JPH0768300A - Method for treating sludge and apparatus therefor - Google Patents

Abstract

PURPOSE:To reduce remarkably the amount of a coagulant to be used and to improve the dehydration property of a flock and the recovery of sludge by installing a flock concentration process, a flock segmentation process, and a flock regeneration process between a flock generation process and a dehydration process. CONSTITUTION:A flock concentration part 30, a flock segmentation part 31, and a flock regeneration part 32 are installed between a flock generation reactor 5 and a dehydrator 4. In the flock concentration part 30, a flock is concentrated by separating mother liquor from the flock generated in the flock generation reactor 5. In the flock segmentation part 31, the concentrated flock is segmented by enforced agitation by an agitator 34 with a motor 35. In the flock regeneration part 32, a coagulant from a coagulant dissolving tank 2 is added to the segmented flock little by little under stirring by an agitator 36 operated slowly with a motor 37 to regenerate and reinforce the flock. The regenerated and reinforced flock is sent to the dehydrator 4 to be dehydrated.

Description

Detailed Description of the Invention

[0001]

The present invention relates to the addition of a coagulant to sludge.
The present invention relates to an improvement in a sludge treatment method and a sludge treatment device in which the flocs are mixed and then the flocs are dehydrated.

[0002]

2. Description of the Related Art Conventional examples are shown in FIGS. FIG. 5 shows an example of a one-agent addition method in which either anionic or cationic coagulant is added to sludge. In this example, a sludge storage tank 1, a flocculant dissolution tank 2, a floc generation reaction tank 3 and a dehydrator 4 are used. In the flocculant dissolving tank 2, the anionic or cationic flocculant is stirred and dissolved by the stirrer 5 and adjusted to a predetermined concentration. When the sludge in the sludge storage tank 1 is fed into the floc generation reaction tank 3 while the flow rate is measured by the pump 7 by the flow meter 8, at the same time, the flocculant in the flocculant dissolution tank 2 is generated by the pump 9 in the floc. It is sent to the reaction tank 3 and added to the sludge. Then, in the floc generation reaction tank 3, the floc is generated by being stirred by the stirrer 10 and mixed with the sludge. This floc overflows with the mother liquor from the floc production reaction tank 3 and overflows the dehydrator 4.
And is forcibly dehydrated to form a sludge cake 11, which is discharged from the dehydrator 4. The sludge cake 11 is conveyed to another place by a conveyor 12, for example. Further, the filtrate containing the coagulant separated by the dehydrator 4 is collected and returned to an inflow source of a raw water tank or a sludge treatment facility (not shown).

FIG. 6 shows an example of a two-component addition method in which both anionic and cationic flocculants are added to sludge. In this example, a sludge storage tank 1 and two flocculant dissolving tanks 2A for anionic and cationic flocculants, respectively.
2B and first and second floc generation reaction tanks 3A
3B and dehydrator 4 are used. Flocculant dissolution tank 2A
・ Agitators 5A and 5B and pump 9A are provided in 2B, respectively.
・ 9B is provided. Then, in the first floc generation reaction tank 3A, the anionic (or cationic) coagulant from the coagulant dissolving tank 2A is added to the sludge from the sludge storage tank 1 and mixed by stirring by the stirrer 10A. After the small flocs are generated, the first floc generation reaction tank 3
From A to the second floc formation reaction tank 3B, the cationic (or anionic) coagulant from the flocculant dissolution tank 2B is added to the floc formation reaction tank 3B, and the stirrer 1
Stirring with 0B mixes to form large flocs.
After that, the same processing as in FIG. 5 is performed.

FIG. 7 shows an example of a three-component addition method in which an alkaline agent such as lime is added before the addition of both anionic and cationic flocculants for pH adjustment and nucleation for hardly dehydrated sludge. Show. In this example, a sludge storage tank 1, two flocculant dissolving tanks 2A and 2B for anionic and cationic flocculants, and first and second floc generation reaction tanks 3A・ 3B, dehydrator 4, stirrer 1
An alkaline agent tank 15 with 3 and a pump 14 and an in-line mixer 16 are used. Then, the sludge from the sludge storage tank 1 is mixed with the alkaline agent from the alkaline agent tank 15 in the in-line mixer 16, and then is fed into the first floc generation reaction tank 3A to dissolve the flocculant dissolving tank 2A.
From the coagulant. The subsequent processing is the same as in FIG. It should be noted that sludge and alkali agent are added to the in-line mixer 1
There is also a method of mixing by a mixing means other than 6. In addition, the addition and mixing of an alkaline agent such as lime may be performed in the sludge storage tank 1 or in the preceding stage.

