JP7471143B2 - Water treatment method and water treatment device - Google Patents

Description

The present invention relates to a water treatment method and a water treatment device that use a separation membrane.

Suppressing biofouling is a major issue when operating separation membranes such as reverse osmosis membranes. Adding a disinfectant is effective in suppressing biofouling. However, it is difficult to accurately determine the necessary and sufficient amount of disinfectant, and in order to reliably suppress biofouling, it is common to add an excessive amount of disinfectant.

The amount of bactericide added is adjusted so that the concentration of residual active ingredients in the concentrated water remains at a specified value, in order to add just the right amount of bactericide necessary to suppress biofouling of the separation membrane and prevent the addition of excessive bactericide.

For example, Patent Document 1 proposes the use of a stabilized hypobromous acid composition as a disinfectant so that the total chlorine concentration in the concentrated water from the reverse osmosis membrane is in the range of 0.05 mg/L or more and less than 10 mg/L.

However, even if you only observe the concentration of residual active ingredients in the concentrated water, it may not be possible to correctly detect an increase or decrease in biofouling on the separation membrane surface, and it may not be possible to adjust the amount of bactericide added appropriately. In other words, even if the concentration of residual active ingredients in the concentrated water is the same, the state of biofouling on the separation membrane surface may differ.

JP 2018-015679 A

The object of the present invention is to provide a water treatment method and water treatment device that can efficiently suppress biofouling of a separation membrane in water treatment using a separation membrane.

The present invention is a water treatment method in which a separation membrane treatment is performed on water to be treated to which a chemical has been added to obtain permeate and concentrated water, in which the chemical is added to the water to be treated in a stage prior to the separation membrane treatment so that "chemical concentration in concentrated water/chemical concentration in water to be treated" is a predetermined value or more, and the active ingredient residual rate R represented by the following formula is 0.4 or more when the flow rate of the water to be treated is Ff, the flow rate of the concentrated water is Fc, the flow rate of the permeated water is Fp, the concentration of the chemical in the water to be treated is Cf, the concentration of the chemical in the concentrated water is Cc, and the concentration of the chemical in the permeated water is Cp .
R = Cc/Cct
Here, Cct = (Cf x Ff - Cp x Fp) / Fc

In the water treatment method, it is preferable that the agent contains a stabilized hypobromous acid composition that includes a bromine-based oxidizing agent and a sulfamic acid compound.

The present invention is a water treatment device that includes a separation membrane treatment means for performing a separation membrane treatment on the water to be treated to which a chemical has been added, to obtain a permeate and a concentrated water, and a control means for controlling the addition of the chemical to the water to be treated in the upstream of the separation membrane treatment so that "chemical concentration in the concentrated water/chemical concentration in the water to be treated" is a predetermined value or more, and the control means controls the addition of the chemical to the water to be treated in the upstream of the separation membrane treatment so that the active ingredient residual rate R represented by the following formula is 0.4 or more, where Ff is the flow rate of the water to be treated, Fc is the flow rate of the concentrated water, Fp is the flow rate of the permeated water, Cf is the concentration of the chemical in the water to be treated, Cc is the concentration of the chemical in the concentrated water, and Cp is the concentration of the chemical in the permeated water .
R = Cc/Cct
Here, Cct = (Cf x Ff - Cp x Fp) / Fc

In the water treatment device, it is preferable that the chemical agent contains a stabilized hypobromous acid composition that includes a bromine-based oxidizing agent and a sulfamic acid compound.

The present invention provides a water treatment method and water treatment device that can efficiently suppress biofouling of a separation membrane in water treatment using a separation membrane.

1 is a schematic configuration diagram illustrating an example of a water treatment device according to an embodiment of the present invention. FIG. 4 is a schematic configuration diagram showing another example of a water treatment device according to an embodiment of the present invention.

The following describes an embodiment of the present invention. This embodiment is an example of implementing the present invention, and the present invention is not limited to this embodiment.

