Water treatment apparatus and water treatment method

Abstract

To provide a water treatment device and a water treatment method capable of recovering a valuable material in high concentration from effluent.SOLUTION: A water treatment device 1 that recovers a valuable material from effluent, comprises a nano filtration device 11 for obtaining NF permeated water and NF concentrated water from effluent using a nano filtration membrane, and semipermeable membrane treatment means of obtaining concentrated water, by using a membrane module 10 comprising a first space 14 and a second space 16 separated by a semipermeable membrane 12 to allow the NF concentrated water to flow through the first space 14 so as to pressurize the first space 14 to force water contained in the NF concentrated water to flow through the semi-permeable membrane 12, and obtaining diluted water by forcing a portion of the NF concentrated water or at least a portion of the concentrated water to flow through the second space 16.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a water treatment apparatus and a water treatment method for recovering valuable substances from wastewater.

[0002] In recent years, a method of recovering valuable substances from wastewater discharged from semiconductor factories and the like using an evaporation method such as an evaporator or membrane distillation has been used. However, since the evaporation method requires a huge amount of energy, a method of reducing the volume of wastewater by a reverse osmosis membrane method in the previous stage of the evaporation method is generally used as in Patent Document 1.

[0003] On the other hand, as a method of concentrating ions contained in wastewater to a high concentration, after removing the hard components or turbidity components of the concentrated liquid of the reverse osmosis membrane module with a nanofiltration membrane or an ultrafiltration membrane as in Patent Document 2, a method of concentrating the permeated water with a semipermeable membrane module has been developed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] An object of the present invention is to provide a water treatment apparatus and a water treatment method capable of recovering valuable substances from wastewater at a high concentration.

Means for Solving the Problems

[0006] The present invention is Contains sulfate ions, ammonium ions, and silicaA water treatment apparatus for recovering valuable substances from wastewater, comprising: a nanofiltration means for obtaining NF permeate water and NF concentrated water from the wastewater using a nanofiltration membrane; and a semipermeable membrane treatment means for obtaining concentrated water by passing the NF concentrated water through the first space and pressurizing the first space to allow the water contained in the NF concentrated water to pass through the semipermeable membrane, using a semipermeable membrane module having a first space and a second space separated by a semipermeable membrane, and passing a part of the NF concentrated water or at least a part of the concentrated water through the second space to obtain diluted water. The nanofiltration membrane exhibits a silica rejection rate in the range of 5% to 20% under conditions of an effective membrane pressure of 1 MPa, 25°C, and pH 7, and an ammonium ion rejection rate and a sulfate ion rejection rate in the range of 90% to 100%. It is a water treatment device.

[0007] The present invention Contains sulfate ions, ammonium ions, and silica A water treatment apparatus for recovering valuable substances from wastewater, comprising: a nanofiltration means for obtaining NF permeate water and NF concentrated water from the wastewater using a nanofiltration membrane; and a semipermeable membrane treatment means for obtaining concentrated water by passing the NF concentrated water through the first space of the first semipermeable membrane module, pressurizing the first space to allow the water contained in the NF concentrated water to pass through the semipermeable membrane, and obtaining concentrated water using the concentrated water using subsequent semipermeable membrane modules, and passing the NF concentrated water or at least a portion of the concentrated water or at least a portion of the diluted water obtained from other semipermeable membrane modules through the second space of each semipermeable membrane module to obtain diluted water. The nanofiltration membrane exhibits a silica rejection rate in the range of 5% to 20% under conditions of an effective membrane pressure of 1 MPa, 25°C, and pH 7, and an ammonium ion rejection rate and a sulfate ion rejection rate in the range of 90% to 100%. It is a water treatment device.

[0008] In the water treatment apparatus described above, it is preferable to further include a return means for returning at least a portion of the diluted water obtained by the semipermeable membrane treatment means to the stage before the nanofiltration means.

[0009] In the water treatment apparatus, the wastewater is The aforementioned Ammonium ions at 2000 mg / L or higher, The aforementioned Sulfate ions at 6000 mg / L or higher, The aforementioned It is preferable that the silica content be 5 mg / L or more.

[0010] In the water treatment apparatus, the nanofiltration membrane has a silica rejection rate under conditions of an effective membrane pressure of 1 MPa, 25°C, and pH 7. 5 ~ 18 The percentage ranges from % to ammonium ion rejection and sulfate ion rejection. 97 It is preferable that the range is between % and 100%.

[0011] In the water treatment apparatus described above, it is preferable to further include a pH adjustment means for adjusting the pH of the wastewater to a range of 4 to 8, prior to the nanofiltration means.

[0012] In the water treatment apparatus described above, it is preferable to further include a temperature adjustment means for adjusting the temperature of the wastewater to a range of 20°C to 35°C, prior to the nanofiltration means.

[0013] The present invention Contains sulfate ions, ammonium ions, and silica A water treatment method for recovering valuable substances from wastewater, comprising: a nanofiltration step of obtaining NF permeate water and NF concentrated water from the wastewater using a nanofiltration membrane; and a semipermeable membrane treatment step of obtaining concentrated water by passing the NF concentrated water through the first space and pressurizing the first space to allow the water contained in the NF concentrated water to pass through the semipermeable membrane, using a semipermeable membrane module having a first space and a second space separated by a semipermeable membrane, and passing a part of the NF concentrated water or at least a part of the concentrated water through the second space to obtain diluted water. Furthermore, the nanofiltration membrane exhibits a silica rejection rate in the range of 5% to 20% and ammonium ion rejection rates and sulfate ion rejection rates in the range of 90% to 100% under conditions of an effective membrane pressure of 1 MPa, 25°C, and pH 7. It is a water treatment method.

[0014] The present invention Contains sulfate ions, ammonium ions, and silicaA water treatment method for recovering valuable substances from wastewater, comprising: a nanofiltration step of obtaining NF permeate water and NF concentrate water from the wastewater using a nanofiltration membrane; and a semi-permeable membrane treatment step of passing the NF concentrate water through the first space of the first-stage semi-permeable membrane module having a first space and a second space partitioned by a semi-permeable membrane, pressurizing the first space to allow the water contained in the NF concentrate water to permeate through the semi-permeable membrane to obtain concentrated water, obtaining concentrated water using the concentrated water and subsequent-stage semi-permeable membrane modules, and passing at least a part of the NF concentrate water or at least a part of the concentrated water or at least a part of the dilution water obtained from another semi-permeable membrane module through the second space of each stage of the semi-permeable membrane module to obtain dilution water. Furthermore, the nanofiltration membrane exhibits a silica rejection rate in the range of 5% to 20% and ammonium ion rejection rates and sulfate ion rejection rates in the range of 90% to 100% under conditions of an effective membrane pressure of 1 MPa, 25°C, and pH 7. It is a water treatment method.

[0015] In the water treatment method, it is preferable to return at least a part of the dilution water obtained in the semi-permeable membrane treatment step to the stage before the nanofiltration step.

[0016] In the water treatment method, the wastewater The aforementioned contains ammonium ions at 2000 mg / L or more, The aforementioned sulfate ions at 6000 mg / L or more, The aforementioned and silica at 5 mg / L or more.

[0017] In the water treatment method, the nanofiltration membrane has a silica rejection rate in the range of 5 ~ 18 % under the conditions of a membrane surface effective pressure of 1 MPa, 25 °C, and pH 7, and an ammonium ion rejection rate and a sulfate ion rejection rate in the range of 97 % to 100%.

[0018] In the water treatment method, it is preferable to further include a pH adjustment step of adjusting the pH of the wastewater to the range of 4 to 8 before the nanofiltration step.

[0019] In the water treatment method, it is preferable to further include a temperature adjustment step of adjusting the temperature of the wastewater to the range of 20 °C to 35 °C before the nanofiltration step. [Effects of the Invention]

[0020] The present invention provides a water treatment apparatus and a water treatment method that can recover valuable substances from wastewater at high concentrations. [Brief explanation of the drawing]

[0021] [Figure 1] This is a schematic diagram showing an example of a water treatment apparatus according to an embodiment of the present invention. [Figure 2] This is a schematic diagram showing another example of a water treatment apparatus according to an embodiment of the present invention. [Figure 3] This is a schematic diagram showing another example of a water treatment apparatus according to an embodiment of the present invention. [Figure 4] This is a schematic diagram showing another example of a water treatment apparatus according to an embodiment of the present invention. [Figure 5] This is a schematic diagram showing another example of a water treatment apparatus according to an embodiment of the present invention. [Figure 6] This is a schematic diagram showing another example of a water treatment apparatus according to an embodiment of the present invention. [Figure 7] This is a schematic diagram showing another example of a water treatment apparatus according to an embodiment of the present invention. [Figure 8] This is a schematic diagram showing another example of a water treatment apparatus according to an embodiment of the present invention. [Figure 9] This graph shows the results of the silica inhibition rate in Example 1. [Modes for carrying out the invention]

[0022] Embodiments of the present invention will be described below. This embodiment is just one example of how the present invention can be implemented, and the present invention is not limited to this embodiment.

[0023] Figure 1 shows a schematic diagram of an example of a water treatment apparatus according to an embodiment of the present invention, and its configuration will be described.

[0024] The water treatment apparatus 1 shown in Figure 1 is a device for recovering valuable substances from wastewater such as ammonia-containing wastewater. The water treatment apparatus 1 includes a nanofiltration apparatus 11 as a nanofiltration means for obtaining NF permeate water and NF concentrated water from ammonia-containing wastewater using a nanofiltration membrane, and a semipermeable membrane module having a first space (concentration side) 14 and a second space (permeation side) 16 separated by a semipermeable membrane 12. The NF concentrated water from the nanofiltration apparatus 11 is passed through the first space 14, and the first space 14 is pressurized to allow the water contained in the NF concentrated water to permeate through the semipermeable membrane 12 to obtain concentrated water, and a portion of the NF concentrated water is passed through the second space 16 to obtain diluted water. For example, the membrane module 10 is a semipermeable membrane treatment means. The water treatment apparatus 1 may also include an NF concentrated water tank for storing NF concentrated water between the nanofiltration apparatus 11 and the membrane module 10.

[0025] In the water treatment apparatus 1 shown in Figure 1, a pipe 25 is connected to the inlet of the nanofiltration apparatus 11 via a pump 21. A pipe 27 is connected to the NF permeate water outlet of the nanofiltration apparatus 11. The NF concentrated water outlet of the nanofiltration apparatus 11 and the first space inlet of the membrane module 10 are connected by a pipe 24 via a pump 18, and a pipe 26 branching off from pipe 24 downstream of the pump 18 is connected to the second space inlet of the membrane module 10 via a valve 22. A pipe 28 is connected to the first space outlet of the membrane module 10 via a valve 23, and the second space outlet of the membrane module 10 and the upstream side of the pump 21 in pipe 25 are connected by a pipe 30.

[0026] Pump 18 is a pressurized pump that is driven at a rotational speed corresponding to the input drive frequency and sucks in NF concentrated water and discharges it under pressure to the membrane module 10. Pump 18 is equipped with an inverter 20 that outputs a drive frequency corresponding to the input command signal to the pump 18. Pump 21 is a pressurized pump that is driven at a rotational speed corresponding to the input drive frequency and sucks in ammonia-containing wastewater and discharges it under pressure to the nanofiltration device 11. Valves 22 and 23 are valves whose opening and closing degree can be adjusted manually or automatically.

[0027] The membrane module 10 has a first space 14 and a second space 16 separated by a semipermeable membrane 12. NF concentrated water is passed through the first space 14 from the inlet of the first space 10 and through the second space 16 from the inlet of the second space 10. By pressurizing the first space 14, the water contained in the NF concentrated water in the first space 14 is permeated through the semipermeable membrane 12 to the second space 16, thereby concentrating the water. In other words, in the water treatment device 1, NF concentrated water is concentrated using the semipermeable membrane 12. The membrane module 10 is a device that supplies NF concentrated water to both the first space 14 and the second space 16 of the membrane module 10 for concentration treatment.

[0028] In the water treatment apparatus 1, ammonia-containing wastewater, which is the water to be treated, is supplied to the nanofiltration apparatus 11 through piping 25 by pump 21. In the nanofiltration apparatus 11, NF permeate water and NF concentrated water are obtained from the ammonia-containing wastewater using a nanofiltration membrane (nanofiltration process). The NF permeate water is discharged through piping 27. The NF permeate water may be discharged outside the system and released into rivers, etc., or it may be recovered by further providing an advanced water treatment method.

