Turbid water treatment system

Abstract

To provide a turbid water treatment system capable of accurately carrying out solid / liquid separation by raising the SS concentration in turbid water present in a raw water tank.SOLUTION: A turbid water treatment system 1 comprises a raw water tank 30 storing turbid water, i.e., water to be treated, a water conduit 10 sending the turbid water from a place where the turbid water is generated to the raw water tank, a neutralization reaction tank 50 neutralizing the water to be treated sent from the raw water tank 30, a flocculation reaction tank 80 in which a flocculant is added to the water to be treated, and a solid-liquid separation tank 90 for separating the water to be treated with the flocculant added thereto, into slurry and supernatant. A submerged pump 11 is provided in the conduit 10 to return the sludge precipitating on the bottom of the conduit 10 into the water to be treated present in the conduit 10.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a turbid water treatment system that treats turbid water generated at construction and civil engineering sites such as dams. [Background technology]

[0002] Conventionally, turbid water generated at construction and civil engineering sites is sent to a raw water tank, where a flocculant such as a polymer flocculant is added, and the water is separated into slurry and supernatant in a solid-liquid separation tank. The separated supernatant is discharged into rivers, etc. The slurry is also sent to a dewatering device, where a dehydrated cake is produced. However, the turbid water supplied to the raw water tank has a variable SS (suspended solids) concentration depending on the site conditions and working conditions. When the SS concentration is high, appropriate treatment can be achieved by increasing the amount of flocculant such as polymer flocculant added. However, when the SS concentration is low, too much flocculant such as polymer flocculant is added, resulting in a poor dehydrated cake. Most of the SS consists of fine soil particles (silt, clay, colloids). The SS concentration indicates the amount of suspended solids (or suspended solids) with a particle size of 2 mm or less that are suspended in the water being treated, and is expressed in ppm (mg / L). Therefore, a method has been proposed in which a part of the slurry in the solid-liquid separation tank is returned to the raw water tank to increase the SS concentration in the raw water tank (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2007-222835 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, the method of Patent Document 1 not only requires the provision of a slurry return line branching off from the slurry delivery line that sends the slurry from the solid-liquid separation tank to the muddy water storage tank in which the slurry is stored and connected to the raw water tank, but also requires the provision of a switching valve that switches between the slurry delivery line and the slurry return line, and a control circuit that controls the opening and closing of this switching valve. In addition, carbon dioxide gas is used to adjust the pH of the water being treated, but in the vaporizer that vaporizes the liquid carbon dioxide gas, hot water evaporates as the liquid carbon dioxide evaporates, so water had to be replenished on a daily basis. If water was not replenished sufficiently, the level of hot water in the vaporizer would drop, which could result in the heater for vaporizing the liquid carbon dioxide gas turning off. If the heater turns off, the liquid carbon dioxide gas cannot be vaporized, and there is a risk that proper pH adjustment will not be performed.

[0005] The present invention has been made in consideration of the problems in the conventional art, and aims to provide a turbid water treatment system that can intentionally increase the SS concentration of turbid water in the raw water tank when the SS concentration is low, thereby accurately performing solid-liquid separation. [Means for solving the problem]

[0006] After extensive research, the inventors have concluded that the reason the SS concentration of the water to be treated in the raw water tank is low is because the water conduit that leads the turbid water from the turbid water generation point to the raw water tank is long and has a gentle gradient, causing some of the mud in the turbid water to settle to the bottom of the conduit before it reaches the raw water tank. They believe that the SS concentration of the water to be treated sent to the raw water tank can be increased if this settled mud is agitated and sent to the raw water tank, and have arrived at this invention. That is, the present invention is a turbid water treatment system comprising a raw water tank for storing turbid water, which is the water to be treated, a water conduit for transporting the turbid water from the source of the turbid water to the raw water tank, a neutralization reaction tank for neutralizing the water to be treated transported from the raw water tank, a coagulation reaction tank for adding a coagulant to the water to be treated, and a solid-liquid separation tank for separating the water to be treated to which the coagulant has been added into a slurry and a supernatant liquid, and is characterized in that the water conduit is provided with an agitation device for agitating the water to be treated in the water conduit and returning mud that has settled to the bottom of the water conduit back into the water to be treated in the water conduit. This allows the SS concentration of the untreated water in the raw water tank to be increased, allowing for proper solid-liquid separation, ensuring that the SS concentration of the untreated water to be discharged is within an acceptable range and producing a dehydrated cake with appropriate properties.

