Water treatment method and water treatment apparatus

Abstract

To provide a water treatment method and a water treatment apparatus capable of concentrating water to be treated containing ammonia and silica while reducing a silica concentration.SOLUTION: There is provided a water treatment method, which is a water treatment method for concentrating water to be treated containing ammonia and silica, the method including: a pH adjustment step of adjusting pH of water to be treated to a range of 7 to 9 with a pH adjustment device 13; and a nanofiltration step of obtaining NF permeated water and NF concentrated water using a nanofiltration membrane in a nanofiltration device 11 for the pH-adjusted water to be treated. The water to be treated contains 1000 mg / L or more of ammonium ions, 1000 mg / L or more of divalent anions, and 5 mg / L or more of silica.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a water treatment method and a water treatment apparatus for concentrating water to be treated containing ammonia and silica.

[0002] In recent years, a method of recovering valuable materials from wastewater discharged from semiconductor factories and the like that contains sulfuric acid, ammonia 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 before the evaporation step is generally used, as disclosed in Patent Document 1.

[0003] On the other hand, as a method for concentrating ions contained in wastewater to a high concentration, as disclosed in Patent Document 2, a method has been developed in which hard components or turbid components in the concentrate of a reverse osmosis membrane module are removed with a nanofiltration membrane or an ultrafiltration membrane, and then the permeated water is concentrated with a semipermeable membrane module.

[0004] Water to be treated, such as wastewater discharged from semiconductor factories and the like, sometimes contains scale components, so membrane clogging occurs when high concentration is performed by semipermeable membrane treatment, which may make concentration difficult. In particular, when silica (SiO₂) is contained in the water to be treated, it is desirable to remove silica in the pretreatment step of the semipermeable membrane treatment, but if the concentration of silica is high, it may be difficult to handle this with chemicals such as dispersants. [Prior Art Literature] [Patent Literature]

[0005] [Patent Document 1] Japanese Unexamined Patent Publication No. 10-323664 [Patent Document 2] Japanese Unexamined Patent Publication No. 2021-045736 [Summary of the Invention] [Problem to be Solved by the Invention]

[0006] The object of the present invention is to provide a water treatment method and a water treatment apparatus that can concentrate treated water containing ammonia and silica by reducing the silica concentration. [Means for solving the problem]

[0007] The present invention sulfate ions, A water treatment method for concentrating water to be treated containing ammonia and silica, comprising: a pH adjustment step of adjusting the pH of the water to be treated to a range of 7 to 9; and a nanofiltration step of obtaining NF permeate water and NF concentrated water from the pH-adjusted water to be treated using a nanofiltration membrane, wherein the water to be treated contains 1000 mg / L or more of ammonium ions, 1000 mg / L or more of divalent anions, and 5 mg / L or more of silica. Furthermore, the nanofiltration membrane exhibits a silica rejection rate in the range of 0-20% and ammonium ion and sulfate ion rejection rates in the range of 90-100% under conditions of an effective membrane pressure of 1 MPa, 25°C, and pH 7. This is a water treatment method.

[0008] In the water treatment method described above, it is preferable to further include an ammonia treatment step for treating the ammonia gas discharged in the nanofiltration step, in which the pH of the water to be treated is adjusted to a range of 8 to 9 in the pH adjustment step.

[0009] In the water treatment method described above, it is preferable to further include a semipermeable membrane treatment step after the nanofiltration step in which the NF concentrated water is treated with a semipermeable membrane to obtain concentrated water and diluted water.

[0011] The present invention sulfate ions, A water treatment apparatus for concentrating water to be treated containing ammonia and silica, comprising: a pH adjustment means for adjusting the pH of the water to be treated to a range of 7 to 9; and a nanofiltration means for obtaining NF permeate water and NF concentrated water from the pH-adjusted water to be treated using a nanofiltration membrane, wherein the water to be treated contains 1000 mg / L or more of ammonium ions, 1000 mg / L or more of divalent anions, and 5 mg / L or more of silica. Furthermore, the nanofiltration membrane exhibits a silica rejection rate in the range of 0-20% and ammonium ion and sulfate ion rejection rates in the range of 90-100% under conditions of an effective membrane pressure of 1 MPa, 25°C, and pH 7. It is a water treatment device.

