JP2002355507A - Flocculating and settling equipment and its controlling method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flocculating and settling equipment which can exhibit desired performance to the whole flocculating and settling system stably by restraining separation efficiency of its cyclone from being deteriorated even when turbidity of raw water becomes high and to provide a control method of the flocculating and settling equipment. SOLUTION: This flocculating and settling equipment provided with a flocculating tank for flocculating the suspended matter in raw water as flocks by adding a granular material and a flocculant, a settling tank for settling the flocks in the water introduced from the flocculating tank and separating the flock-containing water into the treated water and slurry, a sludge withdrawing pump for withdrawing the slurry from the settling tank and the cyclone for separating the withdrawn slurry into sludge and the granular material and returning the separated granular material to the flocculating tank, is characterized in that the pipeline from the upper outlet of the cyclone is branched into a sludge discharging pipeline and a sludge circulating pipeline and the branched sludge circulating pipeline is connected to the suction side of the sludge withdrawing pump.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coagulation sedimentation apparatus for separating suspended matter in raw water into sludge and treated water by coagulation sedimentation by adding a particulate matter and a coagulant, and a method for controlling the same. When separating the slurry taken out from the slurry into sludge and particulate matter by a cyclone, while maintaining the desired cyclone separation performance according to the properties of the raw water, etc., it is possible to operate the coagulation sedimentation apparatus optimally as a whole apparatus and the coagulation sedimentation apparatus. It relates to a control method.

[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 and sedimentation apparatus, it takes a long time to settle the coagulates, and an extremely large sedimentation tank is required. Therefore, the coagulation and sedimentation is more efficiently performed. A device has been proposed.

For example, as a coagulating sedimentation apparatus for removing SS in raw water, a particulate matter (sand) having a particle size of about 10 to 200 μm and a polymer flocculant are added to raw water to remove SS in raw water.
There is known an apparatus comprising a flocculation tank for forming flocs together, a sedimentation tank for separating flocs flowing out of the flocculation tank from treated water, and a cyclone for separating slurry extracted from the sedimentation tank into sand and sludge. ing.

[0004] This type of coagulation and sedimentation apparatus is constructed, for example, as shown in FIG. An inorganic coagulant 103 is added to the raw water 102 introduced into the preliminary coagulation tank 101, and a stirrer 104
And a polymer flocculant 105 is added to the raw water, introduced into a flocculation tank 106, and stirred by a stirrer 107 to form flocs 109 together with the particulate matter (sand) 108. The sludge is settled and separated, and the treated water 112
Get. Sludge extraction pump 113 from the lower part of settling tank 110
To extract the slurry and send it to a cyclone 115 as a separator via a line 114. Cyclone 115
Then, it is centrifuged into sludge and sand, and its upper outlet side 11
6 (referred to as “cyclone upstream side” in this specification), the separated sludge 117 is discharged and sent to the subsequent sludge treatment step, and the lower outlet side 118 (in this specification, “cyclone downstream side”). ), The separated sand 108 is returned to the flocculation tank 106.

[0005]

The conventional coagulation and sedimentation apparatus as shown in FIG. 2 can be applied to the coagulation and sedimentation treatment of water containing turbidity such as river water and wastewater or SS.

Meanwhile, the raw water turbidity concentration of river water has a large difference between normal time and rainy time.
It may be 1000 degrees or more during rainfall compared to several tens degrees. In general, the higher the turbidity, the more it is necessary to increase the amount of an inorganic coagulant such as PAC (polyaluminum chloride).

When such an increase in the turbidity load of the raw water or the addition of the inorganic flocculant increases, the concentration of the sludge slurry precipitated in the precipitation tank 110 increases, and the concentration of the sludge extracted and sent to the cyclone 115 is increased. As a result, the concentration of sludge discharged upstream of the cyclone also increases.

For example, as shown in Table 1, even if the raw water flow rate and the amount of sludge withdrawn from the settling tank 110 are the same,
When the turbidity of the raw water changes (normal [10 degrees], rainfall [100 degrees], flood [1000 degrees]), the amount of PAC added increases accordingly, and both the extracted sludge concentration and the cyclone upstream concentration increase. I do.

