TWI848823B - 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 containing at least one of soluble silica and a hardness component. 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 wastewater discharge on the environment, it is discharged and disposed of after being treated with wastewater purification and volume reduction. Drainage treatment uses solid-liquid separation, membrane separation, and pressure reduction concentration, but the hardness components such as soluble silica and calcium contained in the wastewater do not dissolve and adhere to the pipes and devices used for wastewater treatment, causing so-called scaling, so it is known that the performance of the system is reduced. In order to carry out efficient wastewater treatment, it is necessary to remove the soluble silica and hardness components in the wastewater.

For example, Patent Document 1 describes a method for recovering fresh water from wastewater by adding magnesium salt to wastewater containing soluble silica under alkaline conditions to insolubilize the soluble silica, separating the solid from the liquid, and then treating the wastewater with reverse osmosis membrane or forward osmosis membrane to obtain treated water.

The forward osmosis membrane treatment allows the supply water and the draw solution to exist through the forward osmosis membrane, so that even when there is no pressure, the water can be moved to the draw solution by osmotic pressure. Then, the diluted draw solution is phase-changed by means such as heating, so that fresh water can be obtained while the draw solution can be reused.

The attracting solution for the forward osmosis membrane treatment may be an aqueous solution of ammonium carbonate, a mixture of an inorganic salt and a temperature-sensitive agent, etc. (see 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 FIG. 10 ), thereby increasing the cost of the entire system.

Patent document 3 describes a method of removing hardness components by adding an alkali to wastewater containing hardness components to cause precipitation (so-called lime softening method), coagulating, filtering, and then treating the filtered water with a reverse osmosis membrane. 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 must be added, and in the resin softening method, in order to regenerate the ion exchange resin that adsorbs the hardness component, a high-concentration salt water (sodium chloride aqueous solution) must be passed through, so it is necessary to reduce the cost of chemicals.

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 disinfectants (chlorine disinfectants, oxidants, organic disinfectants) can pass through the forward osmosis membrane, the disinfectant components are not sufficiently diffused to the outlet side of the forward osmosis membrane treatment device, so the forward osmosis membrane cannot be fully sterilized. In addition, organic disinfectants have a particular impact on organisms, the environment, etc. In particular, when the produced water is separated from the dilute suction solution by heating and other treatments and then used, if the produced water contains organic disinfectants, it will significantly limit the applicability for industrial use, food use, drinking use, etc. In addition, in order to discharge part or all of the dilute draw solution containing the bactericidal agent that has passed through the forward osmosis membrane to the outside of the system, part or all of the dilute draw solution must be removed. In addition, chlorine-based bactericidal agents and oxidants reduce the performance of forward osmosis membranes, especially polyamide reverse osmosis membranes. Therefore, when part or all of the dilute draw solution is reprocessed through the reverse osmosis membrane, there is a risk that the bactericidal agent will reduce the performance of the reverse osmosis membrane. [Prior art literature] [Patent literature]

Patent document 1: International Patent Application Publication No. 2013/153587 Patent document 2: Japanese Patent Publication No. 2017-056424 Patent document 3: Japanese Patent Publication No. 2017-170275 Patent document 4: Japanese Patent Publication No. 2014-231039 Patent document 5: Japanese Patent Publication No. 2015-188787 Patent document 6: Japanese Patent Publication No. 2018-015684

[The problem the invention is trying to solve]

The object of the present invention is to provide a water treatment device and a water treatment method which can treat water to be treated containing at least one of soluble silica and a hardness component at a 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. [Technical means for solving the problem]

The present invention is a water treatment device, which treats water to be treated containing at least one of soluble silica and hardness components, and comprises: a pre-treatment device, which has either a soluble silica removal device or a hardness component removal device; a concentration treatment device, which concentrates the pre-treated water obtained by the pre-treatment device; and a forward osmosis membrane treatment device, which uses the concentrated water obtained by the concentration treatment device through forward osmosis membrane treatment, and the pre-treatment device uses the dilute suction solution used in the forward osmosis membrane treatment device.

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

The present invention is a water treatment device, which treats water to be treated containing at least one of soluble silica and hardness components, and comprises: a pre-treatment device, which has either a soluble silica removal device or a hardness component removal device; a first concentration treatment device, which concentrates the pre-treated water obtained by the pre-treatment device; a forward osmosis membrane treatment device, which forward osmosis membrane treatment is performed by the pre-treatment device; The concentrated water produced by the first concentration treatment device; and the second concentration treatment device, which concentrates a part of the dilute attracting solution used in the aforementioned forward osmosis membrane treatment device, uses a part of the dilute attracting solution used in the aforementioned forward osmosis membrane treatment device in the aforementioned pre-treatment device, and reuses the concentrated attracting solution concentrated by the aforementioned second concentration treatment device as the attracting solution in the aforementioned forward osmosis membrane treatment device.

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

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

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

Preferably, the water treatment apparatus further comprises a preparation device for mixing magnesium hydroxide and an acid and reacting them at a pH of less than 7 to prepare an aqueous magnesium salt solution for use as a draw solution in the forward osmosis membrane treatment device.

Preferably, in the water treatment apparatus, the draw 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.

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

In addition, the present invention is a water treatment method, which treats water to be treated that contains at least one of soluble silica and a hardness component, and includes the following steps: a pre-treatment step, which includes any one of a soluble silica removal step and a hardness component removal step; a concentration treatment step, which concentrates the pre-treated water obtained by the aforementioned pre-treatment step; and a forward osmosis membrane treatment step, which treats the concentrated water obtained by the aforementioned concentration treatment step by forward osmosis membrane, and uses the dilute attracting solution used in the aforementioned forward osmosis membrane treatment step in the aforementioned pre-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 obtained by the concentration treatment in the pre-treatment step; a positive osmosis membrane treatment step, in which the pre-treated water is obtained by the positive osmosis membrane treatment in the pre-treatment step; The concentrated water obtained in the first concentration treatment step; and a second concentration treatment step, concentrating a portion of the dilute attracting solution used in the forward osmosis membrane treatment step, using a portion of the dilute attracting solution used in the forward osmosis membrane treatment step in the pre-treatment step, and reusing the concentrated attracting solution concentrated by the second concentration treatment step as the attracting solution in the forward osmosis membrane treatment step.

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

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

Preferably, in the water treatment method, the draw 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.

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

The present invention is a forward osmosis membrane treatment method, which includes: a forward osmosis membrane treatment step of making the treated water contact with a draw solution with a higher concentration than the treated water through a forward osmosis membrane to obtain concentrated water and a dilute draw solution, and a bactericide containing a bromine-based oxidant or a chlorine-based oxidant and a sulfonylamine compound is allowed to exist in the treated water.

The present invention is a forward osmosis membrane treatment method, which includes: a forward osmosis membrane treatment step of making the treated water contact with a draw solution with a higher concentration than the treated water through a forward osmosis membrane to obtain concentrated water and a dilute draw solution, and a bactericide containing a bromine oxidant and a sulfonylamine compound is allowed to exist in the treated water.

The present invention is a forward osmosis membrane treatment method, which includes: a forward osmosis membrane treatment step of making the treated water contact with a draw solution with a higher concentration than the treated water through a forward osmosis membrane to obtain concentrated water and a dilute draw solution, and allowing a bactericide containing bromine and sulfonylamine compounds to exist in the treated water.

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

The present invention is a forward osmosis membrane treatment system, which has: a forward osmosis membrane treatment device that produces concentrated water and a dilute attracting solution by bringing the water to be treated into contact with an attracting solution having a higher concentration than the water to be treated through a forward osmosis membrane, and a bactericide containing a bromine-based oxidant or a chlorine-based oxidant and a sulfonylamine compound is present in the water to be treated.

