Water treatment method and water treatment apparatus

Abstract

To provide a water treatment method and water treatment apparatus capable of suppressing oxidative deterioration of reverse osmosis membrane by a simple method in water treatment using the reverse osmosis membrane.SOLUTION: A water treatment method includes a reverse osmosis membrane treatment process in which water to be treated is passed through a reverse osmosis membrane to obtain permeable water and concentrated water, an oxidant addition process in which an oxidant is added to the water to be treated, and a chemical addition process in which a chemical containing at least one of a stabilizing agent, a reducing agent, and an activating agent is added to the water to be treated. When the state of the chemical addition is detected, if the amount of the agent added is detected to be below a predetermined value or when no addition of the agent is detected, the addition of the oxidant is stopped and controlled, or the amount of the oxidant is controlled to be below a predetermined value.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a water treatment method and a water treatment apparatus using a reverse osmosis membrane.

Background Art

[0002] In water treatment using a reverse osmosis membrane, as a method for suppressing slime on the reverse osmosis membrane, a method of using various slime suppressants is known. For example, oxidizing agents such as hypochlorous acid and hypobromous acid are typical slime suppressants.

[0003] When an oxidizing agent such as hypochlorous acid flows into the reverse osmosis membrane, there has been a problem that the reverse osmosis membrane is oxidatively deteriorated and the rejection rate decreases. Therefore, as countermeasures, detecting residual chlorine in the feed water to the reverse osmosis membrane and controlling to add a reducing agent that reduces the oxidizing agent or a stabilizing agent that stabilizes the oxidizing agent to the feed water can be cited.

[0004] For example, Patent Document 1 describes injecting a reducing agent or a stabilizing agent into the feed water of a reverse osmosis membrane, detecting the free chlorine concentration of the feed water of the reverse osmosis membrane, and controlling the injection amount of the reducing agent or the stabilizing agent based on the detected free chlorine concentration.

[0005] Patent Document 2 describes injecting a reducing agent or a stabilizing agent into the feed water of a reverse osmosis membrane, detecting the halogen concentration of the permeated water of the reverse osmosis membrane, and controlling the injection amount of the reducing agent or the stabilizing agent based on the detected halogen concentration.

[0006] Patent Document 3 describes injecting a stabilizing agent into the feed water of a reverse osmosis membrane, detecting the redox potential of the feed water or the concentrated water of the reverse osmosis membrane, and controlling the injection amount of the stabilizing agent based on the detected redox potential.

[0007] In methods of controlling the chemical injection amount into the feed water to a reverse osmosis membrane, etc. by detecting the free chlorine concentration, halogen concentration, or redox potential, as in Patent Documents 1 to 3, measuring instruments such as an in-line residual chlorine meter or redox potential meter are required, resulting in large-scale auxiliary equipment and control, and high costs.

[0008] Also, it takes time to detect the addition failure of a reducing agent or stabilizer by detecting the free chlorine concentration, halogen concentration, or redox potential, and there are many cases where the oxidizing agent continues to be added to the feed water until the state of insufficient reducing agent or stabilizer is detected. That is, not only is there a risk of oxidative degradation of the reverse osmosis membrane until the addition failure of the reducing agent or stabilizer is detected and the addition of the oxidizing agent is stopped, but there is also a risk that the oxidizing agent leaks into the permeated water of the reverse osmosis membrane and affects the equipment downstream of the reverse osmosis membrane.

[0009] Thus, in water treatment using a reverse osmosis membrane, in order to suppress the oxidative degradation of the reverse osmosis membrane and the equipment downstream of the reverse osmosis membrane, large-scale auxiliary equipment such as in-line measuring instruments is required, and the control is insufficient.

Prior Art Documents

Patent Documents

[0010]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0011] An object of the present invention is to provide a water treatment method and a water treatment apparatus capable of suppressing the oxidative degradation of a reverse osmosis membrane by a simple method in water treatment using a reverse osmosis membrane.

