JP5256261B2 - Method and apparatus for dewatering organic sludge - Google Patents

Description

  The present invention relates to a method and apparatus for dewatering organic sludge. More specifically, the present invention relates to a method and an apparatus for dewatering organic sludge using a polymer flocculant and an inorganic flocculant. The organic sludge is agglomerated with a polymer flocculant, and the agglomerated sludge is concentrated. The present invention relates to a dehydration method and apparatus for adding an inorganic flocculant to concentrated sludge, performing mechanical dehydration, and reducing the moisture content of the dehydrated cake obtained.

In recent years, there has been a demand for reducing the amount of waste and reducing the environmental load, and dewatering technology for organic sludge discharged from wastewater treatment facilities is extremely important. Development is desired. Conventionally, in the case of dewatering organic sludge, “a method of mechanically dewatering after aggregating sludge with a polymer flocculant” (one-component method), “after adding an inorganic flocculant to sludge, The “method of aggregating with a flocculant and performing mechanical dehydration” (inorganic flocculant / pre-addition method) is common.
Another method for dewatering organic sludge is “a method in which sludge is agglomerated with a polymer flocculant, then mechanically concentrated or gravity concentrated, and then an inorganic flocculant is added to perform mechanical dehydration” (inorganic flocculant)・ Post-addition method). This inorganic flocculant and post-addition method is suitable for dewatering organic sludge having a high M alkali component concentration. In the inorganic flocculant / pre-addition method, the inorganic flocculant is consumed by the alkali component in the organic sludge liquid, whereas in the inorganic flocculant / post-addition method, the alkali component is removed by sludge concentration. The consumption of the inorganic flocculant can be reduced. Also, the inorganic flocculant and post-addition method can reduce the moisture content of the dehydrated cake as compared with the one-component method.

  The following prior arts are known as techniques related to the inorganic flocculant and post-addition method. Japanese Patent Application Laid-Open No. 61-149300 (Patent Document 4) describes a first step in which a cationic organic polymer flocculant is added to and mixed with organic sludge, and then floc is generated while stirring the sludge. The organic sludge dewatering method is characterized by comprising a second step of gravity filtering the sludge, and a third step of adding iron salt to the sludge after gravity filtration, mixing and then dehydrating under pressure. Is disclosed. Japanese Patent Laid-Open No. 9-24400 (Patent Document 5) discloses a process of adding a cationic polymer to digested sludge to agglomerate, a process of gravity dehydrating the agglomerated sludge, and an inorganic flocculant to the gravity dehydrated sludge. There is disclosed a method for dewatering digested sludge having a step of adding and refining, and a step of adding an amphoteric polymer to the conditioned sludge and dehydrating with a dehydrator. However, these prior arts do not describe the optimization of the addition amount of the inorganic flocculant, more specifically, the description of the pH of the coagulated sludge after the addition of the inorganic flocculant or the pH of the dewatered separation liquid. In addition, these prior arts do not describe the optimization of concentrated sludge, and more specifically do not describe the floc size of the concentrated sludge.

  The following prior arts are known as techniques related to pH control. JP-A-4-284900 (Patent Document 1) discloses a method in which an organic flocculant is added to organic sludge, granulated and concentrated, and then dehydrated with a mechanical dehydrator. After adding the inorganic flocculant so as to be in the range of 0 to 5.0, add the organic flocculant, granulate and concentrate, and transfer to the transfer pipe that transfers the sludge slurry after granulation and concentration to the mechanical dehydrator A method for dewatering organic sludge, characterized in that 10 to 15% by weight of an inorganic flocculant is line-injected with respect to SS of the slurry to be produced, is disclosed. Japanese Patent Laid-Open No. 10-165999 (Patent Document 2) discloses an inorganic flocculant connected to a sludge supply line to a dehydrator when injecting the inorganic flocculant into the sludge supplied to the dehydrator. A pH meter is installed in the sludge supply pipe at the intermediate point between the connection point of the supply pipe and the dehydrator, the pH of the supplied sludge is measured, and the discharge amount of the supply pump that sends the inorganic flocculant based on the pH A method for adjusting the pH of the supplied sludge in the dehydration process is disclosed.

