JP2019198806A - Water treatment method, and water treatment device - Google Patents

Abstract

To provide a water treatment method capable of producing cleaner treated water.SOLUTION: The water treatment method comprises a process of agitating water to be treated to which an inorganic coagulant is added, in an agitation tank while maintaining the retention time of the water to be treated in the agitation tank not shorter than one minute, a process of adding a cationic polymer coagulant to the water to be treated extracted from the agitation tank, a process of adding an anionic polymer coagulant to the water to be treated to which a cationic polymer coagulant has been added, and a process of separating coagulated floc by solid/liquid separation in a sedimentation tank from the water to be treated to which the anionic polymer coagulant has been added.SELECTED DRAWING: Figure 1

Description

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

  As one of the water treatment devices, a coagulation sedimentation device is widely used for water treatment, wastewater treatment, and the like. In the coagulation sedimentation apparatus, an inorganic flocculant such as iron salt or aluminum salt is added to the water to be treated to condense suspended substances (SS) contained in the water to be treated to form fine flocs, and then polymer. By adding a flocculant, coarsened flocs are formed, and the liquid is separated into sludge and treated water in a sedimentation tank.

  Patent Document 1 discloses a water treatment method in which an inorganic flocculant, a cationic polymer flocculant, and an anionic polymer flocculant are added to water to be treated. According to this document, the cationic polymer flocculant is added together with the inorganic flocculant, or is added immediately after the inorganic flocculant is added (for example, 1 second to 1 minute, particularly 5 seconds to 30 seconds) or thereafter. . Thereafter, an anionic polymer flocculant is added.

International Publication No. 2014/038537

  However, according to the study by the present inventors, depending on the time from the addition of the inorganic flocculant to the addition of the cationic polymer flocculant, the SS concentration of the treated water is increased, and the clarification of the treated water is reduced. It was sometimes damaged.

  The objective of this invention is providing the water treatment method and water treatment apparatus which can obtain a clearer treated water.

According to one aspect of the invention,
A step of stirring the water to be treated to which the inorganic flocculant has been added in a stirring tank, wherein the residence time in the stirring tank of the water to be treated is 1 minute or more;
Adding a cationic polymer flocculant to the water to be treated extracted from the stirring tank;
Adding an anionic polymer flocculant to the water to be treated with the cationic polymer flocculant added;
And a step of separating the aggregated flocs by solid-liquid separation from the water to be treated to which the anionic polymer flocculant is added in the precipitation tank.

According to another aspect of the invention,
A stirring tank for stirring the water to be treated to which the inorganic flocculant has been added in the tank, the stirring tank being configured so that the residence time of the water to be treated is 1 minute or longer;
Means for adding a cationic polymer flocculant to the water to be treated discharged from the stirring tank;
Means for adding an anionic polymer flocculant to the water to be treated with the cationic polymer flocculant;
There is provided a water treatment apparatus including a settling tank for separating agglomerated flocs by solid-liquid separation from water to be treated to which an anionic polymer flocculant is added.

  ADVANTAGE OF THE INVENTION According to this invention, the water treatment method and water treatment apparatus which can obtain clearer treated water are provided.

It is a schematic block diagram which shows one form of the water treatment apparatus which concerns on this invention. It is a schematic block diagram of the water treatment apparatus used by comparative example A1. 10 is a graph showing the results of test A. 10 is a graph showing the results of test B.

The water treatment method according to the present invention includes the following steps.
Step 1: A step of stirring the water to be treated to which the inorganic flocculant has been added in a stirring tank, wherein the residence time in the stirring tank of the water to be treated is 1 minute or longer.
Step 2: A step of adding a cationic polymer flocculant to the water to be treated extracted from the stirring tank.
Step 3: A step of adding an anionic polymer flocculant to the water to be treated to which a cationic polymer flocculant has been added.
Process 4: The process of isolate | separating an aggregation floc by solid-liquid separation from the to-be-processed water to which the anionic polymer flocculant was added in a precipitation tank.