An example of a water treatment device according to an embodiment of the present invention is outlined in FIG. 1, and its configuration will be described.

The water treatment device 1 includes a separation membrane treatment device 12 as a separation membrane treatment means for performing separation membrane treatment on the water to be treated to which a chemical has been added to obtain permeate water and concentrated water, and a control device 32 as a control means for controlling the addition of the chemical to the water to be treated upstream of the separation membrane treatment device 12. The water treatment device 1 may also include a water tank 10 for storing the water to be treated.

In the water treatment device 1 of FIG. 1, a treated water pipe 22 is connected to the treated water inlet of the treated water tank 10. The treated water outlet of the treated water tank 10 and the inlet of the separation membrane treatment device 12 are connected by a treated water pipe 24 via a pump 14. A permeated water pipe 26 is connected to the permeated water outlet of the separation membrane treatment device 12, and a concentrated water pipe 28 is connected to the concentrated water outlet. A chemical addition pipe 30 is connected to the chemical inlet of the treated water tank 10. A treated water chemical concentration measuring device 16 is installed upstream of the pump 14 in the treated water pipe 24 as a treated water chemical concentration measuring means for measuring the chemical concentration in the treated water. A permeated water chemical concentration measuring device 18 is installed in the permeated water pipe 26 as a permeated water chemical concentration measuring means for measuring the chemical concentration in the permeated water. A concentrated water chemical concentration measuring device 20 is installed in the concentrated water pipe 28 as a concentrated water chemical concentration measuring means for measuring the chemical concentration in the concentrated water. The control device 32 is electrically connected to the treated water drug concentration measuring device 16, the permeate water drug concentration measuring device 18, the concentrated water drug concentration measuring device 20, and a drug addition amount adjustment means (not shown) that adjusts the amount of drug added installed in the drug addition piping 30.

The water treatment method and operation of the water treatment device 1 according to this embodiment will be described.

The water to be treated is stored in the water tank 10 as needed through the water pipe 22. In the water tank 10, chemicals are added to the water to be treated through the chemical addition pipe 30 (chemical addition process).

The chemicals may be added upstream of the separation membrane treatment device 12, and may be added in the treated water pipe 22 or in the treated water pipe 24.

The water to be treated with the chemicals added is pumped by pump 14 through water to be treated pipe 24 to separation membrane treatment device 12. In separation membrane treatment device 12, separation membrane treatment is performed on the water to be treated with the chemicals added, and permeated water and concentrated water are obtained (separation membrane treatment process). The permeated water is discharged through permeated water pipe 26, and the concentrated water is discharged through concentrated water pipe 28.

As in the water treatment device 3 shown in FIG. 2, the concentrated water pipe 28 may be connected to the upstream stage of the separation membrane treatment device 12, for example, the water tank 10 to be treated, and the concentrated water may be returned through the concentrated water pipe 28 to the upstream stage of the separation membrane treatment device 12, for example, the water tank 10 to be treated (return process).

The inventors have found that in water treatment in which a chemical is added before the separation membrane treatment, in order to detect an increase or decrease in biofouling on the separation membrane surface in the separation membrane treatment, it is effective to grasp or detect how much of the active ingredient of the chemical is consumed while passing through the separation membrane, and to add the chemical or adjust the amount of chemical added so as to reduce the consumption amount to a predetermined value or less. For example, by controlling the addition of the chemical added to the treated water before the separation membrane so that the chemical remains at a predetermined value or more according to the degree of consumption of the chemical while passing through the separation membrane, biofouling on the separation membrane can be efficiently suppressed with the minimum amount of chemical added.

For example, in the water treatment method and water treatment device 1 according to this embodiment, in the separation membrane treatment process, a chemical is added to the water to be treated prior to the separation membrane treatment so that the "chemical concentration in the concentrated water/chemical concentration in the water to be treated" is equal to or greater than a predetermined value.

