JP5723916B2 - 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 1) discloses 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 2) 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 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 the floc diameter. In JP 2009-165964 A (Patent Document 3), a flocculant is added to sludge generated from a wastewater treatment facility to perform a primary agglomeration treatment, and the sludge after the primary agglomeration 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.

  Among the technologies related to the above-mentioned inorganic flocculant and post-addition method, Japanese Patent Application Laid-Open No. 61-149300 (Patent Document 1) generates flocs on organic sludge with 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 2) 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 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-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 agglomeration flocs and an apparatus for carrying out the same in an inorganic flocculant and post-addition method.

  As a result of diligent research to solve the above-mentioned problems, the present invention is very effective in controlling the size of the aggregate floc in the inorganic flocculant and post-addition method, and adjusting the size of the aggregate floc in the inorganic flocculant and post-addition method. It has been found that the moisture content can be reduced. 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 of adding a flocculant and a dehydration step of mechanically dewatering the concentrated flocculant floc to which the inorganic flocculant is added, wherein the organic sludge is combined with a polymer flocculant. Of the sludge characterized by having an adjustment step of adjusting the size of the aggregated floc formed by adding the flocculent floc formed by adding the inorganic flocculant or the concentrated aggregated floc added with the inorganic flocculant to 0.5 mm to 10 mm This is a dehydration method.
In the sludge dewatering method, the organic sludge is preferably digested sludge.

Further, in the present invention, there is a means for adding a polymer flocculant to the organic sludge, a flocculant tank for aggregating the sludge to form a floc floc, a concentrator for concentrating the formed floc floc, and concentrating 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. A floc adjusting means for adjusting the size of the aggregated floc formed by adding the molecular flocculant to the aggregated floc formed by adding the flocculent floc formed by adding the molecular flocculant or the inorganic flocculant is adjusted to 0.5 mm to 10 mm. The sludge dewatering device is characterized in that it has the above.
In the sludge dewatering apparatus, the organic sludge is preferably digested sludge.

  According to the present invention, in the inorganic flocculant / post-addition method, the moisture content of the cake can be reduced very efficiently by adjusting the size of the floc floc.

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 the reference example 1, and pH. The graph which shows the relationship between the cake moisture content which shows the result of Example 1, and the magnitude | size of a floc.

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.

Reference 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.

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.

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 (4)

  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 to which an inorganic flocculant has been added, which is formed by adding a polymer flocculant to the organic sludge. A method for dewatering sludge, characterized by comprising an adjusting step of adjusting the size of the aggregated floc obtained by concentrating the aggregated floc or the concentrated aggregated floc added with the inorganic flocculant to 0.5 mm to 10 mm.   2. The sludge dewatering method according to claim 1, wherein the organic sludge is digested sludge.   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 an inorganic flocculant addition means for adding a dehydrator and a dehydrator for dewatering the concentrated flocculant floc to which the inorganic flocculant has been added, wherein the polymer flocculant is added to the organic sludge. Characterized by having floc adjusting means for adjusting the size of the agglomerated floc obtained by concentrating the agglomerated floc formed in the above or the concentrated agglomerated floc added with the inorganic flocculant to 0.5 mm to 10 mm in the subsequent stage of the concentrator. Sludge dewatering equipment. 4. The sludge dewatering apparatus according to claim 3, wherein the organic sludge is digested sludge.