JP2014237122A - Coagulation sedimentation equipment and method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably maintain a desirable sludge density after treatment as an entire processing system of coagulation sedimentation regardless of the change of a raw water pollution degree.SOLUTION: The objective coagulation sedimentation equipment is provided with: a first agitation tank for adding an inorganic coagulant to a raw water to mix while agitating; a second agitation tank for adding a polymer coagulant and a sedimentation accelerator comprising an insoluble particulate to the raw water to mix while agitating; a flocculation tank for forming floc including the accelerator as a core; a sedimentation tank for precipitating the floc to divide the raw water into a treated water and a slurry; and a cyclone for dividing the slurry extracted from the sedimentation tank into a sludge and the accelerator and for feeding the divided accelerator to the second agitation tank. The outlet line of a cyclone upper part is branched into a sludge discharge line and a sludge returning line for returning at least a part of the sludge to the first agitation tank, and at least either flow of the sludge discharge line or the sludge returning line is controlled so that the pollution load of the first agitation tank becomes a constant value.

Description

  The present invention relates to a coagulation sedimentation apparatus and a coagulation sedimentation method.

  As a device to precipitate and separate contaminating components in raw water, flocculants and insoluble particulates are added and mixed in raw water, and flocs are formed by agglomerating flocs with insoluble particulates as the core to increase the weight of the flocs and settling speed. There is known a high-speed coagulating sedimentation apparatus that can speed up and perform a sedimentation separation process in a very short time (see, for example, Patent Document 1 below).

  A general coagulation sedimentation device ensures a certain residence time in the sedimentation tank, concentrates the sludge and then pulls it out intermittently, so the concentration of sludge discharged outside the system is as high as 5% or more. stable. On the other hand, in the high-speed coagulating sedimentation apparatus using insoluble granular materials as in Patent Document 1 below, since it is necessary to circulate and reuse insoluble granular materials, it is necessary to continuously draw out the slurry generated in the precipitation tank. is there. For this reason, there is a problem that the sludge concentration discharged out of the system of the apparatus is low, and the sludge concentration largely fluctuates as the turbidity load of the raw water changes.

  Therefore, in Patent Document 2 below, the cyclone upper outlet 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 the sludge extraction pump to discharge to the cyclone upper outlet. A coagulating sedimentation device has been proposed that increases the concentration of sludge produced.

Japanese Patent No. 2634230 Japanese Patent No. 3866054

  However, when the apparatus of Patent Document 2 is used, since the branched sludge circulation line is supplied to the suction side of the sludge extraction pump, the raw water turbidity fluctuates even if a certain amount of sludge is supplied. The sludge concentration in the sludge extraction pump varies. Therefore, when the sludge concentration becomes high, the flow path between the sludge extraction pump and the cyclone may be blocked. Further, if the amount of sludge returned is controlled in accordance with the raw water turbidity in order to control the sludge concentration, the cyclone inlet flow rate may change and the cyclone separation performance may be significantly reduced. If the separation performance of the cyclone is greatly reduced, a large amount of particulate matter (sand) that should be recycled and reused will flow out, making stable operation impossible for the entire coagulation sedimentation system, and deterioration of treated water quality and particulate matter ( Sand) recovery rate will be reduced. Also, if the amount of sludge circulation is determined in response to the condition that the raw water concentration is low with the aim of increasing the sludge concentration, the concentration of the circulation line becomes too high when the raw water concentration is high, and the flow path becomes It may be blocked and become inoperable, or the cyclone separation performance will be extremely lowered.

  Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to stably obtain desired waste mud as a whole coagulation sedimentation treatment system regardless of changes in the raw water pollution concentration and the like. An object of the present invention is to provide a coagulation sedimentation apparatus and a coagulation sedimentation method capable of maintaining the concentration.

  In order to solve the above problems, according to the present invention, there is provided a coagulation sedimentation apparatus that separates suspended substances contained in raw water into sludge and treated water by coagulation sedimentation treatment, wherein an inorganic coagulant is added to the raw water. A first agitation tank that is added and then stirred and mixed; and a first agitation tank that is provided after the first agitation tank and that is added with a settling accelerator composed of a polymer flocculant and insoluble fine particles to the raw water. Two stirring tanks, a flock forming tank provided at the subsequent stage of the second stirring tank and forming a floc of the suspended substance with the settling accelerator as a core, and provided at a subsequent stage of the flock forming tank, The settling tank that separates the raw water into the treated water and the slurry, and the slurry extracted from the settling tank through the sludge extraction line are separated into the sludge and the settling accelerator, and separated. Settling accelerator And a cyclone upper outlet line for transferring the sludge separated by the cyclone, a sludge discharge line for discharging the sludge, and at least a part of the sludge for the first time. A sludge return line that returns to the first stirring tank, and is the sum of products of the turbidity concentration and flow rate of the suspended matter calculated for each of the inflow paths to the first stirring tank. There is provided a coagulation sedimentation apparatus having a function of controlling the flow rate of at least one of the sludge discharge line and the sludge return line so that the pollution load of one stirring tank becomes a constant value.

  When making the said pollution load of a said 1st stirring tank into a constant value, it is preferable to have the function in which the flow volume of the said sludge return line is controlled according to the pollution density | concentration of the said raw | natural water.

  At least one of the sludge discharge line and the sludge return line may be provided with a flow rate control valve for controlling the flow rate of the line.

  From the treated water transfer line for transferring the treated water, a treated water return line for returning at least part of the treated water to the first stirring tank is branched, and the flow rate of the raw water flowing into the first stirred tank Depending on the, the flow rate of at least one of the treated water transfer line after branching of the treated water return line or the treated water return line may be further controlled.

  The flow rate of the treated water return line is controlled according to the flow rate of the raw water so that the residence time held in each of the first agitation tank, the second agitation tank, and the floc forming tank is less than a predetermined threshold value. It may have a function.

  A flow rate control valve for controlling the flow rate of the line may be provided in at least one of the treated water transfer line after the treated water return line branches or the treated water return line.

  The raw water may be steel waste water.

  The raw water is steel drainage mainly composed of iron, having a true specific gravity of 2.43 to 4.80 and an average particle diameter of 5.3 to 42.5 μm, and includes the first stirring tank, the second stirring tank, and the floc The threshold of residence time in the forming tank may be 4 minutes or less, 4 minutes or less, and 12 minutes or less, respectively.

  The raw water is steel drainage mainly composed of coal, having a true specific gravity of 1.37 to 1.48 and an average particle diameter of 10.2 to 23.3 μm, and includes the first stirring tank, the second stirring tank, and the floc The threshold of residence time in the forming tank may be 1.5 minutes or less, 1.5 minutes or less, and 4.5 minutes or less, respectively.

  The sedimentation accelerator may have a maximum particle size of 500 μm or less and a true specific gravity of 2.6 or more.

  The settling accelerator may be slag.

  Moreover, in order to solve the said subject, according to this invention, it is the coagulation sedimentation method which isolate | separates the suspended substance contained in raw | natural water into sludge and treated water by coagulation sedimentation processing, Comprising: The said raw water of a 1st stirring tank An inorganic flocculant is added to the mixture, followed by stirring and mixing, and a settling accelerator composed of a polymer flocculant and insoluble fine particles is added to the raw water in the second stirring tank provided after the first stirring tank. The mixture is stirred and mixed, and a floc forming tank provided downstream of the second stirring tank is used to form a floc of the suspended substance with the sedimentation accelerator as a core, and is provided downstream of the floc forming tank. In the settling tank, the floc is allowed to settle, the raw water is separated into the treated water and slurry, and the slurry extracted from the settling tank by a sludge extraction line is cycloneed with the sludge and the settling accelerator. Separated and separated Supplying the settling accelerator to the second agitation tank, transferring a cyclone upper outlet line for transferring the sludge separated by the cyclone, a sludge discharge line for discharging the sludge, and at least a part of the sludge for the first time. The first agitation which is the sum of products of the turbidity concentration and the flow rate of the suspended matter calculated for each of the inflow paths to the first agitation tank, branched to a sludge return line to be returned to the agitation tank. There is provided a coagulation sedimentation method for controlling the flow rate of at least one of the sludge discharge line or the sludge return line so that the pollution load of the tank becomes a constant value.

  As described above, according to the present invention, it is possible to stably maintain a desired waste mud concentration as a whole of the coagulation sedimentation treatment system, regardless of changes in the pollution concentration of raw water.

