Forward osmosis treatment method and forward osmosis treatment apparatus

Abstract

To provide a forward osmosis treatment method and a forward osmosis treatment device capable of suppressing performance deterioration of a semi-permeable membrane by effectively suppressing clogging of the semi-permeable membrane and the like caused by pollutants without needing an additional complex device and the like.SOLUTION: A forward osmosis treatment method includes a forward osmosis treatment step using a forward osmosis module having a semi-permeable membrane and a first chamber and a second chamber partitioned by the semi-permeable membrane and a washing step washing the semi-permeable membrane. In the forward osmosis treatment step,: a feed solution is supplied into the first chamber; a draw solution having a higher osmotic pressure than the feed solution is supplied into the second chamber; water contained in the feed solution is transferred into the draw solution by contacting the feed solution with the draw solution via the semi-permeable membrane; concentrated liquid which is the concentrated feed solution is discharged from the first chamber; and at least a part of the concentrated liquid is stored in a tank. In the washing step, the semi-permeable membrane is washed by that the concentrated liquid stored in the tank is flowed to the first chamber in a reverse direction to the flow of the feed solution in the forward osmosis step and the draw solution is supplied into the second chamber.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a forward osmosis treatment method and a forward osmosis treatment apparatus.

Background Art

[0002] A forward osmosis treatment method for recovering pure water from a liquid to be treated (feed solution) such as seawater, river water, or wastewater by utilizing the forward osmosis phenomenon is known.

[0003] In forward osmosis treatment, a draw solution (hereinafter sometimes abbreviated as "DS") having a higher osmotic pressure than the feed solution (Feed Solution: hereinafter sometimes abbreviated as "FS") is used. When the FS and the DS are brought into contact with each other through a semipermeable membrane in a forward osmosis module, water moves from the FS having a lower osmotic pressure to the DS having a higher osmotic pressure. This phenomenon is called the forward osmosis (hereinafter sometimes abbreviated as "FO") phenomenon. Then, pure water can be recovered from the DS after passing through the forward osmosis module (that is, the DS from which water has been recovered from the FS) by using various methods.

[0004] Examples of phenomena that reduce the permeation performance of the semipermeable membrane used in forward osmosis treatment include clogging by contaminants such as biofouling, organic fouling, and scaling.

[0005] Biofouling is fouling (dirt) caused by the formation of a biofilm by microorganisms. Organic fouling is fouling (dirt) caused by extracellular metabolites produced by microorganisms contained in seawater or the like. Scaling is a phenomenon in which inorganic components dissolved in seawater precipitate on the membrane surface and clog the semipermeable membrane.

[0006] In order to reduce clogging by such contaminants of the semipermeable membrane, various methods for cleaning a forward osmosis treatment apparatus (forward osmosis module) are known.

[0007] For example, Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2019-166420) describes a method for cleaning a forward osmosis module using a chlorine-based disinfectant. Also, for example, Patent Document 2 (Japanese Unexamined Patent Application Publication No. 2015-188787) describes a method for cleaning a forward osmosis module by adding a chlorine-based disinfectant to FS or DS. Patent Document 3 (Japanese Unexamined Patent Application Publication No. 2020-131095) describes a method for cleaning a forward osmosis module in which a cleaning liquid is flowed through both the flow path of FS and the flow path of DS.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0009] However, the cleaning method of Patent Document 1 has a problem that the oxidation reaction of the forward osmosis membrane proceeds due to the chlorine-based disinfectant, and the performance of the forward osmosis membrane deteriorates. In the cleaning method described in Patent Document 2, there is a problem that the constituent members of the flow path of DS are also subject to the chemical oxidation action of the chlorine-based disinfectant. Further, in the cleaning method described in Patent Document 3, since the supply operation of DS is temporarily stopped, there are problems such as a decrease in the operation rate due to the discharge operation of DS from the part to be cleaned and the time required for the stabilization of the operation state on the DS side after restart.

[0010] Therefore, an object of the present invention is to provide a forward osmosis treatment method and a forward osmosis treatment apparatus that can effectively suppress clogging and the like caused by contaminants on the semipermeable membrane and suppress a decrease in the performance of the semipermeable membrane without requiring additional complicated devices or the like.