[0012] In the water treatment apparatus described above, it is preferable that the pH of the water to be treated is adjusted to a range of 8 to 9 by the pH adjusting means, and the apparatus further comprises ammonia treatment means for treating ammonia gas discharged by the nanofiltration means.

[0013] In the water treatment apparatus described above, it is preferable that the apparatus further comprises, downstream of the nanofiltration means, semipermeable membrane treatment means for obtaining concentrated water and diluted water from the NF concentrated water by using a semipermeable membrane. [[Effects of the Invention]]

[0015] According to the present invention, there can be provided a water treatment method and a water treatment apparatus capable of concentrating water to be treated containing ammonia and silica while reducing the silica concentration. [[Brief Description of the Drawings]]

[0016] [Figure 1] Fig. 1 is a schematic configuration diagram showing one example of a water treatment apparatus according to an embodiment of the present invention. [Figure 2] Fig. 2 is a schematic configuration diagram showing another example of a water treatment apparatus according to an embodiment of the present invention. [Figure 3] Fig. 3 is a schematic configuration diagram showing another example of a water treatment apparatus according to an embodiment of the present invention. [Figure 4] Fig. 4 is a schematic configuration diagram showing another example of a water treatment apparatus according to an embodiment of the present invention. [Figure 5] Fig. 5 is a schematic configuration diagram showing another example of a water treatment apparatus according to an embodiment of the present invention. [Figure 6] Fig. 6 is a schematic configuration diagram showing another example of a water treatment apparatus according to an embodiment of the present invention. [Figure 7] Fig. 7 is a schematic configuration diagram showing another example of a water treatment apparatus according to an embodiment of the present invention. [Figure 8] Fig. 8 is a schematic configuration diagram showing another example of a water treatment apparatus according to an embodiment of the present invention. [Figure 9] Fig. 9 is a graph showing the result of silica rejection in Example 1. [[Mode for Carrying Out the Invention]]

[0017] Embodiments of the present invention will be described below. The present embodiment is an example for carrying out the present invention, and the present invention is not limited to the present embodiment.

[0018] An outline of an example of a water treatment apparatus according to an embodiment of the present invention is shown in FIG. 1, and the configuration thereof will be described.

[0019] The water treatment apparatus 1 shown in FIG. 1 is an apparatus for concentrating water to be treated containing ammonia and silica. The water treatment apparatus 1 comprises a pH adjuster 13 as pH adjusting means for adjusting the pH of the water to be treated to a range of 7 to 9, and a nanofiltration device 11 as nanofiltration means for obtaining NF permeate and NF concentrate from the pH-adjusted water to be treated using a nanofiltration membrane. The water treatment apparatus 1 uses a semipermeable membrane module having a first space (concentration side) 14 and a second space (permeation side) 16 partitioned by a semipermeable membrane 12, passes the NF concentrate from the nanofiltration device 11 into the first space 14, pressurizes the first space 14 to allow water contained in the NF concentrate to permeate through the semipermeable membrane 12 to obtain concentrated water, and may be provided with, for example, a membrane module 10 as semipermeable membrane treatment means for passing a part of the NF concentrate into the second space 16 to obtain diluted water. The water treatment apparatus 1 may be provided with an NF concentrate tank for storing NF concentrate between the nanofiltration device 11 and the membrane module 10. The water treatment apparatus 1 may be provided with an ammonia treatment device 35 as ammonia treatment means for treating ammonia gas discharged from the nanofiltration device 11.

[0020] In the water treatment apparatus 1 shown in Figure 1, piping 31 is connected to the inlet of the pH adjuster 13. The outlet of the pH adjuster 13 and the inlet of the nanofiltration apparatus 11 are connected by piping 25 via pump 21. The NF permeate outlet of the nanofiltration apparatus 11 and the inlet of the ammonia treatment apparatus 35 are connected by piping 27. Piping 37 is connected to the outlet of the ammonia treatment apparatus 35. 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, and piping 26, which branches off from piping 24 downstream of pump 18, is connected to the second space inlet of the membrane module 10 via valve 22. Piping 28 is connected to the first space outlet of the membrane module 10 via valve 23, and piping 30 is connected to the second space outlet of the membrane module 10 and the upstream side of pump 21 in piping 25.

