JP6982759B2 - Water treatment system - Google Patents

Description

The present invention relates to a water treatment system. In particular, it relates to a water treatment system for treating fluorine contained in wastewater from a plant.

With the growing global awareness of the environment, various environmental regulations have been established for exhaust gas, wastewater, waste, etc. emitted from plants in each country and region. For this reason, the plant is equipped with an environmental protection device for removing regulated substances contained in exhaust gas, wastewater, waste, etc. to a predetermined value or less. In the case of environmental protection equipment for power plants, denitration equipment, electrostatic precipitators, and desulfurization equipment are arranged in order in the flow path of exhaust gas, and nitrogen oxides (NO _x ), soot dust, and sulfur oxides (SO) contained in the exhaust gas, respectively. _x ) is removed. The wet limestone gypsum method, which is one of the typical methods of desulfurization equipment, absorbs _{SO 2} by bringing _{exhaust gas into gas-liquid contact with limestone slurry and reacting calcium (Ca) with sulfurous acid gas (SO 2).} At the same time, gypsum is collected as a by-product. The desulfurized wastewater discharged by this method contains regulated substances such as fluorine, nitrogen, and heavy metals, and the wastewater is treated to meet these wastewater standards and discharged to the environment.

In order to treat wastewater, generally, a treatment tank for each regulated substance is provided, and the regulated substance is removed from the wastewater by injecting a treatment agent corresponding to the regulated substance. Since the concentration of the regulated substance contained in the wastewater fluctuates and the effect of the treatment chemical fluctuates depending on the properties of the wastewater, the appropriate amount of the treatment chemical to be charged into the treatment tank fluctuates. For this reason, there have been conventionally proposed proposals for automatic control of the injection amount of the processing agent.

Patent Document 1 relates to a fluorine-containing wastewater treatment apparatus. It is disclosed that the amount of the aluminum salt and the neutralizing agent added for the fluorine treatment is controlled according to the flow rate of the raw water, the fluorine concentration, and the pH in the reaction vessel. The control of the amount of the drug solution is controlled by the feedback control, but the combined use of the feedforward control, the feedforward control and the feedback control is also mentioned.

In Patent Document 2, a coagulant is injected into raw water to agglutinate turbidity in the raw water to form flocs, and the flocs are settled and separated in a sedimentation basin. Disclosed for agglutinating agent injection control. It is disclosed that the time delay of correction, which is a problem of feedback control, is shortened by applying an improved turbidity measurement method in performing correction by feedback control for feedforward control.

Patent Document 3 discloses that a water quality prediction unit that predicts the water quality of wastewater using plant operation information is provided, and feedforward control of water treatment operation conditions is performed based on the predicted water quality.

Japanese Unexamined Patent Publication No. 60-197293 Japanese Unexamined Patent Publication No. 2011-5436 International Publication No. 2017/022113

When the coal type is changed or the power generation load is changed in a thermal power plant, the concentration of components in the desulfurized wastewater fluctuates greatly. In order to properly treat fluorine in wastewater, it is common practice to analyze the fluorine concentration in power plant wastewater (desulfurized wastewater, other wastewater) by hand analysis and use the results to change the amount of chemicals injected. ing. The fluorine concentration in the wastewater is monitored by a fluorine meter, but the measured value of the fluorine meter is greatly affected by interfering substances that fluctuate the measured value in addition to the fluorine concentration, and the fluctuation of the component concentration in the desalted wastewater is quantitative. At present, it is not accurate enough to measure and determine the injection amount of chemicals. For this reason, water quality analysis and operation adjustment when the component concentration fluctuates is a burden on the operator. In addition, the effect of the injection amount of the treatment chemical such as the flocculant varies depending on the wastewater properties. Therefore, if the chemical is injected in excess of the theoretical injection amount so as not to cause insufficient injection, the amount of sludge derived from the flocculant increases accordingly.

Patent Document 1 is intended for fluorine treatment, but does not specifically describe how to calculate and control the amount of chemical solution added from the measured values.

Neither Patent Document 2 nor Patent Document 3 discloses a specific treatment for fluorine treatment. In Patent Document 2, feedback control is also used to correct improper feedforward control due to water quality fluctuations, but there is a time lag between the injection of the chemical and the actual change appearing in the sensor measurement. Is unavoidable, and the larger the response delay, the larger the control fluctuation range may remain.

