JP2000317220A - Flocculating and settling device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flocculating and setting device which is low in a production cost, small in installation space and has no intermediate tank, can more efficiently flocculate rapidly at a flocculating tank and can be subjected to high speed treatment of 30-100 m/h linear velocity at a settling tank. SOLUTION: This device 1 is provided with the flocculating tank 2 for flocculating suspensions in raw water into flocks by adding a flocculating agent and granular powder, the settling tank 3 for settling flocks in the water introduced from the tank 2 to separate the flocks from the treated water and a separator 18 for separating a slurry containing precipitated flocks withdrawn from the tank 3 into sludge and granular powder to return the granular particle to the tank 2. A sludge return line 20 is provided to return a part of the sludge separated at the separator 18 to the raw water.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coagulation and sedimentation apparatus for separating suspended substances in raw water into sludge and treated water by coagulation and sedimentation. The present invention relates to a coagulating sedimentation apparatus capable of improving water quality.

[0002]

2. Description of the Related Art Substances suspended in raw water (hereinafter referred to as SS
Sometimes called [Suspended Solid]. Is known. S in conventional raw water
As a coagulation sedimentation apparatus for removing S, an apparatus is known which simply adds a coagulant to raw water to precipitate coagulation, pulls out the coagulation as sludge, and discharges treated water from the upper part. .

In such a general coagulation / sedimentation apparatus, it takes a long time to settle the coagulates, and an extremely large sedimentation tank is required. A coagulating sedimentation apparatus has been proposed.

[0004] For example, in French Patent No. 1411172, in a coagulation tank, raw water is mixed with a coagulant together with a particle size of 1;
Granules (typically, sand) of about 0 to 200 μm are added, and SS in the raw water is coagulated as relatively large flocs containing granules having a large specific gravity. There is disclosed a coagulating sedimentation apparatus for sedimenting floc in treated water and separating it from treated water. The sediment floc pulled out of the sedimentation tank is separated into sludge and particulate matter by a separator such as a cyclone, and the separated particulate matter is returned to the flocculation tank and used for circulation.

However, in reality, it is difficult to grow the floc to the optimum size and specific gravity in the next precipitation step by stirring in the flocculation tank, so that the floc can only be quickly and efficiently separated. It was difficult to do. Therefore, in actual operation, the linear velocity of the water treatment in the settling tank can be achieved only about 6 to 8 m / h, and it is difficult to achieve a linear velocity of a higher flow velocity.

[0006] Japanese Patent No. 26342 discloses such a situation.
Japanese Patent No. 30 discloses a coagulation / sedimentation apparatus in which an intermediate tank provided with a stirrer is provided between the coagulation tank and the precipitation tank, thereby enabling processing at a high flow rate linear velocity.

This coagulation / sedimentation apparatus is configured as shown in FIG. 4, for example. A raw water 101 is mixed with, for example, an inorganic coagulant 102 and a polymer coagulant 103 together with sand 104 as particulate matter. The SS in the raw water is aggregated while being agitated by the stirrer 106, the water to be treated is introduced into the intermediate tank 107, and the floc growth is further promoted while being agitated by the stirrer 108. Since the treated water containing the grown sand-containing floc is introduced into the sedimentation tank 109, the floc is more efficiently and quickly settled, and can be separated from the treated water 110 in a shorter time. The floc settled at the bottom of the settling tank 109 is drawn out by a sludge drawing pump 111, separated into sludge 113 and sand 104 by a separator 112 made of cyclone or the like, and the separated sand 104 is returned to the flocculation tank 105 for circulation. Is being used. Patent No. 263423
No. 0 describes that the coagulation-sedimentation apparatus enables processing at a linear velocity of 30 to 60 m / h, and even at a high flow rate of 90 m / h.

[0008]

However, in the apparatus proposed in Japanese Patent No. 2634230, it is necessary to provide an intermediate tank 107 with agitation between the flocculation tank 105 and the precipitation tank 109. This leads to an increase in equipment cost, power consumption, and installation area.

