JP2014061486A - Water treatment method and water treatment system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a water treatment method and a water treatment system capable of relatively easily concentrating the water to be treated and efficiently treating the obtained concentrated water.SOLUTION: Provided is a water treatment method comprising:a step in which, in a state where the water to be treated is introduced into a positive osmosis membrane device and is made present on the primary side of a first semi-permeable membrane provided at the positive osmosis membrane device, and a hypertonic solution under the osmotic pressure higher than that of the water to be treated is made present, the water from the water to be treated is permeated from the primary side of the first semi-permeable membrane to the secondary side, thus the water to be treated is concentrated, and concentrated water is obtained; and a step in which the concentrated water is introduced into a reaction tank, and aeration treatment is performed.

Description

  The present invention relates to a water treatment method and a water treatment system using a forward osmosis membrane device.

  Conventionally, water treatment by an activated sludge method for aeration treatment of water to be treated in the presence of microorganisms is widely known, and membrane separation activated sludge method has recently been used as a method for performing water treatment by an activated sludge method with more compact equipment. It is becoming popular. The membrane separation activated sludge method increases the activated sludge concentration in the reaction tank using a microfiltration membrane (MF membrane) or ultrafiltration membrane (UF membrane) to enable highly efficient biological treatment. . Further, Patent Document 1 discloses a water treatment method using a reverse osmosis membrane that can be separated more precisely than an MF membrane or a UF membrane. Permeation is performed by subjecting water to be treated to a membrane separation treatment using a reverse osmosis membrane. A water treatment method that separates water and concentrated water and biologically treats the concentrated water is disclosed. According to the method disclosed in Patent Document 1, high-purity water can be obtained by using a reverse osmosis membrane, while concentrated water contains suspended substances, soluble carbon, nitrogen, phosphorus components, etc. in water to be treated. As a result, the biological treatment can be performed with more compact equipment.

JP 2009-72766 A

  However, when treating the water to be treated using a reverse osmosis membrane as disclosed in Patent Document 1, it is often necessary to perform advanced pretreatment to prevent clogging of the membrane, and the treatment tends to be complicated. Become. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a water treatment method and a water treatment system capable of concentrating water to be treated relatively easily and efficiently treating the obtained concentrated water. Is to provide.

  The water treatment method of the present invention that has been able to solve the above-mentioned problem is that the water to be treated is introduced into the forward osmosis membrane device and treated on the primary side of the first semipermeable membrane provided in the forward osmosis membrane device. By allowing water in the treated water to permeate from the primary side to the secondary side of the first semipermeable membrane in a state where a hypertonic solution having higher osmotic pressure than the treated water is present on the secondary side. The present invention is characterized in that it includes a step of concentrating water to be treated to obtain concentrated water and a step of introducing the concentrated water into a reaction vessel and subjecting to aeration. The water treatment method of the present invention employs a forward osmosis treatment instead of a reverse osmosis treatment to remove and concentrate water from the water to be treated, thereby creating an osmotic pressure difference across a semipermeable membrane as in the reverse osmosis treatment. In contrast, it is not necessary to apply excessive pressure to the water to be treated, and the tolerance for the concentration and size of the solids contained in the water to be treated is widened. Absent. Concentrated water obtained by forward osmosis treatment can reduce the bubbles supplied during the aeration treatment by increasing the salt concentration, and can improve the efficiency of dissolving oxygen in the concentrated water. As a result, the efficiency of the aeration process can be improved.

  The aeration treatment is preferably performed in the presence of microorganisms, whereby organic solutes (soluble substances) in the concentrated water can be removed. Aeration treated water obtained by aeration treatment in the presence of microorganisms may be returned to the forward osmosis membrane device, thereby reducing the solute concentration of water to be treated on the primary side of the first semipermeable membrane. It becomes possible to increase the amount of water permeated through one semipermeable membrane.

  The water treatment method of the present invention further introduces a hypertonic solution into the reverse osmosis membrane device, and permeates the water in the hypertonic solution from the primary side to the secondary side of the second semipermeable membrane provided in the reverse osmosis membrane device. It is preferable to have the process of obtaining treated water by making it, and the process of returning the said hypertonic solution from a reverse osmosis membrane apparatus to a forward osmosis membrane apparatus. In this case, the hypertonic solution circulates between the forward osmosis membrane device and the reverse osmosis membrane device, and the hypertonic solution supplied to the forward osmosis membrane device is concentrated by the reverse osmosis membrane device to maintain the solute concentration as high as desired. Thus, the forward osmosis treatment can be stably performed.

  The present invention also provides a water treatment system suitably used in the water treatment method of the present invention. The water treatment system of the present invention includes a first semipermeable membrane, a primary side on which the treated water exists with the first semipermeable membrane interposed therebetween, and a secondary side on which a hypertonic solution having a higher osmotic pressure than the treated water exists. A forward osmosis membrane device in which the water to be treated is concentrated to obtain concentrated water by permeating the water in the treated water from the primary side to the secondary side of the first semipermeable membrane; And a reaction tank for aeration treatment of the concentrated water discharged from the primary side of the first semipermeable membrane. The water treatment system of the present invention further communicates with the outflow part of the reaction vessel and the primary inflow part of the first semipermeable membrane of the forward osmosis membrane device, and aeration treated water in the reaction vessel is supplied to the first osmosis membrane device. A return channel for transferring to the primary side of the semipermeable membrane may be provided. And a second semipermeable membrane, having a primary side on which the hypertonic solution exists and a secondary side on which treated water having a lower osmotic pressure than the hypertonic solution exists, with the second semipermeable membrane interposed therebetween, A reverse osmosis membrane device is further provided to obtain treated water by permeating the water from the primary side to the secondary side of the second semipermeable membrane; the secondary side outflow portion of the first semipermeable membrane and the second semipermeable membrane A first flow path communicating with the primary side inlet of the membrane and transferring the hypertonic solution from the secondary side of the first semipermeable membrane to the primary side of the second semipermeable membrane; the primary side outflow of the second semipermeable membrane; And a second flow path for communicating the hypertonic solution from the primary side of the second semipermeable membrane to the secondary side of the first semipermeable membrane. It is also preferable.