[0007] In addition, since the agitator is installed so as to be movable along the water conduit, the SS concentration of the water to be treated in the raw water tank can be effectively increased. The same effect can also be obtained by providing an agitation tank midway through the water conduit and installing an agitator inside the agitation tank. In addition, an oil film layer is provided on the upper surface of the hot water in the vaporizer that vaporizes the liquid carbon dioxide gas sent to the neutralization reaction tank to prevent the hot water from evaporating. This makes it possible to significantly increase the frequency with which the vaporizer can be replenished with water, and to virtually eliminate the risk of the heater stopping due to a drop in the water level. [Brief description of the drawings]

[0008] [Figure 1] 1 is a diagram showing a turbid water treatment system according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a diagram showing an example of the arrangement of a water channel and a submersible pump. [Diagram 3] FIG. 2 is a diagram illustrating an example of a vaporizer. [Figure 4] FIG. 13 illustrates another embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] FIG. 1 shows a turbid water treatment system (hereinafter referred to as treatment system 1) according to this embodiment. Treatment system 1 comprises a water conduit 10, a grit settling tank 20, a raw water tank 30, a carbon dioxide gas supplying device 40, a neutralization reaction tank 50, a PAC storage tank 60, a polymer coagulant storage tank 70, a coagulation reaction tank 80, a solid-liquid separation tank 90, a discharge tank 100, a slurry tank 110, and a dehydrated cake production device 120. The headrace 10 is a waterway with a length of about 5 km that guides the turbid water generated at the construction site 2, which is the source of the turbid water, to the raw water tank 30. The turbid water in the headrace 10 flows at a gentle gradient of about 1 / 1500, with a total flow rate of 25 m 3 It flows at about 1 / hr. 2(a) and (b), in this example, a small submersible pump 11 is installed as an agitator at a location in the water conduit 10 where the sludge z has accumulated (for example, near driftwood) to agitate the sludge z accumulated at the bottom of the water conduit 10. Specifically, the submersible pump 11 rotates a rotating shaft 11j of an impeller 11k installed in a suction port 11a at the bottom (the bottom side of the water conduit 10) by a motor (not shown) to suck in the sludge z at the bottom of the water conduit 10 and discharges it from a discharge port 11b into the water w to be treated. This improves the passage environment in the water conduit 10 and increases the SS concentration of the turbid water in the raw water tank 30. In this embodiment, the water conduit 10 is an underground water conduit having a U-shaped cross section, but the cross section may be rectangular. Also, the water conduit 10 may have a portion exposed above ground depending on the topography. As shown in FIG. 1, a water collection tank 12 is provided at the end of the water conduit 10, and the water to be treated sent from the construction site 2 is sent to a sand settling tank 20 by a pumping pump 13 provided in the water collection tank 12. The grit settling tank 20 is provided between the water conduit 10 and the raw water tank 30 as a pretreatment tank for the water to be treated. It causes large particles such as gravel in the water to settle to the bottom of the tank, and sends the water to be treated, including the SS floating on top of the settled sediments, to the raw water tank 30. The raw water tank 30 stores the water to be treated sent from the water conduit 10, and includes a raw water pump 31, a water level gauge 32, and an agitator 33. The raw water supply pump 31 is activated when the water level gauge 32 detects that the water level of the water to be treated in the tank has risen to a predetermined height, and sends the water to be treated stored in the tank to the neutralization reaction tank 50. If the water to be treated in the raw water tank 30 is stirred at predetermined time intervals by the stirrer 33, the SS concentration of the water to be treated in the raw water tank 30 can be kept uniform.