[0009] Therefore, an object of the present invention is to provide a method for efficiently and quickly performing coagulation in a coagulation tank without providing an intermediate tank as described above, and reducing the linear velocity of the treatment in the sedimentation tank to 30.
An object of the present invention is to provide a coagulation sedimentation apparatus which can perform a high-speed treatment of about 100 m / h, is inexpensive, and requires a small installation area.

[0010] As a prior art related to the present invention,
Japanese Unexamined Patent Publication No. Hei 9-141006 discloses a coagulation sedimentation apparatus provided with a line at the bottom of the sedimentation tank for returning the sedimented sediment to the coagulation tank as it is. Since only the largest flocculated floc settled at the bottom will be returned to the flocculation tank side, it is difficult to obtain the function and effect according to the present invention as described below,
This technique basically differs from the present invention in technical idea.

[0011]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, an agglomeration and precipitation apparatus according to the present invention comprises an aggregating tank for aggregating suspended substances in raw water as flocs by adding an aggregating agent and particulate matter; A sedimentation tank for sedimenting floc in the introduced water from the sedimentation tank and separating it into treated water and floc, a slurry containing sedimented floc drawn out from the sedimentation tank is separated into sludge and particulate matter, and the separated particulate matter is returned to the flocculation tank. A coagulating sedimentation apparatus provided with a separator, wherein a sludge return line for returning a part of the sludge separated by the separator to raw water is provided.

In this coagulating sedimentation apparatus, a part of the sludge separated by the separator can be directly returned to the raw water. However, in order to further improve the treatment efficiency, the sludge return line is connected to the sludge return line. Preferably, a classification tower is provided for classifying the sludge into sludge to be discharged, containing larger flocs, and sludge to be returned to raw water, containing smaller flocs. By providing such a classification tower, fine flocs can be selectively returned to the raw water.

In this separation tower, there is a suitable range of the rising speed of the water to be treated (slurry to be treated), and the linear rising speed in the classification tower is preferably in the range of 3 to 8 m / h. Range of rising linear velocity in this classification tower 3
８8 m / h is a linear velocity of 1 m / h in a general concentration tank or the like.
It has a larger linear velocity than h, and has different purposes and performance. By setting the range of the ascending linear velocity as described above, the above-mentioned desirable fine flocks can be efficiently classified from the large flocs, and the fine flocs that have been divided can be reliably and selectively returned to the raw water side.

Furthermore, the sludge return line may be provided with a preliminary flocculation tank for mixing raw water supplied to the flocculation tank, a part of the sludge separated by the separator, and a flocculant. By providing such a preliminary coagulation tank, the coagulation can be started before the coagulation in the coagulation tank, and the predetermined coagulation in the coagulation tank can be performed more quickly.

As the granular material to be used, sand can be typically used, and those having a uniform particle size are particularly preferable. Further, as the flocculant, an inorganic flocculant and a polymer flocculant can be usually used. The inorganic flocculant can efficiently flocculate the suspended substance in the raw water, and the polymer flocculant grows fine flocculated flocs generated by the inorganic flocculant into larger flocs by further entanglement of the polymer. Granules made of sand or the like having a large specific gravity are mixed in the grown flocks, and flocs having a large specific gravity (density) and easy to precipitate are formed as a whole.

Although the separator is not particularly limited,
For example, a cyclone can be used.

In the coagulating sedimentation apparatus according to the present invention as described above, a part of the sludge separated by the separator is returned to the raw water through the sludge return line. This return amount has a suitable range depending on the configuration of the sludge return line, for example, the presence or absence of a classification tower. By the way, the flocculation effect is not only due to the flocculating force of the flocculant, but also due to the absorption of the flocs by physical collision. Therefore, the floc can be grown more effectively as the number of flocs increases. Therefore, if a part of the sludge separated by the separator is returned to the raw water, flocs that have already been aggregated to some extent will be appropriately mixed into the raw water, increasing the chance of physical collisions and increasing the floc. Grows faster. Therefore, the time for coagulation in the coagulation tank (residence time in the tank) is reduced, and the predetermined coagulation in the coagulation tank is performed more efficiently and more reliably.