  The forward osmosis membrane device may be provided in the water to be treated. By providing the forward osmosis membrane device in the water to be treated, water pressure is applied to the treated water on the primary side of the first semipermeable membrane corresponding to the depth of water in which the forward osmosis membrane device is installed, and the primary of the first semipermeable membrane. The penetration of water from the side to the secondary side is promoted, and it becomes easier to concentrate the water to be treated.

  According to the water treatment method and the water treatment system of the present invention, by adopting forward osmosis treatment to remove and concentrate water from the water to be treated, the water to be treated can be concentrated relatively easily, Furthermore, since the concentrated water obtained has a high salt concentration, bubbles supplied by the aeration treatment can be reduced, and the efficiency of the aeration treatment can be improved by increasing the efficiency of dissolving oxygen in the concentrated water. it can.

An example of the water treatment system of this invention is represented. The other example of the water treatment system of this invention is represented. The other example of the water treatment system of this invention is represented. The other example of the water treatment system of this invention is represented.

  The present invention relates to a water treatment method and a water treatment system using a forward osmosis membrane device, and efficiently treats the water to be treated by aeration treatment by increasing the solute concentration of the water to be treated using the forward osmosis membrane device. It is possible to do.

  The water treatment method of the present invention concentrates the water to be treated by introducing the water to be treated into the forward osmosis membrane device and permeating the water in the water to be treated into the semipermeable membrane provided in the forward osmosis membrane device. A forward osmosis treatment step for obtaining concentrated water, and an aeration step for introducing the concentrated water into the reaction tank and performing an aeration treatment. By adopting forward osmosis treatment instead of reverse osmosis treatment to concentrate the treated water, it is possible to avoid overloading the treated water against the osmotic pressure difference across the semipermeable membrane. In the osmosis treatment, the permissible range for the concentration and size of the solid content contained in the water to be treated is widened, so that it is not necessary to perform a pretreatment as advanced as the reverse osmosis treatment. As a result of concentration of the water to be treated in the forward osmosis treatment step, the salt concentration is increased, and the bubbles supplied to the concentrated water during the aeration treatment can be reduced. Therefore, the efficiency of dissolving oxygen in concentrated water is increased, and the efficiency of the aeration process can be improved. Further, although depending on the design conditions of the water treatment system, the amount of concentrated water obtained can be reduced from the amount of water to be treated, and the reaction vessel can be made compact.

  In the present invention, the water to be treated is not particularly limited. The treated water includes organic substances and inorganic substances that can be treated by aeration treatment. For example, the aeration treatment reduces COD (chemical oxygen demand) and BOD (biological oxygen demand) of the treated water. Those are preferred. The water to be treated contains, for example, an organic compound that can be oxidized by aeration treatment. If such water to be treated is used, COD in the water to be treated can be reduced by the water treatment method or the water treatment system of the present invention. Can do. When the water to be treated contains a biodegradable organic compound, the BOD or the like of the water to be treated can be reduced by performing aeration treatment in the presence of microorganisms. The water to be treated may contain an inorganic compound such as a divalent iron salt, and it is possible to oxidize and insolubilize the divalent iron ion by aeration treatment. Examples of water to be treated used in the present invention include sewage, human waste, livestock manure, kitchen wastewater, factory wastewater, landfill leachate, and the like.

  In the forward osmosis treatment step, the treated water is introduced into the forward osmosis membrane device, and the treated water is concentrated by the forward osmosis membrane device to obtain concentrated water having an increased solute concentration. The forward osmosis membrane device is provided with a semipermeable membrane for infiltrating water in the water to be treated. In the present invention, the semipermeable membrane provided in the forward osmosis membrane device is referred to as a “first semipermeable membrane”. Called.

  The first semipermeable membrane provided in the forward osmosis membrane device is not particularly limited as long as it is a membrane that transmits at least water molecules and does not transmit molecules or ions of a certain size or larger, and uses a known semipermeable membrane. Can do. As the first semipermeable membrane, a semipermeable membrane generally used for reverse osmosis treatment may be used, and the material constituting the membrane, the type of membrane, and the like are not particularly limited. Examples of the constituent material of the membrane include cellulose acetate, aromatic polyamide, polyvinyl alcohol, polysulfone, and the like, and examples of the membrane include a hollow fiber membrane, a spiral membrane, and a tubular membrane.