  In addition, JP-A-8-173999 (Patent Document 3) discloses that the first flocculant is added to the sludge generated in the sewage treatment, the pH of the sludge is adjusted to an appropriate pH, and then the second flocculant is added to the sludge. In the sludge dewatering method in which the obtained coagulated sludge is fed to a dehydrator and dehydrated, the first coagulant is polyferric sulfate coagulant, and the appropriate pH is 4. A sludge dewatering method is disclosed in which the second flocculant is a cationic polymer flocculant, which is 0 to 7.0. However, these prior arts are techniques related to the inorganic flocculant and the pre-addition method in which the inorganic flocculant is added prior to the addition of the polymer flocculant, and are different from the present invention relating to the inorganic flocculant and the post-addition method. For this reason, it is impossible to optimally control the addition amount of the inorganic flocculant by applying the pH disclosed in these prior arts to the inorganic flocculant / post-addition method.

  The following prior arts are known as techniques related to the floc diameter. In JP 2009-165964 (Patent Document 6), a flocculant is added to sludge generated from a wastewater treatment facility to perform a primary flocculation treatment, and the sludge after the primary flocculation treatment is concentrated at a high concentration. There is described a dehydration treatment method characterized in that a flocculant is added to the sludge after the concentration treatment to perform a secondary agglomeration treatment, and the high-concentration sludge subjected to the secondary agglomeration treatment is subjected to a dehydration treatment. Further, it is described that flocs having a size of 2 to 4 mm are formed in the primary aggregating treatment, and flocs having a size of 0.5 to 3 mm are formed in the secondary aggregating treatment. In addition, a polymer flocculant is effective in the primary aggregation treatment, a polymer flocculant is effective in the secondary aggregation treatment, and an inorganic flocculant such as polyferric sulfate may be used. Have been described. However, in this prior art, there is no description regarding optimization of the amount of inorganic flocculant added, and more specifically, there is no description regarding the pH of the coagulated sludge after addition of the inorganic flocculant or the pH of the dewatered separation liquid.

  Among the prior arts related to the above pH control, in Japanese Patent Laid-Open No. 4-284900 (Patent Document 1), an inorganic flocculant is added so that the pH of the organic sludge is in the range of 3.0 to 5.0. In addition, the moisture content of the dehydrated cake is reduced. In JP-A-10-165999 (Patent Document 2), the pH of sludge into which an inorganic flocculant has been injected is measured, and the discharge amount of a supply pump that feeds the inorganic flocculant is automatically controlled. Savings in usage. In JP-A-8-173999 (Patent Document 3), polyferric sulfate is added to sludge generated in the sewage treatment, and the pH of the sludge is adjusted to 4.0 to 7.0. The moisture content is reduced. However, these prior arts are technologies related to the inorganic flocculant and the pre-addition method in which the inorganic flocculant is added prior to the addition of the polymer flocculant. Unlike the present invention relating to the inorganic flocculant and the post-addition method, The pH disclosed in these prior arts cannot be optimally controlled by applying the pH to the inorganic flocculant / post-addition method. The reason for this is that, in the inorganic flocculant and post-addition method, the sludge component at the time of adding the inorganic flocculant is the inorganic flocculant because the inorganic flocculant is added after removing the soluble components in the sludge by sludge concentration.・ This is different from the pre-addition method. In particular, in the case of organic sludge with high M alkali concentration, such as digested sludge, the difference between the sludge components at the time of adding the inorganic flocculant between the inorganic flocculant / pre-addition method and the inorganic flocculant / post-addition method is extremely high. Since it is large, it is difficult to apply the optimum pH in the inorganic flocculant / pre-addition method to the inorganic flocculant / post-addition method.

Prior to the present invention, the inventor applied the pH disclosed in the prior art related to the inorganic flocculant / pre-addition method to the inorganic flocculant / pre-addition method to optimally control the amount of inorganic flocculant added. An experiment was conducted to confirm whether it was possible. In the experiment, four types of digested sludge (A, B, C, D) were used. Digested sludges A, B, C, and D were collected from three different sewage treatment plants. Digested sludges A and B were collected from the same sewage treatment plant, but differed in sludge concentration. The TS of the digested sludges A, B, C, and D are 2.2%, 1.3%, 1.8%, and 1.5%, respectively. The experimental procedure is as follows. Polyferric sulfate is added to 250 mL of sludge, and after mixing the sludge and polyferric sulfate with a spatula, the pH of the sludge is measured. Next, a cationic polymer is added to agglomerate sludge and form agglomerated floc. Finally, the aggregated floc was dehydrated with a belt press dehydrator, and the moisture content of the obtained cake was measured.
The experimental results of sludges A to D are shown in FIGS. Here, a weight obtained by subtracting “weight of iron hydroxide precipitated by addition of polyiron” from “measured dry solid weight” was defined as “true dry solid weight”, and the moisture content of the cake was calculated. As can be seen from FIGS. 4 to 7, in the inorganic flocculant / pre-addition method, the result that the moisture content of the cake was reduced in a specific pH range was not obtained.