In the water treatment method and water treatment device 1 according to the present embodiment, for example, in the separation membrane treatment step, the active ingredient residual rate R represented by the following formula is equal to or greater than a predetermined value. For example, in the separation membrane treatment step, a chemical may be added to the water to be treated in a stage prior to the separation membrane treatment so that the active ingredient residual rate R represented by the following formula is equal to or greater than a predetermined value.
R = Cc/Cct
Here, Cct = (Cf x Ff - Cp x Fp) / Fc
Ff: flow rate of treated water Fc: flow rate of concentrated water Fp: flow rate of permeated water Cf: concentration of chemical in treated water Cc: concentration of chemical in concentrated water Cp: concentration of chemical in permeated water

The active ingredient residual rate R expressed by the above formula is preferably 0.4 or more, and more preferably in the range of 0.5 to 0.9. In addition, it is preferable to add a chemical to the water to be treated in the stage before the separation membrane treatment so that the active ingredient residual rate R expressed by the above formula is 0.4 or more, and it is more preferable to add a chemical to the water to be treated in the stage before the separation membrane treatment so that the active ingredient residual rate R is in the range of 0.5 to 0.9. If the active ingredient residual rate R is less than 0.4, biofouling of the separation membrane may not be efficiently suppressed, and if it exceeds 0.9, the water quality of the permeate may be deteriorated. In addition, a chemical may be added to the water to be treated in the stage before the separation membrane treatment so that the active ingredient residual rate R is always a predetermined value or more, or a chemical may be added to the water to be treated in the stage before the separation membrane treatment so that the active ingredient residual rate R is periodically a predetermined value or more. Here, "periodic" means at intervals of 0.1 to 200 hours. The active ingredient residual rate R may be automatically controlled by the control device 32 or may be manually controlled.

<Separation membrane>
The separation membrane is not particularly limited, but examples thereof include reverse osmosis membranes (RO membranes), nanofiltration membranes (NF membranes), microfiltration membranes (MF membranes), and ultrafiltration membranes (UF membranes). Among these, when a reverse osmosis membrane (RO membrane) is used as the separation membrane, the water treatment method according to the embodiment of the present invention can be suitably applied. Furthermore, when a polyamide-based polymer membrane, which is currently mainstream, is used as the reverse osmosis membrane, the water treatment method according to the embodiment of the present invention can be suitably applied.

<Water to be treated>
The water to be treated is not particularly limited, but organic matter-containing water, particularly organic matter-containing water with a high organic matter concentration, is prone to biofouling, which results in a large consumption of chemicals during passage through the separation membrane, and therefore the water treatment method according to the embodiment of the present invention can be suitably applied. Specifically, the TOC concentration of the organic matter-containing water is preferably 0.1 mg/L or more, and more preferably 1 mg/L or more.

The pH of the water to be treated is, for example, in the range of 2 to 12, and preferably in the range of 4 to 11. The lower limit of the pH of the water to be treated is preferably 5.5 or more, more preferably 6.0 or more, and even more preferably 6.5 or more. The upper limit of the pH of the water to be treated is preferably 9.0 or less, and more preferably 8.0 or less.

<Additives>
The agent for controlling the addition is not particularly limited, but examples thereof include bactericides (slime inhibitors), dispersants, etc.

Among these, bactericides are preferred. Examples of bactericides include halocyanoacetamide compounds such as DBNPA (2,2-dibromo-3-nitrilopropionamide), isothiazolone compounds, organic bromine compounds such as bronopol (2-bromo-2-nitropropane-1,3-diol), and oxidizing agents. Halocyanoacetamide compounds such as DBNPA (2,2-dibromo-3-nitrilopropionamide) and oxidizing agents are preferred, as their active ingredients are easily consumed during passage through the separation membrane.