[0021] 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 water to be treated 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.

[0022] 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.

[0023] In the water treatment apparatus 1, the water to be treated, containing ammonia and silica, is sent to the pH adjustment device 13 through piping 31. In the pH adjustment device 13, the pH of the water to be treated is adjusted (pH adjustment step). The water to be treated, whose pH has been adjusted to the range of pH 7 to 9, 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 water to be treated using a nanofiltration membrane (nanofiltration step). 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.

[0024] In the pH adjustment process, the pH of the water to be treated is adjusted to a range of pH 7 to 9. By adjusting the pH of the water to be treated to a range of pH 7 to 9, ammonia and silica permeate through the nanofiltration membrane, and most of the ammonia and silica are contained in the NF permeate. Note that silica is just one example; it is thought that other uncharged components will also permeate through the nanofiltration membrane. At this time, if the pH is below 7, the permeability of ammonia and silica through the nanofiltration membrane may be low, and if the pH exceeds 9, silica may ionize, and the permeability of silica may be low due to the effect of charge repulsion.

[0025] In the pH adjustment process, when the pH of the water to be treated is adjusted to a range of 8 to 9, the ammonia in the water to be treated is gasified. In this case, the water to be treated, whose pH has been adjusted to a range of 8 to 9, is supplied to the nanofiltration device 11, where NF permeate water and NF concentrated water are obtained from the water to be treated using a nanofiltration membrane (nanofiltration process). The NF permeate water is sent through the piping 27 to the ammonia treatment device 35, where the ammonia gas discharged in the nanofiltration process is treated to obtain treated water (ammonia treatment process). In the ammonia treatment process, ammonia gas is recovered from the NF permeate water or the ammonia gas is decomposed.

[0026] The NF concentrated water obtained from the nanofiltration device 11 may be subjected to semipermeable membrane treatment using a semipermeable membrane. With valve 23 open, the NF concentrated water obtained from the nanofiltration device 11 is pressurized and delivered through piping 24 by pump 18 from the first space inlet to the first space 14 of the membrane module 10, and water is passed through. Water may be supplied to the nanofiltration device 11 and the membrane module 10 using only pump 21. Alternatively, with valve 22 open, the NF concentrated water is delivered through piping 26 branched from piping 24 to the second space 16 of the membrane module 10, and water is passed through. A portion of the water contained in the pressurized NF concentrated water permeates from the first space 14 to the second space 16 via the semipermeable membrane 12. At this time, most of the ions and other substances contained in the NF concentrated water cannot permeate through the semipermeable membrane 12, so the water in the first space 14 that did not permeate through the semipermeable membrane 12 is concentrated. Meanwhile, in the second space 16, a portion of the NF concentrated water passed through the piping 26 and the permeate water with a low ion concentration that has permeated through 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 the piping 28, and the diluted water obtained in the second space 16 is discharged from the outlet of the second space through the piping 30. At least a portion of the diluted water may be returned to the upstream side of the pump 21 in the 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).

[0027] 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.

[0028] 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.

[0029] As described above, concentrated water with reduced ammonia and silica content is recovered from the treated water containing ammonia and silica, thereby reducing the volume of the treated water. Furthermore, the NF permeate, concentrated water, and diluted water can be reused.

[0030] Alternatively, as described above, ammonia-concentrated water with reduced silica content is recovered from the treated water containing ammonia and silica, thereby reducing the volume of the treated water.

[0031] 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.

[0032] Because wastewater discharged from semiconductor factories and other sources may contain scale components, membrane clogging can occur during high-concentration treatment using semipermeable membranes, making concentration difficult. In particular, if the water to be treated 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.

[0033] In the water treatment apparatus and water treatment method according to this embodiment, even if silica is present in the water to be treated, the nanofiltration apparatus 11 selectively allows the silica in the water to be treated 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.

[0034] 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 water to be treated, the ratio of silica concentration to ammonium ion concentration in the water to be treated 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] These operations allow the pressure and various flow rates on the first space 14 side to be adjusted to predetermined levels.

[0040] 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.

[0041] 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.

