Water treatment systems, water treatment methods, and programs

Abstract

To provide a water treatment system which can suppress a formation of disinfection by-products.SOLUTION: A water treatment system includes a disinfection by-product concentration estimation part that calculates estimated concentrations of each of the first and second disinfection by-products generated in the process of water purification, and a pre-salt / medium-salt determination part that determines whether at least one of the estimated concentrations of the first and second disinfection by-products exceeds an acceptable value, and if it exceeds the acceptable value, decides not to perform pre-salt injection and to perform medium salt injection.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] Embodiments of the present invention relate to a water treatment system, a water treatment method, and a program. [Background technology]

[0002] At water treatment plants, chlorine is injected to remove ammoniacal nitrogen and metal ions such as iron and manganese, and to disinfect harmful bacteria such as E. coli. The Waterworks Act stipulates that, in the case of free chlorine, the residual chlorine concentration of water flowing from taps in the homes of residents who receive tap water must be managed to be 0.1 mg / L or higher.

[0003] Therefore, considering that residual chlorine concentration decreases in the water pipeline network, it is necessary to maintain a stable residual chlorine concentration at the water treatment plant outlet that takes into account the decrease in the pipeline network.

[0004] However, if the raw water contains ammoniacal nitrogen or metal ions such as iron and manganese, these substances combine with chlorine and consume it. Therefore, if the concentration of these substances increases or fluctuates, it becomes difficult to maintain the residual chlorine within a certain range. For this reason, water treatment plants perform pre-chlorination treatment (hereinafter also referred to as "pre-salting treatment") to react ammoniacal nitrogen and metal ions such as iron and manganese with chlorine beforehand.

[0005] In typical water treatment systems, pre-salting involves injecting chlorine either in the mixing tank or upstream of the mixing tank. Liquid chlorine agents, such as sodium hypochlorite, are widely used for chlorine treatment.

[0006] However, if the raw water contains dissolved organic matter such as humic substances, the dissolved organic matter and chlorine agents chemically react to produce disinfection by-products such as carcinogenic trihalomethanes and haloacetic acids. Here, trihalomethanes are a general term for chloroform, dibromochloromethane, bromodichloromethane, and bromoform, and haloacetic acids are a general term for chloroacetic acid, dichloroacetic acid, and trichloroacetic acid.

[0007] The water quality standards for tap water are established by the Ministerial Ordinance concerning Water Quality Standards based on Article 4 of the Waterworks Act (Ministry of Health, Labour and Welfare Ordinance No. 101 of May 30, 2003), which sets standard values ​​for each type and total amount of trihalomethanes, and for each type of haloacetic acid.

[0008] Generally, powdered activated carbon is injected into the water to be treated in order to remove dissolved organic matter in the raw water that causes the formation of trihalomethanes and haloacetic acids. However, the formation rate of trihalomethanes and haloacetic acids differs depending on whether the chlorine agent is injected before or after the powdered activated carbon is injected, so determining the injection point of the chlorine agent is important.

[0009] However, deciding whether to inject the chlorine agent before or after the powdered activated carbon is not easy. Furthermore, regardless of whether the pre-salting injection point is set before or after the powdered activated carbon injection point, excessive amounts of trihalomethanes or haloacetic acids may be generated. [Prior art documents] [Non-patent literature]

[0010] [Non-Patent Document 1] Shinichi Kimura, et al., "Study on understanding and suppressing the behavior of re-emission during high-concentration 2-MIB removal using finely powdered activated carbon," January 2021, Journal of the Japan Water Works Association, Vol. 90, No. 1. [Overview of the Initiative] [Problems that the invention aims to solve]

[0011] The problem that this invention aims to solve is to provide a water treatment system, a water treatment method, and a program that can suppress the generation of disinfection by-products. [Means for solving the problem]

[0012] The water treatment system of the embodiment includes a disinfection by-product concentration estimation unit that calculates estimated concentration values ​​for a first disinfection by-product and a second disinfection by-product generated during the water purification process, and a pre-salt / intermediate salt determination unit that determines whether at least one of the estimated concentration values ​​of the first disinfection by-product and the second disinfection by-product exceeds an acceptable value, and if it exceeds an acceptable value, determines that pre-salt injection should not be performed and intermediate salt injection should be performed. If neither the estimated concentration of the first disinfection by-product nor the estimated concentration of the second disinfection by-product exceeds an acceptable value, the pre-salt injection point determination unit compares the estimated concentration of the first disinfection by-product and the estimated concentration of the second disinfection by-product, and determines, according to the comparison result, whether to perform a first pre-salt injection, in which a chlorine agent is injected at an injection point located upstream of the powdered activated carbon injection point in the water treatment process, or a second pre-salt injection, in which a chlorine agent is injected at an injection point located downstream of the powdered activated carbon injection point in the water treatment process. It is equipped with. [Brief explanation of the drawing]

[0013] [Figure 1] Figure 1 shows an example of the configuration of a water treatment system according to an embodiment. [Figure 2] Figure 2 shows an example of the functional configuration of the initial drug injection rate assumption unit 200 and the disinfection by-product concentration estimation unit 300. [Figure 3] Figure 3 shows an example of the process mainly performed in the disinfection byproduct concentration estimation unit 300. [Figure 4] Figure 4 shows an example of processing mainly performed by the chlorine injection determination unit 400 and the powder activated carbon injection correction calculation unit 500. [Figure 5] Figure 5 is a graph comparing the concentration of trihalomethanes (THMs) in the treated water when (1) chlorine agent is treated first, followed by powdered activated carbon, and when (2) powdered activated carbon is treated first, followed by chlorine agent. [Figure 6] Figure 6 is a graph comparing the concentrations of haloacetic acids (HAAs) when (1) chlorine agent is treated first, followed by powdered activated carbon, and when (2) powdered activated carbon is treated first, followed by chlorine agent. [Figure 7]Figure 7 is a graph that shows that the slope of the increase in the 2-MIB remaining rate with increasing chlorine injection rate differs when (1) chlorine agent is treated first, followed by powdered activated carbon, and when (2) powdered activated carbon is treated first, followed by chlorine agent. [Figure 8] Figure 8 is a flowchart showing an example of the operation of the water treatment system according to the embodiment. [Modes for carrying out the invention]

[0014] The embodiments will be described below with reference to the drawings.

[0015] (System Configuration) Figure 1 shows an example of the configuration of a water treatment system according to an embodiment.

[0016] This section describes an example of applying the water treatment system according to this embodiment to a rapid filtration type water treatment facility. However, the water treatment system of this embodiment is not limited to rapid filtration type water treatment facilities, but can also be applied to other types of water treatment facilities. For example, it can be applied to membrane filtration type and sand filtration type water treatment facilities.

