JP4416144B2 - Coagulation precipitation method and apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
TECHNICAL FIELD The present invention relates to a coagulation sedimentation method and apparatus for separating suspended substances in raw water into sludge and treated water by coagulation sedimentation, and in particular, a coagulation sedimentation method and apparatus capable of further efficiently concentrating sludge separated by coagulation sedimentation. About.
[0002]
[Prior art]
An apparatus for separating and removing substances suspended in raw water (hereinafter sometimes referred to as SS [Suspended Solid]) by precipitation is known. As a conventional coagulating sedimentation apparatus for removing SS in raw water, an apparatus that simply adds a coagulant to raw water to precipitate the aggregate, pulls the aggregate as sludge, and derives treated water from the top is well known.
[0003]
In such a general coagulation precipitation apparatus, it takes a long time to precipitate the coagulum, and a very large sedimentation tank is required. Therefore, the coagulation precipitation can be performed more efficiently. A device has been proposed.
[0004]
For example, in French Patent No. 1411792, in a coagulation tank, a granular material (typically sand) having a particle size of about 10 to 200 μm is added to the raw water together with a flocculant, and the SS in the raw water has a large specific gravity. There is disclosed a coagulation-precipitation apparatus for agglomerating as a relatively large floc containing water and precipitating the floc in the water to be treated introduced from the coagulation tank in the precipitation tank to separate it from the treated water. The slurry containing the precipitation floc extracted from the precipitation tank is separated into sludge and particulates by a separator such as a cyclone, and the separated particulates are returned to the coagulation tank and recycled. In such a coagulating sedimentation apparatus, it is possible to separate the treated water and the coagulated floc at a high flow rate in a relatively small sedimentation tank.
[0005]
[Problems to be solved by the invention]
In the coagulating sedimentation apparatus as described above, the sludge separated by the separator is actually often concentrated by a sludge storage tank, a dehydrator or the like provided in the subsequent stage. However, while the concentration of the extracted sludge in the above-described general coagulation sedimentation apparatus is about 1 to 2%, in the coagulation sedimentation apparatus using the above granular material, the outlet sludge concentration of the separator is 0.05. It is as low as about 0.5%, and there is a risk that the sludge storage tank provided in the latter stage will be enlarged or the load on the dehydrator will increase.
[0006]
In response to such a problem, although the application is still unpublished, the present applicant has previously proposed a coagulation sedimentation apparatus in which sludge concentration treatment is performed in a classification tower provided at the subsequent stage of the separator. (Japanese Patent Application No. 11-130978).
[0007]
The previously proposed agglomeration precipitation apparatus is configured as shown in FIG. 3, for example. The coagulation sedimentation apparatus 101 includes a coagulation tank 102 and a precipitation tank 103 disposed adjacent thereto. For example, an inorganic flocculant 106 is added to the raw water 105 supplied through the raw water supply line 104 in a preliminary coagulation tank 107, mixed by an agitator 109 driven by a motor 108, and further sent to the coagulation tank 102. Polymer flocculant 110 is injected. In the agglomeration tank 102, sand 111 as a granular material is added. The agglomeration tank 102 is provided with a stirrer 113 driven by a motor 112, and suspended matter in the raw water is a floc containing an inorganic flocculant 106, a polymer flocculant 110, and sand 111 by stirring by the stirrer 113. Aggregated and grown.
[0008]
The treated water containing the grown flocs 114 is introduced into the sedimentation tank 103 via the overflow basin 115. In the settling tank 103, flocs in the introduced water are settled downward, and the settled flocs are separated from the upper treated water 116. A plurality of inclined plates 117 are juxtaposed in the upper part of the sedimentation tank 103 to prevent the floc from flowing out together with the treated water 116. A drawing line 118 for pulling out the settled floc is connected to the bottom of the sedimentation tank 103, and the slurry containing the condensed floc that has settled is pulled out by the sludge drawing pump 119. The extracted slurry is sent to a cyclone 120 as a separator, and separated into sludge 121 and sand 111 by centrifugal separation in the cyclone 120. The separated sand 111 is returned again into the agglomeration tank 102 and recycled.
[0009]
The sludge 121 separated by the cyclone 120 is separated by separation and separation in the classification tower 122 and further separated into the sludge 123 that has been concentrated and the classified water that is returned to the preliminary coagulation tank 107 via the return line 124.