[0029] The NF concentrated water obtained from the nanofiltration device 11 is pressurized and delivered to the first space 14 of the membrane module 10 from the first space inlet by the pump 18 through the piping 24 with the valve 23 open. Water flow to the nanofiltration device 11 and the membrane module 10 may also be performed using only the pump 21. In addition, with the valve 22 open, the NF concentrated water is delivered to the second space 16 of the membrane module 10 from the second space inlet by the piping 26 branched from the piping 24 with the valve 22 open. A portion of the water contained in the pressurized NF concentrated water permeates from the first space 14 to the second space 16 through the semipermeable membrane 12. At this time, most of the ions and other substances contained in the NF concentrated water cannot permeate the semipermeable membrane 12, so the water in the first space 14 that did not permeate the semipermeable membrane 12 is concentrated. On the other hand, in the second space 16, a dilution effect occurs because a portion of the NF concentrated water delivered through the piping 26 and the permeate water with a low ion concentration that permeated the semipermeable membrane 12 merge. The concentrated water obtained in the first space 14 is discharged from the outlet of the first space through the pipe 28, and the diluted water obtained in the second space 16 is discharged from the outlet of the second space through the pipe 30. At least a portion of the diluted water may be returned to the upstream side of the pump 21 in the pipe 25, which is the stage before the nanofiltration device 11 (return process). Here, in the membrane module 10, the first space 14 is pressurized and the water contained in the NF concentrated water in the first space 14 permeates through the semipermeable membrane 12 to the second space 16, thereby obtaining concentrated water in the first space 14 (concentration process) and diluted water in the second space 16 (dilution process) (the above is the semipermeable membrane processing process).

[0030] Here, the pipes 24, 26, pump 18, etc. function as supply means to supply NF concentrated water to both the first space 14 and the second space 16 of the membrane module 10. The pipes 30, etc. function as return means to return at least a portion of the diluted water obtained in the membrane module 10 to the upstream stage of the nanofiltration device 11.

[0031] The dilution water obtained in the second space 16 may be discharged out of the system through the piping 30, or, if necessary, sent to a dilution tank for storage before being discharged out of the system or reused. At least a portion of the dilution water may be returned, for example, to the upstream side of the pump 21 in piping 25 and mixed with NF concentrated water. At least a portion of the dilution water may undergo further treatment, such as reverse osmosis treatment.

[0032] As described above, at least one of ammonia and ammonium ions is recovered as concentrated water from the ammonia-containing wastewater, which is the target of treatment, thereby reducing the volume of the ammonia-containing wastewater. Furthermore, the NF permeate, concentrated water, and diluted water can be reused.

[0033] By passing NF concentrated water through the first space 14 and the second space 16 of the membrane module 10, the osmotic pressure difference between the first space 14 and the second space 16 of the semipermeable membrane 12 is reduced, allowing for the concentration of high concentrations of ions in the NF concentrated water with less energy consumption. In other words, NF concentrated water containing high concentrations of ions can be concentrated at low cost, and the amount of waste liquid with high ion concentrations can be reduced.

[0034] Wastewater discharged from semiconductor factories and other facilities may contain scale components, which can cause membrane clogging during high-concentration treatment using semipermeable membranes, making concentration difficult. For example, if the wastewater contains silica (SiO2), it is desirable to remove the silica as a pretreatment before semipermeable membrane treatment, but if the silica concentration is high, it may be difficult to address this with dispersants or other chemicals.

[0035] In the water treatment apparatus and water treatment method according to this embodiment, even if silica is present in the wastewater, the nanofiltration apparatus 11 selectively allows the silica in the wastewater to pass through the nanofiltration membrane, and by passing the NF concentrated water with reduced silica concentration through the first space 14 of the membrane module 10 or both the first space 14 and the second space 16, the target substance for concentration can be stably concentrated to a high degree.

[0036] It is preferable that at least a portion of the dilution water obtained in the second space 16 is returned to the upstream of the nanofiltration device 11, more preferably that 50-100% of the dilution water is returned to the upstream of the nanofiltration device 11, and even more preferably that 70-100% of the dilution water is returned to the upstream of the nanofiltration device 11. By returning and circulating a predetermined amount or more of the dilution water discharged from the membrane module 10 to the upstream of the nanofiltration device 11, even if silica is present in the ammonia-containing wastewater, the ratio of silica concentration to ammonium ion concentration in the ammonia-containing wastewater supplied to the nanofiltration device 11 can be reduced, thereby reducing the risk of silica scale deposition in the concentration process of the semipermeable membrane treatment.

[0037] As a method for adjusting the supply flow rate of NF concentrated water to the membrane module 10, the permeate flow rate, and the concentrated water flow rate, for example, the following method may be used.

[0038] An inverter 20 is provided on the pump 18 to control the drive frequency and adjust the flow rate of NF concentrated water supplied to the membrane module 10. It is preferable to install the inverter 20 on the pump 18, but it is not necessary. NF concentrated water is supplied to both the first space 14 and the second space 16. A valve 22 is provided before the inlet of the second space 16, and a valve 23 is provided at the outlet of the first space 14. The ratio of the water flow rate supplied to the first space 14 to the water flow rate supplied to the second space 16 can be adjusted by manually or automatically adjusting the opening of valves 22 and 23.

[0039] If the permeate flow rate or concentrated water flow rate is insufficient, the frequency of the inverter 20 of pump 18 can be increased to increase the supply of NF concentrated water.

[0040] A valve 23 is provided at the outlet of the first space 14 of the piping 28, allowing the degree of opening and closing to be adjusted. By adjusting the opening of the valve 23, the concentrated water flow rate and the pressure at the inlet and outlet of the first space 14 can be controlled.

[0041] These operations allow the pressure and various flow rates on the first space 14 side to be adjusted to predetermined levels.

[0042] Furthermore, the supply of NF concentrated water to the first space 14 and the second space 16 may be carried out by separate pumps. When supplying NF concentrated water by separate pumps, an inverter to control the drive frequency may be provided for each pump.

[0043] By passing NF concentrated water of the same or similar concentration through both the first space 14 and the second space 16, the osmotic pressure generated by the semipermeable membrane 12 can be reduced, thereby lowering the required pressure. As a result, NF concentrated water can be concentrated to concentrations that could not be achieved with conventional reverse osmosis membrane methods.

[0044] In this way, valuable substances can be recovered from ammonia-containing wastewater at high concentrations. Furthermore, even if silica is present in the ammonia-containing wastewater, the risk of silica scale precipitation during the concentration process of the semipermeable membrane treatment can be reduced by treating NF concentrated water with reduced silica concentration using a semipermeable membrane.

[0045] Figure 2 shows a schematic of another example of a water treatment apparatus according to an embodiment of the present invention, and its configuration will be described.

[0046] The water treatment apparatus 2 shown in Figure 2 includes a nanofiltration apparatus 11 as a nanofiltration means for obtaining NF permeate water and NF concentrated water from wastewater such as ammonia-containing wastewater using a nanofiltration membrane, and a semipermeable membrane module having a first space (concentration side) 14 and a second space (permeation side) 16 separated by a semipermeable membrane 12, through which the NF concentrated water from the nanofiltration apparatus 11 is passed, and the first space 14 is pressurized to allow the water contained in the NF concentrated water to permeate through the semipermeable membrane 12 to obtain concentrated water, and at least a portion of the concentrated water is passed through the second space 16 to obtain diluted water, for example, a membrane module 10 as a semipermeable membrane treatment means. The water treatment apparatus 2 may also include an NF concentrated water tank for storing NF concentrated water between the nanofiltration apparatus 11 and the membrane module 10.

[0047] In the water treatment apparatus 2 of Figure 2, piping 25 is connected to the inlet of the nanofiltration apparatus 11 via pump 21. Piping 27 is connected to the NF permeate water outlet of the nanofiltration apparatus 11. The NF concentrated water outlet of the nanofiltration apparatus 11 and the first space inlet of the membrane module 10 are connected by piping 24 via pump 18. Piping 28 is connected to the first space outlet of the membrane module 10 via valve 23. Upstream of valve 23, piping 34, which branches off from piping 28, is connected to the second space inlet of the membrane module 10 via valve 32. The second space outlet of the membrane module 10 and the upstream side of pump 21 in piping 25 are connected by piping 36.

[0048] Pump 18 is a pressurized pump that is driven at a rotational speed corresponding to the input drive frequency and sucks in NF concentrated water and discharges it under pressure to the membrane module 10. Pump 18 is equipped with an inverter 20 that outputs a drive frequency corresponding to the input command signal to the pump 18. Pump 21 is a pressurized pump that is driven at a rotational speed corresponding to the input drive frequency and sucks in ammonia-containing wastewater and discharges it under pressure to the nanofiltration device 11. Valves 23 and 32 are valves whose opening and closing degree can be adjusted manually or automatically.

[0049] The membrane module 10 has a first space 14 and a second space 16 separated by a semipermeable membrane 12. NF concentrated water is passed through the first space 14 from the inlet of the membrane module 10, and at least a portion of the concentrated water discharged from the outlet of the first space 14 is passed through the second space 16 from the inlet of the membrane module 10. By pressurizing the first space 14, the water contained in the NF concentrated water in the first space 14 is permeated through the semipermeable membrane 12 to the second space 16, thereby concentrating the water. In other words, in the water treatment device 2, NF concentrated water is concentrated using the semipermeable membrane 12. The membrane module 10 is a device that supplies NF concentrated water to the first space 14 of the membrane module 10 and supplies at least a portion of the concentrated water obtained from the outlet of the first space 14 to the second space 16 of the membrane module 10 for concentration treatment.

[0050] In the water treatment device 2, ammonia-containing wastewater, which is the water to be treated, is supplied to the nanofiltration device 11 through piping 25 by pump 21. In the nanofiltration device 11, NF permeate water and NF concentrated water are obtained from the ammonia-containing wastewater using a nanofiltration membrane (nanofiltration process). The NF permeate water is discharged through piping 27.

[0051] The NF concentrated water obtained from the nanofiltration device 11 is pressurized and delivered through the piping 24 by the pump 18 with the valve 23 open, from the first space inlet to the first space 14 of the membrane module 10. Water flow to the nanofiltration device 11 and the membrane module 10 may also be performed using only the pump 21. A portion of the water contained in the pressurized NF concentrated water permeates from the first space 14 to the second space 16 through the semipermeable membrane 12. At this time, most of the ions and other substances cannot permeate the semipermeable membrane 12, so the water in the first space 14 that did not permeate the semipermeable membrane 12 is concentrated. On the other hand, in the second space 16, a portion of the concentrated water that has been passed through the piping 34 and the permeate water with a low ion concentration that has permeated the semipermeable membrane 12 merge, resulting in a dilution effect. The concentrated water obtained in the first space 14 is discharged from the outlet of the first space through piping 28, and at least a portion of the concentrated water is sent from the inlet of the second space of the membrane module 10 to the second space 16 through piping 34 branched from piping 28 with valve 32 open, and water is passed through. The diluted water obtained in the second space 16 is discharged from the outlet of the second space through piping 36, and at least a portion of the diluted water may be returned to the upstream side of the pump 21 in piping 25, which is the upstream stage of the nanofiltration device 11 (return process). Here, in the membrane module 10, the first space 14 is pressurized and the water contained in the NF concentrated water in the first space 14 permeates through the semipermeable membrane 12 to the second space 16, thereby obtaining concentrated water in the first space 14 (concentration process) and diluted water in the second space 16 (dilution process) (the above is the semipermeable membrane processing process).

[0052] Here, pipes 24, 28, 34, pump 18, etc., function as supply means to supply NF concentrated water to the first space 14 of the membrane module 10, and to supply at least a portion of the concentrated water obtained from the outlet of the first space 14 to the second space 16 of the membrane module 10. Pipes 36, etc., function as return means to return at least a portion of the diluted water obtained in the membrane module 10 to the upstream stage of the nanofiltration device 11.

[0053] The dilution water obtained in the second space 16 may be discharged out of the system through the piping 36, or, if necessary, sent to a dilution tank for storage before being discharged out of the system or reused. At least a portion of the dilution water may be returned, for example, to the upstream side of the pump 21 in the piping 25 and mixed with NF concentrated water. At least a portion of the dilution water may undergo further treatment, such as reverse osmosis treatment.

[0054] As described above, at least one of ammonia and ammonium ions is recovered as concentrated water from the ammonia-containing wastewater, which is the target of treatment, thereby reducing the volume of the ammonia-containing wastewater. Furthermore, the NF permeate, concentrated water, and diluted water can be reused.

[0055] By passing NF concentrated water through the first space 14 of the membrane module 10 and passing at least a portion of the concentrated water obtained in the first space 14 through the second space 16, the osmotic pressure difference between the first space 14 and the second space 16 of the semipermeable membrane 12 is reduced, allowing for the concentration of high concentrations of ions in the NF concentrated water with less energy consumption. In other words, NF concentrated water containing high concentrations of ions can be concentrated at low cost, and the amount of waste liquid with high ion concentrations can be reduced.

[0056] As a method for adjusting the supply flow rate of NF concentrated water to the membrane module 10, the permeate flow rate, and the concentrated water flow rate, for example, the following method may be used.

[0057] An inverter 20 is provided on the pump 18 to control the drive frequency and adjust the flow rate of NF concentrated water supplied to the membrane module 10. It is preferable to install the inverter 20 on the pump 18, but it is not necessary. NF concentrated water is supplied to the first space 14 side, a valve 23 is provided at the outlet of the first space 14, and a valve 32 is provided before the inlet of the second space 16. The ratio of the water flow rate supplied to the first space 14 side to the water flow rate supplied to the second space 16 side can be adjusted by manually or automatically adjusting the opening of valves 23 and 32.

