JP2023108648A - Sludge treatment method using heated flocculant - Google Patents

Abstract

To provide a sludge treatment method using a heated flocculant to perform secondary flocculation by adding a heated flocculant to a concentrated sludge formed by primary flocculation and primary dehydration, and then perform secondary dehydration.SOLUTION: There is provided a sludge treatment method wherein after mixing a sludge and a first flocculant in a primary flocculating section 5 to form a primary flocculated floc, it is concentrated in a primary dehydrator 12, and after mixing the formed concentrated sludge with a second flocculant to form a secondary flocculated floc, it is dehydrated in a secondary dehydrator 14, in which by adding the heated second flocculant to the concentrated sludge, it is possible to efficiently disperse the second flocculant in the concentrated sludge, and since kneadability of the concentrated sludge and the second flocculant is enhanced, coarse and firm flocs can be formed.SELECTED DRAWING: Figure 1

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 firstly flocculated, concentrated, further secondarily flocculated, and then dewatered. The present invention relates to a sludge treatment method using a heated flocculant, characterized in that the flocculant is sometimes heated.

Conventionally, a polymer flocculant or an inorganic flocculant is supplied alone or in combination to sludge generated from wastewater treatment facilities such as sewage, night soil, community wastewater, factories, etc., and after primary flocculation, it is concentrated, and concentrated sludge is produced twice. Sludge treatment methods are known in which sludge is dewatered after subsequent flocculation. In Patent Document 1, after primary flocculation by adding a polymer flocculant to the stock solution in the flocculating device, it is concentrated in a thickening device, and an inorganic flocculant is added to the concentrated sludge supplied into the chute for secondary flocculation. A technique for dewatering with a dehydrator after flocculation is disclosed.

Patent Literature 2 discloses a technique of dissolving a coagulant in heated tap water and injecting the resulting coagulant solution into a dehydrator.

Patent Document 3 discloses a technique of adding a polymer flocculant heated in a chemical feed pipe connected to a flocculation and mixing tank to sludge in the tank.

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

Conventionally, regarding the flocculants used in primary aggregation and secondary aggregation, normal temperature flocculants are generally used. However, since the flocculant at room temperature has high viscosity and low fluidity, it is difficult to disperse in the sludge, and the flocculant and sludge cannot be sufficiently mixed. In addition, in Patent Document 1, when performing the dehydration process, the thickened sludge that is injected into the dehydrator is dehydrated while applying pressure, so it is necessary to perform secondary aggregation before the dehydration process to form strong flocs. was there.

In the techniques of Patent Documents 2 and 3, a heated flocculant is used to flocculate sludge, so the highly fluid flocculant acts on the entire sludge. However, Patent Document 2 is a technique for separately supplying a flocculated solution and thickened sludge to a dehydrator, and does not dehydrate after mixing the flocculated solution and thickened sludge. Since the flocculated solution and thickened sludge are mixed only in the dehydrator, kneadability with sludge cannot be improved. Moreover, the purpose of heating is to efficiently dissolve the flocculant by heating the tap water, and the purpose is not to improve dispersibility with sludge. Patent document 3 heats the polymer flocculant used in the primary flocculation step, and does not describe or suggest a secondary flocculation step for thickened sludge.

The present invention adds a heated flocculant to the thickened sludge formed through the primary flocculation process and the thickening process, and then mixes and secondary flocculates to form strong secondary flocculated flocs. Provided is a sludge treatment method using an agent.

After the sludge and the first flocculant are mixed in the primary flocculating section to form primary flocculated flocs, they are thickened in the primary dewatering section, and the formed thickened sludge is mixed with the second flocculant to form secondary flocculated flocs. In the sludge treatment method in which the second coagulant is added to the thickened sludge after it is formed and dewatered in the secondary dewatering section, the second coagulant having a low viscosity and high fluidity due to the heating is applied to the entire thickened sludge. Since it widely acts on , it is possible to improve the kneadability with sludge, and it is possible to form a strong flocculated floc containing a large amount of SS.