  The forward osmosis membrane device has a primary side and a secondary side across a first semipermeable membrane. In the present invention, the primary side and the secondary side sandwiching the semipermeable membrane are determined based on the permeation direction of the water that permeates the semipermeable membrane, and the water penetrates from the primary side to the secondary side as a whole. To do. It should be noted that water penetrates from the primary side to the secondary side of the semipermeable membrane as a whole even if a part of the water molecules penetrates from the secondary side to the primary side of the semipermeable membrane, Means that permeation from the primary side to the secondary side of the semipermeable membrane is dominant. The forward osmosis membrane device is divided into a primary side and a secondary side of the first semipermeable membrane across the first semipermeable membrane, and water to be treated exists on the primary side of the first semipermeable membrane. .

  In the forward osmosis membrane device, a hypertonic solution having a higher osmotic pressure than the water to be treated exists on the secondary side of the first semipermeable membrane. That is, in the forward osmosis membrane device, the osmotic pressure of the water to be treated existing on the primary side across the first semipermeable membrane is relatively low, and the osmotic pressure of the hypertonic solution existing on the secondary side is relatively high. . In the forward osmosis membrane device, the water in the water to be treated permeates from the primary side to the secondary side of the first semipermeable membrane using the osmotic pressure difference between the water to be treated and the hypertonic solution.

  The hypertonic solution is not particularly limited as long as it is an aqueous solution in which a solute is dissolved and exhibits an osmotic pressure higher than that of water to be treated. Under isothermal conditions, the hypertonic solution having a higher osmotic pressure than the treated water means that the hypertonic solution has a higher solute concentration (molar concentration) than the treated water. The hypertonic solution may be artificially prepared, or a solution having a high solute concentration existing outside may be used as the hypertonic solution. In the former case, a substance soluble in water may be used as the solute. For example, salts, saccharides, water-soluble polymers and the like can be used as the solute. In addition, an acid or an alkali may be used as a solute as long as it does not cause a problem with the semipermeable membrane or the device. In the latter case, brine such as seawater and salt lake water; urine and the like can be used as the hypertonic solution. Further, human waste treated water, landfill leachate treated water, some factory waste water treated water, and the like may contain salts at a relatively high concentration, and such treated water may be used as a hypertonic solution.

  The hypertonic solution may be prepared by reverse osmosis treatment. For example, the solute concentration of a solution having a high solute concentration present outside may be further increased by reverse osmosis treatment and used as a hypertonic solution. In the forward osmosis treatment process, the hypertonic solution is diluted by the permeation of water from the primary side to the secondary side of the first semipermeable membrane, but the hypertonic solution diluted with water is concentrated by the reverse osmosis treatment. The solute concentration may be increased and supplied again to the secondary side of the first semipermeable membrane of the forward osmosis membrane device.

  The osmotic pressures of the water to be treated and the hypertonic solution can be obtained based on the van't Hoff equation using the solute concentration (molar concentration) and temperature as parameters. Alternatively, after setting the water to be treated and the hypertonic solution to have the same liquid level across the semipermeable membrane, the permeation of the water to be treated and the hypertonic solution is observed by observing changes in the respective liquid levels. The magnitude of the pressure may be determined. In this case, if the liquid surface height of the hypertonic solution increases, it is determined that the hypertonic solution has a higher osmotic pressure than the water to be treated.

  In the forward osmosis treatment step, concentrated water is obtained from the treated water by allowing water in the treated water to permeate from the primary side to the secondary side of the first semipermeable membrane as described above. At this time, by adopting forward osmosis treatment instead of reverse osmosis treatment to remove and concentrate water from the treated water, it is treated against the osmotic pressure difference across the semipermeable membrane like reverse osmosis treatment. There is no need to put excessive pressure on the water. Further, in the treatment with a reverse osmosis membrane device, in general, in order to prevent clogging of the device, advanced pretreatment using a microfiltration membrane (MF membrane), an ultrafiltration membrane (UF membrane), activated carbon or the like is required. However, in the treatment with the forward osmosis membrane device, the tolerance for the concentration and size of the solid content contained in the water to be treated is widened, so the device is less likely to be clogged even if the pretreatment is not as advanced as reverse osmosis treatment. . That is, in the forward osmosis membrane device, forward osmosis treatment can be performed even when water to be treated having a slightly higher solid content concentration or water to be treated containing solid contents of various particle sizes is used. Therefore, it becomes possible to efficiently concentrate the water to be treated, and it is not necessary to provide ancillary equipment (for example, pretreatment equipment) for preventing clogging of the apparatus.

  The concentrated water obtained in the forward osmosis treatment step, that is, the concentrated water discharged from the primary side of the first semipermeable membrane of the forward osmosis membrane device is introduced into the reaction tank and aerated. In the aeration process, an oxygen-containing gas (for example, air or pure oxygen) is introduced into the concentrated water to perform an aeration process. By subjecting the concentrated water to an aeration process in the aeration process, COD, BOD, and the like of the concentrated water can be reduced.

  In aeration treatment, it is known from experience that the higher the salt concentration (inorganic ion concentration) of water to be aerated, the smaller the bubbles supplied by aeration. In the present invention, the water to be treated is concentrated to give a salt. By increasing the concentration, bubbles supplied to the concentrated water during the aeration process can be reduced. As a result, the efficiency of dissolving oxygen in concentrated water is increased, and the efficiency of the aeration process can be improved. In addition, depending on the return conditions of the aerated treated water obtained by the aerated treatment, it becomes possible to reduce the amount of concentrated water from the amount of treated water by concentrating the treated water in the forward osmosis treatment process, The reaction tank for aeration can be made compact.