It is the schematic diagram which showed an example of the structure of the coagulation sedimentation apparatus which concerns on the 1st Embodiment of this invention. It is the schematic diagram which showed an example of the structure of the coagulation sedimentation apparatus which concerns on the 2nd Embodiment of this invention.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol.

(Problems of conventional high-speed coagulation sedimentation equipment)
Prior to describing the coagulation sedimentation apparatus according to an embodiment of the present invention, the problems of the high-speed coagulation sedimentation apparatus as disclosed in Patent Document 2 will be described in more detail, and the object of the present invention will be described. explain.

  In the high-speed coagulating sedimentation apparatus as disclosed in Patent Document 1 and Patent Document 2, the sludge separated by the cyclone provided in the apparatus is actually a concentrating apparatus provided at the subsequent stage of the high-speed coagulating sedimentation apparatus. In many cases, it is concentrated by a dehydrator or the like. However, while the concentration of the extracted sludge in a general coagulation sedimentation apparatus (which does not use insoluble fine particles) used in the treatment of steel wastewater is 50 g / L or more, the high speed coagulation sedimentation apparatus uses a cyclone. The upper outlet pollutant concentration is as low as 10 g / L or less. For this reason, there is a possibility that the concentration device provided at the subsequent stage of the high-speed coagulation sedimentation device is increased in size or the load on the dehydrator is increased. In addition, it is desirable to reduce the size of the concentrator provided in the subsequent stage of the coagulation sedimentation apparatus as much as possible. Therefore, it is required that the cyclone upper outlet pollutant concentration in the high-speed coagulating sedimentation apparatus is brought close to that of the extracted sludge in a general coagulating sedimentation apparatus.

  On the other hand, for example, wastewater in which the properties of raw water (in particular, properties such as pollution concentration) fluctuate between non-operation and operation, such as steel wastewater, may be treated. For example, in the case of steel wastewater, the pollution concentration at the time of non-operation is several tens mg / L to several hundred mg / L, whereas at the time of operation, the pollution concentration is 1000 mg / L or more, and the pollution concentration varies greatly.

  As the raw water pollution concentration fluctuates, the sludge slurry concentration in the settling tank also fluctuates, and the sludge concentration extracted from the settling tank and transferred to the cyclone also changes. The concentration of sludge discharged into the water will also fluctuate.

  As shown in Table 1 below, even when the flow rate of raw water flowing into the apparatus and the sludge extraction flow rate from the settling tank are the same, when the pollution concentration of the raw water changes (non-operation: 380 mg / L, operation: 1720 mg / L), the cyclone upper outlet pollutant concentration varies greatly.

  Here, in the high-speed coagulating sedimentation apparatus using insoluble particulate matter, it is necessary to circulate and reuse the insoluble particulate matter, so that the slurry produced in the precipitation tank is continuously drawn out. Therefore, in the high-speed coagulation sedimentation apparatus, the sludge concentration of the sludge discharged to the cyclone upper outlet becomes low, and as illustrated in Table 1 above, it greatly fluctuates with the fluctuation of the raw water pollution concentration.

  In order to cope with such problems and increase the concentration of discharged sludge, in Patent Document 2, the cyclone upper outlet line is branched into a sludge discharge line and a sludge circulation line. Connection to the suction side of the sludge extraction pump is performed. About the connection position of the sludge circulation line in the said patent document 2, since sludge is returned in an apparatus, in order to hold down running cost etc. of an additive chemical etc., sludge is returned to the back | latter stage of an apparatus.

  However, in order to increase the sludge concentration of the discharged sludge, it is necessary to return as much sludge as possible. On the other hand, if a large amount of sludge is returned before the sludge extraction pump, it is transferred from the sedimentation tank to the cyclone. There is a possibility that the line going to will be blocked. Further, in the apparatus disclosed in Patent Document 2, when the sludge return amount is controlled according to the pollution concentration of raw water, the inlet flow rate of the cyclone may change and the cyclone separation performance may be lowered.

  In addition, as described above, depending on the setting of the sludge circulation amount, when the raw water concentration is high, the concentration of the circulation line becomes too high and the operation becomes impossible, or the separation performance of the cyclone is extremely high. It will decline.

  As described above, even the coagulation sedimentation apparatus disclosed in Patent Document 2 has a problem that it may not be able to cope with fluctuations in the contamination concentration of raw water.

  Therefore, the present inventors have conducted further studies on a coagulation sedimentation apparatus that can stably maintain a desired waste mud concentration as a whole coagulation sedimentation treatment system regardless of changes in the raw water pollution concentration. The inventors have conceived of a coagulation sedimentation apparatus and a coagulation sedimentation method according to embodiments of the present invention described below.

(First embodiment)
<About the configuration of the coagulation sedimentation device>
Below, the structure of the coagulation sedimentation apparatus which concerns on the 1st Embodiment of this invention is demonstrated in detail, referring FIG. FIG. 1 is a schematic view schematically showing an example of the configuration of the coagulation sedimentation apparatus according to the present embodiment.

  The coagulation sedimentation apparatus 10 according to this embodiment is an apparatus that separates suspended solids (SS) contained in raw water into sludge and treated water by coagulation sedimentation treatment.

  Here, the raw water (drainage) to be treated by the coagulation sedimentation apparatus 10 according to the present embodiment is not particularly limited, but for example, iron components (iron oxide, etc.) or coal as listed below. It is also possible to treat steel wastewater containing at least.

(A) Ore yard rainwater drainage (true specific gravity: 3.16, average particle size: 5.3 μm)
(B) Coal yard rainwater drainage (true specific gravity: 1.48, average particle size: 10.2 μm)
(C) Dust collection wastewater discharged in the coke production process (true specific gravity: 1.37, average particle size: 23.3 μm)
(D) Spray cooling wastewater discharged in the hot rolling process (true specific gravity: 3.16, average particle size: 30.0 μm)
(E) Dust collection wastewater discharged in the iron making process (true specific gravity: 3.85, average particle size: 42.5 μm)
(F) Dust collection wastewater discharged in the steelmaking process (true specific gravity: 4.80, average particle size: 26.5 μm)
(G) Spray cooling wastewater discharged in the continuous casting process (true specific gravity: 3.09, average particle size: 14.0 μm)
(H) Spray cooling wastewater discharged in the steel bar manufacturing process (true specific gravity: 3.28, average particle size: 32.5 μm)
(I) Spray cooling wastewater discharged in the plate manufacturing process (true specific gravity: 2.43, average particle size: 14.9 μm)

  Here, among the wastewaters, the wastewaters (b) and (c) correspond to steel wastewater containing coal (that is, steel wastewater mainly composed of coal), and among the wastewaters (a), (d), The wastewaters (e), (f), (g), (h) and (i) correspond to steel wastewater containing iron oxide (that is, steel wastewater mainly composed of iron). Moreover, the drainage of said (a) and (b) is a wastewater from which the amount of water fluctuates greatly with the weather, as is clear from its name, and the drainage of the above (c) to (i) This is a wastewater whose water volume fluctuates greatly during operation.

  As shown in FIG. 1, the coagulation sedimentation apparatus 10 according to the present embodiment capable of treating the waste water as described above has a first agitation tank 11 and a second agitation tank in order from the side into which raw water flows. 13, a flock formation tank 15, and a precipitation tank 17.

  Here, in controlling the coagulation sedimentation apparatus 10 according to the present embodiment, it is important to perform control so that the pollution load of the first stirring tank 11 described in detail below becomes a constant value. Here, the pollution load of the first agitation tank 11 is calculated by calculating the product of the turbidity concentration of the suspended substance and the flow rate for each of the inflow paths of the suspended substance flowing into the first agitation tank 11. It is defined as the sum.

  In the coagulation sedimentation apparatus 10 which concerns on 1st Embodiment demonstrated below, the case where the flow volume of the suspended solid which flows into the 1st stirring tank 11 is constant, and the pollution density fluctuates is assumed. Therefore, what becomes an operation factor among the pollution load of the 1st stirring tank 11 prescribed | regulated as mentioned above is a pollution density | concentration. Therefore, in the coagulation sedimentation apparatus 10 described in detail below, the control is performed so that the pollution concentration of the first stirring tank 11 becomes a constant value.