[Raw water]
There is no restriction | limiting in particular about the to-be-processed water (raw water) supplied to a water treatment apparatus, A well-known raw water can be used suitably in the field | area of aggregation precipitation. Raw water, for example, fluorine-containing wastewater discharged from the etching process in the electronics industry, plating wastewater from plating plants, flue gas desulfurization wastewater from power plants, boiler blow wastewater discharged from plants, dyeing wastewater from dyeing plants, etc. Waste water.

[Inorganic flocculant]
Examples of inorganic flocculants include inorganic salts known in the field of coagulation precipitation, such as aluminum salts such as aluminum sulfate and polyaluminum chloride (PAC), and acidic solutions of ferric salts such as ferric chloride and polyferric sulfate. Agents can be used.

[Cationic polymer flocculant]
As the cationic polymer flocculant, those known in the field of aggregation and precipitation can be appropriately used. Examples of the cationic monomer constituting the cationic polymer flocculant include dimethylaminoethyl acrylate / methyl chloride quaternary salt (DAA) and dimethylaminoethyl methacrylate methyl chloride quaternary salt (DAM). Examples of nonionic monomers include acrylamide.

  From the viewpoint of the SS concentration of the treated water, the cationic group ratio of the cationic polymer flocculant (ratio of the cationic monomer to the total amount of the cationic monomer and nonionic monomer) is preferably low, and in particular, the cationic group ratio is 8 mol%. The following cationic polymer flocculants are preferably used. The cationic group ratio of the cationic polymer flocculant can be set to 3 mol% or more, for example.

  The weight average molecular weight of the cationic polymer flocculant can be, for example, 7 million or more, 10 million or more, and 15 million or less. In general, the larger the molecular weight, the better the coagulation ability, but the optimum molecular weight varies depending on the drainage type and sludge dewatering model, so it is better to select each time accordingly.

  The addition amount of the cationic polymer flocculant to the water to be treated is preferably 0.3 to 10 mg / L, for example. When the addition amount is 0.3 mg / L or more, it is easy to obtain the effect of the cationic polymer flocculant (the effect of the combined use of the cationic and anionic polymer flocculant), and the aggregate (even in the case of pellets) It is easy to make good. Although the addition amount may be more than 10 mg / L, in that case, the effect of increasing the particle size of the aggregate (pellet) with respect to the increase in the addition amount is small. Moreover, by making addition amount into 10 mg / L or less, the influence on a back | latter stage installation, for example, obstruction | occlusion of a membrane filtration installation, and the fall of the sludge peelability after spin-drying | dehydration can be prevented easily.

  The cationic polymer flocculant is preferably added to the water to be treated in the form of a solution previously dissolved in water. The concentration of the cationic polymer flocculant in the solution is, for example, 0.05 to 0.3 w / v%.

[Anionic polymer flocculant]
As the anionic polymer flocculant, those known in the field of aggregation and precipitation can be appropriately used. As the anionic polymer flocculant, there can be used those made of a copolymer of an anionic monomer and a nonionic monomer. An anionic monomer is acrylic acid, for example. The nonionic monomer is, for example, acrylamide.

  The optimum value of the anion group ratio of the anionic polymer flocculant (the ratio of the anionic monomer to the total amount of the anionic monomer and the nonionic monomer) varies depending on the properties of the raw water and the pH at the time of aggregation.

  The weight average molecular weight of the anionic polymer flocculant can be, for example, 10 million or more or 15 million or more, and can be 25 million or less. Similar to the cationic polymer flocculant, the larger the molecular weight, the better the coagulation ability. However, the optimum molecular weight differs depending on the drainage species and sludge dewatering model, so it is better to select each time accordingly.

  The amount of the anionic polymer flocculant added to the water to be treated is preferably 0.3 to 10 mg / L, for example. When the addition amount is 0.3 mg / L or more, it is easy to enlarge the aggregate (may be a pellet). The addition amount may be more than 10 mg / L, but in that case, the effect of increasing the particle size of the aggregate is small with respect to the increase in the addition amount. Moreover, by making addition amount into 10 mg / L or less, the influence on a back | latter stage installation, for example, obstruction | occlusion of a membrane filtration equipment, and the fall of the sludge peeling property after spin-drying | dehydration can be prevented easily.

