JP2002066209A - Method for controlling injection of flocculant in water treatment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control the variation in the quality of treated water, while the quality is kept surely within a target level, by optimizing the injection ratio of a polymer flocculant on the premise of the existence of an upper limit in the injection ratio of the polymer flocculant and in consideration of a large variation in the turbidity of raw water. SOLUTION: In water treatment in which suspended substances in the raw water are flocculated by injecting an inorganic flocculant and the polymer flocculant, a formula for calculating the injection ratio of the polymer flocculant to the turbidity of the raw water, is set based on the following two calculation formula, i.e., a calculation formula A in which the injection ratio of the polymer flocculant is made proportional to the injection ratio of the inorganic flocculant and in which a predetermined upper limit injection ratio reaches the ceiling and a calculation formula B in which the injection ratio of the polymer flocculant is made proportional to the injection ratio of the inorganic flocculant so that the injection ratio of the polymer flocculant is the above upper limit injection ratio when the injection ratio of the inorganic flocculant is the maximum injection ratio, and correspondingly to the size of the variation in the turbidity of the raw water and the present turbidity of the raw water, one of the two calculation formulas is selected, and the injection ratio of the polymer flocculant is controlled on the basis of the selected calculation formula.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling the injection of a flocculant suitable for water treatment such as surface water such as river water or lake water as raw water or solid-liquid separation of industrial water or waste water. .

[0002]

2. Description of the Related Art In water purification treatment and wastewater treatment, it is necessary to remove suspended substances in raw water and treat the treated water to a treatment water having a predetermined turbidity or less. There are many. When performing coagulation sedimentation treatment, usually,
Inorganic flocculants and polymer flocculants (especially organic polymer flocculants)
Is used to carry out the coagulation precipitation treatment.

Usually, an inorganic flocculant is first added to raw water, mixed sufficiently with a stirrer or the like to form fine flocs, and then an organic polymer flocculant is added to form coarse flocs. I have to. The coarse floc is settled and separated in a sedimentation basin, and the remaining fine floc is separated by filtration in a filter pond or a filter to finally obtain treated water having a predetermined turbidity or less.

[0004] The injection rate of the flocculant is determined as follows. The injection rate of the inorganic coagulant is artificially controlled based on the result of injection at a value proportional to the turbidity of the raw water or a jar test using a container or a beaker.
On the other hand, the organic polymer flocculant is set at a constant injection rate or is artificially controlled in proportion to the raw water turbidity or based on the results of a jar test or the like.

[0005]

SUMMARY OF THE INVENTION As a polymer flocculant,
For example, when an acrylamide-based organic polymer flocculant is used for water purification treatment, the presence of an acrylamide monomer that is a mutagenic substance poses a problem. Therefore, the injection rate of the acrylamide-based organic polymer flocculant is limited. For example, in Japan, 1 mg / L is specified as the maximum injection rate by the Water Supply Law. Therefore, even if the optimal organic polymer flocculant injection rate obtained by a jar test or the like is 1 mg / L or more, injection cannot be performed at a certain injection rate or more (that is, at an upper limit injection rate or more). Usually, the optimal injection rate of the inorganic coagulant increases or decreases in proportion to the change in raw water turbidity,
Further, the optimal injection rate of the organic polymer flocculant also increases or decreases. Accordingly, for the inorganic flocculant, the injection rate may be changed according to the fluctuation of the raw water turbidity, but for the organic polymer flocculant, depending on the raw water quality, the treatment is performed with the injection rate lower than the optimum injection rate. That would have to happen.

Therefore, when controlling the injection rate of the organic polymer flocculant in proportion to the turbidity of the raw water and the injection rate of the inorganic flocculant, when the injection rate of the inorganic flocculant is relatively low, It is considered that the injection rate of the agent peaks out. That is, when the injection rate of the inorganic coagulant is not less than a certain injection rate, there is a region where the organic polymer coagulant cannot be injected in proportion to the inorganic coagulant. As described above, the upper limit injection rate of an organic polymer flocculant, particularly an acrylamide-based organic polymer flocculant, is 1 mg / L in the Japanese water supply law. Has to be controlled to a practically constant value (upper limit).