[0009]

[Table 1]

The increase in the concentration of the sludge discharged to the upstream side of the cyclone as shown in Table 1 is not a problem in itself, but is rather preferable.
In general, the separation performance depends on the inlet pressure fluctuation, the flow balance on the upstream and downstream sides of the cyclone, the fluid to be separated supplied to the cyclone, and the component to be separated in the fluid to be separated (the above-mentioned coagulation sedimentation device). In the case of, it depends greatly on the concentration of the sludge component). In general, when designed in accordance with certain conditions, it is not possible to cope with an extremely large change, and when a large change occurs, the separation performance is greatly reduced. . Therefore, it is preferable that the cyclone 115 is operated at a constant flow rate as much as possible in accordance with the design specification and suppresses a large fluctuation of the sludge concentration in the fluid to be separated.

However, as shown in Table 1, cyclone 1
Under the condition where the concentration of the extracted sludge sent to the cyclone 115 is largely changed, if the sludge is simply extracted at a constant flow rate in a system as shown in FIG. 2, the degree of change in the concentration of the extracted sludge sent to the cyclone 115 is large. This may lead to a significant decrease in the cyclone 115 separation performance.
If the separation performance of the cyclone 115 is greatly reduced, a large amount of sand to be recycled and re-used will flow out, and the stable operation of the coagulation-sedimentation treatment system as a whole will not be possible. It will also be invited. Also,
Separated sludge that is insufficiently separated from sand is sent from cyclone 115 to a processing step such as sludge concentration at the subsequent stage.
It also leads to a decrease in efficiency in the subsequent processing equipment.

In addition to the above problems, there are also the following problems. In other words, when the entire coagulation and sedimentation apparatus is small, the cyclone is usually small, but when the diameter of the cyclone inlet hole or downstream hole becomes small, when the concentration of the sent sludge becomes high, it is separated. These components are likely to be blocked by the components to be separated or separated components. If it is blocked, the operation becomes impossible or the separation performance extremely deteriorates. Therefore, as a cyclone, it is desired to use a relatively large cyclone which does not cause such a problem of blockage, but if a relatively large cyclone is simply employed despite the fact that the entire apparatus is relatively small, Since the design flow rate of the cyclone (the flow rate of the fluid to be processed to be sent to the cyclone) is also increased, the amount of the cyclone extracted from the sedimentation tank becomes too large, and the recovery rate of the treated water is reduced accordingly.

Accordingly, an object of the present invention is to suppress the decrease in cyclone separation efficiency even when the properties of raw water change, especially when the turbidity of raw water increases, in view of the above problems. Another object of the present invention is to provide a coagulation / sedimentation apparatus capable of stably exhibiting desired performance as a whole coagulation / sedimentation treatment system and a control method therefor.

[0014]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, a coagulation / sedimentation apparatus according to the present invention comprises: a coagulation tank for coagulating a suspended substance in raw water as flocs by adding particulate matter and a coagulant; A sedimentation tank for sedimenting floc in the water introduced from the tank to separate it into treated water and slurry, a sludge extraction pump for extracting the slurry from the sedimentation tank, and separating the extracted slurry into sludge and particulate matter; In the coagulation sedimentation apparatus equipped with a cyclone for returning the wastewater to the flocculation tank, the line from the upper outlet of the cyclone was branched into a sludge discharge line and a sludge circulation line, and the branched sludge circulation line was connected to the suction side of the sludge extraction pump Characterized by the following.

In this coagulation and sedimentation apparatus, it is preferable that a flow control valve is provided in the sludge circulation line.

The method for controlling a coagulation / sedimentation apparatus according to the present invention is a method for controlling a coagulation / sedimentation apparatus as described above, wherein the method comprises controlling the coagulation / sedimentation load of raw water or / and the amount of inorganic coagulant added to raw water. And controlling the flow rate of the sludge circulation line according to the method.

In this method, the turbidity of raw water is detected, and the flow rate of the sludge circulation line can be controlled according to the detected value. Further, the amount of the inorganic flocculant to be added is obtained from the detected turbidity of the raw water, and the flow rate of the sludge circulation line can be controlled according to the turbidity and the amount of the inorganic flocculant.

