Sludge concentration method and sludge treatment system

Abstract

To reduce a cost of a sludge treatment.SOLUTION: A sludge treatment system 1 according to one embodiment includes a flocculation mixing tank 10 for adding a flocculant to sludge discharged from a water treatment system 2 to form a floc, and a separation device 20 for separating the floc into interstitial water and sludge solids while transporting the floc. The separating device 20 includes a separating screen to which floc is supplied, and a vibration mechanism for vibrating the separating screen. The separating screen has a plurality of openings having a diameter of at least 0.1 mm and at most 5.0 mm.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method and a system for treating sludge.

Background Art

[0002] Sludge is generated in sewage treatment plants, industrial wastewater treatment plants, etc. The sludge is finally disposed of after being subjected to various treatments according to its properties and contents. One of the treatments applied to the sludge is concentration treatment (volume reduction).

[0003] Patent Document 1 discloses a sludge concentration transfer device including a sludge concentration moving member on which sludge is placed and a vibration means for vibrating the sludge concentration moving member. According to Patent Document 1, by vibrating the sludge concentration moving member by the vibration means, the sludge can be conveyed in one direction, and the separation liquid of the sludge can be dropped from the separation liquid dropping holes provided in the sludge concentration moving member.

[0004] Patent Document 2 discloses a method and an apparatus for separating solid particles from a suspension. The method disclosed in Patent Document 2 includes a step of draining while classifying by rolling the precipitate separated by sedimentation from the suspension in a cylindrical container.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] Reduction of the cost required for sludge treatment is demanded.

Means for Solving the Problems

[0007] The sludge concentration method according to an embodiment includes a flocculation step of adding a flocculant to the sludge discharged from the water treatment system to form flocs, and a separation step of vibrating the separation screen to which the flocs are supplied to separate the flocs into interstitial water and sludge solids while conveying the flocs. The separation screen is provided with a plurality of openings having a width or diameter of 0.1 mm or more and 5.0 mm or less.

[0008] The sludge treatment system according to an embodiment includes a flocculation mixing tank for adding a flocculant to the sludge discharged from the water treatment system to form flocs, and a separation device for separating the flocs into interstitial water and sludge solids while conveying the flocs. The separation device includes a separation screen to which the flocs are supplied, and a vibration mechanism for vibrating the separation screen. The separation screen is provided with a plurality of openings having a width or diameter of 0.1 mm or more and 5.0 mm or less.

Advantages of the Invention

[0009] According to the present invention, it is possible to reduce the cost required for sludge treatment.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Embodiments for Carrying Out the Invention

[0011] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In all the drawings for explaining the embodiments, the same or substantially the same configurations and elements are denoted by the same reference numerals. Also, once a configuration or element has been described, a repeated explanation will not be given in principle.

[0012] (First Embodiment) <Overview of the sludge treatment system> FIG. 1 is a schematic diagram showing the configuration of a sludge treatment system 1 according to an embodiment. As shown in FIG. 1, the sludge treatment system 1 according to the present embodiment has a flocculation mixing tank 10, a separation device 20, a digestion tank 30, and a dehydrator 40.

[0013] The sludge treatment system 1 is a system for treating sludge. More specifically, the sludge treatment system 1 is a system for performing sludge thickening, digestion, etc. The sludge concentrated by the sludge treatment system 1 is discharged from a water treatment system 2 provided in a sewage treatment facility or an industrial wastewater treatment facility.

[0014] In the water treatment system 2, the polluted components contained in the influent water are converted into sludge by microorganisms. That is, in the water treatment system 2, the polluted components contained in the influent water are removed. As a result, water (treated water) from which the polluted components have been removed and sludge are discharged from the water treatment system 2.

[0015] The sludge treatment system 1 concentrates the sludge discharged from the water treatment system 2 as described above by a sludge thickening method including the steps described below. Note that the water treatment system 2 is not limited to those provided in sewage treatment facilities or industrial wastewater treatment facilities.

[0016] <Flocculation mixing tank / Flocculation step> The agglomeration mixing tank 10 is connected to the water treatment system 2, and sludge discharged from the water treatment system 2 flows in. The agglomeration mixing tank 10 is provided with a stirring device (not shown), and a flocculant is added to the inflowing sludge.

[0017] The flocculant is stored in a flocculant tank (not shown). A supply path for the flocculant is formed by a pipe between the flocculant tank and the agglomeration mixing tank 10, and a pump is provided on the supply path. However, the method of supplying the flocculant to the agglomeration mixing tank 10 and the equipment such as the stirring device are not limited to specific methods and equipment.