The present invention is a forward osmosis membrane treatment system, which has: a forward osmosis membrane treatment device that makes the treated water contact with a draw solution with a higher concentration than the treated water through a forward osmosis membrane to produce concentrated water and a dilute draw solution, and a bactericide containing a bromine oxidant and a sulfonylamine compound is present in the treated water.

The present invention is a forward osmosis membrane treatment system, which has: a forward osmosis membrane treatment device that makes the treated water contact with a draw solution with a higher concentration than the treated water through a forward osmosis membrane to produce concentrated water and a dilute draw solution, and a bactericide containing bromine and sulfonylamine compounds is present in the treated water.

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. [Effect of the invention]

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

Furthermore, the present invention can 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 that can reuse a dilute draw 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 following describes an embodiment of the present invention. This embodiment is an example of the present invention, and the present invention is not limited to this embodiment.

FIG. 1 schematically shows an example of a water treatment device according to an embodiment of the present invention, and explains its structure.

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 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 water treatment method and the operation of the water treatment device 1 according to this embodiment are described below.

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

When the treated water contains soluble silica, the pre-treatment device 10 has: a magnesium reaction device, which adds a 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, a 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 pipeline 18.

When the treated water contains hardness components and the hardness components are removed by lime softening, the pre-treatment device 10 has, for example, an alkali reaction device, which adds alkali to the treated water to make it react and insolubilize the hardness components; a coagulation treatment device, which adds a coagulant to the treated water after the reaction as needed to make it coagulate; and a solid-liquid separation device, which separates the coagulant from the treated water after the coagulation treatment. In the pre-treatment device 10, for example, an alkali is added to the treated water to make the hardness components insoluble (alkali reaction step). Then, a coagulant is added 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 pipeline 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 that performs 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, 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.

The concentrated water obtained by the reverse osmosis membrane treatment is treated by the forward osmosis membrane in the forward osmosis membrane treatment device 14 (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 pipe 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.

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 used in the pre-treatment step in the pre-treatment device 10. Then, the FO concentrated water produced 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 10 includes a device for removing soluble silica, for example, a magnesium salt aqueous solution can be used as the draw solution in the forward osmosis membrane treatment device 14, and the dilute draw solution (dilute magnesium salt aqueous solution) used in the forward osmosis membrane treatment device 14 can be used as the magnesium salt added to the pretreatment device 10.

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

By using the water treatment method and the water treatment apparatus of the present embodiment, water to be treated containing at least one of soluble silica and a hardness component can be treated at low cost.

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

FIG. 3 schematically shows another water treatment device example according to an embodiment of the present invention, and explains its structure.

The water treatment device 5 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 first concentration treatment device for concentrating the previously treated water obtained by the pre-treatment device 10; 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; and a concentration device 34, which is a second concentration treatment device for concentrating a part of the dilute suction solution used by the forward osmosis membrane treatment device 14.

In the water treatment device 5 of FIG. 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-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 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 dilute suction solution piping 36 branched from the dilute suction solution piping 26 is connected to the inlet of the concentrator 34, and the concentrated suction solution outlet of the concentrator 34 is connected to the middle of the suction solution piping 24 by the concentrated suction solution piping 38. The dilute solution piping 40 is connected to the dilute solution outlet of the concentrator 34.

The water treatment method and the operation of the water treatment device 5 according to this embodiment will be described below.

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

When the treated water contains soluble silica, the pre-treatment device 10 has, for example, a magnesium reaction device, which adds a 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, a magnesium salt is added to the treated water under, for example, 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 pipeline 18.

When the treated water contains hardness components and the hardness components are removed by lime softening, the pre-treatment device 10 has, for example, an alkali reaction device, which adds alkali to the treated water to make it react and insolubilize the hardness components; a coagulation treatment device, which adds a coagulant to the treated water after the reaction as needed to make it coagulate; and a solid-liquid separation device, which separates the coagulant from the treated water after the coagulation treatment. In the pre-treatment device 10, for example, an alkali is added to the treated water to make the hardness components insoluble (alkali reaction step). Then, a coagulant is added 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 pipeline 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 that performs 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, the pre-treated water (first concentration treatment step) is obtained by concentration treatment in the reverse osmosis membrane treatment device 12 through the pre-treatment step. The concentrated water (RO concentrated water) obtained 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.

The concentrated water obtained by the first concentration treatment (reverse osmosis membrane treatment) is treated by the forward osmosis membrane in the forward osmosis membrane treatment device 14 (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 pipe 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 pipe 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 pipe 28. The FO concentrated water can also be further concentrated and solidified by a concentration device and a crystallization device as needed.

A portion of the dilute draw solution used in the forward osmosis membrane treatment step is branched from the dilute draw solution pipe 26 and transported to the concentration device 34 through the dilute draw solution pipe 36, and then concentrated in the concentration device 34 (second concentration step). The concentrated draw solution obtained by the second concentration treatment is supplied to the middle of the draw solution pipe 24 through the concentrated draw solution pipe 38, and then reused as the draw solution in the forward osmosis membrane treatment device 14. The dilute solution obtained by the second concentration treatment is discharged through the dilute solution 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 pre-treatment device 10 includes a device for removing soluble silica, for example, a magnesium salt aqueous solution can be used as the draw solution in the forward osmosis membrane treatment device 14, and a portion of the dilute draw solution (dilute magnesium salt aqueous solution) used in the forward osmosis membrane treatment device 14 can be used as the magnesium salt added to the pre-treatment device 10. In addition, a portion of the dilute draw solution (dilute magnesium salt 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 lime softening, for example, an alkaline aqueous solution 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 the water treatment apparatus of the present embodiment, water to be treated containing at least one of soluble silica and a hardness component can be treated at low cost.

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

When the amount of dilute attracting solution diluted by the forward osmosis membrane treatment is larger 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 by 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. Examples thereof include 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 during 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 apparatus of the present embodiment, when the water to be treated contains both soluble silica and hardness components, the pretreatment device (pretreatment step) may include 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 soluble silica removal device (soluble silica removal step) first and the hardness component removal device (hardness component removal step) second, or the hardness component removal device (hardness component removal step) first and the soluble silica removal device (soluble silica removal step) second.

At this time, at least one of a magnesium salt aqueous solution, an alkali aqueous solution, an acid aqueous solution and a sodium chloride aqueous solution is used as the draw solution in the forward osmosis membrane treatment device 14 (forward osmosis membrane treatment step), and the dilute draw solution (at least one of a dilute magnesium salt aqueous solution, a dilute alkali aqueous solution, a dilute acid aqueous solution and a dilute sodium chloride aqueous solution) used in the forward osmosis membrane treatment device 14 can be used in a suitable aspect of the soluble silica removal device (soluble silica removal step) and the hardness component removal device (hardness component removal step) of the pre-treatment device 10 (pre-treatment 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 the front section 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).

[Pre-treatment step: Removal of dissolved silica] In the pre-treatment step when the treated water contains dissolved silica, magnesium salt is added to the treated water under alkaline conditions, for example, to insolubilize the dissolved 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 pH 10.5 to 11.5, and more preferably in the range of pH 11 to 11.5. When the pH in the magnesium reaction step is less than 10 or exceeds 12, the silicon dioxide removal rate will decrease.

The pH adjuster may be a base such as sodium hydroxide or calcium hydroxide, or an inorganic acid such as hydrochloric acid or sulfuric acid as needed.

The temperature in the magnesium reaction step is not particularly limited as long as it is a 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 preferably in the range of 10°C to less than 50°C. When the temperature in the magnesium reaction step is less than 1°C, the insolubilization reaction of silicon dioxide will not be sufficient, and when it is above 50°C, the processing 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 more 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 is preferably in the range of 0.1 to 10 times the weight concentration of silicon dioxide in the treated water, and more preferably in the range of 0.5 to 5 times. When the amount of magnesium salt added is less than 0.1 times the weight concentration of silicon dioxide in the treated water, 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, and iron salts such as ferric chloride and ferric sulfate can also be used. From the perspective of silica removal rate, magnesium salts are preferred.