[0058] If the permeate flow rate or concentrated water flow rate is insufficient, the frequency of the inverter 20 of pump 18 can be increased to increase the supply of NF concentrated water.

[0059] A valve 23 is provided at the outlet of the first space 14 of the piping 28, allowing the degree of opening and closing to be adjusted. By adjusting the opening of the valve 23, the concentrated water flow rate and the pressure at the inlet and outlet of the first space 14 can be controlled.

[0060] These operations allow the pressure and various flow rates on the first space 14 side to be adjusted to predetermined levels.

[0061] Alternatively, a concentrated water tank for storing concentrated water may be provided in the middle of the piping 34, and the supply of NF concentrated water to the first space 14 and the supply of concentrated water to the second space 16 may be carried out by separate pumps. When NF concentrated water and concentrated water are supplied by separate pumps, an inverter to control the drive frequency may be provided for each pump.

[0062] By passing NF concentrated water through the first space 14 and concentrated water of a similar concentration through the second space 16, the osmotic pressure generated by the semipermeable membrane 12 can be reduced, thereby lowering the required pressure. As a result, NF concentrated water can be concentrated to concentrations that could not be achieved with conventional reverse osmosis membrane methods.

[0063] The inlet pressure of the first space 14 is preferably in the range of 7 MPa or less, the inlet pressure of the second space 16 is preferably lower than the inlet pressure of the first space 14, and more preferably the inlet pressure of the second space 16 is 50% or less of the inlet pressure of the first space 14. This reduces the risk of damage to the semipermeable membrane due to pressure.

[0064] It is preferable to make the flow rate on the first space 14 side greater than the flow rate on the second space 16 side. If the flow rate on the first space 14 side is less than or equal to the flow rate on the second space 16 side, the permeate flux may become too high. For example, the pump 18, inverter 20, valve 22, valve 23, valve 32, etc., function as flow rate adjustment means to make the flow rate in the first space greater than the flow rate in the second space.

[0065] If the permeate flux is too large, the concentration difference will become large, which may lead to problems such as a higher risk of fouling and excessively high pressure. Conversely, if the permeate flux is too small, the concentration efficiency may be poor. For these reasons, it is preferable to set the permeate flux of the membrane module 10 in the range of 0.005 m / d to 0.05 m / d, and more preferably in the range of 0.015 m / d to 0.04 m / d. The permeate flux is defined as the permeate flow rate per unit time and per unit membrane area. For example, the pump 18, inverter 20, valve 22, valve 23, valve 32, etc., function as permeate flux adjustment means that control the permeate flux within the above range.

[0066] Note that the installation locations and number of valves are merely examples, and there may be more valves than those shown in Figures 1 and 2, and they may be installed in at least one of the other pipes. In addition, a flow meter may be installed in at least one of each pipe as a means of measuring flow rate, and a pressure gauge may be installed as a means of measuring pressure.

[0067] In the water treatment method and water treatment apparatus according to this embodiment, a multi-stage semipermeable membrane module may be used. An example of such a water treatment apparatus is shown in Figures 3, 4, and 5. The water treatment apparatus shown in Figures 3, 4, and 5 has a structure in which three semipermeable membrane modules are combined in series.

[0068] The water treatment apparatus 3 shown in Figure 3 is a nanofiltration means for obtaining NF permeate water and NF concentrated water from wastewater such as ammonia-containing wastewater using a nanofiltration membrane. It includes a nanofiltration apparatus 11 and a multi-stage connected semipermeable membrane module, each having a first space (concentration side) 14 and a second space (permeation side) 16 separated by a semipermeable membrane 12. The NF concentrated water from the nanofiltration apparatus 11 is passed through the first space 14 of the first stage semipermeable membrane module, and the first space 14 is pressurized to allow the water contained in the NF concentrated water to permeate through the semipermeable membrane 12 to obtain concentrated water. This concentrated water is then used to obtain further concentrated water using subsequent semipermeable membrane modules. Additionally, a semipermeable membrane treatment means is provided, for example, a first-stage membrane module 10a, a second-stage membrane module 10b, and a third-stage membrane module 10c, which obtain diluted water by passing a portion of the NF concentrated water or a portion of the concentrated water through the second space 16 of each stage semipermeable membrane module. Each membrane module has a first space 14 and a second space 16 separated by a semipermeable membrane 12. The water treatment device 3 may include a dilution tank 60a for storing dilution water from the first-stage membrane module 10a, a dilution tank 60b for storing dilution water from the second-stage membrane module 10b, and a dilution tank 60c for storing dilution water from the third-stage membrane module 10c. The membrane module 10 is a device that supplies NF concentrated water to the first and second spaces of the first-stage membrane module, and then sequentially supplies that concentrated water to the first and second spaces of the next-stage membrane module to perform concentration treatment. The water treatment device 3 may also include an NF concentrated water tank for storing NF concentrated water between the nanofiltration device 11 and the membrane module 10.

[0069] In the water treatment apparatus 3 of Figure 3, piping 25 is connected to the inlet of the nanofiltration apparatus 11 via pump 21. Piping 27 is connected to the NF permeate water outlet of the nanofiltration apparatus 11. The NF concentrated water outlet of the nanofiltration apparatus 11 and the first space inlet of the first-stage membrane module 10a are connected by piping 40 via pump 18. Piping 42, which branches off from the downstream side of pump 18 in piping 40, is connected to the second space inlet of the membrane module 10a via valve 22a. The second space outlet of the first-stage membrane module 10a and the inlet of the dilution tank 60a are connected by piping 46. The first space outlet of the first-stage membrane module 10a and the first space inlet of the second-stage membrane module 10b are connected by piping 44. Piping 48, which branches off from piping 44, is connected to the second space inlet of the second-stage membrane module 10b via valve 22b. The second space outlet of the second-stage membrane module 10b and the inlet of the dilution tank 60b are connected by piping 52. The first space outlet of the second membrane module 10b and the first space inlet of the third membrane module 10c are connected by piping 50. Piping 54, which branches off from piping 50, is connected to the second space inlet of the third membrane module 10c via valve 22c. The second space outlet of the third membrane module 10c and the inlet of the dilution tank 60c are connected by piping 58. Piping 56 is connected to the first space outlet of the third membrane module 10c via valve 23. The outlet of the dilution tank 60a and the upstream side of the pump 21 in piping 25 are connected by piping 59. The outlet of the dilution tank 60b and piping 59 are connected by piping 61. The outlet of the dilution tank 60c and piping 59 are connected by piping 63.

[0070] The membrane module 10 is a multi-stage membrane module having a first space 14 and a second space 16 separated by a semipermeable membrane 12. NF concentrated water is supplied to the first and second spaces of the first-stage membrane module, and this concentrated water is sequentially supplied to the first and second spaces of the next-stage membrane module. By pressurizing the first space 14 of each stage, the water contained in the first space 14 is permeated through the semipermeable membrane 12 to the second space 16, thereby concentrating the water. In other words, in the membrane module 10, NF concentrated water is concentrated using the semipermeable membrane 12, and this concentrated water is further concentrated using the semipermeable membrane 12 of the next stage.

[0071] In the water treatment apparatus 3, ammonia-containing wastewater, which is the water to be treated, is supplied to the nanofiltration apparatus 11 through piping 25 by pump 21. In the nanofiltration apparatus 11, NF permeate water and NF concentrated water are obtained from the ammonia-containing wastewater using a nanofiltration membrane (nanofiltration process). The NF permeate water is discharged through piping 27.

[0072] The NF concentrated water obtained in the nanofiltration device 11 is sent through the piping 40 by the pump 18 with valve 23 open to the first space 14a of the first-stage membrane module 10a, and the NF concentrated water branched off from the piping 40 is sent through the piping 42 with valve 22a open to the second space 16a of the first-stage membrane module 10a. The flow of water to the nanofiltration device 11 and the membrane module 10 may be performed using only the pump 21. In the first-stage membrane module 10a, the first space 14a is pressurized and the water contained in the first space 14a is permeated through the semipermeable membrane 12a to the second space 16a (concentration step (first stage)), and diluted water is obtained in the second space 16a (dilution step (first stage)). The diluted water obtained in the second space 16a of the first-stage membrane module 10a is stored in the dilution tank 60a as needed through the piping 46. At least a portion of the dilution water may be returned through the piping 59 to the upstream side of the pump 21 in the piping 25, which is the stage before the nanofiltration device 11 (return step).

[0073] The concentrated water obtained in the first space 14a of the first-stage membrane module 10a is sent through piping 44 to the first space 14b of the second-stage membrane module 10b, and the concentrated water branched off from piping 44 is sent through piping 48 to the second space 16b of the second-stage membrane module 10b with valve 22b open. In the second-stage membrane module 10b, the first space 14b is pressurized and the water contained in the first space 14b is permeated through the semipermeable membrane 12b to the second space 16b (concentration step (second stage)), and diluted water is obtained in the second space 16b (dilution step (second stage)). The diluted water obtained in the second space 16b of the second-stage membrane module 10b is stored in the dilution tank 60b as needed through piping 52. At least a portion of the diluted water may be returned through piping 61, 59 to the upstream side of the pump 21 in piping 25, which is the upstream stage of the nanofiltration device 11 (return step).

[0074] The concentrated water obtained in the first space 14b of the second-stage membrane module 10b is sent through piping 50 to the first space 14c of the third-stage membrane module 10c. The concentrated water branched off from piping 50 is sent through piping 54 to the second space 16c of the third-stage membrane module 10c with valve 22c open. In the third-stage membrane module 10c, the first space 14c is pressurized and the water contained in the first space 14c is permeated through the semipermeable membrane 12c to the second space 16c (concentration process (third stage)), and diluted water is obtained in the second space 16c (dilution process (third stage)) (the above is the semipermeable membrane processing process). The diluted water obtained in the second space 16c of the third-stage membrane module 10c is stored in the dilution tank 60c as needed through piping 58. The concentrated water obtained in the first space 14c of the third-stage membrane module 10c is discharged through piping 56. At least a portion of the dilution water may be returned through pipes 63 and 59 to the upstream side of the pump 21 in pipe 25, which is the upstream stage of the nanofiltration device 11 (return step).

[0075] Here, the pump 18 and pipes 40, 42, 44, 48, 50, 54, etc. function as supply means for supplying NF concentrated water or concentrated water to the first spaces 14a, 14b, 14c and second spaces 16a, 16b, 16c of the membrane modules 10a, 10b, 10c at each stage. The pipes 59, 61, 63, etc. function as return means for returning at least a portion of the diluted water obtained in the membrane module 10 to the upstream stage of the nanofiltration device 11.

[0076] The dilution water obtained in the second spaces 16a, 16b, and 16c of the membrane modules 10a, 10b, and 10c at each stage may be discharged outside the system, or, if necessary, sent to dilution tanks 60a, 60b, and 60c for storage before being discharged outside the system or reused. At least a portion of the dilution water may be returned, for example, to the upstream side of the pump 21 in the piping 25 and mixed with NF concentrated water. At least a portion of the dilution water may be subjected to further treatment, such as reverse osmosis membrane treatment.

[0077] As described above, at least one of ammonia and ammonium ions is recovered from the ammonia-containing wastewater, which is the target of treatment, as concentrated water (final stage concentrated water), thereby reducing the volume of the ammonia-containing wastewater. Furthermore, the NF permeate, concentrated water, and dilution water can be reused.

[0078] The water treatment apparatus 4 shown in Figure 4 is a nanofiltration means for obtaining NF permeate water and NF concentrated water from wastewater such as ammonia-containing wastewater using a nanofiltration membrane. It includes a nanofiltration apparatus 11 and a multi-stage connected semipermeable membrane module, each having a first space (concentration side) 14 and a second space (permeation side) 16 separated by a semipermeable membrane 12. The NF concentrated water from the nanofiltration apparatus 11 is passed through the first space 14 of the first stage semipermeable membrane module, and the first space 14 is pressurized to allow the water contained in the NF concentrated water to permeate through the semipermeable membrane 12 to obtain concentrated water. This concentrated water is then used to obtain further concentrated water using subsequent semipermeable membrane modules, and at least a portion of the concentrated water is passed through the second space 16 of each stage semipermeable membrane module to obtain diluted water. This semipermeable membrane treatment means includes, for example, a first-stage membrane module 10a, a second-stage membrane module 10b, and a third-stage membrane module 10c. Each membrane module has a first space 14 and a second space 16 separated by a semipermeable membrane 12. The water treatment device 4 may include a dilution tank 62a for storing dilution water from the first-stage membrane module 10a, a dilution tank 62b for storing dilution water from the second-stage membrane module 10b, and a dilution tank 62c for storing dilution water from the third-stage membrane module 10c. The membrane module 10 is a device that supplies NF concentrated water to the first space of the first-stage membrane module and then supplies that concentrated water sequentially to the first space of the next-stage membrane module and its own second space to perform concentration treatment. The water treatment device 4 may also include an NF concentrated water tank for storing NF concentrated water between the nanofiltration device 11 and the membrane module 10.

