JP6825999B2 - Operation method of coagulation sedimentation device and coagulation sedimentation device - Google Patents

Description

The present invention relates to a method for operating a granulation type coagulation sedimentation device and a granulation type coagulation sedimentation device.

As one of the water treatment devices, a coagulation sedimentation device is widely used for water treatment and wastewater treatment. The coagulation sedimentation device aggregates suspended substances contained in raw water and precipitates them in a settling tank, and separates the raw water into sludge and treated water. That is, when the raw water supplied to the settling tank passes through the fluidized bed (sludge blanket) due to sludge, suspended substances and flocs in the raw water are captured by the sludge blanket, and the filtered supernatant is obtained as treated water. Will be.

Among such coagulation and sedimentation devices, raw water to which a coagulant is added is stirred in a settling tank by a stirring blade to form coagulation flocs, and further collision and rolling motions are repeated to gradually increase the particle size of the coagulation flocs. A granulation type coagulation-precipitation device that is increased to form spherical pellets is known. In the granulation type coagulation sedimentation device, pellets with high density and high sedimentation speed form a fluidized bed (pellet blanket), which enables higher speed processing and the water flow velocity in the sedimentation tank (pellet blanket). The LV) can be increased to reduce the size of the settling tank.

In the granulation type coagulation sedimentation device, if high-concentration sludge in the settling tank adheres to the stirring blade and becomes a lump, the stirring action may be hindered and the granulation efficiency may decrease. In particular, high-strength pellets in which two types of polymer flocculants (for example, a cationic polymer flocculant and an anionic polymer flocculant, and an amphoteric polymer flocculant and an anionic polymer flocculant) are used in combination as a flocculant. When forming a polymer, the aggregated flocs tend to adhere to other objects, and sludge tends to adhere to the stirring blade. Therefore, in the granulation type coagulation sedimentation device, some methods for suppressing the adhesion / adhesion of high-concentration sludge in the sedimentation tank have been proposed (see, for example, Patent Document 1).

Japanese Patent No. 2723809

At sites such as irrigation water treatment and wastewater treatment, for example, the supply of raw water may be stopped for some reason, and as a result, the steady operation (coagulation sedimentation treatment) of the coagulation sedimentation device may have to be stopped. At this time, the sludge flowing in the settling tank is deposited on the bottom, but if the stop time of the device is long, these stick to each other, and an excessive torque may be applied to the stirring blade when the operation is restarted. .. As a result, the operation may not be restarted normally, and the stirring blade may be damaged. Further, sludge adhering to each other becomes agglomerates in the settling tank, and when the operation is restarted, a drift that avoids these is generated in the settling tank, and the floating flocs may flow out to the treated water. Most of the sludge sticking measures so far have been taken during steady operation as described in Patent Document 1, and no measures have been taken to suppress sludge sticking due to the shutdown of such a device. is the current situation.

Therefore, an object of the present invention is to provide an operation method of a coagulation sedimentation device and a coagulation sedimentation device that suppress the adhesion of sludge in the settling tank due to the suspension of supply of raw water.

In order to achieve the above-mentioned object, the operation method of the coagulation sedimentation device of the present invention agglomerates and precipitates suspended substances contained in the water to be treated in a settling tank, and separates the water to be treated into sludge and treated water. This is a method of operating a coagulation sedimentation device that separates, and while the water to be treated is being supplied to the settling tank, the water to be treated in the settling tank is continuously stirred to granulate the flocs formed in the water to be treated. Then, while the step of forming the fluidized layer by the granulated flocs and the supply of the water to be treated to the settling tank are stopped, the granulated flocs in the settling tank forming the fluidized layer are intermittently formed. includes to a step of stirring, the.

Further, the coagulation sedimentation device of the present invention is a coagulation sedimentation device that coagulates and precipitates suspended substances contained in water to be treated in a settling tank and separates the water to be treated into sludge and treated water. During the supply of the water to be treated to the tank, the water to be treated in the settling tank is continuously stirred to granulate the flocs formed in the water to be treated, and a fluidized layer is formed by the granulated flocs. While the supply of water to be treated to the settling tank is stopped, there is a stirring means for intermittently stirring the granulated flocs in the settling tank that formed the fluidized layer .