FIG. 8 also shows an example of a three-component addition method in which an acidic liquid is added before addition of both anionic and cationic flocculants for pH adjustment and nucleation for hardly dehydrated sludge. . In this example, a sludge storage tank 1, two flocculant dissolving tanks 2A and 2B for anionic and cationic flocculants, and first and second floc generation reaction tanks 3A 3B, dehydrator 4, acid solution tank 18 with pump 17, and in-line mixer 19 are used. Then, the sludge from the sludge storage tank 1 is mixed with the acidic liquid (for example, hydrochloric acid, sulfuric acid band, ferrous sulfate, ferric sulfate, ferric chloride, etc.) from the acidic liquid tank 18 in the in-line mixer 19. Is fed into the first floc formation reaction tank 3A and the flocculant from the flocculant dissolution tank 2A is added. The subsequent processing is the same as in FIG.

[0006]

However, in any of the above-mentioned conventional examples, there is a saturation limit in the floc generation in the floc generation reaction tank, sufficient floc formation cannot be performed, and seemingly aggregated. Even though there are many apparent flocs that are extremely easily decomposed, and there are few flocs that are dense and highly dehydratable for sludge, such flocs are dehydrated as they are with a dehydrator, so dehydration is possible. The dehydration conditions in the process were bad. That is, the dehydration rate, treatment capacity, sludge recovery rate (SS recovery rate), etc. were generally low. Further, although the flocculating agent separated together with water by the dehydration is returned and reused, the dehydrating condition is not improved by the return, and the returned flocculant is recovered by other recovery during the water treatment process. It is expected that decomposition and reaction will occur with water, etc., and it is difficult to confirm the effect of the coagulant of the return component.In addition, in order to maximize the floc generation in the floc generation reaction tank, the sludge properties should be further improved. In order to achieve stable operation against changes in conditions such as changes and changes in concentration, the result is to inject excess flocculant far in excess of the saturation limit into the floc generation reaction tank, and the total amount of flocculant used for sludge is used. The ratio was high.

The reason will be described in detail. First, looking at the combined state of sludge and water, as shown in FIG. 9, the water contained in the sludge 20 is, in order of difficulty from the viewpoint of difficulty of dehydration, internal reserved water 21, surface-adhered water 22, and capillary-bound water. There are (wedge water) 23, pore water 24, and free free water 25. Therefore, free water 25, pore water 24, capillary bound water 2
In the order of 3, surface-attached water 22 and internal reserved water 21, the higher the ratio of the water in the previous order, the easier the dehydration becomes, and it is necessary to increase the free water 25 as much as possible in order to improve the dehydratability. is there.

In dehydration after the formation of flocs, the flocs must have a strength to withstand the shearing force caused by centrifugation, vacuum, compression, etc. during dehydration operations such as centrifugation, vacuum, compression, etc. The weaker the strength, the lower the dehydration rate in the dehydration step, the dehydration treatment capacity, and the sludge recovery rate.

On the other hand, floc formation by the coagulant is carried out by a two-step reaction of coagulation and adsorption / crosslinking. That is, coagulation is to neutralize the interfacial potential (zeta potential) due to colloidal particles and weaken electrostatic repulsion (Coulomb repulsion) to make the interparticle attractive force work. Adsorption / crosslinking is to condense particles. Mainly hydrogen bonds between the functional groups of the polymer, other ionic bonds Van der Waals By using adsorption and cross-linking reaction by utilizing the attractive force to enlarge the particles, when the coagulant is mixed with the sludge as described above. After the small flocs are generated by the condensation, the small flocs are further coupled to each other to become the large flocs. However, for both coagulation and adsorption / crosslinking, when the bonds between the colloidal particles and between the colloidal particles and the polymer of the aggregating agent are stable,
When the saturation limit is reached at which the binding property drops sharply, and even if the amount of the flocculant added is increased, it is impossible to enlarge the flocs, increase the strength and increase the free water commensurate with the increased amount.

