TWI835878B - Water treatment device, and water treatment method - Google Patents

Abstract

The invention provides a water treatment device and a water treatment method capable of treating, at low cost, a water to be treated that contains at least one or other of soluble silica and a hardness component. A water treatment device 1 treats a water to be treated that contains at least one or other of soluble silica and a hardness component, and comprises a pre-treatment device 10 comprising at least one or other of a soluble silica removal unit and a hardness component removal unit, a reverse osmosis membrane treatment device 12 which serves as a concentration unit for concentrating the pre-treated water obtained in the pre-treatment device 10, and a forward osmosis membrane treatment device 14 which performs forward osmosis membrane treatment of the concentrate obtained from the reverse osmosis membrane treatment device 12, wherein the dilute draw solution used in the forward osmosis membrane treatment device 14 is used in the pre-treatment device 10.

Description

Water treatment device and water treatment method

The present invention relates to a water treatment device and a water treatment method for treating water to be treated that contains at least one of soluble silica and hardness components. In addition, the present invention relates to a forward osmosis membrane treatment method, a forward osmosis membrane treatment system, and a water treatment method and a water treatment system using the forward osmosis membrane treatment method and the forward osmosis membrane treatment system.

In order to reduce the impact of drainage on the environment, drainage and volume reduction are carried out before drainage and disposal. Drainage treatment uses solid-liquid separation, membrane separation, vacuum concentration, etc. However, hard components such as soluble silica and calcium contained in the drainage do not dissolve and adhere to the pipes and equipment used for drainage treatment, causing so-called scaling. , so system performance degradation is common. In order to carry out efficient drainage treatment, soluble silica and hardness components in the drainage must be removed.

For example, Patent Document 1 describes a process in which wastewater containing soluble silica is added with magnesium salt under alkaline conditions to insolubilize the soluble silica, followed by solid-liquid separation, followed by reverse osmosis membrane treatment or forward osmosis membrane treatment. A method of treating water and recovering fresh water from drainage.

Forward osmosis membrane treatment allows supply water and suction solution to exist through the forward osmosis membrane, whereby osmotic pressure can be used to move water to the suction solution even when no pressure is applied. Then, the phase of the diluted suction solution is changed by means such as heating, so that fresh water can be obtained and the suction solution can be reused.

The suction solution for forward osmosis membrane treatment can use ammonium carbonate aqueous solution, a mixture of inorganic salts and temperature-sensitive chemicals, etc. (please refer to Patent Document 2).

In order to reuse the suction solution, energy other than heating must be applied, and an additional device for reusing the suction solution must be provided (see Figure 10), which increases the cost of the entire system.

Patent document 3 describes a method of adding an alkali to drainage containing hardness components to cause precipitation (so-called lime softening method), coagulating, filtering, and then treating the filtered water with a reverse osmosis membrane as a method for removing hardness components. In addition, patent document 4 describes a method of removing hardness components by adsorption using an ion exchange resin (resin softening method).

However, in the lime softening method, an alkali agent must be added, and in the resin softening method, in order to regenerate the ion exchange resin that absorbs hardness components, high-concentration brine (sodium chloride aqueous solution) must be passed through, so it is necessary to reduce drug costs.

On the other hand, in a forward osmosis (FO) membrane treatment system that produces concentrated water and a dilute draw solution by bringing the treated water into contact with a draw solution having a higher concentration than the treated water through a forward osmosis membrane, membrane fouling control is an important issue. The sterilization method of the forward osmosis membrane treatment system uses chlorine-based disinfectants such as hypochlorous acid and chloramine, oxidants such as hydrogen peroxide, or organic disinfectants such as 5-chloro-2-methyl-4-isothiazoline-3-one (for example, see patent documents 5 and 6).

However, since these bactericides (chlorine-based bactericides, oxidants, organic bactericides) pass through the forward osmosis membrane, the bactericidal components of the bactericide are not fully diffused to the outlet side of the forward osmosis membrane treatment device, resulting in the inability to The problem of sufficient sterilization of forward osmosis membrane. In addition, organic fungicides in particular have an impact on organisms, the environment, etc. Especially when the production water is separated from a dilute suction solution by heating or other treatment and used, if the production water contains organic fungicides, the suitability for industrial use, food use, drinking use, etc. will be significantly limited. In addition, in order to discharge part or all of the dilute suction solution including the bactericide that has passed through the forward osmosis membrane to the outside of the system, it is necessary to remove part or all of the dilute suction solution. In addition, chlorine-based bactericides and oxidants reduce the performance of forward osmosis membranes, especially polyamide-based reverse osmosis membranes. Therefore, when part or all of the dilute suction solution is reprocessed through the reverse osmosis membrane, these may occur. Bactericides may reduce the performance of reverse osmosis membranes.

[Prior Art Literature]

[Patent Literature]

Patent Document 1: International Patent Application Publication No. 2013/153587 Specification

Patent Document 2: Japanese Patent Application Publication No. 2017-056424

Patent document 3: Japanese Patent Publication No. 2017-170275

Patent Document 4: Japanese Patent Application Publication No. 2014-231039

Patent Document 5: Japanese Patent Application Publication No. 2015-188787

Patent Document 6: Japanese Patent Application Publication No. 2018-015684

An object of the present invention is to provide a water treatment device and a water treatment method that can treat water to be treated containing at least one of soluble silica and hardness components at low cost.

In addition, the purpose of the present invention is to provide a forward osmosis membrane treatment method and a forward osmosis membrane treatment system that inhibit the passage of a bactericidal agent through a forward osmosis membrane and can reuse a dilute attracting solution, and a water treatment method and a water treatment system using the forward osmosis membrane treatment method and the forward osmosis membrane treatment system.

The present invention is a water treatment device that processes water to be treated containing at least one of soluble silica and hardness components, and has: a pre-treatment device having a soluble silica removal device and a hardness component. Any of the removal equipment; the concentration treatment equipment, which concentrates the pre-treated water produced by the aforementioned pre-treatment equipment; and the forward osmosis membrane treatment equipment, whose forward osmosis membrane treats the concentrated water produced by the aforementioned concentration treatment equipment. , the thin suction solution used in the aforementioned forward osmosis membrane treatment equipment is used in the aforementioned pretreatment equipment.

Preferably, in the aforementioned water treatment device, the aforementioned concentration treatment equipment is a reverse osmosis membrane treatment equipment.

The present invention is a water treatment device that processes water to be treated containing at least one of soluble silica and hardness components, and has: a pre-treatment device having a soluble silica removal device and a hardness component. Any of the removal equipment; the first concentration treatment equipment, the concentration treatment of which is obtained by the aforementioned pre-treatment equipment; the forward osmosis membrane treatment equipment, whose forward osmosis membrane treatment is obtained by the aforementioned first concentration treatment equipment Concentrated water; and a second concentration treatment device that concentrates and processes a part of the dilute suction solution used in the aforementioned forward osmosis membrane treatment equipment, and the aforementioned pre-treatment equipment uses the dilute suction solution used in the aforementioned forward osmosis membrane treatment equipment. A part of the concentrated suction solution concentrated by the second concentration treatment equipment is used again as the suction solution in the forward osmosis membrane treatment equipment.

Preferably, in the aforementioned water treatment device, the aforementioned second concentration treatment equipment is a concentration equipment using a semipermeable membrane.

Preferably, in the aforementioned water treatment device, the aforementioned first concentration treatment equipment is a reverse osmosis membrane treatment equipment.

Preferably, in the aforementioned water treatment device, the draw solution used in the aforementioned forward osmosis membrane treatment device is a magnesium salt aqueous solution, and the aforementioned soluble silica removal device uses a dilute magnesium salt aqueous solution used in the aforementioned forward osmosis membrane treatment device.

Preferably, the water treatment device further includes a preparation device that mixes magnesium hydroxide and acid and reacts them at a pH of 7 or less, thereby preparing the suction solution used in the forward osmosis membrane treatment device. Magnesium salt solution.

Preferably, in the water treatment device, the suction solution used in the forward osmosis membrane treatment equipment is an alkali aqueous solution, and the hardness component removal equipment uses a dilute alkali aqueous solution used in the forward osmosis membrane treatment equipment.

Preferably, in the aforementioned water treatment device, the attracting solution used in the aforementioned forward osmosis membrane treatment equipment is an acid aqueous solution or a sodium chloride aqueous solution, and the aforementioned hardness component removal equipment uses the acid dilute aqueous solution or the sodium chloride dilute aqueous solution used in the aforementioned forward osmosis membrane treatment equipment.

In addition, the present invention is a water treatment method, which treats water to be treated containing at least one of soluble silica and hardness components, and includes the following steps: a pretreatment step, which includes removing soluble silica Any one of the steps and the hardness component removal step; the concentration treatment step, the concentration treatment is to obtain pre-treated water through the aforementioned pre-treatment step; and the forward osmosis membrane treatment step, the forward osmosis membrane treatment is obtained through the aforementioned concentration treatment step. Concentrated water, in the aforementioned pretreatment step, use the thin suction solution used in the aforementioned forward osmosis membrane treatment step.

Preferably, in the aforementioned water treatment method, the aforementioned concentration treatment step is a reverse osmosis membrane treatment step.

The present invention is a water treatment method, which treats water to be treated containing at least one of soluble silica and hardness components, and comprises the following steps: a pre-treatment step, which comprises either a soluble silica removal step or a hardness component removal step; a first concentration treatment step, in which the pre-treated water is concentrated by the pre-treatment step; a forward osmosis membrane treatment step, in which the forward osmosis membrane treatment is carried out by the pre-treatment step; The concentrated water obtained in the first concentration treatment step; and the second concentration treatment step, concentration treatment of a portion of the dilute attracting solution used in the aforementioned forward osmosis membrane treatment step, using a portion of the dilute attracting solution used in the aforementioned forward osmosis membrane treatment step in the aforementioned pre-treatment step, and reusing the concentrated attracting solution concentrated by the aforementioned second concentration treatment step as the attracting solution in the aforementioned forward osmosis membrane treatment step.

Preferably, in the aforementioned water treatment method, the aforementioned second concentration treatment step is a concentration step using a semipermeable membrane.

Preferably, in the aforementioned water treatment method, the aforementioned first concentration treatment step is a reverse osmosis membrane treatment step.

Preferably, in the aforementioned water treatment method, the attracting solution used in the aforementioned forward osmosis membrane treatment step is an aqueous solution of a magnesium salt, and the aforementioned soluble silica removal step uses the dilute aqueous solution of a magnesium salt used in the aforementioned forward osmosis membrane treatment step.

Preferably, the aforementioned water treatment method further comprises a preparation step, wherein magnesium hydroxide and an acid are mixed and reacted at a pH below 7 to prepare an aqueous solution of magnesium salt to be used as an attracting solution in the aforementioned forward osmosis membrane treatment step.

Preferably, in the aforementioned water treatment method, the attracting solution used in the aforementioned forward osmosis membrane treatment step is an alkaline aqueous solution, and the aforementioned hardness component removal step uses the alkaline dilute aqueous solution used in the aforementioned forward osmosis membrane treatment step.

Preferably, in the aforementioned water treatment method, the suction solution used in the aforementioned forward osmosis membrane treatment step is an acid aqueous solution or a sodium chloride aqueous solution, and the acid used in the aforementioned forward osmosis membrane treatment step is used in the aforementioned hardness component removal step. Thin aqueous solution or sodium chloride solution.

The present invention is a forward osmosis membrane treatment method, which includes: a forward osmosis membrane treatment step of producing concentrated water and a dilute suction solution by contacting water to be treated with a suction solution having a higher concentration than the water to be treated through a forward osmosis membrane. , and a bactericide containing a bromine-based oxidizing agent or a chlorine-based oxidizing agent and a sulfonamide compound is allowed to exist in the aforementioned water to be treated.

The present invention is a forward osmosis membrane treatment method, which includes: a forward osmosis membrane treatment step of producing concentrated water and a dilute suction solution by contacting water to be treated with a suction solution having a higher concentration than the water to be treated through a forward osmosis membrane. , and a bactericide containing a brominated oxidizing agent and a sulfonamide compound is allowed to exist in the aforementioned water to be treated.

The present invention is a forward osmosis membrane treatment method, which includes: a forward osmosis membrane treatment step of producing concentrated water and a dilute suction solution by contacting water to be treated with a suction solution having a higher concentration than the water to be treated through a forward osmosis membrane. , and a bactericide containing bromine and a sulfonamide compound is allowed to exist in the aforementioned water to be treated.

The present invention is a water treatment method, which includes the aforementioned forward osmosis membrane treatment method, and includes a pre-treatment step and a reverse osmosis membrane treatment step in the preceding stage of the aforementioned forward osmosis membrane treatment step, and the dilute attracting solution obtained by the aforementioned forward osmosis membrane treatment step is used in the aforementioned pre-treatment step.

The present invention is a forward osmosis membrane treatment system, which has: forward osmosis membrane treatment equipment that makes concentrated water and a dilute suction solution by contacting water to be treated with a suction solution having a higher concentration than the water to be treated through a forward osmosis membrane. , and a bactericide containing a bromine-based oxidizing agent or a chlorine-based oxidizing agent and a sulfonamide compound is allowed to exist in the aforementioned water to be treated.

The present invention is a forward osmosis membrane treatment system, which has: forward osmosis membrane treatment equipment that makes concentrated water and a dilute suction solution by contacting water to be treated with a suction solution having a higher concentration than the water to be treated through a forward osmosis membrane. , and a bactericide containing a brominated oxidizing agent and a sulfonamide compound is allowed to exist in the aforementioned water to be treated.

The present invention is a forward osmosis membrane treatment system, which has: forward osmosis membrane treatment equipment that makes concentrated water and a dilute suction solution by contacting water to be treated with a suction solution having a higher concentration than the water to be treated through a forward osmosis membrane. , and a bactericide containing bromine and a sulfonamide compound is allowed to exist in the aforementioned water to be treated.

The present invention is a water treatment system, which has the aforementioned forward osmosis membrane treatment system, and has a pre-treatment device and a reverse osmosis membrane treatment device in the front section of the aforementioned forward osmosis membrane treatment device, and the aforementioned pre-treatment device uses a dilute suction solution prepared by the aforementioned forward osmosis membrane treatment device.

According to the present invention, water to be treated containing at least one of soluble silica and hardness components can be treated at low cost.

In addition, the present invention can provide a forward osmosis membrane treatment method, a forward osmosis membrane treatment system that inhibits the penetration of a bactericide through a forward osmosis membrane and can reuse a dilute suction solution, and water using the forward osmosis membrane treatment method and forward osmosis membrane treatment system. Treatment methods, water treatment systems.

1,3,5,7:Water treatment device

8: Forward osmosis membrane treatment system

9:Water treatment system

10,114: Pre-processing device

12,118:Reverse osmosis membrane treatment device

14:Permeable membrane treatment device

16,120: Treated water piping

18: Pre-treatment water piping

20:Concentrated water piping

22: Through water piping

24,32:Suction solution piping

26,36: Thin suction solution piping

28:FO concentrated water piping

30: Suction solution preparation tank

34,340,342,344,346,348,350: Concentrator

38: Piping for concentrated suction solution

40: diluent piping

42,78: The first section of semi-permeable membrane treatment device

44,80: Second stage semipermeable membrane treatment device

46,82: The third semipermeable membrane treatment device

48,84: First side (first space)

50,86: Secondary side (second space)

52,88: Semipermeable membrane

54,56,58,60,62,64,66,68,90,92,94,96,98,100,102,104,122,124:Piping

70,72,74,106: Pump

110:Forward osmosis membrane

112: Disinfectant adding piping

116: Fouling removal device

126:RO through water piping

128: Backwash drainage piping

[Figure 1] is a schematic structural diagram showing an example of a water treatment device in one embodiment of the present invention.