Examples of oxidizing agents include free halogen compounds such as hypochlorous acid and hypobromous acid, stabilized compositions containing bromine-based or chlorine-based oxidizing agents and sulfamic acid compounds, and combined halogen compounds such as chloramine.

Among these, a stabilized composition containing a bromine-based or chlorine-based oxidizing agent and a sulfamic acid compound is preferred.

The "stabilized composition containing a bromine-based oxidizing agent and a sulfamic acid compound" may be a stabilized hypobromous acid composition containing a mixture of a "bromine-based oxidizing agent" and a "sulfamic acid compound", or may be a stabilized hypobromous acid composition containing a "reaction product of a bromine-based oxidizing agent and a sulfamic acid compound". The "stabilized composition containing a chlorine-based oxidizing agent and a sulfamic acid compound" may be a stabilized hypochlorous acid composition containing a mixture of a "chlorine-based oxidizing agent" and a "sulfamic acid compound", or may be a stabilized hypochlorous acid composition containing a "reaction product of a chlorine-based oxidizing agent and a sulfamic acid compound".

Bromine-based oxidizing agents include bromine (liquid bromine), bromine chloride, bromic acid, bromates, hypobromous acid, etc. Hypobromous acid may be produced by reacting a bromine compound such as sodium bromide with a chlorine-based oxidizing agent such as hypochlorous acid. When the bromine-based oxidizing agent is bromine, there is no chlorine-based oxidizing agent present, and therefore the deterioration effect on separation membranes such as reverse osmosis membranes is significantly reduced.

Examples of chlorine-based oxidizing agents include chlorine gas, chlorine dioxide, hypochlorous acid or its salts, chlorous acid or its salts, chloric acid or its salts, perchloric acid or its salts, and chlorinated isocyanuric acid or its salts. Among these, examples of salts include alkali metal hypochlorite salts such as sodium hypochlorite and potassium hypochlorite, alkaline earth metal hypochlorite salts such as calcium hypochlorite and barium hypochlorite, alkali metal chlorite salts such as sodium chlorite and potassium chlorite, alkaline earth metal chlorite salts such as barium chlorite, other metal chlorite salts such as nickel chlorite, alkali metal chlorate salts such as ammonium chlorate, sodium chlorate and potassium chlorate, alkaline earth metal chlorate salts such as calcium chlorate and barium chlorate, etc. These chlorine-based oxidizing agents may be used alone or in combination of two or more. As the chlorine-based oxidizing agent, it is preferable to use sodium hypochlorite from the viewpoint of handling and the like.

Bromine compounds include sodium bromide, potassium bromide, lithium bromide, ammonium bromide, and hydrobromic acid. Of these, sodium bromide is preferred from the standpoint of formulation costs, etc.

The sulfamic acid compound is a compound represented by the following general formula (1).
_R2NSO3H ( ₁ )
(In the formula, R is independently a hydrogen atom or an alkyl group having 1 to 8 carbon atoms.)

Examples of sulfamic acid compounds include sulfamic acid (amidosulfuric acid) in which both R groups are hydrogen atoms, as well as sulfamic acid compounds in which one of the R groups is a hydrogen atom and the other is an alkyl group having 1 to 8 carbon atoms, such as N-methylsulfamic acid, N-ethylsulfamic acid, N-propylsulfamic acid, N-isopropylsulfamic acid, and N-butylsulfamic acid, sulfamic acid compounds in which both of the R groups are alkyl groups having 1 to 8 carbon atoms, such as N,N-dimethylsulfamic acid, N,N-diethylsulfamic acid, N,N-dipropylsulfamic acid, N,N-dibutylsulfamic acid, N-methyl-N-ethylsulfamic acid, and N-methyl-N-propylsulfamic acid, sulfamic acid compounds in which one of the R groups is a hydrogen atom and the other is an aryl group having 6 to 10 carbon atoms, such as N-phenylsulfamic acid, and salts thereof. Examples of sulfamic acid salts include alkali metal salts such as sodium salts and potassium salts, alkaline earth metal salts such as calcium salts, strontium salts and barium salts, other metal salts such as manganese salts, copper salts, zinc salts, iron salts, cobalt salts and nickel salts, ammonium salts and guanidine salts. Sulfamic acid compounds and their salts may be used alone or in combination of two or more. As the sulfamic acid compound, it is preferable to use sulfamic acid (amidosulfuric acid) from the viewpoint of environmental load, etc.