However, conventionally, in terms of stability of floc strength and stability against changes in conditions such as changes in sludge properties and changes in concentration, it is advantageous that a large amount of coagulant is added. In the production of flocs in a reaction tank, the actual condition is to add an excessive amount of coagulant far more than the minimum amount required for sludge to flocculate.

When added excessively in this way, the coagulant migrates to the free water side free from the sludge and is contained in a larger amount in the free water, and it takes a long time for the above-mentioned coagulation and adsorption / crosslinking reactions. Not only that, the sludge particles cannot adsorb the macromolecule of the coagulant, and the coagulant that does not react even after a long time remains in free water, and a large amount of coagulant remains in the separated water after dehydration treatment. It will be. If this separated water is discharged as it is, it causes pollution by the coagulant,
Generally, this is returned and the flocculant is reused.However, deterioration of flocculation performance, floc strength and dehydration property cannot be denied, and the flocculant returned as described above is used during the water treatment process. , It is expected that decomposition and reaction will occur with other recovered water, etc., and it is difficult to confirm the effect of the return, so there was a vicious circle that the amount of new coagulant added had to be gradually increased. .

In view of the above problems caused by the returned coagulant, in the sludge treatment method disclosed in Japanese Patent Publication No. 59-19760, the floc is formed by adding and mixing the coagulant to the sludge, and then the wood powder is further added. Alternatively, cellulose powder is added and mixed to combine with a flocculant remaining in free water, thereby improving the dehydration property and removing the flocculant contained in the separated water after the dehydration treatment. However, according to this, the desired effect cannot be obtained unless a large amount of wood powder or cellulose powder is used in addition to the coagulant.

The object of the present invention is to greatly reduce the amount of the flocculant used by a simple method as compared with the conventional method without using any other additive such as wood powder or cellulose powder, and to improve the floc. The purpose is to improve the dewaterability of sludge and the recovery rate of sludge.

[0014]

In the sludge treatment method according to the present invention, a flocculant is added to and mixed with sludge to generate flocs, and mother liquor is separated from the flocs (solid-liquid separation, that is, free water and free water contained therein). Excess coagulant is removed from the flocs) to concentrate the flocs, and then the concentrated flocs are subdivided so as to be broken. Then, a flocculant is added and mixed again to the fragmented flocs to regenerate and strengthen the flocs, and then dehydrated.

The aggregating agent used for regenerating and strengthening the finely divided flocs may be the same as the aggregating agent used for the initial floc formation. The flocs once generated can be subdivided easily by forcibly stirring because free water and leaked coagulant are removed and concentrated. The flocculant separated in the concentration step can be reused for the initial floc formation.

The sludge treatment apparatus according to the present invention comprises a floc concentrating section for concentrating flocs by separating mother liquor from the flocs produced between the floc producing reaction tank and the dehydrator, and forcibly stirring the concentrated flocs. And a floc regeneration unit for regenerating and strengthening the flocs by adding and mixing a flocculant to the fragmented flocs.

[0017]

In the present invention, the mother liquor is separated from the flocs that have been formed once and, so to speak, preliminarily dehydrated. As a result, mainly free water of the above water contained in sludge,
Most of the surplus flocculant contained in this free water is removed, and flocs become concentrated. For example, if the concentrated flocs are forcibly stirred and the aggregated state is intentionally broken to be subdivided, the once adsorbed / crosslinked state is forcibly and weakly broken. When a flocculant is added to this, the adsorbed / crosslinked state is forcibly broken down and subdivided into fine particles, and the ionic bond is likely to be formed densely in the deep part of the sludge, and there is a tendency to restore it. Since a flocculant is newly added to the place where the flocculation is present, the reactivity and flocculation of the flocculant with sludge are high, and the floc regeneration is strongly strengthened. Along with this, some pore water, which is originally difficult to separate, capillary bound water, surface attached water, and internal retention water, are also pushed out of the sludge, and the sludge and the coagulant are more closely and firmly bonded. It is expected that the flocs will be highly dehydrated and coarse. When dehydration is finally carried out with a dehydrator after such a floc state, the dehydration rate, sludge recovery rate and dehydration treatment capacity are significantly improved as compared with the conventional case.