[Fig. 2] is a schematic structural diagram showing another example of a water treatment device according to an embodiment of the present invention.

[Figure 3] is a schematic structural diagram showing another example of a water treatment device according to the embodiment of the present invention.

[Fig. 4] is a schematic structural diagram showing an example of a concentration device of the water treatment device according to the embodiment of the present invention.

[Figure 5] is a schematic structural diagram showing another example of a concentration device of a water treatment device in an embodiment of the present invention.

[Fig. 6] is a schematic structural diagram showing another example of a concentration device of the water treatment device according to the embodiment of the present invention.

[Fig. 7] is a schematic structural diagram showing another example of a concentration device of the water treatment device according to the embodiment of the present invention.

[Fig. 8] is a schematic structural diagram showing another example of the concentration device of the water treatment device according to the embodiment of the present invention.

[Fig. 9] is a schematic structural diagram showing another example of the concentration device of the water treatment device according to the embodiment of the present invention.

[Figure 10] is a schematic diagram showing the structure of a conventional water treatment device.

[Fig. 11] is a schematic structural diagram showing an example of a forward osmosis membrane treatment system according to an embodiment of the present invention.

[Figure 12] is a schematic diagram showing an example of a water treatment system in one embodiment of the present invention.

Embodiments of the present invention will be described below. This embodiment is an example of implementing the present invention, and the present invention is not limited to this embodiment.

The following is a schematic diagram of an example of a water treatment device in accordance with an embodiment of the present invention shown in FIG1, and its structure is described.

The water treatment device 1 comprises: a pre-treatment device 10, which is a pre-treatment device having at least one of a soluble silica removal device and a hardness component removal device; a reverse osmosis membrane treatment device 12, which is a concentration treatment device for concentrating the previously treated water obtained by the pre-treatment device 10; and a forward osmosis membrane treatment device 14, which is a forward osmosis membrane treatment device for forward osmosis membrane treatment of the concentrated water obtained by the reverse osmosis membrane treatment device 12.

In the water treatment device 1 of FIG. 1 , the treated water pipe 16 is connected to the treated water inlet of the pre-treatment device 10, and the outlet of the pre-treatment device 10 and the inlet of the reverse osmosis membrane treatment device 12 are connected by the pre-treatment water pipe 18. The concentrated water outlet of the reverse osmosis membrane treatment device 12 and the concentrated water inlet of the forward osmosis membrane treatment device 14 are connected by the concentrated water pipe 20, and the permeated water pipe 22 is connected to the permeated water outlet of the reverse osmosis membrane treatment device 12. The suction solution piping 24 is connected to the suction solution inlet of the forward osmosis membrane treatment device 14, and the dilute suction solution outlet of the forward osmosis membrane treatment device 14 and the dilute suction solution inlet of the pre-treatment device 10 are connected via the dilute suction solution piping 26, and the FO concentrated water piping 28 is connected to the FO concentrated water outlet of the forward osmosis membrane treatment device 14.

The following describes the water treatment method and the operation of the water treatment device 1 of this embodiment.

The treated water containing at least one of soluble silica and hardness components is transported to the pre-treatment device 10 through the treated water pipe 16. In the pre-treatment device 10, at least one of the soluble silica and hardness components is removed (pre-treatment step).

When the water to be treated contains soluble silica, the pretreatment device 10 includes: a magnesium reaction device that adds a magnesium salt to the water to be treated and reacts it to insolubilize the soluble silica; and a coagulation treatment device that adds a coagulant to the water to be treated. Adding to the treated water after the reaction to cause agglomeration; and a solid-liquid separation device that separates the agglomerate from the treated water after the agglutination treatment. In the pretreatment device 10, for example, under alkaline conditions (for example, pH 10 Add magnesium salt to the water to be treated under 12) to insolubilize the soluble silica (magnesium reaction step). Then, if necessary, a coagulant is added to perform aggregation treatment (aggregation treatment step), and the aggregated product is solid-liquid separated (solid-liquid separation step). Then, the pre-treated water produced by solid-liquid separation is transported to the reverse osmosis membrane treatment device 12 through the pre-treated water pipe 18 .

When the water to be treated contains a hardness component and the hardness component is removed by lime softening, the pretreatment device 10 has, for example: an alkali reaction device, which adds an alkali agent to the water to be treated to react and insolubilize the hardness component; A coagulation treatment equipment, which adds a coagulant to the water to be treated after the reaction to agglomerate it as necessary; and a solid-liquid separation equipment, which separates agglomerates from the water to be treated after the coagulation treatment. In the pretreatment device 10, for example, an alkaline agent is added to the water to be treated to insolubilize the hardness component (alkali agent reaction step). Then, a coagulant is added to perform aggregation treatment (aggregation treatment step), and the aggregate is solid-liquid separated (solid-liquid separation step). Then, the pre-treated water produced by solid-liquid separation is transported to the reverse osmosis membrane treatment device 12 through the pre-treated water pipe 18 .

When the water to be treated contains a hardness component and the hardness component is removed by a resin softening method, the pretreatment device 10 has, for example, an ion exchange treatment device that performs ion exchange treatment using an ion exchange resin or the like. In the pretreatment device 10, for example, the water to be treated is passed to an ion exchange tower filled with ion exchange resin as an ion exchange treatment device, and the hardness component is adsorbed and removed (ion exchange step). Then, the pre-treated water produced by the ion exchange treatment is transported to the reverse osmosis membrane treatment device 12 through the pre-treated water pipe 18 . When the ion exchange resin needs to be regenerated, the ion exchange resin is regenerated by using a regenerant.

Next, the pre-treatment step is concentrated in the reverse osmosis membrane treatment device 12 to obtain pre-treated water (concentration treatment step). The concentrated water obtained by the reverse osmosis membrane treatment is transported to the forward osmosis membrane treatment device 14 through the concentrated water pipe 20, and the permeated water is discharged through the permeated water pipe 22.

In the forward osmosis membrane treatment device 14, the forward osmosis membrane processes the concentrated water produced by the reverse osmosis membrane treatment (forward osmosis membrane treatment step). In the forward osmosis membrane treatment device 14, the suction solution is transported to the secondary side of the forward osmosis membrane through the suction solution pipe 24, and then passes through the forward osmosis membrane to allow concentrated water and the suction solution to exist, thereby moving the water to the suction side using osmotic pressure. solution.

The dilute suction solution used in the forward osmosis membrane treatment step is transported to the pretreatment device 10 through the dilute suction solution pipe 26, and is used in the pretreatment device 10 in the pretreatment step. Then, the FO concentrated water produced by the forward osmosis membrane treatment step is discharged through the FO concentrated water pipe 28. FO concentrated water can be recycled and reused.

When the pretreatment device 10 includes a device for removing soluble silica, for example, a magnesium salt aqueous solution can be used as the suction solution in the forward osmosis membrane treatment device 14, and the dilute suction solution (magnesium) used in the forward osmosis membrane treatment device 14 Salt dilute aqueous solution) can be used as the magnesium salt added in the pretreatment device 10.

When the pretreatment device 10 includes a device for removing hardness components by lime softening, an alkaline aqueous solution, for example, can be used as the draw solution in the forward osmosis membrane treatment device 14, and the dilute draw solution (alkaline dilute aqueous solution) used in the forward osmosis membrane treatment device 14 can be used as the alkali added to the pretreatment device 10.

When the pretreatment device 10 includes a device for removing hardness components by a resin softening method, for example, an acid aqueous solution or a sodium chloride aqueous solution can be used as the suction solution in the forward osmosis membrane treatment device 14, and the forward osmosis membrane treatment device 14 The dilute suction solution (a dilute aqueous acid solution or a dilute sodium chloride aqueous solution) used can be used as a regeneration agent for the ion exchange resin in the pretreatment device 10 .

With the water treatment method and water treatment device of this embodiment, water to be treated containing at least one of soluble silica and hardness components can be treated at low cost.

Since the dilute suction solution diluted by the positive osmosis membrane treatment is used in the pre-treatment step, the necessary cost of reusing the suction solution that is originally required can be reduced and no regeneration equipment is required. Since the dilute suction solution is only used to dilute the suction solution originally used in the pre-treatment step, there is almost no additional cost.

FIG3 shows an overview of another water treatment device according to the present invention and explains its structure.

The water treatment device 5 has: a pretreatment device 10 as a pretreatment device having at least one of a soluble silica removal device and a hardness component removal device; and a reverse osmosis membrane treatment device 12 as a concentration treatment by pretreatment. The treatment device 10 produces a first concentration treatment device for previously treated water; a forward osmosis membrane treatment device 14, which serves as a forward osmosis membrane treatment device for treating concentrated water produced by the reverse osmosis membrane treatment device 12; and concentration Device 34 is a second concentration treatment device that serves as a part of the dilute suction solution used by the forward osmosis membrane treatment device 14 for concentration treatment.

In the water treatment device 5 of Figure 3 , the treated water pipe 16 is connected to the treated water inlet of the pre-treatment device 10 , and the outlet of the pre-treatment device 10 and the inlet of the reverse osmosis membrane treatment device 12 are connected by the pre-treated water pipe 18 . The concentrated water outlet of the reverse osmosis membrane treatment device 12 and the concentrated water inlet of the forward osmosis membrane treatment device 14 are connected by a concentrated water pipe 20 , and the permeated water pipe 22 is connected to the permeated water outlet of the reverse osmosis membrane treatment device 12 . The suction solution pipe 24 is connected to the suction solution inlet of the forward osmosis membrane treatment device 14, and the dilute suction solution outlet of the forward osmosis membrane treatment device 14 and the dilute suction solution inlet of the pretreatment device 10 are connected by the dilute suction solution pipe 26, and FO The concentrated water pipe 28 is connected to the FO concentrated water outlet of the forward osmosis membrane treatment device 14 . The thin suction solution pipe 36 branched from the thin suction solution pipe 26 is connected to the inlet of the concentration device 34 , and the concentrated suction solution outlet of the concentration device 34 and the suction solution pipe 24 are connected by the concentrated suction solution pipe 38 . The diluent pipe 40 is connected to the diluent outlet of the concentration device 34 .

The following describes the water treatment method and the operation of the water treatment device 5 of this embodiment.

The water to be treated containing at least one of soluble silica and hardness components is transported to the pretreatment device 10 through the water to be treated pipe 16 . In the pretreatment device 10, at least one of soluble silica and hardness components is removed (pretreatment step).

When the treated water contains soluble silica, the pre-treatment device 10 has, for example, a magnesium reaction device, which adds magnesium salt to the treated water to react and insolubilize the soluble silica; a coagulation treatment device, which adds a coagulant to the treated water after the reaction to coagulate it; and a solid-liquid separation device, which separates the coagulant from the treated water after the coagulation treatment. In the pre-treatment device 10, magnesium salt is added to the treated water under alkaline conditions (e.g., pH 10 to 12) to insolubilize the soluble silica (magnesium reaction step). Then, a coagulant is added as needed to perform coagulation treatment (coagulation treatment step) to separate the coagulant into solid and liquid (solid-liquid separation step). Then, the pre-treated water obtained by solid-liquid separation is transported to the reverse osmosis membrane treatment device 12 through the pre-treated water pipe 18.

When the water to be treated contains a hardness component and the hardness component is removed by lime softening, the pretreatment device 10 has, for example: an alkali reaction device, which adds an alkali agent to the water to be treated to react and insolubilize the hardness component; A coagulation treatment equipment, which adds a coagulant to the water to be treated after the reaction to agglomerate it as necessary; and a solid-liquid separation equipment, which separates agglomerates from the water to be treated after the coagulation treatment. In the pretreatment device 10, for example, an alkaline agent is added to the water to be treated to insolubilize the hardness component (alkali agent reaction step). Then, a coagulant is added to perform aggregation treatment (aggregation treatment step), and the aggregate is solid-liquid separated (solid-liquid separation step). Then, the pre-treated water produced by solid-liquid separation is transported to the reverse osmosis membrane treatment device 12 through the pre-treated water pipe 18 .

When the water to be treated contains hardness components and the hardness components are removed by a resin softening method, the pre-treatment device 10 has an ion exchange treatment device for ion exchange treatment using, for example, an ion exchange resin. In the pre-treatment device 10, for example, the water to be treated is passed to an ion exchange tower filled with an ion exchange resin as an ion exchange treatment device, and the hardness components are removed by adsorption (ion exchange step). The pre-treated water obtained by the ion exchange treatment is then transported to the reverse osmosis membrane treatment device 12 through the pre-treatment water pipe 18. When the ion exchange resin needs to be regenerated, the ion exchange resin is regenerated by passing a regeneration agent.

Next, a concentration process is performed in the reverse osmosis membrane treatment device 12 to obtain pre-treated water through a pre-treatment step (first concentration process step). The concentrated water (RO concentrated water) produced by the first concentration treatment (reverse osmosis membrane treatment) is transported to the forward osmosis membrane treatment device 14 through the concentrated water pipe 20, and then the permeated water (RO permeated water) is discharged through the permeated water pipe 22. .

In the forward osmosis membrane treatment device 14, the concentrated water obtained by the first concentration treatment (reverse osmosis membrane treatment) is treated by the forward osmosis membrane (forward osmosis membrane treatment step). In the forward osmosis membrane treatment device 14, the draw solution is transported to the secondary side of the forward osmosis membrane through the draw solution piping 24, and then passes through the forward osmosis membrane, so that the concentrated water and the draw solution exist, thereby using the osmotic pressure to move the water to the draw solution.

A portion of the dilute draw solution used in the forward osmosis membrane treatment step is transported to the pre-treatment device 10 through the dilute draw solution piping 26, and then used in the pre-treatment step in the pre-treatment device 10. The FO concentrated water obtained by the forward osmosis membrane treatment step is discharged through the FO concentrated water piping 28. The FO concentrated water can also be further concentrated and solidified by a concentration device and a crystallization device as needed.

A part of the dilute suction solution used in the forward osmosis membrane treatment step is branched from the dilute suction solution pipe 26 and transported to the concentration device 34 through the dilute suction solution pipe 36, and is then concentrated in the concentration device 34 (second concentration step) . The concentrated suction solution obtained by the second concentration treatment is supplied to the middle of the suction solution pipe 24 through the concentrated suction solution pipe 38, and is then reused as the suction solution in the forward osmosis membrane treatment device 14. The diluted liquid obtained by the second concentration process is discharged through the diluent pipe 40 . The diluted liquid can also be recycled and reused after ultrafiltration membrane (UF membrane) treatment, reverse osmosis membrane (RO membrane) treatment, ion exchange treatment, etc. as needed.

When the pretreatment device 10 includes a device for removing soluble silica, for example, a magnesium salt aqueous solution can be used as the suction solution in the forward osmosis membrane treatment device 14, and the dilute suction solution (magnesium) used in the forward osmosis membrane treatment device 14 A part of the salt dilute aqueous solution) can be used as the magnesium salt added to the pretreatment device 10. In addition, part of the dilute suction solution (magnesium salt dilute aqueous solution) used in the forward osmosis membrane treatment device 14 can be concentrated in the concentration device 34 and reused as the suction solution in the forward osmosis membrane treatment device 14 .

When the pretreatment device 10 includes a device for removing hardness components by lime softening, an alkaline aqueous solution, for example, can be used as the draw solution in the forward osmosis membrane treatment device 14, and a portion of the dilute draw solution (alkaline dilute aqueous solution) used in the forward osmosis membrane treatment device 14 can be used as the alkali added to the pretreatment device 10. In addition, a portion of the dilute draw solution (alkaline dilute aqueous solution) used in the forward osmosis membrane treatment device 14 can be concentrated in the concentration device 34 and reused as the draw solution in the forward osmosis membrane treatment device 14.

