JP2007029810A - Method and apparatus for concentrating sludge - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for concentrating sludge which enhances a solid recovery rate, also avoids waste of a flocculant and is capable of preventing staining and blocking of a sludge discharge pipe by recovering the most part of flocculated sludge remaining in a sludge flocculation tank when concentration operation is completed as concentrated sludge. <P>SOLUTION: In the method for concentrating the sludge loading the sludge supplied to the sludge flocculation tank 2 with the flocculant to obtain the flocculated sludge, and then supplying the flocculated sludge to solid-liquid separation means 3 to separate this into the concentrated sludge and separated water thereby concentrating the sludge, after terminating a supply of the sludge to the sludge flocculation tank 2, while supplying fresh water to the sludge flocculation tank 2, the flocculated sludge remaining in the sludge flocculation tank 2 is supplied to the solid-liquid separation means 3 to separate this into the concentrated sludge and the separated water. Further, the separated water is circulated from the solid-liquid separation means 3 into the sludge flocculation tank 2 to utilize this as a part of the fresh water. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  In the present invention, a flocculant is added to sludge supplied to a sludge agglomeration tank to obtain agglomerated sludge, and then the agglomerated sludge is supplied to solid-liquid separation means to separate it into concentrated sludge and separated water. It is related with the sludge concentration method and sludge concentration apparatus which concentrate sludge by.

  In order to discard or incinerate various types of sludge, the sludge is dehydrated with a dehydrator. The higher the concentration of the sludge supplied to the dehydrator, the more efficiently the dehydration can be performed. For this reason, prior to the dewatering treatment by the sludge dewatering machine, the sludge is aggregated with a flocculant, and water is separated from the aggregated sludge (aggregated sludge) to concentrate the sludge. Various sludge concentrators have been proposed and put into practical use.

  An example of a screw press type sludge concentrating device previously proposed by the present applicant as a sludge concentrating device is shown in FIG. 3 (see, for example, Patent Document 1).

  That is, FIG. 3 is a schematic diagram showing the basic configuration of a conventional sludge concentrating device 1 ′. The sludge concentrating device 1 ′ shown in FIG. 3 includes a cylindrical tank-shaped sludge aggregating tank 2 having an open top surface and a solid sludge condensing tank. The liquid separation means 3 and a separation liquid tank 4 that contains the separation liquid are included.

  A sludge supply pipe 5 and a sludge discharge pipe 6 are connected to the bottom of the sludge aggregation tank 2, and a drain valve V <b> 1 is provided in the middle of the sludge discharge pipe 6. The sludge agglomeration tank 2 contains a stirrer 7 that is rotationally driven by a motor M1.

  The solid-liquid separation means 3 has a cylindrical filter tube 9 disposed in a vertical direction inside a cylindrical tank-shaped outer tube 8 having a sealed structure, and a spiral screw 10 is rotatably accommodated in the filter tube 9. Configured.

  Here, the peripheral surface of the portion of the filter tube 9 facing the outer tube 8 constitutes a filter surface 9a made of a punching plate or a wedge wire, and the sludge is disposed on the lower side of the filter tube 9. An agglomerated sludge introduction pipe 11 led out from the upper side of the agglomeration tank 2 is connected. A concentrated sludge discharge pipe 12 is led out from the upper side of the filter cylinder 9.

  The spiral screw 10 is rotationally driven by a motor M2 as a drive source, and the outer diameter thereof is set to be slightly smaller than the inner diameter of the filtration surface 9a of the filtration cylinder 9, and the spiral screw 10 A minute gap is formed between the outer peripheral edge of 10 and the filtration surface 9 a of the filtration cylinder 9.

  Further, the separation liquid tank 4 is connected to the upper and lower sides of the outer cylinder by two upper and lower connecting pipes 13, and a separation liquid discharge pipe 14 is led out from the upper side.

  In the sludge concentrator 1 ′ having the above configuration, sludge (raw mud) is supplied from the sludge supply pipe 5 to the sludge agglomeration tank 2, but before that, a flocculant is added to the sludge. Here, as the flocculant, any one can be used as long as it is subjected to sludge flocculation / dehydration treatment. Aluminum sulfate, polyaluminum chloride, ferric chloride, ferrous sulfate, poly Inorganic flocculants such as iron (polyferric sulfate), cationic, anionic, nonionic polymer flocculants, amphoteric polymer flocculants can be used, or inorganic flocculants and polymer flocculants can be used. It can also be used together.

