JP7598531B2 - Sludge treatment method using heated flocculant - Google Patents

Description

The present invention relates to a sludge treatment method in which sludge generated from wastewater treatment facilities such as sewage, night soil, community wastewater, and factories is subjected to primary coagulation, then concentrated, secondary coagulation, and then dewatered, and in particular to a sludge treatment method using a heated coagulant, which is characterized by using a heated coagulant during secondary coagulation.

Conventionally, a sludge treatment method is known in which a polymer coagulant and/or an inorganic coagulant are supplied to sludge generated from wastewater treatment facilities such as sewage, human waste, community wastewater, and factories to cause primary coagulation, then the sludge is concentrated, the concentrated sludge is subjected to secondary coagulation, and then dewatered. Patent Document 1 discloses a technology in which a polymer coagulant is added to the raw liquid in a coagulation device to cause primary coagulation, then the sludge is concentrated in the concentration device, an inorganic coagulant is added to the concentrated sludge supplied in a chute to cause secondary coagulation, and then the sludge is dewatered in a dewatering device.

Patent document 2 discloses a technology in which a flocculant is dissolved in heated drinking water and the resulting flocculant solution is injected into a dehydrator.

Patent document 3 discloses a technology in which a polymer flocculant that has been heated in a chemical supply pipe connected to a flocculation mixing tank is added to the sludge in the tank.

Patent No. 5477373 Patent No. 4177752 JP 2019-10612 A

Conventionally, flocculants used in primary and secondary flocculation are generally at room temperature. However, flocculants at room temperature have high viscosity and low fluidity, making them difficult to disperse in sludge, and the flocculant and sludge cannot be mixed sufficiently. In addition, in Patent Document 1, when performing the dewatering process, the concentrated sludge is dewatered while being pressed into the dewatering device, so it is necessary to perform secondary flocculation before the dewatering process to form strong flocs.

The technologies of Patent Document 2 and Patent Document 3 use a heated flocculant to flocculate sludge, so that the highly fluid flocculant acts on the entire sludge. However, Patent Document 2 is a technology in which the flocculant dissolving solution and the concentrated sludge are supplied separately to a dehydrator, and the flocculant dissolving solution and the concentrated sludge are not mixed and then dehydrated. Since the flocculant dissolving solution and the concentrated sludge are mixed only in the dehydrator, it is not possible to improve the mixing ability with the sludge. In addition, the purpose of heating is to efficiently dissolve the flocculant by heating the clean water, not to improve dispersibility with the sludge. Patent Document 3 is a technology in which the polymer flocculant used in the primary flocculation process is heated, and there is no description or suggestion regarding the secondary flocculation process of the concentrated sludge.

The present invention provides a sludge treatment method using a heated flocculant that can form strong secondary flocs by adding a heated flocculant to concentrated sludge formed through a primary flocculation process and a concentration process, and then mixing and flocculating the sludge for secondary flocculation.

In a sludge treatment method in which a first flocculant, which is a polymer flocculant, an inorganic flocculant alone or a combination of these, is mixed with sludge in a primary flocculation section to form primary flocs, which are then concentrated in a primary dewatering section, and the concentrated sludge thus formed is mixed with a second flocculant, which is an inorganic flocculant, to form secondary flocs, which are then dewatered in a secondary dewatering section, by heating only the second flocculant added to the concentrated sludge, the second flocculant, which has low viscosity and high fluidity due to heating, acts widely on the entire concentrated sludge, thereby improving the mixability with the sludge and enabling the formation of strong flocs containing a large amount of SS.

By heating the second flocculant using a heating device provided on the circumferential surface of a second chemical supply pipe connected to at least one of the primary dehydration section, secondary flocculation section, and secondary dehydration section, the dispersibility of the second flocculant in the sludge can be improved, making it possible to reduce the amount of the second flocculant used, and therefore the amount of the first flocculant used.