[0017] Water treatment facility 1 is equipped with piping 2, intake well 3, mixing tank 4, coagulation and sedimentation tank 5, sand filtration tank 6, and water purification tank 7. Chlorine treatment, adsorption treatment, and coagulation treatment are performed during the water treatment process through each of these parts.

[0018] Chlorine treatment is a process that uses chlorine to oxidize ammoniacal nitrogen and metal ions such as iron and manganese, and to kill harmful bacteria such as E. coli. Depending on where the chlorine is injected, it is divided into pre-chlorine treatment, intermediate chlorine treatment, and post-chlorine treatment (also called pre-salting, intermediate salting, and post-salting, respectively).

[0019] Pre-salting is divided into first pre-salting and second pre-salting. In the first pre-salting, chlorine is injected by the first pre-salting device 10a at an injection point located upstream of the powdered activated carbon injection point in the water treatment process (in this example, before the intake well 3). In the second pre-salting, chlorine is injected by the second pre-salting device 10b at an injection point located downstream of the powdered activated carbon injection point in the water treatment process (in this example, at the mixing tank 4). In the intermediate salting, chlorine is injected by the intermediate salting device 11 in the piping from the sand filtration tank 6 to the water purification tank 7. In the post-salting, chlorine is injected by the post-salting device 12 in the water purification tank 7.

[0020] Adsorption treatment is a process that uses powdered activated carbon to adsorb and remove odor-causing substances and dissolved organic matter from the raw water (water to be treated). Coagulation treatment is a process that uses a coagulant to coagulate and settle turbidity in the raw water (water to be treated).

[0021] Raw water (water to be treated) flows into the intake well 3 through pipe 2. A first pre-salt injection pipe 8 is connected to pipe 2. A first pre-salt injection device 10a, used when performing the first pre-salt injection described above, is connected to the first pre-salt injection pipe 8. The first pre-salt injection device 10a injects chlorine into the water to be treated in pipe 2 from the first pre-salt injection pipe 8.

[0022] The water intake well 3 receives the water to be treated, which is sent through the piping 2, and stabilizes it as water. The water intake well 3 is equipped with a powdered activated carbon injection device 20 for the adsorption treatment described above. The powdered activated carbon injection device 20 performs a powdered activated carbon injection treatment in which powdered activated carbon is injected into the water to be treated. The powdered activated carbon injected into the water to be treated adsorbs odor substances and dissolved organic substances contained in the raw water (water to be treated). The water to be treated after adsorption treatment in the water intake well 3 is led through the piping 2 to the coagulant mixing tank 4.

[0023] Mixing tank 4 receives the water to be treated, which is sent through piping 2. Mixing tank 4 is equipped with a coagulant injection device 30 for the coagulation treatment described above. The coagulant injection device 30 performs a coagulant injection treatment in which a coagulant is injected into the water to be treated. The coagulant injected into the water to be treated coagulates suspended matter (turbidity) such as clay, bacteria, and algae contained in the water to be treated, as well as the powdered activated carbon injected in the intake well 3, and generates fine flocs.

[0024] As flocculants, aluminum-based flocculants and iron-based flocculants are preferred. Examples of aluminum-based flocculants include aluminum sulfate (aluminum sulfate) and polyaluminum chloride (PACl). Examples of iron-based flocculants include iron chloride, iron sulfate, and polysilica iron.

[0025] Furthermore, the mixing tank 4 is connected to a second pre-salt injection device 10b, which is used when performing the second pre-salt injection described above. The second pre-salt injection device 10b injects chlorine into the water to be treated in the mixing tank 4.

[0026] Mixing tank 4 is equipped with a stirrer for agitating the water to be treated. This stirrer is configured, for example, using a flash mixer. The water to be treated, into which a coagulant has been injected in mixing tank 4, is agitated by the stirrer to become mixed water, which is then guided through piping 2 to the coagulation and sedimentation tank 5.

[0027] The coagulation and sedimentation tank 5 consists of a flocculation tank 5b equipped with a flocculator 5a and a sedimentation tank 5c for settling the grown flocs. It separates and recovers turbidity flocs collected by powdered activated carbon and coagulants injected in the intake well 3. The supernatant water from which the flocs have been separated in the coagulation and sedimentation tank 5 is sent to the sand filter tank 6, where any remaining fine microflocs are filtered out. The filtered water then flows out of the sand filter tank 6 and is sent to the water purification tank 7.

[0028] A chlorine injection device 11, used when the aforementioned chlorine injection is performed, is connected to the piping from the sand filtration tank 6 to the water purification reservoir 7. The chlorine injection device 11 injects chlorine into the water to be treated in the piping.

[0029] The water treatment reservoir 7 is connected to a post-salt injection device 12, which is used when the post-salt injection described above is performed. The post-salt injection device 12 injects chlorine into the water to be treated in the water treatment reservoir 7 to adjust the residual chlorine concentration of the treated water sent from the water treatment facility.

[0030] The water treatment system according to this embodiment includes a water quality target setting unit 100, an initial chemical injection rate assumption unit 200, a disinfection byproduct concentration estimation unit 300, a chlorine agent injection determination unit 400, and a powder activated carbon injection correction calculation unit 500.

[0031] In addition, although not shown in the diagrams to avoid complicating the drawings, the water treatment system is equipped with a chemical injection control unit that controls the injection rate or amount of chlorine injected by the first pre-salt injection device 10a, the second pre-salt injection device 10b, the intermediate salt injection device 11, and the post-salt injection device 12, the injection rate or amount of powdered activated carbon injected by the powdered activated carbon injection device 20, and the injection rate or amount of coagulant injected by the coagulant injection device 30. The injection rate or amount of each chemical is determined, for example, by performing a predetermined calculation using an arithmetic formula that includes various variables, with initial values ​​provisionally set in the chemical injection rate initial assumption unit 200.

[0032] The water quality target setting unit 100 sets target values ​​for various physical quantities that indicate the water quality of the treated water.

[0033] The initial chemical injection rate setting unit 200 provisionally sets the injection rates of the chemicals to be injected into the water to be treated (injection rate of the coagulant used in the coagulation treatment, injection rate of the chlorine agent used in the pre-salting treatment, and injection rate of the powdered activated carbon used in the adsorption treatment).

[0034] The disinfection by-product concentration estimation unit 300 estimates the concentrations of trihalomethanes (THMs) and haloacetic acids (HAAs), which are disinfection by-products generated during the water purification process, using the target water quality set by the water quality target setting unit 100 and the injection rates of each chemical provisionally set by the chemical injection rate initial assumption unit 200.

[0035] The chlorine injection determination unit 400 includes a pre-salt / intermediate-salt determination unit 401 and a pre-salt injection point determination unit 402.