[0079] In the water treatment apparatus 4 of Figure 4, piping 25 is connected to the inlet of the nanofiltration apparatus 11 via pump 21. Piping 27 is connected to the NF permeate water outlet of the nanofiltration apparatus 11. The NF concentrated water outlet of the nanofiltration apparatus 11 and the first space inlet of the first-stage membrane module 10a are connected by piping 40 via pump 18. The first space outlet of the first-stage membrane module 10a and the first space inlet of the second-stage membrane module 10b are connected by piping 44. Piping 64, branched from piping 44, is connected to the second space inlet of the membrane module 10a via valve 32a. The second space outlet of the first-stage membrane module 10a and the inlet of the dilution water tank 62a are connected by piping 66. The first space outlet of the second-stage membrane module 10b and the first space inlet of the third-stage membrane module 10c are connected by piping 50. Piping 68, branched from piping 50, is connected to the second space inlet of the membrane module 10b via valve 32b. The second space outlet of the second-stage membrane module 10b and the inlet of the dilution tank 62b are connected by piping 70. Piping 56 is connected to the first space outlet of the third-stage membrane module 10c via valve 23. Upstream of valve 23, piping 72, which branches off from piping 56, is connected to the second space inlet of the membrane module 10c via valve 32c. The second space outlet of the third-stage membrane module 10c and the inlet of the dilution tank 62c are connected by piping 74. The outlet of the dilution tank 62a and the upstream side of pump 21 in piping 25 are connected by piping 59. The outlet of the dilution tank 62b and piping 59 are connected by piping 61. The outlet of the dilution tank 62c and piping 59 are connected by piping 63.

[0080] The membrane module 10 is a multi-stage membrane module having a first space 14 and a second space 16 separated by a semipermeable membrane 12. NF concentrated water is supplied to the first space of the first-stage membrane module, and this concentrated water is sequentially supplied to the first space of the next-stage membrane module and its own second space. By pressurizing the first space 14 of each stage, the water contained in the first space 14 is permeated through the semipermeable membrane 12 to the second space 16, thereby concentrating the water. In other words, in the membrane module 10, NF concentrated water is concentrated using the semipermeable membrane 12, and this concentrated water is further concentrated using the semipermeable membrane 12 of the next stage.

[0081] In the water treatment device 4, ammonia-containing wastewater, which is the water to be treated, is supplied to the nanofiltration device 11 through piping 25 by pump 21. In the nanofiltration device 11, NF permeate water and NF concentrated water are obtained from the ammonia-containing wastewater using a nanofiltration membrane (nanofiltration process). The NF permeate water is discharged through piping 27.

[0082] The NF concentrated water obtained in the nanofiltration device 11 is sent through the piping 40 by the pump 18 to the first space 14a of the first-stage membrane module 10a with the valve 23 open. Water flow to the nanofiltration device 11 and the membrane module 10 may be performed using only the pump 21. In the first-stage membrane module 10a, the first space 14a is pressurized and the water contained in the first space 14a is permeated through the semipermeable membrane 12a to the second space 16a (concentration step (first stage)), and diluted water is obtained in the second space 16a (dilution step (first stage)). The concentrated water obtained in the first space 14a of the first-stage membrane module 10a is sent through the piping 44 to the first space 14b of the second-stage membrane module 10b, and the concentrated water branched off from the piping 44 is sent through the piping 64 with the valve 32a open to the second space 16a of the first-stage membrane module 10a. The dilution water obtained in the second space 16a of the first-stage membrane module 10a is stored in the dilution water tank 62a as needed through the piping 66. At least a portion of the dilution water may be returned through the piping 59 to the upstream side of the pump 21 in the piping 25, which is the stage before the nanofiltration device 11 (return step).

[0083] In the second-stage membrane module 10b, the first space 14b is pressurized, and the water contained in the first space 14b is permeated through the semipermeable membrane 12b to the second space 16b (concentration step (second stage)), and diluted water is obtained in the second space 16b (dilution step (second stage)). The concentrated water obtained in the first space 14b of the second-stage membrane module 10b is sent through the piping 50 to the first space 14c of the third-stage membrane module 10c, and the concentrated water branched off from the piping 50 is sent through the piping 68 with the valve 32b open to the second space 16b of the second-stage membrane module 10b. The diluted water obtained in the second space 16b of the second-stage membrane module 10b is stored in the dilution tank 62b as needed through the piping 70. At least a portion of the diluted water may be returned through the piping 61, 59 to the upstream side of the pump 21 in the piping 25, which is the upstream stage of the nanofiltration device 11 (return step).

[0084] In the third-stage membrane module 10c, the first space 14c is pressurized, and the water contained in the first space 14c is permeated through the semipermeable membrane 12c to the second space 16c (concentration step (third stage)), and diluted water is obtained in the second space 16c (dilution step (third stage)) (the above is the semipermeable membrane processing step). The concentrated water obtained in the first space 14c of the third-stage membrane module 10c is discharged through the pipe 56. The concentrated water branched off from the pipe 56 is sent through the pipe 72 to the second space 16c of the third-stage membrane module 10c with the valve 32c open. The diluted water obtained in the second space 16c of the third-stage membrane module 10c is stored in the dilution tank 62c as needed through the pipe 74. At least a portion of the diluted water may be returned through pipes 63 and 59 to the upstream side of the pump 21 in the pipe 25, which is the upstream stage of the nanofiltration device 11 (return step).

[0085] Here, the pump 18, piping 40, 44, 64, 50, 68, 56, 72, etc. function as supply means to supply NF concentrated water or concentrated water to the first spaces 14a, 14b, 14c and second spaces 16a, 16b, 16c of the membrane modules 10a, 10b, 10c at each stage. The piping 59, 61, 63, etc. function as return means to return at least a portion of the diluted water obtained in the membrane module 10 to the upstream stage of the nanofiltration device 11.

[0086] The dilution water obtained in the second spaces 16a, 16b, and 16c of the membrane modules 10a, 10b, and 10c at each stage may be discharged outside the system, or, if necessary, sent to dilution tanks 62a, 62b, and 62c for storage before being discharged outside the system or reused. At least a portion of the dilution water may be returned, for example, to the upstream side of the pump 21 in the piping 25 and mixed with NF concentrated water. At least a portion of the dilution water may be subjected to further treatment, such as reverse osmosis membrane treatment.

[0087] As described above, at least one of ammonia and ammonium ions is recovered from the ammonia-containing wastewater, which is the target of treatment, as concentrated water (final stage concentrated water), thereby reducing the volume of the ammonia-containing wastewater. Furthermore, the NF permeate, concentrated water, and dilution water can be reused.

[0088] When using a multi-stage membrane module, water flow from the second space may be performed in series. An example of such a water treatment system is shown in Figure 5.

[0089] The water treatment apparatus 5 shown in Figure 5 is a nanofiltration means for obtaining NF permeate water and NF concentrated water from wastewater such as ammonia-containing wastewater using a nanofiltration membrane. It includes a nanofiltration apparatus 11 and a multi-stage connected semipermeable membrane module, each having a first space (concentration side) 14 and a second space (permeation side) 16 separated by a semipermeable membrane 12. The NF concentrated water from the nanofiltration apparatus 11 is passed through the first space 14 of the first stage semipermeable membrane module, and the first space 14 is pressurized to allow the water contained in the NF concentrated water to permeate through the semipermeable membrane 12 to obtain concentrated water. This concentrated water is then used to obtain further concentrated water using subsequent semipermeable membrane modules. Additionally, at least a portion of the concentrated water is passed through the second space 16 of each stage semipermeable membrane module to obtain diluted water. This semipermeable membrane treatment means includes, for example, a first-stage membrane module 10a, a second-stage membrane module 10b, and a third-stage membrane module 10c. Each membrane module has a first space 14 and a second space 16 separated by a semipermeable membrane 12. The membrane module 10 is a device that supplies NF concentrated water to the first space of the first-stage membrane module and then sequentially supplies that concentrated water to the first space of the next-stage membrane module for concentration treatment. The water treatment device 5 may also include an NF concentrated water tank for storing NF concentrated water between the nanofiltration device 11 and the membrane module 10.

[0090] In the water treatment apparatus 5 of Figure 5, piping 25 is connected to the inlet of the nanofiltration apparatus 11 via pump 21. Piping 27 is connected to the NF permeate outlet of the nanofiltration apparatus 11. The NF concentrated water outlet of the nanofiltration apparatus 11 and the first space inlet of the first-stage membrane module 10a are connected via pump 18 and piping 40. The first space outlet of the first-stage membrane module 10a and the first space inlet of the second-stage membrane module 10b are connected via piping 44. The first space outlet of the second-stage membrane module 10b and the first space inlet of the third-stage membrane module 10c are connected via piping 50. Piping 56 is connected to the first space outlet of the third-stage membrane module 10c via valve 23. Upstream of valve 23, piping 76, which branches off from piping 56, is connected to the second space inlet of the membrane module 10c via valve 32. The second space outlet of the third-stage membrane module 10c and the second space inlet of the second-stage membrane module 10b are connected via piping 78. The second space outlet of the second-stage membrane module 10b and the second space inlet of the first-stage membrane module 10a are connected by piping 80. The second space outlet of the first-stage membrane module 10a and the upstream side of the pump 21 in piping 25 are connected by piping 82.

[0091] The membrane module 10 is a multi-stage membrane module having a first space 14 and a second space 16 separated by a semipermeable membrane 12. NF concentrated water is supplied to the first space of the first-stage membrane module, and this concentrated water is sequentially passed through the first space of the next-stage membrane module in series. At least a portion of the concentrated water from the final-stage membrane module is supplied to its own second space, and the resulting diluted water is passed through the second space of the preceding-stage membrane module in series. By pressurizing the first space 14 of each stage, the water contained in the first space 14 is permeated through the semipermeable membrane 12 to the second space 16, thereby concentrating the water. In other words, in the membrane module 10, NF concentrated water is concentrated using the semipermeable membrane 12, and this concentrated water is further concentrated using the semipermeable membrane 12 of the next stage.

[0092] In the water treatment device 5, ammonia-containing wastewater, which is the water to be treated, is supplied to the nanofiltration device 11 through piping 25 by pump 21. In the nanofiltration device 11, NF permeate water and NF concentrated water are obtained from the ammonia-containing wastewater using a nanofiltration membrane (nanofiltration process). The NF permeate water is discharged through piping 27.

[0093] The NF concentrated water obtained in the nanofiltration device 11 is sent through the piping 40 by the pump 18 to the first space 14a of the first-stage membrane module 10a with the valve 23 open. Water flow to the nanofiltration device 11 and the membrane module 10 may be performed using only the pump 21. Meanwhile, the diluted water sent through the second space 16c of the third-stage membrane module 10c and the second space 16b of the second-stage membrane module 10b, as described later, is sent through the piping 80 to the second space 16a of the first-stage membrane module 10a. In the first-stage membrane module 10a, the first space 14a is pressurized and the water contained in the first space 14a permeates through the semipermeable membrane 12a to the second space 16a (concentration step (first stage)), and diluted water is obtained in the second space 16a (dilution step (first stage)). The concentrated water obtained in the first space 14a of the first-stage membrane module 10a is sent through piping 44 to the first space 14b of the second-stage membrane module 10b. The diluted water obtained in the second space 16a of the first-stage membrane module 10a is discharged through piping 82. At least a portion of the diluted water may be returned through piping 82 to the upstream side of the pump 21 in piping 25, which is the upstream stage of the nanofiltration device 11 (return process).

[0094] In the second-stage membrane module 10b, the dilution water supplied via the second space 16c of the third-stage membrane module 10c (described later) is supplied through piping 78 to the second space 16b of the second-stage membrane module 10b. The first space 14b is pressurized, and the water contained in the first space 14b is permeated through the semipermeable membrane 12b to the second space 16b (concentration step (second stage)), and dilution water is obtained in the second space 16b (dilution step (second stage)). The concentrated water obtained in the first space 14b of the second-stage membrane module 10b is supplied through piping 50 to the first space 14c of the third-stage membrane module 10c. The dilution water obtained in the second space 16b of the second-stage membrane module 10b is supplied through piping 80 to the second space 16a of the first-stage membrane module 10a.

[0095] In the third-stage membrane module 10c, concentrated water obtained in the first space 14c of the third-stage membrane module 10c is sent to the second space 16c through pipes 56 and 76 as described below. The first space 14c is pressurized and the water contained in the first space 14c is permeated through the semipermeable membrane 12c to the second space 16c (concentration process (third stage)), and diluted water is obtained in the second space 16c (dilution process (third stage)) (the above is the semipermeable membrane processing process). The concentrated water obtained in the first space 14c of the third-stage membrane module 10c is discharged through pipe 56. The concentrated water branched from pipe 56 is sent to the second space 16c of the third-stage membrane module 10c through pipe 76 with valve 32 open. The diluted water obtained in the second space 16c of the third-stage membrane module 10c is sent to the second space 16b of the second-stage membrane module 10b through pipe 78.