The stabilized hypobromous acid composition may further contain an alkali. Examples of the alkali include alkali hydroxides such as sodium hydroxide and potassium hydroxide. From the viewpoint of product stability at low temperatures, sodium hydroxide and potassium hydroxide may be used in combination. The alkali may be used as an aqueous solution instead of a solid.

Examples of dispersants include polyacrylic acid, polymaleic acid, and phosphonic acid.

<Identifying residual drugs>
There are no particular limitations on the treated water pesticide concentration measuring device 16, the permeate water pesticide concentration measuring device 18, and the concentrated water pesticide concentration measuring device 20 as long as they are capable of measuring pesticide concentrations.

Methods for measuring the residual concentration of halogen-based oxidizing agents include the DPD method and the polarographic method.

The concentration of the drug in the permeate of the separation membrane may be measured automatically or manually by a permeate drug concentration measuring device 18, or may be calculated from the concentration of the drug in the water to be treated and the membrane permeability specific to the drug. The flow rate of the permeate may be measured automatically or manually by a permeate flow rate measuring device installed in the permeate piping 26.

The drug concentration in the concentrate water of the separation membrane may be measured automatically or manually by a concentrate water drug concentration measuring device 20, or may be calculated from the drug concentration in the water to be treated and the membrane permeability specific to the drug. The flow rate of the concentrate water may be measured automatically or manually by a concentrate water flow rate measuring device installed in the concentrate water piping 28.

The concentration of the chemical in the water to be treated at the separation membrane may be measured automatically or manually by a chemical concentration measuring device 16, or may be calculated from the amount of chemical added to the water to be treated and the amount of water to be treated. The flow rate of the water to be treated may be measured automatically or manually by a water to be treated flow rate measuring device installed in the water to be treated piping 24.

The control device 32 is composed of a microcomputer and electronic circuits, which include, for example, a calculation means such as a CPU that calculates a program, and storage means such as ROM and RAM that store the program and the calculation results, and has the function of controlling the amount of chemical added to the treated water by adjusting the flow rate of the pump and the opening and closing degree of the valve installed in the chemical addition piping 30 based on the treated water chemical concentration, permeate water chemical concentration, and concentrated water chemical concentration measured by the treated water chemical concentration measuring device 16, the permeate water chemical concentration measuring device 18, and the concentrated water chemical concentration measuring device 20, or the treated water chemical concentration, permeate water chemical concentration, and concentrated water chemical concentration calculated based on at least one of these measured values. In addition, the control device 32 has the function of controlling the amount of chemicals added to the water being treated by adjusting the flow rate of the pump and the opening and closing degree of the valve installed in the chemical addition piping 30 based on the chemical concentration in the water being treated, the chemical concentration in the permeate water, and the chemical concentration in the concentrated water measured by the chemical concentration measuring device 16, the chemical concentration in the permeate water, and the chemical concentration in the concentrated water measured by the chemical concentration measuring device 18, and the chemical concentration in the treated water calculated based on at least one of these measured values, and the permeate flow rate, concentrated flow rate, and water being treated measured by the permeate flow rate measuring device, concentrated flow rate measuring device, and water being treated flow rate measuring device.

<How to add chemicals>
The agent added in the upstream stage of the separation membrane treatment may be added continuously or intermittently.