The coagulation treatment step is, for example, adding an inorganic coagulant to the treated water after the magnesium reaction in a coagulation tank to coagulate the insoluble matter (coagulation step). Then, in a flocculant forming tank, a polymer coagulant is added to form floccules (flocculant forming step).

Examples of the inorganic coagulant used in the coagulation step include iron-based inorganic coagulants such as ferric chloride and aluminum-based inorganic coagulants such as polyaluminium chloride (PAC). In terms of drug cost and coagulation pH range, iron-based inorganic coagulants are preferred.

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

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

The polymer coagulants used in the flocculant formation step include, for example, cationic polymer coagulants such as polyacrylamide and polyacrylate, anionic polymer coagulants, and nonionic polymer coagulants. In terms of coagulation properties, anionic polymer coagulants are preferred.

Examples of commercially available high molecular weight coagulants include cationic high molecular weight coagulants 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 occurs. In addition, when the pH in the flocculant formation step is less than 9, silicon dioxide is dissolved from the flocculants. Therefore, the flocculant formation step is preferably performed in the range of pH 9 to 11.

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

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

The solid-liquid separation step is to separate the flocculated aggregates in a sedimentation tank (solid-liquid separation step). The treated water obtained by the solid-liquid separation is then transported to the reverse osmosis membrane treatment device 12. On the other hand, the sludge is discharged through the sludge pipe. The sludge can be recovered and reused.

In the solid-liquid separation step, in addition to separation by natural sedimentation, solid-liquid separation can be performed by pressure flotation treatment, membrane filtration treatment, etc., and in terms of separation properties, sedimentation separation is better.

[Pre-treatment step: Removal of hardness components by lime softening] 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 manual, 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).

Alkaline agents used include, 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 can be, for example, in the range of pH 9 to 13, and preferably in the range of pH 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 increases.

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 is carried out, but it can be, for example, in the range of 1°C to 80°C. If the temperature in the alkali reaction step is less than 1°C, the insolubilization reaction of the hardness component will not be sufficient, and if it exceeds 80°C, the heat resistance temperature of the equipment will be problematic.

The reaction time in the alkali reaction step is not particularly limited as long as the insolubilization reaction of the hardness component can be carried out, but it can be, for example, in the range of 10 minutes to 30 minutes. 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, which will increase the equipment cost.

The amount of alkali added is preferably in the range of 1.0 to 2.0 times the molar concentration of the hardness components in the treated water, and more 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 pre-treated water obtained by solid-liquid separation is transported to the reverse osmosis membrane treatment device 12.

[Pre-treatment step: Removal of hardness components by resin softening method] In the pre-treatment step of the resin softening method when the treated water contains hardness components, for example, the treated water is passed through an ion exchange tower filled with ion exchange resin to remove the hardness components by adsorption (ion exchange step). Then, the treated water obtained by ion exchange treatment is transported 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 and IRC-76 (produced by ORGANO Co., Ltd.).

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

The regeneration agent used may be, for example, an acid aqueous solution of hydrochloric acid, sulfuric acid, nitric acid, etc.; an aqueous sodium chloride solution; an aqueous potassium chloride solution, etc., and more than one of them may be used. That is, after regeneration with an acid aqueous solution, additional regeneration with an aqueous sodium chloride solution may be performed as needed. From the viewpoint of the reuse of the attracting solution, an acid aqueous solution and an aqueous sodium chloride solution are preferred. If regenerated with an acid aqueous solution, the ion exchange resin becomes an H form, and if regenerated with an aqueous sodium chloride solution, the ion exchange resin becomes a 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, but in addition to the reverse osmosis membrane treatment device, one or more of the following devices may be used: a membrane filtration device using a nanofiltration membrane, a distillation device, an electrodialysis device, etc. That is, the concentrated water obtained by the reverse osmosis membrane treatment device can be further concentrated by electrodialysis treatment as needed, or the concentrated water obtained by the first reverse osmosis treatment can be further concentrated by the second reverse osmosis treatment. From the perspective of being able to efficiently treat water when the TDS in the pre-treated water is low, the reverse osmosis membrane treatment device is better.

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 for inhibiting scaling of inorganic salts in the system, and a bactericide for inhibiting the generation of microorganisms in the system may also be added.

[Forward osmosis membrane treatment step] The shape of the forward osmosis membrane used in the forward osmosis membrane treatment step is not particularly limited, but for example, hollow yarn membrane, spiral membrane, tubular membrane, plate-bottom frame structure membrane, 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 section or in a plurality of sections 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 stages of forward osmosis membrane treatment are performed in the forward osmosis membrane treatment step, the above-mentioned draw solutions may 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 may be used as a regeneration solution for the softening resin, and a dilute magnesium salt aqueous solution obtained by the second forward osmosis membrane treatment step may be used as a magnesium source for the soluble silica removal step.

[Second concentration treatment step] The second concentration treatment equipment is not particularly limited as long as it can concentrate the dilute absorption solution used in the forward osmosis membrane treatment step, but can be: 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., or 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 a water treatment device according to this embodiment.

The concentration device 340 shown in FIG4 is an example of a pressure-assisted reverse osmosis membrane treatment device. The concentration device 340 is a device having two or more concentration devices that use semipermeable membranes to concentrate the treatment target water, and the above-mentioned dilute suction solution is supplied to the primary side of the first semipermeable membrane and the dilute solution is supplied to the secondary side, and a concentrated solution is obtained from another flow path of the primary side and a diluted solution is obtained from another flow path of the secondary side, and then the diluted solution is supplied to the primary side of the secondary semipermeable membrane, and the primary side of each semipermeable membrane is pressurized so that the water contained in the primary side passes through the secondary side, and a concentrated solution and a diluted solution are obtained in sequence.

The concentrating device 340 includes, for example, a first semipermeable membrane treatment device 42, a second semipermeable membrane treatment device 44, and a third 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, respectively.

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 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., MgCl ₂ : 3 mass %) produced 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 produce a second concentrated liquid (e.g., MgCl ₂ : 10 mass %) and a second dilution liquid (e.g., 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 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., MgCl ₂ : 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., MgCl ₂ : 3 mass %) and a third dilution liquid (e.g., MgCl ₂ : <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. A portion of the second concentrated solution and the third concentrated solution can be reused as the suction solution in the forward osmosis membrane treatment device 14. The third diluted solution 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 draw solution prepared from the above-mentioned dilute draw solution can be reused as the draw solution in the forward osmosis membrane treatment device 14.

In the concentration device 340 shown in Fig. 4, the liquid passed to the secondary side 50 of the first semipermeable membrane treatment device 42 and the second and subsequent semipermeable membrane treatment devices may be a liquid of different composition from the dilute draw solution passed to the primary side 48 of the first semipermeable membrane treatment device 42. Fig. 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 (for example, NaCl: 3 mass%) produced 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 produce a second concentrated liquid (for example, glucose: 20 mass%) and a second dilution liquid (for example, 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 being subjected to 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 reducing the influence of the diffusion of components from the primary side to the secondary side, it is preferable 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 concentrator 34 in the water treatment device 5 of this embodiment.

The concentration device 344 shown in FIG6 is an example of a pressure-assisted reverse osmosis membrane treatment device. The concentration device 344 is a device having one or more concentration devices for concentrating the treatment target water using a semipermeable membrane and further concentrating the concentrated liquid using the semipermeable membrane, and supplying the aforementioned dilute draw solution to the primary side of the first semipermeable membrane, then supplying the concentrated liquid to the primary side of each semipermeable membrane in sequence, and supplying a portion of the aforementioned dilute draw solution or a portion of any concentrated liquid to the secondary side of each semipermeable membrane, and pressurizing the primary side of each semipermeable membrane to allow the water contained in the primary side to pass through the secondary side.