When the pretreatment device 10 includes a device for removing hardness components by a resin softening method, for example, an acid aqueous solution or a sodium chloride aqueous solution can be used as an attracting solution in the forward osmosis membrane treatment device 14, and a portion of the dilute attracting solution (acid dilute aqueous solution or sodium chloride dilute aqueous solution) used in the forward osmosis membrane treatment device 14 can be used as a regeneration agent for the ion exchange resin in the pretreatment device 10. In addition, a portion of the dilute attracting solution (acid dilute aqueous solution or sodium chloride dilute aqueous solution) used in the forward osmosis membrane treatment device 14 can be concentrated in the concentration device 34 and reused as the attracting solution in the forward osmosis membrane treatment device 14.

By using the water treatment method and water treatment device of this embodiment, water to be treated containing at least one of soluble silica and hardness components can be treated at low cost.

Because the thin suction solution diluted by forward osmosis membrane treatment is used in the pretreatment step, the necessary cost of reusing the suction solution can be reduced and no regeneration equipment is required. Because the dilute suction solution is just the suction solution originally used in the dilution pre-treatment step, there is almost no additional cost.

When the amount of dilute attracting solution diluted by the forward osmosis membrane treatment is more than the amount required in the pre-treatment step, a portion of the dilute attracting solution used in the forward osmosis membrane treatment is used in the pre-treatment step, and then a portion of the dilute attracting solution not used in the pre-treatment step is concentrated and reused as the attracting solution in the forward osmosis membrane treatment step, thereby reducing the loss of the dilute attracting solution. Since the concentrated dilute attracting solution is only a portion at this time, the cost can be significantly reduced compared to reusing the entire amount of the concentrated dilute attracting solution.

The water to be treated as the treatment object of the water treatment method and the water treatment device of this embodiment is not particularly limited as long as it contains at least one of soluble silica and hardness components, but examples include: industrial Water, surface water, tap water, groundwater, seawater, desalinated seawater desalinated by reverse osmosis or evaporation, and various wastewaters such as wastewater discharged from semiconductor manufacturing processes.

When the treated water contains dissolved silica, the concentration of dissolved silica is, for example, in the range of 5 to 400 mg/L. When the treated water contains hardness components, the concentration of calcium hardness components is, for example, in the range of 5 to 600 mg/L. The total evaporation residue (TDS: Total Dissolved Solid) in the treated water is, for example, in the range of 100 to 50,000 mg/L.

In the water treatment method and water treatment device of the present embodiment, when the water to be treated contains both soluble silica and hardness components, the pretreatment equipment (pretreatment step) may include a soluble silica removal equipment (soluble silica removal equipment). Both silica removal step) and hardness component removal equipment (hardness component removal step). The order of the soluble silica removal equipment (soluble silica removal step) and the hardness component removal equipment (hardness component removal step) may be the soluble silica removal equipment (soluble silica removal step) first. The second is a hardness component removal device (hardness component removal step), or the first is a hardness component removal device (hardness component removal step), and the second is a soluble silica removal device (soluble silica removal step).

At this time, at least one of a magnesium salt solution, an alkali aqueous solution, an acid aqueous solution, and a sodium chloride aqueous solution is used as the suction solution in the forward osmosis membrane treatment device 14 (forward osmosis membrane treatment step), and the forward osmosis membrane treatment device 14 The dilute suction solution (at least one of magnesium salt dilute aqueous solution, alkaline agent dilute aqueous solution, acid dilute aqueous solution and sodium chloride dilute aqueous solution) used in the pretreatment device 10 (pretreatment step) can be used for soluble silica Aspects suitable for removal equipment (soluble silica removal step) and hardness component removal equipment (hardness component removal step).

In the water treatment method and water treatment device of the present embodiment, there may be a turbidity removal device for removing turbidity components in the treated water. The turbidity removal device may be, for example, a sand filter device, a membrane filter device such as an ultrafiltration (UF) membrane, a pressurized flotation device, etc. There is no particular restriction on the location of the turbidity removal device, but when the turbidity removal device is a sand filter device, it is, for example, in front of the pre-treatment device 10 (pre-treatment step), and when the turbidity removal device is a membrane filter device and a pressurized flotation device, it is between the pre-treatment device 10 (pre-treatment step) and the reverse osmosis membrane treatment device 12 (concentration treatment step).

[Pretreatment step: removal of soluble silica]

When the water to be treated contains soluble silica, in the previous treatment step, a magnesium salt is added to the water to be treated, for example, under alkaline conditions to insolubilize the soluble silica (magnesium reaction step).

The magnesium salt used may be magnesium chloride (MgCl ₂ ), magnesium sulfate (MgSO ₄ ), or a magnesium salt thereof, without particular limitation. However, magnesium chloride is preferred from the viewpoint of suppressing the generation of insoluble substances due to the addition of sulfate.

The pH in the magnesium reaction step is not particularly limited as long as it is an alkaline condition, but can be, for example, in the range of pH 10 to 12, preferably in the range of 10.5 to 11.5, and more preferably in the range of 11 to 11.5. When the pH in the magnesium reaction step is less than 10 or greater than 12, the silicon dioxide removal rate will decrease.

Alkalis such as sodium hydroxide and calcium hydroxide can be used as pH adjusters, and inorganic acids such as hydrochloric acid and sulfuric acid can also be used as needed.

The temperature in the magnesium reaction step is not particularly limited as long as it is the temperature at which the insolubilization reaction of silicon dioxide is carried out, but it can be, for example, in the range of 1°C to less than 50°C, and more in the range of 10°C to less than 50°C. good. When the temperature in the magnesium reaction step is less than 1°C, the insolubilization reaction of silicon dioxide will be insufficient, and when it is above 50°C, the treatment cost will increase.

The reaction time in the magnesium reaction step is not particularly limited as long as the insolubilization reaction of silicon dioxide can be carried out, but it can be, for example, in the range of 1 minute to 60 minutes, and preferably in the range of 5 to 30 minutes. If the reaction time in the magnesium reaction step is less than 1 minute, the insolubilization reaction of silicon dioxide will be insufficient, and if it exceeds 60 minutes, the reaction tank will be too large.

The amount of magnesium salt added relative to the weight concentration of silicon dioxide in the treated water should be in the range of 0.1 to 10 times, and preferably in the range of 0.5 to 5 times. When the amount of magnesium salt added relative to the weight concentration of silicon dioxide in the treated water is less than 0.1 times, the insolubilization reaction of silicon dioxide will be insufficient, and when it exceeds 10 times, the amount of sludge generated will be excessive.

In order to insolubilize soluble silica, in addition to magnesium salts, aluminum salts such as polyaluminum chloride (PAC) and aluminum sulfate; iron salts such as ferric chloride and ferric sulfate can also be used. From the perspective of silica removal rate and other aspects, it is better to use magnesium salt.

The coagulation treatment step is, for example, adding an inorganic coagulant to the treated water after the magnesium reaction in a coagulation tank to agglomerate the insoluble matter (agglomeration step). Then, a polymer flocculant is added to the flocculation forming tank, and then flocculation is formed (flocculation forming step).

Inorganic coagulants used in the agglomeration step include iron-based inorganic coagulants such as ferric chloride, aluminum-based inorganic coagulants such as polyaluminum chloride (PAC), etc., and are determined by the cost of the drug and the agglutination pH range. Look, iron-based inorganic coagulants are better.

The weight ratio of the added amount of the inorganic flocculant to the added magnesium salt should be in the range of 0.1 to 10 times, and more preferably in the range of 1 to 5 times the amount. If the added amount of inorganic coagulant is less than 0.1 times the weight ratio of the added magnesium salt, the aggregation will be insufficient, and if it exceeds 10 times, the amount of sludge will be excessive.

The pH in the agglutination step is, for example, in the range of 3 to 11. When the pH in the agglutination step is less than 3 or exceeds 11, poor agglutination will occur. In addition, when the pH in the coagulation step is less than 9, silica will be eluted from the flocculation, so it is best to conduct the coagulation step within the pH range of 9 to 11.

The temperature in the coagulation step is, for example, in the range of 1°C to 80°C. When the temperature in the coagulation step is less than 1°C or exceeds 80°C, poor coagulation will occur.

Examples of polymer flocculants used in the flocculation formation step include: cationic polymer flocculants such as polyacrylamide series and polyacrylate series; anionic polymer flocculants; nonionic polymer flocculants, etc. In terms of coagulation properties, anionic polymer flocculants are preferred.

Examples of commercially available polymer flocculants include anionic polymer flocculants such as ORFLOCK OA-3H (manufactured by ORGANO Co., Ltd.).

The amount of polymer coagulant added relative to the amount of raw water should be in the range of 0.1 to 10 mg/L, and preferably in the range of 1 to 5 mg/L. When the amount of polymer coagulant added relative to the amount of raw water is less than 0.1 mg/L, it will not promote the formation of flocculation, and when it exceeds 10 mg/L, the polymer coagulant dissolved in the treated water will remain.

The pH in the flocculant formation step is, for example, in the range of 3 to 11. When the pH in the flocculant formation step is less than 3 or exceeds 11, poor coagulation will occur. In addition, when the pH in the flocculant formation step is less than 9, silicon dioxide will be dissolved from the flocculants, so it is best to perform the flocculant formation step in the range of pH 9 to 11.

The temperature in the flocculation forming step is, for example, in the range of 1°C to 80°C. When the temperature in the flocculation formation step is less than 1°C or exceeds 80°C, poor coagulation will occur.

Although the above-mentioned coagulation treatment uses inorganic coagulants and polymer coagulants for the coagulation step and the flocculant formation step, at least one of inorganic coagulants, polymer coagulants, etc. may be used, and at least one of iron-based inorganic coagulants and anionic polymer coagulants is preferably used. When the silicon dioxide that reacts with magnesium salt and becomes insoluble is coagulated, the coagulation and solid-liquid separation properties can be improved by using at least one of iron-based inorganic coagulants and anionic polymer coagulants.

The solid-liquid separation step is, for example, agglomerates formed by solid-liquid separation and flocculation in a sedimentation tank (solid-liquid separation step). Then, the pre-treated water produced by solid-liquid separation is sent to the reverse osmosis membrane treatment device 12 . On the other hand, the sludge is discharged through the sludge pipe. Sludge can be recycled and reused.

In addition to sedimentation separation through natural sedimentation, the solid-liquid separation in the solid-liquid separation step can be exemplified by pressurized flotation treatment, membrane filtration treatment, etc., and in terms of separability and other aspects, sedimentation separation is better.

[Pre-treatment step: remove hardness components by lime softening method]

When the water to be treated contains hardness components, the hardness components can be removed by lime softening. Hardness components are divided into primary hardness and permanent hardness, and primary hardness is removed by alkali such as sodium hydroxide (NaOH), while permanent hardness is removed by adding carbonate such as sodium carbonate (NaCO ₃ ). In this specification, for convenience, carbonate is also recorded as alkali. That is, in the pre-treatment step, alkali is added to the water to be treated to make the hardness components insoluble (alkali reaction step).

The alkali used may be, for example, calcium hydroxide (Ca(OH) ₂ ), sodium hydroxide (NaOH), potassium hydroxide (KOH), calcium bicarbonate (Ca(HCO ₃ ) ₂ ), magnesium bicarbonate (Mg(HCO ₃ ) ₂ ), sodium carbonate (Na ₂ CO ₃ ), potassium carbonate (K ₂ CO ₃ ), etc., and more than one of them may be used. That is, sodium hydroxide and sodium carbonate may be added separately as needed. From the viewpoint of insolubilization efficiency, etc., sodium carbonate is preferred.

The pH in the alkali reaction step is not particularly limited as long as it is an alkaline condition, but it can be in the range of pH 9 to 13, and preferably in the range of 11 to 12. When the pH in the alkali reaction step is less than 9, the hardness component removal rate decreases, and when it exceeds 13, the amount of alkali added will increase.

The temperature in the alkali reaction step is not particularly limited as long as it is a temperature at which the insolubilization reaction of the hardness component proceeds, but it can be in the range of, for example, 1°C to 80°C. The temperature in the alkali reaction step is less than 1℃ When the temperature exceeds 80°C, the insolubilization reaction of the hardness components will be insufficient, and when the temperature exceeds 80°C, there will be problems with the heat-resistant temperature of the equipment.

The alkaline agent reaction step is not particularly limited as long as it can carry out the insolubilization reaction of the hardness component, but it can be in the range of 10 to 30 minutes, for example. If the reaction time in the alkali reaction step is less than 10 minutes, the insolubilization reaction of the hardness component will be insufficient, and if it exceeds 30 minutes, the reaction tank will become larger and the equipment cost will increase.

The amount of alkali added should be in the range of 1.0 to 2.0 times the molar concentration of the hardness components in the treated water, and preferably in the range of 1.0 to 1.2 times. When the amount of alkali added is less than 1.0 times the molar concentration of the hardness components in the treated water, the insolubilization reaction of the hardness components will be insufficient, and when it exceeds 2.0 times, the cost of the drug will increase.

The subsequent coagulation treatment step and solid-liquid separation step are the same as the above-mentioned pre-treatment step (removal of silicon dioxide by magnesium salt). Then, the previously treated water obtained by solid-liquid separation is transported to the reverse osmosis membrane treatment device 12.

[Pre-treatment step: Removing hardness components by resin softening]

In the pretreatment step of the resin softening method when the water to be treated contains hardness components, for example, the water to be treated is passed into an ion exchange tower filled with ion exchange resin, and the hardness components are adsorbed and removed (ion exchange step). Then, the pre-treated water produced by ion exchange treatment is sent to the reverse osmosis membrane treatment device 12 .

The ion exchange resin used in the ion exchange step is a cation exchange resin, and examples thereof include Amberrex 100Na, IRC-76 (manufactured by ORGANO Co., Ltd.), and the like.

When the ion exchange resin needs to be regenerated, the ion exchange resin is regenerated by using a regeneration agent.

Examples of the regenerant used include: acid aqueous solutions of hydrochloric acid, sulfuric acid, nitric acid, etc.; sodium chloride aqueous solution; potassium chloride aqueous solution, etc., and one or more of them may be used. That is, after regeneration with an acid aqueous solution, additional regeneration with a sodium chloride aqueous solution may be performed as necessary. From the viewpoint of reusing the suction solution, an acid aqueous solution or a sodium chloride aqueous solution is preferred. If regenerated by an acid aqueous solution, the ion exchange resin becomes the H form, and if regenerated by the sodium chloride aqueous solution, the ion exchange resin becomes the Na form.

[Concentration treatment step (first concentration treatment step)]

The concentration treatment equipment (first concentration treatment equipment) is not particularly limited as long as it can concentrate the pre-treated water. However, in addition to the reverse osmosis membrane treatment equipment, membrane filtration equipment using nanofiltration membranes, distillation equipment, etc. can also be used. One or more devices such as electrodialysis equipment. That is, the concentrated water obtained by the reverse osmosis membrane treatment device can be further concentrated by electrodialysis treatment, or the concentrated water obtained by the first reverse osmosis treatment can be further concentrated by the second reverse osmosis treatment, as needed. A reverse osmosis membrane treatment device is preferable from the viewpoint of efficient treatment when the TDS of the pre-treatment water is low.

The reverse osmosis membrane used in the reverse osmosis membrane treatment device includes ultra-low pressure reverse osmosis membrane and low pressure reverse osmosis membrane used for pure water production and wastewater recovery, as well as medium pressure reverse osmosis membrane and high pressure reverse osmosis membrane used for seawater desalination. Examples of ultra-low pressure reverse osmosis membrane and low pressure reverse osmosis membrane include ES15 (manufactured by Nitto Denko), TM720D (manufactured by TORAY), BW30HRLE (manufactured by Dow Chemical), and LFC3-LD (manufactured by Hydranautics). Examples of high pressure reverse osmosis membrane include SWC5-LD (manufactured by Hydranautics), TM820V (manufactured by TORAY), and XUS180808 (manufactured by Dow Chemical).