[0010]
However, the following problems remain in the coagulating sedimentation apparatus 101 in which the classification tower 122 is provided to concentrate the sludge as described above.
[0011]
That is, when the raw water is organic wastewater such as biologically treated water (activated sludge, etc.), the sludge downstream of the cyclone 120 is very difficult to settle, so it is difficult to concentrate and concentrate by gravity in the classification tower 122. Sometimes. If the concentration in the classification tower 122 is not performed according to the target, a large amount of sludge circulates in the coagulation sedimentation system, and the balance of the coagulation sedimentation treatment is lost. As a result, the water quality of the treated water may be deteriorated.
[0012]
Moreover, in order to improve the sedimentation and concentration performance of sludge in the classification tower 122, there is a method of increasing the capacity of the tower, but this causes a problem of newly increasing the installation area and cost.
[0013]
Therefore, in view of the above problems, the object of the present invention is to enable the sludge concentration process to be performed efficiently without causing an increase in the size of the apparatus at the subsequent stage of the sludge separator made of a cyclone or the like. It is an object of the present invention to provide a coagulation sedimentation method and apparatus capable of preventing an increase in the size of a sludge storage tank provided downstream of a separator and suppressing an increase in load on a dehydrator without deteriorating the quality of treated water.
[0014]
[Means for Solving the Problems]
In order to solve the above problems, the coagulation sedimentation method according to the present invention adds a flocculant and particulates to raw water, aggregates them together with suspended substances in the raw water, and precipitates the flocs to separate from the treated water. In a coagulation sedimentation method in which sludge containing settled flocs is extracted and separated into sludge and particulates by a separator, and the separated particulates are circulated and reused, the sludge separated by the separator is floated and separated by the rising of bubbles. Thus, the method further comprises separating the sludge into the concentrated sludge and the floating separation treated water. In other words, this is a method in which a new concept of flotation separation is introduced for further concentration of sludge separated by a separator. The floating separation in the present invention means that bubbles are adsorbed on sludge and separated into treated water and sludge by the buoyancy of the bubbles.
[0015]
In this coagulation sedimentation method, the floating separation treated water can be returned to the raw water. The flotation separation process can be performed, for example, by introducing flotation water into sludge separated by a separator and injecting air for generating bubbles into the flotation water. As the flotation separation water, for example, treated water from which flocs are settled and separated, that is, a part of the coagulation-precipitation treated water can be used.
[0016]
The coagulation sedimentation apparatus according to the present invention is a coagulation tank that aggregates suspended substances in raw water as flocs by adding a flocculant and particulates, and a floc in water introduced from the coagulation tank is settled and separated into treated water and flocs. In a coagulating sedimentation apparatus comprising a settling tank and a separator containing a settling floc extracted from the settling tank into sludge and granular materials, and returning the separated granular materials to the coagulating tank. It has a floating separation means for separating sludge into further concentrated sludge and floating separation treated water by floating separation by floating of bubbles.
[0017]
In this coagulation sedimentation apparatus, it can be set as the structure which has the floating separation processing water return line which returns the floating separation processing water isolate | separated by the floating separation means to raw | natural water. Further, it is possible to adopt a configuration in which a floating separation water supply line for supplying floating separation water into which bubble generating air is injected is connected to the floating separation means. The floating separation water supply line may be branched from the treated water discharge line from the settling tank.
[0018]
In addition, in the flotation separation process, it is possible to simply supply air for generating bubbles or add a foaming agent in addition thereto, and adopt a normal pressure flotation treatment method. It is also possible to generate bubbles for levitation separation by injecting the gas into the inside and abruptly reducing the pressure in the levitation separation processing tank (rapidly releasing to atmospheric pressure). In the latter case, a means for pressurizing and injecting air for generating bubbles into the water for floating separation may be provided.
[0019]
The configuration of the levitation separation means itself is not particularly limited. For example, the levitation separation means has a levitation separation tank including at least an inner cylinder and an outer cylinder, and the levitation separation water supply line is connected to the inner cylinder. This makes it possible to more efficiently separate the concentrated sludge and the floating separation treated water.