The concentrating device 344 includes, 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, 102 may have: a pump for pressurizing and sending liquid; a pressure regulating 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) (e.g., MgCl ₂ : 18 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 diluted liquid (secondary side treated water) (e.g., MgCl ₂ : 15 mass %) sent back from the third stage semipermeable membrane treatment device 82 of the final stage described later passes through the pipe 100 and is then transported to the secondary side 86 of the second stage semipermeable membrane treatment 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) (e.g., MgCl ₂ : 23 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 liquid (e.g., MgCl ₂ : 30 mass%) returned from the third stage semipermeable membrane treatment device 82 of the final stage described later passes through the pipe 98 and is then transported to the secondary side 86 of the third stage semipermeable membrane treatment device 82. 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 portion of the concentrated liquid (primary side treated water) (e.g., MgCl ₂ : 30 mass %) of the final stage third-stage semipermeable membrane treatment device 82 is discharged through the pipe 96 and reused as the draw solution in the forward osmosis membrane treatment device 14. The remaining portion of the concentrated liquid of the third-stage semipermeable membrane treatment device 82 passes through the 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 to allow the water contained in the primary side 84 to pass 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, there is no need to prepare a diluent separately. Therefore, 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 draw solution used in the forward osmosis membrane treatment device 14 or a portion of any concentrated solution can be supplied to the secondary side of each semipermeable membrane, and the method is not particularly limited.

For example, as shown in the concentration device 346 of Figure 7, the dilute draw solution used in the forward osmosis membrane treatment device 14 as the treated water can be distributed and supplied to the primary side 84 and the secondary side 86 of the first semipermeable membrane treatment device 78, respectively. Then, the concentrated liquid and the permeate are supplied to the primary side 84 and the secondary side 86 of each section of the semipermeable membrane in sequence, respectively. Then, the primary side of each section of the 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 348 of Figure 8, 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 supplied to the primary side of each semipermeable membrane in sequence, and then a portion of the concentrated liquid of the third semipermeable membrane treatment device 82 of the final stage is supplied to the secondary side 86 of the first semipermeable membrane treatment device 78 and the permeate is supplied to the secondary side of each semipermeable membrane in sequence, 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 Figure 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 liquid can be supplied to the primary side of each semipermeable membrane in sequence, and then a portion of the concentrated liquid 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-mentioned concentrating devices 340, 342, 344, 346, 348, 350, the number of stages of the semipermeable membrane treatment device can be determined according to the desired concentration of the treated water, etc. For example, in the concentrating devices 344, 346, 348, 350, when it is desired to produce a more concentrated treated water (concentrated attracting solution) from a more dilute attracting solution, the number of stages of the semipermeable membrane treatment device can be increased.

In the above-mentioned concentrating devices 340, 342, 344, 346, 348, 350, a membrane module unit having two or more membrane modules connected in parallel can be used as the semipermeable membrane treatment device of each stage. 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.

The semipermeable membrane of the semipermeable membrane treatment device may be, for example, a reverse osmosis membrane (RO membrane), a forward osmosis membrane (FO membrane), a nanofiltration membrane (NF membrane), etc. The semipermeable membrane is preferably a reverse osmosis membrane, a forward osmosis membrane, or a nanofiltration membrane. In addition, when a reverse osmosis membrane, a forward osmosis membrane, or a nanofiltration membrane is used as the semipermeable membrane, the pressure of the target solution on the primary side is preferably 0.5 to 10.0 MPa.

The material constituting the semipermeable membrane is not particularly limited, but examples thereof include cellulose resins such as cellulose acetate resins, polysulfide resins such as polyethersulfide resins, and polyamide resins. Preferably, the material constituting the semipermeable membrane is cellulose acetate resin.

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

[Another example of water treatment device] The schematic structure of another example of water treatment device of the present invention is shown in FIG2. The water treatment device 3 shown in FIG2 further has an attracting solution preparation tank 30 as a preparation device for mixing magnesium hydroxide and an 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 draw solution preparation tank 30 and the draw solution inlet of the forward osmosis membrane treatment device 14 are connected via a draw solution pipe 32 .

The same steps as those of the water treatment device 1 of FIG. 1 are 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 by the pre-treatment step.

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

The concentrated water obtained by the reverse osmosis membrane treatment is treated by the forward osmosis membrane in the forward osmosis membrane treatment device 14 (forward osmosis membrane treatment step). In the forward osmosis membrane treatment device 14, the draw solution prepared by the draw solution preparation tank 30 is transported to the secondary side of the forward osmosis membrane through the draw solution pipe 32, and then the concentrated water and the draw solution are present through the forward osmosis membrane, thereby causing the water to move to the draw solution by osmotic pressure.

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 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 , similarly to the water treatment device 3 of FIG. 2 , a draw solution preparation tank may be further provided as a preparation device for preparing a magnesium salt aqueous solution used as a draw solution by mixing magnesium hydroxide and an acid and reacting them at a pH of less than 7. In the draw solution preparation tank, magnesium hydroxide and an acid are mixed and reacted at a pH of less than 7 to prepare a magnesium salt aqueous solution (preparation step), and the prepared magnesium salt aqueous solution may be transported to the secondary side of the forward osmosis membrane treatment device 14 and used as a draw solution.

The acid used in the preparation step may be, for example, hydrochloric acid, sulfuric acid, nitric acid, etc., and hydrochloric acid or nitric acid is preferred from the viewpoint of inhibiting the formation of poorly soluble substances.

The pH in the preparation step is not particularly limited as long as it is below 7, but may be, for example, in the range of pH 1 to 7, and preferably in the range of pH 2 to 5. When the pH in the preparation step exceeds 7, the magnesium salt will not be sufficiently dissolved, and when it is less than 1, the amount of acid added will be too much.

The temperature in the preparation step is not particularly limited as long as it is a temperature at which the magnesium salt dissolves, but may be, for example, in the range of 1°C to 80°C. If the temperature in the preparation step is less than 1°C, the magnesium salt dissolves insufficiently, and if it exceeds 80°C, the heat resistance of the equipment may be problematic.

The reaction time in the preparation step is not particularly limited as long as the dissolution reaction of the magnesium salt can be carried out, but it can be in the range of 5 minutes to 120 minutes, for example. 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, there will be problems with the equipment.

<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.

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 equipment that produces concentrated water (FO concentrated water) and a dilute draw solution by allowing the treated water (FO treated water) and a draw solution with a higher concentration than the treated water (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 disinfectant addition pipe 112 is connected to the FO treated water pipe 16 as a disinfectant addition device.

The following describes the operation of the forward osmosis membrane treatment method and 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 piping 16 and 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 draw solution is transported to the secondary side of the forward osmosis membrane through the draw solution piping 24 and passes through the forward osmosis membrane 110 so that the FO treated water and the draw solution exist, thereby causing the water to move to the draw solution by osmotic pressure. The dilute draw solution used in the forward osmosis membrane treatment step is discharged through the dilute draw solution piping 26. The FO concentrated water obtained by the forward osmosis membrane treatment step is discharged through the FO concentrated water piping 28. At least one of the dilute suction solution and the FO concentrated water can be recovered and reused.

Here, a bactericide containing a bromine-based oxidant or a chlorine-based oxidant and an amine sulfonic acid compound (hereinafter, sometimes referred to as "forward osmosis membrane bactericide") is allowed to exist in the FO treated water. For example, the forward osmosis membrane bactericide is added to the FO treated water in the FO treated water pipe 16 through the bactericide addition pipe 112. Alternatively, an FO treated water tank for storing FO treated water may be separately provided in the upstream stage of the forward osmosis membrane treatment device 14, and the forward osmosis membrane bactericide may be added to the FO treated water tank.