By heating the second coagulant with a heating device provided on the peripheral surface of a second chemical supply pipe connected to at least one of the primary dewatering section, the secondary coagulation section, and the secondary dehydration section. Since the dispersibility in sludge can be improved, the amount of the second flocculant used can be reduced, and the amount of the first flocculant used can be reduced accordingly.

In the sludge treatment method using a heated coagulant according to the present invention, a second coagulant made of a heated inorganic coagulant is added to the thickened sludge discharged from the primary dehydration unit, and then mixed. agglomerated flocs can be formed. By forming strong aggregated flocs in the preceding stage of dehydration, it is possible to efficiently produce a dehydrated cake with a low moisture content without causing the flocs to slip through the filtration surface of the dehydration section. In addition, the heating device that heats the second flocculant has a simple structure that covers the chemical supply pipe, so it can be easily applied to existing equipment, and since the heating capacity is small, energy-saving and highly efficient sludge. processing can be realized. Further, the chemical supply pipe directly heated by the heating device and the sludge supply pipe indirectly heated by being supplied with the heated second coagulant are not clogged.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic block diagram of the sludge-treatment method which concerns on embodiment of this invention. Similarly, it is a longitudinal side view of a solid-liquid separation part. Similarly, it is an enlarged view of the primary dewatering part shown in FIG. Similarly, it is a longitudinal cross-sectional view of the secondary aggregation part shown in FIG. Similarly, it is a schematic configuration diagram of a sludge treatment method according to another embodiment. Similarly, it is a schematic configuration diagram of a sludge treatment method according to another embodiment.

FIG. 1 is a schematic configuration diagram of a sludge treatment method according to an embodiment of the present invention.
Sludge in the sludge storage tank 2 is supplied from the sludge supply pipe 3 to the primary coagulation section 5 via the sludge supply pump 4 . The sludge supply pipe 3 is connected to a first chemical supply pipe 7 for transferring a polymer flocculant or an inorganic flocculant alone or a combination of flocculants. It is configured such that the agent can be transferred to the primary aggregation section 5 . The primary flocculation section 5 is a flocculation and mixing tank, in which the transferred sludge and first flocculating agent are mixed and agitated by a stirrer in the tank to form primary flocculation flocs. The formed primary aggregated flocs are transferred to the solid-liquid separation unit 1 installed after the primary aggregation unit 5, and then solid-liquid separated. The solid-liquid separation section 1 is composed of a primary dewatering section 12 , a secondary aggregation section 13 and a secondary dehydration section 14 .

In the primary dehydrator 12, concentration is performed using known machines such as a rotary concentrator, a belt concentrator, and a centrifugal dehydrator. A concentrated filtrate is separated while concentrating the primary flocculation flocs supplied from the primary flocculation unit 5 to form concentrated sludge. The formed thickened sludge is transferred to the secondary flocculation section 13 installed after the primary dehydration section 12 .

In the secondary aggregation section 13, the thickened sludge formed in the primary dewatering section 12 is aggregated. Aggregation is also performed in the primary aggregation section 5, but the primary aggregation flocs formed in the primary aggregation section 5 are minute, and when dewatered in the secondary dehydration section 14 after concentration, the flocs may be removed from the filter medium. There is Therefore, they are aggregated again in the secondary aggregation section 13 to form coarse flocs.

The secondary coagulant 13 uses the second coagulant (inorganic coagulant) stored in the second chemical tank 9 . The inorganic flocculant is heated by the heating device 15 before being added to the concentrated sludge. The inorganic flocculant becomes less viscous and more fluid when heated. Therefore, by adding a heated inorganic flocculant to thickened sludge, it can be made to act on the entire sludge. As a result, kneadability with thickened sludge is enhanced, and dense and strong secondary flocculation flocs are formed. The formed secondary aggregated flocs are transferred to the secondary dewatering section 14 . As shown in FIGS. 2, 5, and 6, which will be described later in detail, the secondary aggregation section 13 has a different form depending on the machine used.