  The reaction tank is equipped with an air diffuser for aeration treatment of concentrated water. As a diffuser, a known diffuser generally used for water treatment may be used. The air diffuser may supply oxygen-containing gas to the concentrated water in the reaction tank, or supply concentrated water containing the oxygen-containing gas to the reaction tank.

  When supplying the oxygen-containing gas to the reaction tank, for example, a membrane type diffuser, a diffuser type diffuser, a porous diffuser, or the like may be used as the diffuser. Moreover, you may use the underwater mechanical stirring apparatus which supplies oxygen-containing gas to concentrated water, subdividing with a stirring blade.

  When supplying concentrated water containing an oxygen-containing gas to the reaction tank, for example, a pipe line provided with a gas supply means is provided in the concentrated water of the reaction tank, and the concentrated water is supplied to the reaction tank through the pipe line. Thus, the oxygen-containing gas may be supplied from the gas supply means to the concentrated water flowing through the pipe and supplied to the reaction vessel. As a gas supply means, a gas supply port may be provided in the pipeline, or a gas supply tube may be inserted into the pipeline, and the end of the side not connected to the gas supply port or the pipeline of the gas supply tube should be open to the atmosphere. The oxygen-containing gas may be forcibly supplied by connecting a blower, a compressor, or the like. If the gas supply port or the end of the gas supply pipe that is not connected to the pipe line is open to the atmosphere, the concentrated water flows through the pipe line, and the air in the atmosphere is naturally aspirated by the ejector effect. Air is mixed in the concentrated water. The conduit through which the concentrated water flows is preferably provided as a circulation conduit so that the concentrated water circulates between the reaction tank.

  In the aeration step, it is preferable to perform the aeration treatment in the presence of microorganisms. By performing the aeration treatment in the presence of microorganisms, the concentrated water can be subjected to an aerobic biological treatment, and organic solutes (soluble components) in the concentrated water can be removed. For example, soluble carbon components in concentrated water are removed from the concentrated water as carbon dioxide gas, soluble nitrogen components are removed from the concentrated water as nitrogen gas, and soluble phosphorus components are immobilized on sludge and removed from the concentrated water. The Examples of the aeration process in the presence of microorganisms include an activated sludge method (including a membrane separation activated sludge method), a carrier method, a fixed bed biofilm method, and the like.

  The reaction tank should just have the tank which performs an aeration process at least, and may have the tank which does not perform an aeration process. For example, when the aeration treatment is performed in the presence of microorganisms, nitrogen and / or phosphorus contained in the concentrated water can be removed by further providing an anaerobic tank and / or an oxygen-free tank as a reaction tank. In this case, the concentrated water discharged from the forward osmosis membrane device is generally introduced into an anaerobic tank or an oxygen-free tank as a reaction tank, but in the present invention, the concentrated water is introduced into an aerobic tank. It may be introduced into an anaerobic tank or an oxygen-free tank in advance.

  The concentrated water discharged from the forward osmosis membrane device may be introduced into a settling tank, a flow rate adjusting tank or the like before being introduced into the reaction tank. That is, the concentrated water discharged from the forward osmosis membrane device may be introduced into another tank or device prior to being introduced into the reaction tank.

  Aeration-treated water obtained by aeration treatment of concentrated water in the aeration process is discharged into sewage, rivers, etc., or further processed according to the water quality. The further treatment may be appropriately selected from conventionally known methods. For example, when the aeration treatment is performed in the presence of microorganisms, the aeration treatment water may be subjected to solid-liquid separation treatment (for example, precipitation treatment or membrane separation treatment). preferable. By performing the solid-liquid separation treatment, aerated treated water having a reduced solid content concentration can be obtained. Further, when the dissolved metal concentration of the aerated treated water is high, metal removal treatment (for example, coagulation precipitation treatment or chelation treatment by addition of acid or alkali) may be performed. When solid content such as sludge is generated during the treatment, volume reduction treatment such as concentration and dehydration may be performed.

  When the aeration treatment is performed in the presence of microorganisms, the carbon component, nitrogen component, phosphorus component and the like in the concentrated water are removed, and the solute concentration is reduced. Moreover, also when carrying out the aeration process of the concentrated water containing a bivalent iron ion, bivalent iron ion is oxidized and insolubilized, and the solute density | concentration of concentrated water reduces. Thus, when the solute concentration in the concentrated water is reduced by the aeration treatment, it is also preferable to return the aeration treated water obtained by the aeration treatment to the forward osmosis membrane device, whereby the treated water on the primary side of the first semipermeable membrane. It is possible to increase the amount of water permeated through the first semipermeable membrane by lowering the solute concentration. The aerated treated water returned to the forward osmosis membrane device may have been subjected to solid-liquid separation treatment to reduce the solid content concentration, or the solute concentration further reduced by metal removal treatment. The aerated treated water may include those subjected to these treatments.

  When returning aerated treated water to the forward osmosis membrane device, it is sufficient that a part or all of the aerated treated water is returned to the forward osmosis membrane device, but only a part of the aerated treated water is returned to the forward osmosis membrane device. Is preferred. By returning only a part of the aerated treated water to the forward osmosis membrane device, for example, inorganic salts that cannot be treated by microorganisms are not excessively concentrated in the concentrated water or aerated treated water, and the primary semi-permeable membrane is covered. It is prevented that the solute concentration of the treated water (in this case, the treated aerated treated water will include the returned aerated treated water) becomes too high and the amount of water permeated through the first semipermeable membrane is greatly reduced. The From the viewpoint of making the reaction tank compact, it is preferable that the amount of aerated treated water returned to the forward osmosis membrane device is smaller than the amount of water permeated through the first semipermeable membrane.