The sludge treatment method using a heated flocculant according to the present invention can form strong flocculants by adding a second flocculant consisting of a heated inorganic flocculant to the concentrated sludge discharged from the primary dewatering section and then mixing them. By forming strong flocculants in the pre-dewatering stage, the flocs do not pass through the filtration surface of the dewatering section, and a dehydrated cake with a low moisture content can be efficiently produced. In addition, the heating device that heats the second flocculant has a simple configuration in which it is covered on the chemical supply pipe, so it can be easily applied to existing equipment, and since it has a small heating capacity, it can realize energy-saving and highly efficient sludge treatment. Furthermore, the chemical supply pipe that is directly heated by the heating device and the sludge supply pipe that is indirectly heated by being supplied with the heated second flocculant are not clogged.

1 is a schematic diagram of a sludge treatment method according to an embodiment of the present invention. FIG. FIG. FIG. 3 is an enlarged view of the primary dehydration section shown in FIG. 2 . FIG. 3 is a vertical cross-sectional view of the secondary aggregation portion shown in FIG. 2 . FIG. 4 is a schematic diagram of a sludge treatment method according to another embodiment. FIG. 4 is a schematic diagram of a sludge treatment method according to another embodiment.

FIG. 1 is a schematic diagram of a sludge treatment method according to an embodiment of the present invention.
The sludge in the sludge storage tank 2 is supplied to the primary flocculation section 5 through the sludge supply pipe 3 and the sludge supply pump 4. The sludge supply pipe 3 is connected to a first chemical supply pipe 7 for transporting a polymer flocculant, an inorganic flocculant, or a combination of flocculants, so that the first flocculant in the first chemical tank 6 can be transported to the primary flocculation section 5. The primary flocculation section 5 is a flocculation mixing tank, in which the transported sludge and the first flocculant are mixed and stirred by an agitator in the tank to form primary flocs. The formed primary flocs are transported to the solid-liquid separation section 1 installed after the primary flocculation section 5, and then solid-liquid separation is performed. The solid-liquid separation section 1 is composed of a primary dewatering section 12, a secondary flocculation section 13, and a secondary dewatering section 14.

In the primary dewatering section 12, concentration is performed using known machines such as a rotary concentrator, a belt concentrator, or a centrifugal dewatering machine. The primary flocs supplied from the primary flocculation section 5 are concentrated while the concentrated filtrate is separated to form concentrated sludge. The formed concentrated sludge is transferred to the secondary flocculation section 13 installed downstream of the primary dewatering section 12.

In the secondary flocculation section 13, the concentrated sludge formed in the primary dewatering section 12 is flocculated. Flocculation is also performed in the primary flocculation section 5, but the primary flocs formed in the primary flocculation section 5 are very small and may slip through the filter media when dewatered in the secondary dewatering section 14 after concentration. For this reason, the flocs are flocculated again in the secondary flocculation section 13 to form coarse flocs.

The secondary flocculation section 13 uses the second flocculant (inorganic flocculant) stored in the second chemical tank 9. The inorganic flocculant is heated in a heating device 15 before being added to the concentrated sludge. When heated, the inorganic flocculant's viscosity decreases and its fluidity increases. Therefore, adding the heated inorganic flocculant to the concentrated sludge allows it to act on the entire sludge. This improves the kneading ability with the concentrated sludge, and dense, strong secondary flocs are formed. The formed secondary flocs are transferred to the secondary dewatering section 14. The secondary flocculation section 13 has different shapes depending on the machine used, as shown in Figures 2, 5, and 6, which will be described in detail later.

The secondary dewatering section 14, like the primary dewatering section 12, is composed of a known dewatering device, and while squeezing and dewatering the supplied secondary flocs, separates the dehydrated filtrate and produces a dehydrated cake.

The first chemical supply pipe 7 may be connected to the primary flocculation section 5 to directly supply the first flocculant. A line mixer may also be provided in the sludge supply pipe 3 to improve the kneadability of the sludge.

