JP5745897B2 - Sludge dewatering method - Google Patents

Description

  The present invention relates to a sludge dewatering method and relates to a dewatered filtrate treatment technique.

  Conventionally, as this type of technology, there is one described in Patent Document 1. This is because the flocculant is added to the liquid to be dehydrated supplied from the sludge storage tank and press-fitted into the screw press dehydrator, and the liquid to be dehydrated with the flocculent flocs formed by the flocculant is dehydrated by the screw press dehydrator. The dehydrated separation liquid discharged from the machine is supplied to the separation tank, fine bubbles are mixed and stirred in the dehydration separation liquid stored in the separation tank, and the SS in the dehydrated separation liquid is attached to the fine bubbles to separate the bubbles and separated. The foam layer containing SS is returned to the sludge storage tank, SS is kept in the system, and the dehydrated separation liquid from which SS has been removed is taken out of the system as treated water.

Patent No. 3883400

  However, since screw filter dehydrators and rotary press dehydrators use metal filter media, the sludge to be dewatered is pressed into the dehydrator and filtered. For this reason, the cohesive floc that is press-fitted into the dehydrator needs to have strength to withstand the press-fitting pressure.

  As shown in FIG. 7, when the chemical injection rate is low, the flocculant is consumed for charge neutralization and the flocs floc strength is lowered. If the chemical injection rate necessary for this charge neutralization is exceeded, the cross-linking / floc coarsening proceeds and the aggregate floc strength becomes high, which is the optimum level necessary for dehydration.

  However, the level of flocculation floc strength required for press-fitting filtration exceeds the optimum level required for dehydration, and the chemical injection rate of the polymer flocculant to be added must be increased, resulting in a large running cost.

  Moreover, a punching metal is often used for the metal filter medium. Punching metal has a feature that it is thin and difficult to clog, but has a low capture rate of aggregated flocs, SS leaks out of the screen, and the SS recovery rate tends to decrease.

Further, in the separation tank for storing the drained separation liquid, foaming occurs due to the unreacted residual coagulant remaining in the wastewater, and thus an antifoaming agent or the like is required to suppress foaming.
The present invention solves the above-described problems, and provides a sludge dewatering method capable of reducing the chemical injection rate of the flocculant, improving the SS recovery rate as a whole system, and further suppressing the foaming of drainage. With the goal.

  In order to solve the above problems, the sludge dewatering method of the present invention is to dewater the sludge to be dehydrated through the primary flocculation step, the mixing step, the separation step, the secondary flocculation step, and the dehydration step, and the primary flocculation step. In this step, a flocculant is injected into the sludge to be dehydrated to produce agglomerated sludge, and at least one of the concentrated zone separation liquid discharged from the dehydrator concentration zone and the dehydrated zone separation liquid discharged from the dehydration zone is mixed. In the mixing step, at least one of the concentrated zone separation liquid and the dehydration zone separation liquid supplied from the dehydration step is mixed with the coagulated sludge in the primary coagulation step to produce a mixed sludge. The mixed sludge is separated into a separated liquid and separated sludge, and the flocculant is mixed with the separated sludge of the separation process in the secondary flocculation process to produce the flocculated sludge, and the flocculated sludge of the secondary flocculation process is dehydrated with the dehydrator in the dewatering process. To do And butterflies.

  The sludge dewatering method of the present invention dehydrates sludge to be dehydrated through a mixing step, a separation step, a flocculation step, and a dehydration step, and the concentrated zone separation liquid and dehydration discharged from the concentration zone of the dehydrator in the dehydration step At least one of the dehydration zone separation liquid discharged from the zone is supplied to the mixing process, and at least one of the concentrated zone separation liquid and the dehydration zone separation liquid supplied from the dehydration process to the sludge to be dehydrated in the mixing process, and the flocculant To produce a mixed sludge, and in the separation step, the mixed sludge in the mixing step is separated into a separation liquid and a separated sludge. In the dehydration process, the coagulated sludge in the coagulation process is dehydrated with a dehydrator.

  As described above, according to the present invention, the SS component discharged from the dehydrator with the residual coagulant component attached is returned to the dehydrator, so that the coagulant drug can be used even in a dehydrator that uses a metal filter medium. The injection rate can be reduced, and the running cost can be suppressed.

  Since the SS leaked from the dehydrator can be supplied again to the dehydrator, the SS recovery rate of the entire system can be improved, and the incidental facilities such as the separation liquid processing apparatus can be simplified.