[0020]
In the coagulation sedimentation method and apparatus according to the present invention as described above, a new method of flotation separation is adopted for further concentration of sludge from the separator, and separation and concentration are efficiently performed along with the movement of bubbles where sludge floats. Is done. Since the concentration process is not simply a sedimentation separation but a flotation separation, it is possible to efficiently concentrate even sludge from organic wastewater, which has conventionally been difficult to separate. In addition, since it is a forced separation and concentration process by flotation separation, an exceptionally large flotation separation tank is unnecessary.
[0021]
Therefore, the sludge from the separator can be efficiently concentrated without increasing the size of the apparatus, the concentrated sludge can be efficiently separated from the floating separation treated water, and the floating separation treated water having an extremely low sludge concentration can be converted into a coagulation sedimentation system. It becomes possible to return. As a result of the concentration of sludge to a high concentration, it is possible to prevent the subsequent sludge storage tank from becoming large and to reduce the load on the dehydrator and the like. In addition, since sludge is efficiently separated and removed from the floating separation treated water returned to the coagulation sedimentation system, deterioration of the water quality of the coagulation precipitation system treated water is also prevented.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a coagulation precipitation apparatus and coagulation precipitation method according to an embodiment of the present invention. In FIG. 1, the coagulation precipitation apparatus 1 is provided with the coagulation tank 2 and the precipitation tank 3 arrange | positioned adjacent to it. The raw water 5 is supplied to the preliminary coagulation tank 7 through the raw water supply line 4, where the inorganic coagulant 6 is added. The preliminary coagulation tank 7 is provided with a stirrer 9 driven by a motor 8, and after being stirred by the stirrer 9, the polymer flocculant 10 is further injected when being sent to the coagulation tank 2. ing.
[0023]
In the agglomeration tank 2, sand 11 as a granular material is added. The agglomeration tank 2 is provided with a stirrer 13 driven by a motor 12, and suspended matter in the raw water is a floc containing inorganic flocculant 6, polymer flocculant 10, and sand 11 by stirring by the stirrer 13. Aggregated and grown.
[0024]
In this agglomeration, the inorganic flocculant 6 aggregates suspended substances to produce fine flocs, and the polymer flocculant 10 is entangled with them to grow into larger flocs. The grown flocs have a high specific gravity. As a whole, it grows into a floc that is relatively large and has a large specific gravity and is easy to settle.
[0025]
Water to be treated containing the grown flocs 14 is introduced into the sedimentation tank 3 through the overflow basin 15. In the settling tank 3, the flocs in the introduced water are settled downward, and the settled flocs are separated from the upper treated water 16. A plurality of inclined plates 17 are juxtaposed in the upper part of the settling tank 3 to prevent the floc from flowing out together with the treated water 16.
[0026]
A drawing line 18 for pulling out the settled floc is connected to the bottom of the settling tank 3, and the sludge drawing pump 19 draws the slurry containing the settled flocs. The extracted slurry is sent to a cyclone 20 as a separator, and separated into sludge 21 and sand 11 by centrifugal separation in the cyclone 20. The separated sand 11 is again returned to the agglomeration tank 2 and recycled.
[0027]
The system so far is substantially the same as that shown in FIG. In the present invention, the following flotation separation means is provided after the separator 20 (cyclone).
[0028]
An outlet line 22 for the sludge 21 before concentration from the separator 20 is connected to a floating separation tank 23, and a floating separation water supply line 24 is joined to the sludge outlet line 22. In this embodiment, the floating separation tank 23 has an inner cylinder 25 and an outer cylinder 26, and has a structure in which the tank wall 27 of the floating separation tank 23 is positioned outside the outer cylinder 26. The floating separation water supply line 24 merged with the sludge discharge line 22 is connected so as to face the inner cylinder 25, and bubbles for floating separation are floated in the inner cylinder 25. The scum 28 separated by the flotation separation process is collected above the inner cylinder 25 and in the upper part of the outer cylinder 26, and further sent as a concentrated sludge 29 to a subsequent sludge storage tank and further to a dehydrator. (Not shown).
[0029]
From the bottom of the levitation separation tank 23, the sludge 30 that has settled to the bottom is pulled out. In addition, from the upper part between the outer cylinder 26 and the tank wall 27, the floating separation treated water 31 separated from the sludge is returned to the preliminary coagulation tank 7 through the floating separation treated water return line 32, and into the coagulation sedimentation system. It is designed to be circulated.
