JP6623094B2 - Sludge treatment equipment and sludge treatment method - Google Patents

Description

  The present invention relates to a sludge treatment facility and a sludge treatment method for treating sludge such as sludge and digested sludge generated from a biological treatment process in a sewage treatment plant.

  As such a sludge treatment facility and a sludge treatment method, for example, in Patent Document 1, a polymer flocculant (polymer) is added to the treated sludge for agglomeration treatment, followed by a concentration treatment, and thus the concentrated sludge thus agglomerated and concentrated. It is dehydrated by a centrifugal dehydrator or a screw press type dehydrator and separated into a dehydrated cake and a dehydrated separation liquid. Of these, the dehydrated separation liquid containing residual polymer is returned to the treated sludge before being condensed and concentrated. Thus, what performs efficient coagulation, concentration, and dehydration of sludge is described. In the sludge treatment facility and the sludge treatment method described in Patent Document 1, when the treated sludge is condensed and concentrated, the residual polymer alone cannot be agglomerated. Therefore, the polymer is added to the treated sludge as described above, and the agglomeration treatment is performed. At the same time, the polymer is added to the coagulated and concentrated coagulated sludge for coagulation treatment, and the concentrated separation liquid separated from the coagulated sludge has little residual polymer, so that it is discharged out of the system.

  Patent Document 2 describes that digested sludge having a high alkalinity is diluted and mixed with washing water having a low alkalinity, and the digested sludge is concentrated using a centrifugal concentrator without adding a polymer. In such a sludge treatment facility and a sludge treatment method, the alkalinity and colloidal components contained in the digested sludge can be excluded as a concentrated separation liquid, so that the amount of polymer added in the subsequent dehydration step can be greatly reduced. That is, what is described in Patent Document 2 is a proposal of a sludge treatment facility and a sludge treatment method using a so-called centrifugal concentrator.

JP 2006-035166 A JP-A-57-136999

  By the way, in Patent Document 1, it is described that a double cylindrical sludge concentrating device is used for concentrating the treated sludge. However, in such a concentrating device using a metal filter medium, a polymer is added to the treated sludge. It is necessary to form agglomerated sludge by adding, especially in the case of sludge containing a large amount of components that inhibit agglomeration such as colloid substances in the treated sludge such as digested sludge, the amount of polymer required for the agglomeration treatment Rises significantly. Furthermore, Patent Document 1 describes that the dehydrated separation liquid is returned to the treated sludge before being concentrated as described above, but in order to exert the effect of the residual polymer, the dehydrated separation liquid is used. It is necessary to return a large amount, and the treated sludge is diluted to increase the treated sludge amount.

  Therefore, in the sludge treatment facility and the sludge treatment method described in Patent Document 1, the amount of polymer in the flocculation treatment before the concentration treatment increases due to the influence of the flocculation inhibitor contained in the treated sludge, leading to an increase in polymer cost. Furthermore, since it is necessary to return a large amount of dehydrated separation liquid to the treated sludge, it is necessary to enlarge the concentration apparatus, which is inefficient and uneconomical.

In general, digested sludge is washed by diluting and mixing with water 3 to 4 times the volume of treated sludge so that the alkalinity is 600 CaCO ₃ -mg / L or less, followed by solid-liquid separation. However, in the case of the sludge treatment facility and the sludge treatment method described in Patent Document 2, it is necessary to enlarge the centrifugal concentrator because the amount of treated sludge increases to four times by diluting with water. There is. Furthermore, the water content of the dewatered cake cannot be reduced in the dewatering process because the colloidal substances that inhibit coagulation and dewatering are removed in the sludge washing process and the electrolyte useful for the dewatering is also removed. .

  The present invention has been made under such a background, and efficiently removes a colloidal substance that inhibits sludge aggregation and effectively uses an electrolyte and a residual polymer that reduce the water content of a dehydrated cake. It is another object of the present invention to provide a sludge treatment facility and a sludge treatment method capable of performing an economical sludge treatment.