2 is a vertical cross-sectional side view of a solid-liquid separation section according to an embodiment of the present invention, FIG. 3 is an enlarged view of a primary dewatering section shown in FIG. 2, and FIG. 4 is a vertical cross-sectional view of a secondary flocculation section shown in FIG.
As shown in FIG. 2, the solid-liquid separation section 1 is composed of a primary dewatering section 12, a secondary flocculation section 13, and a secondary dewatering section 14, and is configured such that the concentrated sludge formed in the primary dewatering section 12 can be flocculated in the secondary flocculation section 13, which is connected to the discharge side of the primary dewatering section 12 and the supply side of the secondary dewatering section 14, and then dewatered in the secondary dewatering section 14.

As shown in FIG. 3, the primary dehydration section 12 employs a rotary concentrator 12 having a cylindrical outer tube screen 16 with a filtering surface and a screw shaft 18 around which a helical screw blade 17 is wound, which rotates while sliding against the inner peripheral surface of the outer tube screen 16. The rotary concentrator 12 has an inlet outer tube flange 37 and an outlet outer tube flange 61 fitted to the end of the outer tube screen 16, and forms a concentration chamber 19 between the outer tube screen 16 and the screw shaft 18.

The outer cylinder screen 16 that forms the concentration chamber 19 rotates with the rotation of the outer cylinder drive shaft 24 connected to the outlet outer cylinder flange 61. Meanwhile, the screw shaft 18 is rotatably supported by a sludge supply pipe 21 supported by the front frame 20. The outer cylinder screen 16 and the screw shaft 18 are configured so that they can rotate at different speeds using a drive machine (not shown).

Inside the screw shaft 18, a sludge supply passage 22 is formed that connects the concentration chamber 19 and the sludge supply pipe 21, and the periphery has multiple supply ports 23. The primary flocs supplied by pressure from the sludge supply pipe 3 pass through the sludge supply passage 22 and then flow into the concentration chamber 19 from the supply port 23. The primary flocs that flow into the concentration chamber 19 contain a large amount of water, and the water load is greater than the solid load, so the concentrated filtrate is separated from the outer cylinder screen 16 immediately after pressure. The concentrated filtrate is then further separated by gravity filtration while being transported toward the discharge side.

The primary flocs separated from the concentrated filtrate become concentrated sludge and are discharged from multiple outlets (not shown) formed in the outlet outer cylinder flange 61 into the concentrated sludge tank 27, and then sent to the secondary flocculation section 13.

As shown in FIG. 4, the secondary flocculation section 13 is composed of a thickened sludge tank 27 and a thickened sludge supply pump 28 connected to the lower side wall of the thickened sludge tank 27. The thickened sludge tank 27 temporarily stores the supplied thickened sludge, and the thickened sludge is pressure-fed and supplied to the secondary dewatering section 14 by the thickened sludge supply pump 28.

The second chemical supply pipe 10 is connected to the side of the concentrated sludge tank 27, and is configured so that the second flocculant can be added to the concentrated sludge tank 27. The circumferential surface of the second chemical supply pipe 10 is covered with a heating device 15, which heats the inorganic flocculant supplied to the concentrated sludge tank 27 through the second chemical supply pipe 10. By applying heat to the inside from the circumferential surface of the second chemical supply pipe 10, the inorganic flocculant can be efficiently heated. It is desirable for the heating device 15 to cover the portion of the second chemical supply pipe 10 near the concentrated sludge tank 27 and heat the inorganic flocculant just before supplying it to the concentrated sludge tank 27. This allows the inorganic flocculant to be supplied to the concentrated sludge without cooling. In addition, the concentrated sludge is indirectly heated by adding the heated inorganic flocculant, which improves the dewaterability of the concentrated sludge.

The second flocculant is preferably heated to 40 to 90 degrees. This temperature increases the fluidity of the flocculant, making it easier to disperse in the concentrated sludge. Alternatively, instead of the inorganic flocculant, a polymer flocculant may be heated and added to the concentrated sludge. The heating device 15 is not limited to a known electric jacket heater or a hot water type that supplies a heat medium such as hot water or exhaust gas to the jacket. Alternatively, the heating device 15 may be disposed in the second chemical tank 9 to heat the inorganic flocculant in the second chemical tank 9, or a preheated hot water may be supplied to the inorganic flocculant to heat it. When a heat medium is used, the heat medium generated in other processes such as digestion and incineration can be used, making it possible to effectively use energy.

