JP2002292207A - Apparatus for treating water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To carry out excellent flocculation by using an inorganic flocculant and a macromolecular flocculant (hereinafter called polymer). SOLUTION: The inorganic flocculant is mixed in raw water containing various kinds of suspension colloid, dissolved organic matter or the like in an inorganic flocculant mixing tank 10. The polymer is mixed in the inorganic flocculant-mixed raw water in a polymer mixing tank 18. After that, the formation of flocks is promoted in a flock forming tank 28, which is then settled in a settling tank 30. The supernatant water of the tank 30 is filtered by a sand filter 32, which is then distributed as the treated water. The temperature of the raw water is measured by a thermometer 40. The operation signal of a polymer addition pump 24 showing the amount of the polymer to be added to the tank 18 is fed to the controller 42. The agitation speed of a mixer 20 in the tank 18 is controlled by the controller 42 according to a temperature signal and the operation signal. When the amount of the polymer to be added to the raw water is substantially zero, the agitation speed of the mixer 20 in the tank 18 is made similar to that of the tank 28 to promote the flocculation of inorganic flocks.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water treatment apparatus for performing a coagulation treatment using an inorganic coagulant and an organic polymer coagulant (hereinafter referred to as polymer).

[0002]

2. Description of the Related Art Conventionally, flocculation treatment has been widely performed in water and wastewater treatment and various wastewater treatments in order to remove suspended solids and dissolved organic matter. In this coagulation treatment, an aluminum-based or iron-based inorganic metal salt coagulant such as aluminum sulfate, PAC (polyaluminum chloride), and ferric chloride is generally used as the coagulant.

However, depending on the quality of raw water to be treated,
With these inorganic coagulants alone, a sufficiently large floc is not formed, and the solid-liquid separation speed in the subsequent precipitation step and filtration step is low, and good treated water quality may not be obtained.

On the other hand, in the field of wastewater and sludge treatment, polymers such as polyacrylamide have been widely used for promoting floc formation and sedimentation. In the field of water supply, harmful impurities (acrylamide monomer and the like) may be contained in the polymer, and therefore, its use has not been recognized so far. However, it is possible to keep these impurity concentrations sufficiently low, and in Japan, use has been accepted from 2000 on condition that the impurity concentration is kept below the reference value.

In the coagulation treatment using an inorganic coagulant and a polymer together, first, an inorganic coagulant is injected and mixed in an inorganic mixing tank, and then the polymer is injected and mixed in a polymer mixing tank immediately thereafter. In the stirring in the polymer mixing tank, mixing is performed by rapid stirring so that the polymer is further bonded to fine flocs formed by bonding the inorganic flocculant and the suspended substance in the raw water. Further, in the subsequent stage, slow stirring is performed to grow flocs. Slow stirring is usually performed in a series of tanks of 1 to 4 stages, and the stirring conditions are set such that the stirring intensity is reduced toward the subsequent stage and the floc is grown without breaking the floc.

[0006]

Here, in the conventional wastewater treatment and the like, polymers are used mainly for the purpose of increasing the floc, increasing the sedimentation speed of the floc, and reducing the size of the sedimentation tank. Water quality targets or standards were loose. Therefore, when performing polymer injection,
The addition amount is controlled, but a constant value has been adopted for other conditions such as the stirring intensity.

[0007] However, as in the case of water purification treatment, not only coagulation and sedimentation but also filtration are performed, and severe water quality such as turbidity of 0.1 ° or less is required as filtered water. The present inventors have conducted various experiments and found that the stirring intensity in the polymer mixing tank has a great influence on the achievement of the required water quality.

[0008] In particular, since the polymer solution has a high viscosity and poor dispersibility in water, the higher the injection rate, the higher the intensity of stirring, and the more the dispersion, the more uneven the floc growth. In some cases, the fine particles cannot be completely removed.
Even when the coagulated sediment treatment water is passed through filtration, the quality of the treated water may be deteriorated. Conversely, if the injection rate is low,
If the stirring is performed with the same stirring intensity as in the case of the high injection rate, the floc that has started to grow may be destroyed, and the floc may not grow sufficiently, and the effect on the precipitation treatment may be reduced.