[0036] The pre-salt / intermediate-salt determination unit 401 determines whether to perform pre-salt injection or intermediate-salt injection. Specifically, it determines whether at least one of the estimated concentrations of trihalomethanes and haloacetic acids exceeds the permissible value, and if it exceeds the permissible value, it decides not to perform pre-salt injection and to perform intermediate-salt injection.

[0037] The pre-salt injection point determination unit 402 determines whether to perform a first pre-salt injection or a second pre-salt injection when pre-salt injection is to be performed. Specifically, if neither the estimated concentration of trihalomethanes nor the estimated concentration of haloacetic acids exceeds the permissible value, the estimated concentration of trihalomethanes and the estimated concentration of haloacetic acids are compared, and a decision is made to perform either a first pre-salt injection or a second pre-salt injection according to the result of the comparison. If the estimated concentration of trihalomethanes is equal to or greater than the estimated concentration of haloacetic acids (or exceeds the estimated concentration of disinfection by-products of haloacetic acids), a decision is made to perform a first pre-salt injection; otherwise, a decision is made to perform a second pre-salt injection.

[0038] The powdered activated carbon injection correction calculation unit 500 corrects the powdered activated carbon injection rate (powdered activated carbon injection rate) to be injected into the water to be treated in the water intake well 3, according to the desorption rate of odor substances adsorbed on the powdered activated carbon due to the effect of pre-salting. Specifically, when the first pre-salting is performed, the unit calculates the deficiency in the remaining odor substances of the powdered activated carbon due to the inhibitory effect of the chlorine agent, and when the second pre-salting is performed, the unit calculates the remaining odor substances released from the powdered activated carbon due to the desorption effect of the chlorine agent, and corrects the powdered activated carbon injection rate using the above-mentioned deficiency in the remaining odor substances of the powdered activated carbon or the remaining odor substances of the released portion.

[0039] The functions of the water quality target setting unit 100, the initial assumption unit for chemical injection rate 200, the disinfection by-product concentration estimation unit 300, the chlorine agent injection determination unit 400, and the powdered activated carbon injection correction calculation unit 500 may be implemented as a single computer or divided among multiple computers. Furthermore, each function may be implemented as a program executed by a processor such as a central processing unit in a computer. Details of each function will be described later.

[0040] Piping 2 is equipped with a raw water quality meter set 40, a pre-chlorine indicator meter 50, an odor detection device 60, a dissolved organic matter meter 70, and a flow meter 80. In addition, a pH meter 90 is installed in the mixing tank 4, and a pH meter 91 is installed in the piping between the coagulation and sedimentation tank 5 and the sand filtration tank 6. However, the pH meter 91 is not always necessary. The measurement results from these instruments are sent to the water quality target setting unit 100 and the initial chemical injection rate assumption unit 200.

[0041] Here, the raw water quality meter set 40 measures the turbidity Tu of the raw water. R A turbidity meter 40a measures the pH of the raw water's hydrogen ion concentration index. R pH meter 40b to measure, raw water temperature Tw R It consists of a thermometer 40c that measures the ammoniacal nitrogen concentration NH4 of the raw water. + an ammonia meter or the chlorine demand of raw water Cl R It consists of one or both of the following: a chlorine demand meter that measures the amount of chlorine demand. The odor detection device 60 is an instrument that measures the concentration of moldy odor substances in the raw water, such as dimethylisoborneol (2-MIB) and geosmin. The dissolved organic matter meter 70 uses an ultraviolet spectrophotometer or the like that measures the absorbance of the raw water at ultraviolet wavelengths of 254 nm to 260 nm. The flow meter 80 measures the flow rate Q of the raw water flowing into the intake well 3. The pH meter 90 measures the pH of the hydrogen ion concentration index of the mixed water in the mixing tank 4. A Measure it.

[0042] (Water quality target setting section 100) The water quality target setting unit 100 sets the types Os of odor substances using various measurement results supplied from the raw water quality instrument set 40, and sets the target values of the sedimentation tank supernatant turbidity Tu b (degree), the odor substance concentration C Of (ng / L) of the filtered water, and sets the concentration management target value THMs T of trihalomethanes and the concentration management target value HAAs T of haloacetic acids.

[0043] (Functional configurations of the chemical injection rate initial assumption unit 200 and the disinfection by-product concentration estimation unit 300) Fig. 2 shows an example of the functional configurations of the chemical injection rate initial assumption unit 200 and the disinfection by-product concentration estimation unit 300.

[0044] The chemical injection rate initial assumption unit 200 includes a flocculant injection rate calculation unit 201, a pre-salt injection rate calculation unit 202, and a powdered activated carbon injection rate calculation unit 203.

[0045] The disinfection by-product concentration estimation unit 300 includes a trihalomethanes estimated concentration calculation unit 301 and a haloacetic acids estimated concentration calculation unit 302.

[0046] The flocculant injection rate calculation unit 201 uses the target values of the raw water turbidity Tu R (degree), the raw water temperature Tw R (°C), the flow rate Q (m 3 / h) measured by the flow meter 80, the hydrogen ion concentration index pH A (pH) of the mixed water measured by the pH meter 90 installed at the outlet of the mixing tank 4, and the sedimentation tank supernatant turbidity Tu b (degree) to calculate the appropriate flocculant injection rate I PACl (mg / L) by the following formula.

[0047] I PACl = f(Tu b ,Tu R ,pH A ,Tw R ,Q) ···(1) The pre-salt injection rate calculation unit 202 calculates the ammoniacal nitrogen concentration of the raw water (NH4) when the pre-salt indicator meter 50 is an ammonia meter. + (mg / L) and raw water flow rate Q(m 3 Using (h), the pre-salt injection rate I is calculated using the following equation (2). pre-Cl Calculate (mg / L), and if the pre-salt indicator meter 50 is a chlorine demand meter, then the chlorine demand of the raw water is Cl R (mg / L) and raw water flow rate Q(m 3 Using (L), the pre-salt injection rate I is calculated using the following equation (3). pre-Cl Calculate (mg / L).

[0048] I pre-Cl = f(NH4 + ,Q) ···(2) I pre-Cl = f(Cl R ,Q) ···(3) The powdered activated carbon injection rate calculation unit 203 calculates the type of odor substance Os and its concentration C measured by the odor detection device 60. OR (ng / L), UV absorbance measured with the UV absorbance meter of the soluble organic matter instrument 70. 254R (abs / cm), raw water flow rate Q (mg / L) measured by flow meter 80, target odor substance concentration C in filtered water. Of Using (ng / L), the powdered activated carbon injection rate I is calculated using the following equation (4). CAR Calculate (mg / L).