In the coagulating sedimentation apparatus and the method for controlling the same according to the present invention, the line from the upper outlet of the cyclone is branched into a sludge discharge line and a sludge circulation line, and the branched sludge circulation line is connected to the sludge extraction pump. Since it is connected to the suction side, it is possible to reduce the amount of slurry withdrawn from the sedimentation tank by the amount returned and circulated through the sludge circulation line while keeping the supply flow rate to the cyclone substantially constant. . That is, it is possible to reduce the amount of sludge supplied to the cyclone per hour while keeping the supply flow rate to the cyclone substantially constant. Therefore, when the turbidity of the raw water rises, the flow rate in the sludge circulation line is increased, and the amount of slurry withdrawn from the sedimentation tank is reduced. A large increase in the concentration of the turbid component in the fluid to be treated can be suppressed, and the desired cyclone separation performance is stably exhibited. As a result, the treatment of the entire coagulation / sedimentation system is performed stably and smoothly, and the quality of the treated water is maintained and the deterioration of the recovery rate is prevented.

Further, since the cyclone inlet flow rate can be kept substantially always at the optimal design flow rate, the cyclone separation performance depending on the flow rate is always stably maintained at a good performance. Therefore, large fluctuations in the properties of the discharged sludge discharged from the upstream side of the cyclone and sent to the subsequent sludge treatment facility can be suppressed, and the treatment in the subsequent stage is also stabilized.

Further, since the sludge circulated through the sludge circulation line is supplied to the cyclone again, the inlet flow rate of the cyclone can be made relatively large.
Even when the whole apparatus is relatively small, it is possible to adopt a relatively large cyclone. As a result, occurrence of inconvenience such as blockage in the cyclone portion is reliably prevented.

[0021]

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. In FIG. 1, a coagulating sedimentation apparatus 1 includes a preliminary coagulating tank 2 and a coagulating tank 3.
And a sedimentation tank 4 disposed adjacent thereto. Raw water 6 is introduced into the preliminary flocculation tank 2 through a raw water introduction line 5, an inorganic flocculant 7 is added, and the raw water 6 is stirred by a stirrer 9 driven by a motor 8. In the present embodiment, a turbidity meter 1 for detecting the turbidity of the raw water 6 is provided in the raw water introduction line 5.
0 is provided, and the flow rate of the sludge circulation line in the later-described sludge extraction / separation system can be controlled by the detected value.

The raw water from the pre-coagulation tank 2 is introduced into the coagulation tank 3, at which time the polymer coagulant 11 is injected into the line. Sand 12 as granular material is added into the flocculation tank 3, and the suspended substance of the raw water is mixed with the inorganic flocculant 7, the polymer flocculant 11, and the sand 12 by stirring by a stirrer 14 driven by a motor 13. Flock 1 including
Aggregated as 5. In this coagulation, the inorganic coagulant 7 coagulates the suspended substance to form fine flocs,
In addition, the polymer flocculant 11 is entangled and grows into a larger floc, and the grown floc contains sand 12 as a particulate matter having a large specific gravity, and is relatively large as a whole.
It grows into flocs with a large specific gravity and easy to precipitate.

The to-be-treated water containing the grown floc 15 is introduced into the settling tank 4 through the overflow 16. In the sedimentation tank 4, the flocs in the introduced water are sedimented downward, and the sedimented flocs are separated from the upper treated water 17. A plurality of inclined plates 18 are arranged in parallel in the upper part in the settling tank 4 to prevent the floc from flowing out together with the treated water 17.

At the bottom of the sedimentation tank 4, a drawing line 19 for extracting slurry containing precipitated floc is connected. The drawing line 19 is provided with a sludge extraction pump 21 for feeding the extracted slurry to a cyclone 20. Is provided. In the cyclone 20, the sent slurry is separated by centrifugation into sludge 23 discharged to the cyclone upstream line 22 and sand 12 led out to the cyclone downstream line 24. The separated sand 12 , Is returned to the coagulation tank 3 and used again. This cyclone upstream line 22 is branched into a sludge discharge line 25 for sending sludge 23 to a subsequent sludge treatment facility (for example, a sludge storage tank and a dehydrator, not shown), and a sludge circulation line 26. The circulation line 26 is connected to the suction side of the sludge extraction pump 21.