Also, the viscosity of the water / polymer solution changes depending on the water temperature, the state of dispersion at the time of injection mixing changes, and the processing effect also changes. In particular, at a low water temperature, the viscosity of water / polymer becomes high, so that it is difficult to disperse.

In addition, when the raw water quality is relatively good, the floc formation and sedimentation are good only by injecting the inorganic coagulant, and the sedimentation water quality and the filtered water quality are good and stable,
Polymer injection is not required. When the treatment is performed only with the inorganic coagulant without injecting the polymer, it is necessary to perform the inorganic coagulant injection, short-time rapid stirring, and then slow stirring. Therefore, when the polymer is not injected, if the stirring intensity in the polymer mixing tank is the same as in the case of injecting the polymer, the rapid stirring time becomes too long, and the floc does not become sufficiently large. In that case,
Although there is an option not to use a polymer mixing tank by providing a bypass line, the apparatus becomes complicated and a valve switching operation is required. In addition, during that time, not only is a part of the polymer mixing tank allowed to play, but also maintenance and restarting become complicated.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide a water treatment apparatus capable of performing favorable coagulation treatment.

[0012]

SUMMARY OF THE INVENTION The present invention provides an inorganic flocculant mixing tank for mixing an inorganic flocculant, and an organic polymer flocculant for mixing an organic polymer flocculant with water flowing out of the inorganic flocculant mixing tank. A water mixing apparatus having an inorganic flocculant and an organic polymer flocculant using an inorganic flocculant and an organic polymer flocculant. And the stirring strength in the organic polymer flocculant mixing tank is changed according to the organic polymer flocculant injection rate and the water temperature.

As described above, according to the present invention, the stirring intensity in the organic polymer flocculant mixing tank is changed according to the organic polymer flocculant injection rate and the water temperature. Therefore, the stirring intensity can be maintained at an appropriate level, effective coagulation treatment can be performed, and good treated water can be obtained.

The present invention also provides an inorganic flocculant mixing tank for mixing an inorganic flocculant, and an organic polymer flocculant mixing tank for mixing an organic polymer flocculant with water discharged from the inorganic flocculant mixing tank. In a water treatment apparatus for performing a flocculation treatment using an inorganic flocculant and an organic polymer flocculant, the stirring strength in the organic polymer flocculant mixing tank is calculated from the stirring strength of the preceding inorganic flocculant mixing tank. When the addition amount of the organic polymer flocculant in the organic polymer flocculant mixing tank is substantially 0, the stirring strength of the organic polymer flocculant mixing tank is adjusted to the inorganic mixing tank. It is characterized by a value smaller than the stirring intensity.

As described above, according to the present invention, when the amount of the organic polymer flocculant added to the organic polymer flocculant mixing tank is substantially 0, the stirring strength of the organic polymer flocculant mixing tank is reduced by the above-mentioned inorganic polymer flocculant mixing tank. Make the value smaller than the stirring intensity of the mixing tank.
Therefore, when the organic polymer flocculant is not added, the organic polymer flocculant mixing tank can be used as a part of the subsequent floc forming tank. Therefore, a bypass pipe or the like becomes unnecessary, and a suitable coagulation process can be performed.

Further, there is provided a floc forming tank for facilitating floc formation by slowly stirring the effluent of the organic polymer flocculant mixing tank, wherein the organic polymer flocculant in the organic polymer flocculant mixing tank is provided. When the addition amount of is substantially 0, the stirring strength of the organic polymer flocculant mixing tank is a value smaller than the stirring strength of the inorganic mixing tank and a value equal to or higher than the stirring strength of the floc forming tank. Is preferred. Thereby, suitable floc formation can be performed.

It is preferable that the stirring intensity in the organic polymer flocculant mixing tank is changed in accordance with the organic polymer flocculant injection rate and the water temperature.

The organic polymer coagulant is an anionic or nonionic organic acrylamide monomer starting material and has a molecular weight of 1,000,000 to 3,000,000.
Preferably it is 000 daltons. With such an organic polymer flocculant, formation of flocs after addition of the inorganic flocculant can be suitably performed. It is preferable to prepare a plurality of types of coagulants having different ionic properties and molecular weights in advance, and to use the type having the highest effect according to the quality of raw water.