In the concentration treatment step (first concentration treatment step), chemicals such as a pH adjuster, a scale dispersant that inhibits scaling of inorganic salts in the system, and a bactericide that inhibits the generation of microorganisms in the system may also be added.

[Forward Osmosis Membrane Treatment Steps]

There is no particular limitation on the shape of the forward osmosis membrane used in the forward osmosis membrane treatment step, but for example, hollow yarn membranes, spiral membranes, tubular membranes, membranes with plate-bottom-frame structures, etc. can be used. Examples of the membrane material of the forward osmosis membrane include aromatic polyamide series and cellulose acetate series. In addition, a membrane in which functional proteins and inorganic materials are combined in the base material of the separation membrane to impart separation performance and water permeability can also be used. Examples of the forward osmosis membrane include HP5230 (manufactured by Toyobo), HFFO2 (manufactured by Aquaporin), and OsmoF20 (manufactured by Fruid Technology Solutions). Such forward osmosis membranes can be used in a single segment or in a plurality of segments connected in series. That is, the FO concentrated water obtained by the first forward osmosis membrane treatment can be further concentrated by the second forward osmosis membrane treatment.

As mentioned above, the attracting solution used in the forward osmosis membrane treatment step can be, for example, a magnesium salt aqueous solution, an alkaline aqueous solution, an acid aqueous solution, a sodium chloride aqueous solution, etc. In addition, in addition to the above, any chemical used in the water treatment device can be used without limitation. That is, various coagulants used in the coagulation step, scale dispersants and disinfectants used in the concentration treatment step, etc. can also be used as the attracting solution.

When multiple forward osmosis membrane treatments are performed in the forward osmosis membrane treatment step, the above-mentioned draw solutions can be used in combination. For example, a sodium chloride aqueous solution is used as the draw solution for the first forward osmosis membrane treatment step, and a magnesium salt aqueous solution is used as the draw solution for the second forward osmosis membrane treatment step. In addition, for example, a dilute sodium chloride aqueous solution obtained by the first forward osmosis membrane treatment step can be used as a regeneration solution for softening resin, and a dilute magnesium salt aqueous solution obtained by the second forward osmosis membrane treatment step can be used as a magnesium source for the soluble silica removal step.

[Second concentration step]

The second concentration treatment equipment is not particularly limited as long as it can concentrate the dilute attracting solution used in the forward osmosis membrane treatment step, but can use: a concentration device using a semipermeable membrane such as a nanofiltration membrane treatment device, a reverse osmosis membrane treatment device, a forward osmosis membrane treatment device, a pressure-assisted reverse osmosis membrane treatment device, etc.; a membrane filtration device using a nanofiltration membrane, etc.; a distillation device; an electrodialysis device, etc., one or more of the following devices can be used. From the perspective of reducing concentration costs, a concentration device using a semipermeable membrane is preferred, and a pressure-assisted reverse osmosis membrane treatment device that can reduce the impact of osmotic pressure is preferred, especially when the TDS concentration of the treated water exceeds 5%.

FIG. 4 shows an example of a concentration device in the water treatment device of this embodiment.

The concentration device 340 shown in Figure 4 is an example of a pressure-assisted reverse osmosis membrane treatment device. The concentration device 340 is a device that has two or more concentration devices that use semipermeable membranes to concentrate water to be processed, and supplies the above-mentioned dilute suction solution to one of the primary sides of the first-stage semipermeable membrane and supplies the dilute liquid to the second stage. On the secondary side, a concentrated liquid is produced from another flow path on the primary side and a diluted liquid is produced from another flow path on the secondary side, and then The diluted liquid is supplied to the primary side of the semipermeable membrane of the secondary stage, and the primary side of the semipermeable membrane of each stage is pressurized to allow the water contained in the primary side to pass through the secondary side, thereby producing a concentrated liquid and a diluted liquid in sequence.

The concentration device 340 has, for example, a first-stage semipermeable membrane treatment device 42, a second-stage semipermeable membrane treatment device 44, and a third-stage semipermeable membrane treatment device 46. The semipermeable membrane treatment device has a primary side (first space) 48 and a secondary side (second space) 50 separated by a semipermeable membrane 52.

In the concentration device 340 shown in FIG4 , the pipe 54 is connected to the inlet of the primary side 48 of the first semipermeable membrane treatment device 42 through the pump 70, and the pipe 56 is connected to the outlet of the primary side 48. The outlet of the primary side 48 of the second semipermeable membrane treatment device 44 and the inlet of the secondary side 50 of the first semipermeable membrane treatment device 42 are connected through the pipe 58, and the outlet of the secondary side 50 of the first semipermeable membrane treatment device 42 and the inlet of the primary side 48 of the second semipermeable membrane treatment device 44 are connected through the pipe 60 through the pump 72. The outlet of the primary side 48 of the third-stage semipermeable membrane treatment device 46 and the inlet of the secondary side 50 of the second-stage semipermeable membrane treatment device 44 are connected by a pipe 62, and the outlet of the secondary side 50 of the second-stage semipermeable membrane treatment device 44 and the inlet of the primary side 48 of the third-stage semipermeable membrane treatment device 46 are connected by a pipe 64 through a pump 74. The pipe 66 is connected to the inlet of the secondary side 50 of the third-stage semipermeable membrane treatment device 46 and the pipe 68 is connected to the outlet of the secondary side 50.

The concentration device 340 is a device using a multi-stage semipermeable membrane treatment device having a primary side 48 and a secondary side 50 separated by a semipermeable membrane 52. A portion of the dilute draw solution (e.g., MgCl ₂ : 8 mass %) used in the forward osmosis membrane treatment device 14 as the water to be treated is passed to the primary side 48 of the first-stage semipermeable membrane treatment device 42 through the pipe 54 by the pump 70, and the second concentrated solution (e.g., MgCl ₂ : 10 mass %) prepared in the second-stage semipermeable membrane treatment device 44 described later is passed to the secondary side 50 through the pipe 58, and then the primary side 48 is pressurized to allow the water contained in the primary side 48 to pass through the secondary side 50, thereby preparing a first concentrated solution (e.g., MgCl ₂ : 30 mass %) and a first diluted solution (e.g., MgCl ₂ : 5 mass %) (concentration step (first stage)). The first concentrated liquid (concentrated suction solution) is discharged through the pipe 56 and reused as the suction solution in the forward osmosis membrane treatment device 14.

The first diluent passes through the pipe 60 and is passed to the primary side 48 of the second-stage semipermeable membrane treatment device 44 through the pump 72, and the third concentrated liquid (for example, produced by the third-stage semipermeable membrane treatment device 46 described later) , MgCl ₂ : 3 mass%) is passed to the secondary side 50 through the pipe 62 , and then the primary side 48 is pressurized to allow the water contained in the primary side 48 to pass through the secondary side 50 to obtain a second concentrated liquid (for example, MgCl ₂ : 10 mass%) and the second dilution (for example, MgCl ₂ : 1 mass%) (concentration step (second stage)). The second concentrated liquid passes through the pipe 58 to the secondary side 50 of the first-stage semipermeable membrane treatment device 42 .

The second diluent passes through the pipe 64 and is passed to the primary side 48 of the third-stage semipermeable membrane treatment device 46 through the pump 74, and the diluent (for example, MgCl ₂ :1 mass %) is passed through the pipe 66 to the secondary side. 50, and then pressurize the primary side 48 to allow the water contained in the primary side 48 to pass through the secondary side 50 to prepare a third concentrated liquid (for example, MgCl ₂ : 3 mass%) and a third diluted liquid (for example, MgCl ₂ : < 1% by mass) (concentration step (third section)). The third concentrated liquid passes through the pipe 62 to the secondary side 50 of the second-stage semipermeable membrane treatment device 44 . The third diluent is discharged through pipe 68 . Part of the second concentrated liquid and the third concentrated liquid can be reused as the suction solution in the forward osmosis membrane treatment device 14 . The third diluent can be recovered and reused after ultrafiltration membrane (UF membrane) treatment, reverse osmosis membrane (RO membrane) treatment, ion exchange treatment, etc. as needed.

The pressure-assisted reverse osmosis membrane treatment device reduces the osmotic pressure difference between the primary side 48 and the secondary side 50, and can be operated with less energy than a general reverse osmosis membrane treatment device, so it can be operated at a lower cost.

As described above, the concentrated attracting solution prepared from the above-mentioned dilute attracting solution can be reused as the attracting solution in the forward osmosis membrane treatment device 14.

In the concentration device 340 shown in Figure 4, the liquid flowing to the secondary side 50 of the first-stage semi-permeable membrane treatment device 42 and the semi-permeable membrane treatment devices after the second stage can be the same as the liquid flowing to the first-stage semi-permeable membrane treatment device 42. The dilution of the primary side 48 of the membrane treatment device 42 attracts liquids with different components of the solution. Figure 5 shows an example of such a concentration device.

The concentrating device 342 shown in FIG. 5 is a device having the same structure as the concentrating device 340 shown in FIG. 4 . A portion of the dilute draw solution (e.g., MgCl ₂ : 8 mass %) used in the forward osmosis membrane treatment device 14 as the water to be treated is passed to the primary side 48 of the first-stage semipermeable membrane treatment device 42 through the pipe 54 by the pump 70, and the second concentrated solution (e.g., glucose: 20 mass %) prepared in the second-stage semipermeable membrane treatment device 44 described later is passed to the secondary side 50 through the pipe 58, and then the primary side 48 is pressurized to allow the water contained in the primary side 48 to pass through the secondary side 50, thereby preparing a first concentrated solution (e.g., MgCl ₂ : 30 mass %) and a first diluted solution (e.g., glucose: 10 mass %) (concentration step (first stage)). The first concentrated liquid (concentrated suction solution) is discharged through the pipe 56 and reused as the suction solution in the forward osmosis membrane treatment device 14.

The first dilution liquid passes through the pipe 60 and is passed to the primary side 48 of the second-stage semipermeable membrane treatment device 44 by the pump 72, and the third concentrated liquid (e.g., NaCl: 3 mass%) obtained by the third-stage semipermeable membrane treatment device 46 described later passes through the pipe 62 to the secondary side 50, and then the primary side 48 is pressurized to allow the water contained in the primary side 48 to pass through the secondary side 50 to obtain the second concentrated liquid (e.g., glucose: 20 mass%) and the second dilution liquid (e.g., NaCl: 1 mass%) (concentration step (second stage)). The second concentrated liquid passes through the pipe 58 to the secondary side 50 of the first-stage semipermeable membrane treatment device 42.

The second dilution liquid passes through the pipe 64 and is passed to the primary side 48 of the third-stage semipermeable membrane treatment device 46 by the pump 74, and the dilution liquid (e.g., NaCl: 1 mass%) passes through the pipe 66 to the secondary side 50, and then the primary side 48 is pressurized to allow the water contained in the primary side 48 to pass through the secondary side 50 to obtain a third concentrated liquid (e.g., NaCl: 3 mass%) and a third dilution liquid (e.g., NaCl: <1 mass%) (concentration step (third stage)). The third concentrated liquid passes through the pipe 62 to the secondary side 50 of the second-stage semipermeable membrane treatment device 44. The third dilution liquid is discharged through the pipe 68. The third dilution liquid can be recovered and reused after ultrafiltration membrane (UF membrane) treatment, reverse osmosis membrane (RO membrane) treatment, ion exchange treatment, etc. as needed.

The liquid passed to the secondary side 50 of the first-stage semipermeable membrane treatment device 42 and the semipermeable membrane treatment devices after the second stage is not particularly limited as long as it has an osmotic pressure. Examples include aqueous solutions containing inorganic salts such as sodium chloride, aqueous solutions containing organic substances such as glucose, aqueous solutions containing polymers, and ionic liquids. From the perspective of the influence of the diffusion of the reduced component from the primary side to the secondary side, it is advisable to use a liquid with the same composition as the dilute absorption solution passed to the primary side 48 of the first-stage semipermeable membrane treatment device 42.

FIG. 6 shows another example of the concentration device 34 in the water treatment device 5 of this embodiment.

The concentration device 344 shown in Figure 6 is an example of a pressure-assisted reverse osmosis membrane treatment device. The concentration device 344 is a device that uses a semipermeable membrane to concentrate the treatment target water and further uses a semipermeable membrane to concentrate the water. One or more concentration equipment for concentrated liquid, and the aforementioned thin suction solution is supplied to the primary side of the first semipermeable membrane, and then the concentrated liquid is sequentially supplied to the primary side of each semipermeable membrane, and the aforementioned thin suction solution is A part or part of the concentrated liquid in any section is supplied to the secondary side of each section of semipermeable membrane, and the primary side of each section of semipermeable membrane is pressurized to allow the water contained in the primary side to pass through the secondary side.

The concentration device 344 has, for example, a first-stage semipermeable membrane treatment device 78, a second-stage semipermeable membrane treatment device 80, and a third-stage semipermeable membrane treatment device 82. Each semipermeable membrane treatment device has a primary side (first space) 84 and a secondary side (second space) 86 separated by a semipermeable membrane 88.

In the concentration device 344 shown in FIG6 , the piping 90 is connected to the inlet of the primary side 84 of the first-stage semipermeable membrane treatment device 78 through the pump 106. The outlet of the primary side 84 of the first-stage semipermeable membrane treatment device 78 and the inlet of the primary side 84 of the second-stage semipermeable membrane treatment device 80 are connected by the piping 92. The outlet of the primary side 84 of the second-stage semipermeable membrane treatment device 80 and the inlet of the primary side 84 of the third-stage semipermeable membrane treatment device 82 are connected by the piping 94. The piping 96 is connected to the outlet of the primary side 84 of the third-stage semipermeable membrane treatment device 82. The piping 98 branched from the piping 96 is connected to the inlet of the secondary side 86 of the third-stage semipermeable membrane treatment device 82. The outlet of the secondary side 86 of the third-stage semipermeable membrane treatment device 82 and the inlet of the secondary side 86 of the second-stage semipermeable membrane treatment device 80 are connected by a pipe 100. The outlet of the secondary side 86 of the second-stage semipermeable membrane treatment device 80 and the inlet of the secondary side 86 of the first-stage semipermeable membrane treatment device 78 are connected by a pipe 102. The pipe 104 is connected to the outlet of the secondary side 86 of the first-stage semipermeable membrane treatment device 78. As needed, the pipes 92, 94, 96, 98, 100, and 102 may have: a pump for pressurization and liquid delivery; a pressure adjustment mechanism such as a valve for adjusting the pressure applied to the semipermeable membrane; a tank for temporarily storing treated water, etc.

In the concentrator 344, a portion of the dilute draw solution (e.g., MgCl ₂ : 10 mass %) used in the forward osmosis membrane treatment device 14 as the treated water is transported to the primary side 84 of the first semipermeable membrane treatment device 78 through the pipe 90 by the pump 106. On the other hand, the dilute solution (secondary side treated water) (e.g., MgCl ₂ : 6 mass %) returned from the third semipermeable membrane treatment device 82 as the final stage described later via the secondary side 86 of the second semipermeable membrane treatment device 80 is transported to the secondary side 86 of the first semipermeable membrane treatment device 78 through the pipe 102. In the first-stage semipermeable membrane treatment device 78, the primary side 84 of the semipermeable membrane is pressurized to allow water contained in the primary side 84 to pass through the secondary side 86 (concentration step (first stage)).

The concentrated liquid (primary side treated water) (for example, MgCl ₂ :18% by mass) of the first-stage semipermeable membrane treatment device 78 passes through the pipe 92 and is then transported to the primary side 84 of the second-stage semipermeable membrane treatment device 80 . On the other hand, the diluent (secondary side treated water) (for example, MgCl ₂ :15% by mass) sent back from the third-stage semipermeable membrane treatment device 82 of the final stage described below passes through the pipe 100 and is then transported to the second stage. The secondary side 86 of the semipermeable membrane processing device 80 . Similar to the first stage, in the second stage semipermeable membrane treatment device 80, the primary side 84 of the semipermeable membrane is pressurized to allow the water contained in the primary side 84 to pass through the secondary side 86 (concentration step (second stage)) .