Means for Solving the Problems

[0012] The present invention includes a reverse osmosis membrane treatment step of passing treated water through a reverse osmosis membrane to obtain permeate water and concentrated water, an oxidizing agent addition step of adding an oxidizing agent to the treated water, and a chemical agent addition step of adding a chemical agent containing at least one of a stabilizer, a reducing agent, and an activator to the treated water. When detecting the addition state of the chemical agent and detecting that the addition amount of the chemical agent is less than or equal to a predetermined value or the chemical agent is not added, the addition of the oxidizing agent is controlled to stop, or the addition amount of the oxidizing agent is controlled to be less than or equal to a predetermined value. This is a water treatment method.

[0013] In the water treatment method, it is preferable to detect the addition state of the chemical agent by using at least one of a flow rate sensor and a discharge amount checker.

[0014] In the water treatment method, it is preferable that the oxidizing agent is a chlorine-based oxidizing agent and the activator is potassium iodide.

[0015] The present invention includes a reverse osmosis membrane treatment means for passing treated water through a reverse osmosis membrane to obtain permeate water and concentrated water, an oxidizing agent addition means for adding an oxidizing agent to the treated water, a chemical agent addition means for adding a chemical agent containing at least one of a stabilizer, a reducing agent, and an activator to the treated water, and a control means for detecting the addition state of the chemical agent and controlling the addition of the oxidizing agent to stop or controlling the addition amount of the oxidizing agent to be less than or equal to a predetermined value when detecting that the addition amount of the chemical agent is less than or equal to a predetermined value or the chemical agent is not added. This is a water treatment apparatus.

[0016] In the water treatment apparatus, it is preferable to use at least one of a flow rate sensor and a discharge amount checker as a detection means for detecting the addition state of the chemical agent.

[0017] In the water treatment apparatus, it is preferable that the oxidizing agent is a chlorine-based oxidizing agent and the activator is potassium iodide.

Effects of the Invention

[0018] According to the present invention, a water treatment method and a water treatment apparatus capable of suppressing oxidative degradation of a reverse osmosis membrane in a simple manner in water treatment using a reverse osmosis membrane can be provided.

Brief Description of the Drawings

[0019]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0020] Embodiments of the present invention will be described below. This embodiment is an example of carrying out the present invention, and the present invention is not limited to this embodiment.

[0021] The water treatment apparatus according to the embodiment of the present invention includes a reverse osmosis membrane treatment means for passing treated water through a reverse osmosis membrane to obtain permeated water and concentrated water, an oxidizing agent adding means for adding an oxidizing agent to the treated water, a chemical adding means for adding a chemical containing at least one of a stabilizer, a reducing agent, and an activator to the treated water, and a control means for detecting the addition state of the chemical and controlling the stop of the addition of the oxidizing agent or controlling the addition amount of the oxidizing agent to be below a predetermined value when it is detected that the addition amount of the chemical is below a predetermined value or the chemical is not added.

[0022] An outline of an example of the water treatment apparatus according to the embodiment of the present invention is shown in FIG. 1, and its configuration will be described.

[0023] The water treatment device 1 includes a reverse osmosis membrane treatment device 10 as reverse osmosis membrane treatment means for passing the water to be treated through a reverse osmosis membrane to obtain permeated water and concentrated water, an oxidant addition pipe 20 as oxidant addition means for adding an oxidant to the water to be treated, a chemical addition pipe 22 as chemical addition means for adding a chemical containing at least one of a stabilizer, a reducing agent, and an activator to the water to be treated, and a control device 12 as control means for detecting the addition state of the chemical and, when detecting that the addition amount of the chemical is equal to or less than a predetermined value or that the chemical has not been added, controlling to stop the addition of the oxidant or controlling the addition amount of the oxidant to be equal to or less than the predetermined value. The water treatment device 1 may include a water tank to be treated for storing the water to be treated.