[0049] I CAR = f(O S ,C OR ,Q,UV 254R ,C Of ) ···(4) Pre-salt injection rate I calculated in the initial assumption unit 200 of the drug injection rate pre-Cl (mg / L) and UV absorbance of raw water 254R (abs / cm), raw water temperature Tw R and pH of the hydrogen ion concentration index of the mixed water A The (pH) value is sent to the disinfection by-product concentration estimation unit 300.

[0050] The trihalomethane concentration estimation unit 301 estimates the concentration of trihalomethanes (THMs). The haloacetic acid concentration estimation unit 302 estimates the concentration of haloacetic acids (HAAs). The methods for estimating each concentration will be described later.

[0051] (Processing performed in the disinfection by-product concentration estimation unit 300) Figure 3 shows an example of the process mainly performed in the disinfection byproduct concentration estimation unit 300.

[0052] In Figure 3, the processes measured by instruments 40, 50, 60, 70, 80, and 90 are represented by the symbols 40A, 50A, 60A, 70A, 80A, and 90A, respectively. Furthermore, the processes performed by the water quality target setting unit 100, the initial chemical injection rate assumption unit 200, and the disinfection by-product concentration estimation unit 300 are represented by the symbols 100A, 200A, and 300A, respectively.

[0053] In the disinfection by-product concentration estimation unit 300, a process 300A is performed to estimate the concentration of disinfection by-products. The various information used in process 300A in the disinfection by-product concentration estimation unit 300 is obtained from the process 100A performed in the water quality target setting unit 100 and the process 200A performed in the initial chemical injection rate assumption unit 200. In particular, the initial chemical injection rate assumption unit 200 is used to obtain the coagulant injection rate I obtained in processes 201A, 202A, and 203A, respectively. PACl (mg / L), presalt injection rate I pre-Cl (mg / L), powder activated carbon injection rate I CAR (mg / L) is obtained.

[0054] The calculation process performed in the disinfection by-product concentration estimation unit 300 includes various processes 311A, 312A, 313A, 314A, 315A, 316A, 317A, 301A, and 302A, each of which is calculated using a function or calculation formula described later.

[0055] In process 311A, based on information obtained from the water quality target setting unit 100 or the initial assumption unit 200 for chemical injection rate, the dissolved organic carbon concentration (DOC) of the raw water is determined. R Calculate (mg / L).

[0056] In process 312A, the specific absorbance SUVA (abs·L / (m·mg)) of the raw water is calculated based on the calculation results of process 311A.

[0057] In process 313A, based on information obtained from the water quality target setting unit 100 or the initial assumption unit 200 for chemical injection rate, the fluorescence intensity (FL) of the raw water is determined. R (For example, calculate the fluorescence intensity at a fluorescence wavelength of 425 nm relative to an excitation wavelength of 345 nm.)

[0058] In process 314A, based on information obtained from the water quality target setting unit 100 or the initial chemical injection rate assumption unit 200, the ultraviolet absorbance UV of the treated water remaining after adsorption treatment with powdered activated carbon is determined. 254CAR UV absorbance of raw water 254R RUV (Remaining Value) CAR The (remaining UV absorbance after adsorption treatment) is calculated.

[0059] In process 315A, based on information obtained from the water quality target setting unit 100 or the initial chemical injection rate assumption unit 200, the ultraviolet absorbance UV of the treated water remaining after the coagulation treatment is determined. 254PACl UV absorbance of raw water 254R RUV (Remaining Value) PACl The (remaining UV absorbance after agglomeration treatment) is calculated.

[0060] In process 316A, based on information obtained from the water quality target setting unit 100 or the initial assumption unit 200 of the chemical injection rate, the coefficient F is calculated when combined treatment using powdered activated carbon and coagulant injection is performed. DOM Calculate the (combined processing coefficient).

[0061] In process 317A, based on the calculation results of processes 314A, 315A, and 316A, the UV absorbance of the treated water (filtered water) after passing through the sand filter tank 6 is calculated. 254f UV absorbance of raw water 254R The remaining UV (RUV) value is calculated for this.

[0062] In process 301A, based on the information obtained from the water quality target setting unit 100 or the initial assumption unit 200 for chemical injection rate and the calculation results of process 312A, the estimated concentration values ​​of trihalomethanes (THMs) are calculated. E The concentration (mg / L) is calculated. This calculation is performed by the trihalomethane estimation concentration calculation unit 301 shown in Figure 2.

[0063] In process 302A, based on the information obtained from the water quality target setting unit 100 or the initial assumption unit 200 of the chemical injection rate and the calculation results of process 312A, the concentration estimate value of haloacetic acids HAAs is calculated. E The concentration (mg / L) is calculated. This calculation is performed by the haloacetic acid estimation concentration calculation unit 302 in Figure 2.

[0064] (Details of the process performed in the disinfection by-product concentration estimation unit 300) Here, we will first explain the details of processes 301A and 302A shown in Figure 3, and then explain the details of processes 311A ​​to 317A.

[0065] In process 301A, the estimated concentration of trihalomethanes is THMs. E (mg / L) is determined. In process 302A, the concentration estimate value of haloacetic acids HAAs is obtained. E (mg / L) is required.

[0066] Processes 301A and 302A use equations (5) and (6) below, respectively. These arithmetic formulas are stored in a predetermined memory area.

[0067] THMs E = α0 × SUVA α1 ×RUV α2 ×Tw R α3 ×I pre-Cl α4 ×pH A α5 ...(5) HAAs E = β0 × SUVA β1 ×RUV β2 ×Tw R β3×I pre-Cl β4 ×pH A β5 ···(6) Here, equations (5) and (6) are regression equations in which the coefficients α0 to α5 and β0 to β5 are determined by regression analysis using the treatment conditions and water quality analysis results collected in the preliminary investigation of the water treatment facility 1.

[0068] (5) formula, Tw in (6) formula R is the raw water temperature measured by the thermometer 40c of the raw water quality instrument set 40, I pre-Cl is the pre-salt injection rate (mg / L) calculated by the pre-salt injection rate calculation unit 202 of the chemical injection rate initial assumption unit 200, pH A is the hydrogen ion concentration index (pH) of the mixed water measured by the pH meter 90 attached to the outlet of the mixing tank 4. pH A can be regarded as the average hydrogen ion concentration index (pH) of the treated water. This average hydrogen ion concentration index of the treated water is pH A may also be obtained using not only pH but also the pH value measured by the pH meter 91.

[0069] Also, the SUVA in equations (5) and (6) is the specific absorbance of the raw water (abs·L / (m·mg)), and is obtained from the ultraviolet absorbance UV of the raw water 254R (abs / cm) and the dissolved organic carbon concentration DOC of the raw water R (mg / L) by the following equation (7). The calculation of equation (7) is performed in treatment 312A.