[0042] In this way, water to be treated containing ammonia and silica can be concentrated while reducing the silica concentration. Furthermore, valuable substances can be recovered from the treated water at high concentrations. Even if silica is present in the water to be treated, the risk of silica scale precipitation during the concentration process of the semipermeable membrane treatment can be reduced by treating the NF concentrated water with reduced silica concentration using a semipermeable membrane.

[0043] 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.

[0044] The water treatment apparatus 2 shown in Figure 2 includes a pH adjustment device 13 as a pH adjustment means for adjusting the pH of the water to be treated to a range of 7 to 9, and a nanofiltration device 11 as a nanofiltration means for obtaining NF permeate water and NF concentrated water from the pH-adjusted water to be treated using a nanofiltration membrane. The water treatment apparatus 2 may also include a membrane module 10 as a semipermeable membrane treatment means, for example, which uses a semipermeable membrane module having a first space (concentration side) 14 and a second space (permeation side) 16 separated by a semipermeable membrane 12 to pass the NF concentrated water from the nanofiltration device 11 through the first space 14, pressurize the first space 14 to allow the water contained in the NF concentrated water to permeate through the semipermeable membrane 12 to obtain concentrated water, and pass at least a portion of the concentrated water through the second space 16 to obtain diluted water. The water treatment apparatus 2 may also include an NF concentrated water tank for storing NF concentrated water between the nanofiltration device 11 and the membrane module 10. The water treatment apparatus 2 may also include an ammonia treatment device 35 as an ammonia treatment means for treating the ammonia gas discharged from the nanofiltration device 11.

[0045] In the water treatment apparatus 2 of Figure 2, piping 31 is connected to the inlet of the pH adjuster 13. The outlet of the pH adjuster 13 and the inlet of the nanofiltration apparatus 11 are connected by piping 25 via pump 21. The NF permeate outlet of the nanofiltration apparatus 11 and the inlet of the ammonia treatment apparatus 35 are connected by piping 27. Piping 37 is connected to the outlet of the ammonia treatment apparatus 35. 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. Piping 34, which branches off from piping 28 upstream of valve 23, is connected to the second space inlet of the membrane module 10 via valve 32. Piping 36 connects the second space outlet of the membrane module 10 to the upstream side of pump 21 in piping 25.

[0046] 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 water to be treated and discharges it under pressure to the nanofiltration device 11. Valves 23 and 32 are valves whose degree of opening and closing can be adjusted manually or automatically.

[0047] 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.

[0048] In the water treatment apparatus 2, the water to be treated, containing ammonia and silica, is sent to the pH adjustment device 13 through piping 31. In the pH adjustment device 13, the pH of the water to be treated is adjusted (pH adjustment step). The water to be treated, whose pH has been adjusted to the range of pH 7 to 9, 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 water to be treated using a nanofiltration membrane (nanofiltration step). The NF permeate water is discharged through piping 27.

[0049] In the pH adjustment process, the pH of the water to be treated is adjusted to a range of pH 7 to 9. By adjusting the pH of the water to be treated to a range of pH 7 to 9, ammonia and silica permeate through the nanofiltration membrane, and most of the ammonia and silica are contained in the NF permeate. If the pH of the water to be treated is adjusted to a range of pH 8 to 9 in the pH adjustment process, the water to be treated with a pH adjusted to a range of pH 8 to 9 is supplied to the nanofiltration device 11, where the water to be treated is processed using a nanofiltration membrane to obtain NF permeate and NF concentrated water (nanofiltration process). The NF permeate is then sent through piping 27 to the ammonia treatment device 35, where the ammonia gas discharged in the nanofiltration process is treated to obtain treated water (ammonia treatment process). In the ammonia treatment process, ammonia gas is recovered from the NF permeate or the ammonia gas is decomposed.

[0050] The NF concentrated water obtained from the nanofiltration device 11 may be subjected to semipermeable membrane treatment using a semipermeable membrane. 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 inlet of the first space to the first space 14 of the membrane module 10, and then passed through. Water flow to the nanofiltration device 11 and the membrane module 10 may 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 through the semipermeable membrane 12, so the water in the first space 14 that did not permeate through the semipermeable membrane 12 is concentrated. On the other hand, in the second space 16, a portion of the concentrated water passed through the piping 34 and the permeate water with a low ion concentration that has permeated through 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).

[0051] 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.