The concentrated sludge supply pump 28 uses a positive displacement screw pump such as a single-axis screw pump. The concentrated sludge and heated inorganic coagulant supplied from the concentrated sludge tank 27 are sucked in a spiral shape into a fixed volume gap 36 formed between the rotor 30 and the stator 31 through the suction port 29 connected to the bottom of the concentrated sludge tank 27, and move downward while being mixed. After that, they are further mixed and stirred by a plurality of stirring blades 32 protruding radially from the circumference of the drive shaft 34. Since the concentrated sludge moving through the gap 36 does not pulsate, the secondary flocculation flocs are not destroyed. In addition, the mixing is further promoted by the stirring blades 32 located below, and the flocculation reaction progresses, so that strong and dense secondary flocs can be formed. The rotor 30 and the stirring blades 32 are connected to the drive shaft 34 extended from the drive machine 33, and are configured to be freely rotatable.

Although the second chemical supply pipe 10 is connected to the thickened sludge tank 27, it may be connected to the suction port 29, the side of the thickened sludge supply pump 28, or the secondary dewatering section 14 described below. When connected to the secondary dewatering section 14, it is preferable to connect to the sludge supply side of the secondary dewatering section 14 , such as the supply path 51 in Fig. 2 or the start side of the filtration chamber 48 that receives the thickened sludge, and add the second flocculant to the thickened sludge immediately after it is supplied. Furthermore, the second chemical supply pipe 10 may be branched and connected to the rotary concentrator 12, the thickened sludge supply pump 28, and the secondary dewatering section 14, so that the inorganic flocculant is added simultaneously or alternately to a plurality of selected locations.

Alternatively, as shown in FIG. 3, the second chemical supply pipe 10 may be connected to the screw drive shaft 24 and communicated with the chemical supply passage 38 disposed inside the screw drive shaft 24 and the screw shaft 18, and the heated inorganic coagulant may be supplied from the nozzle hole 39 of the screw shaft 18 that opens into the concentration chamber 19. A non-permeable annular cylinder 40 is connected to the outer cylindrical screen 16 between the final pitches of the screw blades 17 , and the concentrated sludge and the heated inorganic coagulant are mixed along the circumferential surface of the rotating annular cylinder 40. In this form, the inorganic coagulant is added in the upstream of the concentrated sludge supply pump 28, so that the concentrated sludge and the inorganic coagulant can be efficiently mixed in the concentrated sludge supply pump 28 located in the downstream. In this way, the second chemical supply pipe 10 is connected to at least one of the primary dehydration section 12, the secondary coagulation section 13, and the secondary dehydration section 14 described later.

The secondary flocs formed in the secondary flocculation section 13 are pressed into the secondary dewatering section 14 shown in Figure 2 by the thickened sludge supply pump 28. The secondary dewatering section 14 employs a screw press 14 having a cylindrical outer tube screen 46 with a filtering surface and a screw shaft 45 around which are wound helical screw blades 47 that rotate while sliding against the inner circumference of the outer tube screen 46. The screw press 14 has its supply side connected to the discharge port 35 of the thickened sludge supply pump 28, and is constructed integrally with the rotary concentrator 12 placed above.

A filtration chamber 48 is formed between the inner peripheral surface of the outer cylindrical screen 46 and the outer peripheral surface of the screw shaft 45, and is divided into a spiral shape by the screw blades 47. In addition, because a screw shaft 45 is used that expands in a tapered shape from the sludge supply side to the discharge side, the filtration chamber 48 shrinks from the sludge supply side to the discharge side.