In particular, if a classifying tower is provided to selectively return only fine flocs to raw water, the number of flocs to be returned can be increased by the amount of fine flocs even if the return amount is the same. Since the chance of physical collision can be increased, flocs can be more effectively grown. At this time, if the sludge containing flocs is returned in a large amount, the water quality is rather deteriorated. Therefore, it is important to increase the number of flocs with a small return amount. As described above, by selectively returning the fine flocs to the raw water, more effectively, prior to the coagulation in the coagulation tank,
The state of coagulation is advanced to some extent, and the predetermined coagulation in the coagulation tank is performed more efficiently, more quickly, and more reliably. If a preliminary flocculation tank is provided, the preliminary flocculation can be performed more efficiently.

In the present invention, as described above, since the predetermined coagulation in the coagulation tank is performed efficiently, promptly and reliably, the coagulation tank is provided with the optimum coagulation for the next precipitation step without providing an intermediate tank. It can be grown to floc, and a high-speed precipitation treatment of 30 to 100 m / h in a precipitation tank becomes possible. Since there is no need to provide an intermediate tank, the equipment cost is low and the installation area is small. Also, the power cost is significantly reduced as compared with the case where an intermediate tank provided with a stirrer is provided. In addition, since the predetermined coagulation in the coagulation tank is completed in a short time, the size of the coagulation tank can be reduced.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a coagulation / sedimentation apparatus 1 according to one embodiment of the present invention. The coagulation / sedimentation apparatus 1 includes a coagulation tank 2 and a sedimentation tank 3 disposed adjacent thereto. The coagulation tank 2 has a raw water supply line 4
The raw water 5 is supplied via the, and in the present embodiment, the inorganic coagulant 6 and the polymer coagulant 7 are injected in a line. Downstream of the injection position of the inorganic flocculant 6, a mixer 8 such as a static mixer is interposed so that the injected flocculant can be mixed well with the raw water. However,
These coagulants can be directly charged into the coagulation tank 2.

As the inorganic coagulant 6, for example, polyaluminum chloride (PAC), ferric chloride, and ferric sulfate can be used. As the polymer coagulant 7, for example, a nonionic, anionic or amphoteric polymer can be used. Flocculants can be used. Examples of the anionic polymer coagulant 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-methylpropanesulfonic acid salt And a tertiary copolymer of acrylic acid or a salt thereof, acrylamide and 2-acrylamido-2-methylpropanesulfonate, and a partial hydrolyzate of polyacrylamide, but are not particularly limited thereto. A typical nonionic polymer flocculant includes polyacrylamide, but is not particularly limited thereto. Examples of the amphoteric polymer flocculant include at least one cationic monomer such as a tertiary salt and a quaternary salt of dimethylaminoethyl (meth) acrylate (eg, a methyl chloride salt), acrylic acid and a salt thereof. (Salts such as sodium and calcium), 2-
A copolymer of at least one anionic monomer such as acrylamide-2-methylpropanesulfonate (salts such as sodium and calcium), or at least one of the above cationic monomers and at least one of the above 1
Ternary or quaternary or higher copolymers of at least one kind of anionic monomer and at least one kind of nonionic monomer such as acrylamide are exemplified, but not particularly limited thereto. The range of the molecular weight of the polymer flocculant is not particularly limited, but is preferably in the range of 5,000,000 to 20,000,000. 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 economic viewpoint.

In the coagulation tank 2, sand 9 as granular material is added. The flocculation tank 2 is provided with a stirrer 11 driven by a motor 10, and the suspended substance in the raw water is stirred by the stirrer 11 to form a floc containing the inorganic coagulant 6, the polymer coagulant 7, and the sand 9. Agglomerated.