  Next, configuration examples of the water treatment method and the water treatment system of the present invention will be described with reference to the drawings. The present invention is not limited to the embodiments shown in the drawings.

  FIG. 1 shows a first embodiment of the water treatment system of the present invention. The water treatment system shown in FIG. 1 has a forward osmosis membrane device 1 provided with a first semipermeable membrane and a reaction tank 11 provided with an aeration device 12. The water to be treated 21 is introduced into the forward osmosis membrane device 1 and concentrated to obtain concentrated water 25. The concentrated water 25 is introduced into the reaction tank 11 and subjected to an aeration process, whereby an aerated process water 26 is obtained.

  The forward osmosis membrane device 1 has a primary side and a secondary side across a first semipermeable membrane. The treated water 21 is introduced to the primary side of the first semipermeable membrane, and the hypertonic solution 22 having a higher osmotic pressure than the treated water 21 is introduced to the secondary side of the first semipermeable membrane. As a result, in the forward osmosis membrane device 1, the treated water 21 exists on the primary side of the first semipermeable membrane, and the hypertonic solution 22 having a higher osmotic pressure than the treated water 21 exists on the secondary side. . In the forward osmosis membrane device 1, in this state, the water to be treated 21 is permeated from the primary side to the secondary side of the first semipermeable membrane, whereby the water to be treated 21 is concentrated and the concentrated water 25 is obtained. .

  In the water treatment system shown in FIG. 1, seawater is used for the hypertonic solution 22 introduced into the secondary side of the first semipermeable membrane. Seawater is pumped up from the sea and supplied to the forward osmosis membrane device 1, and the hypertonic solution 23 discharged from the forward osmosis membrane device 1 is returned to the sea. Thus, by using seawater as the hypertonic solution 22, forward osmosis treatment can be performed at low cost.

  The concentrated water 25 concentrated by the forward osmosis membrane device 1 is introduced into the reaction tank 11 equipped with the air diffuser 12 and aerated. At this time, the concentrated water 25 has a smaller amount of water than the water 21 to be treated, so that the volume of the reaction tank 11 can be made compact. In addition, since the concentrated water 25 has a higher salt concentration than the water 21 to be treated, the bubbles supplied from the air diffuser 12 in the reaction tank 11 can be reduced to increase the efficiency of dissolving oxygen in the concentrated water 25. The efficiency of the aeration process can be improved.

  FIG. 2 shows a second embodiment of the water treatment system of the present invention. The water treatment system of the second embodiment does not use seawater as a hypertonic solution, but circulates and uses the hypertonic solution while treating it with a reverse osmosis membrane device, and forwardly permeates aeration-treated water that has been solid-liquid separated. It differs from the water treatment system of the first embodiment in that it is returned to the membrane device. In the following description, the description of the same part as the description of the first embodiment is omitted.

  The water treatment system shown in FIG. 2 further includes a reverse osmosis membrane device 5 having a second semipermeable membrane. As the reverse osmosis membrane device 5, a known device used for reverse osmosis treatment may be used, and the material and the form of the membrane constituting the second semipermeable membrane of the reverse osmosis membrane device 5 are not particularly limited.

  The reverse osmosis membrane device 5 has a primary side and a secondary side across the second semipermeable membrane. And the 1st flow path 6 is provided in communication with the secondary side outflow part of the 1st semipermeable membrane of the forward osmosis membrane apparatus 1, and the primary inflow part of the 2nd semipermeable membrane of the reverse osmosis membrane apparatus 5, A second flow path 7 is provided in communication with the primary side outflow portion of the second semipermeable membrane of the reverse osmosis membrane device 5 and the secondary side inflow portion of the first semipermeable membrane of the forward osmosis membrane device 1. The secondary inflow portion and the secondary outflow portion of the first semipermeable membrane, and the primary inflow portion and the primary outflow portion of the second semipermeable membrane are respectively the portion into which the hypertonic solutions 22 and 23 flow in or the outflow portion. To be determined

  The hypertonic solution 23 flowing out from the secondary side of the first semipermeable membrane of the forward osmosis membrane device 1 passes through the first flow path 6 and is transferred to the primary side of the second semipermeable membrane of the reverse osmosis membrane device 5. . In the reverse osmosis membrane device 5, the hypertonic solution 23 exists on the primary side of the second semipermeable membrane, while the treated water having a lower osmotic pressure than the hypertonic solution 23 is present on the secondary side of the second semipermeable membrane. 24 exists. In the reverse osmosis membrane device 5, in this state, the hypertonic solution 23 existing on the primary side of the second semipermeable membrane is pressurized, so that the water in the hypertonic solution 23 is changed from the primary side to the secondary side of the second semipermeable membrane. The treated water 24 is obtained by infiltration. As a result, water is removed from the hypertonic solution 23 by the reverse osmosis membrane device 5 and the solute concentration is increased. The hypertonic solution 22 whose solute concentration has been increased and has flowed out from the primary side of the second semipermeable membrane of the reverse osmosis membrane device 5 passes through the second flow path 7 and becomes the second semipermeable membrane of the forward osmosis membrane device 1. It is transferred to the next side. That is, the hypertonic solution 23 flowing out from the forward osmosis membrane device 1 is introduced into the reverse osmosis membrane device 5 to increase the solute concentration, and the hypertonic solution 22 having the increased solute concentration is transferred from the reverse osmosis membrane device 5 to the forward osmosis membrane device. 1 will be returned.