Means for Solving the Problems

[0011] [1] A forward osmosis treatment method including a forward osmosis step using a forward osmosis module having a semipermeable membrane and a first chamber and a second chamber partitioned by the semipermeable membrane, and a cleaning step of cleaning the semipermeable membrane, wherein: In the forward osmosis step, a feed solution is supplied to the first chamber, a draw solution having a higher osmotic pressure than the feed solution is supplied to the second chamber, and the feed solution and the draw solution are brought into contact with each other through the semipermeable membrane, so that water contained in the feed solution is moved into the draw solution, a concentrate which is the concentrated feed solution is discharged from the first chamber, and at least a part of the concentrate is stored in a tank; In the cleaning step, the concentrate stored in the tank is flowed into the first chamber in a direction opposite to the flow direction of the feed solution in the forward osmosis step, and the draw solution is supplied to the second chamber to clean the semipermeable membrane.

[0012] [2] The forward osmosis treatment method according to [1], wherein in the cleaning step, the supply of the draw solution to the second chamber is performed in the same manner as in the forward osmosis step before performing the cleaning step.

[0013] [3] The forward osmosis treatment method according to [1] or [2], wherein a chlorine-based disinfectant is intermittently or continuously added to the feed solution supplied to the first chamber.

[0014] [4] The forward osmosis treatment method according to [3], wherein at least one of the addition amount and the addition frequency of the chlorine-based disinfectant is adjusted according to the frequency or effect of the cleaning step.

[0015] [5] The forward osmosis treatment method according to any one of [1] to [4], wherein the flow rate of the concentrate supplied from the tank to the first chamber is adjusted.

[0016] [6] The forward osmosis treatment method according to any one of [1] to [5], wherein the concentrate stored in the tank is filtered to remove suspended matter contained in the concentrate and then supplied to the first chamber.

[0017] [7] The method for forward osmosis treatment according to any one of [1] to [6], wherein the concentrated solution stored in the tank is supplied to the first chamber after at least one of its pH, temperature, and oxidation-reduction potential is adjusted.

[0018] [8] A forward osmosis treatment apparatus used for the forward osmosis treatment method according to any one of [1] to [7], comprising: a forward osmosis module having the semipermeable 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 partitioned by the semipermeable membrane; a tank for storing the concentrated solution.

[0019] [9] The forward osmosis treatment apparatus according to [8], further comprising a pump for flowing the concentrated solution stored in the tank into the first chamber.

[0020]

[10] The forward osmosis treatment apparatus according to [8] or [9], further comprising a flow rate adjustment valve for adjusting the flow rate of the concentrated solution supplied from the tank to the first chamber.

[0021]

[11] The forward osmosis treatment apparatus according to any one of [8] to

[10] , further comprising a filtration device for filtering the concentrated solution stored in the tank in a flow path connecting the tank and the first chamber. [Advantages of the Invention]

[0022] According to the present invention, it is possible to provide a forward osmosis treatment method and a forward osmosis treatment apparatus that can effectively suppress clogging and the like caused by contaminants on the semipermeable membrane and suppress a decrease in the performance of the semipermeable membrane without requiring additional complicated devices or the like. [Brief Description of the Drawings]

[0023]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Mode for Carrying Out the Invention

[0024] Hereinafter, embodiments 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. Also, dimensional relationships such as length, width, thickness, depth, etc. have been appropriately changed for the clarity and simplification of the drawings, and do not represent actual dimensional relationships.

[0025] <Forward Osmosis Treatment Method> The forward osmosis treatment method of the present embodiment is a forward osmosis step (S1) using the forward osmosis module 1 and a cleaning step (S2) of cleaning the semipermeable membrane 10, and includes (see FIG. 4).

[0026] 〔Forward Osmosis Step: S1〕 Referring to FIG. 1, the forward osmosis step (S1) is carried out using the forward osmosis module 1 as described above. The forward osmosis module 1 has a semipermeable membrane 10, and a first chamber 11 and a second chamber 12 partitioned by the semipermeable membrane 10.

[0027] In the forward osmosis process (S1), a feed solution (FS) is supplied to the first chamber 11 of the forward osmosis module 1, a draw solution (DS) having an osmotic pressure higher than that of the feed solution is supplied to the second chamber 12 of the forward osmosis module 1, and the FS and the DS are brought into contact with each other via a semipermeable membrane. As a result, due to the forward osmosis phenomenon, water contained in the FS is moved into the DS, and a concentrated solution, which is the concentrated FS, is discharged from the first chamber 11 of the forward osmosis module 1. Further, the diluted DS is discharged from the second chamber 12 of the forward osmosis module 1.