[0019]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing the configuration of the water treatment apparatus according to the embodiment. Raw water composed of surface water, such as river water and lake water, is introduced into the inorganic mixing tank 10. This inorganic mixing tank 10
Includes a stirring blade 12a and a motor 12b for rotating the stirring blade 12a.
Is disposed. Further, the inorganic coagulant in the inorganic coagulant tank 14 is supplied to the inorganic mixing tank 10 by a pump 16. As the inorganic flocculant, for example, PAC (polyaluminum chloride: Al ₂ O ₃₎
10%). In addition, this inorganic mixing tank 10
Is usually less than 300 (S ⁻¹ ) and the residence time is less than 5 minutes, but is not limited thereto.

Next, the water mixed with the inorganic coagulant is introduced into the polymer mixing tank 18. This polymer mixing tank 18
Includes a stirring blade 20a and a motor 20b for rotating the stirring blade 20a.
The polymer flocculant in the polymer flocculant tank 22 is supplied by a pump 24. As the polymer flocculant, for example, a nonionic acrylamide polymer is used. In some cases, an anionic acrylamide polymer is suitable, but is not limited thereto. It is preferable to prepare a plurality of types of coagulants having different ionic properties and molecular weights in advance, and to use the type having the highest effect according to the quality of raw water. The rapid stirring intensity of the polymer mixing tank 18 is set to 300 (S ^-1 ) or more and the residence time is set to about 1 to 10 minutes.

The water mixed with the inorganic coagulant and the polymer coagulant from the polymer mixing tank 18 is supplied to the floc forming tank 28.
Will be introduced. The floc forming tank 28 is composed of three tanks, each of which is provided with a slow agitator 26 of a horizontal axis paddle type. The low-speed stirrer 26 can set the stirring intensity for each tank, and the stirring intensity is usually set to gradually decrease. Then, the floc is coarsened by slow stirring in the floc forming tank 28. The stirring intensity in the floc forming tank 28 is, for example, 100-60-4 from the inlet side tank.
It is set so as to gradually decrease like 0 (S ^-1 ).

The water flocculated by the inorganic coagulant and the polymer coagulant is introduced into the sedimentation tank 30, where solids are precipitated. The solids precipitated in the sedimentation tank 30 are removed as sludge outside the system, and the supernatant water is supplied to a sand filter 32. The sand filter 32 has a filter medium layer inside, and filters and separates the remaining floating solids by the filter medium layer. As a result, filtered water having a quality that can be distributed as tap water can be stably obtained. In addition, the filter medium layer
For example, it is formed of two layers of anthracite, silica sand, three layers of anthracite, silica sand, and garnet.

The filtered water is stored in a treated water tank 34, and is disinfected and then distributed. The treated water tank 34
The treated water in the sand filter 32
And the sand filter 32 can be backwashed. Further, the air from the blower 38 can be supplied to the bottom of the sand filter 32, whereby the air backwash is also performed.

A thermometer 40 is provided on the flow path of the raw water into the inorganic mixing tank 10, and the temperature of the raw water is measured. Since the temperature does not change much in each tank, it may be provided in any tank such as the inorganic mixing tank 10, the polymer mixing tank 18, the floc forming tank 28, and the like. In particular, the water temperature in the polymer mixing tank 18 is important, and it is preferable to provide a thermometer in the polymer mixing tank 18.

The detection result of the thermometer 40 is supplied to the controller 42. The controller 42 is also supplied with a signal about the flow rate of the pump 24 for adding the polymer flocculant. Then, the controller 42 controls the rotation of the motor 20b based on the amount of the water temperature polymer flocculant added, and controls the stirring intensity of the stirrer 20.

The injection rate of the inorganic coagulant, the injection rate of the polymer coagulant, the type of the polymer coagulant, etc. are determined by optimizing the raw water jar test and the like, and are changed according to the turbidity of the raw water. It has become.