  In addition, the SS portion discharged from the dewatering zone has already been flocked, and by returning this flocked SS portion to the sludge to be dewatered, the sludge to be deflocculated becomes a flocs flocs with the SS portion flocked as the core. Facilitate.

  Furthermore, by reducing the unreacted flocculant component contained in the wastewater, troubles caused by the foaming of the wastewater in a separation liquid tank or the like disposed in the subsequent stage can be suppressed, and the amount of chemicals used such as an antifoaming agent is reduced.

  Also, the concentrated zone separation liquid discharged from the concentration zone containing a large amount of unreacted residual flocculant component is mixed with the dehydration zone separation liquid discharged from the dehydration zone having a small residual flocculant component but a high concentration of SS. Thus, the chemical injection rate of the flocculant can be further reduced by attaching the residual flocculant component of the concentrated zone separation liquid to the SS component of the dehydration zone separation liquid.

The block diagram which shows the dehydration method of the sludge in the 1st Embodiment of this invention The block diagram which shows the dehydration method of the sludge in the 2nd Embodiment of this invention. The block diagram which shows the dehydration method of the sludge in the 3rd Embodiment of this invention. The block diagram which shows the dehydration method of the sludge in the 4th Embodiment of this invention. The block diagram which shows the dewatering method of the sludge in the 5th Embodiment of this invention. The top view which shows the saucer of the dehydration separation liquid which is a mixing means in embodiment of this invention The graph which shows the correlation of the chemical injection rate and the aggregation floc strength

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, a first embodiment of the invention will be described with reference to the drawings. As shown in FIG. 1, the sludge dewatering method according to the first embodiment uses the raw sludge stored in the sludge storage tank 1 as the sludge to be dewatered, and performs the primary agglomeration performed in the first agglomeration mixing tank 2. Sludge to be dehydrated through a step, a mixing step performed by the mixing means 3, a separation step performed by the separation device 4, a secondary aggregation step performed in the second agglomeration mixing tank 5, and a dehydration step performed by the screw press dehydrator 6. Is dehydrated.

  In the middle of the sludge pipe 21 for supplying the sludge 7 to be dehydrated from the sludge storage tank 1 to the first flocculation / mixing tank 2, or in the first flocculation / mixing tank 2, the polymer flocculant 8 is injected from the flocculant pipe 22. The injected flocculant is mixed with the sludge to be dehydrated in the first flocculation / mixing tank 2 to produce the flocculated sludge.

  The agglomerated sludge in the first agglomeration and mixing tank 2 is supplied to the mixing means 3 through the sludge pipe 23, and at least a concentrated zone separation liquid discharged from the concentration zone of the screw press dehydrator 6 and a dehydrated zone separation liquid discharged from the dehydration zone. Either one is supplied to the mixing means 3 through the separation liquid pipes 24 and 25, respectively, and the mixed zone 3 is mixed with the concentrated sludge in the first agglomeration and mixing tank 2 by the mixing means 3 to generate mixed sludge. To do.

  In the present embodiment, the concentrated zone separation liquid and the dehydration zone separation liquid are supplied to the mixing means 3 through the separation liquid pipes 24 and 25. However, the mixing means 3 is installed below the screw press dehydrator 6 to provide the concentrated zone separation liquid. It is also possible to cause the dehydration zone separation liquid to flow directly from the screw press dehydrator 6 to the mixing means 3.

  As shown in FIG. 6, the mixing means 3 includes a tray 9 for a dehydrated separation liquid having a square shape in plan view, which is installed at the lower part of the screw press dehydrator 6. Alternatively, the tank can be set separately without using the dehydrating separator tray 9 as the mixing means.

The dewatering separation liquid receiving tray 9 has a stirring portion 9b that is recessed in a pyramid shape toward the discharge port 9a, and performs a mixing action using the water flow of the concentrated zone separation liquid and the dehydration zone separation liquid as a driving force.
The mixed sludge of the mixing means 3 is supplied to the separation device 4 through the sludge pipe 26, and the mixed sludge is separated into the separated liquid and the separated sludge by the separation device 4. The separator 4 can be applied to any type such as a gravity type, a bubble separation type, a screen type, and a belt type.

  The separation liquid is supplied to a subsequent separation liquid tank (not shown) and a separation liquid processing apparatus (not shown), and the separated sludge is quantitatively supplied to the second agglomeration mixing tank 5 through a sludge pipe 27 provided with a metering pump 10. To do. Although the configuration using the metering pump 10 is shown in the present embodiment, other types of pumps and supply means may be employed instead of the metering pump 10. For example, each device is arranged at a position with a difference in elevation, and the separated sludge is supplied from the separation device 4 to the second coagulation mixing tank 5 by natural flow.