[0028] In the present embodiment, at least a part of the concentrated solution (concentrated FS) discharged from the first chamber 11 of the forward osmosis module 1 is stored in the tank 2, for example, while being overflowed (through an introduction flow path for introducing the concentrated solution into the tank 2).

[0029] (Semipermeable membrane) Examples of the semipermeable membrane include semipermeable membranes called reverse osmosis (RO) membranes, forward osmosis (FO) membranes, or nanofiltration (NF) membranes.

[0030] Generally, the pore diameters of RO membranes and FO membranes are about 2 nm or less, and the pore diameter of UF membranes is about 2 to 100 nm. NF membranes are those with a relatively low rejection rate of ions and salts among RO membranes, and generally, the pore diameter of NF membranes is about 1 to 2 nm. When an RO membrane or FO membrane, or an NF membrane is used as the semipermeable membrane, the salt rejection rate of the RO membrane or FO membrane, or NF membrane is preferably 90% or more.

[0031] The material constituting the semipermeable membrane is not particularly limited, and examples thereof include cellulose-based resins, polysulfone-based resins, and polyamide-based resins. The semipermeable membrane is preferably composed of a material containing at least one of a cellulose-based resin and a polysulfone-based resin.

[0032] The cellulose-based resin is preferably a cellulose acetate-based resin. The cellulose acetate-based resin has the characteristics of being resistant to chlorine, which is a bactericide, and being able to suppress the growth of microorganisms. The cellulose acetate-based resin is preferably cellulose acetate, and more preferably triacetate cellulose from the viewpoint of durability.

[0033] The polysulfone resin is preferably a polyethersulfone resin. The polyethersulfone resin is preferably sulfonated polyethersulfone.

[0034] The shape of the semipermeable membrane 10 is not particularly limited, and examples thereof include a hollow fiber membrane and a flat membrane. In FIG. 1, the flat membrane is depicted in a simplified manner as the semipermeable membrane 10, but it is not particularly limited to such a shape. Note that a hollow fiber membrane (hollow fiber type semipermeable membrane) is advantageous in that it can increase the membrane area per module and enhance the membrane separation efficiency per volume compared to a flat membrane or the like.

[0035] Also, the form of the forward osmosis module 1 is not particularly limited. When using a hollow fiber membrane, examples include a module in which the hollow fiber membrane is arranged straight, and a cross-wound type module in which the hollow fiber membrane is wound around a core tube. When using a flat membrane, examples include a laminated type module in which flat membranes are stacked, and a spiral type module in which a flat membrane is formed into a cylindrical shape and wound around a core tube.

[0036] As an example of a specific hollow fiber membrane, a membrane having a single-layer structure entirely composed of a cellulose-based resin can be mentioned. However, the single-layer structure here does not necessarily mean that the entire layer is a uniform membrane. For example, a membrane that is a single material but has a dense layer near the outer peripheral surface, and this dense layer serves as a separation active layer that substantially defines the pore diameter of the hollow fiber membrane may also be acceptable.

[0037] As another example of a specific hollow fiber membrane, a membrane having a two-layer structure with a dense layer made of a polyphenylene-based resin (for example, sulfonated polyethersulfone) on the outer peripheral surface of a support layer (for example, a layer made of polyphenylene oxide) can be mentioned. Also, as another example, a membrane having a two-layer structure with a dense layer made of a polyamide-based resin on the outer peripheral surface of a support layer (for example, a layer made of polysulfone or polyethersulfone) can be mentioned.

[0038] (Feed solution, draw solution) The feed solution is not particularly limited as long as it is a solution containing water. Examples of the feed solution include seawater, river water, brackish water, and wastewater. Examples of the wastewater include industrial wastewater, domestic wastewater, and wastewater from oil fields or gas fields. Note that the feed solution may contain undissolved components.

[0039] The draw solution is not particularly limited as long as it is a liquid having a higher osmotic pressure than the feed solution. Examples of the draw solution include inorganic salt solutions, sugar solutions, or liquids containing gases highly soluble in water (such as ammonia and carbon dioxide), or organic substances, magnetic fine particles, etc. Note that the draw solution may contain undissolved components.