According to the operation method of the coagulation sedimentation device and the coagulation sedimentation device, not only can sludge sticking in the settling tank be suppressed while the supply of water to be treated (raw water) is stopped, but also in the settling tank. By minimizing the destruction of the granulated product, it is possible to minimize the deterioration of the quality of the treated water obtained when the supply of raw water is resumed.

As described above, according to the present invention, it is possible to suppress the sticking of sludge in the settling tank due to the suspension of the supply of raw water.

It is a schematic block diagram of the coagulation sedimentation apparatus which concerns on one Embodiment of this invention. It is a schematic block diagram which shows one modification of the coagulation sedimentation apparatus which concerns on this embodiment. It is a schematic block diagram which shows the other modification of the coagulation sedimentation apparatus which concerns on this embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic configuration diagram of a coagulation sedimentation device according to an embodiment of the present invention.

The coagulation sedimentation device 1 is a granulation type coagulation sedimentation device that separates raw water (treated water) into sludge and supernatant liquid (treated water) by coagulating and precipitating the suspended substances contained in the reaction tank. It has a settling tank 20, a settling tank 20, and a treated water tank 30.

The reaction tank 10 is connected to a raw water tank (not shown) via a raw water supply line L1. In the reaction vessel 10, an inorganic flocculant addition line 11 for adding an inorganic flocculant to the raw water in the reaction vessel 10, a first polymer flocculant addition line 12 for adding a first polymer flocculant, and a pH. Each of the pH adjuster addition lines 13 to which the adjuster is added is connected. Further, the reaction tank 10 is provided with a stirrer 14 for stirring the raw water in the reaction tank 10. Further, a raw water transfer line L2 is connected to the reaction tank 10, and a valve V1 and a second polymer flocculant for adding a second polymer flocculant to the raw water flowing through the raw water transfer line L2 are connected to the raw water transfer line L2. The agent addition line 15 is connected.

The settling tank 20 is connected to the reaction tank 10 via the raw water transfer line L2, and receives the raw water to which each coagulant is added. The settling tank 20 is provided with a stirrer (stirring means) 21 for stirring the raw water in the settling layer 20. By the action of the stirrer 21, the fluidized bed (pellet blanket) A made of granulated flocs (pellets) and the clear supernatant from which suspended substances and flocs have been removed are contained in the settling tank 20 as described later. Liquid (treated water) B is formed. A water collecting tank 22 for collecting the treated water B is provided in the upper part of the settling tank 20, and the treated water transfer for taking out the treated water B overflowing to the water collecting tank 22 to the outside is provided in the water collecting tank 22. Line L3 is connected.

On the side surface of the settling tank 20, a concentrating section 24 that communicates with the inside of the settling tank 20 via the opening 23 is provided. The concentrating unit 24 overflows the excess sludge (pellets floating on the upper part of the pellet blanket A) in the settling tank 20 and setstles the sludge inside the sludge to concentrate the sludge. A sludge extraction line L4 for extracting concentrated sludge (pellets concentrated to a high concentration) C accumulated in the concentration unit 24 is connected to the lower part of the concentration unit 24, and a sludge extraction pump (shown) is connected to the sludge extraction line L4. Sludge) is provided. The position of the concentrating unit 24 is not limited to the illustrated example, and may be, for example, the lower part of the settling tank 20.

The treated water tank 30 is connected to the settling tank 20 (water collecting tank 22) via the treated water transfer line L3, and stores the treated water separated in the settling tank 20. A treated water discharge line L5 for discharging the treated water B taken out from the settling tank 20 and stored in the treated water tank 30 to the outside is connected to the lower part of the treated water tank 30. The treated water discharge line L5 is provided with a treated water discharge pump 31 and a valve V2. A treated water recirculation line L6 for recirculating the treated water in the treated water tank 30 to the raw water transfer line L2 is connected between the treated water discharge pump 31 and the valve V2 of the treated water discharge line L5 via the valve V3. ing. The treated water recirculation line L6 is connected to the raw water transfer line L2 on the upstream side of the connection portion with the second polymer flocculant addition line 15.