On the other hand, even if flocs are broken by force stirring without concentration (solid-liquid separation) of the flocs, and the flocculant is added thereto again, the amount of free water is almost the same. In the first place, the coagulant becomes a state where a new coagulant is added to the place where the surplus is present, and the newly added coagulant is only dissolved in free water, it does not strengthen the floc and is rather wasted. It only increases the number of different coagulants.

On the other hand, even if flocculants are added to sludge and forcedly stirred to strengthen the flocs before floc concentration, most of the flocculants are transferred to free water and dissolved, resulting in a dense ionic bond. It is expected that free water will have a cushioning action between the sludge and the flocculant by forced agitation to inhibit their binding, and it is difficult to strengthen the flocs.

As described above, in the present invention, the flocculant is added twice during flocculation and during regeneration, but the minimum required amount is sufficient during flocculation, which is much more than the conventional amount. Since it is not necessary to add a coagulant, and a much smaller amount is sufficient at the time of regeneration than at the time of generation, the total amount of the coagulant used can be significantly reduced from the conventional amount (about 30 to 90% of the conventional amount).

[0021]

Embodiments of the present invention will now be described with reference to the drawings. The first embodiment of the present invention shown in FIG. 1 is obtained by improving the conventional one-agent addition method shown in FIG. 5 and adding the following constitution to the constitution shown in FIG. That is, between the floc generation reaction tank 5 and the dehydrator 4, the floc concentration section 3
0, a floc subdivision unit 31, and a floc regeneration unit 32 are provided, and a filtrate tank 33 that receives the filtrate from the floc concentration unit 30 and the dehydrator 4 is provided.

The floc concentrating section 30 is a portion for concentrating flocs by separating the mother liquor from the flocs produced in the floc producing reaction tank 5. In the example shown in the figure, it is constituted by a filter such as a rotary screen to produce flocs. The flocs and mother liquor overflowing from the reaction tank 5 are filtered to separate free water and excess coagulant from the flocs. The concentrated flocs are sent to the floc subdivision unit 31, and the filtrate (separated water containing the flocculant) flows into the filtrate tank 33.

The floc subdividing portion 31 is a portion for intentionally breaking and subdividing the floc concentrated in the floc concentrating portion 30. In the illustrated example, the agitator 34 is rotated by a motor 35 to forcibly agitate the concentrated floc. Small (eg 1 mm
Below) subdivide.

The floc reproducing section 32 is a section for adding and mixing the flocculant again to the floc subdivided by the floc subdividing section 31 to regenerate and strengthen the floc. In the example of the figure, the flocculant dissolving tank 2 is used. While adding the anionic or cationic flocculant of 3 to the fragmented floc little by little, stirrer 3
6 is rotated by a motor 37 to mix slowly. The addition amount of the coagulant in the floc regeneration section 32 is sufficient to be about one fifth of the addition amount in the floc generation reaction tank 3. It is more economical to use the same flocculant added in the floc regeneration section 32 as the flocculant added in the floc generation reaction tank 3, but it may be different (for example, one of them may be anion). If so, make the other cationic).

The flocs regenerated and strengthened by the floc regeneration unit 32 are sent to the dehydrator 10 and dehydrated. The dehydrator 4 shown in FIG. 1 is designed to take out separated water in two stages by using a screw press, and the first separated water (filtrate by dehydration treatment) is allowed to flow into the filtrate tank 33 as it is. The separated water is further filtered by a filter 38 to be separated into primary filtered water and secondary filtered water, the primary filtered water is allowed to flow into the filtrate tank 33, and the secondary filtered water is returned to the raw water tank or discharged. It has become. The flocculant collected in the filtrate tank 33 is returned to the floc generation reaction tank 3 by the pump 39.

In the second embodiment of the present invention shown in FIG. 2, the conventional two-agent addition method shown in FIG. 6 is improved, and a structure similar to that of the first embodiment is added to the structure shown in FIG. It is a thing. In this case, only the anionic and cationic coagulants from the two coagulant dissolving tanks 2A and 2B are added at different locations in the floc regeneration section 32, which is different from the first embodiment. Others are the same as those in the first embodiment.

A third embodiment of the present invention shown in FIG. 3 is an improvement of the conventional three-agent addition method shown in FIG. 7, and a fourth embodiment of the present invention shown in FIG. 4 is shown in FIG. It is a similar improvement to the conventional three-agent addition method.