[0040] The osmotic pressure difference (Δπ) ([osmotic pressure of DS] - [osmotic pressure of FS]) between the draw solution (DS) and the feed solution (FS) before being introduced into the forward osmosis module is preferably 0.1 MPa or more and 38 MPa or less, more preferably 1 MPa or more and 15 MPa or less. Note that it is preferable for DS to have a high osmotic pressure necessary for further concentrating the concentrated solution (concentrated FS) in the washing step described later.

[0041] Note that in the forward osmosis step, usually, the hydrostatic pressures (excluding the osmotic pressure) of FS and DS are substantially the same, but in order to increase the amount of permeated water (the amount of water permeating through the semipermeable membrane from FS and migrating to DS), FS may be pressurized so that the hydrostatic pressure (excluding the osmotic pressure) of FS becomes higher than that of DS.

[0042] 〔Washing step (S2)〕 Referring to FIG. 1, in the cleaning step (S2), the concentrated liquid (the feed solution concentrated in the forward osmosis step) stored in the tank 2 is made to flow in the first chamber in a direction opposite to the flow of the feed solution in the forward osmosis step (i.e., from the discharge side of the concentrated liquid (concentrated FS) in the forward osmosis step toward the supply side of the FS) (see the dotted arrow in FIG. 1). Thereby, by supplying the draw solution to the second chamber, water in the concentrated liquid is moved to the draw solution, and by bringing the highly concentrated liquid (the further concentrated concentrated liquid) into contact with the semipermeable membrane, the semipermeable membrane is cleaned.

[0043] Note that the supply of the feed solution to the first chamber in the forward osmosis step is stopped before the cleaning step is carried out.

[0044] The supply of the concentrated liquid from the tank 2 to the discharge side of the first chamber 11 of the forward osmosis module 1 may be carried out via a flow path different from the introduction flow path for introducing from the first chamber 11 of the forward osmosis module 1 to the tank 2, as shown in FIG. 1, or may be carried out via a flow path including at least a part of the introduction flow path.

[0045] On the other hand, a draw solution is supplied to the second chamber. The supply of this draw solution is preferably carried out in the same manner as in the forward osmosis step before the cleaning step is carried out.

[0046] The diluted DS discharged from the second chamber is, for example, subjected to a treatment for recovering water by a reverse osmosis module, or is subjected to a treatment for reusing the DS after water has been recovered. In this way, since the DS often circulates between the second chamber 12 of the forward osmosis module 1 and a complicated treatment path, once the circulation flow of this DS is stopped, extra time and cost are required to circulate the DS again and return to a steady state. Therefore, it is preferable to stop the circulation flow of the DS as little as possible.

[0047] The forward osmosis treatment method and apparatus of the present embodiment have the advantage that the supply of the draw solution to the second chamber can be carried out in the same manner as in the forward osmosis process before the cleaning process is performed, and the cleaning process can be carried out without stopping the circulation flow of the DS. Note that the supply flow rate of the DS during the cleaning process is usually operated at the same flow rate as in the forward osmosis process. However, since the amount of water transferred from the highly concentrated liquid to the DS is less than that during the forward osmosis process, the flow rate of the DS may be reduced from the viewpoint of reducing power during cleaning. Also, the flow rate of the DS may be increased to maintain a certain degree of water recovery from the concentrated liquid, such as increasing the supply flow rate of the concentrated liquid during cleaning compared to the supply flow rate of the FS during the forward osmosis process.

[0048] In the cleaning process, the concentrated liquid is further concentrated in the first chamber 11 to become a liquid with a higher concentration (higher osmotic pressure). Due to the osmotic pressure shock caused by the osmotic pressure difference between the osmotic pressure of this liquid and the osmotic pressure of the FS in the forward osmosis process, a sterilizing effect is produced on microorganisms and the like attached to the semipermeable membrane 10 (mainly on the first chamber 11 side of the semipermeable membrane 10), and the semipermeable membrane 10 is cleaned.

[0049] In the first chamber 11, the osmotic pressure difference between the FS on the inflow side (the discharge side of the concentrated liquid) and the further concentrated concentrated liquid in the cleaning process is larger than that on the discharge side of the FS (the inflow side of the concentrated liquid). For this reason, in the first chamber 11, it is considered that the cleaning effect due to the osmotic pressure difference such as the sterilizing effect due to the osmotic pressure shock is higher on the inflow side of the FS (the discharge side of the concentrated liquid). The inflow side of the FS in the first chamber 11 has a large osmotic pressure difference between the FS and the DS in the forward osmosis process, and a large amount of water permeates, so clogging is likely to occur. According to the above cleaning process, it is possible to efficiently clean the semipermeable membrane in the portion where clogging is likely to occur.