  In order to solve the above-mentioned problems and achieve such an object, the sludge treatment facility of the present invention comprises a concentration means for concentrating the treated sludge connected to the treated sludge supply path, and a concentration by the concentration means. A dewatering means for dewatering the concentrated sludge, a concentrated sludge supply path connecting the concentration means and the dewatering means, and a dewatering drain tank for holding dewatered wastewater dehydrated from the concentrated sludge by the dewatering means, An electrolyte can be supplied to the dewatering drain tank, and the dewatered drain circulation supply path for supplying the dehydrated drainage retained in the dewatering drain tank to the concentrated sludge supply path and circulating it to the dehydrating means. Are connected.

  Further, the sludge treatment method of the present invention provides a concentration step for supplying and concentrating the treated sludge to a concentration means connected to the treated sludge supply channel, and the concentrated sludge concentrated by this concentration step via the concentrated sludge supply channel. A dehydration process for supplying the dehydration means to the dewatering means, a dehydration drainage holding process for holding the dewatered drainage dehydrated from the concentrated sludge in the dehydration process in the dewatering drainage tank, and a dehydration drainage tank in the dehydration drainage holding process. A dehydrating waste water circulation for supplying an electrolyte to the dehydrated waste water held and supplying the dehydrated waste water supplied with the electrolyte to the concentrated sludge supply passage through the dehydration waste water circulation supply passage and circulating it to the dehydrating means. And a supply process.

  In the sludge treatment facility and the sludge treatment method configured as described above, the electrolyte can be supplied to the dewatering drain tank that holds the dewatered drainage that has been dehydrated from the concentrated sludge and separated from the sludge cake. The dewatered wastewater mixed with the supplied electrolyte is supplied to the concentrated sludge supply passage through the dewatered wastewater circulation supply passage and circulated to the dewatering means, and the aggregation of the concentrated sludge is promoted by the mixed electrolyte.

  Further, the electrolyte that promotes the aggregation of the concentrated sludge in this way is dehydrated from the concentrated sludge together with the dewatered wastewater, returned to the dewatered drainage tank, supplied again to the concentrated sludge supply path, and circulated to the dewatering means. There is no need to replenish electrolyte during sludge treatment. For this reason, it is possible to reduce the amount of electrolyte necessary for sludge treatment, and to promote efficient and economical sludge treatment.

  When the dewatered wastewater mixed with the electrolyte supplied to the dewatered drainage tank is supplied to the concentrated sludge supply path via the dewatered drainage circulation supply path and circulated through the dewatering means, The amount of dewatered wastewater supplied to the concentrated sludge supply channel is about 1 to 2 times the volume of the concentrated sludge supplied to the dewatering means, or the sludge concentration of the concentrated sludge after the dewatered wastewater is supplied is mass It is desirable to adjust so that it may become about 3-4 mass%. If the amount of dewatered wastewater supplied to the concentrated sludge is small, the concentration of the concentrated sludge increases, so that it is impossible to achieve efficient dewatering without allowing the polymer and concentrated sludge to react in the subsequent dewatering process. There is a fear. On the other hand, when the supply amount of the dewatered wastewater is large, the adverse effect of the sludge being diluted is greater than the positive effect of the electrolyte and the residual polymer, so that the water content of the dewatered sludge is increased in the subsequent dewatering step.

  Here, first, in the sludge treatment facility, the electrolyte is supplied to the dewatering drain tank before starting the sludge treatment and mixed with the dewatered drainage drained into the dewatering drain tank during the sludge treatment. The sludge bypass passage for bypassing the treated sludge to be supplied to the dewatering means is provided in the treated sludge supply passage, and the electrolyte supplied to the dewatered drain tank is replaced by the electrolyte contained in the dewatered waste water from which the treated sludge has been dehydrated. In the sludge treatment method, the treated sludge supply path and the dewatering means are connected by a sludge bypass path, and the treated sludge is supplied to the dewatering means via the sludge bypass path before starting sludge treatment. And what is necessary is just to supply the said electrolyte contained in the said dewatering drainage which dehydrated this process sludge to the said dewatering drainage tank.