Here, the operation of the coagulation sedimentation device 1 of the present embodiment during steady operation (coagulation sedimentation treatment) will be described.

The raw water containing the suspended substance is supplied to the reaction vessel 10 through the raw water supply line L1. The inorganic flocculant is added to the raw water supplied to the reaction tank 10 through the inorganic flocculant addition line 11, and the first polymer flocculant is added through the first polymer flocculant addition line 12. If necessary, the pH adjuster is added through the pH adjuster addition line 13. In this way, in the reaction tank 10, the inorganic flocculant and the first polymer flocculant are added to the raw water to initiate the agglutination reaction of the suspended substances in the raw water, and flocs are formed. At this time, the agglutination reaction of the suspended substance is promoted by stirring the raw water by the stirrer 14.

The raw water containing the flocs in the aggregation process is supplied to the settling tank 20 through the raw water transfer line L2. At this time, the second polymer flocculant is added to the raw water flowing through the raw water transfer line L2 through the second polymer flocculant addition line 15, and is supplied to the settling tank 20 together with the raw water. When the raw water is supplied into the settling tank 20, the fine flocs in the raw water are continuously agitated by the stirrer 21 to promote the agglutination reaction by the second polymer flocculant, and also collide and roll. By repeating the above steps, the particle size gradually increases and the pellets are granulated into spherical pellets. In this way, a pellet blanket A, which is a fluidized bed of pellets, is formed in the lower part of the settling tank 20.

After that, in the raw water supplied from the raw water transfer line L2, suspended substances and flocs are trapped in the pellet blanket A while passing through the pellet blanket A, and the filtered supernatant liquid (treated water) B becomes the settling tank 20. Ascend to the top of. Then, when the treated water B overflows the water collecting tank 22, it is taken out through the treated water transfer line L3 and stored in the treated water tank 30. The treated water stored in the treated water tank 30 is discharged to the outside by the treated water discharge pump 31 through the treated water discharge line L5. On the other hand, when the interface of the pellet blanket A exceeds the height of the lower end of the opening 23, the pellets on the upper part of the pellet blanket A overflow to the concentrating section 24, settle and concentrate. Then, the concentrated sludge C accumulated in the concentrating section 20 is drawn out to the outside through the sludge drawing line L4, if necessary.

Examples of the inorganic flocculant added to the raw water include an aluminum-based flocculant such as polyaluminum chloride (PAC), an iron-based flocculant such as ferric chloride, or a mixture thereof, and a pH adjuster. Examples thereof include acid agents such as hydrochloric acid and sulfuric acid, and alkaline agents such as sodium hydroxide and calcium hydroxide.

Further, examples of the first polymer flocculant include a cationic polymer flocculant and an amphoteric polymer flocculant, and a cationic polymer flocculant is preferably used. Examples of the cationic polymer flocculant include polymers such as dimethylaminoethyl acrylate / methyl methyl chloride quaternary salt (DAA) and dimethylaminoethyl methacrylate quaternary salt (DAM). The molecular weight of the cationic polymer flocculant is, for example, preferably 7 million or more, and more preferably 10 million or more. As the second polymer flocculant, an anionic polymer flocculant is preferably used, and examples of the anionic polymer flocculant include a polymer of acrylamide and acrylic acid. The molecular weight of the anionic polymer flocculant is, for example, preferably 10 million or more, and more preferably 15 million or more.

In order to surely mix the inorganic flocculant, the first polymer flocculant and the raw water, two reaction tanks are provided, and the inorganic flocculant is added and stirred in one reaction tank, and the other reaction is carried out. The first polymer flocculant may be added and stirred in the tank. In this case, the pH adjuster is preferably added to the reaction vessel to which the inorganic flocculant is added. When the reaction between the inorganic flocculant and the first polymer flocculant and the raw water is completed in a short time, the reaction tank is omitted and the inorganic flocculant and the first polymer flocculant are aggregated in the raw water flowing in the pipe. The agent may be added directly and stirred for a short time with a line mixer or the like instead of the stirrer.