[0050] Note that in the cleaning process, the DS supplied to the second chamber is preferably a DS having a high osmotic pressure (higher than the concentrated liquid) for further concentrating the concentrated liquid, which is the feed solution concentrated in the forward osmosis process.

[0051] The cleaning process is carried out intermittently, for example, during the forward osmosis process. For example, referring to FIG. 4, after the forward osmosis process (S1) is continuously carried out for a predetermined time, the cleaning process (S2) is carried out. After the cleaning process (S2), the next forward osmosis process (S1) is continuously carried out for a predetermined time. Thus, usually, the forward osmosis process (S1) and the cleaning process (S2) are alternately repeated.

[0052] The flow rate of the concentrate supplied from the tank 2 to the first chamber 11 of the FO module 1 is preferably adjusted by a pump 4 or the like. In this case, the flow rate of the concentrate can be optimized so that the cleaning effect by the cleaning process is enhanced.

[0053] The concentrate stored in the tank 2 is preferably filtered by a filtering device 3 having a filter capable of removing the suspended matter in the concentrate, and after the suspended matter contained in the concentrate is removed, it is supplied to the first chamber 11. In this case, the cleaning effect by the cleaning process is enhanced.

[0054] The concentrate stored in the tank 2 is preferably supplied to the first chamber 11 after at least one of its pH, temperature, and redox potential is adjusted. In this case, the characteristics of the concentrate can be optimized so that the cleaning effect by the cleaning process is enhanced. For example, by adjusting the pH of the concentrate, it is considered that the scale-like substance can be dissolved (cleaned) under certain conditions due to the effect of acid shock or the like.

[0055] 〔Addition of Chlorine-based Bactericide〕 In the present embodiment, a chlorine-based bactericide may be added intermittently or continuously to the feed solution supplied to the first chamber. Further, the chlorine-based bactericide may be added to the concentrate. Due to the bactericidal effect of the chlorine-based bactericide on microorganisms, biofouling, organic fouling, etc. of the semipermeable membrane are further reduced.

[0056] However, since there is a problem that the performance of the semipermeable membrane deteriorates due to the acceleration of the oxidation reaction of the semipermeable membrane by the chlorine-based disinfectant, when the chlorine-based disinfectant is added to the feed solution, at least one of the addition amount and the addition frequency of the chlorine-based disinfectant is adjusted so that the acceleration of the oxidation reaction of the semipermeable membrane by the chlorine-based disinfectant is minimized according to the frequency of the cleaning process.

[0057] The chlorine-based disinfectant is not particularly limited, and examples thereof include free chlorine such as chlorine gas, sodium hypochlorite, and calcium hypochlorite, combined chlorine such as monochloramine, or chlorine dioxide. By using monochloramine or chlorine dioxide as the chlorine-based disinfectant, the generation of halogenated organic substances such as trihalomethane can be suppressed. Here, when a solution containing an ammonia product substance such as ammonium hydrogen carbonate is used as the DS, it is preferable to use combined chlorine such as chloramine as the chlorine-based disinfectant in order to prevent a decrease in the bactericidal power of the chlorine-based disinfectant and the alteration of the DS (alteration difficult to regenerate).

[0058] In addition, when the FS is seawater, for example, chlorine gas or sodium hypochlorite generated by a seawater electrolysis device can also be used as the chlorine-based disinfectant.

[0059] The chlorine-based disinfectant may be added continuously or intermittently. However, since by-products such as trihalomethane are likely to be generated when the chlorine-based disinfectant is continuously injected, the generation of trihalomethane can be suppressed by adding the chlorine-based disinfectant intermittently.

[0060] In the above description, a forward osmosis treatment method (forward osmosis treatment apparatus) using one forward osmosis module has been described with reference to FIG. 1. However, in the forward osmosis treatment method (forward osmosis treatment apparatus) of the present embodiment, a plurality of forward osmosis modules (multi-stage forward osmosis modules) may be used (see FIGS. 2 and 3). In this case, the osmotic pressure difference between the FS in the forward osmosis process and the concentrated liquid further concentrated in the cleaning process becomes larger for the upstream forward osmosis modules in the multi-stage. Therefore, in the upstream forward osmosis modules in the multi-stage, it is considered that the cleaning effect due to the osmotic pressure difference such as the sterilization effect due to the osmotic pressure shock is high.