The concentrated liquid (primary side treated water) (for example, MgCl ₂ :23% by mass) of the second-stage semipermeable membrane treatment device 80 passes through the pipe 94 and is then transported to the primary side 84 of the third-stage semipermeable membrane treatment device 82 . On the other hand, the concentrated solution (for example, MgCl ₂ :30% by mass) returned from the third-stage semipermeable membrane treatment device 82 of the final stage described below passes through the pipe 98 and is then transported to the third-stage semipermeable membrane treatment device 82 Secondary side 86. Similar to the first and second stages, in the third stage semipermeable membrane treatment device 82, the primary side 84 of the semipermeable membrane is pressurized to allow the water contained in the primary side 84 to pass through the secondary side 86 (concentration step (third stage) )).

A part of the concentrated liquid (primary side treatment water) (for example, MgCl ₂ :30 mass %) of the third-stage semipermeable membrane treatment device 82 in the final stage is discharged through the pipe 96 and serves as the suction in the forward osmosis membrane treatment device 14 The solution is reused. The remaining portion of the concentrated liquid in the third-stage semipermeable membrane treatment device 82 passes through pipes 96 and 98 and is then transported to the secondary side 86 of the third-stage semipermeable membrane treatment device 82 . As described above, in the third-stage semipermeable membrane treatment device 82, the primary side 84 of the semipermeable membrane is pressurized to allow the water contained in the primary side 84 to pass through the secondary side 86 (concentration step (third stage)).

The dilute liquid (secondary side treated water) (e.g., MgCl ₂ : 15 mass%) of the third stage semipermeable membrane treatment device 82 is transported to the secondary side 86 of the second stage semipermeable membrane treatment device 80 through the pipe 100. As described above, in the second stage semipermeable membrane treatment device 80, the primary side 84 of the semipermeable membrane is pressurized to allow the water contained in the primary side 84 to pass through the secondary side 86 (concentration step (second stage)).

The dilute liquid (secondary side treated water) (e.g., MgCl ₂ : 6 mass%) of the second stage semipermeable membrane treatment device 80 passes through the pipe 102 and is then transported to the secondary side 86 of the first stage semipermeable membrane treatment device 78. As described above, in the first stage semipermeable membrane treatment device 78, the primary side 84 of the semipermeable membrane is pressurized so that the water contained in the primary side 84 passes through the secondary side 86 (concentration step (first stage)). The dilute liquid (secondary side treated water) (e.g., MgCl ₂ : <1 mass%) of the first stage semipermeable membrane treatment device 78 is discharged through the pipe 104. The dilute liquid can be recovered and reused after ultrafiltration membrane (UF membrane) treatment, reverse osmosis membrane (RO membrane) treatment, ion exchange treatment, etc. as needed.

Because the pressure-assisted reverse osmosis membrane treatment device of the concentration device 344 uses a portion of the treated water as a diluent for osmotic pressure assistance, it is not necessary to prepare a diluent separately, so the device structure can be simplified compared to the pressure-assisted reverse osmosis membrane treatment device of the concentration device 340.

As described above, the concentrated attracting solution prepared from the above-mentioned dilute attracting solution is reused as the attracting solution in the forward osmosis membrane treatment device 14.

In such a pressure-assisted reverse osmosis membrane treatment device of the concentration device 344, a portion of the dilute suction solution used in the forward osmosis membrane treatment device 14 or a portion of the concentrated solution of any section can be supplied to the secondary side of each section of the semipermeable membrane. The method is not particularly limited.

For example, as shown in the concentration device 346 in FIG. 7 , the thin suction solution used in the forward osmosis membrane treatment device 14 as the water to be treated can be distributed and supplied to the primary side 84 of the first-stage semipermeable membrane treatment device 78 respectively. , the secondary side 86, and then supply the concentrated liquid and permeate sequentially to the primary side 84 and the secondary side 86 of each section of semipermeable membrane, and then pressurize the primary side of each section of semipermeable membrane to make the primary side contain Water passes through the secondary side.

As shown in the concentration device 348 of FIG8 , the dilute draw solution used in the forward osmosis membrane treatment device 14 as the treated water can be supplied to the primary side 84 of the first semipermeable membrane treatment device 78, and the concentrated liquid is sequentially supplied to the primary side of each semipermeable membrane, and then a portion of the concentrated liquid of the final third semipermeable membrane treatment device 82 is supplied to the secondary side 86 of the first semipermeable membrane treatment device 78 and the permeate is sequentially supplied to the secondary side of each semipermeable membrane, and then the primary side of each semipermeable membrane is pressurized to allow the water contained in the primary side to pass through the secondary side.

As shown in the concentration device 350 of FIG. 9 , the dilute draw solution used in the forward osmosis membrane treatment device 14 as the treated water can be supplied to the primary side 84 of the first semipermeable membrane treatment device 78, and the concentrated solution is sequentially supplied to the primary side of each semipermeable membrane, and then a portion of the concentrated solution of each semipermeable membrane treatment device is supplied to the secondary side 86 of the semipermeable membrane treatment device itself, and then the primary side of each semipermeable membrane is pressurized to allow the water contained in the primary side to pass through the secondary side.

In the above-described concentration devices 340, 342, 344, 346, 348, and 350, the number of stages of the semipermeable membrane treatment device can be determined according to the intended treatment water concentration, etc. For example, in the concentration devices 344, 346, 348, and 350, when it is desired to produce treatment water with a relatively concentrated concentration (concentrated suction solution) from a thin suction solution with a relatively dilute concentration, the number of stages of the semipermeable membrane treatment device can be increased.

In the above-mentioned concentration devices 340, 342, 344, 346, 348, 350, a membrane module unit having two or more membrane modules connected in parallel can be used as a semipermeable membrane treatment device for each section. The number of membrane modules in each membrane module unit can be determined according to the flow rate of the dilute suction solution to be treated, etc.

Semipermeable membranes having a semipermeable membrane treatment device include, for example, reverse osmosis membranes (RO membranes), forward osmosis membranes (FO membranes), nanofiltration membranes (NF membranes), and other semipermeable membranes. The semipermeable membrane is preferably a reverse osmosis membrane, a forward osmosis membrane, or a nanofiltration membrane. In addition, when using a reverse osmosis membrane, forward osmosis membrane, or nanofiltration membrane as a semipermeable membrane, the pressure of the target solution on the primary side is preferably 0.5 to 10.0 MPa.

The semipermeable membrane is not particularly limited, but examples thereof include cellulose-based resins such as cellulose acetate-based resins, polyether-based resins such as polyether-based resins, and polyamide-based resins. The material constituting the semipermeable membrane is preferably cellulose acetate resin.

The shape of the semipermeable membrane is not particularly limited as long as it has a structure that can separately supply the solution to the primary side and the secondary side of the membrane. Examples include spiral type, hollow gauze membrane, plate-bottom frame type, etc.

[Another example of water treatment device]

The schematic structure of another water treatment device example of the embodiment of the present invention is shown in FIG2. The water treatment device 3 shown in FIG2 further has an attracting solution preparation tank 30, which is a preparation device for mixing magnesium hydroxide and acid and reacting them at a pH below 7 to prepare a magnesium salt aqueous solution used as an attracting solution.

In the water treatment device 3 of FIG. 2 , the outlet of the suction solution preparation tank 30 and the suction solution inlet of the forward osmosis membrane treatment device 14 are connected by the suction solution piping 32.

The same as the water treatment device 1 in Figure 1 is performed: a pre-treatment step, which includes any one of a soluble silica removal step and a hardness component removal step; and a concentration step, wherein the concentration step is performed to obtain previously treated water through the pre-treatment step.

On the other hand, in the suction solution preparation tank 30, magnesium hydroxide and acid are mixed and reacted at a pH of 7 or less to prepare a magnesium aqueous salt solution used as the suction solution (preparation step).

In the forward osmosis membrane treatment device 14, the forward osmosis membrane processes the concentrated water produced by the reverse osmosis membrane treatment (forward osmosis membrane treatment step). In the forward osmosis membrane treatment device 14, the suction solution prepared by the suction solution preparation tank 30 is transported to the secondary side of the forward osmosis membrane through the suction solution pipe 32, and then passes through the forward osmosis membrane to allow concentrated water and the suction solution to exist, thereby Water is allowed to move using osmotic pressure to attract the solution.

The dilute suction solution used in the positive osmosis membrane treatment step is transported to the pre-treatment device 10 through the dilute suction solution pipe 26, and then used in the pre-treatment step in the pre-treatment device 10.

In the water treatment device 5 of Fig. 3, like the water treatment device 3 of Fig. 2, it may be further equipped with an suction solution preparation tank for mixing magnesium hydroxide and acid and reacting them at a pH of 7 or less to prepare an suction solution. Equipment for preparing magnesium salt solution. In the suction solution preparation tank, magnesium hydroxide and acid are mixed and reacted at a pH of 7 or below to prepare a magnesium salt solution (preparation step), and the prepared magnesium salt solution can be transported to the secondary side of the forward osmosis membrane treatment device 14 Use as a suction solution.

Examples of the acid used in the preparation step include hydrochloric acid, sulfuric acid, nitric acid, etc., and from the viewpoint of suppressing the production of poorly soluble substances, hydrochloric acid or nitric acid is preferred.

The pH in the preparation step is not particularly limited as long as it is 7 or lower, but it can be in the range of 1 to 7, and preferably in the range of 2 to 5. If the pH in the preparation step exceeds 7, the magnesium salt will not be fully dissolved, and if it is less than 1, the added amount of acid will be too much.

The temperature in the preparation step is not particularly limited as long as the dissolution reaction of the magnesium salt proceeds, but it may be in the range of 1°C to 80°C, for example. If the temperature in the preparation step is less than 1°C, the dissolution reaction of the magnesium salt will be insufficient, and if it exceeds 80°C, there will be problems with the heat resistance of the equipment.

The reaction time in the preparation step is not particularly limited as long as the magnesium salt can be dissolved, but it can be in the range of 5 minutes to 120 minutes. If the reaction time in the preparation step is less than 5 minutes, the dissolution reaction of the magnesium salt will be insufficient, and if it exceeds 120 minutes, the equipment will have problems.

<Forward osmosis membrane treatment method and forward osmosis membrane treatment system>

The following is a schematic diagram of an example of a forward osmosis membrane treatment system, which is one embodiment of the present invention, and its structure is described in FIG11.

The forward osmosis membrane treatment system 8 of this embodiment has a forward osmosis membrane treatment device 14, and the forward osmosis membrane treatment device 14 is a forward osmosis membrane treatment device that produces concentrated water (FO concentrated water) and a dilute draw solution by allowing the water to be treated (FO treated water) and a draw solution with a higher concentration than the water to be treated (FO treated water) to contact through a forward osmosis membrane 110.

In the forward osmosis membrane treatment system 8 of FIG. 11 , the FO treated water pipe 16 is connected to the FO treated water inlet of the forward osmosis membrane treatment device 14 , and the FO concentrated water pipe 28 is connected to the FO concentrated water outlet. The suction solution pipe 24 is connected to the suction solution inlet of the forward osmosis membrane treatment device 14, and the dilute suction solution pipe 26 is connected to the dilute suction solution outlet. The sterilant addition pipe 112 is connected to the FO treated water pipe 16 as a sterilant addition device.

The following describes the forward osmosis membrane treatment method and the operation of the forward osmosis membrane treatment system 8 of this embodiment.

The FO treated water is transported to the primary side of the forward osmosis membrane treatment device 14 through the FO treated water pipe 16 and is subjected to forward osmosis membrane treatment (forward osmosis membrane treatment step) in the forward osmosis membrane treatment device 14 . In the forward osmosis membrane treatment device 14, the suction solution is transported to the secondary side of the forward osmosis membrane through the suction solution pipe 24 and passes through the forward osmosis membrane 110 to allow the FO to be treated water and the suction solution to exist, thereby causing the water to move to the secondary side using osmotic pressure. Attract solution. The dilute suction solution used in the forward osmosis membrane treatment step is discharged through the dilute suction solution pipe 26 . The FO concentrated water produced by the forward osmosis membrane treatment step is discharged through the FO concentrated water pipe 28 . At least one of the dilute suction solution and FO concentrated water can be recovered and reused.

Here, a bactericide containing a bromine-based oxidizing agent or a chlorine-based oxidizing agent and a sulfamic acid compound (hereinafter, sometimes referred to as a "bactericide for forward osmosis membrane") is present in the FO to-be-treated water. For example, the bactericide for the forward osmosis membrane is added to the FO to be treated water in the FO to be treated water pipe 16 through the bactericide adding pipe 112 . It is also possible to provide an additional FO treated water tank for storing FO treated water in the front stage of the forward osmosis membrane treatment device 14, and add a bactericide for the forward osmosis membrane into the FO treated water tank.

Thus, in the forward osmosis membrane treatment method and the forward osmosis membrane treatment system 8 of this embodiment, when the forward osmosis membrane treats the water to be treated, the forward osmosis membrane containing the bromine-based oxidizing agent or the chlorine-based oxidizing agent and the sulfamic acid compound is sterilized. The agent exists in the treated water (FO treated water) treated by the forward osmosis membrane. The present inventors discovered that the bactericide for a forward osmosis membrane containing a bromine-based oxidizing agent or a chlorine-based oxidizing agent and a sulfamic acid compound hardly penetrates the forward osmosis membrane. This bactericide for forward osmosis membrane exerts a more sufficient bactericidal effect on the forward osmosis membrane than conventional chlorine-based bactericides, oxidants, and organic bactericides. In addition, since the bactericide hardly leaks into the suction solution, the dilute suction solution can be reused.

Since the sterilizing active ingredient of the forward osmosis membrane sterilant hardly penetrates the forward osmosis membrane, it is gradually concentrated as it proceeds to the outlet (FO concentrated water outlet) of the forward osmosis membrane treatment device 14 . Therefore, the sterilizing active ingredient of the sterilizing agent can be fully diffused to the outlet (FO concentrated water outlet) side of the forward osmosis membrane treatment device 14 and can be fully sterilized to the outlet side of the forward osmosis membrane.

In the conventional method, when fungicides such as hypochlorous acid, chloramine, hydrogen peroxide, organic fungicides, etc. are added to the FO treated water, part of the FO treated water will be damaged due to the osmotic pressure difference between the FO treated water and the suction solution. Move to the suction solution side, and at the same time part of the bactericide moves to the suction solution side. On the other hand, in the forward osmosis membrane treatment method and the forward osmosis membrane treatment system 8 of this embodiment, by using the above-described bactericide for forward osmosis membranes, it is possible to suppress the permeation of the bactericide through the forward osmosis membrane and reuse the dilute suction solution.

The "bactericide containing a bromine-based oxidizing agent and a sulfamic acid compound" may be a bactericide containing a stabilized hypobromous acid composition containing a mixture of a "bromine-based oxidizing agent" and a "sulfamic acid compound", or a bactericide containing a "bromine-based oxidizing agent" and a "sulfamic acid compound" A fungicide composed of stabilized hypobromous acid, which is the reaction product of oxidants and amine sulfonic acid compounds. The "bactericide containing a chlorine-based oxidizing agent and a sulfamic acid compound" may be a bactericidal agent containing a stabilized hypochlorous acid composition containing a mixture of a "chlorine-based oxidizing agent" and a "sulfamic acid compound", or a bactericidal agent containing a "chlorine-based oxidizing agent" and a "sulfamic acid compound" A bactericide composed of stabilized hypochlorous acid, which is a reaction product of an oxidizing agent and an amine sulfonic acid compound.

