JP6252297B2 - Forward osmosis treatment method and forward osmosis treatment apparatus - Google Patents

Description

  The present invention relates to a forward osmosis treatment method and forward osmosis treatment apparatus using a forward osmosis membrane.

  A forward osmosis treatment method for recovering fresh water from a treatment target liquid (feed solution) such as seawater, river water, or wastewater by using a forward osmosis phenomenon is known. The normal osmosis phenomenon is a phenomenon in which water in a low-concentration solution permeates and moves through a membrane toward a higher-concentration (high osmotic pressure) solution.

  In the forward osmosis water treatment, a draw solution (Draw Solution: hereinafter sometimes abbreviated as “DS”) having a higher osmotic pressure than a feed solution (Feed Solution: hereinafter sometimes abbreviated as “FS”) is used. When DS and FS are brought into contact with each other through the osmosis membrane in the forward osmosis membrane module, water moves from FS having a low osmotic pressure to DS having a high osmotic pressure. And fresh water can be collect | recovered using various methods from DS (namely, DS which collect | recovered water from FS) after passing a forward osmosis membrane module.

  On the other hand, as a procedure of the reverse osmosis water treatment method, a chlorine-based disinfectant such as chlorine gas or sodium hypochlorite is added to the water to be treated to prevent fouling, followed by filtration treatment or the like. A method of supplying treated water to the forward osmosis membrane module is common (see, for example, Patent Documents 1 to 4).

JP 7-171565 A JP 2000-42544 A Japanese Patent Laid-Open No. 7-124559 JP-A-9-29075

  However, Patent Documents 1 to 4 relate to water treatment using a reverse osmosis membrane, and methods for suppressing biofouling have been sufficiently studied for water treatment using a forward osmosis membrane. There wasn't.

  Then, an object of this invention is to provide the forward osmosis processing method and forward osmosis processing apparatus which can suppress the performance fall of the forward osmosis membrane by biofouling.

[1] In a forward osmosis membrane having a first surface and a second surface, the first surface is brought into contact with a feed solution, and the second surface is brought into contact with a draw solution having an osmotic pressure higher than that of the feed solution. And an osmosis step of moving water contained in the feed solution from the first surface side to the second surface side through the forward osmosis membrane;
A forward osmosis treatment method comprising a sterilizing agent adding step of adding a chlorinated sterilizing agent to at least one of the feed solution and the draw solution before the infiltration step.

  [2] The forward osmosis treatment according to [1], including a reducing agent addition step of adding a reducing agent to at least one of the feed solution and the draw solution after the sterilizing agent addition step and before the penetration step. Method.

  [3] The forward osmosis treatment method according to [1] or [2], wherein the chlorine-based disinfectant is intermittently added in the disinfectant addition step.

  [4] The forward osmosis treatment method according to [2], wherein the chlorine-based disinfectant is continuously added in the disinfectant adding step, and the reducing agent is intermittently added in the reducing step.

  [5] The forward osmosis treatment method according to any one of [1] to [4], wherein the chlorine-based disinfectant is chloramine.

[6] A forward osmosis treatment apparatus used in the forward osmosis treatment method according to [1],
The forward osmosis membrane, a first chamber to which the feed solution is supplied, and a second chamber to which the draw solution is supplied, wherein the first chamber and the second chamber are the forward osmosis membrane. A forward osmosis membrane module,
A forward osmosis treatment device comprising: a sterilizing agent addition device for adding a chlorine-based sterilizing agent to at least one of the feed solution supplied to the first chamber and the draw solution supplied to the second chamber. .

  ADVANTAGE OF THE INVENTION According to this invention, the forward osmosis processing method and forward osmosis processing apparatus which can suppress the performance fall of the forward osmosis membrane by biofouling can be provided.

It is a schematic diagram for demonstrating the forward osmosis processing method and forward osmosis processing apparatus of Embodiment 1. It is a schematic diagram for demonstrating the forward osmosis processing method and forward osmosis processing apparatus of Embodiment 2.

