allowing most of the sludge flowing in from the first branch pipe A11 side to be introduced into the second branch pipe A13. In order to prevent the sludge flowing in from the first branch pipe A11 side from being directly transferred to the third branch pipe A15, the third branch pipe A15 may be connected at an angle that is more inclined than perpendicular toward the first branch pipe A11 side (an angle where the angle between the first branch pipe A11 and the third branch pipe A15 is less than 90 degrees), while the second branch pipe A13 is preferably connected in a straight line or at an angle close to a straight line toward the first branch pipe A11.

[0041] Furthermore, the first, second, and third branch pipes A11, A13, and A15 according to the present invention may be connected at various angles other than those described above, but it is preferable for the stirring and mixing of sludge and coagulant that the third branch pipe A15, which is connected to the coagulation mixing tank 80, is more bent than the second branch pipe A13, which is closed off, with respect to the direction in which the first branch pipe A11, which introduces sludge, is facing (the flow direction of the mixed sludge being transported inside the first branch pipe A11).

[0042] Although embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and various modifications are possible within the scope of the claims, specification, and drawings. Furthermore, any shape, structure, or material not directly described in the specification and drawings is within the scope of the technical idea of ​​the present invention as long as it achieves the function and effect of the present invention. For example, the raw sludge may be the primary sedimentation sludge (raw sludge), excess sludge, or a mixture thereof, as well as digested sludge, human waste treatment sludge, septic tank sludge, sludge / slurry containing suspended solids such as organic waste, or oily wastewater. Moreover, the present invention can be applied to sludge other than those described above.

[0043] Furthermore, as described above, the present invention may be used as a sludge thickening system for wastewater (sludge) generated at water treatment plants and industrial wastewater treatment plants, but it can also be used as a liquid mixing device for effectively mixing chemicals with various liquids other than sludge. In other words, the present invention can be applied to any liquid mixing device that adds chemicals to a liquid supply pipe through which the liquid to be treated flows and mixes the liquid and the chemicals in the liquid supply pipe.

[0044] In the above example, a gravity filtration type concentration device was used as the concentration device 90. However, any concentration device that concentrates and separates sludge with formed flocs can be used, such as a rotating disc type deliquidation device, a pressurized flotation type concentration device, or an atmospheric pressure flotation type concentration device.

[0045] Furthermore, the embodiments described above and shown in the figures can be combined, provided that there is no contradiction in their purpose and structure. Also, even if only a part of the descriptions above and shown in the figures is included, each can constitute an independent embodiment, and the embodiments of the present invention are not limited to a single embodiment that combines the above descriptions and figures. [Explanation of symbols]

[0046] 1-1...Sludge thickening system, 10...Raw sludge storage tank, 20...Sludge supply piping (liquid supply piping), 30...Sludge supply pump, 40...Sludge flow meter, 45...Sludge concentration meter, 50...Coagulant dissolving tank, 60...Coagulant supply piping (chemical supply piping), 70...Coagulant supply pump, 75...Coagulant flow meter (polymer flow meter), 80...Coagulation mixing tank, 90...Thickening device, A1...Branch pipe section, A11...First branch pipe, A13...Second branch pipe, A131...Closing plate, A133...Fluid stirring and mixing section, A15...Third branch pipe, B1...Coagulant injection point (chemical injection point).

Claims

1. In a liquid mixing device that adds a chemical to a liquid supply pipe through which a liquid flows and mixes the liquid and the chemical in the liquid supply pipe, A chemical supply pipe for supplying the chemical is connected to the middle of the liquid supply pipe, and the point of connection is designated as the chemical injection point. A liquid mixing device characterized by providing a branched pipe section in the liquid supply piping downstream of the chemical injection point, using the more bent branched pipe as the liquid supply piping through which the liquid flows, and closing the other branched pipe to form a fluid stirring and mixing section.

2. The liquid mixing apparatus according to claim 1, characterized in that the liquid is sludge generated at a wastewater treatment plant, and the chemical is a coagulant that coagulates the sludge.

3. A coagulation and mixing tank to which sludge generated at a wastewater treatment plant is supplied via a sludge supply pipe, A concentration device for separating solid and liquid coagulated sludge, which has been coagulated in the aforementioned coagulation mixing tank, In a sludge thickening system having, A coagulant supply pipe is connected to the middle of the sludge supply pipe to supply a coagulant, and the point of connection is designated as the coagulant injection point. A sludge thickening system characterized by providing a branch pipe section that branches into two in the sludge supply piping downstream of the coagulant injection point, connecting the more bent branch pipe of the branch pipe section to the coagulation mixing tank as the sludge supply piping, and closing the other branch pipe to form a fluid stirring and mixing section.

4. The sludge thickening system according to claim 3, characterized in that the distance from the coagulant injection point of the sludge supply piping to the branch pipe portion is 2 m or more, and the distance from the branch pipe portion to the coagulation mixing tank is 0.5 m or more.

5. The sludge thickening system according to claim 3, characterized in that the wastewater treatment plant is a sewage treatment plant.

6. The sludge thickening system according to claim 3, characterized in that the thickening device is a gravity filtration type thickening device.

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