[0052] 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.

[0053] As described above, concentrated water with reduced ammonia and silica content is recovered from the treated water containing ammonia and silica, thereby reducing the volume of the treated water. Furthermore, the NF permeate, concentrated water, and diluted water can be reused.

[0054] Alternatively, as described above, ammonia-concentrated water with reduced silica content is recovered from the treated water containing ammonia and silica, thereby reducing the volume of the treated water.

[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 includes a pH adjustment device 13 as a pH adjustment means for adjusting the pH of the water to be treated to a range of 7 to 9, and a nanofiltration device 11 as a nanofiltration means for obtaining NF permeate water and NF concentrated water from the pH-adjusted water to be treated using a nanofiltration membrane. The water treatment apparatus 3 uses semipermeable membrane modules connected in multiple stages, 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 device 11 is passed through the first space 14 of the first stage semipermeable membrane module, and concentrated water is obtained by pressurizing the first space 14 to allow the water contained in the NF concentrated water to pass through the semipermeable membrane 12. Further concentrated water is obtained using the subsequent semipermeable membrane modules, and diluted water is obtained 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. For example, the apparatus may also include a first-stage membrane module 10a, a second-stage membrane module 10b, and a third-stage membrane module 10c as semipermeable membrane processing means. 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 the concentrated water to the first and second spaces of the next-stage membrane module for concentration treatment. The water treatment device 3 may include an NF concentrated water tank for storing NF concentrated water between the nanofiltration device 11 and the membrane module 10. The water treatment device 3 may also include an ammonia treatment device 35 as an ammonia treatment means for treating the ammonia gas discharged from the nanofiltration device 11.

[0069] In the water treatment apparatus 3 of Figure 3, piping 31 is connected to the inlet of the pH adjustment device 13. The outlet of the pH adjustment device 13 and the inlet of the nanofiltration device 11 are connected by piping 25 via pump 21. The NF permeate outlet of the nanofiltration device 11 and the inlet of the ammonia treatment apparatus 35 are connected by piping 27. Piping 37 is connected to the outlet of the ammonia treatment apparatus 35. The NF concentrated water outlet of the nanofiltration device 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. A pipe 48 branching from pipe 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 is connected to the inlet of the dilution tank 60b via pipe 52. The first space outlet of the second-stage membrane module 10b is connected to the first space inlet of the third-stage membrane module 10c via pipe 50. A pipe 54 branching from pipe 50 is connected to the second space inlet of the third-stage membrane module 10c via valve 22c. The second space outlet of the third-stage membrane module 10c is connected to the inlet of the dilution tank 60c via pipe 58. A pipe 56 is connected to the first space outlet of the third-stage membrane module 10c via valve 23. The outlet of the dilution tank 60a is connected to the upstream side of the pump 21 in pipe 25 via pipe 59. The outlet of the dilution tank 60b is connected to pipe 59 via pipe 61. The outlet of the dilution tank 60c and pipe 59 are connected by pipe 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, the water to be treated, containing ammonia and silica, is sent to the pH adjustment device 13 through piping 31. In the pH adjustment device 13, the pH of the water to be treated is adjusted (pH adjustment step). The water to be treated, whose pH has been adjusted to the range of pH 7 to 9, 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 water to be treated using a nanofiltration membrane (nanofiltration step). The NF permeate water is discharged through piping 27.

[0072] In the pH adjustment process, the pH of the water to be treated is adjusted to a range of pH 7 to 9. By adjusting the pH of the water to be treated to a range of pH 7 to 9, ammonia and silica permeate through the nanofiltration membrane, and most of the ammonia and silica are contained in the NF permeate. If the pH of the water to be treated is adjusted to a range of pH 8 to 9 in the pH adjustment process, the water to be treated with a pH adjusted to a range of pH 8 to 9 is supplied to the nanofiltration device 11, where the water to be treated is processed using a nanofiltration membrane to obtain NF permeate and NF concentrated water (nanofiltration process). The NF permeate is then sent through piping 27 to the ammonia treatment device 35, where the ammonia gas discharged in the nanofiltration process is treated to obtain treated water (ammonia treatment process). In the ammonia treatment process, ammonia gas is recovered from the NF permeate or the ammonia gas is decomposed.