In the present invention, the input amount of the fluorine-treated chemical (aluminum salt) is optimized according to the change in the concentration of wastewater or treated water by feedforward control or feedback control, and the amount of sludge derived from the flocculant is controlled to be reduced. The task is to adjust the value.

The water treatment system according to the embodiment of the present invention is a water treatment system for treating wastewater containing fluorine, and the treated water and fluorine in which the fluorine contained in the wastewater is reduced by adding an aluminum salt to the wastewater. It has a fluorine treatment tank that separates the sludge containing aluminum hydroxide that has adsorbed aluminum, and a control unit that controls the amount of aluminum salt to be charged into the wastewater. The control unit has a processor and a memory, and has a processor. Executes a control program read into the memory, the control program has an aluminum injection rate calculation unit, an aluminum injection rate correction unit, and a drug input amount calculation unit, and the aluminum injection rate calculation unit has a predetermined fluorine treatment. The aluminum injection rate is calculated based on the adsorption isothermal formula in the tank and the fluorine concentration of the wastewater, and the aluminum injection rate correction unit corrects the aluminum injection rate calculated by the aluminum injection rate calculation unit based on the history of the fluorine concentration of the treated water. The corrected aluminum injection rate corrected by

Other issues and novel features will be apparent from the description and accompanying drawings herein.

In the fluorine treatment of wastewater, while performing wastewater treatment that meets the wastewater standards, it suppresses the excessive input of chemicals and reduces the amount of sludge derived from the coagulant.

This is a configuration example of a fluorine treatment tank. It is a figure explaining the fluorine treatment model. It is the adsorption isotherm of Freundlich obtained so as to match the measured value. It is the adsorption isotherm of Langmuir obtained so as to match the measured value. This is a simulation of the wastewater fluorine concentration C _{0 of an actual plant.} It is a figure explaining the correction method of a control model. It is a figure which shows the control result (simulation) by Example 1. FIG. It is a graph which shows the correlation between the aluminum injection rate in an actual plant, and the amount of fluorine removed. It is a graph which shows the correlation between the aluminum injection rate in an actual plant, and the amount of fluorine removed. It is a figure which shows the control result (simulation) by Example 2. FIG. It is a figure which shows the control result (simulation) by Example 2. FIG. It is a summary of the control result (simulation) by Example 2.

FIG. 1 shows a configuration example of the fluorine treatment tank 100. The fluorine treatment tank 100 has a reaction tank 101, a coagulation tank 102, and a settling tank 103, and the wastewater passes through these tanks in sequence to adsorb and precipitate the treated water containing reduced fluorine and fluorine. Separated from sludge containing aluminum (Al (OH) _2). The agent 111 for treating fluorine and the neutralizing agent 112 are charged into the reaction tank 101. As the drug 111, an aluminum salt such as PAC (polyaluminum chloride) or a sulfate band is used. After adding the aluminum salt, the neutralizing agent 112 is added to adjust the pH of the reaction vessel 101 in order to adjust the pH to the optimum pH for agglutination. As the neutralizing agent 112, for example, hydrochloric acid, sulfuric acid, caustic soda or the like is used. In the coagulation tank 102, the coagulation aid 113 for facilitating the precipitation of aluminum hydroxide generated by the addition of the chemical is charged, and solid-liquid separation is performed in the settling tank 103. It is also common to perform the fluorine treatment in two stages. In this case, the treated water from the fluorine treatment tank 100 is passed through the next stage fluorine treatment tank (not shown) to reduce the fluorine concentration in the wastewater to a target value.

A control unit 200 is provided for controlling the amount of chemicals and the like added to the fluorine treatment tank 100. The control unit 200 has a function of controlling the input amount of each of the drug 111, the neutralizing agent 112, and the coagulation aid 113, and here, the control of the input amount of the drug (aluminum salt) 111 will be described. The other input amounts are also controlled, for example, the neutralizing agent 112 may control the input amount based on the pH of the reaction tank 101, and the coagulation aid 113 may control the input amount according to the input amount of the aluminum salt.