  The anionic polymer flocculant is preferably added to the water to be treated in the form of a solution previously dissolved in water. The concentration of the anionic polymer flocculant in the solution is 0.05 to 0.3 w / v%.

[Settling tank]
As a precipitation tank, a well-known precipitation tank can be used in the field of aggregation precipitation. For example, there is a type of settling tank in which the agglomeration reaction is completed before the water to be treated flows into the settling tank, and then flows into the settling tank. There is also a type of precipitation tank in which aggregation and precipitation are performed in the precipitation tank. As the latter type of precipitation tank, in particular, there is a precipitation tank that is equipped with a stirring blade for performing slow stirring in the precipitation tank and that performs aggregation and granulation operations in the precipitation tank. In a sedimentation tank in which aggregation and granulation are performed in the sedimentation tank, aggregates having a high density and a high sedimentation speed can be formed in the sedimentation tank, so that water treatment can be performed at a higher flow rate.

[Water treatment equipment]
The inorganic flocculant, the cationic polymer flocculant, and the anionic polymer flocculant are added to the water to be treated in this order. Therefore, step 1 is performed before the cationic polymer flocculant and the anionic polymer flocculant are added (before step 2 and before step 3). Step 2 is performed before the anionic polymer flocculant is added (before Step 3).

  Although the example of a water treatment method and a water treatment apparatus is demonstrated using FIG. 1, this invention is not limited by this. Since this water treatment apparatus can be specifically referred to as a “aggregation precipitation apparatus”, it may be referred to as a “aggregation precipitation apparatus” below. In addition, “cationic polymer” and “anionic polymer” in FIG. 1 mean a cationic polymer flocculant and an anionic polymer flocculant, respectively (the same applies to FIG. 2).

・ Process 1
Hereinafter, the stirring tank used in Step 1 may be referred to as “inorganic flocculant reaction tank” or “reaction tank”. Raw water is supplied to the reaction tank 10 from the line L1. The raw water can be supplied to the reaction tank 10 after being subjected to other treatments. The other treatment is, for example, a treatment for forming a suspended substance from ions such as fluorine and metal dissolved in raw water.

In the reaction tank 10, an inorganic flocculant (PAC in FIG. 1) is added to the water to be treated from the line L6, and an alkali for pH adjustment (caustic soda in FIG. 1) is added from the line L7. Stirring is performed by a stirrer 11 provided in the reaction vessel 10. This agitation is performed to uniformly disperse the flocculant and form fine flocs in the reaction vessel to which the inorganic flocculant is added. From the viewpoint of suppressing residual unreacted particles, it is preferable that the stirring strength G value of this stirring is high. Further, since the floc formed in the reaction tank is small and there is no fear of destruction, the stirring strength G value in the reaction tank may be high. Therefore, the stirring intensity G value in the reaction vessel 10 is preferably 100 to 500 s ⁻¹ . The stirring intensity G value can be obtained by the following equation.

  As shown in FIG. 1, the line L6 may be connected to the reaction vessel 10, but it is not necessary, and for example, it may be connected to the line L1. That is, an inorganic flocculant may be added to the raw water (treated water) before flowing into the reaction tank 10.

  The residence time of the water to be treated to which the inorganic flocculant is added in the stirring vessel, that is, the reaction vessel 10 (hereinafter sometimes referred to as “residence time of step 1”) is 1 minute or longer. As long as this residence time is 1 minute or longer, the residence time can be determined according to the drainage species and the substance to be removed. For example, when the raw water is fluorine-containing wastewater, setting the residence time to 15 minutes or more is effective for removing residual fluorine. However, even in this case, if the residence time is 1 minute or longer, clear treated water can be obtained in terms of the SS concentration of treated water. The inorganic flocculant functions to form a core of the floc floc. Therefore, if this residence time is less than 1 minute, the flocculent floc nuclei cannot be sufficiently formed, and even if a cationic polymer flocculant and an anionic polymer flocculant are added thereafter, they are coarse and strong. High floc cannot be sufficiently formed, and it is difficult to obtain clear treated water and to obtain concentrated sludge having a high concentration.

  The reaction vessel 10 can be designed so that the residence time in step 1 is 1 minute or longer.