  Thus, when the sludge to which the flocculant is added is supplied into the sludge aggregation tank 2, the sludge and the flocculant are agitated in the sludge aggregation tank 2 by the agitator 7 that is rotationally driven by the motor M1. The sludge is agglomerated sludge by aggregating solid components contained therein. The agglomerated sludge is introduced from the agglomerated sludge introduction pipe 11 into the filter cylinder 9 from below.

  In the solid-liquid separation means 3, the spiral screw 10 is driven to rotate at a predetermined speed in the filter cylinder 9 by the motor M 2, and the condensed sludge introduced into the filter cylinder 9 is rotated by the rotating spiral screw 10. While being conveyed upward, the water contained therein passes through the filtration surface 9a of the filtration cylinder 9 and is discharged as a separation liquid into the outer cylinder 8, and this separation liquid is separated from the two upper and lower connecting pipes 13 into the separation liquid. It is sent to the tank 4 and accommodated.

  Then, the separation liquid stored in the separation liquid tank 4 is discharged to the outside through the separation liquid discharge pipe 14. Further, the coagulated sludge conveyed upward in the filter cylinder 9 by the rotation of the spiral screw 10 is concentrated by separating water in the middle thereof to become concentrated sludge, and this concentrated sludge is the concentrated sludge discharge pipe. 12 is discharged to the outside and is subjected to a dehydration process by a dehydrator (not shown).

By the way, in such a sludge concentrating device 1 ′, at the end of the concentration operation, the supply of the sludge and the flocculant to the sludge aggregation tank 2 is stopped and the supply of the aggregate sludge to the solid-liquid separation means 3 is stopped ( For example, see Patent Document 2).
JP 2003-164899 A Japanese Patent Laid-Open No. 2002-253908

  However, when the supply of the sludge and the flocculant to the sludge agglomeration tank 2 is stopped at the end of the concentration operation as described above, and the supply of the agglomerated sludge to the solid-liquid separation means 3 is stopped, the agglomerated sludge is generated in the sludge agglomeration tank 2. Since the operation is stopped in a sufficiently remaining state, the agglomerated sludge rots in the sludge agglomeration tank 2 if left as it is. For this reason, conventionally, the drain valve V1 is opened, and the coagulated sludge remaining in the sludge coagulation tank 2 is discharged from the sludge discharge pipe 6 to a raw mud storage tank or the like (not shown), and then the sludge coagulation tank 2 is required. A cleaning method was adopted accordingly.

  However, the above method has the following problems.

  1) Since the coagulated sludge remaining in the sludge coagulation tank 2 is discharged as it is at the end of the operation, the solid matter recovery rate (SS recovery rate) decreases.

  2) Since the flocculent is added to the discharged sludge, the flocculant is wasted.

  3) Since the coagulated sludge is discharged as it is, the sludge discharge pipe 6 may be contaminated or blocked by the coagulated sludge.

  The present invention has been made in view of the above problems, and the purpose of the process is to collect the majority of the coagulated sludge remaining in the sludge coagulation tank at the end of the concentration operation as the concentrated sludge, thereby improving the solid matter recovery rate. An object of the present invention is to provide a sludge concentration method and a sludge concentrator capable of improving, eliminating waste of the flocculant, and preventing contamination and blockage of the sludge discharge pipe.

In order to achieve the above object, the invention described in claim 1 is characterized in that after adding a flocculant to the sludge supplied to the sludge agglomeration tank to obtain agglomerated sludge, the agglomerated sludge is supplied to the solid-liquid separation means. In the sludge concentration method of concentrating sludge by separating the sludge into concentrated sludge and separated water,
After stopping the supply of sludge to the sludge agglomeration tank, while supplying fresh water to the sludge agglomeration tank, the agglomerated sludge remaining in the sludge agglomeration tank is supplied to the solid-liquid separation means, and this is concentrated sludge and separated water. It is characterized by being separated into

  The invention described in claim 2 is characterized in that, in the invention described in claim 1, the separated water is returned from the solid-liquid separation means to the sludge flocculation tank and used as a part of the fresh water.

  A third aspect of the present invention is characterized in that, in the second aspect of the invention, an amount of makeup water substantially equal to the concentrated sludge is supplied to the sludge agglomeration tank as part of the fresh water.