[0010] The carbon dioxide gas supplying device 40 includes a plurality of liquefied carbon dioxide gas cylinders 41 and a vaporizer 42 . Liquefied carbon dioxide gas stored in a liquefied carbon dioxide gas cylinder 41 is sent to a vaporizer 42. As shown in FIG. 3, the vaporizer 42 is equipped with a vaporization tank 42a, a vaporization pipe 42b, a heater 42c, and a water level gauge 42d, and vaporizes the liquid carbon dioxide gas sent from the liquefied carbon dioxide gas cylinder 41 and sends it to the neutralization reaction tank 50. The vaporizer 42a is a container that stores hot water 42m for heating the liquefied carbon dioxide gas, and in this example, an oil film layer 42n is formed on the upper surface of the hot water 42m. For example, the oil film layer 42n may be formed by pouring environmentally friendly oil such as edible oil into the vaporizer 42a. The thickness of the oil film layer 42n is sufficient if it is about 2 cm. Vaporization pipe 42b is a pipe connected at one end to the end of vaporization tank 42a of liquid supply pipe 42P connected to liquefied carbon dioxide gas cylinder 41, and at the other end to the end of vaporization tank 42a of air supply pipe 42Q connected to neutralization reaction tank 50, and most of it is installed in vaporization tank 42a so that vaporization tank 42a is in hot water 42m. In order to reliably vaporize the delivered liquefied carbon dioxide gas, it is preferable to increase the contact area between vaporization pipe 42b and hot water 42m in vaporization tank 42a, for example by making vaporization pipe 42b zigzag. Heater 42c is provided at the bottom of vaporization tank 42a and heats the water in vaporization tank 42a to a predetermined temperature. It is turned on and off by a thermostat (not shown) and is set to turn off when the water level in vaporization tank 42a detected by water level gauge 42d, which detects the water level of hot water 42m, falls below the predetermined water level. The hot water 42m in the evaporation tank 42a naturally evaporates, so in the past it was necessary to replenish it about once every three days. However, in this example, as described above, an oil film layer 42n is provided on the upper surface of the hot water 42m, which makes it possible to prevent (prolong) evaporation of the hot water 42m. This makes it possible to extend the frequency of water replenishment by more than 30 times, and also reduces the risk of the heater stopping due to a drop in the water level to almost zero. The neutralization reaction tank 50 adjusts the pH of the water to be treated by adding vaporized carbon dioxide gas sent from the vaporization tank 42a to the water to be treated sent from the raw water tank 30. As will be described later, the amount of carbon dioxide gas sent to the neutralization reaction tank 50 is adjusted depending on the pH of the water to be treated in the solid-liquid separation tank 90.

[0011] The PAC storage tank 60 stores PAC (polyaluminum chloride), which is an inorganic flocculant, and sends the stored PAC to the flocculation reaction tank 80. The polymer flocculant storage tank 70 stores the polymer flocculant and delivers the stored polymer flocculant to the flocculation reaction tank 80 . The coagulation reaction tank 80 is equipped with a pH meter 81 and an agitator 82, and reacts the water to be treated, the pH of which has been adjusted in the neutralization reaction tank 50, with the PAC sent from the PAC storage tank 60 and the polymer coagulant sent from the polymer coagulant storage tank 70, to coagulate suspended solids in the water to be treated. Hereinafter, PAC and the polymer flocculant will be referred to as "flocculant". The pH meter 81 detects the pH in the flocculation reaction tank 80, and the detected pH value is sent to a valve control device (not shown) that controls the opening and closing of the valve of the liquefied carbon dioxide gas cylinder 41 of the carbon dioxide gas supply device 40. The valve control device controls the opening and closing of the valve of the liquefied carbon dioxide gas cylinder 41 to adjust the amount of carbon dioxide gas sent to the neutralization reaction tank 50. The agitator 82 mixes the liquid to be treated in the flocculation reaction tank 80 with the flocculant that has been added, and sends the mixture to the solid-liquid separation tank 90 .