[0024] In the water treatment device 1 of FIG. 1, a water to be treated pipe 14 is connected to the water to be treated inlet of the reverse osmosis membrane treatment device 10. A permeated water pipe 16 is connected to the permeated water outlet of the reverse osmosis membrane treatment device 10, and a concentrated water pipe 18 is connected to the concentrated water outlet. The oxidant addition pipe 20 is connected to the water to be treated pipe 14. A chemical addition pipe 22 is connected to the downstream side of the connection point of the oxidant addition pipe 20 in the water to be treated pipe 14. The chemical addition pipe 22 may be connected to the upstream side of the connection point of the oxidant addition pipe 20 in the water to be treated pipe 14.

[0025] The control device 12 is connected so as to be able to communicate wired or wirelessly with adjustment means such as pumps and valves for adjusting the addition amount, addition time, etc. of the oxidant installed in the oxidant addition pipe 20. Further, the control device 12 is connected so as to be able to communicate wired or wirelessly with detection means for detecting the addition state of a chemical containing at least one of a stabilizer, a reducing agent, and an activator. The control device 12 may be connected so as to be able to communicate wired or wirelessly with adjustment means such as pumps and valves for adjusting the addition amount, addition time, etc. of the chemical installed in the chemical addition pipe 22. The adjustment means such as pumps and valves for adjusting the addition amount, addition time, etc. of the oxidant installed in the oxidant addition pipe 20 and the detection means for detecting the addition state of a chemical containing at least one of a stabilizer, a reducing agent, and an activator may be connected so as to be able to communicate wired or wirelessly.

[0026] In the water treatment apparatus 1 of FIG. 1, the water to be treated is fed to the reverse osmosis membrane treatment apparatus 10 through the water to be treated pipe 14. Here, in the water to be treated pipe 14, an oxidizing agent is added to the water to be treated through the oxidizing agent addition pipe 20 (oxidizing agent addition step). Further, on the upstream side or the downstream side of the connection point of the oxidizing agent addition pipe 20 in the water to be treated pipe 14, a chemical containing at least one of a stabilizer, a reducing agent, and an activator is added to the water to be treated through the chemical addition pipe 22 (chemical addition step). When a water to be treated water tank for storing the water to be treated is provided, the oxidizing agent and the chemical may be added in the water to be treated water tank, or the oxidizing agent may be added in the water to be treated water tank and the chemical may be added in the water to be treated pipe 14, or the chemical may be added in the water to be treated water tank and the oxidizing agent may be added in the water to be treated pipe 14.

[0027] In the reverse osmosis membrane treatment apparatus 10, reverse osmosis membrane treatment is performed in which the water to be treated is passed through the reverse osmosis membrane to obtain permeated water and concentrated water (reverse osmosis membrane treatment step). The permeated water is discharged through the permeated water pipe 16, and the concentrated water is discharged through the concentrated water pipe 18.

[0028] In the water treatment method and the water treatment apparatus according to the present embodiment, when an oxidizing agent is added, the addition state of the chemical is detected, and when it is detected that the addition amount of the chemical is less than or equal to a predetermined value or the chemical is not added, the addition of the oxidizing agent is stopped and controlled, or the addition amount of the oxidizing agent is controlled to be less than or equal to a predetermined value. Thereby, oxidation deterioration of the reverse osmosis membrane can be suppressed by a simple method in water treatment using a reverse osmosis membrane. Further, when a system is provided after the reverse osmosis membrane treatment apparatus, oxidation deterioration of the system after the reverse osmosis membrane can be suppressed by a simple method. It is not necessary to use measuring instruments such as an in-line residual chlorine meter or an oxidation-reduction potential meter, and it is possible to suppress the scale of auxiliary equipment and control, and to suppress the cost. Furthermore, it is possible to quickly confirm a failure in the addition of a chemical containing at least one of a stabilizer, a reducing agent, and an activator, and it is possible to quickly detect a state in which the chemical is insufficient.