By the way, in the coagulation sedimentation device 1 of the present embodiment, the supply of raw water from the raw water supply line L1 is stopped, for example, when the water level in the raw water tank (not shown) falls below a predetermined water level for some reason. In some cases, the steady operation (coagulation and precipitation treatment) may have to be stopped. At this time, the sludge (pellets) flowing in the settling tank 20 is deposited on the bottom, but if the stop time of the device is long, these stick to each other and become excessive on the stirring blade of the stirrer 21 when the operation is restarted. Torque may act. As a result, the operation may not be restarted normally, and the stirring blade may be damaged. Further, sludge adhering to each other becomes agglomerates in the settling tank, and when the operation is restarted, a drift that avoids these is generated in the settling tank, and the floating flocs may flow out to the treated water.

In order to suppress the sticking of sludge due to the shutdown of such a device, for example, it is conceivable to continuously operate only the stirrer 21 even when the operation is stopped. However, if the stirrer 21 is continuously operated while the supply of raw water into the settling tank 20 is stopped, the pellets (granulated matter) in the settling tank 20 are continuously subjected to excessive pressure, resulting in formation. The granules may be destroyed, and the quality of the treated water obtained when the operation is restarted may deteriorate or become unstable.

Therefore, in the present embodiment, while the supply of raw water to the settling tank 20 is stopped and the steady operation of the apparatus is stopped, the stirrer 21 is operated intermittently to intermittently operate the granules in the settling tank 20. The intermittent stirring step of stirring is performed. As a result, it is possible to effectively suppress the sticking of sludge in the settling tank 20 due to the suspension of the supply of raw water, while minimizing the destruction of the granulated product due to stirring.

In the intermittent stirring step, the stirring interval is not particularly limited, and the optimum stirring interval can be selected according to the time from when the supply of raw water is stopped until the sludge sticks in the settling tank 20. Normally, sludge sticking in the settling tank 20 occurs several hours after the supply of raw water is stopped, but in such a case, if stirring is performed at a frequency of about once an hour. Good. On the other hand, when the amount of the coagulant added during the coagulation treatment is large, or when a high-density, high-settling, high-strength granulated product is formed, the sludge in the settling tank 20 is fixed. It is preferable to stir at shorter time intervals because it becomes easier. For example, when a cationic polymer flocculant (first polymer flocculant) and an anionic polymer flocculant (second polymer flocculant) are used in combination, the particle size is large, the density is high, and the sedimentation rate is high. In order to form granules, the ratio of cationic groups of the cationic polymer flocculant (the molar ratio of the cationic monomer to the total molar amount of the copolymerizing nonionic monomer and the cationic monomer) is 30 mol% or less. Is more preferable, 15 mol% or less is more preferable, and 8 mol% or less is further preferable. This is because, in the above-mentioned cationic group ratio, the ratio of the hydrogen bond portion by the nonionic chain required for coarsening the flocs is large, and the anionic functional group of the anionic substance or the anionic polymer flocculant. This is because it contains a sufficient cation group to obtain a strong crosslinked structure with. In such a case, as described above, the sludge in the settling tank 20 is likely to be fixed, so that it is preferable to perform stirring at a frequency of, for example, about once every 10 to 30 minutes.

The stirring time for each time depends on the stirring speed and sludge properties, but is not particularly limited as long as the stirring blade of the stirrer 21 can surely make one or more rotations in the settling tank 20. In the granulation type coagulation / precipitation device 1 of the present embodiment, the stirring speed by the stirrer 21 is as fast as several rpm to several tens of rpm, so that the stirring time may be several seconds to several tens of seconds. The stirring speed during intermittent stirring does not have to be the same as the stirring speed during steady operation (coagulation and precipitation treatment). For example, when the strength of the granulated product is strong and sludge sticking easily progresses, The stirring speed may be faster than that during steady operation. Alternatively, if the strength of the granulated product is weak and there is a possibility that the granulated product may be destroyed by stirring, the stirring speed may be slower than that during steady operation.