  When the water treatment system shown in FIG. 2 is used, the water treatment method of the present invention introduces water to be treated into the forward osmosis membrane device, and places it on the primary side of the first semipermeable membrane provided in the forward osmosis membrane device. Water to be treated is allowed to permeate from the primary side to the secondary side of the first semipermeable membrane in a state where the water to be treated is present and a hypertonic solution having a higher osmotic pressure than the water to be treated is present on the secondary side. The process of concentrating water to be treated to obtain concentrated water, and introducing a hypertonic solution into the reverse osmosis membrane device from the primary side to the secondary side of the second semipermeable membrane provided in the reverse osmosis membrane device There are a step of obtaining treated water by permeating water in the hypertonic solution and a step of returning the hypertonic solution from the reverse osmosis membrane device to the forward osmosis membrane device.

  In the water treatment system shown in FIG. 2, the hypertonic solution 22 and 23 supplied to the forward osmosis membrane device 1 by circulating the hypertonic solutions 22 and 23 between the forward osmosis membrane device 1 and the reverse osmosis membrane device 5 in this way. Thus, the forward osmosis treatment can be stably carried out while maintaining the solute concentration of the solution as high as desired. That is, the hypertonic solution 23 that flows out from the forward osmosis membrane device 1 is diluted with water and has a lower solute concentration than the hypertonic solution 22 that flows into the forward osmosis membrane device 1. Is supplied again, a sufficient osmotic pressure difference is not ensured between the primary side and the secondary side of the first semipermeable membrane of the forward osmosis membrane device 1, and the amount of water permeating through the first semipermeable membrane is reduced. Therefore, by treating the hypertonic solution 23 flowing out from the forward osmosis membrane device 1 with the reverse osmosis membrane device 5 and returning it to the forward osmosis membrane device 1, the hypertonic solution 22 having an increased solute concentration can be obtained. 1 so that the forward osmosis treatment can be performed stably.

  Further, since the hypertonic solutions 22 and 23 basically circulate through a closed system between the forward osmosis membrane device 1 and the reverse osmosis membrane device 5, contamination of impurities and the like is prevented, and a microfiltration membrane (MF membrane) ), Ultrafiltration membrane (UF membrane), pretreatment with activated carbon or the like, and reverse osmosis treatment can be performed relatively easily.

  The second flow path 7 is preferably provided with a solute concentration adjusting means for the hypertonic solution 22 introduced into the forward osmosis membrane device 1. In FIG. 2, an adjustment tank 9 is provided in the second flow path 7, a solute or dilution water supply device 10 is provided in the adjustment tank 9, and the solute or dilution water is supplied from the supply device 10, thereby allowing the hypertonic solution 22. It is comprised so that the solute density | concentration of can be adjusted. In order to adjust the permeation amount of the first semipermeable membrane of water in the treated water 21 in the forward osmosis membrane device 1, adjusting the solute concentration of the hypertonic solution 22 is a main operating factor. Accordingly, when the hypertonic solution 22 flowing out from the reverse osmosis membrane device 5 does not have a desired solute concentration, the solute concentration of the hypertonic solution 22 is adjusted by the solute concentration adjusting means provided in the second flow path 7. It is preferable to do.

  To the hypertonic solutions 22 and 23, an agent for cleaning the first semipermeable membrane of the forward osmosis membrane device 1 or the second semipermeable membrane of the reverse osmosis membrane device 5 and an agent for preventing fouling are added. Also good. Such agents include acids, alkalis, bactericides, oxidants and the like.

  In the water treatment system shown in FIG. 2, aeration treatment is performed in the presence of microorganisms, and sludge is generated by aeration treatment (aerobic biological treatment) of the concentrated water 25 in the reaction tank 11. Therefore, the aerated treated water 26 containing sludge (microorganisms) flowing out from the reaction tank 11 is solid-liquid separated into the aerated treated water 26 ′ and the sludge 27 which are solid-liquid separated in the sedimentation tank 14 to reduce the solid content concentration. The The aerated treated water 26 ′ that has been subjected to solid-liquid separation is discharged as it is depending on the water quality, or further processed. The sludge 27 may be subjected to volume reduction processing such as concentration and dehydration. Alternatively, at least a part of the sludge 27 may be returned to the reaction tank 11 to adjust the microorganism concentration in the reaction tank 11.

  In the water treatment system shown in FIG. 2, the aerated treated water 26 ′ flowing out from the reaction tank 11 and separated into solid and liquid in the precipitation tank 14 is returned to the forward osmosis membrane device 1. For this purpose, a return passage 15 is provided which communicates with the outflow portion of the reaction tank 11 and the primary inflow portion of the first semipermeable membrane of the forward osmosis membrane device 1. The return flow path 15 is provided so as to return the aerated treated water 26 flowing out from the reaction tank 11 to the primary inflow portion of the first semipermeable membrane of the forward osmosis membrane device 1 directly or via another device or flow path. It only has to be done. The aerated treated water 26 ′ is reduced in solute concentration by being subjected to aerobic biological treatment in the reaction tank 11. Therefore, by introducing this into the primary side of the first semipermeable membrane of the forward osmosis membrane device 1, Decreasing the solute concentration of the treated water on the primary side of the one semipermeable membrane (including the returned aerated treated water 26 ′) to increase the amount of water permeated through the first semipermeable membrane. It becomes possible.