In the present embodiment, PA is used as the inorganic coagulant.
Although C is used, there is no particular limitation as long as iron or aluminum is used as a raw material such as a sulfate band, ferric chloride, ferric sulfate, and polyaluminum sulfate / iron. It is also preferable to add sulfuric acid, hydrochloric acid, carbonic acid, sodium hydroxide, slaked lime, or the like as a coagulation aid.

Next, the setting of the stirring intensity of the stirrer 20 in the polymer mixing tank 18 will be described.

In this embodiment, the polymer injection rate is 0.0
In the case of 1 mg / L or more, the stirring intensity in the polymer mixing tank 18 is changed according to the polymer injection rate and the water temperature. That is, an appropriate G value is calculated according to the temperature and the polymer injection rate, and the G value in the stirrer 20 or the rotation speed of the stirrer 20 is controlled. The stirring intensity G2 in the polymer mixing tank 18 is set to a value larger than the stirring intensity G1 of the preceding inorganic mixing tank 10, and when the G1 value is less than 300S- ¹ , G2
The value is 300 (S ⁻¹ ) or more in G value.

On the other hand, when the polymer injection rate is 0 mg / L, the stirring intensity G2 of the polymer mixing tank 18 is made smaller than the stirring intensity G1 of the inorganic mixing tank 10 at the preceding stage, so that it functions as one of the slow stirring tanks. Thereby, in the polymer mixing tank 18, the coarsening of the inorganic floc is promoted.

First, the value of the stirring intensity G2 is increased as the concentration of the injected polymer increases. Further, it is preferable that the larger the concentration of the polymer stock solution used, the larger the concentration. For example, when performing control in which G2 is proportional to the injection rate,

## EQU00001 ## G2 (S.sup.- ¹ ) = Ga.times.d + Gb (1) where, d: polymer injection rate (mg / L), Ga, Gb
Is a constant, and Ga and Gb are determined in advance by an experiment using an experimental machine or a jar test.

On the other hand, if the water temperature is low, it becomes difficult to mix the polymer. Therefore, the stirring intensity is increased as the temperature decreases.

G2 (S ⁻¹ ) = Ga × d + Gb + Gc (T0−T) (2) Here, Gc is a predetermined constant, T0 is a standard temperature, and T is a water temperature at that time. According to the equation (2), the third term on the left side of the water temperature is zero at the water temperature T0, but is decreased by a predetermined value when the water temperature T becomes higher than T0, and is increased by a predetermined value when the water temperature T becomes lower. Therefore, according to this equation (2), taking into account not only the amount of injected polymer but also the water temperature at that time,
The stirring intensity G2 can be determined. Where the constant G
c is also determined by a jar test at various temperatures.
Note that this equation (2) may be applied only when the water temperature T falls below T0.

When the type of the polymer flocculant is switched to the one having the highest effect according to the quality of the raw water, the constants Ga, Gb, and Gc of the above formulas are determined in advance for each type and are used at the time of switching. It is preferable to calculate the stirring intensity from the conditions of the coagulant constant and the injection rate water temperature.

As described above, according to the present embodiment, the stirring intensity in the polymer mixing tank 18 is changed to an appropriate value according to the polymer injection rate and the water temperature. Thereby, the coagulation effect of the polymer is effectively exerted, and good treated water quality can be obtained.

On the other hand, depending on the conditions, a sufficient treated water quality may be obtained only by coagulation with an inorganic coagulant.
In such a case, there is no need to add a polymer.
However, when the addition of the polymer was stopped, the polymer mixing tank 1
When strong stirring is performed in step 8, the floc becomes fine and the quality of the treated water cannot be made sufficient. Therefore, it is conceivable to provide a bypass pipe to bypass the polymer mixing tank 18 and introduce the polymer into the floc forming tank 28. However,
When such a bypass pipe is provided, a device for controlling the switching must be provided, and a problem arises when the addition of the polymer is restarted.