If the supply of raw water is stopped for a long period of time and intermittent stirring is performed for a long period of time, there is a concern that the granules may be destroyed by the stirring, and that the quality of the treated water obtained when the operation is restarted may be deteriorated. Therefore, in the intermittent stirring step, in order to reduce the destruction of the granulated product due to stirring as much as possible, it is preferable to perform stirring while flowing the granulated product in the settling tank 20, that is, water other than raw water is used in the settling tank 20. It is preferable to stir while passing water through the water.

The water used for water flow is not particularly limited as long as it is water other than raw water that meets certain water quality standards (for example, tap water), but the salt concentration is lower than that of the treated water in the settling tank 20 (for example, pure water). Water, etc.) is not preferred as it causes dissolution of the granules. Therefore, it is preferable to use the treated water taken out from the settling tank 20 from the viewpoint that it is not necessary to install a pipe from the outside of the coagulation settling device 1. In the present embodiment, the valve V1 of the raw water transfer line L2 is closed, the valve V3 of the treated water recirculation line L6 is opened, and the treated water discharge pump 31 is operated to take out the treated water from the settling tank 20 to the treated water tank 30. Water can be refluxed from the treated water reflux line L6 to the settling tank 20 through the raw water transfer line L2. Alternatively, even when the treated water tank 30 is not provided, as shown in FIG. 2, the upper part of the settling tank 20 and the raw water transfer line L2 are connected by the treated water recirculation line L6, and the treated water recirculate to the treated water recirculation line L6. By installing the pump 25, the treated water can be circulated in the same manner. The amount of water flowing to the settling tank 20 does not have to be the same as the raw water supply flow rate during steady operation, but in order to ensure the flow of the granulated product, it must be the same as the raw water supply flow rate during steady operation. preferable.

In addition to this, in order to suppress the destruction of the granules in the intermittent stirring step to the maximum, it is preferable to add a polymer flocculant to the water passing through the settling tank 20. As a result, the reaggregation of the granules destroyed by stirring can be promoted, and clearer treated water can be obtained when the operation is restarted.

The polymer flocculant used at this time is not particularly limited, but it is preferable to use the same polymer flocculant as the polymer flocculant added to the raw water during steady operation. In the present embodiment, two types of polymer flocculants are added stepwise to the raw water during steady operation, and either of them may be used as the polymer flocculant used during intermittent stirring. However, when two types of polymer flocculants are used together during steady operation, the flocs are generally formed by the polymer flocculants added first, and the flocs are adhered to each other by the polymer flocculants added later. Then, the flocs are coarsened (granulated). For example, when the cationic polymer flocculant is added first and the anionic polymer flocculant is added later, the fibrous flocs that are densely tempered with less hydrated water by the cationic polymer flocculant are produced. After being formed, the flocs are adhered to each other by an anionic polymer flocculant to coarsen the flocs. Therefore, at the time of intermittent stirring, it is preferable to use the polymer flocculant added later among the two types of polymer flocculants added to the raw water during steady operation. In the present embodiment, the treated water recirculation line L6 is connected to the raw water transfer line L2 on the upstream side of the connection portion with the second polymer coagulant addition line 15, so that the second polymer coagulation occurs during intermittent stirring. The agent can be added to the settling tank 20.

The implementation of intermittent stirring due to the suspension of the supply of raw water is not limited to the configuration in which two types of polymer flocculants are used in combination during steady operation as in the present embodiment, and as a matter of course, one type of polymer flocculant is used. It is also applicable when using agents. Even in that case, in the intermittent stirring step, it is preferable to use the same polymer flocculant as the polymer flocculant added to the raw water during steady operation, and it is preferable to use a cationic polymer flocculant or an anionic polymer flocculant. In addition, for example, a nonionic polymer flocculant, an amphoteric polymer flocculant, or the like can also be used.