Thus, in the forward osmosis membrane treatment method and the forward osmosis membrane treatment system 8 of the present embodiment, when the forward osmosis membrane is used to treat the treated water, the 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 the treated water (FO treated water) of the forward osmosis membrane treatment. The inventors have found that the forward osmosis membrane bactericide containing a bromine-based oxidant or a chlorine-based oxidant and an amine sulfonic acid compound hardly passes through the forward osmosis membrane. The forward osmosis membrane bactericide exerts a more sufficient bactericidal effect on the forward osmosis membrane than the conventional chlorine-based bactericide, oxidant, and organic bactericide. In addition, since there is almost no leakage of the disinfectant into the suction solution, the dilute suction solution can be reused.

Since the bactericidal active ingredient of the forward osmosis membrane sterilizer hardly permeates the forward osmosis membrane, it gradually concentrates as it advances to the outlet (FO concentrated water outlet) of the forward osmosis membrane treatment device 14. Therefore, the bactericidal active ingredient of the sterilizer can be fully diffused to the outlet (FO concentrated water outlet) side of the forward osmosis membrane treatment device 14 and fully sterilized to the outlet side of the forward osmosis membrane.

In the conventional method, when a disinfectant such as hypochlorous acid, chloramine, hydrogen peroxide, or an organic disinfectant is added to FO treated water, a portion of the FO treated water moves to the side of the suction solution due to the osmotic pressure difference with the suction solution, and a portion of the disinfectant moves to the side of the suction solution. In contrast, in the forward osmosis membrane treatment method and forward osmosis membrane treatment system 8 of the present embodiment, by using the forward osmosis membrane disinfectant, it is possible to suppress the disinfectant from passing through the forward osmosis membrane and reuse the dilute suction solution.

The “fungicide containing a bromine-based oxidizing agent and an amide sulfonic acid compound” may be a fungicide containing a stabilized hypobromous acid composition containing a mixture of a “bromine-based oxidizing agent” and a “amide sulfonic acid compound”, or a fungicide containing a stabilized hypobromous acid composition containing a “reaction product of a bromine-based oxidizing agent and an amide sulfonic acid compound”. The “fungicide containing a chlorine-based oxidizing agent and an amide sulfonic acid compound” may be a fungicide containing a stabilized hypochlorous acid composition containing a mixture of a “chlorine-based oxidizing agent” and a “amide sulfonic acid compound”, or a fungicide containing a stabilized hypochlorous acid composition containing a “reaction product of a chlorine-based oxidizing agent and an amide 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 of the embodiment of the present invention is a method of allowing a stabilized hypobromous acid composition of a "reaction product of a bromine-based oxidant and an amine sulfonic acid compound" or a stabilized hypochlorous acid composition of a "reaction product of a chlorine-based oxidant and an amine sulfonic acid compound" to exist in the water to be treated (FO treated water).

Specifically, the forward osmosis membrane treatment method of the embodiment of the present invention is a method in which a mixture of "bromine", "bromine chloride", "hypobromous acid" or "a reaction product of sodium bromide and hypochlorous acid" and "sulfamic acid compound" is allowed to exist in the water to be treated. Alternatively, a mixture of "hypochlorous acid" and "sulfamic acid compound" is allowed to exist in the water to be treated.

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

In the forward osmosis membrane treatment method of this embodiment, when the bactericide contains a bromine-based oxidant and an amine sulfonic acid compound, the chlorine-based oxidant does not exist, so the deterioration effect on the forward osmosis membrane is lower. When a chlorine-based oxidant is contained, 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, there is no chlorine-based oxidant, 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 "sulfamic acid compound" can be injected into the water to be treated, for example, by an injection pump, etc. The "bromine-based oxidant" or "chlorine-based oxidant" and "sulfamic acid compound" can be added to the water to be treated separately or mixed with stock solutions 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 the "reaction product of a chlorine-based oxidant and an amine sulfonic acid compound" can be injected into the water to be treated, for example, by means of an injection pump.

In the forward osmosis membrane treatment method of the present embodiment, the ratio of the equivalent of the "sulfonamide compound" to the equivalent of the "bromine-based oxidant" or the "chlorine-based oxidant" is preferably greater than 1, and more preferably within the range of greater than 1 and less than 2. When the ratio of the equivalent of the "sulfonamide compound" to the equivalent of the "bromine-based oxidant" or the "chlorine-based oxidant" is less than 1, the membrane may be degraded, and when it exceeds 2, the production 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 have 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.

Examples of bromine-based oxidants include bromine (liquid bromine), bromine chloride, bromic acid, bromate, hypobromous acid, etc. Hypobromous acid can be produced by reacting a bromide such as sodium bromide with a chlorine-based oxidant such as hypochlorous acid.

Among them, the preparation of "bromine and amine sulfonic acid compound (mixture of bromine and amine sulfonic acid compound)" or "reaction product of bromine and amine sulfonic acid compound" using bromine has less by-product of bromic acid and will not further deteriorate the forward osmosis membrane, compared with the preparation of "hypochlorous acid, bromine compound and amine sulfonic acid" and the preparation of "bromine chloride and amine sulfonic acid". Therefore, it is more ideal as a disinfectant for forward osmosis membrane.

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

Bromine compounds include, for example, sodium bromide, potassium bromide, lithium bromide, ammonium bromide, and hydrobromide, etc. 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, chloroisocyanate or its salts, and the like. Among them, the salts include, for example, hypochlorite metal salts such as sodium hypochlorite and potassium hypochlorite; hypochlorite earth metal salts such as calcium hypochlorite and barium hypochlorite; hypochlorite metal salts such as sodium chlorite and potassium chlorite; hypochlorite earth metal salts such as barium chlorite; other hypochlorite metal salts such as nickel chlorite; hypochlorite metal salts such as ammonium chlorate, sodium chlorate and potassium chlorate; hypochlorite earth metal salts such as calcium chlorate and barium chlorate. These chlorine-based oxidants can be used alone or in combination of two or more. From the perspective of operability, sodium hypochlorite is preferably used as the chlorine-based oxidant.

The sulfonamide compound is a compound represented by the following general formula (1). R ₂ NSO ₃ H (1) (wherein R is independently a hydrogen atom or an alkyl group having 1 to 8 carbon atoms.)

Examples of the sulfonate compound include, in addition to sulfonate (amide sulfuric acid) in which both R groups are hydrogen atoms, sulfonate compounds in which one of the two R groups is a hydrogen atom and the other is an alkyl group having 1 to 8 carbon atoms, such as N-methylsulfonate, N-ethylsulfonate, N-propylsulfonate, N-isopropylsulfonate, and N-butylsulfonate; sulfonate compounds in which both of the two R groups are alkyl groups having 1 to 8 carbon atoms, such as N,N-dimethylsulfonate, N,N-diethylsulfonate, N,N-dipropylsulfonate, N,N-dibutylsulfonate, N-methyl-N-ethylsulfonate, and N-methyl-N-propylsulfonate; sulfonate compounds in which one of the two R groups is a hydrogen atom and the other is an aryl group having 6 to 10 carbon atoms, such as N-anilinesulfonate; or salts thereof. Examples of sulfonate salts include alkaline metal salts such as sodium salts and potassium salts; alkaline earth metal salts such as calcium salts, strontium salts, and barium salts; other metal salts such as manganese salts, copper salts, zinc salts, iron salts, cobalt salts, and nickel salts; ammonium salts and guanidine salts. Sulfonate compounds and their salts may be used alone or in combination of two or more. From the perspective of environmental load, sulfonate (sulfuric acid amide) is preferably used as the sulfonate compound.