[0029] The control device 12 is composed of, for example, a microcomputer including an arithmetic means such as a CPU that calculates programs, and a storage means such as a ROM and a RAM that store programs and calculation results, and an electronic circuit. The control device 12 may be a programmable controller (or also called a programmable logic controller) (PLC) that incorporates a microprocessor and controls devices according to programs, or a sensor controller (for example, S3D2 manufactured by OMRON). The control device 12 has a function of detecting the addition state of the chemical agent, and when it detects that the addition amount of the chemical agent is below a predetermined value or that no chemical agent is added, controlling the stop of the addition of the oxidizing agent or controlling the addition amount of the oxidizing agent to be below a predetermined value.

[0030] For example, when the oxidizing agent is being added, the control device 12 detects the discharge flow rate or discharge state of the chemical agent as the addition state of the chemical agent containing at least one of a stabilizer, a reducing agent, and an activator. When it detects that the addition amount of the chemical agent is below a predetermined value or that there is an addition defect where no chemical agent is added, it may control the stop of the addition of the oxidizing agent or control the addition amount of the oxidizing agent to be below a predetermined value. Without passing through the control device 12, when the oxidizing agent is being added, the discharge flow rate or discharge state of the chemical agent may be detected as the addition state of the chemical agent containing at least one of a stabilizer, a reducing agent, and an activator. When it detects that the addition amount of the chemical agent is below a predetermined value or that there is an addition defect where no chemical agent is added, the addition of the oxidizing agent may be controlled to stop or the addition amount of the oxidizing agent may be controlled to be below a predetermined value.

[0031] Examples of the means for detecting the discharge flow rate of the chemical agent include a flow sensor that detects the discharge flow rate of the chemical agent. The flow sensor may be any device that can detect the discharge flow rate of the chemical agent and is not particularly limited. For example, an electromagnetic flow sensor without a movable part and with little pressure loss and deposits, an ultrasonic flow sensor, and a pump equipped with it may be mentioned. The flow rate may be detected by the flow sensor and pulsed.

[0032] As a means for detecting the drug discharge state, for example, a discharge amount checker for detecting the drug discharge state can be mentioned. The discharge amount checker may be any device that can detect the drug discharge state, and there is no particular limitation. For example, a discharge amount checker that can detect the presence or absence of discharge by pulse-outputting the operation of a float or an elliptical gear generated by liquid feeding, or a pressure sensor type discharge amount checker that can detect abnormal discharge pressure or air lock can be mentioned. The discharge amount checker may detect pulsation and output a pulse.

[0033] As a means for detecting the drug discharge state, it may be a device that detects an electrical signal of a pump or the like installed in the drug addition pipe 22. When it is detected from this electrical signal that the power supply of the pump has stopped and no drug is being added, the addition of the oxidant may be stopped or the addition amount of the oxidant may be controlled to be below a predetermined value.

[0034] When the control device 12 detects that the added amount of the drug detected by the pulse output output from a flow sensor, a discharge amount checker, etc. or the electrical signal of the pump is below a predetermined value or no drug is being added, it may control a pump, a valve, etc. installed in the oxidant addition pipe 20 to stop the addition of the oxidant or control the addition amount of the oxidant to be below a predetermined value. Without going through the control device 12, when it is detected that the added amount of the drug detected by the pulse output output from a flow sensor, a discharge amount checker, etc. or the electrical signal of the pump is below a predetermined value or no drug is being added, it may control a pump, a valve, etc. installed in the oxidant addition pipe 20 to stop the addition of the oxidant or control the addition amount of the oxidant to be below a predetermined value. In this case, the flow sensor, the discharge amount checker, etc. will function as control means.