  The invention according to claim 4 is the invention according to any one of claims 1 to 3, wherein after the supply of sludge to the sludge agglomeration tank is stopped, while supplying fresh water to the sludge agglomeration tank, the sludge agglomeration tank The solid-liquid separation means is operated until the sludge concentration within the set value falls below the set value, and when the sludge concentration falls below the set value, the operation of the solid-liquid separation means is stopped and the sludge in the sludge agglomeration tank is discharged. Features.

The invention according to claim 5 is a sludge agglomeration tank for aggregating sludge to which a flocculant is added to obtain agglomerated sludge, and a solid sludge for separating the agglomerated sludge supplied from the sludge agglomeration tank into concentrated sludge and separated water. In the sludge concentrator equipped with the liquid separation means,
A fresh water supply means for supplying fresh water to the sludge agglomeration tank after stopping the supply of sludge to the sludge agglomeration tank is provided.

  According to a sixth aspect of the present invention, in the fifth aspect of the present invention, the fresh water supply means includes a separated water return means for returning the separated water from the solid-liquid separation means to the sludge flocculation tank, and a sludge flocculation tank. It has a makeup water supply means for supplying makeup water.

  The invention according to claim 7 is the invention according to claim 6, wherein the makeup water supply means supplies the amount of makeup water substantially equal to the concentrated sludge to the sludge agglomeration tank as a part of the fresh water. And

  The invention according to claim 8 is the invention according to any one of claims 5 to 7, wherein the solid-liquid separation means includes a filter cylinder in which a spiral screw is rotatably housed, and the filter cylinder inside. And a driving means for rotationally driving the spiral screw, and the outer cylinder is arranged below the liquid level of the sludge agglomeration tank.

  According to the sludge concentration method of Claim 1 implemented using the sludge concentration apparatus of Claim 5, after completion | finish of the concentration operation by a sludge concentration apparatus, after supply of the sludge to a sludge aggregation tank is stopped, sludge The solid-liquid separation means continued to operate while supplying fresh water to the flocculation tank, and most of the flocculated sludge remaining in the sludge flocculation tank was recovered as concentrated sludge, so the solids recovery rate (SS recovery rate) was In addition to being increased, the flocculant added to the sludge before the end of operation is economical and not wasted.

  According to the second aspect of the invention, since the separated liquid separated by the solid-liquid separating means is used as a part of the fresh water, the separated liquid can be efficiently reused.

  According to the third and sixth aspects of the invention, the separated liquid separated by the solid-liquid separating means is circulated in the system and used as a part of fresh water, and the amount of concentrated sludge discharged outside the system is replenished. Since the water is supplied to the sludge agglomeration tank as a shortage of fresh water, the liquid level in the sludge agglomeration tank can be kept constant and a stable operation can be performed.

  According to invention of Claim 4, when the sludge density | concentration in a sludge coagulation tank falls sufficiently and the value becomes below a setting value, a driving | operation will be stopped and the sludge in a sludge coagulation tank will be discharged to a sludge discharge pipe. Therefore, the sludge discharge pipe is not contaminated or clogged, and the sludge agglomeration tank and solid-liquid separation means are not contaminated. Absent.

  According to the eighth aspect of the present invention, since the outer cylinder is disposed below the liquid level of the sludge agglomeration tank, the separation liquid accommodated in the outer cylinder is filled in the outer cylinder and filtered into the separation liquid. The filtration surface of the cylinder is buried, and the entire filtration surface of the filtration cylinder is provided for separating water from the coagulated sludge, and the separation efficiency is increased.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

  FIG. 1 is a schematic diagram showing a basic configuration of a sludge concentration apparatus 1 according to the present invention. In this figure, the same elements as those shown in FIG. Description is omitted.