  FIG. 3 shows a third embodiment of the water treatment system of the present invention. In the water treatment system of the third embodiment, the adjustment tank 8 is provided in the first flow path 6, the submerged membrane filter medium 13 is provided in the reaction tank 11 instead of the precipitation tank 14, and the membrane filter medium 13 is different from the water treatment system of the second embodiment in that the membrane filtrate obtained by solid-liquid separation at 13 is returned to the forward osmosis membrane device 1 as aeration treated water 26. In the following description, the description of the same part as the description of the second embodiment is omitted.

  In the water treatment system shown in FIG. 3, the adjustment tank 8 is provided in the first flow path 6 of the circulation line of the hypertonic solutions 22 and 23, and the adjustment tank 9 is provided in the second flow path 7. The adjustment tank 8 can receive and store the hypertonic solution 23 flowing out from the forward osmosis membrane device 1, and can supply the hypertonic solution 23 to the reverse osmosis membrane device 5 through the first flow path 6. The adjustment tank 9 can receive and store the hypertonic solution 22 that has flowed out of the reverse osmosis membrane device 5, and can supply the hypertonic solution 22 to the forward osmosis membrane device 1 through the second flow path 7. By providing the adjustment tanks 8 and 9 in this way, the processing of the forward osmosis membrane device 1 and the reverse osmosis membrane device 5 can be performed independently.

  For example, in the water treatment system shown in FIG. 2, the amount of the hypertonic solution 23 introduced into the reverse osmosis membrane device 5 is the treatment capacity of the forward osmosis membrane device 1, that is, the hypertonic solution introduced into the forward osmosis membrane device 1. It depends on the amount of 22 and the amount of water permeated through the first semipermeable membrane. However, in the water treatment system shown in FIG. 3, fluctuations in the treatment capacity of the forward osmosis membrane device 1 can be mitigated by the adjustment tank 8, and the amount of the hypertonic solution 23 introduced into the reverse osmosis membrane device 5 can be reduced by forward osmosis. It can be set independently from the processing capability of the membrane device 1. Similarly, fluctuations in the processing capacity of the reverse osmosis membrane device 5 can be mitigated by the adjustment tank 9, and the amount of the hypertonic solution 22 introduced into the forward osmosis membrane device 1 is independent of the processing capacity of the reverse osmosis membrane device 5. Can be set.

  In the water treatment system shown in FIG. 3, a membrane filter medium 13 for solid-liquid separation is provided so as to be immersed in the concentrated water 25 of the reaction tank 11. By immersing the membrane filter medium 13 in the concentrated water 25 of the reaction tank 11, the microorganism concentration (active sludge concentration) of the concentrated water 25 in the reaction tank 11 can be kept high, and the processing load per volume of the reaction tank 11 can be increased. The reaction tank 11 can be made more compact. Moreover, the solid content contained in the concentrated water 25 can be highly solid-liquid separated by the membrane filter medium 13 to obtain the aerated treated water 26 having a very low solid content concentration. The aerated treated water 26 is returned to the primary side of the first semipermeable membrane of the forward osmosis membrane device 1 through the return flow path 15. From the reaction tank 11, concentrated water 25 containing microorganisms (activated sludge) at a high concentration is periodically extracted as sludge 28, and the microorganism concentration (active sludge concentration) in the concentrated water 25 in the reaction tank 11 is adjusted to a desired level. It is preferable.

  The membrane filter medium 13 is preferably provided above the air diffuser 12. By providing the membrane filter medium 13 in this manner, the surface (membrane surface) of the membrane filter medium 13 by the bubbles supplied from the air diffuser 12. Can be washed by a cross flow method, and a stable solid-liquid separation process using the membrane filter medium 13 can be realized.

  As the membrane filter 13, a microfiltration membrane (MF membrane) or an ultrafiltration membrane (UF membrane) may be used. There are no particular restrictions on the material or form of the membrane filter medium 13, and examples of the membrane material include organic membranes such as cellulose acetate, polysulfone, polyethylene, chlorinated polyethylene, polypropylene, and polyacrylonitrile; alumina, zirconia, and the like. Examples of the type of membrane include a hollow fiber membrane, a tubular membrane, a flat membrane, and a monolith membrane.

  FIG. 4 shows a fourth embodiment of the water treatment system of the present invention. In the water treatment system of the fourth embodiment, the forward osmosis membrane device 1 is provided in the water to be treated 21 and the reaction tank 11 is composed of an anaerobic tank 11a and an aerobic tank 11b. Different from the water treatment system of the third embodiment. In the following description, the description of the part overlapping with the description of the third embodiment is omitted.

  In the water treatment system shown in FIG. 4, the forward osmosis membrane device 1 is provided in the water tank 2, and the forward osmosis membrane device 1 is immersed in the water to be treated 21 in the water tank 2. By supplying the treated water 21 to the water tank 2, the treated water 21 is introduced to the primary side of the first semipermeable membrane of the forward osmosis membrane device 1. By providing the forward osmosis membrane device 1 in the treated water 21, water pressure is applied to the treated water 21 on the primary side of the first semipermeable membrane corresponding to the depth of water in which the forward osmosis membrane device 1 is installed. The permeation of water from the primary side to the secondary side of the semipermeable membrane is promoted, and the water 21 to be treated is easily concentrated.