However, if the upper limit of the injection rate of the polymer flocculant is set at the upper limit and the injection rate of the polymer flocculant is actually controlled in accordance with the characteristic, the following problem occurs. If the injection rate of the inorganic coagulant is 66% of the maximum injection rate (this maximum injection rate is determined based on a predetermined maximum value of the raw water turbidity), the upper limit of the organic polymer coagulant is injected. In the case of the ratio, there is no adjustment range of the organic polymer coagulant with respect to the remaining 34% injection ratio adjustment range of the inorganic coagulant, so that it is changed corresponding to the change of the injection ratio of the inorganic coagulant. Unstable conditions cannot be achieved. In other words, in this range, even if the turbidity of the raw water increases, the operation of increasing the polymer coagulant injection rate in response to the increase and suppressing the increase in the turbidity of the treated water cannot be performed. Therefore, even if the absolute value of the treated water turbidity is within a certain target level, the turbidity of the treated water, which has been kept low until then, starts to increase suddenly with the rise of the raw water turbidity. An area is generated, giving an impression as if the predetermined processing, that is, the processing for reducing the turbidity of the final treated water within a predetermined value, was insufficient. In general, such an impression is given to a water treatment department. In addition, since the quality of the treated water that has been stable until then starts to deteriorate relatively rapidly, such a rapid change is not preferable for various processes using the treated water.

[0008] Therefore, an object of the present invention is to presuppose that an upper limit exists for the injection rate of a polymer flocculant and to take into account that the turbidity of raw water may fluctuate greatly. By controlling the injection rate of the agent more optimally, it is possible to suppress the fluctuation of the quality of the treated water while keeping the quality of the treated water within the target level.

[0009]

In order to solve the above-mentioned problems, a method for controlling the injection of a flocculant in water treatment according to the present invention is characterized in that a suspended substance in raw water is injected with an inorganic flocculant and a polymer flocculant. In the water treatment for coagulation, the formula for calculating the injection rate of the polymer flocculant with respect to the raw water turbidity, the injection rate of the polymer flocculant is proportional to the injection rate of the inorganic coagulant, and the upper limit is set at a predetermined upper limit injection rate. Formula A, and the injection rate of the inorganic flocculant is set such that the injection rate of the polymer flocculant becomes the upper limit injection rate when the injection rate of the inorganic flocculant is the maximum injection rate. It is set as two calculation formulas of the calculation formula B proportional to, and according to the magnitude of the fluctuation of the raw water turbidity and the current raw water turbidity, one of the two calculation formulas is selected,
The method comprises controlling the injection rate of the polymer flocculant based on the selected calculation formula.

In this method, it is also possible to actually grasp the magnitude of the fluctuation of the raw water turbidity and control it as described above, or to predict the magnitude of the fluctuation of the raw water turbidity and predict the fluctuation. It is also possible to control as described above based on the value. In the latter case, for example, the magnitude of the fluctuation of the raw water turbidity is predicted from the rate of change of the raw water turbidity, and the maximum value within the predicted fluctuation corresponds to the peak start point of the upper limit injection rate in the calculation formula A. If less than the raw water turbidity, select the calculation formula A, if the maximum value within the predicted fluctuation exceeds the raw water turbidity corresponding to the peak start point of the upper limit injection rate in the calculation formula A, When the raw water turbidity rises to a level lower than the raw water turbidity corresponding to the peaking start point, the calculation formula A
From the calculation formula B.

In addition, in what state the selection and switching of the calculation formulas A and B are performed can be freely determined as appropriate. For example, if the raw water turbidity is equal to or less than a predetermined magnification relative to the average turbidity of the raw water, the calculation formula A is selected, and if the turbidity exceeds the turbidity, the calculation formula B is selected. Can be As the predetermined predetermined magnification,
For example, it can be determined from the range of 2 to 10 times the average turbidity of raw water.

The upper limit injection rate of the polymer flocculant is set, for example, in the range of 0.2 to 2.0 mg / L. When using an acrylamide-based organic polymer flocculant for water purification treatment, in Japan, the upper limit injection rate may be set to 1.0 mg / L.

The injection rate of the inorganic coagulant may be an injection rate proportional to the raw water turbidity as in the conventional method. However, the proportional injection rate may have an inflection point with respect to the characteristic axis of the raw water turbidity.