  The sludge concentrating device 1 according to the present invention is characterized in that it is provided with a fresh water supply means for supplying fresh water to the sludge agglomeration tank 2 after stopping the supply of sludge and the flocculant to the sludge agglomeration tank 2 when the concentration operation is stopped. The fresh water supply means includes a separation liquid return pipe 15 as a separation water return means for returning the separation water accommodated in the separation liquid tank 4 to the sludge aggregation tank 2, and a separation liquid return pump P provided in the middle thereof. The replenishing water supply pipe 16 as a replenishing water supply means for supplying replenishing water to the sludge agglomeration tank 2 and a replenishing water supply pump (not shown) provided in the middle thereof. Here, as shown in the figure, the separation liquid return pipe 15 is led out from the bottom of the separation liquid tank 4 and is connected to the middle of the sludge supply pipe 5 (downstream of the place where the flocculant is added). The supply pipe 16 is also connected to the middle of the sludge supply pipe 5 (downstream of the location where the flocculant is added). An on-off valve V3 is provided in the middle of the separation liquid return pipe 15.

  Further, in the sludge concentrating device 1 according to the present embodiment, the outer cylinder 8 of the solid-liquid separation means 3 is disposed below the liquid level of the sludge agglomeration tank 2, and the filtration surface 9 a of the filter cylinder 9 is disposed on the outer cylinder 8. The other structure is the same as that of the conventional sludge concentrating device 1 ′ shown in FIG.

  Thus, also in the sludge concentrating device 1 according to the present embodiment, the sludge is finally separated into the concentrated sludge and the separated liquid by the solid-liquid separation means 3 as in the conventional sludge concentrating device 1 ′ shown in FIG. The concentrated sludge is discharged to the outside through the concentrated sludge discharge pipe 12 and subjected to a dehydration process by a dehydrator (not shown). The separated liquid passes from the separated liquid tank 4 through the separated liquid discharge pipe 14. Are discharged to the outside. At this time, the on-off valve V2 is closed.

  By the way, in this Embodiment, since the outer cylinder 8 is arrange | positioned below the liquid level of the sludge aggregation tank 2 as mentioned above, the separation liquid accommodated in this outer cylinder 8 is the outer cylinder 8. The filtration surface 9a of the filter cylinder 9 is buried in the separated liquid. For this reason, the filtration surface 9a of the filtration cylinder 9 is provided for separating the moisture from the coagulated sludge, and the separation efficiency is enhanced, so that the filtration cylinder 9, the solid-liquid separation means 3, and the sludge concentrating device. 1 can be downsized as a whole.

  Next, the sludge concentration method at the end of the concentration operation which is the gist of the present invention will be described.

  At the end of the concentration operation by the sludge concentrator 1, the supply of sludge to the sludge flocculation tank 2 and the addition of the flocculant to the sludge are stopped as before, but the on-off valve V2 is opened and the separated liquid return pump P The replenishing water supply pump (not shown) is driven to continue the operation of the solid-liquid separation means 3 while supplying fresh water to the sludge agglomeration tank 2.

  That is, when the supply of sludge to the sludge agglomeration tank 2 is stopped, the agglomerated sludge remains in the sludge agglomeration tank 2, but this agglomerated sludge is sent to the solid-liquid separation means 3 as in the steady operation. Thus, the agglomerated sludge is separated into the separated liquid and the agglomerated sludge is discharged to the outside through the concentrated sludge discharge pipe 12. On the other hand, the separation liquid is returned from the separation liquid tank 4 to the sludge agglomeration tank 2 through the separation liquid return pipe 15 and the sludge supply pipe 5 by the separation liquid return pump P, and used as a part of fresh water. .

Here, when the flow rate of the concentrated sludge discharged from the concentrated sludge discharge pipe 12 is Q ₁ and the flow rate of the separated liquid returned to the sludge flocculation tank 2 is Q ₂ , the liquid level in the sludge flocculation tank 2 is maintained and stabilized. In order to operate, it is necessary to replenish the sludge agglomeration tank 2 with an amount of fresh water equal to the flow rate Q _{1 of the} concentrated sludge discharged outside the system. For this reason, in this embodiment, an amount Q ₃ (= Q ₁ ) of make-up water equal to the flow rate Q _{1 of} concentrated sludge is supplied from the make-up water supply pipe 16 to the sludge aggregation tank 2.

  That is, in the present embodiment, the separation liquid separated by the solid-liquid separation means 3 is circulated in the system and used as a part of fresh water, and an amount equal to the amount of concentrated sludge discharged outside the system. By supplying water to the sludge agglomeration tank 2 as a shortage of clean water, the liquid level in the sludge agglomeration tank 2 is kept constant and a stable operation can be performed.