[0012] In solid-liquid separation tank 90, SS (suspended matter) in the liquid to be treated is flocculated by a flocculant and settles to the bottom of solid-liquid separation tank 90. ​​The supernatant liquid from solid-liquid separation tank 90 is sent to discharge tank 100, and the slurry that has settled to the bottom is sent to slurry tank 110 by withdrawal pump 92 provided at slurry outlet 91 provided at the bottom of solid-liquid separation tank 90. The discharge tank 100 is equipped with a pH meter 101, an SS concentration meter 102, a discharge pump 103, and a return pump 104, and when the pH and SS concentration of the water to be treated in the discharge tank 100 are within a preset allowable range, the discharge pump 103 is used to discharge the water to be treated in the tank to a discharge point 3 such as a nearby river. In this example, the allowable range of pH is set to 6.5 to 8.5, and the allowable range of SS concentration is set to 25 mg / L or less. When either the pH or the turbidity of the water to be treated in the discharge tank 100 is not within the allowable range, the water to be treated in the discharge tank 100 is returned to the raw water tank 30 by the return pump 104 . The slurry tank 110 temporarily stores the slurry sent by the slurry extraction pump 92, and the stored slurry is sent to a dewatered cake producing device 120. The dehydrated cake producing apparatus 120 includes a filter press 121, a dehydrated cake transporter 122, and a filtered water tank 123, and dehydrates the slurry sent from the slurry tank 110 to produce a dehydrated cake 4. The produced dehydrated cake 4 is transported by the dehydrated cake transporter 122 to the dehydrated cake storage area 5 and stored therein. On the other hand, the water generated in the filter press 121 (hereinafter referred to as filtrate) is sent to the filtration tank 123. Since the filtrate contains SS, it is returned to the raw water tank 30.

[0013] Next, the operation of the muddy water treatment system 1 according to the present invention will be described. The turbid water generated at the construction site 2, where the turbid water is generated, is sent via a water conduit 10 to a sand settling tank 20, where large particles such as gravel in the turbid water are allowed to settle and separated, after which the water is sent to a raw water tank 30 which stores the water to be treated. In this example, a small submersible pump 11 is installed in the water conduit 10 to stir the sludge accumulated at the bottom of the water conduit 10 and increase the SS concentration of the turbid water sent to the raw water tank 30. The water to be treated sent from the water conduit 10 is sent to the raw water tank 30 via the grit settling tank 20. When the amount of water to be treated in the raw water tank 30 reaches a predetermined amount (the water level in the tank rises to a predetermined height), the water to be treated is sent to the neutralization reaction tank 50 by the raw water feed pump 31. Carbon dioxide gas in a gaseous state, obtained by vaporizing liquefied carbon dioxide, is sent from the carbon dioxide gas supplying device 40 to the neutralization reaction tank 50, where the carbon dioxide gas reacts with the alkaline ions in the water to be treated. The pH of the water to be treated is generally about pH 10 (alkaline) if the water is muddy cement-based water, for example, but is neutralized by the introduction of carbon dioxide gas. The amount of carbon dioxide gas sent is controlled so that the pH of the water to be treated after neutralization is 6.5 to 8.5. In this example, an oil film layer 42n is formed on the upper surface of the hot water 42m stored in the vaporization tank 42a of the vaporizer 42 that vaporizes the liquefied carbon dioxide gas, thereby preventing the hot water 42m from evaporating. This makes it possible to extend the frequency of refilling water by 30 times or more, and to reduce the risk of the heater stopping due to a drop in the water level to almost zero.