[0018] When a flocculant is added to the sludge in the agglomeration mixing tank 10, flocs are formed. More specifically, the solid components in the sludge are aggregated by the action of the flocculant, and flocs are formed.

[0019] Viewed from another perspective, in the agglomeration mixing tank 10, an agglomeration process is performed in which a flocculant is added to the sludge discharged from the water treatment system 2 to form flocs.

[0020] In the agglomeration process, the sludge to which the flocculant has been added may be stirred as necessary. For example, a stirring device equipped with a propeller, paddle, etc. is installed in the agglomeration mixing tank 10, and they are operated as necessary. By stirring the sludge to which the flocculant has been added, the flocculant is more uniformly dispersed in the sludge and appropriate flocs are formed.

[0021] <Separator / Separation Process> FIG. 2 is a schematic diagram showing the structure of the separation device 20 of the present embodiment. The separation device 20 has a trough 21, a vibration mechanism 22, and a separation screen 23.

[0022] The floc F composed of the interstitial water W and the sludge solids S formed in the agglomeration mixing tank 10 is supplied to the separation device 20. The separation device 20 separates the supplied floc F into the interstitial water W and the sludge solids S while transporting it.

[0023] Viewed in another way, the separation device 20 performs a separation process of separating the flock F composed of the interstitial water W and the sludge solids S into the interstitial water W and the sludge solids S. In the separation process, as a result of the separation of the interstitial water W from the flock F, the sludge is concentrated. Therefore, the separation process can be rephrased as a "concentration process", and the separation device 20 can be rephrased as a "concentration device 20".

[0024] <Trough> The trough 21 has a gutter shape, and the supply side to the digester 30 and the water treatment system 2 on the side opposite to the supply side of the flock F is open, and its interior is partitioned vertically by a separation screen 23. As a result, an upper trough 24 located above the separation screen 23 and a lower trough 25 located below the separation screen 23 are formed inside the trough 21.

[0025] In the following description, the upper trough 24 may be referred to as the "flock separation trough 24" and the lower trough 25 may be referred to as the "filtrate trough 25" for distinction.

[0026] <Vibration mechanism> The vibration mechanism 22 is disposed below the trough 21. The vibration mechanism 22 includes a support member 22a that enables the trough 21 to swing. The support member 22a is composed of an elastic member such as a leaf spring or a coil spring, for example.

[0027] The vibration mechanism 22 includes a drive source 22b and vibrates the trough 21. When the trough 21 vibrates, the separation screen 23 provided in the trough 21 also vibrates in the same manner as the trough 21. That is, the vibration mechanism 22 vibrates the trough 21 and the separation screen 23 integrally.

[0028] The drive source 22b of the vibration mechanism 22 is not particularly limited, and for example, an electromagnet or an electric motor is used. When the drive source 22b is an electromagnet, a current is intermittently passed through the electromagnet. As a result, the trough 21 vibrates by the cooperation of the magnetic force generated by the electromagnet and the elastic restoring force generated by the support member 22a such as a leaf spring.

[0029] Also, when the drive source 22b is an electric motor, an eccentric disk is attached to the rotating shaft of the electric motor. As a result, the trough 21 vibrates due to the cooperation between the centrifugal force generated as the eccentric disk rotates and the elastic restoring force generated by the support member 22a. Note that the vibration mechanism 22 only needs to be able to apply the necessary vibration to the trough 21, and the method of generating the vibration, its installation position, etc. are not particularly limited.

[0030] <Separation screen> The separation screen 23 is a metal plate having a plurality of circular openings 23a, and each opening 23a is formed by punching. That is, the separation screen 23 is a perforated metal.

[0031] As described above, the separation screen 23 divides the inside of the trough 21 into a floc separation trough 24 and a filtrate trough 25. In another view, the separation screen 23 forms the bottom surface of the floc separation trough 24. That is, a large number of holes are opened in the bottom surface of the floc separation trough 24.

[0032] <Transportation and separation> The floc F formed in the agglomeration mixing tank 10 is supplied to one end side in the longitudinal direction of the floc separation trough 24. In another view, the floc F is supplied onto the separation screen 23.

[0033] The floc F supplied onto the separation screen 23 moves in one direction on the separation screen 23 when the separation screen 23 vibrates. More specifically, the floc F moves on the separation screen 23 from one end side in the longitudinal direction of the separation screen 23 toward the other end side.

[0034] The moving direction of the floc F on the separation screen 23 as described above is the conveyance direction of the floc F by the separation device 20, and this direction is parallel or substantially parallel to the longitudinal direction of the separation screen 23.