The secondary dehydration section 14, like the primary dehydration section 12, is composed of a known dehydrator, and separates the dehydrated filtrate while compressing and dewatering the supplied secondary aggregated flocs to produce a dehydrated cake. .

Alternatively, the first chemical supply pipe 7 may be connected to the primary aggregation section 5 to directly supply the first coagulant. In addition, a line mixer may be arranged in the sludge supply pipe 3 in order to improve the kneading property of the sludge.

2 is a longitudinal side view of the solid-liquid separation section according to the embodiment of the present invention, FIG. 3 is an enlarged view of the primary dewatering section shown in FIG. 2, and FIG. 4 is a longitudinal sectional view of the secondary aggregation section shown in FIG. be.
As shown in FIG. 2, the solid-liquid separation unit 1 comprises a primary dehydration unit 12, a secondary aggregation unit 13, and a secondary dehydration unit 14. After aggregation in the secondary aggregation section 13 connected to the discharge side of the section 12 and the supply side of the secondary dehydration section 14 , the secondary dehydration section 14 is configured to dewater.

As shown in FIG. 3, the primary dehydrator 12 has a cylindrical outer cylindrical screen 16 having a filtering surface and a spiral screw blade 17 that rotates while being in sliding contact with the inner peripheral surface of the outer cylindrical screen 16. A rotary concentrator 12 having a screw shaft 18 is employed. The rotary concentrator 12 has an inlet outer cylinder flange 37 and an outlet outer cylinder flange 61 fitted to the ends of the outer cylinder screen 16 to form a concentrating chamber 19 between the outer cylinder screen 16 and the screw shaft 18 .

The outer cylinder screen 16 forming the concentration chamber 19 rotates as the outer cylinder driving shaft 24 connected to the outlet outer cylinder flange 61 rotates. On the other hand, 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 constructed so as to be differentially rotated by a driving machine (not shown).

Inside the screw shaft 18, a sludge supply passage 22 is formed to connect the thickening chamber 19 and the sludge supply pipe 21, and a plurality of supply ports 23 are provided on the peripheral surface. The primary coagulated flocs press-fitted and supplied from the sludge supply pipe 3 pass through the sludge supply channel 22 and then flow into the thickening chamber 19 from the supply port 23 . The primary flocculated flocs that have flowed into the concentration chamber 19 contain a large amount of water, and the water load is greater than the solids load. Then, the concentrated filtrate is further separated by gravity filtration while being transported toward the discharge side.

The primary flocculated flocs from which the concentrated filtrate is separated become thickened sludge, and after being discharged into the thickened sludge tank 27 through a plurality of outlets (not shown) formed in the outlet outer cylinder flange 61, the secondary flocculation unit 13 Sent.

As shown in FIG. 4, the secondary coagulation 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.

A second chemical supply pipe 10 is connected to the side surface of the thickened sludge tank 27 so that the second coagulant can be added to the thickened sludge tank 27 . The circumferential surface of the second chemical supply pipe 10 is covered with a heating device 15 to heat the inorganic flocculant supplied to the thickened sludge tank 27 through the second chemical supply pipe 10 . By applying heat to the inside from the peripheral surface of the second chemical supply pipe 10, the inorganic coagulant can be efficiently heated. It is desirable that the heating device 15 covers the portion of the second chemical supply pipe 10 near the thickened sludge tank 27 and heats the inorganic flocculant immediately before supplying it to the thickened sludge tank 27 . As a result, the inorganic flocculant can be supplied to the concentrated sludge without cooling. Moreover, since the thickened sludge is also indirectly heated by adding the heated inorganic flocculant, the dewaterability of the thickened sludge is improved.