[0035] When using means for detecting the discharge flow rate of the chemical agent, when the discharge flow rate of the chemical agent becomes equal to or less than a predetermined value, the injection of the oxidizing agent may be stopped, or the addition amount of the oxidizing agent may be controlled to be less than a predetermined value. The predetermined value of the discharge flow rate of the chemical agent may be, for example, 1 / 10 of the discharge flow rate during normal chemical agent addition. When it is detected that the discharge flow rate has become 1 / 10 or less of the discharge flow rate during normal chemical agent addition, the addition of the oxidizing agent may be stopped, or the addition amount of the oxidizing agent may be controlled to be less than a predetermined value. The predetermined value of the addition amount of the oxidizing agent may be, for example, 1 / 2 of the addition amount during normal oxidizing agent addition. When it is detected that the discharge flow rate of the chemical agent has become equal to or less than a predetermined value, the addition of the oxidizing agent may be stopped, or the addition amount of the oxidizing agent may be controlled to be, for example, 1 / 2 or less of the addition amount during normal oxidizing agent addition.

[0036] When using means for detecting the discharge state of the chemical agent, when a discharge failure where no chemical agent is added is detected, the addition of the oxidizing agent may be stopped, or the addition amount of the oxidizing agent may be controlled to be, for example, 1 / 2 or less of the addition amount during normal oxidizing agent addition.

[0037] The addition position of the oxidizing agent may be in the upstream stage of the reverse osmosis membrane treatment apparatus 10. When having an upstream system of reverse osmosis membrane treatment such as a membrane treatment apparatus like a turbidity removal membrane, it may be added in the upstream system. Fig. 2 shows a schematic of an example of a water treatment apparatus when the water treatment apparatus has a membrane treatment apparatus such as a turbidity removal membrane as an upstream system of reverse osmosis membrane treatment.

[0038] The water treatment apparatus 3 in Fig. 2 includes a membrane treatment apparatus 24 as membrane treatment means for passing the water to be treated through a membrane such as a turbidity removal membrane to perform membrane treatment, an oxidant addition pipe 20 as oxidant addition means for adding an oxidant to the water to be treated, a reverse osmosis membrane treatment apparatus 10 as reverse osmosis membrane treatment means for passing the membrane-treated water to be treated through a reverse osmosis membrane to obtain permeate water and concentrated water, a chemical addition pipe 22 as chemical addition means for adding a chemical containing at least one of a stabilizer, a reducing agent, and an activator to the water to be treated, and a control device 12 as control means for detecting the addition state of the chemical and, when detecting that the addition amount of the chemical is below a predetermined value or that the chemical has not been added, controlling to stop the addition of the oxidant or controlling the addition amount of the oxidant to be below the predetermined value. The water treatment apparatus 1 may include a water tank to be treated for storing the water to be treated.

[0039] In the water treatment apparatus 3 of Fig. 2, a water to be treated pipe 26 is connected to the water to be treated inlet of the membrane treatment apparatus 24. The water to be treated outlet of the membrane treatment apparatus 24 and the water to be treated inlet of the reverse osmosis membrane treatment apparatus 10 are connected by a water to be treated pipe 14. A permeate water pipe 16 is connected to the permeate water outlet of the reverse osmosis membrane treatment apparatus 10, and a concentrated water pipe 18 is connected to the concentrated water outlet. The oxidant addition pipe 20 is connected to the water to be treated pipe 26. The chemical addition pipe 22 is connected to the water to be treated pipe 14. When a water tank to be treated for storing the water to be treated is provided, the oxidant may be added in the water tank to be treated.