In the method for controlling coagulant injection in water treatment according to the present invention as described above, the calculation formula A and the calculation formula B are used.
By setting the optimum characteristics (calculation formula) according to the raw water condition at that time according to the magnitude of the fluctuation of the raw water turbidity and the current raw water turbidity, the conventional raw water turbidity increases Even in this case, control in a region where the injection rate of the polymer flocculant is suppressed to a constant upper limit injection rate of the plateau can be stopped. Therefore, relatively rapid fluctuation of the treated water turbidity, which has occurred in the conventional control region, does not occur, and stable treated water quality with little fluctuation can be obtained.

By shifting from the control characteristic based on the calculation formula A to the control characteristic based on the calculation formula B, the quality of the treated water may be slightly deteriorated as compared with the case where the control is performed based on the calculation formula A. If water quality within the target level is finally obtained, no particular problem will occur. The advantage of obtaining a stable treated water quality without fluctuation described above is much greater than the disadvantage due to this slight deterioration of water quality,
The stable quality of the treated water also eliminates the adverse effects on each process utilizing the treated water.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a water treatment apparatus for applying a coagulant injection control method in water treatment according to one embodiment of the present invention. In FIG. 1, the turbidity of a raw water 1 is measured by a turbidity meter 2 and sent to an inorganic coagulant mixing tank 3, and an inorganic coagulant 4 is injected into the mixing tank 3 via a pump 5. In the mixing tank 3, the raw water 1 and the injected inorganic flocculant 4 are stirred by a stirrer 7 driven by a motor 6, and the suspended substance in the raw water 1 is combined with the inorganic flocculant 4 to form fine flocs. Agglomerated.

The raw water in the mixing tank 2 in which the fine flocs are formed is sent to the polymer flocculant mixing tank 8, where the raw water is mixed.
A polymer flocculant 9 is injected via a pump 10. In the mixing tank 8, the polymer flocculant 9 is injected and stirred by the stirrer 12 driven by the motor 11, and the fine particles formed in the raw water by the bond between the inorganic flocculant and the suspended substance are formed. The flocs are grown into coarse flocs by the polymer flocculant 9.

The raw water turbidity signal measured by the turbidity meter 2 is sent to a sequencer 13 where
For example, the injection rate of the inorganic coagulant 4 and the injection rate of the polymer coagulant 9 are calculated based on the calculation formula of the characteristics as shown in FIG. The pumps 5 and 10 are controlled based on the calculated injection rates, and the actual injection rates of the inorganic coagulant and the polymer coagulant are controlled. The characteristics shown in FIG. 2 will be described later.

Further, in this embodiment, the water to be treated from the polymer flocculant mixing tank 8 is sent to the three floc forming ponds 14 to which the water to be treated is sequentially transferred, and the horizontal axis provided in each tank. By the stirring by the paddle-type stirrer 15, the series of flocs described above is further advanced.

The water to be treated from the floc forming pond 14 is sent to a sedimentation pond 16, where the coarsened floc is settled and separated. In this embodiment, the partition wall 17 inside the settling basin 16 is used.
Before and after, a downward flow is reversed to an upward flow, and sedimentation separation is promoted. An inclined plate or the like may be provided at a portion where an upward flow or a downward flow is generated to further promote separation.

Precipitated water from the sedimentation basin 16 is sent to a filtration device 18 and filtered by passing through a filtration layer 19. The filter layer 19 can be formed by a filter medium,
For example, it can be formed into a single bed or a double bed using anthracite and / or silica sand.

The treated water from the filtration device 18 is taken out as purified water 20. In this embodiment, the extracted purified water 2
0 is temporarily stored in the purified water tank 21, and the purified water in the tank 21 is sent to the next step or the like as the final treated water 22. From the bottom of the water purification tank 21, part of the purified water in the water purification tank 21 can be supplied to the filtration device 18 by the pump 23 as backwash water for the filtration device 18.

In the water treatment apparatus thus configured, the respective injection rates of the inorganic coagulant 4 and the polymer coagulant 9 are as follows:
It is controlled based on the characteristics as shown in FIG. In the example shown in FIG. 2, it is assumed that the raw water turbidity fluctuates up to 300 degrees. The injection rate (mg / L) of the inorganic flocculant 4 (for example, polyaluminum chloride (PAC)) is set to an injection rate substantially proportional to raw water turbidity. In the example shown in FIG. 2, when the raw water turbidity is 0 to 70 degrees: Inorganic coagulant injection rate = raw water turbidity × 1.0 [mg / L] When the raw water turbidity is 70 to 300 degrees: inorganic coagulant injection Rate = raw water turbidity × 0.7 + 21 [mg /
L] (maximum injection rate = 231 mg / L).