・ Process 2
The water to be treated extracted from the reaction tank 10 is sent to the primary flocculation tank 20 at the subsequent stage via the line L2. The primary aggregation tank 20 is a tank provided with a stirrer 21 as necessary. In the primary flocculation tank, the nonionic chain of the cationic polymer flocculant and the fine flocs derived from the inorganic flocculant are bonded by hydrogen bonding, and the flocs are coarsened. The stirring strength G value in the primary flocculation tank may be smaller than the G value in the reaction tank in order to suppress breakage of flocs. Alternatively, since an anionic polymer flocculant is added later to further coarsen the floc, the G value in the primary flocculation tank may be as high as in the reaction tank. Therefore, the stirring strength G value in the primary flocculation tank 20 is preferably 10 to 500 s ⁻¹ .

  A cationic polymer flocculant is added from the line L8 to the water to be treated which has flowed into the primary flocculation tank 20, and as a result, an aggregate (primary flocculation floc) is formed. In the primary flocculation tank 20, stirring can be performed using a stirrer 21. As shown in FIG. 1, the line L8 may be connected to the primary flocculation tank 20, but this is not necessary, and for example, it may be connected to the line L2. That is, a cationic polymer flocculant may be added to the water to be treated downstream from the reaction tank 10 and upstream from the primary flocculation tank 20. Unless otherwise specified, “upstream” and “downstream” in this specification are based on the flow direction of the water to be treated. Moreover, the stirrer 21 is not necessarily required. Further, the primary flocculation tank 20 is not necessarily required. In this case, for example, a cationic polymer flocculant may be added in a pipe and mixed using a line mixer or the like.

  Residence time of water to be treated in the water treatment apparatus from the addition of the cationic polymer flocculant to the addition of the anionic polymer flocculant (hereinafter referred to as “residence time of step 2”) .) Is preferably 1 minute or longer, more preferably 2 minutes or longer. When the residence time in step 2 is 1 minute or longer, it is easy to obtain a coarse aggregated floc having a high strength, and it is easy to obtain clear treated water and concentrated sludge having a high concentration. In this case, after the flocs derived from the inorganic flocculant and the cationic polymer flocculant are well bonded, the floc is adsorbed by the anionic polymer flocculant. Therefore, it is easy to obtain a crosslinked structure by using a cationic and anionic polymer flocculant in combination. As a result, it becomes easy to obtain a coarse aggregate floc having high strength.

  In order to make the residence time of the process 2 1 minute or more, the residence time in the primary coagulation tank 20 of the water to be treated to which the cationic polymer flocculant is added can be 1 minute or more. The primary flocculation tank 20 can be designed so that this condition is satisfied.

  Means for adding the cationic polymer flocculant to the water to be treated extracted from the reaction tank 10 includes a primary coagulation tank 20 and lines L2 and L8. When the primary flocculation tank 20 is not used, the means includes a line L2 and a line L8 (however, connected to the line L2), and a line mixer for mixing may be used.

・ Process 3
An anionic polymer flocculant is added from the line L9 to the water to be treated extracted from the primary flocculation tank 20 to the line L3. In the treated water supply channel (line L3) to the settling tank 30, an anionic polymer flocculant can be added. In this case, the line L9 is connected to the line L3. Alternatively, an anionic polymer flocculant can be added in the precipitation tank 30. In this case, for example, a precipitation tank (not shown) provided with a center well can be used as the precipitation tank 30, and an anionic polymer flocculant can be added from the line L9 to the water to be treated in the center well.

  Means for adding the anionic polymer flocculant to the water to be treated to which the cationic polymer flocculant has been added includes lines L3 and L9. Alternatively, the means includes a line L3, the center well, and a line L9 (provided that an anionic polymer flocculant can be added to the center well).