An inlet outer cylinder flange 41 is fitted to the supply side end of an outer cylinder screen 46 which forms a filtration chamber 48, and a sprocket 42 is fitted around the inlet outer cylinder flange 41. The sprocket 42 is interlocked with an outer cylinder driver 44 which is mounted on a front frame 43 and can rotate forward and backward, so that the outer cylinder screen 46 can rotate forward and backward. Meanwhile, a screw drive shaft 49 is connected to the discharge side end of the screw shaft 45. The screw drive shaft 49 is configured to be rotatable by being driven by a screw driver 50.

A supply passage 51 is connected to the start end side of the screw shaft 45, and a plurality of supply ports 52 are opened on the circumferential surface. The supply passage 51 is in sliding contact with the discharge port of the thickened sludge supply pump 28, and the secondary flocs supplied by pressure from the thickened sludge supply pump 28 pass through the supply passage 51 and then flow into the filtration chamber 48 from the supply port 52. Since the secondary flocs that flow in have a water load greater than a solid load, a large amount of dewatered filtrate is discharged from the outer cylindrical screen 46. Since the volume of the filtration chamber 48 gradually decreases from the start end side to the discharge side, the secondary flocs transported toward the discharge side are subjected to the volume change of the filtration chamber 48 and the thrust force of the rotating screw blades 47, increasing the internal pressure, and are squeezed and dewatered, and the dewatered filtrate is separated and turned into a cake.

The secondary flocs transported through the filtration chamber 48 are mixed with the heated inorganic flocculant and coarsened, so they do not slip through the outer cylindrical screen 46. In addition, because they have a high SS content and are dense and strong, the dehydration performance of the screw press 14 is improved, and a dehydrated cake with a low moisture content can be obtained in a short time. The dehydrated cake produced is further compressed by the back pressure of the presser 53 connected to the cylinder 54 on the discharge side to reduce its moisture content, and then discharged. Although the outer cylindrical screen 46 is fixed during the dehydration operation, it may be rotated.

In this embodiment, the rotary concentrator 12 is mounted above the screw press 14 and configured as an integral unit, but the mechanism of the primary dehydration unit 12 and the secondary dehydration unit 14 configured as an integral unit is not limited, for example, a belt concentrator may be mounted above. In addition, the primary dehydration unit 12 may be disposed on the inlet side of the screw press 14, or the primary dehydration unit 12 may be connected to the side of the outer cylinder fixed screw press 14 via a concentrated sludge supply pump 28. In addition, each component constituting the solid-liquid separation unit 1 may be connected by piping, and the second chemical supply pipe 10 may be connected to a piping provided between the primary dehydration unit 12 and the secondary flocculation unit 13. As for the configuration of the secondary flocculation unit 13, a known hopper may be disposed between the primary dehydration unit 12 and the secondary dehydration unit 14, and the concentrated sludge may be supplied to the secondary dehydration unit 14 by gravity.

5 and 6 are schematic diagrams of a sludge treatment method according to another embodiment.
5 shows a solid-liquid separation section 1 which is composed of a primary flocculation section 5 which forms primary flocs, a primary dewatering section 12 (belt concentrator) which dewaters the water in the primary flocs by their own weight to form concentrated sludge, a secondary flocculation section 13 which adds a heated inorganic flocculant to the formed concentrated sludge and then mixes it to form secondary flocs, and a secondary dewatering section 14 (belt press) which sandwiches the secondary flocs between belts and squeezes and dewaters them to produce a dewatered cake. The primary dewatering section 12 and the secondary dewatering section 14 are composed of a filter cloth 59 stretched around a plurality of rollers 58 so as to be freely movable.

By adding a heated second flocculant (inorganic flocculant) to the concentrated sludge supplied from the primary dewatering section 12 to the secondary dewatering section 14, the inorganic flocculant disperses efficiently in the sludge, forming dense and strong secondary flocs in a short time. Dense and strong secondary flocs contain a large amount of SS and have low fluidity, so side leakage does not occur. Preventing side leakage also makes it possible to improve the dewatering performance in the secondary dewatering section 14.