  That is, electrolytes such as phosphates, sulfates, bicarbonates, ammonium salts and the like are originally contained in the treated sludge as described above, and the treated sludge supply path through the sludge bypass path before the start of the sludge treatment. Then, the treated sludge is bypassed to the dewatering means and dehydrated, whereby the electrolyte in the treated sludge is held in the dewatered drainage tank together with the dewatered wastewater. Therefore, after the dehydrated wastewater containing a predetermined amount of electrolyte is held in the dewatered wastewater tank, the sludge bypass path is closed and the normal sludge treatment as described above is performed, so that the electrolyte originally contained in the treated sludge is removed. It can be dehydrated by supplying it to the concentrated sludge and circulating it to the dehydrating means while promoting aggregation.

  Similarly, in order to supply the electrolyte to the dewatering drainage tank before starting the sludge treatment and mix it with the dewatered wastewater during the sludge treatment, secondly, in the sludge treatment facility, an electrolyte supply means is provided in the dewatering drainage tank. The electrolyte can be supplied from the electrolyte supply means to the dewatering drain tank, and in the sludge treatment method, the electrolyte supply means is similarly connected to the dewatered drain tank, and at least before the sludge treatment is started. The electrolyte may be supplied from the electrolyte supply means to the dewatering drain tank.

  In this way, by supplying the electrolyte directly to the dewatering drainage tank, coagulation is promoted by adding the electrolyte to the dewatering drainage and mixing with the concentrated sludge, and efficient dehydration can be achieved in the dewatering means. At the same time, the electrolyte contained in the dewatered effluent discharged from the dehydrating means can be circulated for effective use. In addition, when the electrolyte is supplied directly to the dewatered drainage tank by the electrolyte supply means, the electrolytic mass of the dewatered wastewater in the dewatered drainage tank is reduced due to the change in the properties of the treated sludge during the sludge treatment. Even in this case, it is possible to easily replenish the electrolyte and promote aggregation of the concentrated sludge.

  On the other hand, a washing water supply means is connected to the concentration means, and washing water is supplied from the washing water supply means to the treated sludge concentrated by the concentration means, and the treated sludge being concentrated is washed and concentrated. In this manner, so-called repulp washing may be performed. Thus, by performing repulp washing in the concentration means, the colloidal substance in the treated sludge in which the concentration has progressed to some extent can be more efficiently removed. And even if the electrolyte in the treated sludge is discharged together with the colloidal substance by washing the treated sludge in this way, according to the present invention, the electrolyte is mixed with the concentrated sludge supplied to the dewatering means, so that the dehydrated cake The sludge can be efficiently agglomerated.

  In addition, when supplying cleaning water from the cleaning water supply means to the treated sludge being concentrated by the concentration means in this way, the supply amount of the cleaning water supplied from the cleaning water supply means to the concentration means is supplied to the concentration means. It is desirable that the volume is equal to or less than the supplied amount of treated sludge. Even if more cleaning water is supplied, the improvement of the cleaning effect is not recognized, and the amount of unnecessary cleaning water only increases.

  As described above, according to the present invention, it is possible to effectively use the electrolyte that promotes the aggregation of the concentrated sludge and decreases the water content of the dewatered cake, and the water content in the dewatered cake obtained by dewatering the concentrated sludge in the dewatering means. It is possible to reduce the rate and perform an efficient and economical sludge treatment.

It is the schematic explaining the state in the sludge process by one Embodiment of the sludge process equipment and sludge process method of this invention. It is the schematic explaining the 1st means in the case of supplying electrolyte to a dehydration drainage tank before sludge processing in the embodiment shown in FIG. It is the schematic explaining the 2nd means in the case of supplying electrolyte to a dewatering drainage tank before sludge processing in the embodiment shown in FIG.