The control unit 200 includes a processor 201, a memory 202, a water quality database 203, a process database 204, an interface 205, and a bus 206 connecting them. The processor 201 executes a control program loaded in the memory 202 and realizes a function of calculating the input amount of the drug 111. The control program includes a data acquisition unit 207, an aluminum injection rate calculation unit 208, an aluminum injection rate correction unit 209, and a drug input amount calculation unit 210, and the functions performed by the control unit 200 are realized by the control program loaded in the memory 202. To. The data collection unit 207 collects the fluorine concentration C _{0 of the wastewater by the fluorine concentration sensor 104 and the fluorine concentration C 1} of the treated water by the fluorine concentration sensor 105 via the interface 205. The collected fluorine concentration is stored in the water quality database 203, and is appropriately called to the memory 202 to be used for calculating the aluminum injection rate. It is assumed that not only the fluorine concentration but also the amount of wastewater and treated water and other water quality data are collected in the water quality database 203. The aluminum injection rate calculation unit 208 calculates the aluminum injection rate based on the fluorine concentration C ₀ (Example 1) of _{the wastewater stored in the water quality database 203 or the fluorine concentration C 1} (Example 2) of the treated water. The aluminum injection rate correction unit 209 makes a predetermined correction to the aluminum injection rate calculated by the aluminum injection rate calculation unit 208 as necessary, and stores the determined aluminum injection rate in the process database 204. The details of the processing by the aluminum injection rate calculation unit 208 and the aluminum injection rate correction unit 209 will be described later. The chemical input amount calculation unit 210 calculates the charge amount of the chemical 111 based on the information of the aluminum injection rate stored in the process database 204 and the wastewater amount stored in the water quality database 203. Control unit 200, so that the input amount of the amount charged is calculated agents 111 to control the charging amount of the drug 111 by the control instruction S ₁ to be issued via the interface 205.

In Example 1, the amount of aluminum salt charged to the fluorine treatment tank is feedforward controlled to optimize the amount of aluminum salt charged. The fluorine treatment model in Example 1 will be described. FIG. 2A is a diagram for explaining a fluorine treatment model (adsorption isotherm type) in the fluorine treatment tank 100. Assuming that the fluorine concentration of wastewater is C ₀ [mg / l], the fluorine concentration of treated water is C ₁ [mg / l], and the amount of fluorine removed by a chemical (aluminum salt) is F [mg / l], (Equation 1) The relationship holds.

The fluorine treatment tank 100 utilizes the phenomenon of adsorption of fluorine to aluminum hydroxide, and in the settling tank, the fluorine adsorbed on the aluminum hydroxide and the fluorine dissolved in the treated water which is the supernatant thereof are in an equilibrium state. It can be said that. There are several known adsorption isotherms that show the correlation between the concentration and absorption of solutes in a solution when they are adsorbed on a solid at a certain temperature. Here, (1) Freundlich's adsorption isotherm is known. An example of applying the equation and (2) Langmuir's adsorption isotherm is shown. Freundlich's adsorption isotherm is known to empirically match the actual adsorption isotherm in the industrial field. If the aluminum injection rate (equivalent to the aluminum concentration in the treated water) A [mg / l], the adsorption amount V is represented by (Equation 2). Note that a and n are constants.

By substituting (Equation 2) for (Equation 1), (Equation 3) can be obtained.

Freundlich's adsorption isotherm is an unsaturated type adsorption isotherm, but it is considered that the adsorption amount actually saturates as the fluorine concentration in the treated water increases. Therefore, Langmuir's adsorption isotherm, which is compatible with saturated type adsorption isotherms, may be used. In this case, the adsorption amount V is represented by (Equation 4). Here, a is the Langmuir constant and b is the saturated adsorption amount.

By substituting (Equation 4) into (Equation 1), (Equation 5) can be obtained.

_{The relationship between the fluorine concentration C 1} of the treated water in the fluorine treatment tank 100 and the adsorption amount V is actually measured, and the coefficient a, n of (Equation 2) or the coefficient a, b of (Equation 4) is matched so as to match the measured value. To determine. FIG. 2B is an adsorption isotherm of Freundlich for which the coefficients a and n are obtained so as to match the measured values, and FIG. 2C is an adsorption isotherm of Langmuir for which the coefficients a and b are obtained so as to match the same measured values. .. The measured value and the expected value by the adsorption isotherm are in good agreement, and the error can be suppressed to within 20% in both cases (excluding the abnormal value in the measured value). It should be noted that which adsorption isotherm method should be used may be selected according to the actual measurement of the actual plant.

In this way, the coefficient is calculated from the measured value of the actual plant to be controlled to obtain the adsorption isotherm, and the treated water fluorine concentration C ₁ is set as the target fluorine concentration (fixed value) of the fluorine treatment tank 100. For example, in Japan, relates fluorine, effluent standards in waters 15 [mg / l], rivers, because it is defined as 8 [mg / l] except in waters, such as lakes, the treated water fluorine concentration C ₁ May be determined based on these regulation values. By applying (Equation 3) or (Equation 5) based on the adsorption isotherm with the calculated coefficient and the fluorine concentration C _{0 of the} wastewater, the required aluminum concentration and the required amount of aluminum salt input based on this can be obtained. Can be calculated.