In this flocculation, the inorganic flocculant 6 flocculates the suspended substance to form fine flocs, and the polymer flocculant 7 becomes entangled and grows into a larger floc. It contains sand 9 as large particulate matter and grows into relatively large, high specific gravity flocculable flocs as a whole.

The treated water containing the grown floc 13 is introduced into the settling tank 3 via the overflow weir 12. In the sedimentation tank 3, the flocs in the introduced water are sedimented downward, and the sedimented flocs are separated from the upper treated water 14. A plurality of inclined plates 15 are arranged side by side in the upper part of the settling tank 3 to prevent the floc from flowing out together with the treated water 14.

The bottom of the settling tank 3 is connected to a drawing line 16 for drawing out the settled flocs, and a slurry containing the settled flocs is drawn out by a sludge drawing pump 17. The extracted slurry is
It is sent to cyclone 18 as a separator, and cyclone 1
The sludge 19 and the sand 9 are separated by the centrifugal separation in the inside 8. The separated sand 9 is returned to the flocculation tank 2 again and used for circulation.

A part of the sludge 19 separated by the cyclone 18 is returned to the raw water 5 through a sludge return line 20. In this embodiment, the sludge return line 20 is connected to the raw water supply line 4 on the upstream side of the mixer 8, and is returned to the raw water flowing through that part. The amount of sludge to be returned to the raw water and the amount of sludge to be discharged without being returned can be adjusted by valves 21 and 22 (for example, valves capable of adjusting the flow rate).

FIG. 2 shows a coagulation / sedimentation apparatus 31 according to another embodiment of the present invention. In the present embodiment, a classification tower 33 is provided in the sludge return line 32. In the classification tower 33, the sludge slurry from the separator 18 is collected at the bottom thereof and is discharged from the upper part. And the sludge 35 to be returned to the raw water.
By this classification, most of the flocculated flocs contained in the sludge 35 returned to the raw water become fine flocs, and the fine flocs are selectively returned to the raw water. Other configurations are the same as those of the embodiment shown in FIG. 1, and the description is omitted by attaching the same reference numerals as those in FIG.

FIG. 3 shows a coagulation / sedimentation apparatus 41 according to still another embodiment of the present invention. In the present embodiment, the sludge return line 42 is further provided with a preliminary flocculation tank 43 together with the classification tower 33. However, the classification tower 33
To add the pre-coagulation tank 43 without providing
It is also possible to add a preliminary flocculation tank 43 to the sludge return line as shown in FIG. The raw water 5 is introduced into the pre-coagulation tank 43 via the raw water supply line 4, and the mixer 8 is not provided in the present embodiment. In the preliminary coagulation tank 43,
A stirrer 45 driven by a motor 44 is provided. In the present embodiment, the inorganic flocculant 6 is added to the preliminary flocculation tank 43, and the raw water and the returned sludge 35 are stirred and mixed by the stirrer 45 so that the preliminary flocculation proceeds in the tank 43. Has become. Further, in the present embodiment, the polymer flocculant 7 is line-injected between the preliminary flocculation tank 43 and the flocculation tank 2. Other configurations are the same as those in the embodiment shown in FIG. 2, and thus the same reference numerals as those in FIG.

In the coagulating sedimentation apparatus constructed as described above, the flocculation floc 13 containing the inorganic coagulant 6, the polymer coagulant 7 and the sand 9 in the coagulation tank 2 has a size suitable for the next sedimentation step. The floc, which has been agglomerated, grown and contains sand 9 and has a relatively large specific gravity, is rapidly settled and separated from the treated water 14 in the settling tank 3 at a high linear velocity of 30 to 100 m / h. Can be performed.

The slurry containing the precipitated flocculated flocks extracted from the precipitation tank 3 is separated by the separator 18 and a part thereof is returned to the raw water. By returning part of the sludge to the raw water, flocs that have already been flocculated to some extent will be appropriately mixed into the raw water, and starting from the mixed flocs, that is, starting flocculation from the mixed flocs. In addition, the start of predetermined flocculation (coagulation until a floc having a size suitable for the next precipitation step) in the flocculation tank 2 can be hastened.