  FIGS. 1 to 3 show an embodiment of the sludge treatment facility of the present invention. FIG. 1 is a schematic view for explaining the state during the sludge treatment, and FIGS. 2 and 3 are respectively before the sludge treatment. It is the schematic explaining the 1st, 2nd supply means in the case of supplying electrolyte to a dehydration drainage tank. The sludge treatment facility of this embodiment dehydrates the concentrated sludge B concentrated by the concentration means 2 and the concentration means 2 that concentrates the treated sludge A such as digested sludge supplied by being connected to the treated sludge supply path 1. A dewatering means 3, a concentrated sludge supply path 4 connecting the concentrating means 2 and the dewatering means 3, and a dewatering drain tank 5 holding the dewatered wastewater C dehydrated from the concentrated sludge B by the dewatering means 3 are provided.

  As the concentration means 2, for example, as described in Japanese Patent No. 5651074, a processed product supplied to a space between a rotary bowl and a screw conveyor that is rotationally driven coaxially with a differential speed is centrifuged in the rotary bowl. A decanter-type centrifuge that is transported and discharged by a screw conveyor while being separated into solid and liquid by force can be used. However, in the centrifuge described in Japanese Patent No. 5651074, the flocculant supply path is formed on the screw conveyor so as to open closer to the solid content outlet, whereas in this embodiment, the washing water is used. A supply path for the wash water D connected to the supply means 6 is formed in the screw conveyor, and similarly opens near the outlet for the concentrated sludge B.

  The separation liquid and washing water D separated from the treated sludge A in the concentration step by the concentration means 2 are discharged as washing waste water E. At this time, the colloidal substance in the treated sludge A and the electrolyte contained in the treated sludge A are also removed and discharged together with the cleaning waste water E. In addition, as the washing water D, it is desirable to use hot water of about 50 ° C.

  Further, in the concentrated sludge supply path 4, a concentrated sludge holding tank 4A and a concentrated sludge feed pump 4B are arranged in this order toward the dewatering means 3, and the concentrated sludge B discharged from the concentration means 2 After being once held in the concentrated sludge holding tank 4A, it is supplied to the dewatering means 3 by the concentrated sludge feed pump 4B continuously or intermittently by a predetermined amount. Further, the polymer F is added to the concentrated sludge B thus supplied to the dehydrating means 3.

  As the dehydrating means 3, a centrifugal dehydrator, a screw press, a filter press, a belt press or the like can be used. The dewatered sludge (dehydrated cake) G generated by dewatering the concentrated sludge B by the dewatering step in the dewatering means 3 is dried and incinerated, for example, and separated from the dewatered sludge G. The dewatered drainage C is held in the dewatered drainage tank 5 as described above in the dehydrated drainage holding step.

  The dehydrated drain tank 5 can be supplied with an electrolyte, and the dehydrated drain C held in the dehydrated drain tank 5 in the dehydrated drain circulation supply process is supplied to the concentrated sludge supply channel 4 for dehydration. A dewatering drain circulation supply path 7 for circulation to the means 3 is connected. In this embodiment, the dewatering drain circulation supply path 7 is connected between the dewatering drain tank 5 and the concentrated sludge feed pump 4B of the concentrated sludge supply path 4 and the dehydrating means 3, and the concentrated sludge supply path 4 Between the dewatering drain tank 5, a dewatering drain feed pump 7 </ b> A is disposed.

  Moreover, in this embodiment, as the 1st supply means which supplies electrolyte to the dewatering drain tank 5, the process sludge A supplied as shown with a broken line in FIG. A sludge bypass path 8 is provided for bypassing. That is, this sludge bypass passage 8 branches from the treated sludge supply passage 1 before reaching the concentration means 2 and supplies the treated sludge A to the dewatering means 3 without passing through the concentration means 2. The sludge bypass path 8 between the path 1 and the dewatering means 3 and the treated sludge supply path 1 between the sludge bypass path 8 and the concentrating means 2 are provided with valves (not shown), respectively. The supply destination can be switched.