  Among the techniques related to the above-mentioned inorganic flocculant and post-addition method, Japanese Patent Application Laid-Open No. 61-149300 (Patent Document 4) generates flocs on organic sludge using a cationic organic polymer flocculant, and gravity It is disclosed to filter, add an iron salt, mix and dehydrate under pressure. Japanese Patent Laid-Open No. 9-24400 (Patent Document 5) discloses that a cation polymer is added to a digested sludge for agglomeration treatment, the agglomerated sludge is subjected to gravity dehydration, and an inorganic flocculant is added for tempering. It is disclosed that an amphoteric polymer is added to sludge and then dehydrated with a dehydrator. However, these prior arts do not describe the optimization of the addition amount of the inorganic flocculant, more specifically, the description of the pH of the coagulated sludge after the addition of the inorganic flocculant or the pH of the dewatered separation liquid. In addition, these prior arts do not describe the optimization of concentrated agglomerated flocs, more specifically, the size of concentrated agglomerated flocs.

  As described above, the inorganic flocculant / post-addition method differs from the inorganic flocculant / pre-addition method in that the sludge component at the time of adding the inorganic flocculant is different, so an appropriate control method for the amount of inorganic flocculant added is used. It is necessary to consider. In addition, in the inorganic flocculant / post-addition method, it is necessary to examine an appropriate control method for concentrated flocculent flocs. This is because the permeability and reactivity of the inorganic flocculant greatly depend on the size of the floc floc.

JP-A-4-284900 Japanese Patent Laid-Open No. 10-165999 JP-A-8-173999 JP-A-61-149300 Japanese Patent Laid-Open No. 9-24400 JP 2009-165964 A

  An object of the present invention is to provide a method for controlling the amount of inorganic flocculant added in an inorganic flocculant / post-addition method and an apparatus for carrying out the method. Another object of the present invention is to provide a method for controlling agglomeration flocs and an apparatus for carrying out the method in an inorganic flocculant and post-addition method.

  As a result of earnest research to solve the above-mentioned problems, the present invention determines the amount of the inorganic flocculant to be added depending on the pH of the floc floc to which the inorganic flocculant is added or the pH of the dehydrated separation liquid in the inorganic flocculant and post-addition method. And found that the moisture content of the cake can be reduced very efficiently. Further, the present inventor has found that the moisture content of the cake can be reduced extremely efficiently by adjusting the size of the floc floc in the inorganic flocculant and post-addition method. The present invention has been completed based on these new findings.

That is, in the present invention, a polymer flocculant is added to organic sludge and the sludge is agglomerated to form agglomerated floc, a concentration step for concentrating the formed agglomerated floc, and the concentrated agglomerated floc is inorganic. A sludge dewatering method comprising an inorganic flocculant addition step for adding a flocculant and a dehydration step for mechanically dewatering the concentrated flocculant floc to which the inorganic flocculant has been added. The sludge dewatering method is characterized in that an inorganic flocculant is added so that the pH of the flocs floc to which the agent is added or the pH of the dehydrated filtrate is 3-6. The dehydration method may include an adjusting step of adjusting the size of the aggregated floc concentrated by adding the inorganic flocculant to 0.5 mm to 10 mm .

Furthermore, in the present invention, there is a means for adding a polymer flocculant to organic sludge, a flocculant tank that agglomerates the sludge to form a floc floc, a concentrator that concentrates the floc floc formed, and A sludge dewatering device having an inorganic flocculant addition means for adding an inorganic flocculant to the flocculent floc and a dehydrator for dewatering the concentrated flocculant floc to which the inorganic flocculant has been added, wherein the inorganic flocculant is added The sludge dewatering apparatus is characterized by having a control means for controlling the amount of the inorganic flocculant added so that the pH of the sludge or dehydrated filtrate is 3-6. In the dehydrating apparatus, the control means may have a pH sensor for measuring pH, and floc adjusting means for adjusting the size of the aggregated floc concentrated by adding an inorganic flocculant to 0.5 mm to 10 mm. Can be provided after the inorganic flocculant addition means .