[0061] 〔Treatment after forward osmosis treatment〕 As a method for separating and recovering water from the DS (the diluted DS discharged from the second chamber 12) from which water in the FS has been recovered by passing through the second chamber 12 of the forward osmosis module 1 due to the forward osmosis phenomenon, for example, reverse osmosis treatment, distillation, heating and cooling operations (thermal separation operations), etc. can be mentioned.

[0062] In the reverse osmosis (RO) treatment, the diluted DS discharged from the FO module 1 is pressurized by a booster pump to a pressure (hydrostatic pressure) higher than the osmotic pressure of the diluted DS and supplied to the RO module. By allowing the water in the diluted DS supplied to the RO module to permeate through the RO membrane, fresh water can be obtained from the diluted DS. The remaining diluted DS that did not permeate through the RO membrane is concentrated, and the concentrated diluted DS can be reused as DS.

[0063] In addition, when the draw substance contained in the DS is an inorganic salt, a low melting point substance, or the like, water in the DS may be separated and recovered by crystallization treatment. When the draw substance is a gas with high solubility in water, water in the DS may be separated and recovered by gas diffusion. When the draw substance is a stimulus-responsive substance such as a temperature-responsive substance, water in the DS may be separated and recovered by separation utilizing phase change. For example, when using a temperature-responsive polymer, a temperature change with the cloud point as the change point is made to separate water in the DS. When the draw substance is magnetic fine particles, water in the DS may be separated and recovered by magnetic separation. When the draw substance is a sugar solution, water in the DS may be separated and recovered by nanofiltration (NF).

[0064] In this way, using the forward osmosis treatment method (forward osmosis treatment apparatus) of the present embodiment, water can be separated and recovered from the feed solution (FS) by forward osmosis treatment using a semipermeable membrane. That is, the forward osmosis treatment method (forward osmosis treatment apparatus) of the present embodiment can be used, for example, in a seawater desalination method (seawater desalination apparatus) for obtaining fresh water from seawater or the like.

[0065] <Forward osmosis treatment apparatus> An example of a forward osmosis treatment apparatus that can be suitably used in the forward osmosis treatment method of the present embodiment will be described.

[0066] Referring to FIG. 1, the forward osmosis treatment apparatus of the present embodiment includes at least a forward osmosis module 1 and a tank 2 for storing the concentrated solution (concentrated feed solution). The forward osmosis module 1 has a semipermeable membrane 10, and a first chamber 11 and a second chamber 12 partitioned by the semipermeable membrane 10.

[0067] The forward osmosis treatment apparatus preferably further includes a pump 4 for flowing the concentrated solution stored in the tank 2 into the first chamber 11. The forward osmosis treatment apparatus may further include a flow rate adjustment valve for adjusting the flow rate of the concentrated solution supplied from the tank 2 to the first chamber.

[0068] The forward osmosis treatment apparatus may include a pump (not shown) for transferring the feed solution (FS) to the first chamber 11 of the forward osmosis module 1, and a pump (not shown) for transferring the draw solution (DS) to the inside (second chamber) 12 of the hollow fiber membrane 10.

[0069] The forward osmosis treatment apparatus preferably further includes a filtration device 3 for filtering the concentrated liquid stored in the tank 2 in the flow path connecting the tank 2 and the first chamber 11.

[0070] According to the forward osmosis treatment method (forward osmosis treatment apparatus) of the present embodiment, since microorganisms are killed by the osmotic pressure shock due to the osmotic pressure difference between the feed solution in the forward osmosis step and the concentrated liquid in the washing step, biofouling and organic fouling can be reduced.

[0071] Therefore, according to the forward osmosis treatment method (forward osmosis treatment apparatus) of the present embodiment, clogging (biofouling, organic fouling, etc.) due to contaminants on the semipermeable membrane can be effectively suppressed without the need for additional complicated devices, etc., and a decrease in the performance of the semipermeable membrane can be suppressed.

[0072] <Hollow fiber membrane module> Hereinafter, with reference to FIGS. 5 and 6, an example of a forward osmosis (FO) module (hollow fiber membrane module) using a hollow fiber membrane as a semipermeable membrane will be described.