  In such a first supply means, the treated sludge A is dehydrated by supplying the treated sludge A to the dewatering means 3 through the sludge bypass path 8 as shown by the solid line in FIG. The dewatered sludge G is treated as described above as in the case of dewatering the concentrated sludge B, and the dewatered wastewater C is held in the dewatered wastewater tank 5. Since the electrolyte originally contained in the treated sludge A remains as it is in the dewatered drainage C that has not been concentrated by the concentration means 2 as described above, this electrolyte is supplied to the dewatered drainage tank 5.

  Further, in the present embodiment, as the second supply means for supplying the electrolyte to the dewatered drain tank 5, an electrolyte supply means 9 is connected to the dehydrated drain tank 5 as shown by the broken line in FIG. That is, the electrolyte supply means 9 does not show a solution such as water containing an electrolyte H such as phosphate, sulfate, bicarbonate, ammonium salt as shown by a solid line in FIG. 3 before normal sludge treatment. It is supplied directly to the dewatering drain tank 5 by a pump or the like, and the electrolyte H in this solution is supplied to the dewatering drain tank 5. 1 to 3 show both the first and second supply means, it is sufficient that at least one of the first and second supply means is provided.

  In one embodiment of the sludge treatment facility of the present invention in which the sludge treatment facility of the present invention and the treatment sludge A such as digested sludge are treated by the sludge treatment facility, the first and the second as described above before the normal sludge treatment. The electrolyte can be supplied to the dewatering drain tank 5 by at least one of the supply means 2, and the dewatering means 3 dehydrates the concentrated sludge B concentrated by the concentration means 2 during normal sludge treatment. The dewatered wastewater C separated and discharged from the sludge G is mixed with the electrolyte thus supplied in the dewatered wastewater tank 5.

  The dewatered waste water C thus mixed with the electrolyte is mixed with the concentrated sludge B supplied to the dewatering means 3 from the concentrated sludge supply path 4 via the dewatered waste water circulation supply path 7, whereby this concentrated sludge. Also in B, the electrolyte removed together with the washing waste water E by the concentration means 2 is mixed. For this reason, aggregation of the concentrated sludge B in the dehydrating means 3 is promoted by the electrolyte thus mixed, so that the water content of the dehydrated sludge G discharged from the dehydrating means 3 can be reduced. For example, as described above It is possible to reduce the fuel and the like when the dewatered sludge G is dried and incinerated.

  In addition, the electrolyte that promotes the aggregation of the concentrated sludge B in this way is separated from the dewatered sludge in the dewatering means 3 and returned to the dewatered wastewater tank 5 while being mixed with the dewatered wastewater C. Then, the concentrated sludge supply path 4 is circulated to the dehydrating means 3 to promote the aggregation of the concentrated sludge B. Therefore, it is not necessary to replenish electrolyte in the dewatering drainage tank 5 during normal sludge treatment, and the amount of electrolyte necessary for agglomeration of the concentrated sludge B can be reduced, which is efficient and economical. . A part of the dewatered wastewater C drained into the dewatered drainage tank 5 is circulated from the concentrated sludge supply path 4 to the dewatering means 3 via the dewatered drainage circulation supply path 7, and the rest as shown in FIG. It is discharged by overflowing from the dewatering drain 5.

  Furthermore, in this embodiment, after adding the polymer F to the concentrated sludge B supplied to the dewatering means 3 from the concentrated sludge supply path 4 and aggregating the concentrated sludge B, the dewatered means 3 dehydrates and solid-liquid separates. However, a part of the added polymer F remains in the dewatered waste water C discharged from the dewatering means 3. For this reason, since the dewatered waste water C including not only the electrolyte but also the residual polymer is mixed with the concentrated sludge B, in this embodiment, the amount of the polymer F added can be reduced and the water content of the dehydrated sludge G can be reduced. it can.