The injection rate (mg / L) of the polymer flocculant 9 (for example, anionic polymer flocculant) is calculated by the following calculation formulas A and B with respect to the raw water turbidity. The calculation formula A calculates the injection rate of the polymer coagulant in proportion to the injection rate of the inorganic coagulant, and when the proportional portion reaches a predetermined upper limit injection rate, the upper limit injection rate is reached. Set to expression. That is, A = (inorganic coagulant injection rate × 0.006) [mg / L],
Raw water turbidity of 213 degrees or higher reaches the upper limit of injection rate (1 mg / L)

The calculation formula B is set so that the injection rate of the polymer flocculant becomes the upper limit injection rate (1 mg / L) when the injection rate of the inorganic flocculant is the maximum injection rate (231 mg / L). The injection rate of the molecular coagulant is set in a calculation formula that is proportional to the injection rate of the inorganic coagulant. That is, B = (inorganic coagulant injection rate ÷ 231) [mg / L], 1 mg / L at 300 ° C.

The control to be performed in accordance with the calculation formula A or the calculation formula B set as described above is selected according to the magnitude of the fluctuation of the raw water turbidity and the current raw water turbidity. The injection rate of the polymer flocculant is controlled based on the selected calculation formula.

For example, when the fluctuation range of the raw water turbidity is 2
If it is assumed that the angle falls within 13 degrees, only the calculation formula A may be selected. In this case, since the injection rate of the polymer flocculant is not controlled in the region where the turbidity of the raw water is 213 degrees or more, the turbidity of the treated water does not suddenly change as described above.

As shown in FIG. 2, the raw water turbidity is up to 30.
When it is assumed that the turbidity fluctuates to 0 degrees, for example, when the raw water turbidity is low, control is performed based on the calculation formula A, and when the raw water turbidity exceeds a predetermined value, the control is performed based on the calculation formula B. Switch to control. The raw water turbidity at the switching timing is set to, for example, a turbidity of a predetermined magnification (for example, a magnification determined from a range of 2 to 10 times) with respect to the average turbidity of the raw water. At the time of this switching, the turbidity of the raw water is still relatively low, so the difference between the calculation formulas A and B is small as shown in FIG. Can be kept small. In order to suppress the change in the turbidity of the treated water at this time, for example, the injection rate is kept for a certain period of time with respect to the change in the turbidity of the raw water, and is gradually changed, thereby reducing the quality of the treated water. The influence can be suppressed to a smaller extent.

In the state where the control is shifted to the calculation formula B, the injection rate of the polymer flocculant is suppressed to be lower than that of the calculation formula A, so that the water quality (turbidity) of the treated water is calculated in absolute value. A
May be slightly worse than in the case of control based on However, since the purpose of the treated water quality is to be within the target level (for example, turbidity is within 0.1 degree), no particular problem occurs as long as the target water level can be achieved.

In the control of the polymer coagulant injection rate based on the calculation formula B, since the injection rate has no peak, even if the raw water turbidity increases, the polymer coagulant injection rate simply and slowly changes in proportion. Is done. As a result, the quality of the treated water is stably maintained at a value within the target level without a sudden change. In other words, such inconveniences as sudden fluctuations in treated water quality, such as when a polymer coagulant injection rate has a plateau region, and a sudden deterioration of treated water quality when raw water turbidity exceeds a certain level. Is avoided.

Therefore, in the method according to the present invention, an optimal calculation formula is selected in accordance with the magnitude of the turbidity of the raw water and the turbidity of the raw water at that time, and the polymer coagulant is added at the optimal injection rate. By injecting, it becomes possible to stably obtain treated water having a target water quality.