It is desirable to heat the second flocculant to 40 to 90 degrees. At this temperature, the fluidity of the flocculant is increased, and it becomes easier to disperse in the thickened sludge. Further, instead of the inorganic flocculant, a polymer flocculant may be heated and added to the thickened sludge. The heating device 15 is not limited to a known electric jacket heater, a hot water type that supplies a heating medium such as hot water or exhaust gas to the jacket portion, or the like. In addition, a heating device 15 is arranged in the second chemical tank 9 to heat the inorganic coagulant in the second chemical tank 9, or preheated hot water is supplied to the inorganic coagulant to heat it. You can take measures. When a heat medium is used, energy can be effectively used because the heat medium generated in other processes such as digestion and incineration can be used.

The thickened sludge supply pump 28 employs a positive displacement screw pump such as a single screw pump. The thickened sludge and the heated inorganic flocculant supplied from the thickened sludge tank 27 pass through the suction port 29 connected to the bottom of the thickened sludge tank 27, and flow through the fixed volume of the rotor 30 and the stator 31 formed between the rotor 30 and the stator 31. After being spirally sucked into the gap 36 and moving downward while being mixed, the mixture is further mixed and stirred by a plurality of stirring blades 32 protruding radially around the driving shaft 34 . Since the thickened sludge moving through the voids 36 does not pulsate, the secondary flocculation flocs are not destroyed. In addition, since the agglomeration reaction proceeds by further mixing by the stirring blades 32 positioned below, strong and dense secondary agglomerated flocs can be formed. The rotor 30 and the stirring blades 32 are connected to a driving shaft 34 extending from a driving machine 33 so as to be 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 surface of the thickened sludge supply pump 28, or the secondary dehydrator 14, which will be described later. When connecting to the secondary dehydration unit 14, for example, it is connected to the sludge supply side of the secondary dehydration unit, such as the supply path 51 in FIG. It is desirable to add a second flocculant to. 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 dehydrator 14, and the inorganic flocculant may be added simultaneously or alternately to a plurality of selected locations. .

In addition, as shown in FIG. 3, the second chemical supply pipe 10 is connected to the screw drive shaft 24 and communicated with the screw shaft 18 and the chemical supply path 38 disposed inside the screw drive shaft 24, and the concentration chamber 19 is A heated inorganic flocculant may be supplied from the nozzle hole 39 of the screw shaft 18 opened to the outside. An impermeable ring-shaped cylinder 40 is connected to the outer cylinder screen 16 between the final pitches of the screw blades 18, and the thickened sludge and the heated inorganic flocculant flow along the peripheral surface of the rotating ring-shaped cylinder 40. mixed. In this form as well, since the inorganic flocculant is added before the thickened sludge feed pump 28, the thickened sludge and the inorganic flocculant can be efficiently mixed in the thickened sludge feed pump 28 located at the latter stage. Thus, the second chemical supply pipe is connected to at least one of the primary dewatering section 12, the secondary aggregation section 13, and the secondary dehydration section 14, which will be described later.

The secondary coagulation flocs formed in the secondary coagulation section 13 are forced into the secondary dehydration section 14 shown in FIG. The secondary dehydrator 14 has a cylindrical outer cylindrical screen 46 having a filtering surface, and a screw shaft 45 around which a spiral screw blade 47 rotates while slidingly contacting the inner circumference of the outer cylindrical screen 46 . A screw press 14 is employed. The screw press 14 is connected on the supply side to the discharge port 35 of the thickened sludge supply pump 28 and is integrated with the rotary thickener 12 placed above.

Between the inner peripheral surface of the outer cylindrical screen 46 and the outer peripheral surface of the screw shaft 45, a filtration chamber 48 spirally partitioned by screw blades 47 is formed. Further, since the screw shaft 45 is tapered and expanded from the sludge supply side to the discharge side, the filtration chamber 48 is reduced from the sludge supply side to the discharge side.