  As will be described later, it is important that the contamination concentration of the first agitation tank 11 is within a contamination concentration range that is set according to the critical contamination concentration for preventing the sludge extraction line 25 from being blocked.

  The raw water to be subjected to the coagulation sedimentation process flows into the first agitation tank 11 through the raw water inflow line 21. A turbidimeter 101 is provided in the raw water inflow line 21, and the pollution concentration of the raw water flowing into the first stirring tank 11 is managed. In the first stirring tank 11, the inorganic flocculant is added to the raw water through the inorganic flocculant addition line, and then the raw water is stirred and mixed by the motor-driven stirrer 103. As the suspended particles contained in the raw water are aggregated by the added inorganic flocculant, fine flocs are generated.

  The kind of the inorganic flocculant is not particularly limited, and known inorganic flocculants can be used according to the properties of the raw water. Examples of such inorganic flocculants include known aluminum salts and iron salts such as polyaluminum chloride (PAC), ferric chloride, and ferric sulfate.

  Here, the addition amount of the inorganic flocculant is not particularly limited, and may be appropriately determined according to the properties of raw water to be treated.

  The raw water to which the inorganic flocculant is added in the first agitation tank 11 flows into the second agitation tank 13 together with the generated fine aggregation flocs. In the second agitation tank 13, the polymer flocculant is added to the raw water via the polymer flocculant addition line, and the sedimentation accelerator is added via the sedimentation accelerator addition line. Then, the raw water is stirred and mixed by a motor-driven stirrer 103. As the suspended particles contained in the raw water agglomerate due to the added polymer flocculant, the fine flocs grow little by little, and the growing floc and the added sedimentation accelerator are mixed. .

  The kind of the polymer flocculant is not particularly limited, and known ones can be used according to the properties of the raw water. As such a polymer flocculant, for example, a nonionic, anionic, cationic, or amphoteric polymer flocculant 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. It is possible to use a terpolymer of acrylic acid or a salt thereof, acrylamide and 2-acrylamido-2-methylpropanesulfonate, a partial hydrolyzate of polyacrylamide, and the like. For example, polyacrylamide can be used as the nonionic polymer flocculant. Examples of amphoteric polymer flocculants include, for example, 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 A ternary or quaternary copolymer of a kind of cationic monomer and at least one kind of anionic monomer and at least one kind of nonionic monomer such as acrylamide may be used. Is possible. Here, the molecular weight of the polymer flocculant is not particularly limited, but is preferably in the range of 5 million to 20 million, for example. These polymer flocculants can be used alone or as a mixture.

  The settling accelerator added to the raw water is made of insoluble fine particles. Examples of the insoluble fine particles that can be used as the sedimentation promoting material include sand particles such as natural sand and artificial sand (hereinafter simply referred to as “sand”) and various slags (for example, granulated blast furnace slag). The sedimentation accelerator preferably has a maximum particle size of 500 μm or less and a true specific gravity of 2.6 or more. The sedimentation promoting material having a maximum particle size of 500 μm or less can be obtained by, for example, sieving the sedimentation promoting material to be used. Further, the maximum particle size of the settling accelerator is preferably 400 μm or less, and more preferably 300 μm or less. By using such a sedimentation promoting material, it is possible to achieve a desired sedimentation speed in the subsequent sedimentation tank 17.

  Here, the addition rate of the polymer flocculant and the settling accelerator is not particularly limited, and may be appropriately determined according to the properties of raw water to be treated.

  In addition, in the coagulation sedimentation apparatus 10 which concerns on this embodiment, since the sedimentation promoting material is circulated and utilized as mentioned later, it is not necessary to always add the sedimentation promoting material to the second stirring tank 13. What is necessary is just to add a new sedimentation promoting material, when the quantity of the sedimentation promoting material which exists in the coagulation sedimentation apparatus 10 whole becomes less than the quantity which should be maintained.

  The raw water to which the polymer flocculant and the settling accelerator are added in the second agitation tank 13 flows into the flock formation tank 15. In the floc forming tank 15, the polymer flocculant is added through the polymer flocculant addition line, and the raw water is stirred by the motor-driven stirrer 103 to form a floc having the sedimentation promoting material as a core. More specifically, the fine floc formed in the first stirring tank 11 is cross-linked by the polymer flocculant added in the second stirring tank 13, and a larger floc is formed in the floc forming tank 15. Will be. Since the formed floc contains insoluble fine particles having a large specific gravity, the floc formed in the floc forming tank 15 is a floc that is relatively large in size and large in specific gravity and easily settles.

  In addition, what is necessary is just to select suitably the compound used as said inorganic flocculant or said polymer flocculent according to the surface charge of the said floc decided according to the physical property of the whole water quality, such as pH, temperature, a viscosity.

  The raw water in which flocs are formed in the floc forming tank 15 flows into the settling tank 17. In the settling tank 17, the floc is allowed to settle to separate the raw water into treated water and slurry. The sedimentation tank 17 is provided with a sludge scraping machine 105, and the flocs that have settled in the precipitation tank 17 can be scraped efficiently. In addition, an inclined plate 107 is provided inside the sedimentation tank 17 according to this embodiment, so that flocs existing in the sedimentation tank 17 can be settled more efficiently. The treated water obtained by separating the floc in the settling tank 17 is transferred to the outside of the coagulating sedimentation apparatus 10 via the treated water outflow line 23. In addition, the pollutant density | concentration of the treated water transferred by the treated water outflow line 23 can be utilized as a management value at the time of controlling the raw water treatment in the coagulation sedimentation apparatus 10 which concerns on this embodiment.

  Here, in the coagulation sedimentation apparatus 10 according to this embodiment, since the sedimentation speed of flocs can be increased by using a sedimentation accelerator having a large specific gravity such as sand or slag, the surface load factor (sedimentation) of the sedimentation tank 17 The amount of water flowing into the tank / the bottom area of the settling tank) can be reduced. Thereby, in this embodiment, size reduction of the coagulation sedimentation apparatus 10 can be achieved compared with a general coagulation sedimentation apparatus.

  A sludge extraction line 25 for extracting the slurry containing the precipitated floc is connected to the bottom of the precipitation tank 17. The sludge extraction pump 109 provided in the sludge extraction line 25 allows the slurry to be continuously added to the precipitation tank 17. Pulled out from. The end of the sludge extraction line 25 is connected to the inlet of the cyclone 111, and the slurry extracted from the settling tank 17 is transferred to the cyclone 111 in a state having a predetermined pressure, flow rate, and the like.

  On the other hand, the treated water separated by the settling tank 17 flows into the treated water pit 19. In the treated water pit 19, the treated water is temporarily retained, and then extracted from the treated water pit 19 by the treated water transfer pump 115 and transferred by the treated water transfer line 23.

  The cyclone 111 separates the slurry transferred by the sludge extraction line 25 into sludge and a sedimentation promoting material. The separated sedimentation promoting material is supplied to the second agitation tank 13 through a cyclone lower outlet line 27 connected to the bottom of the cyclone 111. Further, the separated sludge is transferred by a cyclone upper outlet line 29 connected to the top of the cyclone 111. Thus, in the coagulation sedimentation apparatus 10 according to the present embodiment, the sludge extraction line 25 and the cyclone lower outlet line 27 form a circulation line for the sedimentation promoting material.

  The cyclone upper outlet line 29 through which the sludge separated by the cyclone 111 is transferred is branched into a sludge return line 31 and a sludge discharge line 33, as shown in FIG. The sludge return line 31 is a line for returning at least part of the sludge transferred through the cyclone upper outlet line 29 to the first stirring tank 11, and the sludge discharge line 33 transfers the cyclone upper outlet line 29. It is a line for discharging the part except the sludge returned to the 1st stirring tank 11 among the sludge to be performed to the outside of the coagulation sedimentation apparatus 10. The sludge discharged by the sludge discharge line 33 is transferred to a concentrating device (not shown), a dehydrator (not shown), etc. provided in the subsequent stage of the coagulation sedimentation apparatus 10. In addition, the turbidity density | concentration of the sludge discharged | emitted from the sludge discharge line 33 can be utilized as a management value at the time of controlling the raw water process in the coagulation sedimentation apparatus 10 which concerns on this embodiment.