[0040] The control device 12 is connected so as to be communicable by wire or wirelessly with adjustment means such as pumps and valves for adjusting the addition amount, addition time, etc. of the oxidant installed in the oxidant addition pipe 20. Further, the control device 12 is connected so as to be communicable by wire or wirelessly with detection means for detecting the addition state of a chemical agent containing at least one of a stabilizer, a reducing agent, and an activator. The control device 12 may be connected so as to be communicable by wire or wirelessly with adjustment means such as pumps and valves for adjusting the addition amount, addition time, etc. of the chemical agent installed in the chemical agent addition pipe 22. The adjustment means such as pumps and valves for adjusting the addition amount, addition time, etc. of the oxidant installed in the oxidant addition pipe 20 and the detection means for detecting the addition state of a chemical agent containing at least one of a stabilizer, a reducing agent, and an activator may be connected so as to be communicable by wire or wirelessly.

[0041] In the water treatment device 3 of FIG. 2, the water to be treated is fed to the membrane treatment device 24 through the water to be treated pipe 26. Here, in the water to be treated pipe 26, an oxidant is added to the water to be treated through the oxidant addition pipe 20 (oxidant addition step). In the membrane treatment device 24, the water to be treated to which the oxidant has been added is passed through a membrane such as a turbidity removal membrane, and membrane treatment is performed (membrane treatment step). The water to be treated that has undergone membrane treatment and to which the oxidant has been added is fed to the reverse osmosis membrane treatment device 10 through the water to be treated pipe 14. Here, in the water to be treated pipe 14, a chemical agent containing at least one of a stabilizer, a reducing agent, and an activator is added to the water to be treated through the chemical agent addition pipe 22 (chemical agent addition step).

[0042] In the reverse osmosis membrane treatment device 10, reverse osmosis membrane treatment is performed in which the water to be treated is passed through the reverse osmosis membrane to obtain permeate water and concentrated water (reverse osmosis membrane treatment step). The permeate water is discharged through the permeate water pipe 16, and the concentrated water is discharged through the concentrated water pipe 18.

[0043] In the water treatment device 3, in the same manner as above, when detecting the addition state of the chemical agent and detecting that the addition amount of the chemical agent is equal to or less than a predetermined value or that the chemical agent has not been added, the addition of the oxidant is controlled to stop or the addition amount of the oxidant is controlled to be equal to or less than a predetermined value.

[0044] [Water to be treated] There is no particular limitation on the water to be treated. Examples of the water to be treated include environmental waters such as groundwater, river water, and seawater, and wastewaters discharged from various factories and the like.

[0045] [Oxidizing agent] The oxidizing agent may be any substance having an action of oxidizing other substances, and there is no particular limitation. Examples thereof include chlorine-based oxidizing agents, bromine-based oxidizing agents, a stabilized hypochlorous acid composition containing a chlorine-based oxidizing agent and a sulfamic acid compound, a stabilized hypobromous acid composition containing a bromine-based oxidizing agent and a sulfamic acid compound, and the like.

[0046] Examples of the 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, chlorinated isocyanuric acid or its salts, chloramine, and the like. Among these, examples of the 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, ammonium chlorate, alkali metal chlorate salts such as sodium chlorate and potassium chlorate, alkaline earth metal chlorate salts such as calcium chlorate and barium chlorate, and the like. These chlorine-based oxidizing agents may be used alone or in combination of two or more. From the viewpoint of handleability and the like, it is preferable to use sodium hypochlorite as the chlorine-based oxidizing agent.

[0047] Examples of the bromine-based oxidizing agents include bromine (liquid bromine), bromine chloride, bromic acid, bromate, hypobromous acid, and the like. Hypobromous acid may be produced by reacting a bromine compound such as sodium bromide with a chlorine-based oxidizing agent such as hypochlorous acid.

[0048] Examples of the bromine compound include sodium bromide, potassium bromide, lithium bromide, ammonium bromide, and hydrobromic acid. Among these, sodium bromide is preferred from the viewpoint of formulation cost and the like.

[0049] The "stabilized hypochlorous acid 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". The "stabilized hypobromous acid 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".

[0050] The sulfamic acid compound is a compound represented by the following general formula (1). R 2 NSO 3 H (1) (In the formula, R is independently a hydrogen atom or an alkyl group having 1 to 8 carbon atoms.)