  On the other hand, in this embodiment, the sludge bypass path 8 is connected to the treated sludge supply path 1 as the first supply means for supplying the electrolyte to the dewatered drainage tank 5 in this way, and it is concentrated during normal sludge treatment. The treated sludge A supplied by the means 2 is supplied to the dewatering means 3 and dehydrated before the sludge treatment, and the electrolyte contained in the dewatered wastewater C is extracted and supplied to the dewatered wastewater tank 5. Therefore, since the electrolyte originally contained in the treated sludge A is used, it is possible to promote more efficient and economical sludge treatment without requiring a chemical containing the electrolyte.

  Further, as the second supply means, in the present embodiment, an electrolyte supply means 9 is connected to the dewatered drain tank 5, and the electrolyte H can be directly supplied from the electrolyte supply means 9 to the dehydrated drain tank 5. . In such a second supply means, it is necessary to supply a chemical or the like containing electrolyte H as a solution, but it is easy to stabilize the electrolyte concentration of dewatered wastewater C mixed with concentrated sludge B, Furthermore, even when the electrolyte of the dewatered wastewater C mixed with the concentrated sludge B is insufficient due to the change in the properties of the treated sludge A during normal sludge treatment, the electrolyte H is supplied from the electrolyte supply means 9 to the dewatered wastewater tank 5. Can be replenished.

  It should be noted that at least one of the first and second supply means may be provided as described above. However, as shown in FIGS. 1 to 3, both the first and second supply means are provided. For example, before the normal sludge treatment, the electrolyte is supplied to the dewatered drain tank 5 by the sludge bypass passage 8 of the first supply means, and there is a shortage of the electrolyte of the dehydrated waste water C during the normal sludge treatment. When it occurs, the electrolyte H can be replenished by the electrolyte supply means 9 of the second supply means, so that it is possible to treat sludge efficiently and stably.

  Further, in the present embodiment, the treatment sludge A is concentrated using a decanter-type centrifuge in the concentration means 2, and the polymer of the treatment sludge is always added to the filtration system thickener to form agglomerated sludge. On the other hand, in such a decanter type centrifugal concentrator, it is not always necessary to add a polymer, and the amount of the polymer added can be further reduced. However, in order to maintain the SS recovery rate in the concentration means 2, the polymer may be finely injected in a range of 0.6% by mass or less with respect to the TS of the treated sludge A.

  Furthermore, in the present embodiment, in the concentrating means 2, the washing water supply means 6 is connected to the decanter type centrifuge, and the washing water is supplied to the treated sludge A that has been concentrated to some extent by the washing water supply means 6. D is injected. Thereby, since the colloidal substance slightly remaining in the concentrated sludge B is further removed and discharged together with the washing waste water E, it becomes possible to promote more efficient aggregation of the concentrated sludge B in the dewatering means 3. Further, by washing the treatment sludge A while concentrating it in the concentration means 2 as in the present embodiment, the amount of washing water is reduced by 1 / compared with the conventional sludge washing in which washing water is mixed with the treatment sludge before concentration. It can be reduced to about 4.

  However, the colloidal substance can be sufficiently removed from the treated sludge A according to the centrifuge as described above without connecting the washing water supply means 6 to the concentration means 2. Further, even when the cleaning water supply means 6 is connected to the concentration means 2 and the cleaning water D is supplied in this way, the supply amount of the cleaning water D is relative to the supply amount of the treated sludge A supplied to the concentration means 2. It is desirable that the volume is equal to or less than the same amount, and even if more cleaning water D is supplied, the cleaning effect is not improved, and only the cleaning water D treated as cleaning wastewater E increases. Become.