[0035] Also, one longitudinal end side of the flock separation trough 24 to which the flock F is supplied is the upstream side in the conveyance direction, and the other longitudinal end side of the flock separation trough 24 is the downstream side in the conveyance direction.

[0036] In other words, one longitudinal end side of the separation screen 23 to which the flock F is supplied is the upstream side in the conveyance direction, and the other longitudinal end side of the separation screen 23 is the downstream side in the conveyance direction.

[0037] The flock F moving on the separation screen 23 is separated into the interstitial water W and the sludge solids S during its movement. The separation of the flock F into the interstitial water W and the sludge solids S is realized and promoted by the vibration of the separation screen 23 and the accompanying vibration of the flock F.

[0038] The interstitial water W separated from the sludge solids S by the vibration falls into the filtrate trough 25 through the openings 23a of the separation screen 23. On the other hand, the sludge solids S separated from the interstitial water W by the vibration are sent to the digestion tank 30.

[0039] That is, each opening 23a provided in the separation screen 23 has a size that allows the interstitial water W to pass through while preventing the sludge solids S from passing through.

[0040] However, since the separation screen 23 and the sludge solids S on the separation screen 23 are constantly vibrating, the sludge solids S do not clog the openings 23a. Therefore, the separation screen 23 does not need to be cleaned, or at least it is not necessary to frequently clean it using a large amount of cleaning water. Thus, the running cost of the separation device 20 and the entire system including the separation device 20 is reduced.

[0041] Here, the interstitial water W contained in the flock F supplied onto the separation screen 23 is gradually discharged from the separation screen 23 as the flock F moves from the upstream side to the downstream side in the conveyance direction, and accordingly, the concentration of the sludge solids S is increased.

[0042] Viewed another way, on the upstream side of the separation screen 23, the sludge solids S are not sufficiently consolidated. Therefore, there is a risk that a large amount of sludge solids S will flow out from the separation screen 23 together with the interstitial water W to be filtered. On the other hand, on the downstream side of the separation screen 23, the sludge solids S are sufficiently consolidated. Therefore, the amount of sludge solids S flowing out from the separation screen 23 together with the interstitial water W to be filtered is small.

[0043] Therefore, by making the size of the opening 23a provided on the upstream side of the separation screen 23 different from the size of the opening 23a provided on the downstream side of the separation screen 23, the efficiency of filtering the interstitial water W and concentrating the sludge solids S can be increased.

[0044] Specifically, the separation screen 23 is partitioned into a first region on the upstream side and a second region on the downstream side. Further, an opening 23a having a width or diameter smaller than that of the opening 23a provided in the second region is provided in the first region. For example, an opening 23a with a diameter of 1.0 mm is provided in the first region, and an opening 23a with a diameter of 1.5 mm is provided in the second region.

[0045] Also, it is configured by a combination of a first screen disposed on the upstream side of the separation screen 23 and a second screen disposed on the downstream side. Further, an opening 23a smaller than the opening 23a provided in the second screen is provided in the first screen. For example, an opening 23a with a diameter of 1.0 mm is provided in the first screen, and an opening 23a with a diameter of 1.5 mm is provided in the second screen.

[0046] From the viewpoint of improving the separation accuracy and separation efficiency, the diameter D of the opening 23a is preferably 0.1 mm or more and 5.0 mm or less, and more preferably 0.3 mm or more and 5.0 mm or less. Also, the opening ratio of the separation screen 23 is preferably 10% or more, and more preferably 20% or more and 50% or less.

[0047] Further, the vibration direction of the separation screen 23 preferably has an angle of 10 degrees or more and 80 degrees or less with respect to the conveyance direction of the flock F. The amplitude of the separation screen 23 is preferably 0.01 mm or more and 50.0 mm or less, and the vibration frequency is preferably 1 time / second or more and 1,000 times / second or less.

[0048] Furthermore, the vibration direction of the separation screen 23 more preferably has an angle of 15 degrees or more and 60 degrees or less with respect to the conveyance direction of the flock F. The amplitude of the separation screen 23 is more preferably 0.05 mm or more and 10.0 mm or less, and the vibration frequency is more preferably 10 times / second or more and 500 times / second or less.

[0049] FIG. 3 is an explanatory diagram showing the relationship between the conveyance direction of the flock F and the vibration direction of the separation screen 23.

[0050] The vibration mechanism 22 vibrates (reciprocates) the separation screen 23. In the present embodiment, the vibration mechanism 22 vibrates (reciprocates) the separation screen 23 obliquely. More specifically, the vibration mechanism 22 vibrates (reciprocates) the separation screen 23 in the direction indicated by the arrow A in FIG. 3.