[0070] SUVA = (100×UV 254R ) / DOC R ···(7) The ultraviolet absorbance UV of the raw water 254R (abs / cm) is the measured value by the ultraviolet absorbance meter installed as the dissolved organic matter meter 70 in the pipe 2. Also, when the water source of the raw water does not fluctuate, UV 254R (abs / cm) and DOC R (mg / L) have a strong correlation, and the following equation (8) can be applied. DOC R (mg / L) is UV 254RIt can be calculated from equation (8). The calculation of equation (8) is performed in process 311A.

[0071] DOC R = c×UV 254R ×d ···(8) Here, c and d are constants, and when the organic matter composition of the water source is stable throughout the year, they can be obtained through prior investigation.

[0072] Also, RUV is the residual rate of ultraviolet absorbance after adsorption treatment with powdered activated carbon and removal treatment with a flocculant, that is, the ultraviolet absorbance UV of the treated water (filtered water) after passing through the sand filtration tank 6 254f of the ultraviolet absorbance UV of the raw water 254R and can be estimated by the following equation (9) from the action of the powdered activated carbon and flocculant injected between the intake well 3 and the coagulation sedimentation tank 5. The calculation of equation (9) is performed in process 317A.

[0073] RUV = F DOM ×RUV CAR ×RUV PACl ···(9) Here, F DOM is the coefficient (combined treatment coefficient) when combined treatment with powdered activated carbon and flocculant injection is performed, and when either is performed alone, F DOM = 1.0. The calculation of F DOM is performed in process 316A. Also, RUV CAR is the residual rate of the ultraviolet absorbance UV of the treated water remaining after adsorption treatment with powdered activated carbon 254CAR of the ultraviolet absorbance UV of the raw water 254R and is estimated by the following equation (10). The calculation of equation (10) is performed in process 314A.

[0074] RUV CAR = f(I CAR ,UV 254R ,K DOM ,N DOM ) ···(10) ]>Here, I CARThe powder activated carbon injection rate (mg / L) is substituted with the value calculated by the powder activated carbon injection rate calculation unit 203 of the initial assumption unit 200 for the chemical injection rate. 254R This is the ultraviolet absorbance of the raw water measured with a raw water ultraviolet intensity meter. DOM , N DOM These are coefficients, and represent the adsorption coefficients for organic matter adsorption by powdered activated carbon. The values ​​obtained from jar tests or other methods used for prior evaluation of the powdered activated carbon to be used are applied.

[0075] Also, RUV in equation (9) PACl UV absorbance of treated water remaining after coagulation treatment 254PACl UV absorbance of raw water 254R This is the remaining rate (remaining ultraviolet absorbance after agglomeration treatment), and is estimated by the following equation (11). The calculation of equation (11) is performed in treatment 315A.

[0076] RUV PACl = α × I PACl β ...(11) Here, I PACl is the coagulant injection rate (mg / L). α and β are coefficients, respectively, and the values ​​obtained from the prior jar test are applied.

[0077] (Processing performed in the chlorine injection determination unit 400 and the powdered activated carbon injection correction calculation unit 500) Figure 4 shows an example of the processing mainly performed by the chlorine injection determination unit 400 and the powder activated carbon injection correction calculation unit 500.

[0078] In Figure 4, the processes performed in the chlorine injection determination unit 400 and the powder activated carbon injection correction calculation unit 500 are represented by symbols 400A and 500A, respectively. The symbols 40A, 50A, 60A, 70A, 80A, 90A, and 100A, 200A, 300A are as described above.

[0079] The processes 400A performed in the chlorine injection determination unit 400 include determination process 401A and determination process 402A.

[0080] The determination process 401A is a process for determining whether to perform pre-salt injection or mid-salt injection, and is performed by the pre-salt / mid-salt determination unit 401 in Figure 1.

[0081] The determination process 402A is a process for determining whether to perform the first pre-salt injection or the second pre-salt injection when pre-salt injection is to be performed, and is performed by the pre-salt injection point determination unit 402 in Figure 1.

[0082] Details of the various processes performed in the chlorine injection determination unit 400 will be explained later.

[0083] The processing 500A performed by the powder activated carbon injection correction calculation unit 500 includes processing 501A, 502A, 503A, and 504A.

[0084] In procedure 501A, when a medium salt injection is performed, the powder activated carbon injection rate I assumed in procedure 200A is used. CAR Powdered activated carbon injection rate I without correction car This is the process to be adopted.

[0085] Process 502A is a process that calculates the ΔRC (Deficit Rate of Odor-Retaining Substances) due to the inhibitory effect of chlorine on powdered activated carbon when the first pre-salt injection is performed.

[0086] Process 503A is a process that calculates the residual odor substance ΔRC released from the powdered activated carbon due to the desorption action of the chlorine agent when a second pre-salt injection is performed.

[0087] Process 504A uses the above ΔRC calculated in process 502A or process 503A to determine the powder activated carbon injection rate I CAR The corrected value for the powder activated carbon injection rate I car This is the process to be adopted.

[0088] Details of the various processes performed in the powder activated carbon injection correction calculation unit 500 will be explained later.

[0089] (Details of the process performed in the chlorine injection detection unit 400) In judgment process 401A, the target value for trihalomethane concentration THMs set in the water quality target setting unit 100 is used. T And the estimated concentration values ​​of trihalomethanes (THMs) estimated by the disinfection byproduct concentration estimation unit 300. E In addition to comparing them, the target values ​​for controlling the concentration of haloacetic acids are HAAs. T And the estimated concentration value of haloacetic acids, HAAs, estimated by the disinfection byproduct concentration estimation unit 300. E Compare them.

[0090] Estimated concentration values ​​of trihalomethanes (THMs) E The target value for controlling the concentration of trihalomethanes is THMs. T If the above is true (or the concentration control target value THMs) T (If it is greater than) or estimated value of haloacetic acid concentration HAs E The target value for controlling the concentration of haloacetic acids is HAAs. T If the above is true (or if the concentration control target value of HAAs is exceeded) T If the value is greater than the limit, the concentration of disinfection by-products exceeds the permissible limit, making it difficult to suppress the generation of disinfection by-products by pre-salt injection. In this case, it is decided not to perform pre-salt injection using the first pre-salt injection device 10a or the second pre-salt injection device 10b, and instead to perform intermediate salt injection using the intermediate salt injection device 11. Otherwise, it is considered possible to suppress the generation of disinfection by-products by pre-salt injection, and it is decided to perform pre-salt injection, and the determination process 402 is performed. If it is decided to perform intermediate salt injection, chlorine is injected by the intermediate salt injection device 11.