  When the forward osmosis membrane device 1 is provided in the water 21 to be treated, it is preferable to provide the air diffuser 3 in the water tank 2 below the forward osmosis membrane device 1. By providing the air diffuser 3 as described above, the membrane surface of the first semipermeable membrane of the forward osmosis membrane device 1 can be washed by the cross-flow method with the bubbles supplied from the air diffuser 3. It prevents clogging of the permeable membrane and facilitates the forward osmosis treatment stably. As the air diffuser 3 installed in the water tank 2, an air diffuser that can be installed in the reaction tank 11 (aerobic tank 11b) may be used.

  In the water treatment system shown in FIG. 4, a screen 4 for removing impurities is provided between the inflow portion of the water to be treated 21 in the water tank 2 and the forward osmosis membrane device 1. By providing the screen 4, coarse impurities are removed from the water 21 to be treated, damage to the forward osmosis membrane device 1 and other facilities and equipment can be prevented, and water treatment can be suitably performed.

  In the water treatment system shown in FIG. 4, the reaction tank 11 includes an anaerobic tank (anoxic tank) 11a and an aerobic tank 11b, and a membrane filter medium 13 is immersed in the aerobic tank 11b. The concentrated water 25 concentrated in the forward osmosis membrane device 1 is first introduced into the anaerobic tank 11a of the reaction tank 11, and then introduced into the aerobic tank 11b. The sludge 28 is extracted from the aerobic tank 11b, and at least a part of the sludge 28 is returned to the anaerobic tank 11a. By treating the concentrated water 25 in this way, nitrogen in the concentrated water 25 can be biologically removed. That is, organic nitrogen in the concentrated water 25 is nitrified in the aerobic tank 11b, and this is returned to the anaerobic tank 11a and denitrified using the BOD in the concentrated water 25, whereby the organic nitrogen in the concentrated water 25 is obtained. Nitrogen can be removed as nitrogen gas.

  The present invention can be used for water treatment of sewage, human waste, livestock manure, kitchen wastewater, factory wastewater, landfill leachate and the like.

1: Forward osmosis membrane device 5: Reverse osmosis membrane device 6: First flow channel 7: Second flow channel 11: Reaction tank 12: Air diffuser 15: Return flow channel 21: Water to be treated 22, 23: Hypertonic solution 24 : Treated water 25: Concentrated water 26, 26 ': Aerated treated water

Claims (8)

The treated water is introduced into the forward osmosis membrane device, the treated water is present on the primary side of the first semipermeable membrane provided in the forward osmosis membrane device, and the osmotic pressure is higher on the secondary side than the treated water. A step of concentrating the water to be treated to obtain concentrated water by allowing the water in the water to be treated to permeate from the primary side to the secondary side of the first semipermeable membrane in the presence of the hypertonic solution;
A water treatment method comprising: introducing the concentrated water into a reaction tank and performing aeration treatment.   The water treatment method according to claim 1, wherein the aeration treatment is performed in the presence of a microorganism.   The water treatment method according to claim 1, further comprising a step of returning aeration-treated water obtained by the aeration treatment to the forward osmosis membrane device. Further, treated water is obtained by introducing the hypertonic solution into the reverse osmosis membrane device and permeating the water in the hypertonic solution from the primary side to the secondary side of the second semipermeable membrane provided in the reverse osmosis membrane device. Process,
The water treatment method according to any one of claims 1 to 3, further comprising a step of returning the hypertonic solution from the reverse osmosis membrane device to the forward osmosis membrane device. A first semipermeable membrane, a primary side on which the treated water is present with the first semipermeable membrane interposed therebetween, and a secondary side on which a hypertonic solution having a higher osmotic pressure than the treated water is present; Forward osmosis membrane device in which the water to be treated is concentrated to obtain concentrated water by infiltrating the water from the primary side to the secondary side of the first semipermeable membrane,
A water treatment system comprising: a reaction vessel that includes an air diffuser and aeration treatment of the concentrated water discharged from the primary side of the first semipermeable membrane.   The primary tank side of the first semipermeable membrane of the forward osmosis membrane device communicates with the outflow portion of the reaction vessel and the primary side inflow portion of the first semipermeable membrane of the forward osmosis membrane device. The water treatment system according to claim 5, further comprising a return flow path for transferring to the water. Water in the hypertonic solution comprising a second semipermeable membrane, a primary side on which the hypertonic solution exists and a secondary side on which treated water having a lower osmotic pressure than the hypertonic solution exists, with the second semipermeable membrane interposed therebetween Is further provided with a reverse osmosis membrane device for obtaining treated water by permeating from the primary side to the secondary side of the second semipermeable membrane,
The hypertonic solution is transferred from the secondary side of the first semipermeable membrane to the primary side of the second semipermeable membrane in communication with the secondary side outflow portion of the first semipermeable membrane and the primary side inflow portion of the second semipermeable membrane. A first flow path,
A hypertonic solution is transferred from the primary side of the second semipermeable membrane to the secondary side of the first semipermeable membrane in communication with the primary side outflow portion of the second semipermeable membrane and the secondary inflow portion of the first semipermeable membrane. The water treatment system according to claim 5 or 6, wherein a second flow path is provided.   The water treatment system according to any one of claims 5 to 7, wherein the forward osmosis membrane device is provided in water to be treated.

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