[0051] Therefore, the inclination angle θ1 of the arrow A with respect to the conveyance direction of the flock F corresponds to the angle that the vibration direction of the separation screen 23 has with respect to the conveyance direction of the flock F. It should be noted that the conveyance direction of the flock F is parallel or substantially parallel to the longitudinal direction of the separation screen 23 as already described.

[0052] By vibrating the separation screen 23 obliquely with respect to the conveyance direction of the flock F, the conveyance and separation of the flock F are realized simultaneously and more reliably.

[0053] <Backflow process> Referring to FIG. 1 again. The interstitial water W separated by the separation device 20 is returned to the water treatment system 2. More specifically, the interstitial water W that has fallen into the filtrate trough 25 (FIG. 2) is returned to the water treatment system 2 as concentrated filtrate. In other words, a backflow process of returning the interstitial water W to the water treatment system is performed.

[0054] <Digester / Digestion Process> On the other hand, the sludge solids S separated by the separation device 20 are digested. More specifically, the sludge solids S are transferred to the digester 30 and anaerobically digested. The digester 30 is, for example, a tank made of metal or concrete having airtightness and corrosion resistance.

[0055] Viewed from another perspective, in the digester 30, a digestion process is performed in which the sludge solids S separated by the separation device 20 are heated to 35°C to 40°C in a state where air and light are blocked, and anaerobic digestion is carried out. In the digestion process, the sludge solids S are heated, stirred, and circulated as necessary. The sludge solids S are anaerobically digested for 20 to 30 days under the above conditions. However, the digestion period of the sludge is appropriately changed according to temperature conditions and the like.

[0056] Here, the sludge solids S stored in the digester 30 have a certain amount of interstitial water W removed by the separation device (concentration device) 20 and are concentrated. Viewed from another perspective, the sludge solids S processed in the digestion process have a certain amount of interstitial water W removed and are concentrated in the previous process (separation process / concentration process). That is, concentrated sludge is fed into the digester 30.

[0057] As a result, the volume of the digester 30 can be reduced to reduce the initial cost (construction cost). In addition, since the sludge solids S in the digester 30 can be heated, stirred, and circulated with less energy, the running cost can also be reduced.

[0058] Note that digestion gas is generated in the digestion process. More specifically, a part of the concentrated sludge stored in the digester 30 is converted into methane gas, carbon dioxide, etc. The digestion gas is used for power generation or for heating the concentrated sludge in the digester 30.

[0059] <Dehydrator / Dehydration Process> When the digestion process is completed, the thickened sludge is sent as digested sludge to the dehydrator 40. The dehydrator 40 removes moisture from the digested sludge to form a dewatered cake. The dewatered cake is taken out from the dehydrator 40 and finally disposed of.

[0060] Viewed another way, the dehydrator 40 performs a dehydration process of removing moisture from the digested sludge solids S to form a dewatered cake.

[0061] (Second Embodiment) <Overview of the sludge treatment system> Next, a sludge treatment system according to another embodiment will be described. However, the sludge treatment system according to this embodiment and the sludge treatment system 1 according to the first embodiment have many common points. Therefore, the description of the same configuration as that of the sludge treatment system 1 according to the first embodiment will be omitted as appropriate, and only the different configurations will be described.

[0062] <Separator / Separation process> FIG. 4 is a schematic diagram showing the structure of the separator 50 of this embodiment. The separator 50 has a trough 51, a vibration mechanism 52, and a separation screen 53, just like the separator 20 of the first embodiment, and performs a separation process similar to the separation process of the first embodiment.

[0063] More specifically, similar to the first embodiment, the flock F formed in the agglomeration mixing tank 10 is supplied to the separator 50. The separator 50 separates the supplied flock F into the interstitial water W and the sludge solids S while conveying it.

[0064] <Trough> The trough 51 has the same gutter shape as the trough 21. Also, the inside of the trough 51 is partitioned vertically by the separation screen 53. As a result, an upper trough 54 located above the separation screen 53 and a lower trough 55 located below the separation screen 53 are formed inside the trough 51. In the following description, the upper trough 54 may be referred to as the "flock separation trough 54" and the lower trough 55 may be referred to as the "filtrate trough 55" for distinction.

[0065] The flocs F formed in the agglomeration mixing tank 10 are supplied onto the separation screen 53 of the separation device 50. However, the separation device 50 of the present embodiment includes a floc supply path 60 that the separation device 20 does not have. In the present embodiment, the flocs F are supplied onto the separation screen 53 via this floc supply path 60.