As the inorganic flocculant used in the present invention, for example, polyaluminum chloride (PAC), sulfate band, ferric chloride and ferric sulfate can be used. Anionic or amphoteric polymer flocculants can be used. Examples of the anionic polymer coagulant include a polymer of acrylic acid or a salt thereof, a copolymer of acrylic acid or a salt thereof and acrylamide, and a copolymer of acrylamide and 2-acrylamido-2-methylpropanesulfonic acid salt A terpolymer of acrylic acid or a salt thereof, acrylamide and 2-acrylamido-2-methylpropanesulfonic acid salt,
Examples thereof include partial hydrolysates of polyacrylamide, but are not particularly limited thereto. A typical nonionic polymer flocculant includes polyacrylamide, but is not particularly limited thereto. Examples of the amphoteric polymer flocculant include at least one cationic monomer such as a tertiary salt and a quaternary salt of dimethylaminoethyl (meth) acrylate (eg, a methyl chloride salt), acrylic acid and a salt thereof. (Salts such as sodium and calcium), 2-acrylamide-2-
A copolymer of at least one anionic monomer such as methylpropane sulfonate (salts such as sodium and calcium), or at least one cationic monomer and at least one anion And tertiary or quaternary copolymers of a nonionic monomer such as an acrylamide with an ionic monomer, but are not particularly limited thereto. Although the range of the molecular weight of the polymer flocculant is not particularly limited,
A range of 10 million is preferred. These polymeric flocculants are:
It can be used alone or as a mixture.

Further, in the present invention, when the fluctuation range of the turbidity of the raw water cannot be grasped in advance, it is possible to predict the magnitude of the fluctuation and perform the selection and switching control of the calculation formulas A and B in the same manner as described above. It is possible. Since the turbidity of the raw water 1 can be continuously measured by the turbidity meter 2, the magnitude of the fluctuation of the raw water turbidity is predicted from the speed of the turbidity change by comparing the magnitude of the fluctuation of the raw water turbidity with comparative data set in advance. It is possible. That is,
When the turbidity change rate is high, it is predicted that relatively large turbidity fluctuations may occur based on comparisons with comparative data such as past actual data. It is expected that only a degree change will occur.

Using the turbidity fluctuation predicted in this way, as described above, when the maximum value within the predicted fluctuation is equal to or less than the raw water turbidity corresponding to the peak start point of the upper limit injection rate in the calculation formula A, Is selected, when the maximum value within the predicted fluctuation exceeds the raw water turbidity corresponding to the peaking start point of the upper limit injection rate in the calculation formula A, the raw water turbidity corresponding to the peaking start point When the raw water turbidity rises to a lower value (a predetermined switching turbidity value), the calculation formula A may be switched to the calculation formula B. By this control, control substantially similar to the above embodiment can be performed.

[0035]

[Experiment conditions]

・ Raw water flow rate: 200m ³ / day ・ Inorganic flocculant mixing tank: 555L effective capacity (residence time 4 minutes), with stirrer ・ Polymer flocculant mixing tank: 555L effective capacity (residence time 4min), with stirrer ・ Flocculation Pond: Horizontal paddle system x 3 tanks (total residence time of 3 tanks: 30 minutes)-Sedimentation basin: Residence time: 40 minutes, surface load factor: 10 mm / min-Filter: tower diameter: 1200 mm, water flow rate: 150 m / day, filtration Layer composition: anthracite (height: 400 mm) + silica sand (height: 400 mm)-Raw water turbidity: 4 to 300 degrees (average turbidity: 8.0 degrees)-Raw water pH: 7.2 to 7.5 -Inorganic flocculant: PAC (injection proportional to raw water turbidity) (PAC: polyaluminum chloride)-Organic polymer flocculant: Anionic polymer flocculant 0.1-1.0 mg / L-Organic polymer flocculant Formula: Less than 5 times and more than 5 times the average raw water turbidity Toggles

An example in which the raw water turbidity varies from 4 to 300 degrees with respect to the average raw water turbidity of 8.0 degrees and the upper limit injection rate of the organic polymer flocculant is 1 mg / L will be described. FIG. 2 shows the injection rate of the inorganic flocculant PAC and the anionic organic polymer flocculant with respect to the raw water turbidity. Inorganic coagulant PAC: Raw water turbidity 0-70 degrees: PAC = turbidity × 1.0 mg / L Raw water turbidity 70-300 degrees: PAC = turbidity × 0.7 + 21 mg / L, maximum 231 mg / L; The calculation formulas A and B of the polymer flocculant are as follows: A = (PAC × 0.006) mg / L, turbidity of raw water 213
1 mg / L B = (PAC ÷ 231) mg / L at a temperature of 30 ° C. or higher, and 1 mg / L at a raw water turbidity of 300 ° C. Since switching is performed at less than 5 times and at least 5 times the average raw water turbidity, the formula A, 40-3
00 degrees is represented by the formula B

In the case of only the control based on the calculation formula A, when the raw water turbidity is 213 degrees or more and the organic polymer flocculant injection rate is 1 mg /
Since it is L, there is no follow-up property for raw water turbidity higher than L. That is, in the range of high raw water turbidity, the state of flocs formed in the floc forming tank changes greatly, and the quality of the sedimentation water also changes.