In the forward osmosis membrane treatment method of this embodiment, an alkali may be further present. Examples of the alkali include alkali hydroxides such as sodium hydroxide and potassium hydroxide. In view of the stability of the product at low temperatures, sodium hydroxide and potassium hydroxide may be used together. In addition, the alkali may be used in the form of an aqueous solution rather than a solid.

The shape of the forward osmosis membrane used in the forward osmosis membrane treatment step is not particularly limited, but for example, a hollow yarn membrane, a spiral membrane, a tubular membrane, a membrane with a plate bottom frame structure, 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 give 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 an aromatic polyamide series or an amide series to give 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 forward osmosis membranes 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 stage or in a plurality of stages 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, because of their different operating methods, forward osmosis membranes and reverse osmosis membranes have different membrane structures and properties. Reverse osmosis membranes apply 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 membrane of the forward osmosis membrane is lower than that of the reverse osmosis membrane, the mechanical strength of the reverse osmosis membrane does not have to be the same, 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.

The attracting solution used in the forward osmosis membrane treatment step may be, for example, an inorganic salt aqueous solution such as an aqueous solution of ammonium carbonate, an aqueous solution of magnesium salt, an aqueous solution of sodium salt, etc.; an organic aqueous solution such as sucrose, glucose, an organic polymer, etc.; an ionic liquid, etc. The dilute attracting solution used in the forward osmosis membrane treatment step may be used in another step as is, or water may be separated from the dilute attracting solution by heating the dilute attracting solution, performing membrane separation, etc., and then the obtained water and concentrated attracting solution may be reused. When multiple stages of forward osmosis membrane treatment are performed in the forward osmosis membrane treatment step, the above-mentioned attracting solutions may be used in combination.

The water to be treated (FO treated water) is not particularly limited, but examples thereof include industrial water, surface water, tap water, groundwater, seawater, desalinated water obtained by desalination of seawater by reverse osmosis or evaporation, and various types of wastewater such as wastewater discharged in semiconductor manufacturing processes.

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 deteriorates.

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

Furthermore, in order to control the occurrence of scaling when a dispersant is not used, for example, the operating conditions of the forward osmosis membrane treatment device, such as the recovery rate, water temperature, and pH, 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 scaling, is below 0.

Forward osmosis membrane treatment systems are used in, for example, seawater desalination, wastewater volume reduction, concentration of valuables, and concentration of food and beverages.

<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 of the embodiment of the present invention includes the forward osmosis membrane treatment method described above, and includes a pre-treatment step and a reverse osmosis membrane treatment step in the preceding stage of the forward osmosis membrane treatment step, and uses the dilute draw solution obtained by the forward osmosis membrane treatment step in the pre-treatment step. In addition, the water treatment system of the embodiment of the present invention includes the forward osmosis membrane treatment system described above, and includes a pre-treatment device and a reverse osmosis membrane treatment device in the preceding stage of the forward osmosis membrane treatment device, and uses the dilute draw solution obtained by the forward osmosis membrane treatment device in the pre-treatment device.

FIG. 12 shows an overview of an example of a water treatment system according to an embodiment of the present invention, and explains its structure.

The water treatment system 9 of this embodiment has: a pre-treatment device 114, which is a pre-treatment device for pre-treatment of 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 the RO concentrated water obtained by reverse osmosis membrane treatment. The water treatment system 9 may have a turbidity removal device 116 as 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 operation of the water treatment method and 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 pre-treatment device 114, the soluble silica, hardness components and the like contained in the water to be treated are removed (pre-treatment step).

When the treated water contains soluble silica, the pre-treatment device 114 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 114, 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). The solid-liquid separation treatment water obtained by solid-liquid separation is transported as pre-treatment water to the filth removal device 116 through the pipe 122, and then subjected to filth removal treatment by UF membrane or the like, and after the filth components etc. are removed (filth removal step), it is transported to the reverse osmosis membrane treatment device 118.

When the treated water contains hardness components and the hardness components are removed by lime softening, the pre-treatment device 114 has, for example, an alkali reaction device, which adds alkali to the treated water to react and insolubilize the hardness components; a coagulation treatment device, which adds a coagulant to the treated water after the reaction to coagulate it as needed; and a solid-liquid separation device, which separates the coagulant from the treated water after the coagulation treatment. In the pre-treatment device 114, for example, an alkali is added to the treated water to insolubilize the hardness components (alkali 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). The solid-liquid separation treatment water obtained by solid-liquid separation is transported as pre-treatment water to the filth removal device 116 through the pipe 122, and then subjected to filth removal treatment by UF membrane or the like, and after the filth components etc. are removed (filth removal step), it is 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 passing a regeneration agent.

Next, the treated water after the turbidity removal treatment is treated by reverse osmosis membrane in the reverse osmosis membrane treatment device 118 to produce RO concentrated water and RO permeate 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 piping 16, and the RO permeate water is discharged through the RO permeate water piping 126. In addition, in the turbidity removal device 116, the membrane can be backwashed at predetermined intervals. For example, RO permeate water is supplied to the turbidity removal device 116 as backwash water, and the backwash drainage is discharged through the backwash drainage piping 128.

The RO concentrated water obtained by the reverse osmosis membrane treatment is treated by the forward osmosis membrane in the forward osmosis membrane treatment device 14 (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 RO concentrated water and the draw solution exist, thereby using the osmotic pressure to move the water to the draw 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 separately set a FO treated water tank for storing RO concentrated water (FO treated water) in the upstream 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.

The forward osmosis membrane disinfectant exerts a more effective disinfection effect on the forward osmosis membrane than the conventional chlorine disinfectants, oxidants, and organic disinfectants. By using the forward osmosis membrane disinfectant in the water treatment method of the present embodiment, the bactericidal active ingredients hardly pass through the forward osmosis membrane, so the dilute attracting solution diluted by the forward osmosis membrane treatment can be used in the pretreatment and the dilute attracting solution can be reused. When the dilute attracting solution contains the organic disinfectant, the backwash drainage of the filth removal device 116 and the RO permeated water of the reverse osmosis membrane treatment device 118 contain the bactericidal active ingredients. When the dilute suction solution contains chlorine-based disinfectants or oxidants, the membranes may be degraded when the chlorine-based disinfectants or oxidants flow into the sludge removal device 116 or the reverse osmosis membrane treatment device 118. When the above-mentioned disinfectant for forward osmosis membrane is used, since the bactericidal active ingredient hardly permeates the forward osmosis membrane, such a risk 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 is used in the pre-treatment step in the pre-treatment device 114. The FO concentrated water produced 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 draw solution in the forward osmosis membrane treatment device 14, and the dilute draw solution (dilute magnesium salt aqueous solution) used in the forward osmosis membrane treatment device 14 can be used 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 an attracting solution in the forward osmosis membrane treatment device 14, and 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 114.

By using the water treatment method and water treatment apparatus of the present embodiment, water to be treated containing at least one of soluble silica and a hardness component, for example, can be treated at low cost.

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

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, but can be, for example, water containing at least one of soluble silica and hardness components, and can include: industrial water, surface water, tap water, groundwater, seawater, desalinated water obtained by desalting seawater by reverse osmosis or evaporation, various wastewaters such as wastewater discharged in semiconductor manufacturing processes, etc.

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 apparatus of the present embodiment, when the water to be treated contains both soluble silica and hardness components, the pretreatment device (pretreatment step) may include 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 soluble silica removal device (soluble silica removal step) first and the hardness component removal device (hardness component removal step) second, or the hardness component removal device (hardness component removal step) first and the soluble silica removal device (soluble silica removal step) second.