・ Process 4
In order to separate the flocs from the water to be treated to which the anionic polymer flocculant has been added, the precipitation tank 30 is used. The water to be treated to which the anionic polymer flocculant is added flows into the precipitation tank 30 from the lower part or the bottom part through the line L3 (or through the center well in the precipitation tank). The sludge blanket Z1 is formed by the upward flow of the water to be treated. The settling tank 30 in this example is a granulation type settling tank. In this settling tank, the water to be treated to which the anionic polymer flocculant is added is agglomerated and granulated by stirring in the settling tank. The sludge blanket (pellet blanket) Z1 is formed with pellet sludge. For this stirring, the settling tank 30 is provided with a stirrer 31 for stirring the water to be treated driven by the motor M. A layer Z2 of clarified water is formed on the sludge blanket Z1. From the clarified water layer Z2, clarified water is discharged to the line L4 as treated water. In this way, the aggregated floc (pellet sludge) is separated from the clarified water by solid-liquid separation.

  A concentrating part 33 that communicates with the inside of the precipitation tank 30 through an opening 32 is provided on a side surface of the precipitation tank 30. The concentration unit 33 forms a tank different from the precipitation tank. Part of the pellet sludge in the sedimentation tank 30 (pellets floating above the sludge blanket Z1) is overflowed and transferred to the concentration unit 33, where it is sedimented and concentrated in the concentration unit 33. Connected to the lower part of the concentration unit 33 is a line L5 for extracting the concentrated sludge from the layer Z3 of concentrated sludge (pellet concentrated to a high concentration) accumulated in the concentration unit 33. The pump P discharges the concentrated sludge from the line L5 to the outside of the coagulation sedimentation apparatus.

[Test A]
<Examples A1 to A4>
A continuous water flow test was carried out using a water treatment apparatus having the configuration shown in FIG. That is, PAC and cationic polymer flocculant were added in separate tanks. The test conditions were as follows.

Test condition raw water: Kaolin simulated drainage (containing kaolin at a concentration of 100 mg / L. The water for creating simulated drainage was groundwater filtered. Conductivity: 0.3 mS / cm).
Capacity of the reaction tank and the primary flocculation tank: 23.8 L each.
Agitation strength G value in the reaction tank and the primary flocculation tank: 105 s ⁻¹ respectively.
Raw water flow rate:
Example A1: 40 L / h (precipitation tank water flow LV (linear velocity): 5 m / h, residence time in the reaction tank and primary coagulation tank: 36.4 minutes each).
Example A2: 80 L / h (precipitation tank water flow LV: 10 m / h, residence time in the reaction tank and primary coagulation tank: 18.2 minutes each).
Example A3: 120 L / h (precipitation tank water flow LV: 15 m / h, residence time in the reaction tank and primary coagulation tank: 12.1 minutes each).
Example A4: 240 L / h (precipitation tank water flow LV: 30 m / h, residence time in the reaction tank and primary coagulation tank: 6.1 minutes each).
PAC addition amount (concentration in treated water after addition): 120 mg / L.
Cationic polymer flocculant addition amount (concentration in treated water after addition): 0.5 mg / L.
Cationic group ratio of cationic polymer flocculant: 8 mol%.
Anionic polymer flocculant addition amount (concentration in treated water after addition): 1.0 mg / L.
Anionic group ratio of anionic polymer flocculant: 4 mol%.
Precipitation tank diameter: φ (diameter) 100 mm.

  In addition, the water flow LV of the settling tank is based on the flow path cross-sectional area in the sludge blanket Z1 portion of the settling tank. That is, in calculating this water flow LV, the concentration unit 33 is not considered.

<Comparative Examples A1 to A4>
A continuous water flow test was performed using the water treatment apparatus shown in FIG. This water treatment apparatus is obtained by adding the following modification to the water treatment apparatus used in Example A1. That is, raw water was supplied from the line L2. Further, the PAC supply line L6 and the alkali supply line L7 were connected to the primary flocculation tank 20. The reaction vessel 10 was not used.

  That is, in this example, PAC and cationic polymer flocculant were added to the water to be treated in the same tank. In other words, PAC and the cationic polymer flocculant were added to the water to be treated substantially simultaneously.

  In Comparative Examples A1 to A4, a continuous water flow test was performed in the same manner as in Examples A1 to A4 except for the above. Therefore, in Comparative Examples A1 to A4, the residence times in the primary flocculation tank are the same as those in Examples A1 to A4, respectively.