[0066] <Floc supply path> The floc supply path 60 is located above the separation screen 53. More specifically, in the vertical direction, the floc supply path 60 is located above the separation screen 53, and in the conveyance direction of the flocs F, it is located upstream of the separation screen 53.

[0067] FIG. 5 is a partially enlarged view showing the floc supply path 60 shown in FIG. 4 and its vicinity. The floc supply path 60 includes an upstream flow path wall 61 and a downstream flow path wall 62 that face each other, and has a trough shape as a whole. The floc supply path 60 is installed such that the upstream flow path wall 61 is disposed upstream in the conveyance direction of the flocs F, and the downstream flow path wall 62 is disposed downstream in the conveyance direction of the flocs F.

[0068] Here, the upstream flow path wall 61 is lower than the downstream flow path wall 62. For this reason, the flocs F that have flowed into the floc supply path 60 flow out of the floc supply path 60 over the upstream flow path wall 61. Viewed in another way, the flocs F overflow the upstream flow path wall 61 toward the upstream in the conveyance direction of the flocs F. In other words, the flocs F overflow the upstream flow path wall 61 in a direction opposite to the moving direction of the flocs F on the separation screen 53.

[0069] The flocs F that have flowed out of the floc supply path 60 in the above direction flow down onto the separation screen 53. In the present embodiment, the height of the floc supply path 60 with respect to the separation screen 53 is 200.0 mm. More specifically, the height h1 of the end face of the upstream flow path wall 61 with respect to the separation screen 53 is 200.0 mm.

[0070] As described above, the outflow direction (overflow direction) of the flock F from the flock supply path 60 is opposite to the moving direction (conveying direction of the flock F) of the flock F on the separation screen 53. For this reason, immediately after the flock F has fallen onto the separation screen 53, it temporarily moves upstream in the conveying direction. That is, the flock F temporarily flows backward. As a result, the moving speed (flow velocity) of the flock F on the separation screen 53 is reduced. Viewed another way, the residence time of the flock F on the separation screen 53 is extended, and the separation of the flock F is promoted. That is, the concentration of the sludge is promoted.

[0071] <Flock input area> Referring to FIG. 4 again, the separation screen 53 is provided with an opening 53a that is the same as the opening 23a provided in the separation screen 23. However, there is no opening 53a at the position where the flock F falls as described above.

[0072] More specifically, a flock input area 70 without an opening 53a is provided at the position where the flock F on the separation screen 53 falls. The flock F flowing out from the flock supply path 60 falls onto the flock input area 70 on the separation screen 53.

[0073] The method for forming the flock input area 70 is not particularly limited, but in the present embodiment, the flock input area 70 is formed by a leakage prevention plate 71 disposed on the separation screen 53. The leakage prevention plate 71 forms a flock input area 70 without an opening 53a on the separation screen 53 by closing a part of the plurality of openings 53a.

[0074] By dropping the flock F into the flock input area 70, leakage of the flock F due to the momentum of the drop is prevented. More specifically, it is prevented that the flock F passes through the separation screen 53 as it is without being separated into the interstitial water W and the sludge solids S. However, there is some variation in the drop position of the flock F.

[0075] Therefore, it is preferable that the flock input region 70 is provided over a range of 25.0 mm or more, and more preferably over a range of 50.0 mm or more, on the upstream side and the downstream side in the conveyance direction of the flock F from directly below the flock supply path 60. Therefore, in the present embodiment, the flock input region 70 is provided over a range of 50.0 mm on the upstream side and the downstream side in the conveyance direction of the flock F from directly below the flock supply path 60.

[0076] The leakage prevention plate 71 of the present embodiment is formed of the same material as the separation screen 53 and has the same thickness as the separation screen 53. However, the material and thickness of the leakage prevention plate 71 do not necessarily have to be the same as those of the separation screen 53. For example, the leakage prevention plate 71 may be formed of a synthetic resin.

[0077] Note that the higher the height of the flock supply path 60 with respect to the separation screen 53, the greater the impact that the flock F receives when it falls onto the separation screen 53 (leakage prevention plate 71). Therefore, from the viewpoint of maintaining the shape of the flock F, it is preferable that the height of the flock supply path 60 with respect to the separation screen 53 is as low as possible. That is, the height h1 shown in FIG. 5 is preferably as low as possible. Specifically, the height h1 is preferably 300.0 mm or less.