  In the second flocculation / mixing tank 5, the flocculant is mixed with the separated sludge supplied from the separation device 4 to generate the flocculated sludge. This flocculant may be the polymer flocculant 8 supplied to the first flocculent mixing tank 2, or may be an inorganic flocculant such as polyferric sulfate.

  The screw press dehydrator 6 dehydrates the coagulated sludge in the second coagulation / mixing tank 5, discharges the dehydrated cake outside the system, and discharges the concentrated zone separation liquid discharged from the concentration zone and the dehydration zone as described above. The dehydration zone separation liquid can be supplied to the mixing means 3 through the separation liquid pipes 24 and 25, respectively.

  The screw press dehydrator 6 in the present embodiment has a configuration having a concentration zone in the first half and a dehydration zone in the second half, and the concentrated zone separation liquid discharged from the concentration zone in the first half is unreacted residual agglomeration. The dehydration zone separation liquid discharged from the dehydration zone in the latter half is high in the concentration of SS, although the residual coagulant component is small.

  Because of such a configuration, the concentration zone separation liquid and the dehydration zone separation liquid are mixed by the mixing means 3, and the residual flocculant component of the concentration zone separation liquid is adhered to the SS component of the dehydration zone separation liquid. By concentrating the SS component to which the residual flocculant component adheres with the separation device 4 and returning it to the screw press dehydrator 6, the drug injection rate of the flocculant is reduced even in the screw press dehydrator 6 using a metal filter medium. Running costs can be reduced.

  Furthermore, since the mixed sludge is produced by mixing the separated liquid of the screw press dehydrator 6 with the coagulated sludge of the first coagulation mixing tank 2 by the mixing means 3, the dewatering performance is improved by the effect of the residual coagulant, and the screw The sludge concentration supplied to the press dehydrator 6 is increased, and the dewatering performance is further improved. Moreover, in this Embodiment, since the aggregation floc destroyed by the metering pump 10 is aggregated again in the 2nd aggregation mixing tank 5, and it throws into the screw press dehydrator 6, dehydration performance improves further.

  Since the SS leaked from the punching metal or the like that is the metal filter material of the screw press dehydrator 6 can be supplied again to the screw press dehydrator 6, the SS recovery rate as a whole system can be improved, and the separation liquid processing device, etc. Ancillary facilities can be simplified.

  The SS portion discharged from the dewatering zone has already been flocked. By returning the flocked SS portion to the sludge to be dewatered, the flocked SS portion serves as a nucleus, and the mixing means 3 and the second The coagulation mixing tank 5 promotes coagulation flocking of the sludge to be dehydrated.

  Furthermore, by reducing the unreacted flocculant component contained in the wastewater, troubles caused by the foaming of the wastewater in a separation liquid tank or the like disposed in the subsequent stage can be suppressed, and the amount of chemicals used such as an antifoaming agent is reduced.

If the concentrated zone separation liquid and the dehydration zone separation liquid are mixed using the water flow generated in the tray 9 for the dehydration separation liquid, there is no need to provide a separate mixing tank or the like.
In the present embodiment, since the separated sludge is quantitatively supplied by the metering pump 10, the rapid flow rate fluctuation is eliminated and the operation of the screw press dehydrator 6 is stabilized.
(Second Embodiment)
In the first embodiment, the first aggregation / mixing tank 2 and the second aggregation / mixing tank 5 are used. However, it is possible to eliminate the first agglomeration mixing tank 2.
This configuration is shown in FIG. 2 as a second embodiment.

In the configuration shown in FIG. 2, the same reference numerals are given to the components described in FIG. 1 and the description thereof is omitted.
Here, it is set as the structure provided only with the one aggregation mixing tank 51 arrange | positioned in the front | former stage of the screw press dehydrator 6. FIG.

  The sludge dewatering method according to this configuration is dehydrated through a mixing step performed by the mixing means 3, a separation step performed by the separation device 4, a coagulation step performed by the coagulation mixing tank 51, and a dehydration step performed by the screw press dehydrator 6. The target sludge is dehydrated.

The polymer flocculant 8 is injected from the flocculant pipe 22 in the middle of the sludge pipe 21 that supplies the dewatered sludge 7 from the sludge storage tank 1 to the mixing means 3.
The concentrated zone separation liquid discharged from the concentration zone of the screw press dehydrator 6 and the dehydrated zone separation liquid discharged from the dehydration zone are supplied to the mixing means 3 via the separation liquid pipes 24 and 25, respectively, and the mixing means 3 supplies the sludge 7 to be dehydrated. A mixed sludge is produced by mixing the concentrated zone separation liquid and the dehydration zone separation liquid.