[0051] Examples of sulfamic acid compounds include, in addition to sulfamic acid (sulfuric amide) in which both of the two R groups are hydrogen atoms, sulfamic acid compounds in which one of the two 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, N-butylsulfamic acid, etc., sulfamic acid compounds in which both of the two 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, N-methyl-N-propylsulfamic acid, etc., sulfamic acid compounds in which one of the two R groups is a hydrogen atom and the other is an aryl group having 6 to 10 carbon atoms, such as N-phenylsulfamic acid, or salts thereof. Examples of sulfamate salts include alkali metal salts such as sodium salt and potassium salt, alkaline earth metal salts such as calcium salt, strontium salt, barium salt, etc., other metal salts such as manganese salt, copper salt, zinc salt, iron salt, cobalt salt, nickel salt, etc., ammonium salt, guanidine salt, etc. The sulfamic acid compound and these salts may be used alone or in combination of two or more. From the viewpoint of environmental load, etc., it is preferable to use sulfamic acid (sulfuric amide) as the sulfamic acid compound.

[0052] 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 temperature, etc., sodium hydroxide and potassium hydroxide may be used in combination. Further, the alkali may be used not in solid form but as an aqueous solution.

[0053] As a stabilized hypobromous acid composition, in order not to deteriorate the reverse osmosis membrane more, those containing bromine and a sulfamic acid compound, or those containing a mixture of bromine and a sulfamic acid compound, for example, a mixture of bromine, a sulfamic acid compound, an alkali, and water, or those containing a reaction product of bromine and a sulfamic acid compound, for example, a mixture of a reaction product of bromine and a sulfamic acid compound, an alkali, and water are preferred.

[0054] Since the concentration of the stabilized hypobromous acid composition can be measured on-site in the same way as hypochlorous acid and the like, more accurate concentration control is possible.

[0055] The pH of the stabilized hypobromous acid composition is, for example, more than 13.0, and more preferably more than 13.2. When the pH of the stabilized hypobromous acid composition is 13.0 or less, the active halogen in the stabilized hypobromous acid composition may become unstable.

[0056] The bromic acid concentration in the stabilized hypobromous acid composition is preferably less than 5 mg / kg. When the bromic acid concentration in the stabilized hypobromous acid composition is 5 mg / kg or more, the bromate ion concentration in the water to be treated may increase.

[0057] [Agent] As the stabilizer, any substance can be used as long as it can form a bound halogen with a halogen such as chlorine or bromine and suppress the oxidative deterioration of the reverse osmosis membrane, and there is no particular limitation. For example, the sulfamic acid compound described above, amine compounds such as ammonia, etc. can be mentioned. The stabilizer may be used alone or in combination of two or more.

[0058] As the reducing agent, any substance can be used as long as it can reduce an oxidizing agent such as a chlorine-based oxidizing agent, and there is no particular limitation. For example, sodium sulfite, sodium bisulfite, sodium thiosulfate, sulfurous acid gas, etc. can be mentioned. The reducing agent may be used alone or in combination of two or more.

[0059] The activator may be any substance that can change its bactericidal performance as a new oxidizing agent when oxidized by an oxidizing agent, and there is no particular limitation. For example, bromine compounds such as sodium bromide, iodides such as potassium iodide, etc. may be mentioned. The activator may be used alone or in combination of two or more kinds.

[0060] The stabilizer, reducing agent, and activator may be used alone or in combination of two or more kinds. When using two or more kinds in combination, two or more chemical addition means such as chemical addition pipes and adjustment means such as pumps and valves may be used.