At this time, at least one of a magnesium salt aqueous solution, an alkali aqueous solution, an acid aqueous solution and a sodium chloride aqueous solution is used as the attracting solution in the forward osmosis membrane treatment device 14 (forward osmosis membrane treatment step), and the dilute attracting solution (at least one of a dilute magnesium salt aqueous solution, a dilute alkali aqueous solution, a dilute acid aqueous solution and a dilute sodium chloride aqueous solution) used in the forward osmosis membrane treatment device 14 can be used in a suitable aspect of the soluble silica removal device (soluble silica removal step) and the hardness component removal device (hardness component removal step) of the pre-treatment device 114 (pre-treatment step).

The filth removal device may be, for example, a sand filter, a membrane filter such as an ultrafiltration (UF) membrane, a pressurized flotation device, etc. There is no particular limitation on the location of the filth removal device, 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-treatment step are as described above. In the removal of dissolved 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 118 through the turbidity removal device 116. In the removal of hardness components in the resin softening method, the pre-treated water obtained by ion exchange treatment can be transported to the reverse osmosis membrane treatment device 118 or transported to the reverse osmosis membrane treatment device 118 through the turbidity removal device 116.

A bactericide containing a bromine-based oxidant or a chlorine-based oxidant and an amine sulfonic acid compound ("bactericide for forward osmosis membrane") can be allowed to exist in concentrated water as FO treated water in the water treatment devices 1, 3, and 5 of Figures 1 to 3. For example, the bactericide for forward osmosis membrane is added to the FO treated water (concentrated water) in the concentrated water pipe 20 through the bactericide addition pipe. A concentrated water tank for storing FO treated water (concentrated water) can also be separately provided in the upstream section of 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 the bactericide for forward osmosis membrane is added to the concentrated water tank.

[Reverse osmosis membrane treatment step] The polyamide polymer membrane, which has become the mainstream recently, can be used ideally as the reverse osmosis membrane used in the reverse osmosis membrane treatment step. The polyamide polymer membrane has a relatively low resistance to oxidants, so when free chlorine and the like continuously contact the polyamide polymer membrane, the membrane performance is significantly reduced. However, by using the above-mentioned forward osmosis membrane disinfectant in the water treatment method of this embodiment, the bactericidal active ingredients hardly pass through the forward osmosis membrane, so even the polyamide polymer membrane hardly produces such a significant reduction in membrane performance.

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 according to the TDS, pH, water temperature and other conditions of the water being treated in each stage.

In the concentration step, pH adjusters, scale dispersants to inhibit scaling of inorganic salts in the system, and fungicides to inhibit the growth of microorganisms in the system may also be added.

<Bactericide for positive osmotic membrane> The bactericide for positive osmotic 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 "sulfonamic 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, the bromine compound, the chlorine-based oxidizing agent, and the sulfamic acid compound are as described above.

An example of a commercially available product of a stabilized hypochlorous acid composition containing a chlorine-based oxidant and an amide sulfonic acid compound is "KURIVERTER IK-110" manufactured by Kurita Industries Co., Ltd.

In order to prevent the forward osmosis membrane from being further deteriorated, the forward osmosis membrane disinfectant of this embodiment is preferably one containing bromine and an amine sulfonic acid compound (one containing a mixture of bromine and an amine sulfonic acid compound), for example, a mixture of bromine, an amine sulfonic acid compound, an alkali and water, or a reaction product of bromine and an amine sulfonic acid compound, for example, a mixture of a reaction product of bromine and an amine sulfonic acid compound, an alkali and water.

The disinfectant for positive osmosis membrane of this embodiment includes a disinfectant containing a stabilized hypobromous acid composition including a bromine-based oxidant and an amine sulfonic acid compound, and in particular, a disinfectant containing a stabilized hypobromous acid composition including bromine and an amine sulfonic acid compound. Compared with disinfectants containing a chlorine-based oxidant and an amine sulfonic acid compound (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 use concentrations, the effect on membrane degradation can be substantially ignored. Therefore, it is most suitable as a disinfectant.

The forward osmosis membrane disinfectant of this embodiment is different from the disinfectant of hypochlorous acid, etc., because it hardly passes through the forward osmosis membrane, so it has almost no effect on the dilute absorption solution. In addition, the concentration can be measured on site like hypochlorous acid, so more accurate concentration management can be performed.

The pH of the forward osmotic membrane disinfectant is, for example, higher than 13.0, and more preferably higher than 13.2. When the pH of the forward osmotic membrane disinfectant is lower than 13.0, the effective halogen in the forward osmotic membrane disinfectant may 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 bactericide for positive osmosis membrane> The bactericide for positive osmosis membrane of this embodiment is prepared by mixing a bromine-based oxidant or a chlorine-based oxidant and an amine sulfonic acid compound, and can further be mixed with a base.

The method for producing a forward osmotic membrane disinfectant containing a stabilized hypobromous acid composition comprising bromine and an amine sulfonic acid compound preferably comprises the following steps: adding bromine to a mixed solution comprising water, an alkali and an amine sulfonic acid compound in an inert gas environment to react, or adding bromine to a mixed solution comprising water, an alkali and an amine sulfonic acid compound in an inert gas environment. By adding to react in an inert gas environment or adding in an inert gas environment, the concentration of bromic acid ions in the forward osmotic membrane disinfectant is reduced, thereby reducing the concentration of bromic acid ions in the dilute attracting solution.

The inert gas used is not particularly limited, but from the perspective of manufacturing and the like, 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 during bromine addition is preferably 6% or less, preferably 4% or less, more preferably 2% or less, and particularly preferably 1% or less. When the oxygen concentration in the reactor during bromine reaction exceeds 6%, the amount of bromic acid generated in the reaction system will increase.

The bromine addition rate relative to the total amount of the forward osmosis membrane bactericidal agent 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 relative to the total amount of the forward osmosis membrane bactericidal agent exceeds 25% by weight, the amount of bromic acid generated in the reaction system will increase. When it is less than 1% by weight, the bactericidal power will be very poor.

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

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

<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% by 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, the evaporator is used to replace the concentration operation of the forward osmosis membrane treatment device to produce concentrated water with TDS 20% in the same manner. 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 suction 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] Energy cost ratio Embodiment 1 1 Comparison Example 1 6.1 Comparison Example 2 4.5

Thus, it can be understood that the treatment method of Example 1 can be concentrated at a low energy cost compared to the treatment methods of Comparative Examples 1 and 2, and thus the treated water containing at least one of soluble silica and hardness components can be treated at a low cost.

<Example 2> Industrial water containing TDS 100ppm and dissolved silica 15ppm was concentrated using the water treatment device shown in Figure 3. 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%. A portion of the dilute magnesium chloride solution diluted by the forward osmosis membrane treatment was added intact to the dissolved silica removal device, and the remaining portion was concentrated to 30% magnesium chloride using the concentration device of the structure of Figure 6 and reused as the suction solution of the forward osmosis membrane treatment device. The energy cost used for the forward osmosis membrane treatment was calculated. 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% in the same manner. 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 suction 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.

[Table 2] Energy cost ratio Embodiment 2 1 Comparison Example 3 3.0 Comparison Example 4 2.1

Thus, it can be understood that the treatment method of Example 2 can be concentrated at a low energy cost compared to the treatment methods of Comparative Examples 3 and 4, and thus the treated water containing at least one of soluble silica and hardness components can be treated at a low cost.

[Preparation of stabilized hypobromous acid composition (composition 1)] In a nitrogen environment, mix: liquid bromine: 16.9 weight % (wt%), sulfamic acid: 10.7 weight %, sodium hydroxide: 12.9 weight %, potassium hydroxide: 3.94 weight %, water: the remainder, to prepare a stabilized hypobromous acid composition (composition 1). The pH of the stabilized hypobromous acid composition is 14, and the total chlorine concentration is 7.5 weight %. The total chlorine concentration is a value 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 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 measurement is performed under the following conditions. Electrode type: glass electrode type pH meter: DKK-TOA, IOL-30 type 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 Measuring temperature: 25°C Measurement value: immerse the electrode in the measuring solution, and use the value after stabilization as the measurement value, 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, water: the remainder, and prepare stabilized hypochlorous acid composition (composition 2). The pH of composition 2 is 13.7, and the total chlorine concentration is 6.2% by weight.