  The amount of sludge returned to the first stirring tank 11 (sludge return amount) is controlled according to the turbidity of the raw water detected by the turbidimeter 101 by a flow rate control valve 113 provided in the line. The flow rate control valve 113 may be provided in at least one of the sludge return line 31 and the sludge discharge line 33. As shown in FIG. 1, the sludge return line 31 is provided with a sludge return amount control valve 113a. Further, the sludge discharge line 33 may be provided with a sludge discharge amount control valve 113b.

  Thus, in the coagulation sedimentation apparatus 10 according to the present embodiment, a circulation line for returning sludge to the first agitation tank 11 is formed by the sludge extraction line 25, the cyclone upper outlet line 29, and the sludge return line 31. . In the coagulation sedimentation apparatus 10 according to the present embodiment, the sludge is not returned to the downstream side of the coagulation sedimentation apparatus as much as possible as conventionally performed, but the first agitation tank positioned on the most upstream side of the coagulation sedimentation apparatus. Return the sludge to 11. Thereby, as explained in full detail below, in the coagulation sedimentation apparatus 10 which concerns on this embodiment, irrespective of the change of the pollutant density | concentration of raw | natural water, maintaining a desired waste mud density | concentration stably as the whole coagulation sedimentation processing system. Is possible.

  In the above description, the case where the polymer flocculant is added to both the second stirring tank 13 and the flock forming tank 15 through the polymer flocculant addition line has been described. However, the second stirring tank 13 and the flock forming tank are described. What is necessary is just to determine suitably the addition ratio of the polymer flocculent added to 15 according to the property etc. of the raw | natural water made into a process target. Further, depending on the properties of raw water to be treated, the polymer flocculant may be added only to either the second stirring tank 13 or the flock forming tank 15.

<Regarding the control method of the coagulation sedimentation apparatus>
Then, the control method of the coagulation sedimentation apparatus 10 as shown in FIG. 1 is demonstrated in detail.
In the high-speed coagulation sedimentation apparatus including the coagulation sedimentation apparatus 10 according to the present embodiment, it is important to appropriately form flocs. When examining floc formation in a high-speed coagulating sedimentation apparatus, the so-called GCT value defined as the product of the stirring intensity G, the turbidity concentration C, and the stirring duration (that is, the residence time) T is used as an index. There are many cases.

  When examining floc formation of each processing tank constituting the coagulation sedimentation apparatus 10 according to the present embodiment, among the operating factors that define the GCT value, the stirring intensity G can be determined by the following guidelines, for example. It is.

  For example, the agitation strength G required for the first agitation tank 11 is determined so as to uniformly generate and grow fine aggregated flocs composed of suspended particles contained in raw water and an inorganic flocculant. . The agitation strength G required for the second agitation tank 13 is determined such that the fine agglomeration flocs generated in the first agitation tank 11 grow with the polymer aggregating agent and are uniformly mixed with the settling accelerator. Is done. Further, the stirring strength G required for the floc forming tank 15 is determined to be a stirring strength at which flocs having the sedimentation promoting material as a core are generated by combining and growing the aggregated floc and the sedimentation promoting material.

  Once the stirring intensity G is determined in accordance with the above guidelines, the actual operation is performed at the determined stirring intensity (almost constant value including an allowable error range). Among them, the operating factors in the actual operation are the pollution concentration C and the residence time T.

  In the coagulation sedimentation apparatus 10 according to the present embodiment, the concentration of discharged sludge is maintained at a predetermined high value regardless of the pollution concentration of the raw water in order to reduce the load on the concentration device and dehydrator provided in the subsequent stage. Is important. For this purpose, the contamination concentration (concentration of “sludge” + “precipitation promoter”) in the sludge extraction line 25 is as high as possible so that the separation performance of the cyclone 111 is maintained and the sludge extraction line 25 is not blocked. It is required to maintain the value.

  In designing the coagulation sedimentation apparatus 10, in order to maintain the flow rate and pressure for realizing the desired separation performance in the cyclone 111, the performance of the sludge extraction pump 109, the length of piping, The sludge flow rate and the like are set, and the limit pollution concentration for preventing the sludge extraction line 25 from being blocked is set. Target values such as a residence time in the settling tank 17, a sedimentation speed, and a pollution concentration are set according to the set limit pollution concentration. Moreover, the target value of the flock formation tank 15, the 2nd stirring tank 13, and the 1st stirring tank will be set in order by the said target value in the sedimentation tank 17 being set. Thereby, it is calculated | required in order to make the residence time as the whole coagulation sedimentation apparatus 10, the addition rate of the sedimentation acceleration | stimulation material in the coagulation sedimentation apparatus 10 whole, and the turbidity density | concentration of the sludge extraction line 25 below a limit turbidity density | concentration. The range of the pollutant concentration of the 1 stirring tank 11 is determined.

  In addition, once the residence time in each treatment tank, and hence the residence time of the coagulation sedimentation apparatus 10 as a whole, is once determined from the above viewpoint, the actual operation is performed based on the decided residence time. . More specifically, the overall residence time of the coagulation sedimentation apparatus 10 is controlled to be equal to or less than a predetermined threshold because it becomes difficult to control the entire apparatus if it becomes too long. Such a threshold value is not particularly limited, but for example, it is preferable to set a residence time capable of realizing a sedimentation speed of 100 m / hr or more. Therefore, in the coagulation sedimentation apparatus 10 according to the present embodiment, the operating factor to be noted is the pollution concentration C.

  Here, when the pollution concentration of the 1st stirring tank 11 becomes small, the pollution concentration of the discharged sludge may fall compared with a general coagulation sedimentation apparatus. Therefore, the pollutant concentration in the first stirring tank 11 is equal to or higher than a predetermined threshold that is comparable to the pollutant concentration in a general coagulation sedimentation apparatus, and the pollutant concentration in the sludge extraction line 25 is equal to or lower than the limit pollutant concentration. Controlled by value. That is, by controlling the sludge return amount by the sludge return line 31 so that the pollutant concentration in the first agitation tank 11 is equal to or higher than a predetermined threshold, the pollutant concentration in the sludge extraction line 25 is controlled to be equal to or lower than the limit pollutant concentration. It becomes possible to increase the turbidity concentration of the sludge discharged from the sludge discharge line 33.

  In order to perform such control, in the coagulation sedimentation apparatus 10 according to the present embodiment, the turbidity meter 101 measures the turbidity of raw water flowing into the first stirring tank 11 as needed, and the turbidity obtained from the turbidity meter 101 is obtained. The sludge return amount by the sludge return line 31 is controlled according to the concentration. More specifically, when the turbidity of the raw water obtained by the turbidimeter 101 is small, the amount of sludge returned by the sludge return line 31 is controlled to be increased. When the turbidity of the raw water is high, the sludge is returned. Control is made so that the amount of sludge returned by the line 31 is reduced. Thereby, it becomes possible to maintain the pollution concentration of the 1st stirring tank 11 more than a predetermined target value. Note that the predetermined target value is preferably determined so as to be the maximum value of fluctuation of the sludge concentration in the raw water. That is, since the sludge return amount by the sludge return line 31 is controlled so as to fill in the fluctuation of the raw water sludge concentration, in order to reduce the sludge return amount as much as possible, the maximum value of the fluctuation of the raw water sludge concentration is maintained. It is preferable.

  The method for determining the amount of sludge returned according to the pollution concentration of the raw water is not particularly limited, and any known method can be used. For example, by preparing a database such as a look-up table in which the turbidity of raw water and the sludge return amount are associated with each other in advance in the control device (not shown) of the coagulation sedimentation apparatus 10, the sludge return amount is prepared. Can be determined.

  In addition, the pollutant concentration in the sludge extraction line 25 can be monitored by installing a measuring device such as a turbidimeter in the line. For example, the pollutant concentration in the sludge extraction line 25 can be estimated by the following method. Is possible. That is, in the coagulation sedimentation apparatus 10 according to the present embodiment, the sum of the pollution amount of the sludge discharge line 33, the pollution amount of the sludge return line 31, and the pollution amount of the cyclone lower outlet line 27 is the pollution of the sludge extraction line 25. It has become a quantity. Further, since it has been confirmed that almost the entire amount of the settling accelerator present in the coagulation sedimentation apparatus 10 has been recovered, it can be considered to be almost constant. Therefore, based on the amount of sludge discharged from the sludge discharge line 33 and the amount of sedimentation accelerator present in the coagulation sedimentation apparatus 10, the amount of sludge in the sludge extraction line 25 is estimated from the above relationship, and the sludge is thereby obtained. It is possible to estimate the contamination concentration of the drawing line 25.