In the present embodiment, even when the polymer is not used, the formation of flocs can be further promoted, not only by changing the stirring intensity, but not by inhibiting the formation of flocs. That is, for example, the stirring intensity in the polymer mixing tank 18 is set to about 100 (S ⁻¹ ), which is equivalent to the stirring intensity in the first tank of the floc forming tank 28. Thereby, better treated water quality can be obtained than when the polymer mixing tank 18 is not used while being bypassed. Further, since only the stirring intensity is changed, the effect that the apparatus is simplified and the operation management becomes easy can be obtained.

Therefore, in the present embodiment, when the amount of the polymer added is 0.1 mg / L or more, the stirrer 20 is controlled based on the above equation (2), and the amount of the polymer added is 0.1 m / L.
When it can be regarded as substantially 0 mg / L which is not more than g / L, the stirring intensity is set to a value equivalent to the stirring intensity of the floc forming tank 28 (particularly, the stirring intensity of the first tank). As a result, it is possible to carry out a treatment that always provides good treated water.

[0039]

EXAMPLES In order to confirm the effect of the present invention, a treatment experiment was conducted for 6 months using the following experimental apparatus using water from a lake or marsh as raw water.

1. Experimental conditions (1) Coagulation / sedimentation filtration device of comparative example Raw water flow rate: 1,000 m ³ / hour Inorganic mixing tank: residence time 3 minutes, stirring intensity 200
(S- ¹ )-Polymer mixing tank: residence time 5 minutes, stirring intensity 400 (S
^-1 )-Floc forming tank: 3-stage horizontal paddle type, residence time 30 minutes G value-residence time, first stage 100 (S- ¹ ) 10 minutes, 2
Stage 60 (S- ¹ ) 10 minutes, Stage 40 (S- ¹ )
10 minutes (Between the inorganic mixing tank and the floc forming tank, there is a pipe that can bypass the polymer mixing tank and a valve associated therewith.) • Sedimentation tank: sedimentation tank with an upward-flow type inclined plate, residence time 40
Min, ascending speed 3m / h ・ Sand filter: 400mm anthracite Effective diameter 1.0
mm Equivalent coefficient 1.4, silica sand 400mm Effective diameter 0.
5mm Equalization coefficient 1.3, Filtration speed 200m / day, 48
Backwash once a time ・ Inorganic flocculant: PAC (polyaluminum chloride), injection rate 40-60 mg / l ・ Polymer: Nonionic polyacrylamide, concentration of dissolving solution 1000 mg / L

(2) Coagulation-sedimentation filtration device of the present invention In the device of the present invention, (i) the stirring intensity of the polymer mixing tank is automatically controlled, and (ii) there is no pipe for bypassing the polymer mixing tank. Although the device is simpler than that of the comparative example, the device configuration and processing conditions of the comparative example are the same in other respects.

The details of the automatic control of the stirring intensity are as follows. -The stirrer is of a flash mixer type and its rotation speed is variable. The stirring intensity is controlled by the G value, and is automatically changed to the number of revolutions corresponding to the G value. -The stirring intensity makes the G value linearly proportional to the polymer injection rate. The G value determination conditional expression is

G (S ⁻¹ ) = 500 × d + 350 (3) Here, d is a polymer injection rate (mg / L), and this equation corresponds to the above-described equation (1), and Ga is a constant.
= 500 and Gb = 350. This condition was determined based on the results of a jar test performed in advance.

If the water temperature is less than 15 degrees after the sixth month,
Each time the water temperature drops by one degree, the G value is changed to the value of equation (3) by 5
(S ⁻¹ ) The value was added. The equation (4) was applied only when the water temperature was lower than 15 degrees. That is,

G (S ⁻¹ ) = 500 × d + 350 + 5 × (15−T) (4) This equation (4) corresponds to the above-mentioned equation (2), and Gc = 5 and T0 = 15, which are constants. This condition was determined based on the results of a jar test performed in advance.

When no polymer was injected, the G value was set to 100 (S ^-1 ).

In this experiment, no polymer was added,
When added, the addition amount was 0.1 mg / L or more.