<Example 3> Industrial wastewater concentrated to 8 wt% of total evaporated residue (TDS) was used as FO treated water, and then a 30 wt% _MgCl2 solution was used as an attracting solution to perform forward osmosis membrane treatment. The flow rate of the attracting solution was adjusted so that the flow rate at the FO concentrated water outlet was 50% of the flow rate at the FO treated water inlet (concentration ratio 2 times). A cellulose acetate FO membrane (HPC3205, manufactured 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 disinfectant for the forward osmosis membrane so that the total chlorine concentration at the FO treated water inlet was 1 ppmCl. The operation was continued for a total of 200 hours, and then the pressure loss (water pressure difference) from the FO treated water inlet to the FO concentrated water outlet of the positive permeation membrane treatment device and the rejection rate of the disinfectant were evaluated. In addition, the water pressure difference after the start of operation was 0.02MPa. The results are shown in Table 3. Bactericide rejection rate [%] = (1-(dilute suction solution flow rate × dilute suction solution total chlorine concentration/FO treated water × FO treated water total chlorine concentration))

<Example 4> A 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 1 ppmCl. The forward osmosis membrane treatment was carried out in the same manner as in Example 3. The results are shown in Table 3.

<Comparative Example 5> Sodium hypochlorite as a chlorine-based disinfectant was added to the FO treated water instead of the stabilized hypobromous acid composition (composition 1) as a disinfectant for the forward osmosis membrane, and the free chlorine concentration at the inlet of the FO treated water was made 1 ppmCl. The 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> 5-Chloro-2-methyl-4-isothiazoline-3-one was added as an organic bactericide to the FO treated water, and the stabilized hypobromous acid composition (composition 1) was substituted as a forward osmosis membrane bactericide to make the TOC at the inlet of the FO treated water 10ppm. The forward osmosis membrane treatment was carried out in the same manner as in Example 3. The results are shown in Table 3. The forward osmosis membrane treatment was carried out in the same manner as in Example 3. The results are shown in Table 3.

[table 3] Pressure loss from inlet to outlet [MPa] Disinfectant blocking rate [%] Embodiment 3 0.02 ＞99 Embodiment 4 0.05 ＞99 Comparison Example 5 >0.2 75 Comparison Example 6 >0.2 82

[Results] In Example 3, the increase in the water pressure difference of the positive osmosis membrane can be suppressed. The bactericide also blocked more than 99%. In Example 4, there was a similar tendency, but the water pressure difference increased slightly. In Comparative Examples 5 and 6, the water pressure difference was greater than 0.2MPa and exceeded the allowable water pressure difference of the membrane (0.2MPa). The bactericide blocking 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 a positive osmosis membrane and the dilute attracting solution can be reused.

1,3,5,7: Water treatment device 8: Forward osmosis membrane treatment system 9: Water treatment system 10,114: Pretreatment device 12,118: Reverse osmosis membrane treatment device 14: Osmosis membrane treatment device 16,120: Treated water piping 18: Pretreatment water piping 20: Concentrated water piping 22: Permeated water piping 24,32: Suction solution piping 26,36: Dilute suction solution piping 28: FO concentrated water piping 30: Suction solution preparation tank 34,340,342,344,346,348,350: Concentration device 38: Concentrated suction solution piping 40: Dilution piping 42,78: First stage semipermeable membrane treatment device 44,80: Second stage semipermeable membrane treatment device 46,82: Third stage semipermeable membrane treatment device 48,84: Primary 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: Positive osmosis membrane 112: Disinfectant addition piping 116: Turbidity removal device 126: RO permeate piping 128: Backwash drainage piping

[Figure 1] is a schematic structural diagram showing an example of a water treatment device according to an embodiment of the present invention. [Figure 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 an embodiment of the present invention. [Figure 4] is a schematic structural diagram showing an example of a concentrator of the water treatment device according to an embodiment of the present invention. [Figure 5] is a schematic structural diagram showing another example of a concentrator of the water treatment device according to an embodiment of the present invention. [Figure 6] is a schematic structural diagram showing another example of a concentrator of the water treatment device according to an embodiment of the present invention. [Figure 7] is a schematic structural diagram showing another example of a concentrator of the water treatment device according to an embodiment of the present invention. [Figure 8] is a schematic structural diagram showing another example of a concentration device of a water treatment device according to an embodiment of the present invention. [Figure 9] is a schematic structural diagram showing another example of a concentration device of a water treatment device according to an embodiment of the present invention. [Figure 10] is a schematic structural diagram showing a conventional water treatment device. [Figure 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 structural diagram showing an example of a water treatment system according to an embodiment of the present invention.

Claims (10)

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, for performing concentration treatment on the pre-treated water obtained by the pre-treatment device; and a forward osmosis membrane treatment device, for performing forward osmosis membrane treatment on the concentrated water obtained by the concentration treatment device, wherein the dilute suction solution used in the forward osmosis membrane treatment device is directly used in the treatment of any one of the soluble silica removal device and the hardness component removal device. As in claim 1, the water treatment device, wherein the attracting solution used in the forward osmosis membrane treatment device is a magnesium salt aqueous solution, and the soluble silica removal device uses a dilute magnesium salt aqueous solution used in the forward osmosis membrane treatment device; the treated water contains soluble silica; and the pre-treatment device is a magnesium reaction device. The water treatment device of claim 1, 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 treated water contains hardness components; The pre-treatment device is an alkaline reaction device. A water treatment device as claimed in claim 1, wherein the attracting solution used in the forward osmosis membrane treatment device is an acid aqueous solution or a sodium chloride aqueous solution, and the hardness component removal device uses the acid dilute aqueous solution or the sodium chloride dilute aqueous solution used in the forward osmosis membrane treatment device; the treated water contains hardness components; the pre-treatment device is an ion exchange treatment device filled with an ion exchange resin; and the dilute attracting solution is used to regenerate the ion exchange resin. A water treatment device as claimed in any one of claims 1 to 4, wherein the concentration treatment equipment is a reverse osmosis membrane treatment 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, including any one of a soluble silica removal step and 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, and directly using the dilute attracting solution used in the forward osmosis membrane treatment step in the treatment of any one of the soluble silica removal step and the hardness component removal step. As in claim 6, the water treatment method, wherein the attracting solution used in the forward osmosis membrane treatment step is a magnesium salt aqueous solution, and the soluble silica removal step uses a dilute magnesium salt aqueous solution used in the forward osmosis membrane treatment step; the treated water contains soluble silica; and the pre-treatment step is a magnesium reaction step. As in claim 6, the water treatment method, wherein the attracting solution used in the forward osmosis membrane treatment step is an alkaline aqueous solution, and the hardness component removal step uses the alkaline dilute aqueous solution used in the forward osmosis membrane treatment step; the treated water contains hardness components; and the pre-treatment step is an alkaline reaction step. The water treatment method of claim 6, wherein the attracting solution used in the forward osmosis membrane treatment step is an acid aqueous solution or a sodium chloride aqueous solution, and the hardness component removal step uses the acid dilute aqueous solution or the sodium chloride dilute aqueous solution used in the forward osmosis membrane treatment step; the treated water contains hardness components; the pre-treatment step is a step using an ion exchange treatment device filled with an ion exchange resin; the dilute attracting solution is used to regenerate the ion exchange resin. A water treatment method as claimed in any one of claims 6 to 9, wherein the concentration treatment step is a reverse osmosis membrane treatment step.

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