An inlet outer cylinder flange 41 is fitted to the feed side end of the outer cylinder screen 46 forming the filtration chamber 48 , and a sprocket 42 is fitted to the inlet outer cylinder flange 41 . The sprocket 42 is interlocked with a reversible outer cylinder driving device 44 placed on the front frame 43, so that the outer cylinder screen 46 can rotate reversibly. On the other hand, the screw shaft 45 has a screw drive shaft 49 connected to the discharge side end. The screw driving shaft 49 is configured to be rotatable by being driven by a screw driving machine 50 .

A supply passage 51 is connected to the starting end side of the screw shaft 45, and a plurality of supply ports 52 are opened on the peripheral surface. The supply path 51 is in sliding contact with the discharge port of the thickened sludge supply pump 28, and the secondary flocculated flocs press-fitted and supplied from the thickened sludge supply pump 28 pass through the supply path 51 and then from the supply port 52 to the filter chamber. Flow into 48. Since the secondary flocculated floc that has flowed in has a larger water load than the solids load, a large amount of dewatered filtrate is discharged from the outer cylindrical screen 46 . Since the volume of the filtration chamber 46 gradually decreases toward the discharge side from the starting end side, the secondary flocculated flocs transferred toward the discharge side change the volume of the filtration chamber 46 and the thrust due to the rotating screw blades 47. The dehydrated filtrate is separated by compressing and dehydrating while increasing the internal pressure by receiving force to form a cake.

The secondary coagulated flocs transported through the filtration chamber 48 are mixed with the heated inorganic coagulant and coarsened, so that the outer cylindrical screen 46 does not pass through. In addition, since the SS content is high and the cake is dense and firm, the dewatering performance of the screw press 14 is enhanced, and a dehydrated cake with a low moisture content can be obtained in a short time. The produced dehydrated cake is subjected to back pressure by a presser 53 provided on the discharge side and connected to the cylinder 54, and is further compressed to reduce the water content, and then discharged. Although the outer cylindrical screen 46 is fixed during the dewatering operation, it may be rotated.

In this embodiment, the rotary concentrator 12 is placed above the screw press 14 and configured integrally. The mechanism of the dewatering section 13 is not limited. Alternatively, the primary dewatering unit 12 may be arranged on the inlet side of the screw press 14, or the primary dewatering unit 12 may be connected to the side surface of the fixed outer cylinder type screw press 14 via a thickened sludge supply pump 28. . Alternatively, each component constituting the solid-liquid separation unit 1 may be connected by a pipe, and the second chemical supply pipe 10 may be connected to the pipe provided between the primary dehydration unit 12 and the secondary aggregation unit 13. . Regarding the configuration of the secondary flocculation section 13, a known hopper is arranged between the primary dehydration section 12 and the secondary dehydration section 14, and the thickened sludge is naturally flowed down to the secondary dehydration section 14 using gravity and supplied. may

5 and 6 are schematic configuration diagrams of a sludge treatment method according to another embodiment.
FIG. 5 shows a primary flocculation unit 5 that forms primary flocculation flocs, and a primary dehydration unit 12 (belt thickener) that dehydrates water in the primary flocculation flocs by its own weight to form thickened sludge. After adding a heated inorganic flocculant to the thickened sludge, a secondary flocculation unit 13 that mixes to form secondary flocculation, and a secondary flocculation unit that sandwiches the secondary flocculation flocs between belts and compresses and dehydrates to produce a dehydrated cake. A dewatering section 14 (belt press) and a solid-liquid separation section 1 are shown. The primary dehydrating section 12 and the secondary dehydrating section 14 are constructed by movably winding a filter cloth 59 around a plurality of rollers 58 .