The sludge circulation line 26 has a flow meter 27
In addition, a flow control valve 28 is provided, and the flow rate of the circulated sludge is controlled according to the turbidity signal of the raw water 6 detected by the turbidity meter 10 described above. In addition to this control, the sludge circulation flow rate may be controlled according to the amount of the inorganic coagulant 7 added. For example, the amount of the inorganic flocculant 7 to be added is calculated in accordance with the turbidity detected by the turbidity meter 10, and the sludge circulation flow rate in the sludge circulation line 26 is calculated in accordance with the turbidity and the amount of the inorganic flocculant 7 added. Can also be controlled.

The coagulation / sedimentation apparatus 1 configured as described above
Is operated and controlled as follows. The turbidity is measured as the turbidity load of the raw water 6 introduced into the preliminary flocculation tank 2 by the turbidimeter 10.
In the sludge circulation line 2 according to the detected turbidity.
The circulating sludge flow rate in 6 is controlled by a flow rate control valve 28 while being checked by a flow meter 27. That is, when the turbidity load of the raw water 6 increases, control is performed such that the circulating sludge flow rate in the sludge circulation line 26 is increased according to the degree of the increase. Sludge extraction pump 21
Is substantially constant, the circulating sludge is returned to the suction side of the sludge withdrawing pump 21, so that the amount of the returned sludge and the flow of the sludge drawn out of the sedimentation tank 4 are reduced.

Accordingly, the amount of slurry supplied to the cyclone 20 is kept constant at the discharge flow rate of the sludge extraction pump 21, and the flow rate of the slurry discharged from the sedimentation tank 4 is reduced. As a result, even if the turbidity load of the raw water 6 increases, a large increase in the turbid component supplied to the cyclone 20 is suppressed, and a decrease in the separation performance of the cyclone 20 due to a large increase in the turbid component is suppressed. Can be In addition, since the supply flow rate to the cyclone 20 is maintained at a substantially constant flow rate, the cyclone 20 can exhibit the desired separation performance as designed in terms of flow rate. Therefore, good cyclone 20 separation performance is maintained,
The sand 12 to be separated is stably and satisfactorily separated and returned to the coagulation tank 3, and the sludge 23 to be discharged is stably and satisfactorily separated, and a part thereof is sent to a subsequent sludge treatment facility. Can be Since the stable separation treatment is performed smoothly, the operation of the coagulation and sedimentation apparatus 1 as a whole is stabilized, good water quality of the treated water is maintained, and deterioration of the recovery rate is also prevented. In addition, stable treatment is possible even in the sludge treatment equipment at the subsequent stage.

Further, the sludge circulated through the sludge circulation line 26 is supplied to the cyclone 20 again.
The inlet flow rate of the cyclone 20 can be made relatively large from the beginning, and even if the entire apparatus is relatively small, a relatively large cyclone 20 can be used. . As a result, the occurrence of inconvenience such as blockage at the cyclone 20 portion, that is, at the inlet portion or the outlet portion on the downstream side is reliably prevented. Further, the concentration of the turbid component of the slurry sent through the drawing line 19 is suppressed from becoming extremely high, and the flow rate of the line from the sludge drawing pump 21 to the cyclone 20 is maintained at a relatively large flow rate. In addition, the occurrence of inconvenience such as blockage in the drawing line 19 can be reliably prevented.

The apparatus for coagulation and sedimentation according to the present invention and the method for controlling the same are not limited to river water and the like, and any apparatus to which the apparatus according to the present invention can be applied (for example, biologically coagulated sedimentation of treated water and heavy metals). Applicable.

The kind of the inorganic coagulant and the high molecular coagulant used in the present invention is not particularly limited. Examples of the inorganic coagulant include polyaluminum chloride (PAC),
Ferric chloride and ferric sulfate can be used. As the polymer flocculant, for example, a nonionic, anionic or amphoteric polymer flocculant 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, acrylamide and 2-acrylamide-
2-methylpropanesulfonic acid salt copolymer, acrylic acid or a salt thereof, acrylamide and 2-acrylamide-
Examples include a terpolymer of 2-methylpropanesulfonic acid salt and a partial hydrolyzate of polyacrylamide.
It is not particularly limited to these. A typical nonionic polymer flocculant includes polyacrylamide, but is not particularly limited thereto. Examples of the amphoteric polymer flocculants include tertiary salts of dimethylaminoethyl (meth) acrylate and 4
At least one cationic monomer such as a grade salt (eg, methyl chloride salt), acrylic acid and its salts (eg, salts such as sodium and calcium), and 2-acrylamido-2-methylpropane sulfonate (eg, sodium, calcium). Or a copolymer of at least one anionic monomer such as acrylamide or the like, or at least one cationic monomer and at least one anionic monomer and at least one such as acrylamide. Examples include a ternary or quaternary or higher copolymer with one kind of nonionic monomer,
It is not particularly limited to these. Although the range of the molecular weight of the polymer flocculant is not particularly limited, it is 5,000,000 to 200,000,000.
A range of 10,000 is preferred. These polymer flocculants can be used alone or as a mixture.