That is, the forward osmosis membrane treatment method of the embodiment of the present invention is a method of allowing a mixture of a "bromine-based oxidant" and a "sulfonic acid compound" or a mixture of a "chlorine-based oxidant" and a "sulfonic acid compound" to exist in the water to be treated (FO treated water). Therefore, it is considered that a stabilized hypobromous acid composition or a stabilized hypochlorous acid composition is generated in the water to be treated.

In addition, the forward osmosis membrane treatment method according to the embodiment of the present invention is to stabilize the hypobromous acid composition of "the reaction product of the bromine-based oxidizing agent and the sulfamic acid compound" or the "reaction product of the chlorine-based oxidizing agent and the sulfamic acid compound" ” is a method in which a stabilized hypochlorous acid composition is present in the water to be treated (FO water to be treated).

Specifically, the forward osmosis membrane treatment method according to the embodiment of the present invention uses "bromine", "bromine chloride", "hypobromous acid" or "reactant of sodium bromide and hypochlorous acid" and "sulfamic acid compound". "The mixture is present in the water being treated. Alternatively, a mixture of "hypochlorous acid" and "amine sulfonic acid compound" is present in the water to be treated.

In addition, the forward osmosis membrane treatment method of the embodiment of the present invention is a method for allowing a stabilized hypobromous acid composition of "reaction product of bromine and sulfamic acid compound", "reaction product of bromine chloride and sulfamic acid compound", "reaction product of hypobromous acid and sulfamic acid compound" or "reaction product of sodium bromide and hypochlorous acid and reaction product of sulfamic acid compound" to exist in the water to be treated. Alternatively, a method for allowing a stabilized hypochlorous acid composition of "reaction product of hypochlorous acid and sulfamic acid compound" to exist in the water to be treated.

In the forward osmosis membrane treatment method of the embodiment of the present invention, although the stabilized hypobromous acid composition or the stabilized hypochlorous acid composition exerts a bactericidal effect equal to or higher than that of conventional bactericides such as chlorine-based oxidants such as hypochlorous acid, it has less effect on the deterioration of the forward osmosis membrane than conventional bactericides such as chlorine-based oxidants, and thus can inhibit the fouling of the forward osmosis membrane and inhibit the oxidative degradation of the forward osmosis membrane. Therefore, the stabilized hypobromous acid composition or the stabilized hypochlorous acid composition used in the forward osmosis membrane treatment method of the present embodiment is suitable as a bactericide used in the method of treating the water to be treated using a forward osmosis membrane.

In the forward osmosis membrane treatment method of this embodiment, when "a bactericide containing a bromine-based oxidizing agent and a sulfamic acid compound" is used, the chlorine-based oxidizing agent does not exist, so the influence on the deterioration of the forward osmosis membrane is smaller. When chlorine-based oxidants are included, there is a risk of generating chloric acid.

In the forward osmosis membrane treatment method of this embodiment, when the "bromine-based oxidant" is bromine, the chlorine-based oxidant does not exist, so the effect on the deterioration of the forward osmosis membrane is significantly low.

In the forward osmosis membrane treatment method of this embodiment, the "bromine-based oxidant" or "chlorine-based oxidant" and "sulfonamic acid compound" can be injected into the water to be treated, for example, by an injection pump. The "bromine-based oxidant" or "chlorine-based oxidant" and "sulfonamic acid compound" can be added to the water to be treated separately or mixed with the original solution and added to the water to be treated.

In addition, the "reaction product of a bromine-based oxidant and an amine sulfonic acid compound" or "reaction product of a chlorine-based oxidant and an amine sulfonic acid compound" can be injected into the treated water, for example, by using an injection pump.

In the forward osmosis membrane treatment method of this embodiment, the ratio of the equivalent of the "amine sulfonic acid compound" to the equivalent of the "bromine-based oxidizing agent" or "chlorine-based oxidizing agent" is preferably 1 or more and within the range of 1 or more and 2 or less. Better. If the ratio of the equivalent of the "amine sulfonic acid compound" to the equivalent of the "bromine-based oxidizing agent" or "chlorine-based oxidizing agent" is less than 1, the membrane may deteriorate, and if it exceeds 2, the manufacturing cost will increase.

Calculated by effective chlorine concentration, the total chlorine concentration in contact with the positive osmosis membrane should be between 0.01 and 100 mg/L. If it is less than 0.01 mg/L, it will not achieve a sufficient sterilization effect, and if it is greater than 100 mg/L, it may cause deterioration of the positive osmosis membrane and corrosion of the piping, etc.

Bromine-based oxidants include, for example, bromine (liquid bromine), bromine chloride, bromic acid, bromate, hypobromous acid, etc. Hypobromous acid can be produced by reacting bromides such as sodium bromide with chlorine-based oxidants such as hypochlorous acid.

Among them, the preparations using bromine, "bromine and amine sulfonic acid compound (mixture of bromine and amine sulfonic acid compound)" or "reaction product of bromine and amine sulfonic acid compound" have less byproducts of bromic acid and will not further deteriorate the forward osmosis membrane, compared with the preparations of "hypochlorous acid, bromine compound and amine sulfonic acid" and "bromine chloride and amine sulfonic acid". Therefore, they are more ideal as disinfectants for forward osmosis membranes.

That is, in the forward osmosis membrane treatment method according to the embodiment of the present invention, it is preferable that bromine and a sulfamic acid compound be present in the water to be treated (a mixture of bromine and a sulfamic acid compound be present). In addition, it is preferable to allow the reaction product of bromine and sulfamic acid compound to exist in the water to be treated.

Bromine compounds include, for example, sodium bromide, potassium bromide, lithium bromide, ammonium bromide, and hydrobromic acid. Among them, sodium bromide is preferred in terms of the cost of the preparation.

Examples of the chlorine-based oxidizing agent 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 isocyanic acid or its salts, and the like. Examples of the salt include: alkali metal hypochlorite salts such as sodium hypochlorite and potassium hypochlorite; alkaline earth gold hypochlorite salts such as calcium hypochlorite and barium hypochlorite Salts; 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. These chlorine-based oxidizing agents can be used singly or in combination of two or more. From the perspective of operability and other aspects, sodium hypochlorite is suitable for chlorine-based oxidants.

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.)

Examples of sulfamic acid compounds include: sulfamic acid (amide sulfonic acid) in which both of the two R groups are hydrogen atoms, N-methyl sulfamic acid, N-ethyl sulfamic acid, and N-propyl sulfonic acid. Amines in which one of the two R groups is a hydrogen atom and the other R group is an alkyl group with 1 to 8 carbon atoms, such as amine sulfonic acid, N-isopropyl amine sulfonic acid, and N-butyl amine sulfonic acid. Sulfonic acid compounds; N,N-dimethylaminesulfonic acid, N,N-diethylaminesulfonic acid, N,N-dipropylaminesulfonic acid, N,N-dibutylaminesulfonic acid, N- Methyl-N-ethylamine sulfonic acid, N-methyl-N-propylamine sulfonic acid, etc. are amine sulfonic acid compounds in which both R groups are alkyl groups with 1 to 8 carbon atoms; N-aniline An amine sulfonic acid compound in which one of the two R groups of sulfonic acid is a hydrogen atom and the other R group is an aryl group having 6 to 10 carbon atoms; or a salt thereof, etc. Examples of amine sulfonates include alkali metal salts such as sodium salt and potassium salt; alkaline earth metal salts such as calcium salt, strontium salt, and barium salt; manganese salt, copper salt, zinc salt, iron salt, cobalt salt, and nickel salt. Other metal salts; ammonium salts and guanidinium salts, etc. A sulfamic acid compound and its salt can be used individually by 1 type or in combination of 2 or more types. From the viewpoint of environmental load, etc., it is preferable to use amide sulfonic acid (amide sulfate) as the sulfamic acid compound.

In the forward osmosis membrane treatment method of this embodiment, a base may be further present. Examples of the base include alkali hydroxides such as sodium hydroxide and potassium hydroxide. From the perspective of product stability at low temperatures, sodium hydroxide and potassium hydroxide can be used together. Furthermore, the base may be used not in solid form but in the form of an aqueous solution.

The shape of the forward osmosis membrane used in the forward osmosis membrane treatment step is not particularly limited, but for example, hollow yarn membranes, spiral membranes, tubular membranes, membranes with plate-bottom frame structures, etc. can be used. Examples of the membrane material of the forward osmosis membrane include aromatic polyamide series, cellulose acetate series, polyketone series, etc. In addition, a membrane in which functional proteins and inorganic materials are combined in the base material of the separation membrane to impart separation performance and water permeability can also be used. The forward osmosis membrane treatment method of this embodiment can ideally use a membrane in which functional proteins and inorganic materials are combined in the base material of the aromatic polyamide series and amide series to impart separation performance and water permeability as a forward osmosis membrane. It is known that such membranes are particularly susceptible to deterioration caused by the chlorine-based oxidants commonly used.

Examples of the forward osmosis membrane include HP5230 (manufactured by Toyobo), HFFO2 (manufactured by Aquaporin), and OsmoF20 (manufactured by Fruid Technology Solutions). These forward osmosis membranes can be used in a single section or multiple sections connected in series. That is, the concentrated water obtained by the first forward osmosis membrane treatment can be further concentrated by the second forward osmosis membrane treatment.

However, the forward osmosis membrane and reverse osmosis membrane have different membrane structures and properties due to their different operating methods. The reverse osmosis membrane applies high pressure to the primary side of the membrane, so the membrane thickness is made thick to maintain mechanical strength that can withstand the pressure. On the other hand, because the pressure applied to the forward osmosis membrane is lower than that of the reverse osmosis membrane, the mechanical strength of the reverse osmosis membrane is not as good as that of the reverse osmosis membrane, and the concentration polarization inside the membrane must be further suppressed, so the membrane thickness needs to be made thin. The membrane is made to best suit the required operating conditions. As a result, although the reverse osmosis membrane and the forward osmosis membrane have the same membrane material, they have different membrane structures, so the permeation performance and blocking performance are different. Therefore, when the reverse osmosis membrane used in reverse osmosis membrane treatment is used for forward osmosis purposes, sufficient performance cannot be obtained.

Examples of the suction solution used in the forward osmosis membrane treatment step include inorganic aqueous solutions such as ammonium carbonate aqueous solution, magnesium aqueous solution, and sodium aqueous solution; organic aqueous solutions of sucrose, glucose, organic polymers, etc.; ionic liquids, etc. The dilute suction solution used in the forward osmosis membrane treatment step can be used unchanged in another step, or the water can be separated from the dilute suction solution by heating, membrane separation, etc., and then reused. water and concentrated suction solution. When performing multiple stages of forward osmosis membrane treatment in the forward osmosis membrane treatment step, the above-mentioned suction solutions can be used in combination.

The water to be treated (FO to be treated) is not particularly limited, but examples include: industrial water, surface water, tap water, groundwater, seawater, seawater desalination water desalinated by reverse osmosis or evaporation, for example, in semiconductors Various types of drainage such as drainage discharged from manufacturing processes, etc.

The pH of the treated water is, for example, in the range of 2 to 12, and preferably in the range of 4 to 11. When the pH of the treated water is less than 2 or exceeds 12, the positive osmosis membrane will deteriorate.

In a forward osmosis membrane treatment device, when the pH of the water to be treated is 5.5 or higher and scale occurs, a dispersant can be used together with the above-mentioned bactericide to inhibit scale. Examples of dispersants include polyacrylic acid, polymaleic acid, phosphonic acid, and the like. The amount of dispersant added to the water to be treated is, for example, in the range of 0.1 to 1,000 mg/L based on the concentration in FO concentrated water.

In addition, in order to control the occurrence of scale without using a dispersant, for example, the recovery rate, water temperature, pH and other operating conditions of the forward osmosis membrane treatment device can be adjusted so that the concentration of silica in the FO concentrated water is below the solubility and the Langelier index, which is an indicator of calcium scale, is below 0.

For example, the use of positive osmosis membrane treatment systems includes seawater desalination, wastewater volume reduction, concentration of valuables, concentration of food and beverages, etc.

<Water treatment method, water treatment system>

Next, a water treatment method and a water treatment system using the above-mentioned forward osmosis membrane treatment method and forward osmosis membrane treatment system will be described.

The water treatment method according to the embodiment of the present invention includes the above-mentioned forward osmosis membrane treatment method, and includes a pre-treatment step and a reverse osmosis membrane treatment step before the forward osmosis membrane treatment step, and in the pre-treatment step, a forward osmosis membrane treatment method is used. A water treatment method for the thin suction solution prepared in the treatment step. In addition, the water treatment system according to the embodiment of the present invention has the above-mentioned forward osmosis membrane treatment system, and has a pre-treatment device and a reverse osmosis membrane treatment device in the front stage of the forward osmosis membrane treatment device, and uses a forward osmosis membrane treatment device in the pre-treatment device. Water treatment system for thin suction solutions produced by permeable membrane treatment equipment.

Next, an outline of an example of a water treatment system according to an embodiment of the present invention is shown in FIG. 12 and its structure is explained.

The water treatment system 9 of this embodiment has: a pretreatment device 114, which is a pretreatment device for pre-treating the treated water; a reverse osmosis membrane treatment device 118, which is a reverse osmosis membrane treatment device for performing reverse osmosis membrane treatment to obtain pre-treated water by pre-treatment and producing RO concentrated water and RO permeated water; and a forward osmosis membrane treatment device 14, which is a forward osmosis membrane treatment device for performing forward osmosis membrane treatment of RO concentrated water obtained by reverse osmosis membrane treatment. The water treatment system 9 may have a turbidity removal device 116, which is a turbidity removal device for performing turbidity removal treatment to obtain pre-treated water by pre-treatment.

In the water treatment system 9 of FIG. 12 , the treated water pipe 120 is connected to the pre-treated water inlet of the pre-treatment device 114, and the outlet of the pre-treatment device 114 and the inlet of the filth removal device 116 are connected by a pipe 122, and the outlet of the filth removal device 116 and the inlet of the reverse osmosis membrane treatment device 118 are connected by a pipe 124. The RO concentrated water outlet of the reverse osmosis membrane treatment device 118 and the FO pre-treated water inlet of the forward osmosis membrane treatment device 14 are connected by the FO treated water pipe 16, and the RO permeate water pipe 126 is connected to the RO permeate water outlet of the reverse osmosis membrane treatment device 118. The suction solution piping 24 is connected to the suction solution inlet of the forward osmosis membrane treatment device 14, and the dilute suction solution outlet of the forward osmosis membrane treatment device 14 and the dilute suction solution inlet of the pre-treatment device 114 are connected by the dilute suction solution piping 26, and the FO concentrated water piping 28 is connected to the FO concentrated water outlet of the forward osmosis membrane treatment device 14. The backwash drainage piping 128 can also be connected to the backwash drainage outlet of the filth removal device 116.

The following describes the water treatment method and the operation of the water treatment system 9 of this embodiment.

The water to be treated is transported to the pre-treatment device 114 through the water to be treated pipe 120 . In the pretreatment device 114, a removal process (pretreatment step) of soluble silica, hardness components, etc. contained in the water to be treated is performed.

When the water to be treated contains soluble silica, the pretreatment device 114 has, for example, a magnesium reaction device that adds magnesium salt to the water to be treated and reacts it to insolubilize the soluble silica; and an agglomeration treatment device that agglomerates the water. The agent is added to the treated water after the reaction to cause it to agglomerate; and the solid-liquid separation equipment separates the agglomerates from the treated water after the agglutination treatment. In the pretreatment device 114, a magnesium salt is added to the water to be treated under, for example, alkaline conditions (for example, pH 10 to 12) to insolubilize soluble silica (magnesium reaction step). Then, if necessary, a coagulant is added to perform aggregation treatment (aggregation treatment step), and the aggregated product is solid-liquid separated (solid-liquid separation step). The solid-liquid separation treated water produced by solid-liquid separation is transported to the turbidity removal device 116 through the pipe 122 as pre-treatment water, and is then subjected to turbidity removal treatment by a UF membrane or the like, and after the turbidity components and the like are removed (turbidity (mass removal step) and transported to the reverse osmosis membrane treatment device 118.