[0073] When the forward osmosis module 1 is a hollow fiber membrane module, for example, a draw solution (DS) is supplied to the outside (second chamber) 12 of the hollow fiber membrane 10 of the hollow fiber membrane module (forward osmosis module) 1, and a feed solution (FS) is supplied into the inside (first chamber) 11 of the hollow fiber membrane 10 of the forward osmosis module 1. Thereby, FS and DS are brought into contact with each other through the hollow fiber membrane (semipermeable membrane) 10. In this state, due to the forward osmosis phenomenon, the water contained in FS permeates through the hollow fiber membrane 10 and moves into DS.

[0074] In FIGS. 5 and 6, the FO module (hollow fiber membrane module) 1 is a single element type hollow fiber membrane module in which one hollow fiber membrane element is loaded into one pressure vessel 100.

[0075] The forward osmosis module 1 has a semipermeable membrane (hollow fiber membrane) 10, an outside of the hollow fiber membrane (second chamber) 12 to which DS is supplied, and an inside of the hollow fiber membrane (hollow part: first chamber) 11 to which FS is supplied. The first chamber 11 and the second chamber 12 are partitioned by the hollow fiber membrane 10.

[0076] The hollow fiber membrane element includes a porous distribution pipe 13 having a plurality of holes 13a arranged at the center, a plurality of hollow fiber membranes 10 arranged around the porous distribution pipe 13, and a resin wall (end part 14) that fixes the porous distribution pipe 13 and the plurality of hollow fiber membranes 10 at both ends thereof. Each of the plurality of hollow fiber membranes 10 has openings 10a and 10b at both ends thereof.

[0077] Note that the form of the FO module 1 is not particularly limited, and it may be a module in which a plurality of hollow fiber membranes are arranged in a straight line, or a cross-wound type module in which a plurality of hollow fiber membranes are wound around a core tube.

[0078] The hollow fiber membrane element has a DS supply port 111a and a DS discharge port 111b that communicate with the inside 11 of the plurality of hollow fiber membranes 10 and the outside of the hollow fiber membrane module. The inflow side opening 10a of the hollow fiber membrane 10 is connected to the FS supply port 110a, and the outflow side opening 10b communicates with the FS discharge port 110b.

[0079] The porous distribution pipe 13 is not particularly limited as long as it is a tubular body having a plurality of holes 13a. By the porous distribution pipe 13, for example, the DS supplied into the hollow fiber membrane module from the DS supply port 111a can be distributed to the outside 12 of the hollow fiber membrane. The holes 13a are preferably provided radially in each direction with the central axis of the porous distribution pipe as a base point. Further, the porous distribution pipe 13 is preferably positioned at a substantially central portion of the hollow fiber membrane element.

[0080] FS flows into the interior 11 of the hollow fiber membrane 10 from the inflow-side opening 10a via the FS supply port 110a, flows out from the outflow-side opening 10b, and flows out to the outside via the FS discharge port 110b.

[0081] DS flows into the interior of the porous distribution pipe 13 via the DS supply port 111a, flows out from the holes 13a, and is supplied to the outside 12 of the hollow fiber membrane 10. The DS that has passed through the outside 12 of the hollow fiber membrane 10 flows out to the outside via the DS discharge port 111b.

[0082] In particular, when using an organic-based DS (DS containing an organic substance), in order to prevent the DS from leaking to the FS side, the hollow fiber membrane module 1 having the configuration shown in FIGS. 6 and 7 can also be used. The end portion 14 of the hollow fiber membrane element has a structure in which an outer peripheral ring (not shown) is fitted into the outer peripheral portion of the resin wall that seals and fixes the hollow fiber membrane 10. The hollow fiber membrane module in FIG. 6 is different from the hollow fiber membrane module in FIG. 5 in that O-ring grooves are provided on the outer peripheral surface of the outer peripheral ring of the outer peripheral portion of the resin wall at both ends of the hollow fiber membrane element. Also, between the hollow fiber membrane module in FIG. 6 and the hollow fiber membrane module in FIG. 5, the mounting position of the DS discharge port 111b provided on the side surface of the pressure vessel 100 is different. By providing a groove for an O-ring on the outer peripheral surface of the end portion 14 (outer peripheral ring) of the hollow fiber membrane element and installing an O-ring in the groove, the hollow fiber membrane element can be fixed liquid-tightly to the inner peripheral surface of the pressure vessel, preventing direct contact between the FS and the DS. The end portion of the hollow fiber membrane element has a structure in which an outer peripheral ring (not shown) is fitted into the outer peripheral portion of the end portion 14 composed of the resin wall and the outer peripheral ring that seals and fixes the hollow fiber membrane 10. On the other hand, the hollow fiber membrane module in FIG. 7 is different from the hollow fiber membrane module in FIG. 6 in that the O-ring groove is provided on the inner peripheral surface of the pressure vessel 100.