[0096] Here, the pump 18, piping 40, 44, 50, 56, 76, 78, 80, etc. function as supply means to supply NF concentrated water or concentrated water or diluted water to the first spaces 14a, 14b, 14c and second spaces 16a, 16b, 16c of the membrane modules 10a, 10b, 10c at each stage. Piping 82, etc. function as return means to return at least a portion of the diluted water obtained in the membrane module 10 to the upstream stage of the nanofiltration device 11.

[0097] The dilution water obtained in the second space 16a of the membrane module 10a may be discharged outside the system, or, if necessary, sent to a dilution tank for storage and then discharged outside the system, or reused. At least a portion of the dilution water may be returned, for example, to the upstream side of the pump 21 in the piping 25 and mixed with NF concentrated water. At least a portion of the dilution water may be subjected to further treatment, such as reverse osmosis membrane treatment.

[0098] As described above, at least one of ammonia and ammonium ions is recovered from the ammonia-containing wastewater, which is the target of treatment, as concentrated water (final stage concentrated water), thereby reducing the volume of the ammonia-containing wastewater. Furthermore, the NF permeate, concentrated water, and dilution water can be reused.

[0099] In the water treatment apparatus 3 shown in Figure 3, water treatment apparatus 4 shown in Figure 4, and water treatment apparatus 5 shown in Figure 5, the concentrated water supplied to each membrane module becomes more concentrated as it progresses from the first stage to the subsequent membrane modules, resulting in a higher concentration. Because the water is ultimately concentrated to a high concentration, this method, which can reduce osmotic pressure, makes it possible to concentrate the water to concentrations that were difficult to achieve with conventional reverse osmosis membrane methods due to the influence of osmotic pressure.

[0100] When NF concentrated water is supplied to the first-stage membrane module 10a, a pressure of, for example, 7 MPa or less is applied, and the supply of concentrated water to the subsequent membrane modules is carried out by the pressure applied to the first-stage membrane module 10a. The inlet pressure of the first space 14 in each membrane module is preferably in the range of 7 MPa or less, the inlet pressure of the second space 16 is preferably lower than the inlet pressure of the first space 14, and more preferably the inlet pressure of the second space 16 is 50% or less of the inlet pressure of the first space 14. This reduces the risk of semipermeable membrane damage due to pressure.

[0101] It is preferable to make the flow rate on the first space 14 side of each membrane module 10 greater than the flow rate on the second space 16 side. If the flow rate on the first space 14 side is less than or equal to the flow rate on the second space 16 side, the flow rate on the first space 14 side of the subsequent membrane module may be insufficient. For example, the pump 18, inverter 20, valves 22a, 22b, 22c, valve 23, valves 32a, 32b, 32c, valve 32, etc. function as flow rate adjustment means to make the flow rate in the first space greater than the flow rate in the second space.

[0102] If the permeation flux is too large, the concentration polarization of the membrane surface will increase, which can lead to problems such as a higher risk of fouling and excessively high pressure. Conversely, if the permeation flux is too small, the concentration efficiency may be poor. For these reasons, it is preferable to set the permeation flux of each membrane module 10 in the range of 0.005 m / d to 0.05 m / d, and more preferably in the range of 0.015 m / d to 0.04 m / d. For example, the pump 18, inverter 20, valves 22a, 22b, 22c, valve 23, valves 32a, 32b, 32c, valve 32, etc., function as permeation flux adjustment means to control the permeation flux within the above range.

[0103] Note that the installation locations and number of valves are merely examples, and may be greater than the number shown in Figures 3, 4, and 5, and may be installed in at least one of the other pipes. In addition, a flow meter may be installed in at least one of each pipe as a means of measuring flow rate, and a pressure gauge may be installed as a means of measuring pressure.

[0104] Furthermore, Figures 3, 4, and 5 show examples of the apparatus configuration, and the arrangement of the semipermeable membrane modules, the method of supplying the water, etc., may be changed as appropriate.

[0105] The water treatment device in Figure 5 is preferable because, since water is passed in series through the first and second spaces of each membrane module, the overall water volume can be reduced compared to the water treatment devices in Figures 3 and 4, and the power of the pump can be reduced.

[0106] In the water treatment method and water treatment apparatus according to this embodiment, a multi-stage membrane module may be used, and a membrane module unit comprising multiple membrane modules connected in parallel may be used as the membrane module for each stage. An example of a water treatment apparatus with such a configuration is shown in Figures 6 and 7. The water treatment apparatus shown in Figures 6 and 7 has a structure in which the first stage combines four semipermeable membrane modules in parallel, the second stage combines four semipermeable membrane modules in parallel, the third stage combines two semipermeable membrane modules in parallel, and the fourth stage combines two semipermeable membrane modules in parallel, and these are connected in series in four stages.

[0107] The water treatment apparatus 6 shown in Figure 6 is a nanofiltration means for obtaining NF permeate water and NF concentrated water from wastewater such as ammonia-containing wastewater using a nanofiltration membrane. It includes a nanofiltration apparatus 11 and a multi-stage connected semipermeable membrane module having a first space (concentration side) 14 and a second space (permeation side) 16 separated by a semipermeable membrane 12. The NF concentrated water from the nanofiltration apparatus 11 is passed through the first space 14 of the first stage semipermeable membrane module, and the first space 14 is pressurized to allow the water contained in the NF concentrated water to permeate through the semipermeable membrane 12 to obtain concentrated water. This concentrated water is then used to obtain further concentrated water using subsequent semipermeable membrane modules, and a portion of the NF concentrated water or a portion of the concentrated water is passed through the second space 16 of each stage semipermeable membrane module to obtain diluted water. The semipermeable membrane treatment means includes, for example, a first-stage membrane module unit 100a, a second-stage membrane module unit 100b, a third-stage membrane module unit 100c, and a fourth-stage membrane module unit 100d. The first-stage membrane module unit 100a comprises, for example, four membrane modules connected in parallel; the second-stage membrane module unit 100b comprises, for example, four membrane modules connected in parallel; the third-stage membrane module unit 100c comprises, for example, two membrane modules connected in parallel; and the fourth-stage membrane module unit 100d comprises, for example, two membrane modules connected in parallel. Each membrane module 10 has a first space 14 and a second space 16 separated by a semipermeable membrane 12. The water treatment device 6 may also include an NF concentration tank 84 for storing NF concentrated water and a concentration tank 86 for storing concentrated water from the fourth-stage membrane module unit 100d. The membrane module unit 100 is a device that supplies NF concentrated water to the first and second spaces of each membrane module in the first-stage membrane module unit, and then sequentially supplies that concentrated water to the first and second spaces of each membrane module in the next-stage membrane module unit to perform concentration processing.

[0108] In the water treatment apparatus 6 of Figure 6, piping 25 is connected to the inlet of the nanofiltration apparatus 11 via pump 21. Piping 27 is connected to the NF permeate outlet of the nanofiltration apparatus 11. The NF concentrated water outlet of the nanofiltration apparatus 11 is connected to the inlet of the NF concentrated water tank 84 via piping 29. The outlet of the NF concentrated water tank 84 is connected to the first and second space inlets of each membrane module in the first-stage membrane module unit 100a via piping 88 through pump 18. The first space outlet of each membrane module in the first-stage membrane module unit 100a is connected to the first and second space inlets of each membrane module in the second-stage membrane module unit 100b via piping 90. The first space outlet of each membrane module in the second-stage membrane module unit 100b is connected to the first and second space inlets of each membrane module in the third-stage membrane module unit 100c via piping 94. The first space outlets of each membrane module in the third-stage membrane module unit 100c and the first and second space inlets of each membrane module in the fourth-stage membrane module unit 100d are connected by piping 98. The first space outlets of each membrane module in the fourth-stage membrane module unit 100d are connected to the inlet of the concentration tank 86 by piping 104. Piping 92 is connected to the second space outlets of each membrane module in the first-stage membrane module unit 100a, piping 96 is connected to the second space outlets of each membrane module in the second-stage membrane module unit 100b, piping 102 is connected to the second space outlets of each membrane module in the third-stage membrane module unit 100c, and piping 106 is connected to the second space outlets of each membrane module in the fourth-stage membrane module unit 100d. Pipings 96, 102, and 106 may merge into piping 92. Piping 92 is connected to the upstream side of the pump 21 in piping 25.

[0109] The membrane module unit 100 is a multi-stage membrane module unit that includes a membrane module 10 having a first space 14 and a second space 16 separated by a semipermeable membrane 12. NF concentrated water is supplied to the first and second spaces of each membrane module in the first-stage membrane module unit, and this concentrated water is sequentially supplied to the first and second spaces of each membrane module in the next-stage membrane module unit. By pressurizing the first space 14 of each stage membrane module, the water contained in the first space 14 is permeated through the semipermeable membrane 12 to the second space 16, thereby concentrating the water. In other words, in the membrane module unit 100, NF concentrated water is concentrated using the semipermeable membrane 12, and this concentrated water is further concentrated using the semipermeable membrane 12 of the next stage.

[0110] In the water treatment device 6, ammonia-containing wastewater, which is the water to be treated, is supplied to the nanofiltration device 11 through piping 25 by pump 21. In the nanofiltration device 11, NF permeate water and NF concentrated water are obtained from the ammonia-containing wastewater using a nanofiltration membrane (nanofiltration process). The NF permeate water is discharged through piping 27.

[0111] The NF concentrated water obtained from the nanofiltration device 11 is stored in the NF concentrated water tank 84 as needed, and then pumped from the NF concentrated water tank 84 through piping 88 by the pump 18 to the first space 14 and second space 16 of each membrane module in the first-stage membrane module unit 100a. The water may be supplied to the nanofiltration device 11 and the membrane modules 10 using only the pump 21. In each membrane module of the first-stage membrane module unit 100a, the first space 14a is pressurized and the water contained in the first space 14 is permeated through the semipermeable membrane 12 to the second space 16 (concentration step (first stage)), and diluted water is obtained in the second space 16 (dilution step (first stage)). The diluted water obtained in the second space 16 of the first-stage membrane module 10 is stored in the dilution water tank as needed through piping 92 and then discharged. At least a portion of the diluted water may be returned through piping 92 to the upstream side of the pump 21 in piping 25, which is the upstream stage of the nanofiltration device 11 (return step).

[0112] The concentrated water obtained in the first space 14 of each membrane module in the first-stage membrane module unit 100a is sent through the piping 90 to the first space 14 and second space 16 of each membrane module in the second-stage membrane module unit 100b. In each membrane module of the second-stage membrane module unit 100b, the first space 14 is pressurized and the water contained in the first space 14 permeates through the semipermeable membrane 12 to the second space 16 (concentration step (second stage)), and diluted water is obtained in the second space 16 (dilution step (second stage)). The diluted water obtained in the second space 16 of each membrane module in the second-stage membrane module unit 100b is stored in a dilution tank as needed through the piping 96 and then discharged. At least a portion of the diluted water may be returned through the piping 96 and 92 to the upstream side of the pump 21 in the piping 25 which is the upstream stage of the nanofiltration device 11 (return step).

[0113] The concentrated water obtained in the first space 14 of each membrane module in the second-stage membrane module unit 100b is sent through the piping 94 to the first space 14 and second space 16 of each membrane module in the third-stage membrane module unit 100c. In each membrane module of the third-stage membrane module unit 100c, the first space 14 is pressurized and the water contained in the first space 14 permeates through the semipermeable membrane 12 to the second space 16 (concentration step (third stage)), and diluted water is obtained in the second space 16 (dilution step (third stage)). The diluted water obtained in the second space 16 of each membrane module in the third-stage membrane module unit 100c is stored in a dilution tank as needed through the piping 102 and then discharged. At least a portion of the diluted water may be returned through the piping 102, 96, and 92 to the upstream side of the pump 21 in the piping 25 which is the upstream stage of the nanofiltration device 11 (return step).

[0114] The concentrated water obtained in the first space 14 of each membrane module in the third-stage membrane module unit 100c is sent through piping 98 to the first space 14 and second space 16 of each membrane module in the fourth-stage membrane module unit 100d. In each membrane module of the fourth-stage membrane module unit 100d, the first space 14 is pressurized and the water contained in the first space 14 permeates through the semipermeable membrane 12 to the second space 16 (concentration step (fourth stage)), and diluted water is obtained in the second space 16 (dilution step (fourth stage)) (the above is the semipermeable membrane processing step). The concentrated water obtained in the first space 14 of each membrane module in the fourth-stage membrane module unit 100d is stored in the concentration tank 86 as needed through piping 104 and then discharged. The diluted water obtained in the second space 16 of each membrane module in the fourth-stage membrane module unit 100d is stored in the dilution tank as needed through piping 106 and then discharged. At least a portion of the dilution water may be returned to the upstream side of the pump 21 in the piping 25, which is the stage before the nanofiltration device 11, through piping 106, 102, 96, and 92 (return step).