[0073] The NF concentrated water obtained from the nanofiltration device 11 may be subjected to semipermeable membrane treatment using a semipermeable membrane. The NF concentrated water obtained from the nanofiltration device 11 is sent through 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 piping 40 is sent through piping 42 with valve 22a open to the second space 16a of the first-stage membrane module 10a. 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 dilution 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).

[0074] 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).

[0075] 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).

[0076] 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.

[0077] 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.

[0078] As described above, concentrated water (final-stage concentrated water) with reduced ammonia and silica content is recovered from the treated water containing ammonia and silica, thereby reducing the volume of the treated water. Furthermore, the NF permeate, concentrated water, and diluted water can be reused.

[0079] Alternatively, as described above, ammonia-concentrated water (final-stage concentrated water) with reduced silica content is recovered from the treated water containing ammonia and silica, thereby reducing the volume of the treated water.

[0080] The water treatment apparatus 4 shown in Figure 4 includes a pH adjustment device 13 as a pH adjustment means for adjusting the pH of the water to be treated to a range of 7 to 9, and a nanofiltration device 11 as a nanofiltration means for obtaining NF permeate water and NF concentrated water from the pH-adjusted water to be treated using a nanofiltration membrane. The water treatment apparatus 4 uses semipermeable membrane modules connected in multiple stages, 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 device 11 is passed through the first space 14 of the first stage semipermeable membrane module, and concentrated water is obtained by pressurizing the first space 14 to allow the water contained in the NF concentrated water to pass through the semipermeable membrane 12. Further concentrated water is obtained using the 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. For example, the apparatus may also include a first-stage membrane module 10a, a second-stage membrane module 10b, and a third-stage membrane module 10c as semipermeable membrane processing means. 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 include an NF concentrated water tank for storing NF concentrated water between the nanofiltration device 11 and the membrane module 10. The water treatment device 4 may also include an ammonia treatment device 35 as an ammonia treatment means for treating ammonia gas discharged from the nanofiltration device 11.

[0081] In the water treatment apparatus 4 of Figure 4, piping 31 is connected to the inlet of the pH adjuster 13. The outlet of the pH adjuster 13 and the inlet of the nanofiltration apparatus 11 are connected by piping 25 via pump 21. The NF permeate outlet of the nanofiltration apparatus 11 and the inlet of the ammonia treatment apparatus 35 are connected by piping 27. Piping 37 is connected to the outlet of the ammonia treatment apparatus 35. 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, which branches off 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 tank 62a are connected by piping 66. 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 68, which branches off from piping 50, is connected to the second space inlet of membrane module 10b via valve 32b. The second space outlet of the second membrane module 10b and the inlet of dilution tank 62b are connected by piping 70. Piping 56 is connected to the first space outlet of the third membrane module 10c via valve 23. Piping 72, which branches off from piping 56 upstream of valve 23, is connected to the second space inlet of membrane module 10c via valve 32c. The second space outlet of the third membrane module 10c and the inlet of dilution tank 62c are connected by piping 74. The outlet of dilution tank 62a and the upstream side of pump 21 in piping 25 are connected by piping 59. The outlet of dilution tank 62b and piping 59 are connected by piping 61. The outlet of dilution tank 62c and pipe 59 are connected by pipe 63.

[0082] 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.

[0083] In the water treatment device 4, the water to be treated, containing ammonia and silica, is sent to the pH adjustment device 13 through the piping 31. In the pH adjustment device 13, the pH of the water to be treated is adjusted (pH adjustment step). The water to be treated, whose pH has been adjusted to the range of pH 7 to 9, is supplied to the nanofiltration device 11 through the piping 25 by the pump 21. In the nanofiltration device 11, NF permeate water and NF concentrated water are obtained from the water to be treated using a nanofiltration membrane (nanofiltration step). The NF permeate water is discharged through the piping 27.