Although a screw press was used as a dehydrator in each of the above embodiments, various conventionally used dehydrators such as a centrifugal dehydrator, a vacuum dehydrator, a belt press type dehydrator, and a filter press are used. The present invention can improve the filtration / dehydration efficiency by using any of these. Furthermore, the reaction between sludge and the coagulant is not limited to the reaction method described above, and the present invention can be applied to the four-agent addition method, and the coagulant and its auxiliary agent may be added any number of times.

[0029]

As described above in detail, according to the present invention, the mother liquor is separated (solid-liquid separation) from the flocs that have been formed and then preliminarily dehydrated, whereby mainly free water contained in sludge and the free water. After removing most of the excess flocculant contained in water to concentrate the flocs, the floc's flocculation state was intentionally broken and subdivided, and then the flocculant was added and mixed again to subdivide the flocs. Agglomerates each other again strongly and densely, and is regenerated as coarse flocs with a higher density that are more strongly agglomerated than when they were first formed, and then dehydrated, so the dewaterability of flocs and sludge recovery rate are dramatically higher than before. Improve to. In addition, the flocculant is added twice during floc formation and during regeneration, but the minimum required amount is sufficient during floc formation, and it is not necessary to add a much larger excess of flocculant as in the conventional case. In addition, since a much smaller amount is sufficient at the time of regeneration than at the time of generation, the total amount of the coagulant used can be greatly reduced as compared with the conventional one. As a result, the coagulant contained in the recovered sludge cake can be reduced, and the sludge cake can be easily treated.

[Brief description of drawings]

FIG. 1 is a flowchart showing a first embodiment of the present invention applied to a one-agent addition method of adding either anionic or cationic coagulant to sludge.

FIG. 2 is a flowchart showing a second embodiment of the present invention applied to a two-component addition method in which both anionic and cationic flocculants are added to sludge.

FIG. 3 is a flowchart showing a third embodiment of the present invention applied to a three-component addition method in which an alkaline agent such as lime is added before the addition of both of the above coagulants.

FIG. 4 is a flowchart showing a fourth embodiment of the present invention applied to a three-agent addition method in which an acidic liquid is added before the addition of both of the above coagulants.

FIG. 5 is a flowchart showing an example of a conventional one-agent addition method.

FIG. 6 is a flowchart showing an example of a conventional two-agent addition method.

FIG. 7 is a flowchart showing an example of a conventional three-agent addition method in which an alkaline agent such as lime and anionic and cationic coagulants are added.

FIG. 8 is a flow chart showing an example of a conventional three-agent addition method of adding an acidic liquid and anionic and cationic coagulants.

FIG. 9 is a schematic diagram showing a combined state of sludge and water.

[Explanation of symbols]

 1 Sludge storage tank 2.2A / 2B Flocculant dissolution tank 3.3A / 3B Flock generation reaction tank 4 Dehydrator 30 Flock concentration section 31 Flock subdivision section 32 Flock regeneration section

Claims (5)

[Claims] 1. A sludge treatment method comprising a floc generation step of adding and mixing a flocculant to sludge to generate flocs, and a dehydration step of dehydrating the flocs, wherein a sludge treatment step is performed between the floc generation step and the dehydration step. , A floc concentration step of separating mother liquor from the generated flocs to concentrate the flocs, a floc subdivision step of subdividing the concentrated flocs, and adding and mixing a flocculant to the subdivided flocs to form the flocs. A sludge treatment method comprising a floc regeneration process for enhancing regeneration. 2. The sludge treatment method according to claim 1, wherein the same flocculant used in the floc generation step is used in the floc regeneration step. 3. The flocs are subdivided by forcibly stirring the flocs in the floc subdividing step.
Sludge treatment method described in. 4. The sludge treatment method according to claim 1, wherein the flocculant separated and collected in the floc concentration step is reused in the floc generation step. 5. A sludge treatment apparatus having a floc generation reaction tank for generating flocs by adding and mixing a flocculant to sludge, and a dehydrator for dehydrating the flocs, wherein the floc generation reaction tank and the dehydrator are provided. In the meantime, a floc concentration part that concentrates the flocs by separating the mother liquor from the generated flocs, a floc subdivision part that forcibly stirs the concentrated flocs to subdivide the flocs, and an aggregating agent for the subdivided flocs. A sludge treatment device, comprising: a floc regeneration unit that reinforces the floc by adding and mixing.