In addition, the amount of makeup water Q ₃ supplied to the sludge agglomeration tank 2 is slightly larger than the flow rate Q _{1 of the} concentrated sludge to be discharged, a small amount of separation liquid is discharged out of the system from the separation liquid discharge pipe 14, and the remainder is separated as separation liquid By returning through the return pipe 15, the liquid level in the sludge agglomeration tank 2 can be stably kept substantially constant without finely controlling the amount of makeup water.

  In addition, as replenishment water, the treated water etc. which were processed with waste water treatment facilities, such as city water, industrial water, and a sewage treatment facility, can be used.

  Thus, when the operation of the solid-liquid separation means 3 is continued while supplying fresh water to the sludge aggregation tank 2 as described above, the solid content (SS) in the aggregate sludge remaining in the sludge aggregation tank 2 is aggregated. Since it is recovered as sludge, the sludge concentration in the sludge agglomeration tank 2 gradually decreases. And if this sludge density | concentration falls sufficiently and falls below a preset value, a driving | operation will be stopped, the drain valve V1 will be opened, and the sludge in the sludge aggregation tank 2 will be discharged | emitted to the sludge discharge pipe 6. FIG.

  As described above, in the present embodiment, at the end of the concentration operation by the sludge concentrator 1, the supply of sludge to the sludge agglomeration tank 2 and the addition of the flocculant to the sludge are stopped, and then the sludge agglomeration tank 2 The solid-liquid separation means 3 is continuously operated while supplying fresh water (separated liquid + makeup water), and most of the coagulated sludge remaining in the sludge coagulation tank 2 is collected as concentrated sludge. (SS recovery rate) is increased, and the flocculant added to the sludge before the end of the operation is not wasted and is economical.

  In addition, when the sludge concentration in the sludge flocculation tank 2 is sufficiently lowered and the value falls below the set value, the operation is stopped and the sludge in the sludge flocculation tank 2 is discharged to the sludge discharge pipe 6. The discharge pipe 6 is not contaminated or clogged, and the sludge agglomeration tank 2 and the solid-liquid separation means 3 are not contaminated. These need to be washed (washed) after operation. There is no.

  Furthermore, in the present embodiment, since the separated liquid separated by the solid-liquid separating means 3 is returned to the sludge aggregation tank 2 and used as a part of fresh water, the amount of replenishing water can be reduced and economical. is there.

  In the present embodiment, the separation liquid is returned to the sludge agglomeration tank 2 and used as a part of fresh water. However, the separation liquid may be discharged as it is, and all of the fresh water may be covered with makeup water. .

  In the present embodiment, the addition of the flocculant is stopped together with the stoppage of the sludge supply to the sludge flocculation tank 2, but the addition of the flocculant is stopped by supplying fresh water, It may be after being supplied to the solid-liquid separation means 3 to some extent.

  Next, examples of the present invention will be specifically described in comparison with comparative examples. However, the examples given below are not intended to limit the present invention in any way.

The operation of concentrating excess sludge (concentration: 1.0%) obtained by treating sewage with an oxidation ditch was performed under the following conditions.
(1) Test equipment:
The sludge concentration apparatus 1 according to the present invention shown in FIG. 1 and the conventional sludge concentration apparatus 1 ′ shown in FIG. 3 were used.

<Sludge flocculation tank> Effective capacity: 1 m ³
<Solid-liquid separation means> Filtration cylinder dimensions: Diameter φ 350 mm x Height H 600 mm
(2) Operating conditions (common):
Common operating conditions are shown in Table 1.

（３）運転の停止方法：
・比較例：
運転終了後、汚泥凝集槽内の凝集汚泥をそのまま汚泥排出管へ排出した後、汚泥凝集槽を水洗した。

(3) How to stop operation:
・ Comparative example:
After the operation was completed, the coagulated sludge in the sludge coagulation tank was discharged as it was to the sludge discharge pipe, and then the sludge coagulation tank was washed with water.

-Method of the present invention:
After completion of the operation, the separated liquid was returned to the sludge aggregation tank at a flow rate of 16 m ³ / h for 6 minutes. The amount of makeup water and the amount of concentrated sludge were 4 m ³ / h.
(4) Operation result:
-Separation liquid SS during steady operation: Comparative example-The method of the present invention was 30 mg / L.

  -The time-dependent change of the sludge density | concentration in the sludge coagulation tank at the time of the operation stop by this invention method was as showing in FIG.