  In the present embodiment, the concentrated zone separation liquid and the dehydration zone separation liquid are supplied to the mixing means 3 through the separation liquid pipes 24 and 25. However, the mixing means 3 is installed below the screw press dehydrator 6 to provide the concentrated zone separation liquid. It is also possible to cause the dehydration zone separation liquid to flow directly from the screw press dehydrator 6 to the mixing means 3.

  The mixed sludge of the mixing means 3 is supplied to the separation device 4 through the sludge pipe 26, and the mixed sludge is separated into the separated liquid and the separated sludge by the separation device 4. The separation liquid is supplied to a subsequent separation liquid tank (not shown) and a separation liquid processing apparatus (not shown), and the separated sludge is quantitatively supplied to the agglomeration mixing tank 51 through a sludge pipe 27 provided with a metering pump 10.

  Although the configuration using the metering pump 10 is shown in the present embodiment, other types of pumps and supply means may be employed instead of the metering pump 10. For example, each device is arranged at a position with a difference in elevation, and the separated sludge is supplied from the separation device 4 to the coagulation mixing tank 51 by natural flow.

  In the flocculation mixing tank 51, the flocculant is mixed with the separated sludge supplied from the separation device 4 to generate the flocculated sludge. This flocculant may be the polymer flocculant 8 previously injected, or may be an inorganic flocculant such as polyferric sulfate.

The screw press dehydrator 6 dehydrates the coagulated sludge in the coagulation mixing tank 51 and discharges the dewatered cake out of the system. As described above, the concentrated zone separation liquid discharged from the concentration zone and the dehydration zone separation liquid discharged from the dehydration zone. Are supplied to the mixing means 3 through the separation liquid pipes 24 and 25, respectively. Other basic functions and effects are the same as those of the first embodiment.
(Third embodiment)
In the first embodiment, the first aggregation / mixing tank 2 and the second aggregation / mixing tank 5 are used. However, the second aggregation / mixing tank 5 may be eliminated.

This configuration is shown in FIG. 3 as a third embodiment. In the configuration shown in FIG. 3, the same reference numerals are given to the components described in FIG. 1 and the description thereof is omitted.
Here, it is set as the structure provided only with the one aggregation mixing tank 52 arrange | positioned in the front | former stage of the mixing means 3. FIG. Other configurations are the same as those in FIG. 1, and the basic operational effects are the same as those in the first embodiment.

  The sludge dewatering method in this configuration is the sludge to be dehydrated through the coagulation step performed in the coagulation mixing tank 52, the mixing step performed by the mixing means 3, the separation step performed by the separation device 4, and the dehydration step performed by the screw press dehydrator 6. Is dehydrated.

  In the middle of the sludge pipe 21 for supplying the dewatered sludge 7 from the sludge storage tank 1 to the flocculation / mixing tank 52, or in the flocculation / mixing tank 52, the polymer flocculant 8 is injected from the flocculant pipe 22, and the injected flocculant is flocculated. The mixing sludge is mixed with the sludge to be dehydrated in the mixing tank 52 to generate agglomerated sludge.

  Aggregated sludge in the agglomeration mixing tank 52 is supplied to the mixing means 3 through the sludge pipe 23, and the concentrated zone separation liquid discharged from the concentration zone of the screw press dehydrator 6 and the dehydrated zone separation liquid discharged from the dehydration zone are separated into the separation liquid pipe 24. , 25 to supply the mixing means 3, and the mixing means 3 mixes the concentrated zone separation liquid and the dehydration zone separation liquid with the aggregated sludge in the aggregation mixing tank 52 to generate mixed sludge.

  In the present embodiment, the concentrated zone separation liquid and the dehydration zone separation liquid are supplied to the mixing means 3 through the separation liquid pipes 24 and 25. However, the mixing means 3 is installed below the screw press dehydrator 6 to provide the concentrated zone separation liquid. It is also possible to cause the dehydration zone separation liquid to flow directly from the screw press dehydrator 6 to the mixing means 3.

  The mixed sludge of the mixing means 3 is supplied to the separation device 4 through a sludge pipe 26, and the mixed sludge is separated into a separated liquid and a separated sludge by the separation device 4. The separation liquid is supplied to a subsequent separation liquid tank (not shown) and a separation liquid processing apparatus (not shown), and the separated sludge is quantitatively supplied to the screw press dehydrator 6 through a sludge pipe 27 provided with a metering pump 10.