  FIG. 3 shows the test results. In FIG. 3, the horizontal axis represents the water flow LV of the settling tank 30, and the vertical axis represents the SS concentration of the treated water. In FIG. 3, “separate addition” means data of Examples A1 to A4, and “simultaneous addition” means data of Comparative Examples A1 to A4.

  It is clear that clear treated water can be obtained when adding the inorganic flocculant and the cationic polymer flocculant separately (in the same reaction tank) separately (in separate reaction tanks). It became. Moreover, the difference of the treated water SS density | concentration (difference between the case of simultaneous addition and the case of another addition) became so remarkable that the sedimentation tank water flow LV increased.

Furthermore, in the test (Example A4 and Comparative Example A4) in which the sedimentation tank water flow LV was 30 m / h, the sludge overflowed from the sludge blanket Z1 part was settled and concentrated for 30 minutes, and the concentrated sludge was extracted. It was as follows when the sludge density | concentration of each concentrated sludge was measured.
Sludge concentration in the case of simultaneous addition (Comparative Example A4): 2.4% by mass.
Sludge concentration in the case of separate addition (Example A4): 3.5% by mass.

  About the sludge density | concentration, the case where the inorganic flocculant and the cationic polymer flocculant were added to another tank showed a higher value than the case where it was added to the same tank. That is, it can be said that the latter was able to form an agglomerate having a high sedimentation rate and high concentration.

[Test B]
In this test, the influence of the residence time in step 1 was investigated. The water treatment apparatus used in Example A1 was used. However, by changing the size of the inorganic flocculant reaction tank 10, the residence time in this tank, that is, the residence time in Step 1 was changed. The water flow LV of the settling tank 30 was 30 m / h. In Examples B1 and B2, the residence time in step 1 was set to 1 (reaction tank capacity 4 L) and 2 (reaction tank capacity 8 L), respectively. In Comparative Example B1, the residence time in Step 1 was 0.5 minutes (reaction tank capacity 2 L). In this test, the residence time in the primary flocculation tank was all 6.1 minutes.

  Except for the above, the same test as in Example A1 was performed. FIG. 4 shows the test results. In this figure, Example A4 (residence time of step 1: 6.1 minutes. Precipitation tank water flow LV 30 m / h), Comparative example A4 (retention time of process 1: 0 minutes. Precipitation tank water flow LV: 30 m / h) h) is also shown. In FIG. 4, the horizontal axis represents the residence time in step 1, and the vertical axis represents the SS concentration of the treated water obtained.

  As a result of the experiment, by setting the residence time in Step 1 to 1 minute or longer, and thus adding the cationic polymer flocculant after the condensation reaction with the inorganic flocculant for 1 minute or longer, the water flow LV of the precipitation tank It became clear that clear treated water can be obtained even if the water content is high.

[Test C]
<Example C1 and Comparative Example C1>
A continuous water flow test was conducted using a large water treatment apparatus. In Example C1 and Comparative Example C1, each had the same configuration as the water treatment device used in Example A1 and Comparative Example A1, but a larger water treatment device was used. The test conditions are as follows.

Test condition raw water: Kaolin simulated wastewater (containing kaolin at a concentration of 100 mg / L. Water for preparing simulated wastewater was obtained by filtering groundwater).
Raw water flow rate: 19 m ³ / h (precipitation tank flow LV: 20 m / h, residence time in reaction tank and primary coagulation tank: 3.2 minutes each).
Capacity of reaction tank and primary flocculation tank: 1000 L each.
Agitation strength G value in the reaction tank and the primary flocculation tank: 387 s ⁻¹ .
PAC addition amount (concentration in treated water after addition): 120 mg / L.
Cationic polymer flocculant addition amount (concentration in treated water after addition): 0.5 mg / L.
Cationic group ratio of cationic polymer flocculant: 8 mol%.
Anionic polymer flocculant addition amount (concentration in treated water after addition): 1.0 mg / L.
Anionic group ratio of anionic polymer flocculant: 4 mol%.
Precipitation tank diameter: φ1100 mm.