  The control method for the coagulation sedimentation apparatus 10 according to the present embodiment has been described in detail above.

  Thus, according to the coagulation sedimentation apparatus and the coagulation sedimentation method according to the first embodiment of the present invention, the amount of sludge returned to the first stirring tank is controlled according to the pollution concentration of the raw water. Even if the pollution concentration of the raw water fluctuates, the waste mud concentration can be set to the desired concentration (for example, general agglomeration) without causing problems such as deterioration of the quality of treated water, reduction of sedimentation speed, and reduction of cyclone separation efficiency. It is possible to maintain the waste mud concentration of the precipitation device at 5% or more.

(Second Embodiment)
In the coagulation sedimentation apparatus according to the embodiment of the present invention, in order to collect and use the sedimentation promoting material, it is necessary to continuously extract sludge. When the pollution concentration of raw water fluctuates in such a coagulation sedimentation apparatus, the waste mud pollution concentration becomes unstable as described in the first embodiment, and as a result, the waste mud pollution concentration fluctuates.

  In addition, when the amount of raw water flowing into the first agitation tank 11 decreases, the residence time of each treatment tank becomes longer, floc breakage due to excessive agitation occurs, and the quality of the treated water deteriorates. End up.

  Therefore, if both the pollution concentration of raw water and the fluctuation | variation of flow volume arise, as shown in the following Table 2, both the cyclone upper exit pollution density and the quality of treated water will fluctuate.

  In the second embodiment to be described below, the case where not only the turbidity of the suspended substance but also the flow rate fluctuate as described above is used as an example. A coagulation sedimentation apparatus capable of stably maintaining a desired waste mud concentration as a whole treatment system will be described in detail.

<About the configuration of the coagulation sedimentation device>
Below, the structure of the coagulation sedimentation apparatus which concerns on the 2nd Embodiment of this invention is demonstrated in detail, referring FIG. In the following description, the difference from the coagulation sedimentation apparatus according to the first embodiment will be noted, and the description of the same configuration as the coagulation sedimentation apparatus according to the first embodiment will be simplified. FIG. 2 is a schematic view schematically showing an example of the configuration of the coagulation sedimentation apparatus according to the present embodiment.

  The coagulation sedimentation apparatus 10 according to this embodiment is an apparatus that separates suspended solids (SS) contained in raw water into sludge and treated water by coagulation sedimentation treatment.

  Here, the raw water (drainage) to be treated by the coagulation sedimentation apparatus 10 according to the present embodiment is the same as the raw water to be treated by the coagulation sedimentation apparatus 10 according to the first embodiment, and therefore detailed description thereof. Is omitted.

  As shown in FIG. 2, the coagulation sedimentation apparatus 10 according to the present embodiment has a first agitation tank 11, a second agitation tank 13, a flock formation tank 15, and a precipitation tank 17 in order from the side into which raw water flows. And comprising.

  As described above, in the coagulation sedimentation apparatus 10 according to the second embodiment described below, it is assumed that both the flow rate of the suspended substance flowing into the first stirring tank 11 and the pollution concentration fluctuate. Therefore, in the coagulation sedimentation apparatus 10 according to the present embodiment, not only the pollution concentration becomes an operating factor as in the coagulation sedimentation apparatus 10 according to the first embodiment, but the pollution load itself defined by the pollution concentration and the flow rate. Is an operating factor. Therefore, in the coagulation sedimentation apparatus 10 described in detail below, the control is performed so that the pollution load of the first stirring tank 11 becomes a constant value.

  At this time, although the pollution load of the first stirring tank 11 becomes an operation factor, the pollutant concentration of the first stirring tank 11 which is one of the factors defining the pollution load is the sludge extraction as in the first embodiment. It is important to set the range of the contamination concentration set according to the limit contamination concentration so as not to block the line 25.

  The raw water to be subjected to the coagulation sedimentation process flows into the first agitation tank 11 through the raw water inflow line 21. The raw water inflow line 21 is provided with a turbidity meter 101 and a flow meter 102, and the pollution concentration and the inflow amount of raw water flowing into the first stirring tank 11 are managed.

  Here, the 1st stirring tank 11, the 2nd stirring tank 13, the flock formation tank 15, the sedimentation tank 17, and the treated water pit 19 in the coagulation sedimentation apparatus 10 concerning this embodiment are the coagulation sedimentation apparatus concerning 1st Embodiment. 10 has the same configuration as the first agitation tank 11, the second agitation tank 13, the flock formation tank 15, the precipitation tank 17, and the treated water pit 19. Further, the sludge extraction line 25, the cyclone lower outlet line 27, the sludge discharge line 33, the cyclone 111, and the flow control valve 113 in the coagulation sedimentation apparatus 10 according to the present embodiment are also included in the coagulation sedimentation apparatus 10 according to the first embodiment. The sludge extraction line 25, the cyclone lower outlet line 27, the sludge discharge line 33, the cyclone 111 and the flow rate control valve 113 have the same configuration. Therefore, detailed description is omitted below.

  The cyclone upper outlet line 29 to which the sludge separated by the cyclone 111 is transferred is the first except that the turbidity meter 101 is provided and the sludge concentration of the sludge flowing through the cyclone upper outlet line 29 is controlled. It has the same configuration as the cyclone upper outlet line in the coagulation sedimentation apparatus 10 according to the embodiment. Further, the sludge return line 31 is the same as the sludge return line 31 in the coagulation sedimentation apparatus 10 according to the first embodiment except that the flow meter 102 is provided and the flow rate of the sludge flowing through the sludge return line 31 is managed. It has the composition of. Therefore, detailed description is omitted below.

  On the other hand, in the coagulation sedimentation apparatus 10 according to the present embodiment, as shown in FIG. 2, at least a part of the treated water is returned to the first stirring tank 11 from the treated water transfer line 23 to which the treated water is transferred. The treated water return line 35 is branched. As a result, the treated water transfer line 23 after the treated water return line 35 has branched functions as a treated water outflow line 37 for causing the treated water to flow out of the coagulation sedimentation apparatus 10. In addition, the turbidity meter 101 is provided in the treated water outflow line 37, and the turbidity concentration of the treated water flowing out from the treated water outflow line 37 controls the raw water treatment in the coagulation sedimentation apparatus 10 according to the present embodiment. It is used as a management value when

  The amount of treated water returned to the first stirring tank 11 (treated water return amount) is controlled by a flow rate control valve 117 provided in the line. The flow rate control valve 117 may be provided in at least one of the treated water return line 35 and the treated water outflow line 37. As shown in FIG. 2, the treated water return amount control valve is provided in the treated water return line 35. 117a may be provided, and the treated water outflow control valve 117b may be provided in the treated water outflow line 37. Here, the treated water return line 35 is provided with a flow meter 102, and the flow rate of treated water flowing through the treated water return line 35 is managed.

  Thus, in the coagulation sedimentation apparatus 10 according to this embodiment, the sludge extraction line 25, the cyclone upper outlet line 29, and the sludge return line 31 form a circulation line for returning the sludge to the first stirring tank 11, and the processing A circulation line for returning the treated water to the first stirring tank 11 is formed by the water transfer line 23 and the treated water return line 35. In the coagulation sedimentation apparatus 10 according to the present embodiment, the sludge is not returned to the downstream side of the coagulation sedimentation apparatus as much as possible as conventionally performed, but the first agitation tank positioned on the most upstream side of the coagulation sedimentation apparatus. The sludge is returned to 11, and the treated water separated by the coagulation sedimentation treatment is deliberately returned to the first stirring tank 11 located on the most upstream side of the coagulation sedimentation apparatus. Thus, as will be described in detail below, in the coagulation sedimentation apparatus 10 according to the present embodiment, a desired waste mud concentration stably as a whole coagulation sedimentation treatment system regardless of changes in both the turbidity concentration and flow rate of raw water. Can be maintained.

<Regarding the control method of the coagulation sedimentation apparatus>
Then, the control method of the coagulation sedimentation apparatus 10 as shown in FIG. 2 is demonstrated in detail.
Also in the coagulation sedimentation apparatus 10 according to the present embodiment, floc formation can be examined using the GCT value as described in the first embodiment as an index.