[0091] In judgment process 402A, the estimated concentration of trihalomethanes is THMs. E and estimated values ​​of haloacetic acids HAs E By comparing the estimated concentrations of trihalomethanes (THMs), E Haloacetic acid estimated value HAs E If the above applies (or if the estimated value of haloacetic acids is HAs) EIf the value is greater than the value, it is decided to perform the first pre-salt injection without performing the second pre-salt injection. If it is decided to perform the first pre-salt injection, the chlorine agent is injected by the first pre-salt injection device 10a.

[0092] Meanwhile, the estimated concentration of haloacetic acids is HAs E This is the estimated concentration value of trihalomethanes (THMs). E If the above applies (or if the estimated concentration of trihalomethanes is THMs) E If the value is greater than the value, it is decided to skip the first pre-salting and instead perform the second pre-salting injection. If it is decided to perform the second pre-salting injection, the chlorine agent is injected by the second pre-salting injection device 10b.

[0093] The inventors confirmed through the following tests that the above-described process has the effect of suppressing the generation of disinfection by-products that pose a high risk of formation.

[0094] The test used simulated raw water prepared by adjusting pure water with humic acid and fulvic acid to achieve a 1:1 ratio of soluble organic carbon concentrations, resulting in a total soluble organic carbon concentration of approximately 3.0 mg / L. The concentrations of trihalomethanes (THMs) and haloacetic acids (HAAs) were compared under the following conditions: (1) First, 1-3 mg / L of sodium hypochlorite was added to the raw water, stirred at 150 rpm for 30 minutes using a jar tester, then 5 mg / L of powdered activated carbon was added and stirred at the same speed for 60 minutes; and (2) First, 5 mg / L of powdered activated carbon was added to the raw water, stirred at 150 rpm for 60 minutes using a jar tester, then 1-3 mg / L of sodium hypochlorite was added and stirred at the same speed for 30 minutes.

[0095] Figure 5 shows a graph comparing the concentration of trihalomethanes (THMs) in the treated water, and Figure 6 shows a graph comparing the concentration of haloacetic acids (HAAs) in two cases: (1) when the water is treated with chlorine followed by powdered activated carbon, and (2) when the water is treated with powdered activated carbon followed by chlorine. In the graphs in Figures 5 and 6, the horizontal axis shows the chlorine injection rate (mg / L), and the vertical axis shows the concentration of trihalomethanes (THMs) or haloacetic acids (HAAs) (μg / L).

[0096] As shown in Figure 5, the concentration of trihalomethanes (THMs) in the treated water is lower when the treatment is performed in the order of (1) chlorine agent → powdered activated carbon than when the treatment is performed in the order of (2) powdered activated carbon → chlorine agent. Similarly, as shown in Figure 6, the concentration of haloacetic acids (HAAs) is lower when the treatment is performed in the order of (2) powdered activated carbon → chlorine agent than when the treatment is performed in the order of (1) chlorine agent → powdered activated carbon.

[0097] Therefore, it can be seen that the risk of disinfection byproduct formation can be reduced by performing pre-salting before powdered activated carbon treatment when there is a high risk of trihalomethane (THMs) formation, and by performing pre-salting after powdered activated carbon treatment when there is a high risk of haloacetic acid (HAAs) formation.

[0098] (Details of the processing performed by the powder activated carbon injection correction calculation unit 500) In treatment 500A, for example, the powdered activated carbon injection rate I is determined according to the desorption rate of odor substances adsorbed onto the powdered activated carbon due to the pre-salting treatment. car Change it.

[0099] Here, referring to the graph in Figure 7, we will explain that the slope of the increase in the 2-MIB retention rate with increasing chlorine injection rate differs between (1) when the treatment is performed in the order of chlorine agent → powdered activated carbon and (2) when the treatment is performed in the order of powdered activated carbon → chlorine agent. In the graph in Figure 7, the horizontal axis shows the chlorine injection rate (mg / L), and the vertical axis shows the retention rate RC of dimethylisoborneol (2-MIB). 2-MIB (%) indicates the percentage.

[0100] Figure 7 shows the chlorine agent injection rate (mg / L) and the 2-MIB concentration after treatment for the following cases: (1) adding 1-3 mg / L of sodium hypochlorite and stirring in a jar tester at 150 rpm for 30 minutes, then adding 5 mg / L of powdered activated carbon and stirring at the same speed for 60 minutes; and (2) adding 5 mg / L of powdered activated carbon and stirring in a jar tester at 150 rpm for 60 minutes, then adding 1-3 mg / L of sodium hypochlorite and stirring at the same speed for 30 minutes. 2-MIB The 2-MIB concentration in the raw water C 2-MIBR Remaining rate RC 2-MIB (=C 2-MIB / C 2-MIBR This shows the relationship with ).

[0101] Comparing the cases where (1) chlorine agent was treated first, then powdered activated carbon, and (2) powdered activated carbon was treated first, the 2-MIB remaining rate RC increased with increasing chlorine agent injection rate under both conditions. 2-MIB Although both show an increase, the slope of the increase differs, and it can be seen that the increase is greater when the treatment is in the order of (2) powdered activated carbon → chlorine agent than when the treatment is in the order of (1) chlorine agent → powdered activated carbon.

[0102] This is because, (1) when the treatment is performed in the order of chlorine agent → powdered activated carbon, the chlorine agent acts as a competitor or inhibitor in the adsorption of 2-MIB by the powdered activated carbon, whereas (2) when the treatment is performed in the order of powdered activated carbon → chlorine agent, 2-MIB is adsorbed by the powdered activated carbon that is injected first, but the subsequent treatment with the chlorine agent causes 2-MIB to desorb from the powdered activated carbon.

[0103] Therefore, the powder activated carbon injection rate I assumed by the powder activated carbon injection rate calculation unit 203 of the initial assumption unit 200 of the chemical injection rate CAR If left as is, the concentration of odor substances due to inhibition or desorption by chlorine will exceed the target level.

[0104] In this embodiment, to address the above problem, when the first pre-salt injection is performed, the ΔRC for the remaining odor substance in the powdered activated carbon due to the inhibitory effect of the chlorine agent is estimated in treatment 502A using the following formula.

[0105] ΔRC = δ 1st ×Exp(n 1st ×I pre-Cl ) ···(12) Here, I pre-Cl is the pre-salt injection rate, δ 1st n is the constant of the first pre-salt. 1st This is the coefficient.

[0106] On the other hand, when a second pre-salt injection is performed, the residual odor substance ΔRC released from the powdered activated carbon by the desorption action of the chlorine agent in treatment 503A is estimated by the following formula.

[0107] ΔRC = δ 2st ×Exp(n 2st ×I pre-Cl ) ···(13) Here, I pre-Cl is the pre-salt injection rate, δ 2nd n is the constant of the second pre-salt. 2nd This is the coefficient.