Except for the above, in the same manner as in Example A1 (Example C1) or in the same manner as in Comparative Example A1 (Comparative Example C1), a continuous water flow test was performed to measure the SS concentration of the treated water obtained. . The results were as follows.
Example C1: 1.8 mg / L.
Comparative Example C1: 5.2 mg / L.

<Example C2 and Comparative Example C2>
In Example C2 and Comparative Example C2, respectively, except that a cationic polymer flocculant having a cation group ratio of 3 mol% was used as the cationic polymer flocculant, in the same manner as in Example C1 and Comparative Example C1, A continuous water test was performed to measure the SS concentration of the treated water. The results were as follows.
Example C2: 1.2 mg / L.
Comparative Example C2: 4.3 mg / L.

  From these results, it was found that it is better to add an inorganic flocculant and a cationic polymer flocculant separately even when the apparatus is enlarged.

[Test D]
The water treatment performance when the raw water type was changed was investigated. As raw water, fluorine-containing water was used.

<Examples D1 to D2, Comparative Examples D1 to D4>
In Examples D1 and D2, the water treatment apparatus used in Example A1 was modified as follows and used. That is, a tank (not shown) provided with a stirrer was added upstream of the reaction tank 10. Raw water was supplied to this tank. In this tank, Ca (OH) ₂ (slaked lime aqueous solution) and HCl (hydrochloric acid) were added to the raw water and stirred. From this tank, water to be treated containing a sparingly soluble fluorine compound (CaF ₂ ) as a suspended substance was extracted, and this water to be treated was supplied to the line L1.

In Comparative Examples D1 to D4, the water treatment apparatus used in Comparative Example A1 was modified and used in the same manner as described above. However, the water to be treated containing a hardly soluble fluorine compound (CaF ₂ ) was supplied to the line L2.

  In Example D1, the residence time of the reaction tank and the primary flocculation tank is 6.1 minutes, respectively. In Example D2, the residence time of the reaction tank and the primary flocculation tank is 5.2 minutes, respectively. In Comparative Examples D1 to D4, there is no reaction tank, the residence times of the primary flocculation tanks of Comparative Examples D1 and D3 are 6.1 minutes, and the residence times of the primary flocculation tanks of Comparative Examples D2 and D4 are 5.2 minutes, respectively. is there.

Test conditions The test conditions are as follows.
Raw water: Fluorine-containing simulated waste water (fluorine concentration 520 mg / L, water containing many other ions, conductivity 3.6 mS / cm).
Raw water flow rate: as shown in Table 1.
Reaction tank, primary coagulation tank capacity: 23.8 L.
Reaction tank, primary agglomeration tank stirring strength G value: 105 s ⁻¹ .
PAC addition amount (concentration in treated water after addition): 700 mg / L.
Cationic polymer flocculant addition amount (concentration in treated water after addition): shown in Table 1.
Cationic polymer flocculant cationic group ratio: 8 mol%.
Anionic polymer flocculant addition amount (concentration in treated water after addition): shown in Table 1.
Anionic polymer flocculant anion group ratio: 4 mol%.
Precipitation tank diameter: φ100 mm.

  Except for the above, SS was treated in the same manner as in Example A1 (Examples D1 to D2) or as in Comparative Example A1 (Comparative Examples D1 to D4). Concentration was measured. The results are shown in Table 1.

  As a result of the experiment, even when the type of raw water is changed, when the inorganic flocculant and the cationic polymer flocculant are added to the same reaction tank (Comparative Examples D1 to D4), they are added to separate reaction tanks (Examples) It became clear that D1 and D2) can obtain clear treated water.

  In addition, the inorganic flocculant and the cationic polymer flocculant were added simultaneously, and the total amount of the polymer flocculant was increased to 6 mg / L (Comparative Examples D3 and D4). When the polymer flocculant is added separately and the total amount of the polymer flocculant is 3 mg / L (Examples D1 and D2), the treated water SS is lower and clear treated water is obtained. Therefore, the amount of the polymer flocculant used can be reduced.

[Test E]
A jar test was performed according to the following procedure, and the size of the aggregate was examined.