[0115] Here, the pump 18 and the pipes 88, 90, 94, 98, etc. function as supply means to supply NF concentrated water or concentrated water to the first space 14 and second space 16 of each membrane module unit 100a, 100b, 100c, 100d at each stage. The pipes 92, 96, 102, 106, etc. function as return means to return at least a portion of the diluted water obtained in the membrane module 10 to the upstream stage of the nanofiltration device 11.

[0116] The dilution water obtained in the second space 16 of each membrane module unit 100a, 100b, 100c, and 100d in each stage may be discharged outside the system, or, if necessary, sent to a dilution tank for storage and then discharged outside the system, or reused. At least a portion of the dilution water may be returned, for example, to the upstream side of the pump 21 in the piping 25 and mixed with NF concentrated water. At least a portion of the dilution water may be subjected to further treatment, such as reverse osmosis membrane treatment.

[0117] As described above, at least one of ammonia and ammonium ions is recovered from the ammonia-containing wastewater, which is the target of treatment, as concentrated water (final stage concentrated water), thereby reducing the volume of the ammonia-containing wastewater. Furthermore, the NF permeate, concentrated water, and dilution water can be reused.

[0118] The water treatment apparatus 7 shown in Figure 7 is a nanofiltration means for obtaining NF permeate water and NF concentrated water from wastewater such as ammonia-containing wastewater using a nanofiltration membrane. It includes a nanofiltration apparatus 11 and a multi-stage connected semipermeable membrane module having a first space (concentration side) 14 and a second space (permeation side) 16 separated by a semipermeable membrane 12. The NF concentrated water from the nanofiltration apparatus 11 is passed through the first space 14 of the first stage semipermeable membrane module, and the first space 14 is pressurized to allow the water contained in the NF concentrated water to permeate through the semipermeable membrane 12 to obtain concentrated water. This concentrated water is then used to obtain further concentrated water using subsequent semipermeable membrane modules. Additionally, at least a portion of the concentrated water is passed through the second space 16 of each stage semipermeable membrane module to obtain diluted water. For example, the semipermeable membrane treatment means includes a first-stage membrane module unit 100a, a second-stage membrane module unit 100b, a third-stage membrane module unit 100c, and a fourth-stage membrane module unit 100d. The first-stage membrane module unit 100a comprises, for example, four membrane modules connected in parallel; the second-stage membrane module unit 100b comprises, for example, four membrane modules connected in parallel; the third-stage membrane module unit 100c comprises, for example, two membrane modules connected in parallel; and the fourth-stage membrane module unit 100d comprises, for example, two membrane modules connected in parallel. Each membrane module 10 has a first space 14 and a second space 16 separated by a semipermeable membrane 12. The water treatment device 7 may also include an NF concentration tank 84 for storing NF concentrated water and a concentration tank 86 for storing concentrated water from the fourth-stage membrane module unit 100d. The membrane module unit 100 is a device that supplies NF concentrated water to the first space of the first-stage membrane module and then sequentially supplies that concentrated water to the first space of the next-stage membrane module to perform concentration treatment.

[0119] In the water treatment apparatus 7 of Figure 7, piping 25 is connected to the inlet of the nanofiltration apparatus 11 via pump 21. Piping 27 is connected to the NF permeate outlet of the nanofiltration apparatus 11. The NF concentrated water outlet of the nanofiltration apparatus 11 and the inlet of the NF concentrated water tank 84 are connected by piping 29. The outlet of the NF concentrated water tank 84 and the first space inlet of each membrane module of the first-stage membrane module unit 100a are connected by piping 108 via pump 18. The first space outlet of each membrane module of the first-stage membrane module unit 100a and the first space inlet of each membrane module of the second-stage membrane module unit 100b are connected by piping 110. The first space outlet of each membrane module of the second-stage membrane module unit 100b and the first space inlet of each membrane module of the third-stage membrane module unit 100c are connected by piping 112. The first space outlets of each membrane module in the third-stage membrane module unit 100c and the first space inlets of each membrane module in the fourth-stage membrane module unit 100d are connected by piping 114. The first space outlets of each membrane module in the fourth-stage membrane module unit 100d and the inlet of the concentration tank 86 are connected by piping 116. Piping 118, which branches off from piping 116, is connected to the second space inlets of each membrane module in the fourth-stage membrane module unit 100d. The second space outlets of each membrane module in the fourth-stage membrane module unit 100d and the second space inlets of each membrane module in the third-stage membrane module unit 100c are connected by piping 120. The second space outlets of each membrane module in the third-stage membrane module unit 100c and the second space inlets of each membrane module in the second-stage membrane module unit 100b are connected by piping 122. The second space outlets of each membrane module in the second-stage membrane module unit 100b and the second space inlets of each membrane module in the first-stage membrane module unit 100a are connected by piping 124. The second space outlets of each membrane module in the first-stage membrane module unit 100a and the upstream side of the pump 21 in piping 25 are connected by piping 126.

[0120] The membrane module unit 100 is a multi-stage membrane module unit that includes a membrane module 10 having a first space 14 and a second space 16 separated by a semipermeable membrane 12. NF concentrated water is supplied to the first space of each membrane module in the first-stage membrane module unit, and this concentrated water is sequentially passed through the first space of each membrane module in the next-stage membrane module unit in series. At least a portion of the concentrated water from each membrane module in the final-stage membrane module unit is supplied to its own second space, and the resulting diluted water is passed through the second space 16 of each membrane module in the preceding membrane module unit in series. By pressurizing the first space 14 of each stage, the water contained in the first space 14 is permeated through the semipermeable membrane 12 to the second space 16, thereby concentrating the water. In other words, in the membrane module unit 100, NF concentrated water is concentrated using the semipermeable membrane 12, and this concentrated water is further concentrated using the semipermeable membrane 12 of the next stage.

[0121] In the water treatment device 7, ammonia-containing wastewater, which is the water to be treated, is supplied to the nanofiltration device 11 through piping 25 by pump 21. In the nanofiltration device 11, NF permeate water and NF concentrated water are obtained from the ammonia-containing wastewater using a nanofiltration membrane (nanofiltration process). The NF permeate water is discharged through piping 27.

[0122] The NF concentrated water obtained from the nanofiltration device 11 is stored in the NF concentrated water tank 84 as needed, and then pumped from the NF concentrated water tank 84 through the piping 108 by the pump 18 to the first space 14 of each membrane module in the first-stage membrane module unit 100a. The water flow to the nanofiltration device 11 and the membrane module 10 may be performed using only the pump 21. Meanwhile, the diluted water that has been sent through the second space 16 of each membrane module in the fourth-stage membrane module unit 100d, the second space 16 of each membrane module in the third-stage membrane module unit 100c, and the second space 16 of each membrane module in the second-stage membrane module unit 100b is sent through the piping 124 to the second space 16 of each membrane module in the first-stage membrane module unit 100a. In each membrane module of the first-stage membrane module unit 100a, the first space 14 is pressurized, and the water contained in the first space 14 is permeated through the semipermeable membrane 12 to the second space 16 (concentration step (first stage)), and diluted water is obtained in the second space 16 (dilution step (first stage)). The concentrated water obtained in the first space 14 of each membrane module of the first-stage membrane module unit 100a is sent through the piping 110 to the first space 14 of each membrane module of the second-stage membrane module unit 100b. The diluted water obtained in the second space 16 of each membrane module of the first-stage membrane module unit 100a is discharged through the piping 126. At least a portion of the diluted water may be returned through the piping 126 to the upstream side of the pump 21 in the piping 25 which is the upstream stage of the nanofiltration device 11 (return step).

[0123] In each membrane module of the second-stage membrane module unit 100b, the dilution water, which has been supplied via the second space 16 of each membrane module of the fourth-stage membrane module unit 100d (described later) and the second space 16 of each membrane module of the third-stage membrane module unit 100c, is supplied through the piping 122 to the second space 16 of each membrane module of the second-stage membrane module unit 100b. The first space 14 is pressurized and the water contained in the first space 14 permeates through the semipermeable membrane 12 to the second space 16 (concentration step (second stage)), and dilution water is obtained in the second space 16 (dilution step (second stage)). The concentrated water obtained in the first space 14 of each membrane module of the second-stage membrane module unit 100b is supplied through the piping 112 to the first space 14 of each membrane module of the third-stage membrane module unit 100c. The dilution water obtained in the second space 16 of each membrane module in the second-stage membrane module unit 100b is sent through the piping 124 to the second space 16 of each membrane module in the first-stage membrane module unit 100a.

[0124] In each membrane module of the third-stage membrane module unit 100c, the dilution water supplied via the second space 16 of each membrane module of the fourth-stage membrane module unit 100d (described later) is supplied through the piping 120 to the second space 16 of each membrane module of the third-stage membrane module unit 100c. The first space 14 is pressurized, and the water contained in the first space 14 permeates through the semipermeable membrane 12 to the second space 16 (concentration step (third stage)), and dilution water is obtained in the second space 16 (dilution step (third stage)). The concentrated water obtained in the first space 14 of each membrane module of the third-stage membrane module unit 100c is supplied through the piping 114 to the first space 14 of each membrane module of the fourth-stage membrane module unit 100d. The dilution water obtained in the second space 16 of each membrane module of the third-stage membrane module unit 100c is supplied through the piping 122 to the second space 16 of each membrane module of the second-stage membrane module unit 100b.

[0125] In each membrane module of the fourth-stage membrane module unit 100d, concentrated water obtained in the first space 14 of each membrane module of the fourth-stage membrane module unit 100d is sent to the second space 16 through pipes 116 and 118 as described below. The first space 14 is pressurized and the water contained in the first space 14 permeates through the semipermeable membrane 12 to the second space 16 (concentration process (fourth stage)), and diluted water is obtained in the second space 16 (dilution process (fourth stage)) (the above is the semipermeable membrane processing process). The concentrated water obtained in the first space 14 of each membrane module of the fourth-stage membrane module unit 100d is sent through pipe 116, stored in a concentrated water tank 86 as needed, and then discharged. The concentrated water branched off from pipe 116 is sent through pipe 118 to the second space 16 of each membrane module of the fourth-stage membrane module unit 100d. The dilution water obtained in the second space 16 of each membrane module in the fourth-stage membrane module unit 100d is sent through the piping 120 to the second space 16 of each membrane module in the third-stage membrane module unit 100c.

[0126] Here, the pump 18 and piping 108, 110, 112, 114, 116, 118, 120, 122, 124, etc. function as supply means to supply NF concentrated water or concentrated water or diluted water to the first space 14 and second space 16 of each membrane module unit 100a, 100b, 100c, 100d at each stage. Piping 126, etc. function as return means to return at least a portion of the diluted water obtained in the membrane module 10 to the upstream stage of the nanofiltration device 11.

[0127] The dilution water obtained in the second space 16 of each membrane module of the membrane module unit 100a may be discharged outside the system, or, if necessary, sent to a dilution tank for storage and then discharged outside the system, or reused. At least a portion of the dilution water may be returned, for example, to the upstream side of the pump 21 in the piping 25 and mixed with NF concentrated water. At least a portion of the dilution water may be subjected to further treatment, such as reverse osmosis membrane treatment.

[0128] As described above, at least one of ammonia and ammonium ions is recovered from the ammonia-containing wastewater, which is the target of treatment, as concentrated water (final stage concentrated water), thereby reducing the volume of the ammonia-containing wastewater. Furthermore, the NF permeate, concentrated water, and dilution water can be reused.

[0129] When NF concentrated water is supplied to each membrane module of the first-stage membrane module unit 100a, a pressure of, for example, 7 MPa or less is applied, and the supply of concentrated water to the subsequent membrane module units is carried out by the pressure applied to each membrane module of the first-stage membrane module unit 100a. The inlet pressure of the first space 14 in each membrane module is preferably in the range of 7 MPa or less, the inlet pressure of the second space 16 is preferably lower than the inlet pressure of the first space 14, and more preferably the inlet pressure of the second space 16 is 50% or less of the inlet pressure of the first space 14. This reduces the risk of semipermeable membrane damage due to pressure.

[0130] It is preferable to make the flow rate on the first space 14 side of each membrane module 10 greater than the flow rate on the second space 16 side. If the flow rate on the first space 14 side is less than or equal to the flow rate on the second space 16 side, the flow rate on the first space 14 side of the subsequent membrane module may be insufficient. For example, a pump 18 or the like functions as a flow rate adjustment means to make the flow rate in the first space greater than the flow rate in the second space.

[0131] If the permeation flux is too large, the concentration difference will become large, which may lead to problems such as a higher risk of fouling and excessively high pressure. Conversely, if the permeation flux is too small, the concentration efficiency may be poor. For these reasons, it is preferable to set the permeation flux of each membrane module 10 in the range of 0.005 m / d to 0.05 m / d, and more preferably in the range of 0.015 m / d to 0.04 m / d. For example, a pump 18 or the like functions as a permeation flux adjustment means to control the permeation flux within the above range.