DESCRIPTION OF SYMBOLS 1 Treated sludge supply path 2 Concentration means 3 Dehydration means 4 Concentrated sludge supply path 4A Concentrated sludge holding tank 4B Concentrated sludge feed pump 5 Dewatered drain tank 6 Washing water supply means 7 Dehydrated waste water circulation supply path 7A Dehydrated waste water feed pump 8 Sludge Bypass path (first supply means)
9 Electrolyte supply means (second supply means)
A Treated sludge B Concentrated sludge C Dewatered wastewater D Washed water E Washed wastewater F Polymer G Dehydrated sludge H Electrolyte

Claims (12)

A concentration means for concentrating the treated sludge connected to the treated sludge supply path, a dewatering means for dewatering the concentrated sludge concentrated by the concentration means, and a concentrated sludge supply path connecting the concentration means and the dewatering means And a dewatering drain tank for holding dewatered wastewater dehydrated from the concentrated sludge by the dewatering means,
An electrolyte can be supplied to the dewatering drain tank, and the dewatered water circulation supply path for supplying the dehydrated drainage retained in the dewatering drain tank to the concentrated sludge supply path and circulating it to the dehydrating means. A sludge treatment facility characterized by being connected.   The treated sludge supply path is provided with a sludge bypass path for bypassing the treated sludge to be supplied to the dewatering means, and the electrolyte supplied to the dewatered drain tank is the dewatered wastewater from which the treated sludge has been dehydrated. The sludge treatment facility according to claim 1, wherein the sludge treatment facility is an electrolyte contained in the sludge.   The sludge according to claim 1 or 2, wherein an electrolyte supply means is connected to the dewatering drain tank, and the electrolyte can be supplied from the electrolyte supply means to the dewatering drain tank. Processing equipment.   The washing water supply means is connected to the concentration means, and the washing water is supplied from the washing water supply means to the treated sludge concentrated by the concentration means. The sludge treatment facility according to any one of the above. The sludge treatment facility according to any one of claims 1 to 4, wherein a polymer flocculant is added to the concentrated sludge supplied to the dewatering means. A concentration step of supplying the treated sludge to a concentration means connected to the treated sludge supply channel and concentrating it;
A dewatering step of dewatering the concentrated sludge concentrated in this concentration step by supplying the dewatering means via the concentrated sludge supply channel;
A dewatering wastewater holding step for holding the dewatered wastewater dehydrated from the concentrated sludge in the dewatering drainage tank by this dewatering step;
In the dewatering drainage holding step, an electrolyte is supplied to the dewatered drainage held in the dewatering drainage tank, and the dewatered wastewater supplied with the electrolyte is supplied to the concentrated sludge supply path through the dewatering drain circulation supply path. And a dewatering waste water circulation supplying step for circulating to the dewatering means. The treated sludge supply path and the dewatering means are connected by a sludge bypass path, and the treated sludge is dehydrated by supplying the treated sludge to the dewatering means via the sludge bypass path before starting the sludge treatment. The sludge treatment method according to claim 6 , wherein the electrolyte contained in the dewatered waste water is supplied to the dewatered waste water tank. The sludge according to claim 6 or 7 , wherein an electrolyte supply means is connected to the dewatering drain tank, and the electrolyte is supplied from the electrolyte supply means to the dewatering drain tank at least before starting sludge treatment. Processing method. In the concentration step, by connecting the cleaning water supply means to the concentration means, claim 6, characterized in that to supply the cleaning water from the cleaning water supply means to the treated sludge in the concentrate by said concentrating means The sludge treatment method according to claim 8 . The supply amount of the wash water supplied from the wash water supply means to the concentration means is equal to or less than the volume of the treated sludge supplied to the concentration means. The sludge treatment method according to claim 9 . The sludge treatment method according to any one of claims 6 to 10, wherein a polymer flocculant is added to the concentrated sludge supplied to the dewatering means. The supply amount of the dewatered wastewater supplied from the dewatered drainage tank to the concentrated sludge supply channel is set such that the sludge concentration of the concentrated sludge after the dewatered wastewater is supplied is about 3 to 4% by mass. It adjusts to these, The sludge processing method as described in any one of Claims 6-11 characterized by the above-mentioned.

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