[0030]
Air for generating bubbles 33 for floating separation is injected into the floating separation water supply line 24. In the present embodiment, the air 33 is injected as pressurized air. The floating separation water supply line 24 is provided with a pressurizing pump 34 and a pressurizing tank 35. When the injected air is supplied into the inner cylinder 25 after being brought into a predetermined pressurizing state. Air bubbles can be generated by rapidly releasing to a reduced pressure state (atmospheric pressure state).
[0031]
Although the water supplied to the floating separation water supply line 24 can be collected from another system, it is branched from the line of the treated water 16 from the settling tank 3 and a part of the treated water 16 is used. Is efficient.
[0032]
In the apparatus as described above, the sludge 21 having a relatively low concentration from the separator 20 is separated into the sludge 29 further concentrated in the floating separation tank 23. Since this levitation separation process is forcibly separated in accordance with the bubble levitation operation, a large tank is unnecessary, and high separation efficiency can be obtained by the forced separation force.
[0033]
Further, unlike the sedimentation separation process using gravity, it is possible to efficiently concentrate and separate even sludge that is difficult to settle, such as organic sludge as described above.
[0034]
As a result, the concentration of the sludge 29 sent from the flotation separation tank 23 to the subsequent stage is concentrated to a much higher concentration than that using the classification tower shown in FIG. And the load on the dehydrator can be reduced.
[0035]
In addition, sludge is efficiently removed from the floating separation treated water 31 returned to the pre-flocculation tank 7, and the concentration of sludge in the floating separation treated water 31 is extremely low. There is nothing and the quality of the treated water 16 is not deteriorated.
[0036]
FIG. 2 shows a coagulation precipitation apparatus and coagulation precipitation method according to another embodiment of the present invention. In this embodiment, the levitating separation tank 41 is configured to have an inner cylinder 42 and a tank wall 43 configured as a common wall with the outer cylinder, and the levitated separation treated water is formed from the bottom of the levitating separation tank 41. 44 is returned directly to the pre-flocculation tank 7 via the return line 45. Other configurations are the same as those of the apparatus shown in FIG.
[0037]
In the present embodiment, compared with the embodiment shown in FIG. 1, since the sedimentation sludge is not extracted from the bottom of the flotation separation tank, the sludge concentration in the flotation separation treated water 44 returned to the preliminary coagulation tank 7 is slightly higher. However, since the concentrated sludge is efficiently removed by the floating separation treatment, the absolute value of the sludge concentration in the floating separation treated water 44 is low. Since the returned floating separation treated water 44 is subjected to the coagulation sedimentation treatment together with the raw water, the quality of the treated water from the precipitation tank 3 is substantially reduced as long as the sludge concentration of the floating separation treated water 44 is kept low. Will not be adversely affected. That is, since the sludge concentration and separation performance by the floating separation process in the floating separation tank 41 is high, it is possible to further simplify the apparatus of FIG.
[0038]
The inorganic flocculant and polymer flocculant used in the present invention are not particularly limited, but as the inorganic flocculant, for example, polyaluminum chloride (PAC), ferric chloride, ferric sulfate can be used. As the polymer flocculant, for example, nonionic, anionic or amphoteric polymer flocculants can be used. Examples of the anionic polymer flocculant include a polymer of acrylic acid or a salt thereof, a copolymer of acrylic acid or a salt thereof and acrylamide, and a copolymer of acrylamide and 2-acrylamido-2-methylpropanesulfonate. , A terpolymer of acrylic acid or a salt thereof, acrylamide and 2-acrylamido-2-methylpropanesulfonate, a partial hydrolyzate of polyacrylamide, and the like, but is not particularly limited thereto. A typical example of the nonionic polymer flocculant includes polyacrylamide, but is not particularly limited thereto. Examples of amphoteric polymer flocculants include at least one cationic monomer such as dimethylaminoethyl (meth) acrylate tertiary salt and quaternary salt (such as methyl chloride salt), acrylic acid and salts thereof. (Salts such as sodium and calcium), copolymers of at least one anionic monomer such as 2-acrylamido-2-methylpropanesulfonate (salts such as sodium and calcium), or at least one of the above Examples of the cationic monomer and terpolymer or quaternary copolymer of at least one anionic monomer and at least one nonionic monomer such as acrylamide, In particular, it is not limited to these. The molecular weight range of the polymer flocculant is not particularly limited, but a range of 5 million to 20 million is preferable. These polymer flocculants can be used alone or as a mixture. The addition amount of the polymer flocculant is generally about 0.3 to 2 mg / l from an economical viewpoint.