  Here, among the operating factors that define the GCT value, the stirring intensity G can be determined in the same manner as the guideline described in the first embodiment.

  Once the stirring intensity G is determined in accordance with the above guidelines, the actual operation is performed at the determined stirring intensity (almost constant value including an allowable error range). Among them, the operating factors in the actual operation are the pollution concentration C and the residence time T.

  Of these two types of operating factors, first, it is important to control the residence time T of the coagulation sedimentation apparatus 10 to be equal to or less than a desired threshold value and maintain the quality of the treated water at a good value. For this purpose, it is important to prevent the breakage of flocs due to changes in the raw water flow rate, and the residence time in each treatment tank in the equipment is maintained at a desired value that does not destroy the flocs regardless of changes in the raw water flow rate. It is important to do. From the above, the residence time in each treatment tank in the apparatus is maintained at a desired value that does not destroy the floc regardless of the change in the raw water flow rate (that is, the residence time in each treatment tank is less than a predetermined threshold value). First of all, it is important.

  In order to perform such control, in the coagulation sedimentation apparatus 10 according to the present embodiment, the flow rate of raw water flowing into the first stirring tank 11 is measured at any time by the flow meter 102, and the first stirring tank obtained from the flow meter 102 is obtained. 11, the amount of treated water returned by the treated water return line 35 is controlled in accordance with the amount of raw water flowing into the water 11. More specifically, when the inflow of raw water obtained by the flow meter 102 is small, control is performed so that the amount of treated water returned by the treated water return line 35 is increased. Control is performed so that the amount of the treated water returned by the water return line 35 is reduced. Thereby, the total flow rate of the raw water and the treated water flowing into the first stirring tank 11 is quantified, and it is possible to control the residence time of each treatment tank including the flock formation tank 15 to be a desired threshold value or less. Become.

  Moreover, in order to stabilize the pollutant concentration of waste mud, it is important to control the pollutant load of the 1st stirring tank 11 to a fixed value as demonstrated in 1st Embodiment. In the case of the coagulation sedimentation apparatus 10 shown in FIG. 2, there are three inflow paths for the suspended matter flowing into the first stirring tank 11, the raw water inflow line 21, the sludge return line 31, and the treated water return line 35. Therefore, in this embodiment, the pollution load L of the first agitation tank 11 includes the pollution concentration Tb1 and flow rate F1 of the raw water inflow line 21, the pollution concentration Tb3 and flow rate F3 of the sludge return line 31, and the treated water return line 35. Using the pollution concentration Tb2 and the flow rate F2, the following expression 101 is expressed.

  Pollution load L = F1 × Tb1 + F2 × Tb2 + F3 × Tb3 (Equation 101)

  Here, among the six types of operating factors used in the above equation 101, the pollution concentrations Tb2 and Tb3 are values that are controlled to desired values in a steady state, and therefore can be treated as constants. Further, the pollution concentration Tb1 and the flow rate F1 are fluctuating values. Therefore, in order to set the pollution load L of the first agitation tank 11 to a constant value, the flow rate F2 of the treated water return line 35 and the flow rate F3 of the sludge return line 31 according to fluctuations in the pollution concentration Tb1 and the flow rate F1 It will suffice if it is controlled.

  Here, the flow rate F2 of the treated water return line 35 is appropriately controlled as described above in order to set the residence time of each treatment tank to a predetermined threshold value or less. Therefore, in order to set the pollution load L of the first stirring tank 11 to a constant value, the flow rate is set as needed so that the fluctuation of the pollution concentration Tb1 and the flow rate F1 and the residence time of each treatment tank are less than a predetermined threshold value. In response to F2, the flow rate F3 of the sludge return line 31 may be controlled. Therefore, the flow rate F3 of the sludge return line 31 is controlled to be a value obtained by the following expression 102. Table 3 below shows an example of the flow rate F3 of the sludge return line calculated based on the following equation 102. In addition, the value shown in the following Table 3 is an example to the last, and each characteristic of the coagulation sedimentation apparatus 10 which concerns on this embodiment is not limited to the value shown below.

  F3 = (L−F1 × Tb1−F2 × Tb2) / Tb3 (Equation 102)

  In designing the coagulation sedimentation apparatus 10 based on such a viewpoint, in order to maintain a flow rate, a pressure, and the like for realizing a desired separation performance in the cyclone 111, the sludge extraction pump 109 is associated with the sludge extraction line 23. Performance, pipe length, sludge flow rate, and the like are set, and a limit pollution concentration for preventing the sludge extraction line 23 from being blocked is set. Target values such as a residence time in the settling tank 17, a sedimentation speed, and a pollution concentration are set according to the set limit pollution concentration. Moreover, by setting the target value in the sedimentation tank 17, target values such as the flock formation tank 15, the second stirring tank 13, and the residence time of the first stirring tank are set in order. Thereby, the residence time as the whole coagulation sedimentation apparatus 10, the addition rate of the sedimentation promoter in the coagulation sedimentation apparatus 10 whole, etc. are determined.

  Here, since the raw water flowing into the first agitation tank 11 flows from the first agitation tank 11 to the flock formation tank 15 by overflow, the residence time of each tank depends on the amount of raw water flowing into the first agitation tank 11 and the treatment. It is determined by the total value of the treated water return amount for returning at least a part of the treated water drawn from the water pit 19 to the first stirring tank 11.

  Therefore, in the coagulation sedimentation apparatus 10 according to this embodiment, the amount of water flowing into the first stirring tank 11 is important. For this reason, in this embodiment, the flow rate F1 of the raw water flowing into the first stirring tank 11 is measured at any time by the flow meter 102, and according to the inflow amount F1 of the raw water into the first stirring tank 11 obtained from the flow meter 102. The treated water return amount by the treated water return line 31 is controlled. More specifically, when the inflow amount F1 of the raw water obtained by the flow meter 102 is small, control is performed so that the treated water return amount through the treated water return line 35 is increased, and when the inflow amount F1 of the raw water is large. The amount of treated water returned by the treated water return line 35 is controlled to be small. Thereby, since the total amount of raw water and treated water flowing into the first stirring tank 11 is stably quantified, the residence time of each processing tank from the first stirring tank 11 to the flock formation tank 15 is less than a desired threshold value. It becomes possible to control to become. Incidentally, the capacity of each treatment tank is designed in advance so that the residence time of each treatment tank falls within a predetermined range in the steady state as described above, so that the raw water flowing into the first stirring tank 11 and the treatment By setting the total amount of water, the residence time of each treatment tank can be controlled within an appropriate range.

  The residence time of each treatment tank may be determined according to the properties of the raw water in accordance with the determination guideline as described above, but can be set to the following values, for example. For example, when the raw water to be treated is a steel wastewater mainly composed of iron and having a true specific gravity of 2.43 to 3.28 and an average particle diameter of 5.3 to 32.5 μm, the first stirring tank 11 and the second The residence time thresholds in the agitation tank 13 and the floc forming tank 15 may be 4 minutes or less, 4 minutes or less, and 12 minutes or less, respectively. In addition, when the raw water to be treated is steel wastewater mainly composed of coal and having a true specific gravity of 1.37 to 1.48 and an average particle size of 10.2 to 23.3 μm, the first stirring tank 11 and the second The residence time thresholds in the stirring tank 13 and the floc forming tank 15 may be 1.5 minutes or less, 1.5 minutes or less, and 4.5 minutes or less, respectively.

  Here, the reason why the residence time when treating the steel wastewater mainly composed of coal is about 1/3 times the residence time when treating the steel wastewater mainly composed of iron (iron oxide) This is because the floc formed from the steel drainage mainly composed of iron is more fragile than the flock formed from the steel drainage mainly composed of iron.

  The method for determining the treated water return amount according to the inflow amount of the raw water is not particularly limited, and any known method can be used. For example, a database such as a lookup table in which the inflow amount of raw water and the return amount of treated water are associated with each other is prepared in advance in a control device (not shown) of the coagulation sedimentation apparatus 10, thereby treating the treated water. It is possible to determine the return amount.