By adding a heated second coagulant (inorganic coagulant) to the thickened sludge supplied from the primary dehydration unit 12 to the secondary dehydration unit 14, the inorganic coagulant is efficiently dispersed in the sludge. Dense and strong secondary aggregated flocs can be formed in a short period of time. The dense and strong secondary aggregated flocs contain a large amount of SS and have low fluidity, so side leaks do not occur. By preventing side leaks, it is also possible to improve the dehydration performance in the secondary dehydration section 14 .

In addition, the means for adding the second flocculant is not limited, for example, the primary dehydration unit 12 and the secondary An aggregating-mixing tank is installed between the dewatering units 14, and the material is added to the aggregating-mixing tank.

FIG. 6 shows a second flocculant (inorganic flocculant ) is added. After the primary agglomerated flocs are supplied to a supply chamber 57 formed between the rotating inner drum 55 and outer drum 56 , the solid matter having a high mass density is transferred to the outer drum 56 by radial centrifugal force applied to the rotating body. A separated liquid with a low mass density located inside the solid matter is discharged while it settles or accumulates on the inner peripheral surface of the solid matter. In the primary dewatering section 12 at the front stage of the centrifuge, concentrated sludge is formed while separating moisture from the primary coagulated flocs by centrifugal force, and mixed with the heated second coagulant to form secondary coagulated flocs. The formed secondary flocculated flocs are subjected to centrifugal force in the secondary dewatering unit 14 at the latter stage of the centrifugal separator to further separate the moisture in the secondary flocs to form a dehydrated cake. The centrifuge 1 supports an outer shell 56 rotated by a motor (not shown) and an inner shell 55 having a screw 60 and rotating at a differential speed relative to the outer shell 56 inside the outer shell 56 .

By performing secondary aggregation using a heated inorganic coagulant, the primary aggregated flocs and the coagulant can be efficiently mixed in the centrifuge, so that strong secondary aggregated flocs can be formed in a short period of time. As a result, the dehydrated cake having a low water content can be produced in a short time, so that the driving time of the motors for driving the inner drum 55 and the outer drum 56 can be reduced, leading to a reduction in running costs.

Although the primary dehydration, secondary agglomeration and secondary dehydration are performed in one device, even if it is a method of separately performing two centrifuges or a combination of a centrifuge and another dehydrator good. In addition, although the present embodiment and FIGS. 5 and 6 employ the aggregating and mixing tank as the primary aggregating section 5, the present invention is not limited to this.

The present invention is not limited to the embodiments described above and illustrated in the drawings, and modifications can be made without departing from the gist of the invention described in the claims.

In the sludge treatment method using a heated flocculant according to the present invention, by flocculating sludge using a heated flocculant during the secondary flocculation step, it is possible to improve the kneadability with the sludge and shorten the time. can form coarse and strong aggregated flocs. As a result, the amount of coagulant used can be reduced, and the coagulant does not flow out without reacting with the sludge. In addition, since strong aggregated flocs can be supplied to the dehydrator, dehydration can be efficiently performed in the subsequent dehydration step. The reduced operating time of the solid-liquid separator used in the dehydration process reduces the amount of fuel used, leading to a reduction in carbon dioxide emissions. INDUSTRIAL APPLICABILITY The present invention is a dehydration treatment method that reduces the amount of coagulant used and the operating time of a solid-liquid separator, and enables environmentally friendly operation.

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

Claims (2)

After the sludge and the first flocculant are mixed in the primary flocculating section (5) to form primary flocculated flocs, they are concentrated in the primary dewatering section (12), and the thickened sludge thus formed is mixed with the second flocculant. In the sludge treatment method for forming secondary flocculated flocs and then dewatering in the secondary dewatering section (14),
A sludge treatment method using a heated coagulant, characterized by adding a heated second coagulant to thickened sludge. around a second chemical supply pipe (10) connected to at least one of the primary dehydration section (12), the secondary aggregation section (13) and the secondary dehydration section (14); The sludge treatment method using a heated flocculant according to claim 1, characterized in that the heating is performed by a heating device (15) provided on the surface.

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