[0078] <Retention part> As shown in FIG. 4, the separation device 50 is provided with a plurality of retention parts 80. Each retention part 80 extends in a direction intersecting the conveyance direction of the flock F and crosses the separation screen 53. In the following description, the retention part 80 may be referred to as a "retention plate 80".

[0079] In the present embodiment, each retention plate 80 extends in a direction orthogonal to the conveyance direction of the flock F. In other words, each retention plate 80 extends in a direction orthogonal to the longitudinal direction of the separation screen 53. In other words, each retention plate 80 extends in the width direction of the separation screen 53.

[0080] FIG. 6 is a partially enlarged view showing the retention plate 80 shown in FIG. 4 and its vicinity. Each retention plate 80 has a predetermined height h2 with respect to the separation screen 53. For this reason, the flock F supplied onto the separation screen 53 moves downstream in the conveyance direction while overcoming the plurality of retention plates 80.

[0081] Viewed another way, each retention portion 80 inhibits the movement of the flock F on the separation screen 53. As a result, the residence time of the flock F on the separation screen 53 is further extended, and the separation of the interstitial water W constituting the flock F is further promoted. That is, the concentration of the sludge solids S is further promoted.

[0082] There are no particular restrictions on the number, height, interval, etc. of the retention plates 80. However, from the viewpoint of the balance between the improvement of the concentration effect by extending the residence time and the shortening of the processing time by accelerating the conveyance speed, the height h2 of the retention plate 80 with respect to the separation screen 53 is preferably 1.0 mm or more and 50.0 mm or less, more preferably 1.0 mm or more and 30.0 mm or less, and even more preferably 1.0 mm or more and 20.0 mm or less. Also, the interval P (FIG. 4) between adjacent retention plates 80 in the conveyance direction of the flock F is preferably 50.0 mm or more and 1500.0 mm or less. Therefore, in the present embodiment, the height h2 of the retention plate 80 with respect to the separation screen 53 is set to 3.0 mm. Also, the interval P between adjacent retention plates 80 in the conveyance direction of the flock F is set to 300.0 mm.

[0083] <Concentrated sludge discharge region> As shown in FIG. 4, the length of the flock separation trough 54 in the conveyance direction of the flock F is longer than the length of the filtrate trough 55 in the same direction. Viewed another way, a concentrated sludge discharge region 90 that protrudes downstream of the end of the filtrate trough 55 is provided at the end of the flock separation trough 54.

[0084] FIG. 7 is a partially enlarged view showing the concentrated sludge discharge region 90 shown in FIG. 4 and its vicinity. The method of forming the concentrated sludge discharge region 90 is not particularly limited. In the present embodiment, the concentrated sludge discharge region 90 is formed by a transfer plate 91 connected to the tip of the separation screen 53.

[0085] The transfer plate 91 is not provided with an opening such as the opening 53a provided in the separation screen 53. Also, the surface of the transfer plate 91 is flush with the surface of the separation screen 53. That is, the concentrated sludge discharge region 90 is a region that is continuously connected to the separation screen 53 without a step, and is a region capable of transporting the sludge solids S farther (forward) from the interstitial water W.

[0086] The transfer plate 91 of the present embodiment is formed of the same material as the separation screen 53 and has the same thickness as the separation screen 53. However, the material and thickness of the transfer plate 91 do not necessarily have to be the same as those of the separation screen 53. For example, the transfer plate 91 may be formed of a synthetic resin.

[0087] <Water stop plate> As shown in FIGS. 4 and 7, a water stop plate 101 is provided at the downstream end of the filtrate trough 55 in the conveying direction. More specifically, at the downstream end of the separation screen 53 in the conveying direction, a water stop plate 101 that protrudes vertically downward with respect to the back surface of the separation screen 53 is provided.

[0088] The interstitial water W separated from the sludge solids S by vibration falls into the filtrate trough 55 through the opening 53a of the separation screen 53. However, a part of the interstitial water W moves to the downstream side in the conveying direction along the back surface of the separation screen 53.

[0089] The water stop plate 101 prevents the gap water W that has moved downstream in the conveyance direction along the back surface of the separation screen 53 from entering the concentrated sludge discharge area 90. In other words, the water stop plate 101 prevents the gap water W from moving downstream beyond the end of the separation screen 53. Based on the above object of the water stop plate 101, the protruding length L of the water stop plate 101 with respect to the separation screen 53 is preferably 3.0 mm or more, and more preferably 10.0 mm or more. Therefore, in the present embodiment, the protruding length L of the water stop plate 101 with respect to the separation screen 53 is set to 10.0 mm.