  Moreover, when the pollution load of the 1st stirring tank 11 becomes small, the pollution density | concentration of the discharged sludge may fall compared with a general coagulation sedimentation apparatus. Therefore, the pollution load of the first agitation tank 11 is equal to or higher than a predetermined threshold value that is comparable to the pollution load in a general coagulation sedimentation apparatus, and the pollution concentration of the sludge extraction line 25 is less than the limit pollution concentration. Controlled to a constant value. That is, by controlling the sludge return amount by the sludge return line 31 based on the above 102 so that the pollution load of the first stirring tank 11 becomes a predetermined constant value, the pollution concentration in the sludge extraction line 25 is limited. It becomes possible to raise the pollution density of the sludge discharged | emitted from the sludge discharge line 33, controlling to below a pollution density.

  In order to perform such control, in the coagulation sedimentation apparatus 10 according to this embodiment, the turbidity meter 101 measures the pollutant concentrations Tb1 to Tb3 as needed, and the flowmeter 102 measures the flow rates F1 to F3 as needed. In accordance with these measurement results, the sludge return amount by the sludge return line 31 is controlled based on the above equation 102.

  The control method for the coagulation sedimentation apparatus 10 according to the present embodiment has been described in detail above.

  Thus, according to the coagulation sedimentation apparatus and the coagulation sedimentation method according to the second embodiment of the present invention, the treated water and sludge are returned to the first agitation tank according to fluctuations in the raw water pollution concentration and flow rate. Therefore, it is possible to quantify the amount of raw water and keep the residence time and surface load factor of each treatment tank constant without providing an adjustment tank in the front stage of the apparatus or performing series division of the coagulation sedimentation equipment. Furthermore, the waste mud concentration can be set to a desired concentration (for example, 5% or more, which is the waste mud concentration of a general coagulating sedimentation apparatus) without causing problems such as deterioration of treated water quality, decrease in sedimentation speed, and cyclone separation efficiency. ) Can be maintained. As a result, in the coagulation sedimentation apparatus and the coagulation sedimentation method according to the embodiment of the present invention, it is possible to stabilize the treated water quality and the waste mud concentration. By using such a coagulation sedimentation apparatus and coagulation sedimentation method, the installation space of the coagulation sedimentation apparatus is extremely narrow, and even when raw water with a large amount of water fluctuation, such as steel wastewater, is treated, Treated water quality and waste mud concentration can be maintained very simply.

  Subsequently, the coagulation sedimentation apparatus according to the embodiment of the present invention will be specifically described with reference to experimental examples. In addition, the experimental example shown below is only an example for specifically explaining the coagulation precipitation apparatus according to the embodiment of the present invention, and the coagulation precipitation apparatus according to the embodiment of the present invention is limited to the following example. Do not mean.

Example 1-Verification example of coagulation sedimentation apparatus according to the first embodiment (Example 1)
Two types of coke dust collection wastewater having different pollution concentrations were used as raw water, and the coagulation sedimentation treatment was performed by the coagulation sedimentation apparatus 10 according to the first embodiment of the present invention shown in FIG. At this time, polyaluminum chloride (PAC) was used as the inorganic flocculant, and the addition rate was 50 mg / L. Further, a weak anionic polymer flocculant (molecular weight: 16 million) was used as the polymer flocculant, and the addition rate was 1.0 mg / L. The weak anionic polymer flocculant was added at 10% of the total addition rate to the second stirring tank 13 and 90% of the total addition rate was added to the flock formation tank 15. Further, sand particles (natural sand) are used as the sedimentation promoting material, and the concentration of the sedimentation promoting material in the floc-forming tank 15 represented by (abundance of sedimentation-accelerating material in the flock-forming tank 15 / water amount in the flock-forming tank 15). Of 10 g / L. The maximum particle size of the sand particles used was 300 μm, and the true specific gravity was 2.6. Using these, the coagulation sedimentation apparatus 10 was controlled so that the pollution concentration of the first stirring tank 11 would be 3600 mg / L or more.

  In the present embodiment, the length of the sludge extraction line 25 is about 15 m, and the limit pollution concentration of the sludge extraction line 25 is 150 g / L (15%).

  In this embodiment, the amount of raw water injected into the first agitation tank 11 (raw water flow rate), the sludge extraction flow rate from the settling tank 17, and the surface load factor of the settling tank 17 (the amount of water flowing into the settling tank / the amount of the settling tank) The bottom area is as shown in Table 4 below. Moreover, the sludge return amount by the sludge return line 31 was set as shown in the following Table 4 according to the pollution concentration of raw water. The cyclone upper outlet pollution concentration obtained as a result of the treatment and the pollution concentration of the treated water are also shown in Table 4 below.

(Comparative Example 1)
In Example 1 above, except that sludge was not returned by the sludge return line 31 (sludge return amount was set to zero), in the same manner as in Example 1, two types of coke dust collection wastewater having different pollution concentrations were used. On the other hand, a coagulation sedimentation treatment was performed. The treatment conditions and the results obtained are shown together in Table 5 below.

(Comparative Example 2)
In the first embodiment, the return destination of the sludge by the sludge return line 31 is not the first stirring tank 11 but the suction side of the sludge extraction pump 109 (that is, as the return destination similar to the above-mentioned Patent Document 2), Coagulation sedimentation treatment was performed on two different types of coke dust collection wastewater. Here, in order to keep the amount of slurry flowing into the cyclone 111 constant, the amount of sludge returned was constant regardless of the pollution concentration of the raw water. The treatment conditions and the results obtained are shown together in Table 6 below.

  As is clear from Table 4, in the coagulation sedimentation apparatus 10 according to the first embodiment of the present invention, the cyclone upper outlet pollution concentration (also the waste mud concentration) is 50000 mg / L regardless of the pollution concentration of the raw water. became. Since the waste mud concentration in a general coagulation sedimentation apparatus (apparatus that intermittently extracts sludge) is about 50000 mg / L, the coagulation sedimentation apparatus 10 according to the first embodiment of the present invention has a very high concentration. It can be seen that the sludge concentration is achieved. Moreover, in the coagulation sedimentation apparatus 10 which concerns on the 1st Embodiment of this invention, even if it is a case where the pollution density | concentration of raw | natural water changes from 1720 mg / L to 380 mg / L or less to 1/4 or less, the constant cyclone top part It can be seen that the outlet pollution concentration is realized.

  On the other hand, in Comparative Example 1 in which the sludge was not returned, as is clear from Table 5, the value of the cyclone upper outlet pollutant concentration was extremely small and fluctuated according to the change in the pollutant concentration of the raw water. I understand.

  Further, in Comparative Example 2 in which the return destination of the sludge is the suction side of the sludge extraction pump 109, the cyclone upper outlet pollution concentration is higher than that in Comparative Example 1, but the cyclone upper outlet pollution is changed according to the change in the raw water pollution concentration. It can be seen that the concentration fluctuates.

  As described above, in the coagulation sedimentation apparatus and the coagulation sedimentation method according to the first embodiment of the present invention, the desired waste mud concentration is stably maintained as the entire coagulation sedimentation treatment system regardless of the change in the pollution concentration of the raw water. It became clear that this would be possible.

Example 2-Verification example of coagulation sedimentation apparatus according to second embodiment (Example 2)
Coke dust collection drainage (true specific gravity: 1.37, average particle size: 23.3 μm) is used as raw water, and coagulation sedimentation processing is performed by the coagulation sedimentation apparatus 10 according to the second embodiment of the present invention shown in FIG. went. At this time, polyaluminum chloride (PAC) was used as the inorganic flocculant, and the addition rate was 50 mg / L. Further, a weak anionic polymer flocculant (molecular weight: 16 million) was used as the polymer flocculant, and the addition rate was 1.0 mg / L. The weak anionic polymer flocculant was added at 10% of the total addition rate to the second stirring tank 13 and 90% of the total addition rate was added to the flock formation tank 15. Further, sand particles (natural sand) are used as the sedimentation promoting material, and the concentration of the sedimentation promoting material in the floc-forming tank 15 represented by (abundance of sedimentation-accelerating material in the flock-forming tank 15 / water amount in the flock-forming tank 15). Of 10 g / L. The maximum particle size of the sand particles used was 300 μm, and the true specific gravity was 2.6. Using these, the coagulation sedimentation apparatus 10 was controlled.

  In this embodiment, the raw water injection amount (raw water flow rate) F1 and the pollution concentration Tb1, the pollution load L of the first stirring tank, the sludge extraction flow rate from the sedimentation tank 17, the first stirring tank to the flock, Each residence time of the formation tank 15 and the surface load factor of the settling tank 17 (the amount of water flowing into the settling tank / the bottom area of the settling tank) are as shown in Table 7 below. The sludge return amount F3 by the sludge return line 31 and the treated water return amount F2 by the treated water return line 35 were set as shown in Table 7 below. The cyclone upper outlet pollution concentration Tb3 and the treatment water pollution concentration Tb2 obtained as a result of the treatment are also shown in Table 7 below.