[0132] Furthermore, at least one valve may be installed in each pipe, and there are no particular restrictions on the location or number of valves. In addition, a flow meter may be installed in at least one pipe as a means of measuring flow rate, and a pressure gauge may be installed in at least one pipe as a means of measuring pressure.

[0133] Furthermore, Figures 6 and 7 show an example of the apparatus configuration, and the number of semipermeable membrane modules, the number of parallel modules, the arrangement, and the method of supplying the water may be changed as appropriate.

[0134] In order to concentrate the substances to be recovered from NF-concentrated water to a desired concentration in the membrane module, it is preferable to arrange multiple membrane modules in series. When using multi-stage membrane modules as in water treatment devices 3, 4, 5, 6, and 7, the number of membrane module stages should be determined according to the desired concentration of the treated water. For example, if you want to obtain treated water with a higher concentration from NF-concentrated water with a lower concentration, you should increase the number of membrane module units.

[0135] When using membrane module units, such as those in water treatment devices 6 and 7, which have multiple membrane modules connected in parallel as membrane modules in each stage, the number of membrane modules in each membrane module unit can be determined by the flow rate of NF concentrated water, etc.

[0136] A concentration tank or dilution tank may be provided in one or more stages of the membrane module, or a concentration tank or dilution tank may be provided in each stage of the membrane module.

[0137] The wastewater to be treated is, for example, wastewater discharged from factories, and is not particularly limited. The wastewater is ammonia-containing wastewater, such as wastewater containing ammonium ions, wastewater containing sulfate ions and ammonium ions, or wastewater containing sulfate ions, ammonium ions and silica. Examples include wastewater discharged from semiconductor factories and wastewater discharged from chemical plants. In particular, semiconductor factories use ammonia for cleaning wafers, and sulfuric acid is used for scrubbing to treat the ammonia. Therefore, the wastewater contains ammonium ions and sulfate ions. Generally, evaporation methods such as evaporators and membrane distillation are used to recover ammonia and sulfuric acid from wastewater. However, by equipping the water treatment apparatus according to this embodiment before the evaporator or membrane distillation apparatus and supplying concentrated water from the semipermeable membrane module to the evaporator or membrane distillation apparatus, the amount of water to be treated in the evaporator or membrane distillation apparatus can be reduced, the load can be reduced, and ammonia and sulfuric acid can be recovered efficiently.

[0138] The wastewater before being sent to the nanofiltration device 11 (or, if a pretreatment means is provided, after pretreatment and before being sent to the nanofiltration device 11) may contain ionic components such as monovalent ions and divalent ions at a certain concentration or higher, and may also contain uncharged substances. The wastewater is, for example, ammonia-containing wastewater containing ammonium ions at a concentration of 2000 mg / L or more, and preferably contains ammonium ions at a concentration of 2000 to 100000 mg / L. The ammonia-containing wastewater may further contain, for example, sulfate ions at a concentration of 6000 mg / L or more and silica as an uncharged substance at a concentration of 5 mg / L or more, and preferably contains sulfate ions at a concentration of 20000 to 250000 mg / L and silica as an uncharged substance at a concentration of 5 to 50 mg / L.

[0139] The nanofiltration device 11 can be any device that can obtain NF permeate water and NF concentrated water using a nanofiltration membrane (NF membrane) for wastewater, and there are no particular restrictions.

[0140] Here, a nanofiltration membrane refers to a membrane that has an NaCl rejection rate of 10% to 70% when filtering an aqueous NaCl solution with a concentration of 2000 mg / liter under operating pressure of 1.5 MPa and temperature of 25°C. The membrane material is not particularly limited, but examples include cellulose resins such as cellulose acetate resin, polysulfone resins such as polyethersulfone resin, and polyamide resin. The membrane shape is not particularly limited, but examples include spiral type and hollow fiber type. The primary pressure during operation is preferably in the range of 0.5 MPa to 10 MPa.

[0141] The nanofiltration membrane is preferably one in which the silica rejection rate is in the range of 0-20% and the ammonium ion rejection rate and sulfate ion rejection rate are in the range of 90-100% under conditions of an effective membrane pressure of 1 MPa, 25°C, and pH 7, and more preferably one in which the silica rejection rate is in the range of 5-18% and the ammonium ion rejection rate and sulfate ion rejection rate are in the range of 97-100%. If the silica rejection rate of the nanofiltration membrane exceeds 20%, the risk of silica scale deposition in the membrane module 10 may increase if silica is present in the ammonia-containing wastewater. If the ammonium ion rejection rate and sulfate ion rejection rate of the nanofiltration membrane are less than 90%, the recovery rate of ammonia and sulfuric acid may decrease.

[0142] Here, the rejection rates of each component—silica, ammonium ions, and sulfate ions—to determine the properties of the nanofiltration membrane can be calculated using the following formula: Rejection rate (%) = 100 - 100 × {[A / ((B+C) / 2)]} A: Ion concentration of each component in the permeate (mg / L) B: Ion concentration of each component in the water supply (mg / L) C: Ion concentration of each component in concentrated water (mg / L) The water supply and nanofiltration membrane treatment conditions for determining the silica, ammonium ion, and sulfate ion rejection rates of the above-mentioned nanofiltration membrane are as follows. Water supply: An aqueous solution containing ammonium sulfate at a concentration of 16,500 mg / L and silica at a concentration of 20 mg / L. Nanofiltration membrane treatment conditions: Water temperature 25°C, permeate flux 0.4 m3 / m 2 / d, recovery rate 15% Here, recovery rate (%) = 100 × [amount of permeate water in nanofiltration membrane treatment (m³) 3 [Amount of water supplied for nanofiltration membrane treatment (m³)] / [Amount of water supplied for nanofiltration membrane treatment (m³)] 3 / h)

[0143] Examples of semipermeable membranes 12 included in the membrane module include reverse osmosis membranes (RO membranes), forward osmosis membranes (FO membranes), and nanofiltration membranes (NF membranes). Reverse osmosis membranes, forward osmosis membranes, and nanofiltration membranes are preferred as semipermeable membranes.

[0144] The material constituting the semipermeable membrane 12 is not particularly limited, but examples include cellulose resins such as cellulose acetate resins, polysulfone resins such as polyethersulfone resins, and polyamide resins.

[0145] Examples of semipermeable membrane shapes for the semipermeable membrane 12 include flat membranes, hollow fiber membranes, and spiral membranes. Hollow fiber membranes are preferred because they allow for a larger surface area of ​​the semipermeable membrane.

[0146] The recovered material from the concentrated water consists of at least one of the ammonia and ammonium ions contained in the NF concentrated water, as well as dissolved solids (TDS). Examples of dissolved solids include inorganic salts such as sodium sulfate, calcium sulfate, sodium chloride, and calcium chloride.

[0147] The water treatment method and water treatment apparatus according to this embodiment may include at least one pretreatment step (pretreatment means) prior to the nanofiltration step (nanofiltration means), such as a membrane treatment step (membrane treatment means) using a microfiltration membrane (MF membrane), an ultrafiltration membrane (UF membrane), etc., a reverse osmosis membrane treatment step (reverse osmosis membrane treatment means), a coagulation and sedimentation treatment step (coagulation and sedimentation treatment means), an organic matter removal treatment step (organic matter removal treatment means), a pH adjustment step (pH adjustment means), and a temperature adjustment step (temperature adjustment means).

[0148] If turbidity is present, pretreatment such as coagulation and sedimentation, membrane separation, or pressurized flotation may be performed before the nanofiltration process (nanofiltration apparatus 11).

[0149] Prior to the nanofiltration process (nanofiltration device 11), pH and temperature adjustment of the wastewater may be performed. An example of such a water treatment apparatus is shown in Figure 8.

[0150] The water treatment apparatus 8 in Figure 8 may, in addition to the configuration of the water treatment apparatus 2 in Figure 2, further include a pH adjustment device 13 as a pH adjustment means for adjusting the pH of wastewater and a temperature adjustment device 15 as a temperature adjustment means for adjusting the temperature of wastewater, prior to the nanofiltration process (nanofiltration device 11).

[0151] In the water treatment apparatus 8 of Figure 8, piping 31 is connected to the inlet of the pH adjuster 13. The outlet of the pH adjuster 13 and the inlet of the temperature adjuster 15 are connected by piping 33. The outlet of the temperature adjuster 15 and the inlet of the nanofiltration apparatus 11 are connected by piping 25 via a pump 21. The connection order of the pH adjuster 13 and the temperature adjuster 15 may be reversed. The other configurations are the same as those of the water treatment apparatus 2 of Figure 2. In the water treatment apparatuses 1, 3, and 7 of Figures 1 and 3 to 7, a pH adjuster 13 and a temperature adjuster 15 may be provided.

[0152] In the water treatment apparatus 8, the ammonia-containing wastewater, which is the water to be treated, is sent to the pH adjustment device 13 through the piping 31. In the pH adjustment device 13, the pH of the ammonia-containing wastewater is adjusted (pH adjustment step). The pH-adjusted ammonia-containing wastewater is sent to the temperature adjustment device 15 through the piping 33. In the temperature adjustment device 15, the temperature of the ammonia-containing wastewater is adjusted (temperature adjustment step). The connection order of the pH adjustment device 13 and the temperature adjustment device 15 may be reversed, and the pH of the ammonia-containing wastewater may be adjusted after the temperature adjustment of the ammonia-containing wastewater (temperature adjustment step).

[0153] The ammonia-containing wastewater, whose pH and temperature have been adjusted, is supplied to the nanofiltration device 11 through the piping 25 by the pump 21. Subsequently, the nanofiltration process and the semipermeable membrane treatment process are carried out in the same manner as the water treatment device 2 in Figure 2. Water may be supplied to the nanofiltration device 11 and the membrane module 10 using only the pump 21.

[0154] As described above, at least one of ammonia and ammonium ions is recovered as concentrated water from the ammonia-containing wastewater, which is the target of treatment, thereby reducing the volume of the ammonia-containing wastewater. Furthermore, the NF permeate, concentrated water, and diluted water can be reused.

[0155] The pH adjustment device 13 includes, for example, means for adding a pH adjusting agent such as a piping for adding a pH adjusting agent, a pH measuring device, a pH adjustment tank, etc. It is preferable to add a pH adjusting agent in the pH adjustment tank to adjust the pH of the wastewater to a range of pH 4 to 8, preferably a range of pH 4 to 7. If the pH of the wastewater is less than 4, the rejection rate of ammonium ions by the nanofiltration membrane may decrease if the wastewater contains ammonia, and if the pH exceeds 8, if the wastewater contains ammonia, ammonia will start to gasify and permeate the nanofiltration membrane, which may reduce the concentration efficiency of ammonia. pH adjustment may also be performed in piping, etc., without providing a pH adjustment tank.

[0156] Examples of pH adjusters include acids such as hydrochloric acid and sulfuric acid, and alkalis such as sodium hydroxide.

[0157] The temperature control device 15 includes, for example, a temperature control tank, a heating device such as a heater, a cooling device such as a cooler, a heat exchanger, a heat pump, etc. It is preferable to adjust the temperature of the wastewater to a range of 20°C to 35°C, and if the wastewater contains silica, it is more preferable to adjust it to a range of 25°C to 35°C in order to suppress the precipitation of silica scale. If the temperature of the wastewater is below 20°C, the silica precipitation concentration may decrease if the wastewater contains silica, and if it exceeds 35°C, the blocking performance of the nanofiltration membrane and semipermeable membrane may decrease.

[0158] Before passing water through the semipermeable membrane module downstream of the nanofiltration device 11, pH and temperature adjustments may be performed again. The pH and water temperature when water passes through the semipermeable membrane module should be determined by the water quality of the wastewater, the material of the semipermeable membrane module, etc. For example, it is preferable that the pH of the wastewater be in the range of 4 to 8 and the water temperature be in the range of 20°C to 35°C.

[0159] pH adjustment can be performed, for example, by setting up a pH adjustment tank and adding a pH adjusting agent in the tank to adjust the pH.

[0160] Water temperature can be adjusted, for example, by providing a water temperature adjustment tank and heating it with a heating device such as a heater, or by providing a heat exchanger.

[0161] This specification includes the embodiments described below. (1) A water treatment device for recovering valuable materials from wastewater, A nanofiltration means for obtaining NF permeate water and NF concentrated water from the wastewater using a nanofiltration membrane, A semipermeable membrane module having a first space and a second space separated by a semipermeable membrane is used to obtain concentrated water by passing the NF concentrated water through the first space and pressurizing the first space to allow the water contained in the NF concentrated water to pass through the semipermeable membrane, and a semipermeable membrane processing means is used to obtain diluted water by passing a part of the NF concentrated water or at least a part of the concentrated water through the second space, A water treatment device equipped with the following features.