According to the present invention, in the inorganic flocculant / post-addition method, the amount of the inorganic flocculant added is determined by the pH of the floc floc to which the inorganic flocculant is added or the pH of the dehydrated separation liquid, and the water content of the cake is reduced extremely efficiently. it can. Further, according to the present invention, in the inorganic flocculant / post-addition method, the cake moisture content can be reduced extremely efficiently by adjusting the size of the floc floc.
As another effect of the present invention, it is possible to suppress the scale adhering to the filtration surface of the dehydrator or the piping through which the dehydrated separation liquid passes. This is because the production of magnesium ammonium phosphate (MAP), which is the main component of the scale, can be suppressed by controlling the pH of the flocculation floc to which the inorganic flocculant is added or the pH of the dehydrated separation liquid.

The flow block diagram which shows an example of the dehydration apparatus of this invention. The graph which shows the relationship between the cake moisture content which shows the result of Example 1, and pH. The graph which shows the relationship between the cake moisture content which shows the result of Example 2, and the magnitude | size of a floc. The graph which shows the relationship between the cake water content in sludge A and pH by the well-known pre-addition method. The graph which shows the relationship between the cake moisture content in sludge B and pH by a well-known pre-addition method. The graph which shows the relationship between the cake water content in sludge C and pH by the well-known pre-addition method. The graph which shows the relationship between the cake moisture content in sludge D and pH by the well-known pre-addition method.

The present invention relates to a method for controlling the amount of inorganic flocculant added in an inorganic flocculant / post-addition method and an apparatus for carrying out the same. The present invention also relates to a method for controlling agglomeration flocs and an apparatus for carrying out the method in an inorganic flocculant and post-addition method. Hereinafter, embodiments of the present invention will be described in detail.
FIG. 1 is a flow configuration diagram showing an embodiment of the dehydrating apparatus of the present invention. In FIG. 1, organic sludge is supplied from a sludge storage tank 1 to a coagulation tank 4. The polymer flocculant is supplied from the polymer flocculant dissolution tank to the aggregation tank 4. In the aggregating tank 4, organic sludge and a polymer flocculant are mixed to form an agglomerated floc. In the concentrator 5, the aggregated floc is concentrated. In the floc adjuster 6, the aggregated floc is adjusted to an appropriate size. The inorganic flocculant is supplied from the inorganic flocculant storage tank 3 to the inorganic flocculant adding machine 7 and added to the floc floc. The floc floc to which the inorganic flocculant is added is dehydrated in the dehydrator 9. The pH of the flocculation floc to which the inorganic flocculant is added is measured by the pH sensor 8. The amount of the inorganic flocculant added is determined by the inorganic flocculant addition pump controller 10 based on the pH of the floc floc to which the inorganic flocculant has been measured as measured by the pH sensor 8. The inorganic flocculant is added by the inorganic flocculant addition pump 11.

In the floc adjuster 6, the floc floc is preferably adjusted to 0.5 to 10 mm. More preferably, the size of the aggregation floc is adjusted to 0.5 to 5 mm. The reason for this is that when the flocculent floc is large, the inorganic flocculant cannot penetrate to the inside of the flocculent floc, and the effect of the inorganic flocculant is hardly exhibited. On the other hand, when the aggregation floc is small, the inorganic flocculant can penetrate into the inside of the aggregation floc, but the small aggregation floc is disadvantageous for dehydration by a dehydrator. When the floc diameter is adjusted to the above-mentioned floc diameter, the inorganic flocculant penetrates into the inside, and the inorganic flocculant can be used efficiently, and at the same time, the dehydration can be performed efficiently. When using a screw press dehydrator, the size of the flocs floc is preferably adjusted to 1 to 5 mm. When using a belt press dehydrator, it is preferable that the size of the aggregate floc is adjusted to 0.5 to 3 mm.
The inorganic flocculant is preferably added so that the pH of the floc floc to which the inorganic flocculant is added is 3 to 6. More preferably, the inorganic flocculant is added so that the pH of the floc floc to which the inorganic flocculant has been added is 3.5 to 5.5. More preferably, the inorganic flocculant is added so that the pH of the floc floc to which the inorganic flocculant is added is 3.5 to 4.5.