(Comparative Example 3)
In the second embodiment, the coke dust collection drainage is performed in the same manner as in the second embodiment except that the return of the sludge by the sludge return line 31 and the return of the treated water by the treated water return line 35 are not performed. Then, the coagulation sedimentation treatment was performed. The treatment conditions and the results obtained are shown together in Table 8 below.

  As is apparent from Table 7, in the coagulation sedimentation apparatus 10 according to the second embodiment of the present invention, the cyclone upper outlet pollution concentration (also the waste mud concentration) is 50000 mg / day irrespective of the pollution concentration and flow rate of the raw water. L and the SS of treated water was 20 mg / L. Since the waste mud concentration in a general coagulation sedimentation device (device that intermittently extracts sludge) is about 50000 mg / L, the coagulation sedimentation device 10 according to the second embodiment of the present invention has a very high concentration. It can be seen that the sludge concentration is achieved. Moreover, in the coagulation sedimentation apparatus 10 which concerns on embodiment of this invention, even if it is a case where the pollution density | concentration of raw | natural water changes from 1720 mg / L to 100 mg / L, the cyclone top exit pollution density and SS of process water are implement | achieved. You can see that it is made.

  On the other hand, in Comparative Example 3 in which the sludge and the treated water were not returned, as is clear from Table 8, the value of the cyclone upper outlet pollution concentration greatly fluctuated and the treated water SS also fluctuated. .

  As described above, in the coagulation sedimentation apparatus and the coagulation sedimentation method according to the second embodiment of the present invention, a desired waste mud concentration can be stably obtained as a whole coagulation sedimentation treatment system regardless of changes in the contamination concentration and flow rate of raw water. It became clear that it was possible to maintain.

  The same results as in Experimental Example 1 and Experimental Example 2 were obtained when blast furnace granulated slag (maximum particle size: 400 μm, true specific gravity: 2.8) was used as the sedimentation accelerator instead of the sand particles. I was able to get it. Moreover, it replaces with coke dust collection waste_water | drain, and also when the process is similarly performed with respect to the various waste_water | drain enumerated by said (b), (e)-(i), it is the same as that of the said Experimental example 1 and Experimental example 2. I was able to get the results.

  The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.

DESCRIPTION OF SYMBOLS 10 Coagulation sedimentation apparatus 11 1st stirring tank 13 2nd stirring tank 15 Flock formation tank 17 Settling tank 19 Treated water pit 21 Raw water inflow line 23 Treated water outflow line 25 Sludge extraction line 27 Cyclone lower outlet line 29 Cyclone upper outlet line 31 Sludge Return line 33 Sludge discharge line 35 Treated water return line 37 Treated water outflow line 101 Turbidimeter 102 Flow meter 103 Stirrer 105 Sludge scraper 107 Inclined plate 109 Sludge extraction pump 111 Cyclone 113, 117 Flow control valve 113a Sludge return amount control Valve 113b Sludge discharge control valve 117a Treated water return control valve 117b Treated water outflow control valve

Claims (12)

A coagulation sedimentation device that separates suspended substances contained in raw water into sludge and treated water by coagulation sedimentation treatment,
A first stirring tank for stirring and mixing after adding an inorganic flocculant to the raw water;
A second agitation tank, which is provided at the subsequent stage of the first agitation tank and agitates and mixes after adding a sedimentation accelerator composed of a polymer flocculant and insoluble fine particles to the raw water;
A floc-forming tank that is provided downstream of the second stirring tank and forms a floc of the suspended substance with the sedimentation promoting material as a core;
A settling tank which is provided at a subsequent stage of the floc forming tank and sinks the floc to separate the raw water into the treated water and slurry;
A cyclone for separating the slurry extracted from the settling tank by a sludge extraction line into the sludge and the settling accelerator, and supplying the separated settling accelerator to the second stirring tank;
With
A cyclone upper outlet line for transferring the sludge separated by the cyclone is branched into a sludge discharge line for discharging the sludge and a sludge return line for returning at least a part of the sludge to the first stirring tank. And
The sludge discharge so that the pollution load of the first agitation tank, which is the sum of products of the turbidity concentration and flow rate of the suspended matter calculated for each of the inflow paths to the first agitation tank, becomes a constant value. A coagulation sedimentation apparatus having a function of controlling the flow rate of at least one of the line and the sludge return line.   The coagulation sedimentation apparatus of Claim 1 which has a function in which the flow volume of the said sludge return line is controlled according to the pollution density | concentration of the said raw | natural water, when making the said pollution load of a said 1st stirring tank into a constant value.   The coagulation sedimentation apparatus according to claim 1 or 2, wherein a flow rate control valve for controlling a flow rate of the line is provided in at least one of the sludge discharge line and the sludge return line. From the treated water transfer line for transferring the treated water, a treated water return line for returning at least a part of the treated water to the first stirring tank is branched,
According to the flow rate of the raw water flowing into the first agitation tank, the function of controlling the flow rate of at least one of the treated water transfer line after the treated water return line or the treated water return line is further controlled. The coagulation sedimentation apparatus of any one of Claims 1-3 which have.   The flow rate of the treated water return line is controlled according to the flow rate of the raw water so that the residence time held in each of the first agitation tank, the second agitation tank, and the floc forming tank is less than a predetermined threshold value. The coagulation sedimentation apparatus of Claim 4 which has the function to be performed.   The flow rate control valve which controls the flow volume of a line is provided in at least any one of the said treated water transfer line after the said treated water return line branch, or the said treated water return line, The Claim 4 or 5 Coagulation sedimentation equipment.   The coagulation sedimentation apparatus according to any one of claims 1 to 3, wherein the raw water is steel wastewater. The raw water is a steel drainage mainly composed of iron and having a true specific gravity of 2.43 to 4.80 and an average particle diameter of 5.3 to 42.5 μm.
The coagulation sedimentation apparatus according to claim 5 or 6, wherein thresholds of residence time in the first stirring tank, the second stirring tank, and the floc forming tank are 4 minutes or less, 4 minutes or less, and 12 minutes or less, respectively. . The raw water is a steel drainage mainly composed of coal and having a true specific gravity of 1.37 to 1.48 and an average particle diameter of 10.2 to 23.3 μm.
The threshold values of the residence time in the first stirring tank, the second stirring tank, and the floc forming tank are 1.5 minutes or less, 1.5 minutes or less, and 4.5 minutes or less, respectively. The coagulation sedimentation apparatus described in 1.   The coagulation sedimentation apparatus according to any one of claims 1 to 9, wherein the sedimentation promoting material has a maximum particle size of 500 µm or less and a true specific gravity of 2.6 or more.   The coagulation sedimentation apparatus according to claim 1, wherein the settling accelerator is slag. A coagulation sedimentation method for separating suspended substances contained in raw water into sludge and treated water by coagulation sedimentation treatment,
After adding an inorganic flocculant to the raw water of the first stirring tank, stirring and mixing,
To the raw water in the second agitation tank provided at the subsequent stage of the first agitation tank, after adding a settling accelerator composed of a polymer flocculant and insoluble fine particles, agitated and mixed,
In the floc forming tank provided at the subsequent stage of the second stirring tank, the flocs of the suspended substance with the sedimentation promoting material as a core are formed,
In the sedimentation tank provided at the subsequent stage of the floc forming tank, the floc is allowed to settle, and the raw water is separated into the treated water and slurry,
The slurry extracted by the sludge extraction line from the settling tank is separated into the sludge and the settling accelerator with a cyclone, and the separated settling accelerator is supplied to the second stirring tank,
A cyclone upper outlet line for transferring the sludge separated by the cyclone is branched into a sludge discharge line for discharging the sludge and a sludge return line for returning at least a part of the sludge to the first stirring tank. The sludge so that the pollution load of the first agitation tank, which is the sum of products of the turbidity concentration and the flow rate of the suspended matter calculated for each of the flow paths into the first agitation tank, becomes a constant value. The coagulation sedimentation method characterized by controlling the flow volume of at least any one of a discharge line or the sludge return line.

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