[0108] Next, the target value RC for the residual rate of odor substances after treatment. T Subtracting the above ΔRC from (RC T -ΔRC) is set as the new target value for residual odor substances, and the powdered activated carbon injection rate I is calculated using the following formula. CAR Correct it.

[0109] I CAR = f(O S ,(RC T -ΔRC), Q, UV 254R ) ···(14) In this way, the powdered activated carbon injection rate I CAR The corrected value for the powder activated carbon injection rate I car By adopting this, the appropriate powdered activated carbon injection rate I car The powdered activated carbon injection will be performed by the powdered activated carbon injection device 20.

[0110] (Example flowchart) Next, an example of the operation of the water treatment system of this embodiment will be explained with reference to the flowchart in Figure 8.

[0111] First, the water quality target setting unit 100 sets target values ​​for various physical quantities that indicate the water quality of the treated water. Specifically, for example, the target value for controlling the concentration of trihalomethanes is THMs. T and target values ​​for controlling the concentration of haloacetic acids (HAAs) T This is set (step S1).

[0112] In the initial chemical injection rate setting unit 200, the injection rates of the chemicals to be injected into the water to be treated are provisionally set. Specifically, the injection rate of the coagulant used in the coagulation treatment (coagulant injection rate) I PACl , the injection rate of chlorine used in pre-salting (pre-salting injection rate) pre-Cl The injection rate of powdered activated carbon used in the adsorption treatment (powdered activated carbon injection rate) CAR These are calculated and provisionally set (step S2).

[0113] In the disinfection by-product concentration estimation unit 300, the concentrations of trihalomethanes (THMs) and haloacetic acids (HAAs), which are disinfection by-products generated during the water purification process, are estimated using the target water quality set by the water quality target setting unit 100 and the injection rates of each chemical provisionally set by the chemical injection rate initial assumption unit 200 (Step S3).

[0114] The pre-salt / intermediate salt determination unit 401 of the chlorine injection determination unit 400 determines whether to perform pre-salt injection or intermediate salt injection. Specifically, it determines the estimated concentration of trihalomethanes, THMs. E The target value for controlling the concentration of trihalomethanes is THMs. T Is it above (or is it the concentration control target value THMs)? T (or greater than), or estimated values ​​of haloacetic acid concentrations (HAAs) E The target value for controlling the concentration of haloacetic acids is HAAs. T Is it above (or is it the concentration control target value HAAs)? TIt is determined whether it is greater than (Step S4).

[0115] If either condition is met in step S4 (at least one of them), the concentration of disinfection by-products exceeds the permissible value, and it is determined that suppressing the generation of disinfection by-products by pre-salt injection is difficult. In that case, it is decided that pre-salt injection will not be performed using the first pre-salt injection device 10a or the second pre-salt injection device 10b, and intermediate salt injection will be performed using the intermediate salt injection device 11 (step S5). Then, the powder activated carbon injection rate I, which was provisionally set in step S2, is determined. CAR The powdered activated carbon injection rate I remains unchanged without correction. car It is adopted as such, and controlled to carry out powdered activated carbon injection and medium salt injection (step S6).

[0116] On the other hand, if none of the above conditions apply in step S4, it is considered that the generation of disinfection by-products by pre-salt injection can be suppressed. In that case, the pre-salt injection point determination unit 402 of the chlorine agent injection determination unit 400 determines whether to perform the first pre-salt injection or the second pre-salt injection. Specifically, the estimated concentration values ​​of trihalomethanes (THMs) are used. E Haloacetic acid estimated value HAs E Is it above (or is it an estimated value of haloacetic acids HAAs)? E It is determined whether it is greater than (step S7).

[0117] If applicable in step S7, it is decided to perform the first pre-salt injection without performing the intermediate salt injection or the second pre-salt injection (step S8). In that case, the powdered activated carbon injection correction calculation unit 500 calculates the ΔRC for the remaining odor substance rate of the powdered activated carbon due to the inhibitory effect of the chlorine agent, and uses this ΔRC to perform the powdered activated carbon injection rate I CAR The corrected value is the powder activated carbon injection rate I car It is adopted as such, and controlled to carry out the first pre-salt injection and powdered activated carbon injection (step S9).

[0118] On the other hand, if the conditions in step S7 are not met, it is decided to perform a second pre-salt injection without performing a mid-salt injection or a first pre-salt injection (step S10). In that case, the powder activated carbon injection correction calculation unit 500 calculates the residual odor substance ΔRC released from the powder activated carbon due to the desorption action of the chlorine agent, and uses this ΔRC to determine the powder activated carbon injection rate I CAR The corrected value is the powder activated carbon injection rate I car It is adopted as such, and controlled to perform powder activated carbon injection and second pre-salt injection (step S11).

[0119] (summary) As detailed above, according to the embodiment, it is possible to suppress the generation of disinfection by-products.

[0120] For example, in the above embodiment, the disinfection by-product concentration estimation unit 300 can estimate the concentrations of trihalomethanes (THMs) and haloacetic acids (HAAs), which are disinfection by-products generated during the water purification process, using the target water quality set by the water quality target setting unit 100 and the injection rates of each chemical provisionally set by the chemical injection rate initial assumption unit 200.

[0121] Furthermore, in the determination by the pre-salt / intermediate-salt determination unit 401 of the chlorine agent injection determination unit 400, the estimated concentration value of trihalomethanes is THMs. E The target value for controlling the concentration of trihalomethanes is THMs. T If the above is true (or the concentration control target value THMs) T (If it is greater than) or estimated value of haloacetic acid concentration HAs E The target value for controlling the concentration of haloacetic acids is HAAs. T If the above is true (or if the concentration control target value of HAAs is exceeded) T If the value is greater than the limit, the concentration of disinfection by-products exceeds the permissible limit, making it difficult to suppress the generation of disinfection by-products by pre-salt injection. Therefore, pre-salt injection by the first pre-salt injection device 10a and the second pre-salt injection device 10b is not performed, and it is decided to perform intermediate salt injection by the intermediate salt injection device 11, thereby avoiding the excessive generation of disinfection by-products.

[0122] Furthermore, if the concentration of disinfection by-products does not exceed the permissible value, the pre-salt injection point determination unit 402 of the chlorine agent injection determination unit 400 will determine the estimated concentration of trihalomethanes (THMs). E and estimated concentrations of haloacetic acids (HAAs) E The two are compared, and based on the comparison results, either the first or second pre-salt injection is selected, thereby suppressing the generation of disinfection by-products with a high risk of formation. Furthermore, since the injection point of the chlorine agent can be determined in a way that suppresses the generation of disinfection by-products with a high risk of formation, oxidation (removal) of ammoniacal nitrogen and metal ions such as iron and manganese by the pre-salt becomes possible.