  Although the configuration using the metering pump 10 is shown in the present embodiment, other types of pumps and supply means may be employed instead of the metering pump 10. For example, each device is arranged at a position with a difference in elevation, and the separated sludge is supplied from the separation device 4 to the screw press dehydrator 6 by natural flow.

The screw press dehydrator 6 dehydrates the separated sludge, discharges the dehydrated cake outside the system, and mixes the concentrated zone separation liquid discharged from the concentration zone and the dehydrated zone separation liquid discharged from the dehydration zone through the separation liquid pipes 24 and 25, respectively. Supply to means 3.
(Fourth embodiment)
In the first embodiment, the first aggregation / mixing tank 2 and the second aggregation / mixing tank 5 are used. However, the second aggregation / mixing tank 5 may be eliminated.

This configuration is shown in FIG. 4 as a fourth embodiment. In the configuration shown in FIG. 4, the same components as those described in FIG.
Here, it is set as the structure provided only with the one aggregation mixing tank 52 arrange | positioned in the back | latter stage of the mixing means 3. FIG. Other configurations are the same as those in FIG. 1, and the basic operational effects are the same as those in the first embodiment.

  The sludge dewatering method in this configuration is to dewater the sludge to be dehydrated through a coagulation step performed in the coagulation mixing tank 52, a separation step performed by the separation device 4, and a dehydration step performed by the screw press dehydrator 6. The mixed sludge produced | generated at the mixing process of the mixing means 3 to the tank 52 is supplied.

  In the middle of the sludge pipe 21 for supplying the dewatered sludge 7 from the sludge storage tank 1 to the flocculation / mixing tank 52, or in the flocculation / mixing tank 52, the polymer flocculant 8 is injected from the flocculant pipe 22, and the injected flocculant is flocculated. The mixing sludge is mixed with the sludge to be dehydrated in the mixing tank 52 to generate agglomerated sludge.

  The agglomerated sludge in the agglomeration mixing tank 52 is separated into a separation liquid and a separated sludge by the separation device 4. The separation liquid is supplied to a subsequent separation liquid tank (not shown) and a separation liquid processing apparatus (not shown), and the separated sludge is quantitatively supplied to the screw press dehydrator 6 through a sludge pipe 27 provided with a metering pump 10.

  Although the configuration using the metering pump 10 is shown in the present embodiment, other types of pumps and supply means may be employed instead of the metering pump 10. For example, each device is arranged at a position with a difference in elevation, and the separated sludge is supplied from the separation device 4 to the screw press dehydrator 6 by natural flow.

  The screw press dehydrator 6 dehydrates the separated sludge, discharges the dehydrated cake outside the system, and mixes the concentrated zone separation liquid discharged from the concentration zone and the dehydrated zone separation liquid discharged from the dehydration zone through the separation liquid pipes 24 and 25, respectively. The concentrated zone separation liquid and the dehydration zone separation liquid are mixed by the mixing means 3 to generate mixed sludge, and the mixed sludge is supplied to the coagulation mixing tank 52 by the sludge pipe 26.

In the present embodiment, the concentrated zone separation liquid and the dehydration zone separation liquid are supplied to the mixing means 3 through the separation liquid pipes 24 and 25. However, the mixing means 3 is installed below the screw press dehydrator 6 to provide the concentrated zone separation liquid. It is also possible to cause the dehydration zone separation liquid to flow directly from the screw press dehydrator 6 to the mixing means 3.
(Fifth embodiment)
In the first embodiment, the first flocculation / mixing tank 2 and the second flocculation / mixing tank 5 are used, but the second flocculation / mixing tank 5 is eliminated, and the first agglomeration / mixing tank 2 is screw-pressed. It is also possible to supply the dewatering sludge to the dehydrator 6.

This configuration is shown in FIG. 5 as a fourth embodiment. In the configuration shown in FIG. 5, the same components as those described in FIG.
Here, only one coagulation-mixing tank 53 arranged in the front stage of the screw press dehydrator 6 is provided, and the dewatering sludge is supplied from the coagulation-mixing tank 53 to the screw press dehydrator 6.