[0090] The transfer plate 91 and the water stop plate 101 may be a single plate member or separate plate members. In the former case, for example, a part of a plate member bent in an L shape can be used as the transfer plate 91, and the other part can be used as the water stop plate 101.

[0091] Note that the vibration mechanism 52 shown in FIG. 4 has the same structure as the vibration mechanism 22 shown in FIG. 2, and vibrates the trough 51 and the separation screen 53 on the same principle as the vibration mechanism 22.

[0092] The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the gist thereof. For example, in another embodiment, the digestion tank 30 is omitted. In other words, the digestion process is omitted. In this case, the concentrated sludge discharged from the separation devices 20 and 50 is sent to the dehydrator 40 and dehydrated without passing through the digestion tank 30. Even in such an embodiment, an improvement in dehydration performance (for example, improvement in the water content of the dehydrated cake, increase in the sludge treatment amount per unit time, etc.) can be expected as compared with the case of dehydrating un-concentrated sludge.

[0093] The separation screens 23 and 53 may be installed with a downward slope toward the downstream side in the conveyance direction of the floc F. That is, a downward gradient may be provided to the separation screens 23 and 53.

[0094] By changing the degree of the downward slope of the separation screens 23, 53, the conveying performance of the separation devices 20, 50 can be adjusted. For example, by increasing the inclination angle θ2 shown in FIG. 8, the moving speed of the flock F on the separation screens 23, 53 can be increased. That is, the conveying speed of the flock F can be increased.

[0095] However, if the conveying speed of the flock F is increased, although the processing time is shortened, there is a risk that the separation (concentration of sludge) of the flock F will become insufficient. Therefore, it is preferable to determine the inclination angle θ2 in consideration of the balance between the shortening of the processing time by accelerating the conveying speed of the flock F and the improvement of the separation performance (concentration performance) by ensuring the residence time of the flock F. From such a viewpoint, the inclination angle θ2 of the separation screens 23, 53 is preferably within 45 degrees with respect to the horizontal plane HP, and more preferably within 20 degrees.

[0096] Note that the inclination angle θ2 shown in FIG. 8 is the inclination angle of the separation screens 23, 53 with respect to the horizontal plane HP. Further, when the separation screens 23, 53 are inclined, the conveying direction of the flock F serving as a reference for the vibration direction (inclination angle θ1) of the separation screens 23, 53 is also inclined by the same angle, but the vibration direction (inclination angle θ1) of the separation screens 23, 53 with respect to the conveying direction of the flock F does not change.

[0097] In the example shown in FIG. 8, a downward slope is provided to the separation screens 23, 53 by tilting the separation devices 20, 50 (troughs 21, 51). However, only the separation screens 23, 53 may be tilted. For example, the separation screens 23, 53 may be attached obliquely to the troughs 21, 51. In this case, even if the separation devices 20, 50 are installed horizontally, the separation screens 23, 53 are inclined with respect to the horizontal plane HP.

[0098] The separation screens 23, 53 are not limited to punching metal. The separation screens 23, 53 may be replaced with, for example, wedge wire screens, metal meshes, etc. Also, the shape of the openings 23a, 53a provided in the separation screens 23, 53 is not limited to circular, and may be rectangular, for example. When the openings 23a, 53a are rectangular, the above numerical values related to the diameter D of the openings 23a, 53a correspond to the numerical values related to the width of the openings 23a, 53a.

Explanation of Signs

[0099] 1... sludge treatment system, 2... water treatment system, 10... coagulation mixing tank, 20, 50... separation device (concentration device), 21, 51... trough, 22, 52... vibration mechanism, 22a... support member, 22b... drive source, 23, 53... separation screen, 23a, 53a... opening, 24, 54... upper trough (floc separation trough), 25, 55... lower trough (filtrate trough), 30... digestion tank, 40... dehydrator, 60... floc supply path, 61... upstream side flow path wall, 62... downstream side flow path wall, 70... floc input region, 71... leakage prevention plate, 80... retention part (retention plate), 90... concentrated sludge discharge region, 91... transfer plate, 101... water stop plate, D... diameter, F... floc, HP... horizontal plane, L... protrusion length, P... interval, S... sludge solid, W... interstitial water, θ1, θ2... inclination angle, h1, h2... height

Claims

1. A flocculation step of adding a flocculant to sludge discharged from a water treatment system to form flocs, and a separation step of separating the flocs into interstitial water and sludge solids while conveying the flocs by vibrating a separation screen to which the flocs are supplied. The sludge concentration method is characterized in that the separation screen is provided with a plurality of openings having a width or diameter of 0.1 mm or more and 5.0 mm or less.