[0123] Furthermore, in the powder activated carbon injection correction calculation unit 500, the powder activated carbon injection rate I is calculated according to the injection point of the chlorine agent. car Since this can be properly corrected, it is possible to prevent exceeding the target value for odor treatment.

[0124] The various functions constituting the water treatment system in the above-described embodiment can be implemented by a computer. In this case, the functions may be implemented by recording a program for implementing these functions on a computer-readable recording medium, loading the program recorded on this recording medium into a computer system, and executing it. Here, "computer system" includes hardware such as the OS and peripheral devices. Furthermore, "computer-readable recording medium" refers to portable media such as flexible disks, magneto-optical disks, ROMs, CD-ROMs, and storage devices such as hard disks built into a computer system. Moreover, "computer-readable recording medium" may also include those that dynamically hold programs for a short period of time, such as communication lines used when transmitting programs via networks such as the Internet or communication lines such as telephone lines, and those that hold programs for a certain period of time, such as volatile memory inside a computer system that acts as a server or client in such cases. Furthermore, the above-mentioned program may only implement a part of the functions described above, and may also be able to implement the above-mentioned functions in combination with programs already recorded in the computer system.

[0125] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents. [Explanation of symbols]

[0126] 1...Water treatment facility, 2...Piping, 3...Intake well, 4...Mixing tank, 5...Coagulation and sedimentation tank, 6...Sand filter tank, 7...Water purification tank, 8...First pre-salt injection pipe, 10a...First pre-salt injection device, 10b...Second pre-salt injection device, 11...Intermediate salt injection device, 12...Post-salt injection device, 20...Activated carbon injection device, 30...Coagulant injection device, 40...Raw water quality meter set, 50...Pre-salt indicator meter, 60...Odor detection device, 70...Dissolved organic Physical instrument, 80...flow meter, 90...pH meter, 91...pH meter, 100...water quality target setting unit, 200...initial assumption unit for chemical injection rate, 201...coagulant injection rate calculation unit, 202...pre-salt injection rate calculation unit, 203...powdered activated carbon injection rate calculation unit, 300...disinfection by-product concentration estimation unit, 400...chlorine agent injection determination unit, 401...pre-salt / intermediate salt determination unit, 402...pre-salt injection point determination unit, 500...powdered activated carbon injection correction calculation unit.

Claims

1. A disinfection by-product concentration estimation unit calculates estimated concentrations of a first disinfection by-product and a second disinfection by-product generated during the water purification process, A pre-salt / intermediate-salt determination unit determines whether at least one of the estimated concentration values ​​of the first disinfection by-product and the second disinfection by-product exceeds an acceptable value, and if it exceeds an acceptable value, it decides not to perform pre-salt injection and to perform intermediate-salt injection. If neither the estimated concentration of the first disinfection by-product nor the estimated concentration of the second disinfection by-product exceeds an acceptable value, the pre-salt injection point determination unit compares the estimated concentration of the first disinfection by-product and the estimated concentration of the second disinfection by-product, and determines, according to the comparison result, whether to perform a first pre-salt injection, injecting the chlorine agent at an injection point located upstream of the powdered activated carbon injection point in the water treatment process, or a second pre-salt injection, injecting the chlorine agent at an injection point located downstream of the powdered activated carbon injection point in the water treatment process. A water treatment system equipped with the following features.

2. The first disinfection by-product is a trihalomethane, The second disinfection by-product is a haloacetic acid. The water treatment system according to claim 1.

3. The aforementioned pre-salt injection point determination unit is: If the estimated concentration of the first disinfection by-product is equal to or greater than the estimated concentration of the second disinfection by-product, or if it exceeds the estimated concentration of the second disinfection by-product, it is decided to perform the first pre-salt injection; otherwise, it is decided to perform the second pre-salt injection. The water treatment system according to claim 2.

4. The system further comprises a powder activated carbon injection correction calculation unit for correcting the powder activated carbon injection rate, The aforementioned powder activated carbon injection correction calculation unit is: When the first pre-salt injection is performed, the deficiency in the remaining odor substances of the powdered activated carbon due to the inhibitory effect of the chlorine agent is calculated, When the second pre-salt injection described above is carried out, the residual rate of odor substances released from the powdered activated carbon due to the desorption action of the chlorine agent is calculated, The powdered activated carbon injection rate is corrected using the remaining odor substance percentage of the powdered activated carbon or the remaining odor substance percentage of the released portion. The water treatment system according to claim 1.

5. The disinfection by-product concentration estimation unit is, The concentration estimates of the first disinfection by-product and the concentration estimates of the second disinfection by-product are calculated using a regression equation that includes at least the specific absorbance of the raw water, the residual UV absorbance after adsorption treatment with powdered activated carbon and removal treatment with a coagulant, the temperature of the raw water, the pre-salt injection rate, and the average hydrogen ion concentration index of the water to be treated. A water treatment system according to any one of claims 1 to 4.

6. The disinfection by-product concentration estimation unit calculates the estimated concentrations of the first and second disinfection by-products generated during the water purification process, The pre-salt / intermediate salt determination unit determines whether at least one of the estimated concentration values ​​of the first disinfection by-product and the second disinfection by-product exceeds an acceptable value. If it exceeds an acceptable value, it is decided not to perform pre-salt injection and to perform intermediate salt injection. If neither the estimated concentration of the first disinfection by-product nor the estimated concentration of the second disinfection by-product exceeds the permissible value, the estimated concentration of the first disinfection by-product and the estimated concentration of the second disinfection by-product are compared, and based on the result of the comparison, it is determined whether to perform a first pre-salt injection, injecting the chlorine agent at an injection point located upstream of the powdered activated carbon injection point in the water treatment process, or a second pre-salt injection, injecting the chlorine agent at an injection point located downstream of the powdered activated carbon injection point in the water treatment process. A water treatment method, including

7. On the computer, A function to calculate estimated concentrations of the first and second disinfection by-products generated during the water purification process, The system has a function to determine whether at least one of the estimated concentration values ​​of the first disinfection by-product and the second disinfection by-product exceeds an acceptable value, and if it exceeds an acceptable value, to decide to perform intermediate salt injection instead of pre-salt injection. If neither the estimated concentration of the first disinfection by-product nor the estimated concentration of the second disinfection by-product exceeds the permissible value, the system compares the estimated concentration of the first disinfection by-product with the estimated concentration of the second disinfection by-product and, based on the comparison result, determines whether to perform a first pre-salt injection, injecting chlorine at an injection point located upstream of the powdered activated carbon injection point in the water treatment process, or a second pre-salt injection, injecting chlorine at an injection point located downstream of the powdered activated carbon injection point in the water treatment process. A program to achieve this.

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