  As shown in FIG. 2, the sludge concentration in the sludge agglomeration tank decreased from 1% to 0.088% in 6 minutes.

・ SS recovery rate:
Table 2 shows the results of calculating the SS recovery rate.

本発明方法では、排出されるＳＳの合計量は３．７６ｋｇと、比較例の１２．８８ｋｇの約１／３となり、又、ＳＳ回収率は比較例の９８．９％から９９．７％に向上した。

In the method of the present invention, the total amount of discharged SS is 3.76 kg, which is about 1/3 of 12.88 kg of the comparative example, and the SS recovery rate is increased from 98.9% of the comparative example to 99.7%. Improved.

  From the above results, the effects of the present invention can be confirmed.

  The present invention can be applied to any sludge concentrating device other than the screw press type and a sludge concentrating method using the same, and the type of sludge to be treated is not limited.

It is the schematic which shows the basic composition of the sludge concentration apparatus which concerns on this invention. It is a figure which shows a time-dependent change of the sludge density | concentration in the sludge aggregation tank at the time of the concentration operation stop of the sludge concentration apparatus which concerns on this invention. It is the schematic which shows the basic composition of the conventional sludge concentration apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Sludge concentration apparatus 2 Sludge aggregation tank 3 Solid-liquid separation means 4 Separation liquid tank 5 Sludge supply pipe 6 Sludge discharge pipe 7 Stirrer 8 Outer cylinder 9 Filtration cylinder 9a Filtration surface 10 Spiral screw 11 Aggregated sludge introduction pipe 12 Concentrated sludge discharge pipe 13 Connection pipe 14 Separation liquid discharge pipe 15 Separation liquid return pipe 16 Supplementary water supply pipe M1, M2 Motor P Separation liquid return pump V1 Drain valve V2 On-off valve

Claims (8)

After adding a flocculant to sludge supplied to the sludge coagulation tank to obtain agglomerated sludge, the sludge is concentrated by supplying the agglomerated sludge to solid-liquid separation means and separating it into concentrated sludge and separated water. In the sludge concentration method to
After stopping the supply of sludge to the sludge agglomeration tank, while supplying fresh water to the sludge agglomeration tank, the agglomerated sludge remaining in the sludge agglomeration tank is supplied to the solid-liquid separation means, and this is concentrated sludge and separated water. A method for concentrating sludge, characterized in that   The sludge concentration method according to claim 1, wherein the separated water is returned from the solid-liquid separation means to the sludge agglomeration tank and used as a part of the fresh water.   3. The sludge concentration method according to claim 2, wherein an amount of make-up water substantially equal to the concentrated sludge is supplied to the sludge agglomeration tank as a part of the fresh water.   After stopping the supply of sludge to the sludge agglomeration tank, while supplying fresh water to the sludge agglomeration tank, operating the solid-liquid separation means until the sludge concentration in the sludge agglomeration tank becomes a set value or less, the sludge concentration The sludge concentration method according to any one of claims 1 to 3, wherein when the value becomes equal to or less than a set value, the operation of the solid-liquid separation means is stopped and the sludge in the sludge flocculation tank is discharged. A sludge aggregating apparatus comprising a sludge aggregating tank for aggregating sludge to which an aggregating agent is added to obtain agglomerated sludge, and a solid-liquid separation means for separating the agglomerated sludge supplied from the sludge aggregating tank into concentrated sludge and separated water. In
A sludge concentrating device comprising a fresh water supply means for supplying fresh water to the sludge agglomeration tank after the supply of sludge to the sludge agglomeration tank is stopped.   The fresh water supply means includes separation water return means for returning the separated water from the solid-liquid separation means to the sludge flocculation tank, and makeup water supply means for supplying makeup water to the sludge flocculation tank. The sludge concentration apparatus according to claim 5.   7. The sludge concentrating apparatus according to claim 6, wherein the makeup water supply means supplies a volume of makeup water substantially equal to the concentrated sludge to the sludge aggregation tank as a part of the fresh water.   The solid-liquid separation means includes a filtration cylinder in which a spiral screw is rotatably accommodated, an outer cylinder in which the filtration cylinder is accommodated, and a drive means for rotationally driving the spiral screw. The sludge concentrating device according to any one of claims 5 to 7, wherein a cylinder is disposed below the liquid level of the sludge aggregation tank.

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