[0039]
【The invention's effect】
As described above, according to the coagulation sedimentation method and the coagulation sedimentation apparatus of the present invention, the sludge from the separator can be efficiently concentrated to a higher concentration in a small flotation separation tank, and the low concentration flotation separation treatment can be performed. Efficient separation from water. Since the separated sludge can be concentrated to a desired concentration, it is possible to reduce the size of the subsequent sludge storage tank and reduce the load on the dehydrator. Moreover, since the sludge concentration of the floatation separation treated water returned to the coagulation sedimentation system can be kept extremely low, the water quality of the coagulation sedimentation treatment water can be kept stable and high.
[Brief description of the drawings]
FIG. 1 is an overall configuration diagram of a coagulation precipitation apparatus according to an embodiment of the present invention.
FIG. 2 is an overall configuration diagram of a coagulation precipitation apparatus according to another embodiment of the present invention.
FIG. 3 is an overall configuration diagram of a coagulation precipitation apparatus (Japanese Patent Application No. 11-130978) previously proposed by the present applicant.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Coagulation precipitation apparatus 2 Coagulation tank 3 Precipitation tank 4 Raw water supply line 5 Raw water 6 Inorganic flocculant 7 Pre-coagulation tank 8 Motor 9 Stirrer 10 Polymer flocculant 11 Sand as granular material 12 Motor 13 Stirrer 14 Aggregation floc 15 Overflow 16 treated water 17 inclined plate 18 drawing line 19 sludge drawing pump 20 cyclone as separator 21 sludge before concentration 22 sludge derivation line 23, 41 flotation separation tank 24 flotation separation water supply line 25, 42 inner cylinder 26 outer cylinder 27 , 43 Tank wall 28 Scum 29 Concentrated sludge 30 Sedimented sludge 31, 44 Flotation separation treated water 32, 45 Flotation separation treated water return line 33 Injection air 34 Pressure pump 35 Pressure tank

Claims (10)

  Add flocculant and granular material to raw water and coagulate as floc together with suspended substances in raw water. In the coagulation-precipitation method in which the separated granular material is recycled and reused, the sludge separated by the separator is separated into the further concentrated sludge and the floatation-separated water by flotation separation by floating of bubbles. A coagulation precipitation method characterized by the above.   The coagulation sedimentation method according to claim 1, wherein the floating separation treated water is returned to the raw water.   The coagulation sedimentation method according to claim 1 or 2, wherein the floating separation water is introduced into the sludge separated by the separator, and the air for generating bubbles is injected into the floating separation water.   The coagulation sedimentation method according to claim 3, wherein a part of the treated water from which the floc is settled and separated is used as the floating separation water.   A coagulation tank that aggregates suspended substances in raw water as flocs by adding a flocculant and particulates, a precipitation tank that settles flocs in the water introduced from the coagulation tank and separates them into treated water and flocs, and extracts from the precipitation tank In a coagulation sedimentation device equipped with a separator that separates sludge containing sedimented floc into sludge and particulate matter and returns the separated particulate matter to the coagulation tank, the sludge separated by the separator is levitated and separated by the rise of bubbles And a flocculating / separating device characterized in that the flocculating / separating device further comprises a levitating / separating means for separating the concentrated sludge and the levitating / separating water.   The coagulation sedimentation apparatus according to claim 5, further comprising a flotation separation treated water return line for returning the flotation separation treated water separated by the flotation separation means to the raw water. The coagulating sedimentation apparatus according to claim 5 or 6 , wherein a floating separation water supply line for supplying floating separation water into which bubble generating air is injected is connected to the floating separation means.   The coagulating sedimentation apparatus according to claim 7, wherein the floating separation water supply line is branched from the treated water discharge line from the sedimentation tank.   9. The coagulation precipitation apparatus according to claim 7 or 8, further comprising means for pressurizing and injecting air for generating bubbles into the water for floating separation.   The coagulation sedimentation apparatus according to any one of claims 7 to 9, wherein the flotation separating means has a flotation separation tank including at least an inner cylinder and an outer cylinder, and a flotation separation water supply line is connected to the inner cylinder.

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