[0014] Next, the water to be treated, which has had its pH adjusted in the neutralization reaction tank 50, is reacted with flocculants (PAC and polymer flocculant) in the flocculation reaction tank 80 to flocculate suspended solids, and then sent to the solid-liquid separation tank 90, where the water to be treated is separated into a slurry and a supernatant liquid. The supernatant liquid is sent to the discharge tank 100, and the slurry that has settled to the bottom is sent to the slurry tank 110. In the discharge tank 100, when the pH and SS concentration of the water to be treated are within a preset allowable range, the discharge pump 103 is used to discharge the water to be treated in the tank to a discharge point 3 such as a nearby river. On the other hand, the slurry in the slurry tank 110 is sent to a dehydrated cake producing device 120. The sent slurry is dehydrated in a filter press 121 to produce a dehydrated cake 4. The filtrate generated in the filter press 121 is sent to a filtration tank 123 and then returned to the raw water tank 30. In this way, in this embodiment, the submersible pump 11 is provided in the water conduit 10 to increase the SS concentration of the untreated water sent to the raw water tank 30, so that solid-liquid separation can be performed appropriately. Therefore, the SS concentration of the untreated water to be discharged can be reliably kept within the allowable range, and a dehydrated cake with appropriate properties can be produced. In addition, an oil film layer 42n is provided on the upper surface of the hot water 42m in the vaporizer 42 that vaporizes the liquid carbon dioxide gas to prevent the hot water from evaporating, so that the frequency of refilling the vaporizer 42 with water can be significantly increased.

[0015] Although the present invention has been described above using the embodiments, the technical scope of the present invention is not limited to the scope described in the above embodiments. It is clear to those skilled in the art that various modifications and improvements can be made to the above embodiments. It is clear from the claims that such modifications and improvements can also be included in the technical scope of the present invention.

[0016] For example, in the above embodiment, a small submersible pump 11 is used as the stirring device, but a well-known stirrer having a structure in which a stirring blade is rotated by a motor may be used. Further, in this example, one submersible pump 11 is used, but submersible pumps 11 may be disposed at multiple locations within the water conduit 10, or one submersible pump may be moved within the water conduit 10. 4, a stirring tank 14 may be provided in the water conduit 10, and a stirring device such as a submersible pump 11 may be installed in the stirring tank 14 to stir the sludge z accumulated at the bottom of the stirring tank 14. The stirring tanks 14 may be provided at multiple locations in the water conduit 10. [Explanation of symbols]

[0017] 1. Turbid water treatment system, 2. Construction site, 3. Discharge point, 4. Dewatered cake, 5 Dehydrated cake storage area, 10 water channel, 11 submersible pump, 12 water collection tank, 13 pumping pump, 14 mixing tank, 20 grit settling tank, 30 raw water tank, 31 raw water pump, 32 water level gauge, 33 agitator, 40 Carbon dioxide gas supply device, 41 Liquefied carbon dioxide gas cylinder, 42 Vaporizer, 42a vaporization tank, 42b vaporization pipe, 42c heater, 42d water level gauge, 42m hot water, 42n oil film layer, 42P liquid supply pipe, 42Q air supply pipe, 50 Neutralization reactor, 60 PAC storage tanks, 70 Polymer coagulant storage tank, 80 coagulation reaction tank, 81 pH meter, 82 agitator, 90 solid-liquid separation tank, 91 slurry outlet, 92 withdrawal pump, 100 discharge tank, 101 pH meter, 102 SS concentration meter, 103 discharge pump, 104 Return pump, withdrawal pump, 110 slurry tank, 120 dehydrated cake preparation device, 121 filter press, 122 dehydrated cake transporter, 123 filtration water tank.

Claims

1. A turbid water treatment system comprising: a raw water tank for storing turbid water, which is water to be treated; a water conduit for transporting the turbid water from a generation point of the turbid water to the raw water tank; a neutralization reaction tank for neutralizing the water to be treated transported from the raw water tank; a flocculation reaction tank for adding a flocculant to the water to be treated; and a solid-liquid separation tank for separating the water to which the flocculant has been added into a slurry and a supernatant liquid, A muddy water treatment system characterized in that the water conduit is provided with an agitation device that agitates the water to be treated in the water conduit and returns mud that has settled to the bottom of the water conduit back into the water to be treated in the water conduit.

2. 2. The muddy water treatment system according to claim 1, wherein an agitator is installed so as to be movable along the water channel.

3. 2. The muddy water treatment system according to claim 1, further comprising an agitation tank provided in the water conduit, and an agitation device installed in the agitation tank.

4. The turbid water treatment system according to any one of claims 1 to 3, characterized in that an oil film layer is provided on the upper surface of the warm water in a vaporizer that vaporizes the liquid carbon dioxide gas sent to the neutralization reaction tank.

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