When the water to be treated contains a hardness component and the hardness component is removed by lime softening, the pretreatment device 114 has, for example, an alkali reaction device that adds an alkali agent to the water to be treated to react and insolubilize the hardness component; A coagulation treatment equipment, which adds a coagulant to the water to be treated after the reaction to agglomerate it as necessary; and a solid-liquid separation equipment, which separates agglomerates from the water to be treated after the coagulation treatment. In the pretreatment device 114, for example, an alkali agent is added to the water to be treated to insolubilize the hardness component (alkali agent reaction step). Then, if necessary, a coagulant is added to perform aggregation treatment (aggregation treatment step), and the aggregated product is solid-liquid separated (solid-liquid separation step). The solid-liquid separation treated water produced by solid-liquid separation is transported to the turbidity removal device 116 through the pipe 122 as pre-treatment water, and is then subjected to turbidity removal treatment by a UF membrane or the like, and after the turbidity components and the like are removed (turbidity (mass removal step) and transported to the reverse osmosis membrane treatment device 118.

When the water to be treated contains hardness components and the hardness components are removed by a resin softening method, the pre-treatment device 114 has an ion exchange treatment device that performs ion exchange treatment using, for example, an ion exchange resin. In the pre-treatment device 114, for example, the water to be treated is passed to an ion exchange tower filled with an ion exchange resin as an ion exchange treatment device, and the hardness components are removed by adsorption (ion exchange step). The pre-treated water obtained by the ion exchange treatment is transported to the turbidity removal device 116 through the pipe 122, and then turbidity removal treatment is performed by a UF membrane, etc., and after the turbidity components are removed (turbidity removal step), it is transported to the reverse osmosis membrane treatment device 118. When the ion exchange resin needs to be regenerated, the ion exchange resin is regenerated by using a regeneration agent.

Next, the reverse osmosis membrane treatment device 118 processes the pre-treated water after the turbidity removal treatment to produce RO concentrated water and RO permeated water (reverse osmosis membrane treatment step). The RO concentrated water produced by the reverse osmosis membrane treatment is transported to the primary side of the forward osmosis membrane treatment device 14 as FO treated water through the FO treated water pipe 16 , and the RO permeated water is discharged through the RO permeated water pipe 126 . In addition, in the turbidity removal device 116, the membrane can be backwashed every predetermined time. For example, RO permeated water or the like is supplied to the turbidity removal device 116 as backwash water, and the backwash drainage water is discharged through the backwash drainage pipe 128 .

In the forward osmosis membrane treatment device 14, the forward osmosis membrane processes the RO concentrated water produced by the reverse osmosis membrane treatment (forward osmosis membrane treatment step). In the forward osmosis membrane treatment device 14, the suction solution is transported to the secondary side of the forward osmosis membrane through the suction solution pipe 24, and then passes through the forward osmosis membrane to allow the RO concentrated water and the suction solution to exist, whereby the water is moved to the secondary side by osmotic pressure. Attract solution.

Here, a forward osmosis membrane bactericide containing a bromine-based oxidant or a chlorine-based oxidant and an amine sulfonic acid compound is allowed to exist in RO concentrated water (FO treated water). For example, the forward osmosis membrane bactericide is added to the RO concentrated water (FO treated water) in the FO treated water pipe 16 through the bactericide addition pipe 112. It is also possible to set up a FO treated water tank for storing RO concentrated water (FO treated water) in the front section of the forward osmosis membrane treatment device 14, for example, between the reverse osmosis membrane treatment device 118 and the forward osmosis membrane treatment device 14, and add the forward osmosis membrane bactericide to the FO treated water tank.

This bactericide for forward osmosis membrane exerts a more sufficient bactericidal effect on the forward osmosis membrane than conventional chlorine-based bactericides, oxidants, and organic bactericides. By using the above-mentioned bactericide for forward osmosis membranes in the water treatment method of this embodiment, the bactericidal active ingredients hardly penetrate the forward osmosis membrane. Therefore, a thin suction solution diluted by the forward osmosis membrane treatment can be used in the pretreatment and can Reuse dilute suction solution. When the thin suction solution contains an organic bactericide, the backwash drainage of the turbidity removal device 116 and the RO permeated water of the reverse osmosis membrane treatment device 118 contain bactericidal active ingredients. When the dilute suction solution contains a chlorine-based bactericide or an oxidizing agent, the chlorine-based bactericide or oxidizing agent flows into the turbidity removal device 116 or the reverse osmosis membrane treatment device 118 and causes membrane degradation. When using the above-mentioned bactericide for forward osmosis membranes, the active bactericidal ingredients hardly penetrate the forward osmosis membrane, so such risks can be suppressed.

The dilute draw solution used in the forward osmosis membrane treatment step is transported to the pre-treatment device 114 through the dilute draw solution piping 26 and used in the pre-treatment step in the pre-treatment device 114. The FO concentrated water obtained by the forward osmosis membrane treatment step is discharged through the FO concentrated water piping 28. The FO concentrated water can be recovered and reused.

When the pretreatment device 114 includes a device for removing soluble silica, for example, a magnesium salt aqueous solution can be used as the suction solution in the forward osmosis membrane treatment device 14, and a dilute suction solution used in the forward osmosis membrane treatment device 14 can be used. (magnesium salt dilute aqueous solution) as the magnesium salt added to the pretreatment device 114.

When the pretreatment device 114 includes a device for removing hardness components by lime softening, for example, an alkaline aqueous solution can be used as the draw solution in the forward osmosis membrane treatment device 14, and the dilute draw solution (alkaline dilute aqueous solution) used in the forward osmosis membrane treatment device 14 can be used as the alkali added to the pretreatment device 114.

When the pretreatment device 114 includes a device for removing hardness components by a resin softening method, for example, an acid aqueous solution or a sodium chloride aqueous solution can be used as the suction solution in the forward osmosis membrane treatment device 14, and the forward osmosis membrane treatment device 14 The dilute suction solution (a dilute aqueous acid solution or a dilute sodium chloride aqueous solution) used can be used as a regeneration agent for the ion exchange resin in the pretreatment device 114 .

By using the water treatment method and water treatment device of this embodiment, water to be treated, for example, containing at least one of soluble silica and hardness components, can be treated at low cost.

Because the thin suction solution diluted by forward osmosis membrane treatment is used in the pretreatment step, the necessary cost of reusing the suction solution can be reduced and no regeneration equipment is required. Because the dilute suction solution is just the suction solution originally used in the dilution pre-treatment step, there is almost no additional cost.

The water to be treated by the water treatment method and the water treatment device of this embodiment is not particularly limited, but may be water containing at least one of soluble silica and hardness components, and may include, for example, industrial water, surface water, tap water, groundwater, seawater, desalinated water obtained by desalinating seawater by reverse osmosis or evaporation, and various types of wastewater such as wastewater discharged in semiconductor manufacturing processes.

When the water to be treated contains soluble silica, the concentration of soluble silica is in the range of, for example, 5 to 400 mg/L. When the water to be treated contains a hardness component, the concentration of the calcium hardness component is, for example, in the range of 5 to 600 mg/L. The pervaporation residue (TDS: Total Dissolved Solid) in the treated water is in the range of, for example, 100 to 50000 mg/L.

In the water treatment method and water treatment device of the present embodiment, when the treated water contains both soluble silica and hardness components, the pretreatment device (pretreatment step) may have both a soluble silica removal device (soluble silica removal step) and a hardness component removal device (hardness component removal step). The order of the soluble silica removal device (soluble silica removal step) and the hardness component removal device (hardness component removal step) may be the first soluble silica removal device (soluble silica removal step) and the second hardness component removal device (hardness component removal step), or the first hardness component removal device (hardness component removal step) and the second soluble silica removal device (soluble silica removal step).

At this time, at least one of a magnesium salt solution, an alkali aqueous solution, an acid aqueous solution, and a sodium chloride aqueous solution is used as the suction solution in the forward osmosis membrane treatment device 14 (forward osmosis membrane treatment step), and the forward osmosis membrane treatment device 14 Thin suction solutions (magnesium salt aqueous solution, alkaline aqueous solution, acid aqueous solution) used in At least one of aqueous solution and sodium chloride dilute aqueous solution) can be used in the soluble silica removal equipment (soluble silica removal step) and the hardness component removal equipment (hardness component) of the pretreatment device 114 (pretreatment step) Remove appropriate aspects from step).

The turbidity removal equipment may include, for example, a sand filter, a membrane filter such as an ultrafiltration (UF) membrane, a pressurized flotation device, etc. There is no particular restriction on the location of the turbidity removal equipment, such as the front section of the pre-treatment device 114 (pre-treatment step) or between the pre-treatment device 114 (pre-treatment step) and the reverse osmosis membrane treatment device 118 (reverse osmosis membrane treatment step).

The details of the pre-processing steps are as described above. In the removal of soluble silica and hardness components in the lime softening method, the pre-treated water obtained by solid-liquid separation can be transported to the reverse osmosis membrane treatment device 118 or transported to the reverse osmosis membrane treatment device through the turbidity removal device 116 118. In the hardness component removal by the resin softening method, the pre-treated water obtained by ion exchange treatment can be sent to the reverse osmosis membrane treatment device 118 or sent to the reverse osmosis membrane treatment device 118 through the turbidity removal device 116 .

A bactericide ("bactericide for forward osmosis membrane") containing a bromine-based oxidizing agent or a chlorine-based oxidizing agent and a sulfamic acid compound can be stored in the water treatment devices 1, 3, and 5 in Figures 1 to 3 as a concentration of the FO treated water. in water. For example, the bactericide for the forward osmosis membrane is added to the FO treated water (concentrated water) in the concentrated water pipe 20 through the bactericide addition pipe. It is also possible to set up a concentration tank for storing FO treated water (concentrated water) before the forward osmosis membrane treatment device 14, for example between the reverse osmosis membrane treatment device 12 and the forward osmosis membrane treatment device 14, and add positive water to the concentration tank. Permeable membranes with biocides.

[Reverse osmosis membrane treatment steps]

Polyamide-based polymer membranes, which have become mainstream recently, can be ideally used as reverse osmosis membranes used in reverse osmosis membrane treatment steps. Polyamide-based polymer membranes have relatively low resistance to oxidants. Therefore, when free chlorine, etc. are continuously contacted with the polyamide-based polymer membrane, the membrane performance is significantly reduced. However, by using the above-mentioned bactericide for forward osmosis membranes in the water treatment method of this embodiment, the bactericidal active ingredients hardly penetrate the forward osmosis membrane, so even the polyamide-based polymer membrane hardly produces such remarkable membrane performance. reduce.

Reverse osmosis membrane treatment can be used by connecting multiple reverse osmosis membrane treatments in series or in parallel. The concentrated water obtained by the first reverse osmosis membrane treatment can be further concentrated by the second and third reverse osmosis membrane treatments, or the permeate obtained by the first reverse osmosis membrane treatment can be subjected to another reverse osmosis membrane treatment to further improve the water quality.

The reverse osmosis membrane used in the reverse osmosis membrane treatment step includes ultra-low pressure reverse osmosis membrane and low pressure reverse osmosis membrane used for pure water production and wastewater recovery, as well as medium pressure reverse osmosis membrane and high pressure reverse osmosis membrane used for seawater desalination. Examples of ultra-low pressure reverse osmosis membrane and low pressure reverse osmosis membrane include ES15 (manufactured by Nitto Denko), TM720D (manufactured by TORAY), BW30HRLE (manufactured by Dow Chemical), and LFC3-LD (manufactured by Hydranautics). Examples of high pressure reverse osmosis membrane include SWC5-LD (manufactured by Hydranautics), TM820V (manufactured by TORAY), and XUS180808 (manufactured by Dow Chemical). When using multiple reverse osmosis membrane steps, different types of membranes can be selected based on the TDS, pH, water temperature and other conditions of the water being treated in each stage.

In the concentration treatment step, chemicals such as pH adjusters, scale dispersants that inhibit the scaling of inorganic salts in the system, and bactericides that inhibit the generation of microorganisms in the system can also be added.

<Bactericide for positive osmosis membrane>

The bactericide for positive osmosis membrane of this embodiment contains a bactericide of a stabilized hypobromous acid composition containing a mixture of a "bromine-based oxidant or a chlorine-based oxidant" and a "sulfonic acid compound" or a stabilized hypochlorous acid composition, and may further contain an alkali.

The positive osmotic membrane disinfectant of this embodiment contains a stabilized hypobromous acid composition comprising "a reaction product of a bromine-based oxidant and an amide sulfonic acid compound" or a stabilized hypochlorous acid composition comprising "a reaction product of a chlorine-based oxidant and an amide sulfonic acid compound", and may further contain an alkali.

The bromine-based oxidizing agent, bromine compound, chlorine-based oxidizing agent and sulfamic acid compound are as described above.

An example of a commercially available product of a stabilized hypochlorous acid composition containing a chlorine-based oxidizing agent and a sulfamic acid compound is "KURIVERTER IK-110" manufactured by Kurita Industrial Co., Ltd.

In order to prevent further deterioration of the forward osmosis membrane, the bactericide for the forward osmosis membrane in this embodiment is preferably one containing bromine and a sulfamic acid compound (a mixture containing a bromine and a sulfamic acid compound), for example, one containing a bromine and a sulfamic acid compound. , a mixture of alkali and water, or a reaction product of bromine and a sulfamic acid compound, such as a reaction product of bromine and a sulfamic acid compound, a mixture of alkali and water.

The disinfectant for positive osmosis membrane of this embodiment includes a disinfectant containing a stabilized hypobromous acid composition containing a bromine-based oxidant and an amine sulfonic acid compound, and in particular, a disinfectant containing a stabilized hypobromous acid composition containing bromine and an amine sulfonic acid compound. Compared with disinfectants containing chlorine-based oxidants and amine sulfonic acid compounds (chloramine sulfonic acid, etc.), although the oxidizing power is high and the sludge inhibition power and sludge stripping power are significantly high, it hardly causes significant membrane degradation like hypochlorous acid with the same high oxidizing power. At normal usage concentrations, the effect on membrane degradation can be substantially ignored. Therefore, it is most suitable as a disinfectant.

The bactericide for the forward osmosis membrane of this embodiment is different from bactericides such as hypochlorous acid in that it hardly permeates the forward osmosis membrane and therefore hardly affects the dilute suction solution. In addition, the concentration can be measured on site in the same way as hypochlorous acid, etc., so more accurate concentration management can be performed.

The pH of the positive osmotic membrane disinfectant is, for example, higher than 13.0, and preferably higher than 13.2. When the pH of the positive osmotic membrane disinfectant is lower than 13.0, the effective halogen in the positive osmotic membrane disinfectant will be unstable.

The concentration of bromic acid in the positive osmotic membrane disinfectant should be less than 5 mg/kg. When the concentration of bromic acid in the positive osmotic membrane disinfectant is above 5 mg/kg, the concentration of bromic acid ions in the dilute attracting solution will increase.

<Manufacturing method of disinfectant for positive osmosis membrane>

The bactericide for forward osmosis membranes in this embodiment is prepared by mixing a bromine-based oxidant or a chlorine-based oxidant and a sulfamic acid compound, and an alkali may be further mixed.