However, in the case of such feedforward control, if the deviation between the wastewater property when the coefficient of the adsorption isotherm is obtained and the wastewater property during actual operation becomes large, the deviation from the control target will occur. Factors that cause deviation in drainage properties include, for example, switching of coal types. In the case of a coal-burning boiler, the amount of fluorine contained in coal varies greatly depending on the production area, etc., so the amount of fluorine contained in wastewater fluctuates greatly by switching the coal type used by the boiler. In addition, various substances are dissolved in the wastewater, and some substances inhibit the adsorption of fluorine, so changes in the irrigation water also affect the effect of feedforward control.

FIG. 3 simulates the fluctuation of the _{wastewater fluorine concentration C 0} that may occur in the actual plant based on the measured value in the actual plant. As described above, the wastewater fluorine concentration C ₀ fluctuates due to changes in the coal type and various factors, and there is a possibility that the aluminum salt will be insufficient or excessive when input based on a predetermined model. Therefore, in this embodiment, the input amount of the aluminum salt is determined by the corrected aluminum injection rate A'(= αA) obtained by multiplying the aluminum injection rate A [mg / l] obtained by the adsorption isotherm by the correction coefficient α. An example of how to determine the correction coefficient α will be described with reference to FIG. In this example, the value of the correction coefficient α is controlled based _{on the treated water fluorine concentration C 1.}

The target value of the fluorine concentration in the treated water is set to C _1T, and C _{1L to} C _1H (C _1L <C _1T <C _1H ) is set as a dead zone. For example, it may be set as ± 20% of the target value C _1T. If this dead zone is exceeded to the low concentration side, it is judged that fluorine removal is excessive and α is reduced, and if it exceeds the dead zone to the high concentration side, it is judged that fluorine removal is insufficient. And increase α. In the example of FIG. 4, the treated water fluorine concentration C ₁ was _{lower than C 1L} at the time point 401, so that α was reduced from 1.0 to 0.9, and the treated water fluorine concentration C ₁ was higher than _{C 1H at the time points 402 and 403.} This increases α from 0.9 to 1.0 and α from 1.0 to 1.1, respectively.

FIG. 5 shows a simulation result of how the treated water fluorine concentration C ₁ fluctuates when the wastewater fluorine concentration C _{0 fluctuates as shown in FIG.} The solid line is the result when the input amount of the aluminum salt is corrected by the correction coefficient α in FIG. 4, and the dotted line is the result when the correction is not performed. In this way, by making corrections based on the history of the treated water fluorine concentration C ₁ , it is possible to suppress that the amount of the drug input is excessive and continues for a long period of time, or that the amount of the drug is too small and continues for a long time. The fluctuation range of the concentration C ₁ can be suppressed to be smaller. That is, it is possible to optimize the input amount of the aluminum salt.

The correspondence between the control program shown in FIG. 1 and the processing in the first embodiment will be described. The aluminum injection rate calculation unit 208 calculates the aluminum injection rate A based on the adsorption isotherm formula in the fluorine treatment tank and the fluorine concentration C _{0 of the wastewater.} The aluminum injection rate correction unit 209 calculates the corrected aluminum injection rate A', in which the calculated aluminum injection rate A is corrected by the correction coefficient α based on the history of the fluorine concentration of the treated water. Although the method of reflecting the history of the fluorine concentration of the treated water using the dead zone has been described, the method is not limited to this method. For example, depending on how the wastewater quality fluctuates, it may be desirable to be able to flexibly adjust the standard as appropriate, instead of changing the correction coefficient based on a predetermined standard. Specifically, the fluorine concentration range to be a dead zone and the amount of change of the correction coefficient once may be adjusted according to the history of the fluorine concentration of the treated water, and the aluminum injection rate may be corrected according to the adjusted standard. The chemical charge calculation unit 210 calculates the amount of aluminum salt to be charged into the wastewater based on the corrected aluminum injection rate A'.