  Hereinafter, an embodiment of a forward osmosis treatment system of the present invention will be described with reference to the drawings. In the drawings, the same reference numerals represent the same or corresponding parts. In addition, dimensional relationships such as length, width, thickness, and depth are changed as appropriate for clarity and simplification of the drawings, and do not represent actual dimensional relationships.

(Embodiment 1)
Hereinafter, the forward osmosis treatment method and forward osmosis treatment apparatus of the present embodiment will be described with reference to FIG.

  The forward osmosis treatment apparatus used in the present embodiment includes a forward osmosis membrane module 1. The forward osmosis membrane module 1 includes a forward osmosis membrane 10, a first chamber 21 to which FS is supplied, and a second chamber 22 to which DS is supplied. The first chamber 21 and the second chamber 22 are: It is partitioned by a forward osmosis membrane 10.

  The forward osmosis membrane is not particularly limited, and various known semipermeable membranes that can be used for forward osmosis can be used. However, the forward osmosis membrane is made of a cellulose-based material or a chlorine-resistant polyamide-based material. A semipermeable membrane can be suitably used. Examples of the cellulose-based material include cellulose acetate, and preferably cellulose triacetate (CTA). Examples of the chlorine-resistant polyamide-based material include polyamide polymer polymers having high oxidation resistance as disclosed in JP-A-62-244404. When such a material is used as the material for the forward osmosis membrane, there is an advantage that the membrane performance is hardly deteriorated by the addition of the chlorine-based disinfectant to FS and DS.

  Although it does not specifically limit as a shape of a forward osmosis membrane, For example, a flat membrane, a spiral membrane, or a hollow fiber membrane is mentioned. In addition, in FIG. 1, although the flat film simplified as a forward osmosis membrane is drawn, it is not limited to this.

  The forward osmosis treatment device used in the present embodiment includes a sterilizing agent addition device 51 for adding a chlorine-based sterilizing agent to the FS supplied to the first chamber 21 and a DS supplied to the second chamber 22. Is provided with a bactericidal agent addition device 52 for adding a chlorine-based bactericidal agent.

  The forward osmosis treatment method of this embodiment is a method of separating and collecting water from a feed solution (treatment target water) by forward osmosis using a semipermeable membrane.

  In this embodiment, the feed solution contains microorganisms that cause biofouling. Examples of the feed solution containing microorganisms include seawater, river water, brackish water, domestic wastewater, and oilfield or gasfield wastewater. In addition, the component which is not melt | dissolving may be contained in the feed solution.

  The draw solution is not particularly limited as long as it has a higher osmotic pressure than the feed solution. Examples of the draw solution include inorganic salt solutions, sugar solutions, and gases having high solubility in water (such as ammonia and carbon dioxide). And liquid containing organic matter, magnetic fine particles, or organic polymer. The draw solution may contain undissolved components.

  Specifically, the forward osmosis treatment method of the present invention includes the following bactericide addition step, permeation step, separation step, and DS circulation step.

(Bactericidal agent addition process)
In this step, a chlorine-based disinfectant is added from the disinfectant addition device 51 to the FS supplied to the first chamber 21 of the forward osmosis membrane module 1. Further, a chlorine-based disinfectant is added from the disinfectant addition device 52 to the FS supplied to the second chamber 22 of the forward osmosis membrane module 1.

  The chlorine-based disinfectant is not particularly limited, and examples thereof include chlorine gas, free chlorine such as sodium hypochlorite and calcium hypochlorite, bonded chlorine such as monochloramine, and chlorine dioxide. By using monochloramine or chlorine dioxide as a chlorine-based disinfectant, it is possible to suppress the formation of halogenated organic substances such as trihalomethane (Patent Document 3: JP-A-7-124559, Patent Document 4: JP-A-9). -29075). Here, in the case of using a solution containing an ammonia-generating substance such as ammonium hydrogen carbonate as DS, chlorine is used in order to prevent the sterilizing power of the chlorine-based disinfectant from being reduced and the alteration of DS (deterioration that is difficult to regenerate). It is preferable to use bound chlorine such as chloramine as the system fungicide.