The method for manufacturing a bactericide for forward osmosis membranes containing a stabilized hypobromous acid composition containing bromine and a sulfamic acid compound preferably includes the following steps: adding bromine to a mixture containing water, an alkali and a sulfamic acid compound under an inert gas environment to react in a liquid, or add bromine to a solution containing water, alkali and amine under an inert gas environment. in a mixture of sulfonic acid compounds. By adding and reacting in an inert gas environment or adding in an inert gas environment, the bromate ion concentration in the forward osmosis membrane bactericide decreases, and therefore the bromate ion concentration in the dilute suction solution decreases.

There is no particular restriction on the inert gas used, but from the perspective of manufacturing and other aspects, it is preferably at least one of nitrogen and argon, and nitrogen is particularly preferred from the perspective of manufacturing cost.

The oxygen concentration in the reactor when adding bromine is preferably below 6%, but preferably below 4%, more preferably below 2%, and particularly preferably below 1%. When the oxygen concentration in the reactor exceeds 6% during the bromine reaction, the amount of bromic acid generated in the reaction system will increase.

The bromine addition rate relative to the total amount of the bactericide for the forward osmosis membrane is preferably 25% by weight or less, and more preferably 1% by weight or more and 20% by weight or less. When the bromine addition rate exceeds 25% by weight relative to the total amount of bactericide for forward osmosis membranes, the amount of bromic acid generated in the reaction system will increase. When the content is less than 1% by weight, the bactericidal effect will be poor.

The reaction temperature when adding bromine should be controlled within the range of 0°C to 25°C. However, from the perspective of manufacturing cost, it is better to control the reaction temperature to be within the range of 0°C to 15°C. When the reaction temperature when adding bromine exceeds 25°C, the amount of bromic acid generated in the reaction system will increase, and when it is lower than 0°C, it will freeze.

Example

Hereinafter, examples and comparative examples will be given to explain the present invention in more detail. However, the present invention is not limited to the following examples.

<Implementation Example 1>

Industrial water containing TDS 100ppm and dissolved silica 15ppm was concentrated using the water treatment device shown in Figure 1. The water was concentrated to TDS 8% using a reverse osmosis membrane treatment device. The concentrated water was supplied to a forward osmosis membrane treatment device (forward osmosis membrane: HP5230 (manufactured by Toyobo)), and then a 30 wt% magnesium chloride solution was supplied as an attracting solution to produce FO concentrated water with TDS 20%. The diluted magnesium chloride solution diluted by the forward osmosis membrane treatment was added intact to the dissolved silica removal device. The energy cost for the forward osmosis membrane treatment was calculated. The results are shown in Table 1.

<Comparative example 1>

In the water treatment device used in Example 1, an evaporator is used to replace the concentration operation of the forward osmosis membrane treatment device to produce concentrated water with TDS 20%. The energy cost used for the evaporator is calculated and compared with Example 1. The results are shown in Table 1.

<Comparative example 2>

In the water treatment device used in Example 1, a 30 wt% ammonium carbonate solution was used as the draw solution of the forward osmosis membrane treatment device, and concentrated water with a TDS of 20% was similarly produced. The dilute ammonium carbonate solution diluted by the forward osmosis membrane treatment was transported to the regeneration device and regenerated by heat (regeneration step). The energy cost for the forward osmosis membrane treatment (including the energy supplied to the regeneration step) was calculated. The results are shown in Table 1.

[Table 1]

In this way, it can be understood that through the processing method of Example 1, compared with the processing methods of Comparative Examples 1 and 2, it is possible to concentrate at a lower energy cost, and therefore it is possible to process at least one of the soluble silica and hardness components at a low cost. One of the treated water.

<Implementation Example 2>

Industrial water containing TDS 100 ppm and soluble silica 15 ppm was concentrated using the water treatment device shown in Figure 3. Concentrate to TDS8% through reverse osmosis membrane treatment device. This concentrated water was supplied to a forward osmosis membrane treatment device (forward osmosis membrane: HP5230 (Toyobo Co., Ltd.)), and then a 30% by weight magnesium chloride solution was supplied as a suction solution to prepare TDS20% FO concentrated water. A part of the dilute magnesium chloride solution diluted by forward osmosis membrane treatment is added to the soluble silica removal device as it is, and the remaining part is concentrated to 30% of magnesium chloride using the concentration device with the structure of Figure 6 and is used as normal Reuse of suction solution in permeable membrane treatment device. Calculate the energy cost for forward osmosis membrane treatment. The results are shown in Table 2.

<Comparative Example 3>

In the water treatment device used in Example 2, the evaporator is used to replace the concentration operation of the forward osmosis membrane treatment device to produce concentrated water with TDS 20%. The energy cost used for the evaporator is calculated and compared with Example 2. The results are shown in Table 2.

<Comparative Example 4>

In the water treatment device used in Example 2, a 30 wt% ammonium carbonate solution was used as the draw solution of the forward osmosis membrane treatment device, and concentrated water with a TDS of 20% was similarly produced. The dilute ammonium carbonate solution diluted by the forward osmosis membrane treatment was transported to the regeneration device and regenerated by heat (regeneration step). The energy cost for the forward osmosis membrane treatment (including the energy supplied to the regeneration step) was calculated. The results are shown in Table 2.

In this way, it can be understood that through the processing method of Example 2, compared with the processing methods of Comparative Examples 3 and 4, it is possible to concentrate at a lower energy cost, so that at least one of the soluble silica and hardness components can be processed at a low cost. One of the treated water.

[Preparation of stabilized hypobromous acid composition (composition 1)]

In a nitrogen environment, the following were mixed: 16.9 wt% liquid bromine, 10.7 wt% sulfamic acid, 12.9 wt% sodium hydroxide, 3.94 wt% potassium hydroxide, and the remainder of water to prepare a stabilized hypobromous acid composition (composition 1). The pH of the stabilized hypobromous acid composition was 14, and the total chlorine concentration was 7.5 wt%. The total chlorine concentration was measured by the total chlorine measurement method (DPD (diethyl-p-phenylenediamine) method) using a multi-item water quality analyzer DR/4000 from HACH (mg/L is equivalent to Cl ₂ ). The detailed preparation method of the stabilized hypobromous acid composition is as follows.

While controlling the flow rate of nitrogen by a mass flow controller to maintain the oxygen concentration in the reaction container at 1%, 1436 g of water and 361 g of sodium hydroxide were added and mixed into four 2 L flasks filled by continuous injection, and then 300 g of amine sulfonic acid was added and mixed. While cooling the reaction solution to keep the temperature at 0 to 15°C, 473 g of liquid bromine was added, and then 230 g of 48% potassium hydroxide solution was added to obtain the target stabilized hypobromous acid composition (composition 1) with a weight ratio of amine sulfonic acid 10.7%, bromine 16.9%, and a ratio of amine sulfonic acid equivalent to bromine equivalent of 1.04 based on the weight ratio of the total composition. The pH of the resulting solution was measured by a glass electrode method and was 14. The bromine content of the resulting solution was measured by converting bromine into iodine using potassium iodide and then using sodium thiosulfate redox titration. The result was 16.9%, which is 100.0% of the theoretical content (16.9%). In addition, the oxygen concentration in the reaction vessel during the bromine reaction was measured using "OXYGEN MONITOR JKO-02 LJDII" manufactured by JIKCO Co., Ltd. In addition, the bromic acid concentration was less than 5 mg/kg.

In addition, pH measurements were performed under the following conditions.

Electrode type: glass electrode type

pH meter: Made by DKK-TOA, model IOL-30

Electrode calibration: Performed by two-point calibration 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℃

Measurement value: Immerse the electrode in the measuring liquid, use the value after stabilization as the measurement value, and take the average value of 3 measurements.

[Preparation of stabilized hypochlorous acid composition (composition 2)]

Mix: 12% sodium hypochlorite aqueous solution: 50% by weight, sulfamic acid: 12% by weight, sodium hydroxide: 8% by weight, and water: the remainder to prepare a stabilized hypochlorous acid composition (composition 2). The pH of composition 2 was 13.7, and the total chlorine concentration was 6.2% by weight.

<Implementation Example 3>

Industrial wastewater concentrated to 8% by weight of pervaporation residue (TDS) was used as the FO treated water, and then a 30% by weight _MgCl2 solution was used as the suction solution to perform forward osmosis membrane treatment. Adjust the flow rate of the suction solution so that the flow rate at the FO concentrated water outlet is 50% of the FO treated water inlet (concentration rate is 2 times). A FO membrane made of cellulose acetate (HPC3205, produced by Toyobo) was used as a forward osmosis membrane (FO membrane). A stabilized hypobromous acid composition (composition 1) was added to the FO treated water as a bactericide for the forward osmosis membrane so that the total chlorine concentration at the FO treated water inlet was 1 ppmCl. This operation was continued for a total of 200 hours, and then the pressure loss (water flow pressure difference) from the FO treated water inlet to the FO concentrated water outlet of the forward osmosis membrane treatment device and the bactericide rejection rate were evaluated. In addition, the water pressure difference after the start of operation is 0.02MPa. The results are shown in Table 3.

Inhibition rate of fungicides [%] = (1-(Thin suction solution flow rate × dilute suction solution total chlorine concentration/FO treated water × FO treated water total chlorine concentration))

<Implementation Example 4>

The stabilized hypochlorous acid composition (composition 2; chloramine sulfonic acid) was added to the FO treated water instead of the stabilized hypobromous acid composition (composition 1) as a disinfectant for the forward osmosis membrane, so that the total chlorine concentration at the inlet of the FO treated water was 1ppmCl. The forward osmosis membrane treatment was carried out in the same manner as in Example 3. The results are shown in Table 3.

<Comparison Example 5>

Add sodium hypochlorite as a chlorine-based bactericide to replace the stabilized hypobromous acid composition (composition 1) as a bactericide for the forward osmosis membrane in the FO treated water, so that the free chlorine concentration at the FO treated water inlet is 1 ppmCl, except that Except for this, forward osmosis membrane treatment was carried out in the same manner as in Example 3. The results are shown in Table 3.

<Comparative Example 6>

Add a 5-chloro-2-methyl-4-isothiazolin-3-one-substituted stabilized hypobromous acid composition (composition 1) as an organic bactericide to the FO treated water as a bactericide for forward osmosis membranes , except that the TOC at the FO to be treated water inlet was 10 ppm, forward osmosis membrane treatment was performed in the same manner as in Example 3. The results are shown in Table 3. Except for this, forward osmosis membrane treatment was performed in the same manner as in Example 3. The results are shown in Table 3.

[result]

In Example 3, the increase in the water flow pressure difference of the forward osmosis membrane can be suppressed. Fungicides also prevent more than 99%. In Example 4, the same tendency was observed, but the water flow pressure difference increased slightly. In Comparative Examples 5 and 6, through The water pressure difference is >0.2MPa and exceeds the allowable water pressure difference of the membrane (0.2MPa). The bactericide prevention rate was also less than 85%, and it was confirmed that the bactericidal active ingredient leaked into the dilute suction solution.

Thus, it can be understood that by using a stabilized hypobromous acid composition or a stabilized hypochlorous acid composition as a bactericide, the bactericide can be inhibited from passing through the positive osmosis membrane and the dilute attracting solution can be reused.

Claims (16)

A water treatment device for treating water containing at least one of soluble silica and hardness components, comprising: a pre-treatment device, including any one of a soluble silica removal device and a hardness component removal device; a concentration treatment device, which performs concentration treatment on the pre-treated water obtained by the pre-treatment device; and a forward osmosis membrane treatment device, which performs forward osmosis membrane treatment on the concentrated water obtained by the concentration treatment device, wherein the pre-treatment device uses a dilute suction solution used in the forward osmosis membrane treatment device. As in claim 1, the water treatment device, wherein the concentration treatment equipment is a reverse osmosis membrane treatment equipment. A water treatment device that treats water to be treated containing at least one of soluble silica and hardness components, and has: a pre-treatment device, which has a soluble silica removal device and a hardness component removal device. Either one; the first concentration treatment equipment, which concentrates the pre-treated water produced by the pre-treatment equipment; the forward osmosis membrane treatment equipment, which subjects the concentrated water produced by the first concentration treatment equipment to normal treatment. Osmosis membrane treatment; and a second concentration treatment equipment, which concentrates a part of the thin suction solution used in the forward osmosis membrane treatment equipment, and the pretreatment equipment uses the solution used in the forward osmosis membrane treatment equipment. A part of the dilute suction solution, and the concentrated suction solution concentrated by the second concentration treatment equipment is used again as the suction solution in the forward osmosis membrane treatment equipment. As in claim 3, the water treatment device, wherein the second concentration treatment equipment is a concentration treatment equipment using a semipermeable membrane. A water treatment device as claimed in claim 3 or 4, wherein the first concentration treatment equipment is a reverse osmosis membrane treatment equipment. The water treatment device of any one of claims 1 to 4, wherein the suction solution used in the forward osmosis membrane treatment equipment is a magnesium salt solution, and the forward osmosis membrane treatment equipment is used in the soluble silica removal equipment A dilute aqueous solution of magnesium salt used in. A water treatment device as claimed in any one of claims 1 to 4, wherein the attracting solution used in the forward osmosis membrane treatment device is an alkaline aqueous solution, and the hardness component removal device uses a dilute alkaline aqueous solution used in the forward osmosis membrane treatment device. The water treatment device of any one of claims 1 to 4, wherein the suction solution used in the forward osmosis membrane treatment equipment is an acid aqueous solution or a sodium chloride aqueous solution, and the hardness component removal equipment uses the forward osmosis membrane treatment A dilute aqueous solution of acid or a dilute aqueous solution of sodium chloride used in the equipment. A water treatment method for treating water to be treated that contains at least one of soluble silica and hardness components comprises the following steps: a pre-treatment step, comprising either a soluble silica removal step or a hardness component removal step; a concentration treatment step, subjecting the pre-treated water obtained by the pre-treatment step to a concentration treatment; and a forward osmosis membrane treatment step, subjecting the concentrated water obtained by the concentration treatment step to a forward osmosis membrane treatment, wherein the dilute attracting solution used in the forward osmosis membrane treatment step is used in the pre-treatment step. The water treatment method of claim 9, wherein the concentration treatment step is a reverse osmosis membrane treatment step. A water treatment method that treats water to be treated containing at least one of soluble silica and hardness components, and includes the following steps: a pre-treatment step, including a soluble silica removal step and a hardness component removal step. Any one of them; the first concentration treatment step is to subject the pre-treated water obtained through the pre-treatment step to concentration treatment; the forward osmosis membrane treatment step is to subject the concentrated water obtained through the first concentration treatment step to Treat with forward osmosis membrane; and a second concentration treatment step, subject a part of the dilute suction solution used in the forward osmosis membrane treatment step to concentration treatment, and use the forward osmosis membrane treatment step in the pre-treatment step A part of the dilute suction solution used, and the concentrated suction solution concentrated by the second concentration treatment step is reused as the suction solution in the forward osmosis membrane treatment step. As in claim 11, the water treatment method, wherein the second concentration treatment step is a concentration treatment step using a semipermeable membrane. The water treatment method of claim 11 or 12, wherein the first concentration treatment step is a reverse osmosis membrane treatment step. The water treatment method according to any one of claims 9 to 12, wherein the suction solution used in the forward osmosis membrane treatment step is a magnesium salt solution, and the forward osmosis membrane treatment is used in the soluble silica removal step The dilute aqueous solution of magnesium salt used in this step. A water treatment method as claimed in any one of claims 9 to 12, wherein the attracting solution used in the forward osmosis membrane treatment step is an alkaline aqueous solution, and the alkaline dilute aqueous solution used in the forward osmosis membrane treatment step is used in the hardness component removal step. The water treatment method according to any one of claims 9 to 12, wherein the suction solution used in the forward osmosis membrane treatment step is an acid aqueous solution or a sodium chloride aqueous solution, and the forward osmosis membrane is used in the hardness component removal step. A dilute aqueous acid solution or a dilute aqueous sodium chloride solution used in the treatment step.