The amount of the polymer flocculant added during intermittent stirring may be an amount sufficient to reaggregate the portion destroyed by stirring, for example, about 1/10 of the amount required during steady operation. You may. Alternatively, the addition amount may be the same as that required during steady operation in order to avoid complication of control. However, if the amount added is too large, the reaggregation of flocs may be excessively promoted and the sludge may be fixed. Therefore, the amount of the polymer flocculant added in the intermittent stirring step is limited to 10 mg / L. Is preferable.

Further, it goes without saying that the implementation of intermittent stirring due to the suspension of the supply of raw water is not limited to the settling tank having a specific configuration, and can be applied to the settling tank having various configurations. For example, as shown in FIG. 3, in addition to the above-mentioned stirrer 21 having a plurality of stirring blades, a plurality of a plurality of coagulated flocs are formed on the inner peripheral surface of the settling tank 20 in order to further suppress adhesion and sticking to the stirring blades. It can also be applied to a configuration in which a fixed wing 26 is attached.

Next, the present invention will be described in more detail with reference to specific examples.

(Example 1)
In this embodiment, the coagulation sedimentation apparatus shown in FIG. 1 is used to perform steady operation until a pellet blanket having a predetermined height is formed in the sedimentation layer, and then the supply of raw water is stopped and steady operation is performed. The treated water turbidity was measured when the steady operation was restarted after the time was stopped. A reaction vessel having a volume of 200 L was used, and a settling vessel having a volume of 39 L was used. As the water to be treated (raw water), a 500 mg / L kaolin suspension was used.

During steady operation, polyaluminum chloride (PAC) was added to the raw water at a concentration of 150 mg / L as an inorganic flocculant, and the cation group ratio was 0.5 mg / L as the first polymer flocculant. 5 mol% of the cationic polymer flocculant was added, and 5% concentration of sodium hydroxide was added as a pH adjuster in an amount such that the pH of the raw water in the reaction vessel became 7, and the second As the polymer flocculant, an anionic polymer flocculant having an anion group ratio of 4 mol% was added at a concentration of 1.0 mg / L. The amount of water flowing through the settling tank (flow rate of raw water supplied to the settling tank) was 830 L / h (water flow LV was 20 m / h), and the stirring speed of the raw water in the settling tank was 10 rpm. The treated water turbidity during steady operation was 0.39 degrees.

While the steady operation was stopped, an intermittent stirring step was performed to intermittently stir the granules in the settling tank. The stirring interval was once an hour (three times in total), the stirring time for each stirring was 30 seconds, and the stirring speed was 10 rpm, which was the same as in steady operation. In the intermittent stirring step, water is not passed through the settling tank and no polymer flocculant is added.

(Example 2)
In the intermittent stirring step, the treated water turbidity was measured under the same conditions as in Example 1 except that the treated water was stirred while passing the treated water through the settling tank with the same amount of water flow as in the steady operation.

(Example 3)
In the intermittent stirring step, the treated water turbidity was measured under the same conditions as in Example 2 except that an anionic polymer flocculant was added to the treated water at a concentration of 0.2 mg / L when the water was passed through the settling tank. went.

(Comparative Example 1)
The treated water turbidity was measured under the same conditions as in Example 1 except that the settling tank was continuously stirred at the same stirring speed as during the steady operation even when the steady operation was stopped.

(Comparative Example 2)
An attempt was made to measure the treated water turbidity under the same conditions as in Example 1 except that the settling tank was not agitated while the steady operation was stopped.

Table 1 shows the measurement results of Examples 1 to 3 and Comparative Examples 1 and 2.