<Other configurations>
At a downstream stage of the separation membrane treatment, at least one of a reverse osmosis membrane treatment device, a UV treatment device, or an ion exchange treatment device may be provided, and at least one of a reverse osmosis membrane treatment, a UV treatment, or an ion exchange treatment may be performed on the permeate of the separation membrane treatment.

The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[Preparation of stabilized hypobromous acid composition]
A stabilized hypobromous acid composition was prepared by mixing 16.9% by weight (wt%) of liquid bromine, 10.7% by weight of sulfamic acid, 12.9% by weight of sodium hydroxide, 3.94% by weight of potassium hydroxide, and the remainder of water under a nitrogen atmosphere. The pH of the stabilized hypobromous acid composition was 14, and the total chlorine concentration was 7.5% by weight. The total chlorine concentration was a value (mg-Cl ₂ /L) measured by a total chlorine measurement method (DPD (diethyl-p-phenylenediamine) method) using a HACH multi-item water quality analyzer DR/4000. The detailed preparation method of the stabilized hypobromous acid composition is as follows.

1436g of water and 361g of sodium hydroxide were added and mixed into a 2L four-necked flask sealed with continuous injection while controlling the flow rate of nitrogen gas with a mass flow controller so that the oxygen concentration in the reaction vessel was maintained at 1%, and then 300g of sulfamic acid was added and mixed. After that, 473g of liquid bromine was added while maintaining cooling so that the temperature of the reaction liquid was 0-15°C, and further 230g of 48% potassium hydroxide solution was added, and the target stabilized hypobromous acid composition was obtained, which has a weight ratio of 10.7% sulfamic acid and 16.9% bromine to the total amount of the composition, and the equivalent ratio of sulfamic acid to bromine is 1.04. The pH of the resulting solution was measured by the glass electrode method and was 14. The bromine content of the resulting solution was 16.9% when measured by a method of converting bromine to iodine with potassium iodide and then performing oxidation-reduction titration with sodium thiosulfate, which was 100.0% of the theoretical content (16.9%). In addition, the oxygen concentration in the reaction vessel during the bromine reaction was measured using an oxygen monitor JKO-02 LJDII manufactured by JIKO Co., Ltd. The bromate concentration was less than 5 mg/kg.

The pH was measured under the following conditions.
Electrode type: Glass electrode type pH meter: IOL-30 type, manufactured by DKK-TOA Electrode calibration: Two-point calibration was performed using neutral phosphate pH (6.86) standard solution (type 2) manufactured by Kanto Chemical Co., Ltd. and borate pH (9.18) standard solution (type 2) manufactured by the same company. Measurement temperature: 25°C
Measurement value: Immerse the electrode in the measurement solution, and the value after stabilization is the measurement value, which is the average of three measurements.

<Examples 1 to 5>
Separation membrane treatment was carried out under the following experimental conditions. In Examples 1 to 5, the concentrations of chemicals in the water to be treated, the permeate, and the concentrated water were measured, and chemicals were added to the water to be treated so that the ratio of "chemical concentration in the concentrated water/chemical concentration in the water to be treated" was equal to or greater than a predetermined value. The results are shown in Table 1.

(Experimental conditions)
Test water: Mock water (groundwater + organic matter (10 mg/L as TOC))
Separation membrane: reverse osmosis membrane (DOW BW30-XFR)
Flow rate: treated water = 840 L/h, concentrated water = 700 L/h, permeated water = 140 L/h
Permeate recovery rate in separation membrane treatment: 17%
Drug: the stabilized hypobromous acid composition prepared above. Drug active ingredient detection method: DPD method (Hach spectrophotometer "DR-3900")