  Further, as the chlorine-based disinfectant, for example, when FS is seawater, chlorine gas or sodium hypochlorite generated by a seawater electrolyzer can be used. In this case, the seawater electrolysis device becomes the bactericide addition device.

  The chlorine-based disinfectant may be added continuously or intermittently. However, continuous injection of a chlorine-based disinfectant facilitates the generation of by-products such as trihalomethane, so that the generation of trihalomethane can be suppressed by intermittently adding a chlorine-based disinfectant (Patent Document 2: JP, 2000-42544, A).

(Penetration process)
In this step, FS is caused to flow into the first chamber 21 of the forward osmosis membrane module 1 to bring the FS into contact with the first surface 11 of the forward osmosis membrane 10 and in the second chamber 22 of the forward osmosis membrane module 1. The DS is caused to flow into the second surface 12 of the forward osmosis membrane 10. In this state, due to the forward osmosis phenomenon, water contained in the FS passes through the forward osmosis membrane 10 from the first surface 11 side to the second surface 12 side and moves into the DS.

(Water separation process)
In this step, DS that has recovered the water in the FS by the forward osmosis phenomenon by passing through the second chamber 22 of the forward osmosis membrane module 1 is sent to the water separation device 3. In the water separation device 3, the water in the DS is separated and recovered. As a method for separating the draw substance added to increase the osmotic pressure in the DS and the water contained in the DS, an appropriate method is selected depending on the type of the draw substance. For example, if the draw substance is an inorganic salt or a low-melting substance, select crystallization treatment, gas diffusion if the gas is highly soluble in water, magnetic separation if it is a magnetic fine particle, ion exchange if it is a sugar solution. be able to. Examples of common separation methods include distillation and reverse osmosis membrane treatment. The separated water is sent to a tank or the like and sent to the next purification step or the like.

(DS circulation process)
In this step, a DS concentrated solution containing a draw solute separated from water in a high concentration is caused to flow from the water separation device 3 to the DS adjustment device 4. And DS for supplying to the forward osmosis membrane module 1 is prepared by adjusting the density | concentration, temperature, etc. of DS concentrate. The DS is circulated by supplying the DS to the second chamber 22 of the forward osmosis membrane module 1. A chlorine-based disinfectant is added to the DS by the chlorine-based disinfectant adding step.

(Embodiment 2)
The present embodiment is different from the first embodiment in that chlorine is added to DS, but the other points are the same as those in the first embodiment, and therefore, duplicate description is omitted.

  With reference to FIG. 2, the forward osmosis treatment device used in the present embodiment is on the downstream side (between the sterilizing agent adding device 51 and the first chamber 21) of the sterilizing agent adding device 51 for adding the sterilizing agent to the FS. , A reductant addition device 61 for adding a reductant to FS, and a downstream side of a bactericidal agent addition device 52 for adding a bactericidal agent to DS (between the bactericidal agent addition device 52 and the second chamber 22). In addition, a reducing agent adding device 62 for adding a reducing agent to the DS is provided.

  The forward osmosis treatment method of the present embodiment includes the same bactericidal agent addition step, the permeation step, the separation step, and the DS circulation step as in the first embodiment, and further between the bactericidal agent addition step and the permeation step. The following reducing agent addition process is included.

(Reducing agent addition process)
A reducing agent is added to FS and DS after the fungicide adding step and before the infiltration step. Specifically, after the chlorine-based disinfectant is added to the FS from the disinfectant adding device 51 and before the FS flows into the first chamber 21 of the forward osmosis membrane module 1, the reducing agent is added by the reducing agent adding device 61. Add to FS. Further, after the chlorine-based disinfectant is added to the DS from the disinfectant adding device 52, before the DS flows into the second chamber 22 of the forward osmosis membrane module 1, the reducing agent adding device 62 adds the reducing agent to the DS. To do.