In particular, if the classifying tower 33 is provided to selectively return only the fine flocs to the raw water, the number of flocs returned by the same return amount can be increased, and the flocs at the time of coagulation can be reduced. The chance of collision can be increased, and the speed of agglomeration due to absorption of flocs can be increased.
Therefore, prior to the coagulation in the coagulation tank 2, the coagulation tank 2 is brought into a state where coagulation progresses to a certain extent, and the predetermined coagulation in the coagulation tank 2 is performed more efficiently, more quickly, and more reliably.

If a preliminary flocculation tank 43 is provided and the inorganic flocculant 6 and the returned fine floc are mixed before entering the flocculation tank 2, the flocculation nucleus is formed more efficiently, Will be more efficiently aggregated, and will be performed more quickly and more reliably.

As described above, by returning a part of the separated sludge to the raw water side, predetermined flocculation in the flocculation tank 2
It is performed very efficiently, quickly and reliably, and can be grown to the flocculation floc optimum for the next precipitation step in the flocculation tank 2 without providing an intermediate tank as shown in FIG. 30 to 100 in the precipitation tank 3
A high-speed precipitation treatment of m / h becomes possible. Since there is no need to provide an intermediate tank, the equipment cost is low and the installation area is small. In addition, the power cost is greatly reduced as compared with the case where an intermediate tank provided with a stirrer as shown in FIG. 4 is provided. Further, by performing the coagulation to some extent in advance, the predetermined coagulation in the coagulation tank 2 is completed in a short time, so that the coagulation tank 2 can be downsized.

The coagulating sedimentation apparatus according to the present invention has the following features.
For example, when the turbidity of the raw water is low and it is difficult to form a desired floc in the flocculation tank 2, or when the turbidity of the raw water fluctuates greatly, it becomes extremely easy to form a desired floc suitable for precipitation. Therefore, it is particularly suitable. More specifically, the present invention is particularly effective when applied to the treatment of river water in which the quality of raw water varies greatly, or the treatment of wastewater containing organic matter, which is generally difficult to coagulate.

The following experiment was conducted to confirm the effect of the coagulation / sedimentation apparatus according to the present invention.

[Experiment] PAC as an inorganic coagulant was injected into artificial turbid water in which kaolin was added to raw water as a suspended substance, followed by line mixing, and a polymer as a high-molecular coagulant was injected. And the experiment was conducted under the following conditions, and the turbidity of the treated water was measured.

Experimental machine: Coagulation tank capacity: 500 liters Precipitation tank: 500 mm □ × 3000 mmH (with inclined plate) Classification tower: 300 mmφ × 2500 mmH ・ Operating conditions: Raw water flow rate: 15 m ³ / h (Sedimentation tank linear velocity [LV] = 60 m / h) PAC injection amount: 20 mg / l Polymer injection amount: 0.5 mg / l (polyacrylamide anionic polymer) Sludge withdrawal from the lower part of the classification tower: 5% of the sludge withdrawn from the sedimentation tank The corresponding amount was withdrawn intermittently once an hour.

The results are shown in Table 1. From the results of Comparative Examples 1 and 2, and Examples 1 and 3, it can be seen that the quality of the treated water can be improved by returning a part of the sludge to the raw water. However, when only a part of the sludge is returned to the raw water, the amount of the returned water is limited, and if the amount is returned to a large amount, the water quality is rather deteriorated (Example 2).

Therefore, if a classification tower is provided, it is possible to obtain an excellent quality of treated water while returning to a large amount (Examples 4 to 6). However, even in this case, an optimum condition range exists, and good results are obtained particularly when the LV of the classification tower is in the range of 3 to 8 m / h (Examples 4 to 6). 7, 8), it was found that the quality of the treated water deteriorated. Therefore, when designing the actual apparatus, a desirable range in terms of conditions may be selected together with the configuration of the sludge return line.