When biofouling occurs, the reverse osmosis membrane surface is clogged, and the permeability (flux) of the membrane decreases. Here, flux refers to the permeation flux of the permeated water of the reverse osmosis membrane, and indicates the amount of permeated water per unit area of the membrane under specified conditions. The decrease rate of flux was evaluated by "decrease rate of permeated water flux of RO membrane in the last 7 days (following formula)". In Examples 1 to 3, the R value was maintained at 0.4 or more, and almost no decrease in permeated water flux was confirmed. In addition, due to the accuracy of the meter of the concentration measurement device, a variation of 2% or less cannot be said to be a significant difference.
"Reduction rate of RO membrane permeate flux in the last 7 days" = 100 - (Flux at time of measurement / Flux 7 days before measurement) x 100

On the other hand, in Examples 4 and 5, although the effective concentration of the drug in the concentrated water was at the same level as in Examples 1 to 3, the R value was less than 0.4, and a slight decrease in the permeate flux due to biofouling was observed.

<Examples 6 and 7>
Separation membrane treatment was carried out for a longer period of time under the same experimental conditions as in Examples 1 to 5. In Examples 6 and 7, the concentrations of chemicals in the water to be treated, the permeate, and the concentrated water were measured, and chemicals were added to the water to be treated so that the ratio of "chemical concentration in the concentrated water/chemical concentration in the water to be treated" was equal to or greater than a predetermined value. The results are shown in Table 2.

The results of Examples 6 and 7 show that controlling the addition of chemicals using the R value can suppress biofouling for a longer period of time.

In this way, the method of the embodiment was able to effectively suppress biofouling of the separation membrane in water treatment using the separation membrane.

1, 3 Water treatment device, 10 Treated water tank, 12 Separation membrane treatment device, 14 Pump, 16 Treated water pesticide concentration measuring device, 18 Permeate water pesticide concentration measuring device, 20 Concentrated water pesticide concentration measuring device, 22, 24 Treated water piping, 26 Permeate water piping, 28 Concentrated water piping, 30 Pesticide addition piping, 32 Control device.

Claims (4)

In a separation membrane treatment process, a separation membrane treatment is performed on the treated water to which a chemical has been added to obtain a permeate and a concentrated water,
The chemical is added to the water to be treated in the preceding stage of the separation membrane treatment so that the "chemical concentration in the concentrated water/chemical concentration in the water to be treated" is equal to or greater than a predetermined value;
A water treatment method characterized in that, when the flow rate of the water to be treated is Ff, the flow rate of the concentrated water is Fc, the flow rate of the permeated water is Fp, the concentration of the drug in the water to be treated is Cf, the concentration of the drug in the concentrated water is Cc, and the concentration of the drug in the permeated water is Cp, the active ingredient residual rate R represented by the following formula is 0.4 or more .
R = Cc/Cct
Here, Cct = (Cf x Ff - Cp x Fp) / Fc The water treatment method according to claim 1 ,
The water treatment method according to claim 1, wherein the agent contains a stabilized hypobromous acid composition containing a bromine-based oxidizing agent and a sulfamic acid compound. A separation membrane treatment means for performing a separation membrane treatment on the water to be treated to which the chemical has been added to obtain a permeate and a concentrated water;
A control means for controlling the addition of the chemical to the water to be treated in the upstream of the separation membrane treatment so that the "chemical concentration in the concentrated water/chemical concentration in the water to be treated" is equal to or greater than a predetermined value;
Equipped with
The control means controls the addition of the chemical to the water to be treated in the upstream of the separation membrane treatment so that the effective ingredient residual rate R, expressed by the following formula, is 0.4 or more, when the flow rate of the water to be treated is Ff, the flow rate of the concentrated water is Fc, the flow rate of the permeated water is Fp, the concentration of the chemical in the water to be treated is Cf, the concentration of the chemical in the concentrated water is Cc, and the concentration of the chemical in the permeated water is Cp .
R = Cc/Cct
Here, Cct = (Cf x Ff - Cp x Fp) / Fc The water treatment device according to claim 3 ,
13. A water treatment device, wherein the chemical agent contains a stabilized hypobromous acid composition containing a bromine-based oxidizing agent and a sulfamic acid compound.