2. Raw water from the experiment ・ One month from the start of the experiment: The average turbidity is about 20 ° C and the alga is 20
About 00 particles / mL occurred. Water temperature was 20-25 degrees. 2 months to 3 months from the start of the experiment: turbidity averages 30 degrees and algae are 1
The breeding was very large at 10,000 to 20,000 / mL. Water temperature was 25-30 degrees. 3 months to 4 months after the start of the experiment: The turbidity was about 10 degrees, and the number of algae was greatly reduced to about 500 / mL. Also,
Water temperature was 25-20 degrees. -5 months after the start of the experiment: The turbidity increased to 20 degrees again. Water temperature was 20-15 degrees. Also, 500 algae / m
It was about L. -6 months from the start of the experiment: turbidity of about 20 degrees, water temperature of 15 to 1
It was 0 degrees.

3. Experimental results-One month from the start of the experiment: A process was performed in which 0.1 mg / L of the polymer was injected. The stirring intensity was set to the same value as the G value of 400 (S ⁻¹ ) in both the comparative device and the present invention device. The processing result is
Both devices are equivalent, precipitation treatment water turbidity 0.3-0.4 degrees,
The filtered water turbidity was 0.03 degrees.

2nd to 3rd months: Algae (blue algae) with poor cohesion grow in the raw water, and at a polymer injection rate of 0.1 mg / L, sufficient water quality is obtained in both the turbidity of the precipitated water and the turbidity of the filtered water. In particular, the filtration water turbidity cannot stably achieve the treatment target of 0.1 degree.

Therefore, the injection rate was increased to 0.3 mg / L. Accordingly, the apparatus of the present invention automatically adjusts the stirring intensity of the polymer mixing tank to a G value of 500 according to the conditional expression (4).
(S ^{- 1} ). The stirring intensity of the comparison device is 400
(S ⁻¹ ) remains. The turbidity of the settling water was slightly unstable in the comparative device at 0.4 to 0.7 degrees, whereas the device of the present invention was stable at 0.3 to 0.4 degrees. . In addition, the turbidity of the filtered water was 0.04 ° in the comparative device, while the turbidity of the device of the present invention was 0.03 °, and the same treatment effect as in the first month was obtained. .

Fourth month: The occurrence of algae in the raw water has subsided, the turbidity of the raw water has decreased, and the water has become relatively easy to treat. Therefore, the injection of the polymer was stopped. The turbidity of the precipitation treatment water was slightly higher than that in the case of performing the injection, but the injection of the polymer was stopped because it was determined that sufficient treatment could be performed by filtration.

In the apparatus of the present invention, the agitation G value of the polymer mixing tank was automatically reduced to 100 (S ^-1 ) to make one of the floc forming tanks. The comparative device did not flow water into the polymer mixing tank, but flowed water directly from the inorganic mixing tank to the floc forming tank by a bypass pipe. The turbidity of the sedimentation treatment water is 0.9 ~
1.1 degree, while the device of the present invention 0.8 degree
で 1.0 degrees. In the apparatus of the present invention, the sedimentation water turbidity was slightly better due to the longer aggregation.
The turbidity of the filtered water was 0.04 to 0.05 degrees in the comparative device and 0.04 degrees in the device of the present invention, which was better than the comparative device.

5th month: Since the turbidity of the raw water increased again, 0.1 mg / L of the polymer was injected. In the apparatus of the present invention, after the injection is started, the turbidity of the settling water is 1.0 degree only by increasing the stirring G value of the polymer mixing tank.
It gradually improved to 0.4 degrees. On the other hand, in the comparison device, the coagulation and sedimentation treatment by passing water through the polymer mixing tank that had not been used for about one month caused the sedimentation water turbidity to temporarily change due to the water remaining in the mixing tank. It became unstable, rising to 1.2 degrees, and took about 4 hours to stabilize.

Sixth month: Since the raw water temperature was lower than 15 degrees, a mechanism for automatically adjusting the stirring intensity according to the conditional expression (3) to which the water temperature was corrected was adopted. The polymer injection rate is 0.
1 mg / L. During the period in which the water temperature dropped from 20 degrees to 15 degrees, the G value of the device changed from 400 to 425 (S ^-1 ). On the other hand, the G value of the comparison device remains at 400 (S ⁻¹ ). During this period, the turbidity of the sedimentation treatment water was 0.5
０．６0.6 degrees, while the comparison device 0.
The transition was 5 to 0.7 degrees, and the device of the present invention was better.