FIG. 1 shows one embodiment of the present invention, and is not limited to the illustrated one. For example, the floc adjuster 6 may be omitted, and the inorganic flocculant adding machine 7 may adjust the size of the floc floc appropriately and simultaneously add the inorganic flocculant to the floc floc. Further, the floc adjuster 6 may be omitted, and the inorganic flocculant adder 7 may be disposed at the subsequent stage of the concentrator 5. Further, the floc adjuster may be omitted, and the inorganic flocculant adding machine 7 may be integrated with the concentrator 5. Further, the floc adjuster 6 may be arranged at the subsequent stage of the inorganic flocculant adder 7.
The pH sensor 8 may be installed in a dehydrated filtrate storage tank or a dehydrated filtrate discharge line. In this case, the addition amount of the inorganic flocculant is determined by the pH of the dehydrated filtrate measured by the pH sensor 8. In this case, the inorganic flocculant is preferably supplied to the inorganic flocculant adder 7 so that the pH of the dehydrated filtrate is 3-6. More preferably, the inorganic flocculant is supplied so that the pH of the dehydrated filtrate is 3.5 to 5.5. More preferably, the inorganic flocculant is supplied so that the pH of the dehydrated filtrate is 4-5.

The pH sensor 8 may be installed in the inorganic flocculant adding machine 7. When the properties of the organic sludge are stable, the amount of the inorganic flocculant added can be determined by examining the relationship between the amount of the inorganic flocculant added and the pH of the flocculent floc mixed with the inorganic flocculant in advance. . In such a case, the pH sensor 8 may be omitted.
The organic sludge used in the present invention is organic sludge generated in sewage treatment, human waste treatment, and various industrial wastewater treatment. For example, first sedimentation basin sludge, surplus sludge, anaerobic digested sludge, aerobic digested sludge, septic tank sludge, digested and desorbed liquid and the like can be mentioned. The organic sludge may contain an inorganic substance.

Examples of the polymer flocculant used in the present invention include a cationic polymer flocculant and an amphoteric polymer flocculant.
Examples of the inorganic flocculant used in the present invention include ferric chloride, aluminum sulfate, aluminum chloride, polyaluminum chloride, and polyiron sulfate.
As the dehydrator used in the present invention, a conventional dehydrator used for sludge dehydration can be used. For example, a screw press dehydrator, a belt press dehydrator, a centrifugal dehydrator, a vacuum dehydrator, a filter press dehydrator, a multiple disk dehydrator, and the like can be given.
As the concentrator used in the present invention, a conventional gravity concentrator or mechanical concentrator used for sludge dewatering can be used. For example, a belt concentrator, a centrifugal concentrator, an elliptical plate concentrator and the like can be mentioned.
A stirrer conventionally used for sludge can be used for the floc adjuster used in the present invention. For example, a paddle type stirrer, a drum type stirrer, etc. are mentioned.

Example 1
A sludge dewatering test was conducted using an inorganic flocculant and post-addition method. Four types of digested sludge (A, B, C, D) were used. Digested sludges A, B, C, and D were collected from three different sewage treatment plants. Digested sludges A and B were collected from the same sewage treatment plant, but differed in sludge concentration. The TS of the digested sludges A, B, C, and D are 2.2%, 1.3%, 1.8%, and 1.5%, respectively. A cationic polymer was used as the polymer flocculant. The cationic polymer is dimethylaminoethyl methacrylate or dimethylaminoethyl acrylate. Poly ferric sulfate was used as the inorganic flocculant. The experimental procedure is as follows. Cationic polymer was added to 250 mL of sludge to cause the sludge to flocculate and form agglomerated floc. The aggregated floc was then concentrated using a 1 mm screen. Next, polyferric sulfate was added to the aggregated floc, and the aggregated floc and ferric sulfate were mixed. Next, the pH of the aggregated floc mixed with polyferric sulfate was measured. Finally, the aggregated floc was dehydrated with a belt press dehydrator, and the moisture content of the obtained cake was measured.

The experimental results are shown in Table 1. Here, a weight obtained by subtracting “weight of iron hydroxide precipitated by addition of polyiron” from “measured dry solid weight” was defined as “true dry solid weight”, and the moisture content of the cake was calculated.

From Table 1, the pH of the aggregated floc to which polyferric sulfate is added is “6 or less than 3”, “5.5 or less than 3.5”, “4.5 or less than 3.5” When the average value of the moisture content of the dehydrated cake is calculated, they are 80.2%, 79.9%, and 79.7%, respectively. From this result, the pH of the aggregated floc added with polyferric sulfate is preferably adjusted to pH 3-6, more preferably pH 3.5-5.5, and even more preferably pH 3.5-4.5. It can be seen that the moisture content of the cake can be reduced.
FIG. 2 shows a relationship between the moisture content of cake and pH of sludge C, which is a typical example. From FIG. 2, it can be seen that the pH of the aggregated floc mixed with polyferric sulfate gradually decreases as the injection rate of polyferric sulfate increases. It can be seen that the moisture content of the cake gradually decreases until the pH of the agglomerated floc mixed with polyferric sulfate is about 4-5, and is constant or increased when the pH is higher than 4-5.