Further, in the case of the feed-forward control of this embodiment, it is desirable that the drainage side fluorine concentration sensor 104 (see FIG. 1) continuously monitors the drainage and calculates the aluminum injection rate, while the treated water is treated. Since it takes several hours for the side fluorine concentration sensor 105 to appear as the fluorine concentration of the treated water, it is sufficient to monitor the side fluorine concentration sensor 105 at a lower frequency than the fluorine concentration sensor 104. Therefore, in FIG. 1, an example in which the concentration sensor is connected to the control unit 200 online for control is shown, but the fluorine concentration of the treated water is measured with higher accuracy and transmitted to the control unit 200 offline. You may try to do it.

In the second embodiment, the amount of the aluminum salt charged into the fluorine treatment tank is controlled by feedback control. In calculating the initial input amount for this purpose, the following empirical formula (Equation 6) is used.

This empirical formula is derived from the operational data in the actual plant. As shown in FIG. 6, from the operation data of the actual plant, the aluminum injection rate A [mg / l] and the amount of fluorine removed by the chemical (aluminum salt) F [mg / l] (fluorine concentration C ₀ [mg of wastewater). Equal to the difference between / l] and the fluorine concentration C ₁ [mg / l] in the treated water, see (Equation 1)) has a positive correlation. _{FIG. 7 is a logarithmic display of the fluorine concentration C 1} [mg / l] of the treated water limited to a predetermined range from the data of FIG. 6, and in this example, the correlation equation of (Equation 6) is a = 7.8. , N = 1.3.

In Example 2, FIG. 8 shows a simulation result of the fluctuation of the treated water fluorine concentration C ₁ [mg / l] when the fluctuation of the waste fluorine fluorine concentration C _{0 [mg / l] shown in FIG. 3 occurs.} In the second embodiment, the initial control value is determined based on (Equation 6), and thereafter, the aluminum injection rate A is corrected from the deviation from the target treated water concentration. In FIG. 8, the target treated water concentration is set to 5 [mg / l], and the control method is also a simple P control. In this example, the average treated water concentration is 5.2 [mg / l] and the maximum value is 13.9 [mg / l]. In the case of feedback control, in order to suppress the control delay due to the fluctuation of the wastewater fluorine concentration, it can be expected that the fluctuation range is reduced by shortening the control delay amount. Further, although P control is applied this time, feedback control to which PI control and PID control are applied may be performed. However, since the delay time until the fluctuation of the wastewater fluorine concentration C ₀ [mg / l] _{is reflected in the treated water fluorine concentration C 1} [mg / l] is unavoidable, the treated water fluorine concentration C due to the control delay is unavoidable. _{Fluctuations of 1} [mg / l] are essential in feedback control.

Therefore, in this embodiment, the target value of the treated water fluorine concentration is changed according to the history of the _{treated water fluorine concentration C 1.} Further, the output sensitivity to the deviation width may be increased (that is, the amount of aluminum salt to be increased or decreased with respect to the predetermined deviation width may be increased). In the example of FIG. 9, the target value of the treated water fluorine concentration is 8 [mg / l], and the treated water fluorine concentration C ₁ is in the range of 50% to 200% (4 to 16 [mg / l]) (dead zone). If it exceeds, the target value and output sensitivity are changed. At this time, the average treated water concentration was 5.9 [mg / l], and the maximum value was 14.8 [mg / l].

FIG. 10 summarizes the simulation results. Cases 1 and 2 have no correction, and only the setting of the target value is different. When the target value is set to 6 [mg / l], the maximum value exceeds the drainage standard for Japanese waters of 15 [mg / l]. In this way, when performing feedback control, it is possible to increase the average treated water concentration while suppressing the increase in the maximum value by correcting the target value and output sensitivity according to the history of the treated water fluorine concentration. It is possible. As a result, it can be seen that the amount of aluminum that is excessively charged in order to satisfy the treated water standard is reduced.

The correspondence between the control program shown in FIG. 1 and the processing in the second embodiment will be described. The aluminum injection rate calculation unit 208 calculates the initial charge amount of the aluminum salt by the initial charge amount calculation formula (Equation 6) of the fluorine treatment tank, and thereafter, based on the deviation amount between the fluorine concentration of the treated water and the target fluorine concentration. Calculate the aluminum injection rate. The feedback control method may be any of P control, PI control, and PID control. The chemical charge calculation unit 210 calculates the amount of aluminum salt to be charged into the wastewater based on the calculated aluminum injection rate A. The aluminum injection rate correction unit 209 changes the value of the target fluorine concentration of the treated water based on the history of the fluorine concentration of the treated water. Further, the output sensitivity to the amount of deviation between the fluorine concentration of the treated water and the target fluorine concentration may be increased based on the history of the fluorine concentration of the treated water.