[0031]

As described above, according to the coagulating sedimentation apparatus and the control method of the present invention, the sludge circulation line branched from the upstream line of the cyclone is connected to the suction side of the sludge extraction pump, and the sludge is removed. The amount of slurry withdrawn from the settling tank can be reduced according to the turbidity of the raw water while keeping the supply flow rate from the drawing pump to the cyclone constant, so that the good cyclone separation performance can be stably maintained. As a result, stable and smooth operation of the entire apparatus becomes possible. Therefore, even when the turbidity of the raw water increases, a decrease in the quality of the treated water and a decrease in the recovery rate can be prevented, and a stable operation of the subsequent sludge treatment process can be maintained.

Further, even when the whole apparatus is relatively small, a relatively large cyclone can be employed, which causes inconvenience such as blockage at the cyclone part and the drawing line. Occurrence can also be prevented.

[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 conventional coagulation / sedimentation apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Coagulation settling apparatus 2 Preliminary coagulation tank 3 Coagulation tank 4 Precipitation tank 5 Raw water introduction line 6 Raw water 7 Inorganic coagulant 9 Stirrer 10 Turbidity meter 11 Polymer coagulant 12 Granular sand 14 Stirrer 15 Coagulation floc 16 Overflow 17 Treatment water 18 Inclined plate 19 Sludge extraction line 20 Cyclone 21 Sludge extraction pump 22 Cyclone upstream line 23 Sludge 24 Cyclone downstream line 25 Sludge discharge line 26 Sludge circulation line 27 Flow meter 28 Flow control valve

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B03B 5/28 B03B 5/28 B C02F 1/56 ZAB C02F 1/56 ZABZ 11/00 11/00 Z / / E03F 5/14 E03F 5/14 F term (reference) 2D063 DB01 DB07 4D015 BA21 BB09 BB12 DA04 DA13 DA16 DB03 DB08 DB12 DB13 DB19 DB30 DC06 DC07 DC08 EA01 EA03 EA32 FA03 FA19 4D059 AA06 BK30 CA28 EB20 4D07 A0320A

Claims (5)

[Claims] 1. A flocculation tank for flocculating a suspended substance in raw water as a floc by adding a particulate matter and a flocculant, and a sedimentation tank for sedimenting floc in water introduced from the flocculation tank and separating it into treated water and slurry. A sludge extraction pump for extracting the slurry from the sedimentation tank, and a cyclone for separating the extracted slurry into sludge and particulate matter, and returning the separated particulate matter to the flocculation tank. A coagulating sedimentation apparatus characterized in that the line is branched into a sludge discharge line and a sludge circulation line, and the branched sludge circulation line is connected to the suction side of a sludge extraction pump. 2. The coagulating sedimentation apparatus according to claim 1, wherein a flow control valve is provided in the sludge circulation line. 3. The method for controlling a coagulating sedimentation apparatus according to claim 1 or 2, wherein the flow rate of the sludge circulation line depends on the turbidity load of raw water and / or the amount of inorganic coagulant added to raw water. And controlling the coagulation sedimentation apparatus. 4. The method according to claim 3, wherein the turbidity of the raw water is detected, and the flow rate of the sludge circulation line is controlled according to the detected value. 5. The amount of the inorganic flocculant to be added is determined from the detected turbidity of the raw water, and the flow rate of the sludge circulation line is controlled according to the turbidity and the amount of the inorganic flocculant.
3. The method for controlling a coagulation sedimentation apparatus according to item 1.