<Jartest E1>
As raw water, the same raw water as that used in Example A1 was used. Into a beaker, 500 mL of raw water was added, and an inorganic flocculant (PAC) was added thereto to a concentration of 120 mg / L, adjusted to pH 7 with NaOH, and rapidly stirred at 150 rpm for 5 minutes. Subsequently, a cationic polymer flocculant was added to a concentration of 0.5 mg / L, and rapid stirring was performed at 150 rpm for 1 minute. Subsequently, an anionic polymer flocculant was added to a concentration of 1 mg / L, rapid stirring at 150 rpm was performed for 1 minute, and then slow stirring at 40 rpm was performed for 3 minutes.

<Jartest E2>
After the addition of the cationic polymer flocculant, the same test as in the jar test E1 was conducted except that the rapid stirring time before the addition of the anionic polymer flocculant was 2 minutes.

<Jartest E3>
The same operation as in the jar test E1 was performed until rapid stirring (5 minutes) after the addition of the inorganic flocculant. Subsequently, a cationic polymer flocculant and an anionic polymer flocculant were simultaneously added, and after rapid stirring at 150 rpm for 1 minute, slow stirring at 40 rpm was performed for 5 minutes.

<Jartest E4>
After the addition of the cationic polymer flocculant, the same test as in the jar test E1 was conducted except that the rapid stirring time before the addition of the anionic polymer flocculant was 30 seconds.

  In each jar test, the size (aggregation floc diameter) of aggregates contained in the obtained liquid was measured. The results are shown in Table 2.

  From this result, it can be said that the stirring time from the addition of the cationic polymer flocculant to the addition of the anionic polymer flocculant is preferably 1 minute or longer, and therefore the residence time in Step 2 is preferably 1 minute or longer.

  As a result, the following can be said. That is, after adding the inorganic flocculant, the reaction is performed by stirring for 1 minute or longer (the residence time in Step 1 is 1 minute or longer), then the cationic polymer flocculant is added, and finally the anionic polymer flocculant To form agglomerates, for example, when the water flow LV of the settling tank is as high as 5 m / h or more, particularly 10 m / h or more, it is clear even if the addition amount of the polymer flocculant is small. Treated water can be obtained. In addition, the sedimentation rate of the aggregate itself increases, so that sedimentation concentration tends to proceed. Therefore, when sludge is settled and concentrated, concentrated sludge having a higher concentration can be obtained.

Claims (7)

A step of stirring the water to be treated to which the inorganic flocculant has been added in a stirring tank, wherein the residence time in the stirring tank of the water to be treated is 1 minute or more;
Adding a cationic polymer flocculant to the water to be treated extracted from the stirring tank;
Adding an anionic polymer flocculant to the water to be treated with the cationic polymer flocculant added;
And a step of separating the aggregated flocs by solid-liquid separation from the water to be treated to which the anionic polymer flocculant is added in the precipitation tank.   The water treatment method according to claim 1, wherein a residence time of water to be treated from the addition of the cationic polymer flocculant to the addition of the anionic polymer flocculant is 1 minute or more. In the supply channel of the water to be treated to the settling tank or the settling tank, the anionic polymer flocculant is added,
The water treatment method according to claim 1 or 2, wherein the water to be treated to which the anionic polymer flocculant is added is granulated by stirring in a sedimentation tank, and a sludge blanket is formed with pellet sludge.   The water treatment method according to claim 3, wherein a part of the pellet sludge that forms the sludge blanket is transferred to another tank, and is settled and concentrated in the other tank.   The water treatment method according to any one of claims 1 to 4, wherein a water passage speed in the settling tank is 5 m / h or more.   The water treatment method according to claim 5, wherein a water passage speed in the settling tank is 10 m / h or more. A stirring tank for stirring the water to be treated to which the inorganic flocculant has been added in the tank, the stirring tank being configured so that the residence time of the water to be treated is 1 minute or longer;
Means for adding a cationic polymer flocculant to the water to be treated discharged from the stirring tank;
Means for adding an anionic polymer flocculant to the water to be treated with the cationic polymer flocculant;
A water treatment apparatus comprising: a settling tank that separates aggregate flocs by solid-liquid separation from water to be treated to which an anionic polymer flocculant is added.

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