The results of these experiments are summarized as follows: (i) The treated water quality of the apparatus of the present invention for automatically changing the stirring intensity of the polymer mixing tank in accordance with the polymer injection rate was constantly better and more stable than the comparative apparatus. (Ii) Also in the case of the treatment in which the polymer was not injected, the present apparatus in which the polymer mixing tank was one of the coagulation tanks had better treated water quality, and the transition to the polymer injection treatment was easier. (Iii) It can be said that the treated water quality of the device of the present invention in which the stirring intensity is changed according to the water temperature was better than that of the comparative device.

[0055]

As described above, according to the present invention,
The stirring intensity in the organic polymer flocculant mixing tank is changed according to the organic polymer flocculant injection rate and the water temperature. Therefore, the stirring intensity can be maintained at an appropriate level, effective coagulation treatment can be performed, and good treated water can be obtained.

In the present invention, when the addition amount of the organic polymer flocculant in the organic polymer flocculant mixing tank is substantially 0, the stirring strength of this organic polymer flocculant mixing tank is reduced by the inorganic mixing tank. To a value smaller than the stirring intensity of Therefore, when the organic polymer flocculant is not added, the organic polymer flocculant mixing tank can be used as a part of the subsequent floc forming tank. Therefore, a suitable coagulation process can be performed without the need for a bypass pipe or the like.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an overall configuration of a water treatment apparatus according to an embodiment.

[Explanation of symbols]

10 inorganic mixing tank, 18 polymer mixing tank, 20 stirrer, 28 floc forming tank, 30 sedimentation tank, 32 sand filter, 40 thermometer, 42 controller.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Yuichiro Toba 1-2-8 Shinsuna, Koto-ku, Tokyo Organo Corporation F-term (reference) 4D015 BA21 BA24 BB09 BB12 DA04 DB02 DC06 DC08 EA06 EA07

Claims (5)

[Claims] 1. An inorganic flocculant mixing tank for mixing an inorganic flocculant, and an organic polymer flocculant mixing tank for mixing an organic polymer flocculant with water discharged from the inorganic flocculant mixing tank. ,
In a water treatment apparatus for performing a flocculation treatment using an inorganic flocculant and an organic polymer flocculant, the stirring strength in the organic polymer flocculant mixing tank is set to a value larger than the stirring strength of the preceding inorganic flocculant mixing tank. In addition, a water treatment apparatus that changes the stirring strength in the organic polymer flocculant mixing tank according to the organic polymer flocculant injection rate and the water temperature. 2. An inorganic flocculant mixing tank for mixing an inorganic flocculant, and an organic polymer flocculant mixing tank for mixing an organic polymer flocculant with water discharged from the inorganic flocculant mixing tank, In a water treatment apparatus for performing a flocculation treatment using an inorganic flocculant and an organic polymer flocculant, the stirring strength in the organic polymer flocculant mixing tank is set to a value larger than the stirring strength of the preceding inorganic flocculant mixing tank. When the addition amount of the organic polymer flocculant in the organic polymer flocculant mixing tank is substantially 0, the stirring strength of the organic polymer flocculant mixing tank is smaller than the stirring strength of the inorganic mixing tank. Water treatment equipment to value. 3. The apparatus according to claim 2, further comprising a floc forming tank for facilitating floc formation by slowly stirring the effluent of the organic polymer flocculant mixing tank,
When the addition amount of the organic polymer flocculant in the organic polymer flocculant mixing tank is substantially 0, the stirring strength of the organic polymer flocculant mixing tank is smaller than the stirring strength of the inorganic mixing tank. A water treatment apparatus having a value equal to or higher than the stirring intensity in the floc forming tank. 4. The water treatment apparatus according to claim 2, wherein the stirring strength in the organic polymer flocculant mixing tank is changed according to the organic polymer flocculant injection rate and the water temperature. 5. The water treatment apparatus according to claim 1, wherein the organic polymer flocculant is an anionic or nonionic organic acrylamide monomer as a raw material.