The means of adding the second flocculant is not limited, and may be selected as appropriate, for example by spraying it when the concentrated sludge overflows from the primary dewatering section 12 to the secondary dewatering section 14, or by adding it to a flocculation mixing tank installed between the primary dewatering section 12 and the secondary dewatering section 14.

In FIG. 6, a known centrifuge is used in the solid-liquid separation section 1, and a heated second flocculant (inorganic flocculant) is added when the primary flocculant formed in the primary flocculant section 5 is subjected to solid-liquid separation. The primary flocculant is supplied to a supply chamber 57 formed between the rotating inner body 55 and outer body 56, and the solids with high mass density are precipitated or deposited on the inner surface of the outer body 56 by the centrifugal force in the radial direction applied to the rotor, while the separated liquid with low mass density located inside the solids is discharged. In the primary dewatering section 12 at the front stage of the centrifuge, concentrated sludge is formed while separating the water in the primary flocculant by centrifugal force, and the concentrated sludge is mixed with the heated second flocculant to form secondary flocculant. The formed secondary flocculant is further separated from the secondary flocculant by centrifugal force in the secondary dewatering section 14 at the rear stage of the centrifuge, and becomes a dehydrated cake. The centrifuge 1 supports an outer barrel 56 that is rotated by a motor (not shown) and an inner barrel 55 that has a screw 60 and rotates at a differential speed relative to the outer barrel 56 inside the outer barrel 56.

By using a heated inorganic coagulant for secondary coagulation, the primary coagulated flocs and the coagulant can be mixed efficiently inside the centrifuge, so strong secondary coagulated flocs can be formed in a short time. As a result, dehydrated cake with a low moisture content can be produced in a short time, which reduces the operating time of the motors that drive the inner body 55 and outer body 56, leading to reduced running costs.

Although the primary dehydration, secondary flocculation, and secondary dehydration are performed in one device, they may be performed separately using two centrifuges or a combination of a centrifuge and another dehydrator. In addition, this embodiment and Figures 5 and 6 use a flocculation mixing tank as the primary flocculation section 5, but this is not limiting.

The present invention is not limited to the present embodiment described above and illustrated in the drawings, and modifications are possible without departing from the spirit of the invention as defined in the claims.

The sludge treatment method using a heated flocculant according to the present invention uses a heated flocculant during the secondary flocculation step to flocculate the sludge, thereby improving the mixing ability with the sludge and forming large, strong flocculant flocs in a short time. This reduces the amount of flocculant used and prevents the flocculant from flowing out unreacted with the sludge. Furthermore, strong flocculant flocs can be supplied to the dewatering device, allowing efficient dewatering in the subsequent dewatering step. The reduction in the operating time of the solid-liquid separator used in the dewatering step reduces the amount of fuel used, which also leads to a reduction in carbon dioxide emissions. The present invention is a dewatering treatment method that reduces the amount of flocculant used and the operating time of the solid-liquid separator, and allows for environmentally friendly operation.

5 Primary flocculation section 10 Second chemical supply pipe 12 Primary dehydration section 13 Secondary flocculation section 14 Secondary dehydration section 15 Heating device

Claims (2)

A sludge treatment method comprising mixing a first flocculant, which is a polymer flocculant, an inorganic flocculant, or a combination of a polymer flocculant and an inorganic flocculant, with sludge in a primary flocculation section (5) to form primary flocs, which are then concentrated in a primary dewatering section (12), and mixing the concentrated sludge with a second flocculant, which is an inorganic flocculant, to form secondary flocs, which are then dewatered in a secondary dewatering section (14);
Only the second flocculant added to the concentrated sludge is heated.
A sludge treatment method using a heated flocculant. The sludge treatment method using a heated flocculant as described in claim 1, characterized in that the second flocculant is heated by a heating device (15) provided on the peripheral surface of a second chemical supply pipe (10) connected to at least one of the primary dewatering section (12), the secondary flocculation section (13), and the secondary dewatering section (14).

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