[0061] When using a chlorine-based oxidizing agent or a bromine-based oxidizing agent as the oxidizing agent, a stabilizer, a reducing agent, and an activator may be used as the chemicals. When using a stabilized hypochlorous acid composition containing a chlorine-based oxidizing agent and a sulfamic acid compound or a stabilized hypobromous acid composition containing a bromine-based oxidizing agent and a sulfamic acid compound as the oxidizing agent, a reducing agent and an activator may be used as the chemicals. The water treatment method and water treatment apparatus according to this embodiment can be preferably applied when using a chlorine-based oxidizing agent as the oxidizing agent and potassium iodide as the activator as the chemical from the viewpoints of bactericidal power, influence on the reverse osmosis membrane, economy, etc.

[0062] In the water treatment method and water treatment apparatus according to this embodiment, in addition to the oxidizing agent, stabilizer, reducing agent, and activator, other agents such as bactericides such as isothiazolone compounds other than the above oxidizing agent, scale dispersants such as acrylic acid-based polymers and maleic acid-based polymers, corrosion inhibitors such as heavy metals, phosphates, and azole compounds, and tracers such as lithium salts and fluorescent substances may be used.

[0063] In the water treatment method and water treatment apparatus according to the present embodiment, as the pre-stage system that may be provided in the pre-stage of the reverse osmosis membrane treatment, in addition to the membrane treatment apparatuses such as the above-mentioned turbidity removal membrane and safety filter, a sand filtration apparatus, an activated carbon tower, etc. may be mentioned. As the post-stage system that may be provided in the post-stage of the reverse osmosis membrane treatment, EDI, an ion exchange resin tower, an activated carbon tower, etc. may be mentioned. According to the water treatment method and water treatment apparatus according to the present embodiment, the influence of the oxidizing agent on the post-stage system of the reverse osmosis membrane can be suppressed.

Explanation of symbols

[0064] 1,3 Water treatment apparatus, 10 Reverse osmosis membrane treatment apparatus, 12 Control apparatus, 14,26 Water to be treated piping, 16 Permeate water piping, 18 Concentrated water piping, 20 Oxidizing agent addition piping, 22 Chemical agent addition piping, 24 Membrane treatment apparatus.

Claims

1. A reverse osmosis membrane treatment step of passing the water to be treated through a reverse osmosis membrane to obtain permeate water and concentrated water; An oxidizing agent addition step of adding an oxidizing agent to the water to be treated; A chemical agent addition step of adding a chemical agent containing at least one of a stabilizer, a reducing agent, and an activator to the water to be treated; comprising: Detecting the addition state of the chemical agent, and when it is detected that the addition amount of the chemical agent is below a predetermined value or the chemical agent is not added, controlling to stop the addition of the oxidizing agent or controlling the addition amount of the oxidizing agent to be below a predetermined value. A water treatment method characterized by this.

2. The water treatment method according to Claim 1, characterized in that the addition state of the chemical agent is detected using at least one of a flow rate sensor and a discharge amount checker.

3. The water treatment method according to Claim 1 or 2, characterized in that the oxidizing agent is a chlorine-based oxidizing agent and the activator is potassium iodide.

4. Reverse osmosis membrane treatment means for passing the water to be treated through a reverse osmosis membrane to obtain permeate water and concentrated water; Oxidizing agent addition means for adding an oxidizing agent to the water to be treated; Chemical agent addition means for adding a chemical agent containing at least one of a stabilizer, a reducing agent, and an activator to the water to be treated; Control means for detecting the addition state of the chemical agent and, when it is detected that the addition amount of the chemical agent is below a predetermined value or the chemical agent is not added, controlling to stop the addition of the oxidizing agent or controlling the addition amount of the oxidizing agent to be below a predetermined value; A water treatment apparatus characterized by comprising this.

5. The water treatment apparatus according to Claim 4, characterized in that at least one of a flow rate sensor and a discharge amount checker is used as the detection means for detecting the addition state of the chemical agent.

6. The water treatment apparatus according to Claim 4 or 5, characterized in that the oxidizing agent is a chlorine-based oxidizing agent and the activator is potassium iodide.

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