Reference example 1
A sludge dewatering test was conducted using an inorganic flocculant and post-addition method. Three types of digested sludge (C, E, F) were used. Digested sludge C, E, and F were collected from three different sewage treatment plants. The TS of digested sludges C, E, and F are 1.8%, 1.7%, and 2.8%, respectively. A cationic polymer was used as the polymer flocculant. The cationic polymer is dimethylaminoethyl methacrylate or dimethylaminoethyl acrylate. Poly ferric sulfate was used as the inorganic flocculant. The experimental procedure is as follows. Cationic polymer was added to 250 mL of sludge to cause the sludge to flocculate and form agglomerated floc. The aggregated floc was then concentrated using a 1 mm screen. Next, polyferric sulfate was added to the aggregated floc, and the aggregated floc and ferric sulfate were mixed. At this time, the size of the aggregated floc mixed with polyferric sulfate was measured. Finally, the aggregated floc was dehydrated with a belt press dehydrator, and the moisture content of the obtained cake was measured.

図３に典型的な例である汚泥Ｃの含水率とフロックの大きさの関係を示す。横軸の撹拌回数は、重力落下による撹拌回数を表す。図３より、撹拌回数の増加と共にフロック大きさが低下することが分かる。ケーキ含水率は、フロック大きさが１０ｍｍ以上のとき最も高く、フロック大きさの低下と共に、低減することが分かる。 The experimental results are shown in Table 2. From Table 2, it can be seen that the moisture content of the cake can be reduced by adjusting the size of the aggregated floc added with ferric sulfate to preferably 0.5 to 10 mm, more preferably 0.5 to 5 mm.

FIG. 3 shows the relationship between the moisture content of sludge C, which is a typical example, and the size of flocs. The number of times of stirring on the horizontal axis represents the number of times of stirring due to gravity drop. FIG. 3 shows that the floc size decreases as the number of stirrings increases. It can be seen that the moisture content of the cake is highest when the floc size is 10 mm or more, and decreases with a decrease in the floc size.

  1: Sludge storage tank, 2: Polymer flocculant dissolution tank, 3: Inorganic flocculant storage tank, 4: Coagulation tank, 5: Concentration tank, 6: Flock adjuster, 7: Inorganic flocculant addition machine, 8: pH sensor, 9: dehydrator, 10: controller, 11: inorganic flocculant addition pump

Claims (5)

  Addition of a polymer flocculant to organic sludge, agglomeration step for agglomerating the sludge to form agglomeration flocs, a concentration step for concentrating the formed agglomeration flocs, and inorganic for adding an inorganic flocculant to the concentrated agglomeration flocs A sludge dewatering method comprising a flocculant addition step and a dewatering step of mechanically dewatering the concentrated flocculent floc added with the inorganic flocculant, wherein the flocculant floc added with the inorganic flocculant in the inorganic flocculant addition step A method for dewatering sludge, comprising adding an inorganic flocculant so that the pH of the water or the pH of the dehydrated filtrate is 3 to 6. 2. The sludge dewatering method according to claim 1, further comprising an adjusting step of adjusting the size of the concentrated flocculation floc to which the inorganic flocculant is added to 0.5 mm to 10 mm .   A means for adding a polymer flocculant to organic sludge, a flocation tank for aggregating the sludge to form a floc floc, a concentrator for concentrating the floc floc formed, and an inorganic flocculant in the concentrated floc floc A sludge dewatering device having a means for adding an inorganic flocculant and a dehydrator for dewatering the concentrated flocculent floc to which the inorganic flocculant has been added, wherein the pH of the sludge or dehydrated filtrate to which the inorganic flocculant has been added A sludge dewatering apparatus comprising a control means for controlling the amount of the inorganic flocculant added so that the ratio is 3 to 6. 4. The sludge dewatering apparatus according to claim 3 , wherein the control means includes a pH sensor for measuring pH. Claim 3 or 4, wherein it has a flock adjusting means for adjusting the size of the flocs of the sludge concentrating said inorganic coagulant is added to 0.5mm~10mm downstream of inorganic coagulant adding means Sludge dewatering equipment .

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