[0083] In the hollow fiber membrane modules shown in FIGS. 5, 6, and 7, in the above-described cleaning step (S2), the concentrated liquid stored in the tank 2 is supplied to the FS discharge port 110b, and the interior (first chamber) 11 of the hollow fiber membrane is flowed from the FS discharge port 110b in the direction of the FS supply port 110a (opposite to the direction of the arrow).

[0084] Here, the form in which DS is supplied to the outside of the hollow fiber membrane and FS is supplied to the inside of the hollow fiber membrane has been described, but it is not limited thereto. That is, FS may be supplied to the outside of the hollow fiber membrane and DS may be supplied to the inside of the hollow fiber membrane.

Explanation of Reference Numerals

[0085] 1 Forward osmosis module (hollow fiber membrane module), 10 Semipermeable membrane (hollow fiber membrane), 10a Inlet side opening, 10b Outlet side opening, 11 First chamber (inside of hollow fiber membrane), 12 Second chamber (outside of hollow fiber membrane), 100 Pressure vessel, 110a FS supply port, 110b FS discharge port, 111a DS supply port, 111b DS discharge port, 13 Porous distribution pipe, 13a Hole, 14 End, 2 Tank, 3 Filter device, 4 Pump.

Claims

1. A forward osmosis treatment method including a forward osmosis step using a forward osmosis module having a semipermeable membrane and a first chamber and a second chamber partitioned by the semipermeable membrane, and a cleaning step of cleaning the semipermeable membrane, wherein: In the forward osmosis step, a feed solution is supplied to the first chamber, a draw solution having an osmotic pressure higher than that of the feed solution is supplied to the second chamber, and the feed solution and the draw solution are brought into contact with each other through the semipermeable membrane, so that water contained in the feed solution is moved into the draw solution, a concentrated solution, which is the concentrated feed solution, is discharged from the first chamber, and at least a part of the concentrated solution is stored in a tank; In the cleaning step, the concentrated solution stored in the tank is flowed through the first chamber in a direction opposite to the flow direction of the feed solution in the forward osmosis step, and the draw solution is supplied to the second chamber to clean the semipermeable membrane. A forward osmosis treatment method.

2. The forward osmosis treatment method according to claim 1, wherein in the cleaning step, the supply of the draw solution to the second chamber is performed in the same manner as in the forward osmosis step before the cleaning step is performed.

3. The forward osmosis treatment method according to claim 1 or 2, wherein a chlorine-based bactericide is intermittently or continuously added to the feed solution supplied to the first chamber.

4. The forward osmosis treatment method according to claim 3, wherein at least one of the addition amount and the addition frequency of the chlorine-based bactericide is adjusted according to the implementation frequency or effect of the cleaning step.

5. The forward osmosis treatment method according to any one of claims 1 to 4, wherein the flow rate of the concentrated solution supplied from the tank to the first chamber is adjusted.

6. The forward osmosis treatment method according to any one of claims 1 to 5, wherein the concentrated solution stored in the tank is filtered, and after suspended matter contained in the concentrated solution is removed, it is supplied to the first chamber.

7. The forward osmosis treatment method according to any one of claims 1 to 6, wherein the concentrated solution stored in the tank is supplied to the first chamber after at least one of its pH, temperature, and redox potential is adjusted.

8. A forward osmosis treatment apparatus used in the forward osmosis treatment method according to any one of claims 1 to 7, comprising: A forward osmosis module including a semipermeable membrane, a first chamber and a second chamber partitioned by the semipermeable membrane; A tank for storing the concentrated solution. A forward osmosis treatment apparatus.

9. The forward osmosis treatment apparatus according to claim 8, further comprising a pump for flowing the concentrated liquid stored in the tank into the first chamber.

10. The forward osmosis treatment apparatus according to claim 8 or 9, further comprising a flow rate adjustment valve for adjusting the flow rate of the concentrated liquid supplied from the tank to the first chamber.

11. The forward osmosis treatment apparatus according to any one of claims 8 to 10, further comprising a filtration device for filtering the concentrated liquid stored in the tank in a flow path connecting the tank and the first chamber.

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