2. The sludge concentration method according to claim 1, wherein the opening ratio of the separation screen is 10.0% or more.

3. The sludge concentration method according to claim 1, wherein the vibration direction of the separation screen has an angle of 10 degrees or more and 80 degrees or less with respect to the conveyance direction of the flocs, the amplitude of the separation screen is 0.01 mm or more and 50.0 mm or less, and the vibration frequency is 1 time / second or more and 1,000 times / second or less.

4. The separation screen is installed with a downward slope toward the downstream side in the conveyance direction of the flocs, and the inclination angle of the separation screen with respect to the horizontal plane is within 45 degrees. The sludge concentration method according to claim 1.

5. The sludge concentration method according to claim 1, further comprising a reflux step of returning the interstitial water to the water treatment system.

6. The sludge concentration method according to claim 1, further comprising a dehydration step of removing moisture from the sludge solids to form a dewatered cake.

7. The sludge concentration method according to claim 6, further comprising a digestion step performed before the dehydration step, and in the digestion step, the sludge solids are digested in a state where air is blocked.

8. A flocculation mixing tank for adding a flocculant to sludge discharged from a water treatment system to form flocs, and a separation device for separating the flocs into interstitial water and sludge solids while conveying the flocs. The sludge treatment system is characterized in that the separation device includes a separation screen to which the flocs are supplied and a vibration mechanism for vibrating the separation screen, and the separation screen is provided with a plurality of openings having a width or diameter of 0.1 mm or more and 5.0 mm or less.

9. The separation screen has a first region and a second region located downstream of the first region in the conveyance direction of the flocs, and the width or diameter of the openings provided in the first region is smaller than the width or diameter of the openings provided in the second region. The sludge treatment system according to claim 8.

10. The separation screen has a first screen and a second screen provided with the openings, wherein the width or diameter of the opening provided in the first screen is smaller than the width or diameter of the opening provided in the second screen, and the first screen is arranged upstream of the second screen in the conveying direction of the flock. The sludge treatment system according to claim 8.

11. The vibration mechanism vibrates the separation screen using an electromagnet or an electric motor as a drive source. The sludge treatment system according to claim 8.

12. The opening ratio of the separation screen is 10.0% or more. The sludge treatment system according to claim 8.

13. The vibration mechanism vibrates the separation screen in a vibration direction having an angle of 10 degrees or more and 80 degrees or less with respect to the conveying direction of the flock, with an amplitude of 0.01 mm or more and 50.0 mm or less, and a vibration frequency of 1 time / second or more and 1,000 times / second or less. The sludge treatment system according to claim 8.

14. The separation device is located above the separation screen and includes a flock supply path for supplying the flock to the separation screen. The flock supply path has an upstream channel wall located upstream in the conveying direction of the flock and a downstream channel wall located downstream in the conveying direction. The flock flowing into the flock supply path overflows the upstream channel wall toward the upstream side in the conveying direction and flows down onto the separation screen. The sludge treatment system according to claim 8.

15. The height of the flock supply path with respect to the separation screen is 300.0 mm or less. The sludge treatment system according to claim 14.

16. A flock input region without the opening is provided at a position on the separation screen where the flock flows down from the flock supply path. The sludge treatment system according to claim 14.

17. The flock input region is provided over a range of 25.0 mm or more respectively upstream and downstream in the conveying direction from directly below the flock supply path. The sludge treatment system according to claim 16.

18. The separation device includes a plurality of retention parts provided on the separation screen. The sludge treatment system according to claim 8, wherein each of the retention parts extends in a direction intersecting with the conveyance direction of the flock and crosses the separation screen.

19. The sludge treatment system according to claim 18, wherein the interval between the adjacent retention parts in the conveyance direction is 50.0 mm or more and 1500.0 mm or less.

20. The sludge treatment system according to claim 18, wherein the height of each of the retention parts with respect to the separation screen is 1.0 mm or more and 50.0 mm or less.

21. The separation device has a trough provided with the separation screen. Inside the trough, an upper trough located above the separation screen and a lower trough located below the separation screen are formed. The sludge treatment system according to claim 8, wherein the length of the upper trough in the conveyance direction of the flock is longer than the length of the lower trough in the same direction.

22. The sludge treatment system according to claim 21, wherein a water stop plate for preventing the movement of the interstitial water is provided at an end of the lower trough on the downstream side in the conveyance direction.

23. The sludge treatment system according to claim 22, wherein the water stop plate protrudes vertically downward with respect to the back surface of the separation screen.

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