[0162] (2) A water treatment device for recovering valuable materials from wastewater, A nanofiltration means for obtaining NF permeate water and NF concentrated water from the wastewater using a nanofiltration membrane, A semipermeable membrane processing means that uses a multi-stage connected semipermeable membrane module having a first space and a second space separated by a semipermeable membrane, through which the NF concentrated water is passed through the first space of the first stage semipermeable membrane module, pressurizes the first space to allow the water contained in the NF concentrated water to pass through the semipermeable membrane to obtain concentrated water, further obtains concentrated water using the subsequent semipermeable membrane modules, and passes the NF concentrated water or at least a portion of the concentrated water or at least a portion of the diluted water obtained from other semipermeable membrane modules through the second space of each stage semipermeable membrane module to obtain diluted water, A water treatment device equipped with the following features.

[0163] (3) A water treatment apparatus as described in (1) or (2), A water treatment apparatus further comprising a return means for returning at least a portion of the diluted water obtained by the semipermeable membrane treatment means to the stage before the nanofiltration means.

[0164] (4) A water treatment apparatus described in any one of (1) to (3), The aforementioned nanofiltration membrane has a silica rejection rate in the range of 0-20% and an ammonium ion rejection rate and sulfate ion rejection rate in the range of 90-100% under conditions of an effective membrane pressure of 1 MPa, 25°C, and pH 7, in a water treatment apparatus.

[0165] (5) A water treatment apparatus described in any one of (1) to (4), A water treatment apparatus further comprising a pH adjusting means for adjusting the pH of the wastewater to a range of 4 to 8, preceding the nanofiltration means.

[0166] (6) A water treatment apparatus described in any one of (1) to (5), A water treatment apparatus further comprising a temperature adjustment means for adjusting the temperature of the wastewater to a range of 20°C to 35°C, prior to the nanofiltration means.

[0167] (7) A water treatment method for recovering valuable materials from wastewater, The aforementioned wastewater is subjected to a nanofiltration process using a nanofiltration membrane to obtain NF permeate water and NF concentrated water, A semipermeable membrane processing step is performed using a semipermeable membrane module having a first space and a second space separated by a semipermeable membrane, passing the NF concentrated water through the first space, pressurizing the first space to allow the water contained in the NF concentrated water to pass through the semipermeable membrane to obtain concentrated water, and passing a portion of the NF concentrated water or at least a portion of the concentrated water through the second space to obtain diluted water. A water treatment method, including

[0168] (8) A water treatment method for recovering valuable materials from wastewater, The aforementioned wastewater is subjected to a nanofiltration process using a nanofiltration membrane to obtain NF permeate water and NF concentrated water, A semipermeable membrane processing step is performed using a multi-stage connected semipermeable membrane module having a first space and a second space separated by a semipermeable membrane, passing the NF concentrated water through the first space of the first stage semipermeable membrane module, pressurizing the first space to allow the water contained in the NF concentrated water to pass through the semipermeable membrane to obtain concentrated water, further obtaining concentrated water using the subsequent semipermeable membrane modules, and passing the NF concentrated water or at least a portion of the concentrated water or at least a portion of the diluted water obtained from other semipermeable membrane modules through the second space of each stage semipermeable membrane module to obtain diluted water. A water treatment method, including

[0169] A water treatment method as described in (9), (7), or (8), A water treatment method comprising returning at least a portion of the diluted water obtained in the semipermeable membrane treatment step to the stage preceding the nanofiltration step.

[0170] A water treatment method described in any one of (10), (7), to (9), The water treatment method is characterized in that the wastewater contains 2000 mg / L or more of ammonium ions, 6000 mg / L or more of sulfate ions, and 5 mg / L or more of silica. [Examples]

[0171] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0172] <Example 1> Wastewater containing ammonia, with an ammonium ion concentration of 4500 mg / L, a sulfate ion concentration of 12000 mg / L, and a silica concentration of 30 mg / L, was concentrated using a spiral-type NF membrane (a membrane with a silica rejection rate of 15% and ammonium ion and sulfate ion rejection rates of 99% under conditions of effective membrane pressure of 1 MPa, 25°C, and pH 7). During this process, the pH of the treated water was varied within the range of 4 to 9. The silica concentrations in the treated water, concentrated water, and permeate after passing through the NF membrane were measured using molybdenum yellow spectrophotometric analysis. The silica rejection rate was calculated from each silica concentration. The rejection rate is calculated as: Rejection rate % = (1 - (NF permeate water silica concentration / NF supply water silica concentration)) × 100. The NF membrane was operated under the following conditions: supply water rate of 840 L / h, NF concentrated water rate of 720 L / h, and NF permeate water rate of 120 L / h. The results of the silica rejection rate are shown in Figure 9.

[0173] Furthermore, using the water treatment apparatus 2 shown in Figure 2, when the NF membrane was concentrated with a recovery rate of 60% and then concentrated to the silica precipitation concentration of 120 mg / L in the subsequent semipermeable membrane module, Table 1 shows the ratio of the ammonium ion concentration of the concentrated water in the semipermeable membrane module to the ammonium ion concentration in the treated water at each pH condition (water temperature 25±1℃). The return rate of the diluted water from the semipermeable membrane module to the NF membrane module upstream was assumed to be 100%.

[0174] [Table 1]

[0175] As shown in Figure 9, the higher the pH of the treated water, the lower the silica blocking rate of the NF membrane, and the silica escaped to the permeate side of the NF membrane. In other words, the silica concentration on the NF concentrated water side was not concentrated, making it possible to concentrate other coexisting substances. As shown in Table 1, as the pH of the treated water increased and the silica blocking rate decreased, the concentration of the final concentrated water could also be increased. At pH 9, it was possible to concentrate the water to a concentration exceeding the solubility of ammonium sulfate under these concentration conditions.

[0176] <Example 2> Using an NF membrane, water with an ammonium ion concentration of 4500 mg / L, a sulfate ion concentration of 12000 mg / L, and a silica concentration of 30 mg / L was concentrated at pH 7 and a water temperature of 25 ± 1°C with a recovery rate of 60% in the NF membrane, and then concentrated to the silica precipitation concentration of 120 mg / L in a subsequent semipermeable membrane module. Table 2 shows the ratio of the ammonium ion concentration of the concentrated water in the semipermeable membrane module to the ammonium ion concentration in the water being treated, when the return rate of the dilution water from the semipermeable membrane module that returns to the preceding NF membrane was changed to three patterns: 0%, 50%, and 100%.

[0177] [Table 2]

[0178] As shown in Table 2, when the dilution water return rate of the semipermeable membrane module was 0%, the concentration ratio of the final concentrated water in the semipermeable membrane module was 9.5 times. However, when the return rate was set to 50% and 100%, the ammonium ion concentration in the final concentrated water increased to 12.2 times and 14.9 times, respectively.

[0179] Thus, the apparatus and method of the examples made it possible to recover valuable substances from ammonia-containing wastewater at high concentrations. [Explanation of symbols]

[0180] 1,2,3,4,5,6,7,8 Water treatment equipment, 10,10a,10b,10c Membrane modules, 11 Nanofiltration equipment, 12,12a,12b,12c Semipermeable membranes, 13 pH adjustment equipment, 14,14a,14b,14c First space, 15 Temperature control equipment, 16,16a,16b,16c Second space, 18,21 Pumps, 20 Inverters, 22,22a,22b,22c,23,32,32a,32b,32c Valves: 24, 25, 26, 27, 28, 29, 30, 31, 33, 34, 36, 40, 42, 44, 46, 48, 50, 52, 54, 56, 58, 59, 61, 63, 64, 66, 68, 70, 72, 74, 76, 78, 80, 82, 88, 90, 92, 94, 96, 98, 102, 104, 106, 108, 110, 112, 114, 116, 118, 120, 122, 124, 126 Piping: 60a, 60b, 60c, 62a, 62b, 62c Dilution tank: 84 NF concentration tank: 86 Concentration tank: 100, 100a, 100b, 100c, 100d Membrane module unit.

Claims

1. A water treatment apparatus for recovering valuable substances from wastewater containing sulfate ions, ammonium ions, and silica, A nanofiltration means for obtaining NF permeate water and NF concentrated water using a nanofiltration membrane for the wastewater, A semipermeable membrane module having a first space and a second space separated by a semipermeable membrane is used to obtain concentrated water by passing the NF concentrated water through the first space and pressurizing the first space to allow the water contained in the NF concentrated water to pass through the semipermeable membrane, and a semipermeable membrane processing means is used to obtain diluted water by passing a part of the NF concentrated water or at least a part of the concentrated water through the second space, Equipped with, The water treatment apparatus is characterized in that the nanofiltration membrane has a silica rejection rate in the range of 5% to 20% and an ammonium ion rejection rate and sulfate ion rejection rate in the range of 90% to 100% under conditions of an effective membrane pressure of 1 MPa, 25°C, and pH 7.

2. A water treatment apparatus for recovering valuable substances from wastewater containing sulfate ions, ammonium ions, and silica, A nanofiltration means for obtaining NF permeate water and NF concentrated water using a nanofiltration membrane for the wastewater, A semipermeable membrane processing means that uses a multi-stage connected semipermeable membrane module having a first space and a second space separated by a semipermeable membrane, through which the NF concentrated water is passed to the first space of the first stage semipermeable membrane module, pressurizes the first space to allow the water contained in the NF concentrated water to pass through the semipermeable membrane to obtain concentrated water, further concentrates this concentrated water using subsequent semipermeable membrane modules, and passes the NF concentrated water or at least a portion of the concentrated water or at least a portion of the diluted water obtained from other semipermeable membrane modules through the second space of each stage semipermeable membrane module to obtain diluted water, Equipped with, The water treatment apparatus is characterized in that the nanofiltration membrane has a silica rejection rate in the range of 5% to 20% and an ammonium ion rejection rate and sulfate ion rejection rate in the range of 90% to 100% under conditions of an effective membrane pressure of 1 MPa, 25°C, and pH 7.

3. A water treatment apparatus according to claim 1 or 2, A water treatment apparatus further comprising a return means for returning at least a portion of the diluted water obtained by the semipermeable membrane treatment means to the stage before the nanofiltration means.

4. A water treatment apparatus according to claim 1 or 2, The water treatment apparatus is characterized in that the nanofiltration membrane has a silica rejection rate in the range of 5 to 18% and an ammonium ion rejection rate and sulfate ion rejection rate in the range of 97% to 100% under conditions of an effective membrane pressure of 1 MPa, 25°C, and pH 7.

5. A water treatment apparatus according to claim 1 or 2, A water treatment apparatus further comprising a pH adjusting means for adjusting the pH of the wastewater to a range of 4 to 8, prior to the nanofiltration means.

6. A water treatment apparatus according to claim 1 or 2, A water treatment apparatus further comprising a temperature adjustment means for adjusting the temperature of the wastewater to a range of 20°C to 35°C, prior to the nanofiltration means.

7. A water treatment method for recovering valuable substances from wastewater containing sulfate ions, ammonium ions, and silica, The aforementioned wastewater is subjected to a nanofiltration process using a nanofiltration membrane to obtain NF permeate water and NF concentrated water, A semipermeable membrane processing step is performed using a semipermeable membrane module having a first space and a second space separated by a semipermeable membrane, passing the NF concentrated water through the first space, pressurizing the first space to allow the water contained in the NF concentrated water to pass through the semipermeable membrane to obtain concentrated water, and passing a portion of the NF concentrated water or at least a portion of the concentrated water through the second space to obtain diluted water. Includes, The aforementioned nanofiltration membrane is characterized in that, under conditions of an effective membrane pressure of 1 MPa, 25°C, and pH 7, the silica rejection rate is in the range of 5% to 20%, and the ammonium ion rejection rate and sulfate ion rejection rate are in the range of 90% to 100%.

8. A water treatment method for recovering valuable substances from wastewater containing sulfate ions, ammonium ions, and silica, The aforementioned wastewater is subjected to a nanofiltration process using a nanofiltration membrane to obtain NF permeate water and NF concentrated water, A semipermeable membrane processing step is performed using a multi-stage connected semipermeable membrane module having a first space and a second space separated by a semipermeable membrane, passing the NF concentrated water through the first space of the first stage semipermeable membrane module, pressurizing the first space to allow the water contained in the NF concentrated water to pass through the semipermeable membrane to obtain concentrated water, further obtaining concentrated water using the subsequent semipermeable membrane modules, and passing the NF concentrated water or at least a portion of the concentrated water or at least a portion of the diluted water obtained from other semipermeable membrane modules through the second space of each stage semipermeable membrane module to obtain diluted water, Includes, The aforementioned nanofiltration membrane is characterized in that, under conditions of an effective membrane pressure of 1 MPa, 25°C, and pH 7, the silica rejection rate is in the range of 5% to 20%, and the ammonium ion rejection rate and sulfate ion rejection rate are in the range of 90% to 100%.

9. A water treatment method according to claim 7 or 8, A water treatment method characterized by returning at least a portion of the diluted water obtained in the semipermeable membrane treatment step to the stage preceding the nanofiltration step.

10. A water treatment method according to claim 7 or 8, A water treatment method characterized in that the wastewater contains 2,000 mg / L or more of ammonium ions, 6,000 mg / L or more of sulfate ions, and 5 mg / L or more of silica.

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