100: Fluorine treatment tank, 101: Reaction tank, 102: Coagulation tank, 103: Sedimentation tank, 104, 105: Fluorine concentration sensor, 111: Chemical, 112: Neutralizer, 113: Aggregation aid, 200: Control unit, 201: Processor, 202: Memory, 203: Water quality database, 204: Process database, 205: Interface, 206: Bus.

Claims (9)

A water treatment system that treats wastewater containing fluorine.
A fluorine treatment tank that separates treated water containing reduced fluorine contained in the wastewater and sludge containing aluminum hydroxide adsorbing fluorine by adding an aluminum salt to the wastewater.
It has a control unit that controls the amount of the aluminum salt to be charged into the wastewater.
The control unit has a processor and a memory, and the processor executes a control program read into the memory.
The control program has an aluminum injection rate calculation unit, an aluminum injection rate correction unit, and a drug input amount calculation unit.
The aluminum injection rate calculation unit calculates the aluminum injection rate based on the adsorption isotherm formula in the fluorine treatment tank and the fluorine concentration of the wastewater, which are predetermined.
The aluminum injection rate correction unit calculates a corrected aluminum injection rate obtained by correcting the aluminum injection rate calculated by the aluminum injection rate calculation unit with a correction coefficient based on the history of the fluorine concentration of the treated water.
The chemical charge calculation unit is a water treatment system that calculates the amount of aluminum salt to be charged into the wastewater based on the corrected aluminum injection rate. In claim 1,
The adsorption isotherm is a water treatment system that is a Freundlich adsorption isotherm or a Langmuir adsorption isotherm. In claim 1,
The aluminum injection rate correction unit determines a fluorine concentration range that is insensitive to the target fluorine concentration of the treated water, and if the fluorine concentration of the treated water is in the fluorine concentration range that is insensitive, the value of the correction coefficient is set. A water treatment system that maintains and changes the value of the correction coefficient when the fluorine concentration of the treated water exceeds the fluorine concentration range set as the dead zone. In claim 3,
A water treatment system in which the amount of change in the value of the correction coefficient when the fluorine concentration range of the dead zone or the fluorine concentration of the treated water exceeds the fluorine concentration range of the dead zone can be adjusted. In claim 3,
A water treatment system in which the frequency of measuring the fluorine concentration of the treated water is lower than the frequency of measuring the fluorine concentration of the waste water. A water treatment system that treats wastewater containing fluorine.
A fluorine treatment tank that separates treated water containing reduced fluorine contained in the wastewater and sludge containing aluminum hydroxide adsorbing fluorine by adding an aluminum salt to the wastewater.
It has a control unit that controls the amount of the aluminum salt to be charged into the wastewater.
The control unit has a processor and a memory, and the processor executes a control program read into the memory.
The control program has an aluminum injection rate calculation unit, an aluminum injection rate correction unit, and a drug input amount calculation unit.
The aluminum injection rate calculation unit calculates the initial charge amount of the aluminum salt by the predetermined initial charge amount calculation formula of the fluorine treatment tank, and thereafter, the fluorine concentration of the treated water and the target fluorine concentration of the treated water. Calculate the aluminum injection rate based on the amount of deviation from
The chemical input amount calculation unit calculates the input amount of the aluminum salt to be charged into the wastewater based on the aluminum injection rate calculated by the aluminum injection rate calculation unit.
The aluminum injection rate correction unit is a water treatment system that changes the value of the target fluorine concentration of the treated water based on the history of the fluorine concentration of the treated water. In claim 6,
The aluminum injection rate correction unit is a water treatment system that further enhances the output sensitivity with respect to the amount of deviation between the fluorine concentration of the treated water and the target fluorine concentration of the treated water based on the history of the fluorine concentration of the treated water. In claim 6,
The aluminum injection rate calculation unit is a water treatment system that controls the aluminum injection rate by P control, PI control, or PID control. In claim 6,
The aluminum injection rate correction unit determines a fluorine concentration range that is insensitive to the target fluorine concentration of the treated water, and if the fluorine concentration of the treated water is in the fluorine concentration range of the insensitive zone, the target fluorine of the treated water. A water treatment system that maintains a concentration value and changes the target fluorine concentration value of the treated water when the fluorine concentration of the treated water exceeds the fluorine concentration range set as the dead zone.

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