[0040]

[Table 1]

[0041]

As described above, according to the coagulation / sedimentation apparatus of the present invention, a part of the sludge separated by the separator is returned to the raw water. The treatment in the precipitation tank can be performed at a high speed of a linear velocity of 30 to 100 m / h without providing an intermediate tank between the flocculation tank and the precipitation tank. Since there is no need to provide an intermediate tank, the entire apparatus can be configured at low cost, the installation area is small, and the power cost required for operation is small.

Further, prior to the coagulation in the coagulation tank, the suspended solids in the raw water can be appropriately coagulated.
Predetermined coagulation in the coagulation tank can be completed in a short time, the residence time in the coagulation tank is reduced, and the size of the coagulation tank can be reduced. Furthermore, by performing such prior aggregation, predetermined aggregation in the aggregation tank is more efficiently and reliably performed, and as a result, the quality of treated water can be improved.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of a coagulation / sedimentation apparatus according to an embodiment of the present invention.

FIG. 2 is an overall configuration diagram of a coagulation / sedimentation apparatus according to another embodiment of the present invention.

FIG. 3 is an overall configuration diagram of a coagulation / sedimentation apparatus according to still another embodiment of the present invention.

FIG. 4 is an overall configuration diagram of a conventional coagulation / sedimentation apparatus.

DESCRIPTION OF SYMBOLS 1, 31, 41 Coagulation and sedimentation apparatus 2 Coagulation tank 3 Precipitation tank 4 Raw water supply line 5 Raw water 6 Inorganic coagulant 7 Polymer coagulant 8 Mixer 9 Sand as granules 10 Motor 11 Stirrer 12 Overflow 13 Grown floc 14 Treated water 15 Inclined plate 16 Extraction line 17 Sludge extraction pump 18 Cyclone as separator 19 Sludge 20, 32, 42 Sludge return line 21, 22 Valve 33 Classification tower 34 Discharged sludge 35 Classified raw water Sludge returned to waste 43 Pre-coagulation tank 44 Motor 45 Stirrer

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (reference) C02F 1/52 C02F 1/52 K 11/12 11/12 Z 11/14 11/14 EF term (reference 4D015 BA04 BA06 BA09 BB08 BB12 CA10 DA04 DA16 DB03 DB43 DB45 4D059 AA06 BE39 BK30 CA28 4D062 BA04 BA06 BA09 BB08 BB12 CA10 DA04 DA16 DB03 DB43 DB45 4D071 AA53 AA62 CA01 CA03 CA05 DA20

Claims (6)

[Claims] 1. A flocculation tank for flocculating suspended substances in raw water as flocs by adding a flocculant and particulate matter, and a sedimentation tank for sedimenting flocs in water introduced from the flocculation tank and separating them into treated water and flocs. A slurry containing sedimentation floc drawn out of the sedimentation tank, separated into sludge and particulate matter, and a separator for returning the separated particulate matter to the flocculation tank; A coagulating sedimentation device, comprising a sludge return line for returning the wastewater to raw water. 2. A sludge return line having a classification tower for classifying sludge from the separator into sludge to be discharged, including larger flocs, and sludge, including smaller flocs, to be returned to raw water. The coagulation sedimentation device according to claim 1, which is provided. 3. The ascending linear velocity in the classification tower is 3 to 8 m /
The coagulating sedimentation device according to claim 2, which is in the range of h. 4. A pre-coagulation tank for mixing raw water supplied to the coagulation tank, a part of the sludge separated by the separator, and a coagulant in the sludge return line.
The coagulation sedimentation apparatus according to any one of the above. 5. The coagulation sedimentation apparatus according to claim 1, wherein the granular material is sand. 6. The apparatus according to claim 1, wherein the coagulant comprises an inorganic coagulant and a polymer coagulant.