The sludge dewatering method in this configuration is to dewater the sludge to be dehydrated through a coagulation step performed in the coagulation mixing tank 53 and a dehydration step performed in the screw press dehydrator 6.
In the middle of the sludge pipe 21 for supplying the sludge 7 to be dehydrated from the sludge storage tank 1 to the flocculation / mixing tank 53 or in the flocculation / mixing tank 53, the polymer flocculant 8 is injected from the flocculant pipe 22, and the injected flocculant is flocculated The mixing tank 53 is mixed with the sludge to be dehydrated to produce agglomerated sludge. At this time, the separated sludge of the separation device 4 described later is mixed.

  The agglomerated sludge in the agglomeration mixing tank 53 is supplied to the screw press dehydrator 6 through the sludge pipe 31 and dehydrated. The screw press dehydrator 6 dehydrates the coagulated sludge, discharges the dehydrated cake out of the system, and mixes the concentrated zone separation liquid discharged from the concentration zone and the dehydrated zone separation liquid discharged from the dehydration zone through the separation liquid pipes 24 and 25, respectively. Supply to means 3.

  In the present embodiment, the concentrated zone separation liquid and the dehydration zone separation liquid are supplied to the mixing means 3 through the separation liquid pipes 24 and 25. However, the mixing means 3 is installed below the screw press dehydrator 6 to provide the concentrated zone separation liquid. It is also possible to cause the dehydration zone separation liquid to flow directly from the screw press dehydrator 6 to the mixing means 3.

  After the concentration zone separation liquid and the dehydration zone separation liquid are mixed by the mixing means 3, the separation apparatus 4 separates the separation zone liquid and the separation sludge, and the separation sludge is supplied to the coagulation mixing tank 53 by the metering pump 33 through the sludge pipe 32. . In the flocculation mixing tank 53, as described above, the polymer flocculant 8 is injected into the sludge to be dehydrated, and the separated sludge of the separation device 4 is mixed to generate the flocculated sludge.

  Although the configuration using the metering pump 33 is shown in the present embodiment, other types of pumps and supply means may be employed instead of the metering pump 33. For example, each device is arranged at a position with a difference in elevation, and the separated sludge is supplied from the separation device 4 to the coagulation mixing tank 53 by natural flow.

  In this configuration, since the SS component to which the residual flocculant component is adhered is directly returned to the flocculent mixing tank 53, the residual flocculant component can be reused before the flocculating effect of the residual flocculant component deteriorates. The dehydrating property is improved. In addition, the separation sludge of the separation device 4 may be returned to the sludge pipe 21 or the flocculant pipe 22 as well as the coagulation mixing tank 53.

DESCRIPTION OF SYMBOLS 1 Sludge storage tank 2 1st coagulation mixing tank 3 Mixing means 4 Separation apparatus 5 2nd coagulation mixing tank 6 Screw press dehydrator 7 Sludge to be dehydrated 8 Polymer flocculant

Claims (2)

The dewatering target sludge is dehydrated through the primary flocculation step, the mixing step, the separation step, the secondary flocculation step, and the dehydration step,
In the primary flocculation process, flocculant is injected into the sludge to be dewatered to produce flocculated sludge,
Supplying at least one of the concentrated zone separation liquid discharged from the concentration zone of the dehydrator in the dehydration process and the dehydration zone separation liquid discharged from the dehydration zone to the mixing process;
In the mixing step, the agglomerated sludge in the primary agglomeration step is mixed with at least one of the concentrated zone separation liquid supplied from the dehydration step and the dehydration zone separation liquid to produce a mixed sludge,
In the separation process, the mixed sludge in the mixing process is separated into a separated liquid and a separated sludge,
In the secondary flocculation process, flocculant is mixed with the separated sludge in the separation process to produce flocculated sludge,
A method for dewatering sludge, characterized in that the dewatering process dehydrates the coagulated sludge in the secondary coagulation process with a dehydrator. The dehydration target sludge is dehydrated through the mixing step, separation step, coagulation step and dehydration step,
Supplying at least one of the concentrated zone separation liquid discharged from the concentration zone of the dehydrator in the dehydration process and the dehydration zone separation liquid discharged from the dehydration zone to the mixing process;
At least one of the concentrated zone separation liquid supplied from the dehydration process and the dehydration zone separation liquid and the flocculant are mixed with the sludge to be dehydrated in the mixing process to produce mixed sludge,
In the separation process, the mixed sludge in the mixing process is separated into a separated liquid and a separated sludge,
In the coagulation process, the coagulant is mixed with the separation sludge of the separation process to produce coagulated sludge,
A method for dewatering sludge, comprising dewatering the coagulated sludge in the coagulation step with a dehydrator in the dehydration step.

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