  Examples of the reducing agent include, but are not limited to, sodium bisulfite, sodium sulfite, ferrous ammonium sulfate, sodium thiosulfate, sodium ascorbate, and the like. Therefore, sodium bisulfite is preferable. The concentration of the reducing agent added is 0.1 to 10 mg / L under general conditions although it depends on the concentration of the chlorine-based disinfectant.

  As in this embodiment, after the bactericidal agent addition step and before the permeation step, by adding a reducing agent to FS and DS, the biofouling is suppressed and the oxidative deterioration of the forward osmosis membrane is suppressed. Can do.

  The reducing agent may be added continuously or intermittently. In addition, by continuously adding a chlorine-based disinfectant and intermittently adding a reducing agent, the disinfectant is intermittently injected, and the biofouling suppressing effect and the oxidative deterioration of the forward osmosis membrane (See Patent Document 1: Japanese Patent Laid-Open No. 7-171565).

  Although the forward osmosis membrane may be exposed to free chlorine or the like by addition of a chlorine-based disinfectant, a semipermeable membrane made of a polyamide-based material or the like that does not have chlorine resistance is used as the forward osmosis membrane. When used, it is necessary to remove free chlorine in FS and DS that come into contact with the forward osmosis membrane by addition of a reducing agent as in Embodiment 2 to prevent deterioration in membrane performance due to chlorine. On the other hand, when a chlorine-resistant material such as a cellulose-based material and a chlorine-resistant polyamide-based material is used as the material for the forward osmosis membrane, a reduction agent addition step is not necessarily required because the membrane performance is hardly deteriorated by chlorine. .

  In addition, although Embodiment 1 and 2 demonstrated the case where a chlorine-type disinfectant was added to both FS and DS, as another embodiment, for example, DS does not contain a microorganism and only FS contains a microorganism. In that case, chlorine may not be added to DS, but a chlorine-based disinfectant may be added only to FS. Further, for example, when FS does not contain microorganisms and only DS contains microorganisms, a chlorine-based disinfectant may be added only to DS without adding a chlorine-based disinfectant to FS.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  DESCRIPTION OF SYMBOLS 1 Forward osmosis membrane module, 10 Forward osmosis membrane, 11 1st surface, 12 2nd surface, 21 1st chamber, 22 2nd chamber, 3 Water separator, 4 DS adjustment device, 51,52 Chlorine type disinfectant addition device 61, 62 Reducing agent addition device.

Claims (3)

In a forward osmosis membrane having a first surface and a second surface, the first surface is brought into contact with a feed solution, and the second surface is brought into contact with a draw solution having an osmotic pressure higher than that of the feed solution. A permeation step of moving water contained in the feed solution from the first surface side to the second surface side through the forward osmosis membrane;
Prior to said infiltration step, and the feed solution and process disinfectant added continuously adding a chlorine-based germicide to both of the draw solution,
After the disinfectant addition step and before the permeation step, a reducing agent addition step of intermittently adding a reducing agent to both the feed solution and the draw solution;
Including, forward osmosis treatment method. The forward osmosis treatment method according to claim 1 , wherein the chlorine-based disinfectant is chloramine. A forward osmosis treatment apparatus used in the forward osmosis treatment method according to claim 1,
The forward osmosis membrane, a first chamber to which the feed solution is supplied, and a second chamber to which the draw solution is supplied, wherein the first chamber and the second chamber are the forward osmosis membrane. A forward osmosis membrane module,
And wherein the feed solution supplied to the first chamber, and, fungicides adding device for adding a chlorine-based germicide to both of the draw solution fed into the second chamber,
A reducing agent addition device for adding a reducing agent to both the feed solution and the draw solution downstream of the disinfectant addition device and upstream of the forward osmosis membrane module;
A forward osmosis treatment apparatus.

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