[0084] In the pH adjustment process, the pH of the water to be treated is adjusted to a range of pH 7 to 9. By adjusting the pH of the water to be treated to a range of pH 7 to 9, ammonia and silica permeate through the nanofiltration membrane, and most of the ammonia and silica are contained in the NF permeate. If the pH of the water to be treated is adjusted to a range of pH 8 to 9 in the pH adjustment process, the water to be treated with a pH adjusted to a range of pH 8 to 9 is supplied to the nanofiltration device 11, where the water to be treated is processed using a nanofiltration membrane to obtain NF permeate and NF concentrated water (nanofiltration process). The NF permeate is then sent through piping 27 to the ammonia treatment device 35, where the ammonia gas discharged in the nanofiltration process is treated to obtain treated water (ammonia treatment process). In the ammonia treatment process, ammonia gas is recovered from the NF permeate or the ammonia gas is decomposed.

[0085] The NF concentrated water obtained from the nanofiltration device 11 may be subjected to semipermeable membrane treatment using a semipermeable membrane. The NF concentrated water obtained from 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 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 64 to the second space 16a of the first-stage membrane module 10a with valve 32a open. The diluted water obtained in the second space 16a of the first-stage membrane module 10a is stored in the dilution tank 62a as needed through piping 66. At least a portion of the diluted water may be returned through piping 59 to the upstream side of the pump 21 in piping 25, which is the upstream stage of the nanofiltration device 11 (return process).

[0086] 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).

[0087] 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).

[0088] 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.

[0089] 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.

[0090] As described above, concentrated water (final-stage concentrated water) with reduced ammonia and silica content is recovered from the treated water containing ammonia and silica, thereby reducing the volume of the treated water. Furthermore, the NF permeate, concentrated water, and diluted water can be reused.

[0091] Alternatively, as described above, ammonia-concentrated water (final-stage concentrated water) with reduced silica content is recovered from the treated water containing ammonia and silica, thereby reducing the volume of the treated water.

[0092] 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.

[0093] The water treatment apparatus 5 shown in Figure 5 includes a pH adjustment device 13 as a pH adjustment means for adjusting the pH of the water to be treated to a range of 7 to 9, and a nanofiltration device 11 as a nanofiltration means for obtaining NF permeate water and NF concentrated water from the pH-adjusted water to be treated using a nanofiltration membrane. The water treatment apparatus 5 uses semipermeable membrane modules connected in multiple stages, 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 concentrated water is obtained by pressurizing the first space 14 to allow the water contained in the NF concentrated water to permeate through the semipermeable membrane 12. 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 apparatus may include a first-stage membrane module 10a, a second-stage membrane module 10b, and a third-stage membrane module 10c as semipermeable membrane processing means. 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 the concentrated water to the first space of the next-stage membrane module for concentration treatment. The water treatment device 5 may include an NF concentrated water tank for storing NF concentrated water between the nanofiltration device 11 and the membrane module 10. The water treatment device 5 may also include an ammonia treatment device 35 as an ammonia treatment means for treating the ammonia gas discharged from the nanofiltration device 11.

[0094] In the water treatment apparatus 5 of Figure 5, piping 31 is connected to the inlet of the pH adjuster 13. The outlet of the pH adjuster 13 and the inlet of the nanofiltration apparatus 11 are connected by piping 25 via pump 21. The NF permeate outlet of the nanofiltration apparatus 11 and the inlet of the ammonia treatment apparatus 35 are connected by piping 27. Piping 37 is connected to the outlet of the ammonia treatment apparatus 35. 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. 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 56 is connected to the first space outlet of the third stage membrane module 10c via valve 23. Upstream of valve 23, pipe 76, which branches off from pipe 56, is connected to the second space inlet of 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 by pipe 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 pipe 80. The second space outlet of the first-stage membrane module 10a and the upstream side of pump 21 in pipe 25 are connected by pipe 82.

[0095] 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.

[0096] In the water treatment apparatus 5, the water to be treated, containing ammonia and silica, is sent to the pH adjustment device 13 through the piping 31. In the pH adjustment device 13, the pH of the water to be treated is adjusted (pH adjustment step). The water to be treated, whose pH has been adjusted to the range of pH 7 to 9, is supplied to the nanofiltration device 11 through the piping 25 by the pump 21. In the nanofiltration device 11, NF permeate water and NF concentrated water are obtained from the water to be treated using a nanofiltration membrane (nanofiltration step). The NF permeate water is discharged through the piping 27.