In Comparative Example 2, after the steady operation was stopped for 4 hours, a load exceeding the maximum torque (0.98 Nm) was applied to the stirrer, the stirrer could not be operated, and the steady operation was restarted. I couldn't. Therefore, the treated water turbidity could not be measured, but it is considered that this is because the sludge adhered in the settling tank because the agitation in the settling tank was not performed when the supply of raw water was stopped. .. On the other hand, in Examples 1 to 3 and Comparative Example 1, since the steady operation was normally restarted, the sludge was fixed in the settling tank by stirring in the settling tank when the supply of raw water was stopped. Can be seen to be suppressed. On the other hand, when Examples 1 to 3 and Comparative Example 1 are compared, in Examples 1 to 3, the water quality is deteriorated as compared with the steady operation before the supply of raw water is stopped, but the degree of deterioration is observed in Comparative Example 1. It was confirmed that the destruction of the granules due to stirring was minimized. Further, in Examples 1 to 3, good results were obtained in the order of Example 3, Example 2, and Example 1, which were water flow to the settling tank and polymer aggregation in the intermittent stirring step. It is considered that this is the effect of adding the agent.

1 Coagulation and sedimentation device 10 Reaction tank 11 Inorganic coagulant addition line 12 First polymer coagulant addition line 13 pH adjuster addition line 14 Stirrer 15 Second polymer coagulant addition line 20 Sedimentation tank 21 Stirrer 22 Collection Water tank 23 Opening 24 Concentrator 25 Treated water recirculation pump 30 Treated water tank 31 Treated water discharge pump L1 Raw water supply line L2 Raw water transfer line L3 Treated water transfer line L4 Sludge extraction line L5 Treated water discharge line L6 Treated water recirculation line V1, V2 , V3 valve

Claims (11)

It is an operation method of a coagulation sedimentation device that aggregates and precipitates suspended substances contained in water to be treated in a settling tank and separates the water to be treated into sludge and treated water.
While the water to be treated was supplied to the settling tank, the water to be treated in the settling tank was continuously stirred to granulate the flocs formed in the water to be treated , and the granulated. The process of forming a fluidized bed with flocs and
Wherein while said to sedimentation tank supply treated water is stopped, and a step of intermittently agitating the granulated flocs in the settling tank, which had formed the fluidized layer, aggregation How to operate the settling device. The first aspect of the present invention, wherein the step of intermittently stirring the granulated flocs includes stirring the granulated flocs while passing water other than the water to be treated through the settling tank. How to operate the coagulation sedimentation device. The method for operating a coagulation sedimentation device according to claim 2, wherein the water other than the water to be treated is the treated water taken out from the settling tank. The method for operating a coagulation / precipitation device according to claim 2 or 3, wherein a polymer flocculant is added to water other than the water to be treated. The method for operating a coagulation-precipitating device according to claim 4, wherein the amount of the polymer flocculant added is 10 mg / L or less. A step of adding a polymer flocculant to the water to be treated supplied to the settling tank is included.
The aggregation according to claim 4 or 5, wherein the polymer flocculant added to water other than the water to be treated is the same polymer flocculant as the polymer flocculant added to the water to be treated. How to operate the settling device. The step of adding the polymer flocculant includes stepwise addition of a plurality of types of the polymer flocculant.
The polymer flocculant added to water other than the water to be treated is the same polymer flocculant as the polymer flocculant finally added to the water to be treated among the plurality of types of polymer flocculants. , The method of operating the coagulation sedimentation apparatus according to claim 6. The plurality of types of polymer flocculant, and a cationic polymer flocculant and A anion polymer flocculant, operating method of coagulating sedimentation apparatus according to claim 7. The method for operating a coagulation-precipitating device according to claim 8, wherein the ratio of cation groups of the cationic polymer flocculant is 8 mol% or less. In the step of intermittently stirring the granulated flocs, the granulated flocs are agitated by the stirring blades rotating in the settling tank and the fixed blades attached to the inner peripheral surface of the settling tank. The method for operating a coagulation sedimentation apparatus according to any one of claims 1 to 9, which comprises the above. A coagulation and sedimentation device that aggregates and precipitates suspended substances contained in water to be treated in a settling tank and separates the water to be treated into sludge and treated water.
During the supply of the water to be treated to the settling tank, the water to be treated in the settling tank was continuously stirred to granulate the flocs formed in the water to be treated, and the granulated. A fluidized bed is formed by flocs, and while the supply of the water to be treated to the settling tank is stopped, the granulated flocs in the settling tank forming the fluidized bed are intermittently stirred. Coagulation sedimentation device with means.

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