Conversely, in the case of the control based on the calculation formula B, although there is a followability to the raw water turbidity, the injection rate is smaller than the optimum injection rate as a whole. That is, although the injection rate of the organic polymer is not always the optimum, the floc formation state and the sedimentation treated water are stable with respect to the change in the turbidity of the raw water, which is convenient for operation management.

Since the raw water turbidity is usually 10 degrees or less, in most cases, the operation is performed under the optimal coagulation conditions according to the calculation formula A. When the turbidity becomes high, the control is switched to the control by the calculation formula B, and the quality of the treated water is slightly deteriorated. Further, the relationship between the suspended substance in the raw water, the inorganic flocculant, and the organic polymer flocculant is almost constant, and the influence on the sludge treatment is small.

[0040]

As described above, according to the method for controlling the injection of a coagulant in water treatment according to the present invention, the calculation formula A and the calculation formula A are calculated in accordance with the turbidity of raw water and the raw water turbidity at that time. By appropriately switching and selecting Formula B, and controlling the injection rate of the polymer flocculant based on the selected calculation formula, it is possible to control the polymer flocculant injection rate to the optimum, and to maintain the polymer flocculant injection rate within the target level. It is possible to reliably obtain treated water of the same quality and to achieve stable treated water quality.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a water treatment apparatus to which a coagulant injection control method in water treatment according to an embodiment of the present invention is applied.

FIG. 2 is a characteristic diagram for controlling the injection rate of a flocculant with respect to raw water turbidity in the apparatus of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Raw water 2 Turbidity meter 3 Inorganic flocculant mixing tank 4 Inorganic flocculant 5 Pump 6 Motor 7 Stirrer 8 Polymer flocculant mixing tank 9 Polymer flocculant 10 Pump 11 Motor 12 Stirrer 13 Sequencer 14 Flock forming pond 15 Paddle stirrer 16 Sedimentation pond 17 Partition wall 18 Filtration device 19 Filtration layer 20 Purified water 21 Purified water tank 22 Final treated water 23 Pump

Claims (5)

[Claims] In a water treatment in which a suspended substance in raw water is coagulated by injecting an inorganic coagulant and a polymer coagulant, an equation for calculating an injection rate of the polymer coagulant with respect to raw water turbidity is calculated by polymer coagulation. Formula A in which the injection rate of the agent is proportional to the injection rate of the inorganic coagulant and reaches a plateau at a predetermined upper limit injection rate,
Formula B in which the injection rate of the polymer flocculant is proportional to the injection rate of the inorganic flocculant so that the injection rate of the polymer flocculant becomes the upper limit injection rate when the injection rate of the inorganic flocculant is the maximum injection rate. 2
One of the two formulas is set according to the magnitude of the fluctuation of the raw water turbidity and the current raw water turbidity, and the injection of the polymer flocculant is performed based on the selected calculation formula. A method for controlling the injection of a flocculant in water treatment, comprising controlling a rate. 2. The magnitude of the fluctuation of the raw water turbidity is predicted from the rate of change of the raw water turbidity, and the maximum value within the predicted fluctuation is the raw water turbidity corresponding to the plateau start point of the upper limit injection rate in the calculation formula A. If the maximum value within the predicted fluctuation exceeds the raw water turbidity corresponding to the peak start point of the upper limit injection rate in the calculation formula A, the peak value is selected. When the raw water turbidity rises to a level lower than the raw water turbidity corresponding to the starting point, the calculation formula B
The method for controlling the injection of a coagulant in the water treatment according to claim 1, wherein the method is switched to: 3. When the raw water turbidity is equal to or less than a predetermined predetermined magnification with respect to the average turbidity of the raw water, the calculation formula A is selected. select,
The method for controlling the injection of a coagulant in the water treatment according to claim 1 or 2. 4. An upper limit injection rate of the polymer flocculant of 0.2 to 0.2.
4. The amount is set within a range of 2.0 mg / L.
The method for controlling injection of a flocculant in water treatment according to any one of the above. 5. The method according to claim 1, wherein the injection rate of the inorganic coagulant is proportional to the turbidity of the raw water.