[0097] In the pH adjustment process, the pH of the water to be treated is adjusted to a range of pH 7 to 9. By adjusting the pH of the water to be treated to a range of pH 7 to 9, ammonia and silica permeate through the nanofiltration membrane, and most of the ammonia and silica are contained in the NF permeate. If the pH of the water to be treated is adjusted to a range of pH 8 to 9 in the pH adjustment process, the water to be treated with a pH adjusted to a range of pH 8 to 9 is supplied to the nanofiltration device 11, where the water to be treated is processed using a nanofiltration membrane to obtain NF permeate and NF concentrated water (nanofiltration process). The NF permeate is then sent through piping 27 to the ammonia treatment device 35, where the ammonia gas discharged in the nanofiltration process is treated to obtain treated water (ammonia treatment process). In the ammonia treatment process, ammonia gas is recovered from the NF permeate or the ammonia gas is decomposed.

[0098] The NF concentrated water obtained from the nanofiltration device 11 may be subjected to semipermeable membrane treatment using a semipermeable membrane. The NF concentrated water obtained from 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).

[0099] 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.

[0100] 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.

[0101] 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.

[0102] 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.

[0103] As described above, concentrated water (final-stage concentrated water) with reduced ammonia and silica content is recovered from the treated water containing ammonia and silica, thereby reducing the volume of the treated water. Furthermore, the NF permeate, concentrated water, and diluted water can be reused.

[0104] Alternatively, as described above, ammonia-concentrated water (final-stage concentrated water) with reduced silica content is recovered from the treated water containing ammonia and silica, thereby reducing the volume of the treated water.

[0105] 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.

[0106] 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.

[0107] 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.

[0108] 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.

[0109] 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.

[0110] 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.

[0111] 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.

[0112] 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.

[0113] The water treatment apparatus 6 shown in Figure 6 includes a pH adjustment device 13 as a pH adjustment means for adjusting the pH of the water to be treated to a range of 7 to 9, and a nanofiltration device 11 as a nanofiltration means for obtaining NF permeate water and NF concentrated water from the pH-adjusted water to be treated using a nanofiltration membrane. The water treatment device 6 uses 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 device 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. For example, the semipermeable membrane treatment means may include 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. The water treatment device 6 may also include an ammonia treatment device 35 as an ammonia treatment means for treating the ammonia gas discharged from the nanofiltration device 11.

[0114] In the water treatment apparatus 6 of Figure 6, piping 31 is connected to the inlet of the pH adjustment device 13. The outlet of the pH adjustment device 13 and the inlet of the nanofiltration device 11 are connected by piping 25 via pump 21. The NF permeate outlet of the nanofiltration device 11 and the inlet of the ammonia treatment apparatus 35 are connected by piping 27. Piping 37 is connected to the outlet of the ammonia treatment apparatus 35. The NF concentrated water outlet of the nanofiltration device 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 and second space inlets of each membrane module of the first-stage membrane module unit 100a are connected by piping 88 via pump 18. The first space outlet of each membrane module of the first-stage membrane module unit 100a and the first and second space inlets of each membrane module of the second-stage membrane module unit 100b are connected by piping 90. The first space outlet of each membrane module in the second-stage membrane module unit 100b is connected to the first space inlet and second space inlet of each membrane module in the third-stage membrane module unit 100c by piping 94. The first space outlet of each membrane module in the third-stage membrane module unit 100c is connected to the first space inlet and second space inlet of each membrane module in the fourth-stage membrane module unit 100d by piping 98. The first space outlet of each membrane module in the fourth-stage membrane module unit 100d is connected to the inlet of the concentration tank 86 by piping 104. In the first-stage membrane module unit 100a, piping 92 is connected to the second space outlet of each membrane module; in the second-stage membrane module unit 100b, piping 96 is connected to the second space outlet of each membrane module; in the third-stage membrane module unit 100c, piping 102 is connected to the second space outlet of each membrane module; and in the fourth-stage membrane module unit 100d, piping 106 is connected to the second space outlet of each membrane module. Piping 96, 102, and 106 may merge into piping 92. Piping 92 is connected to the upstream side of the pump 21 in piping 25.

[0115] 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.

[0116] In the water treatment device 6, the water to be treated, containing ammonia and silica, is sent through piping 31 to the pH adjustment device 13. In the pH adjustment device 13, the pH of the water to be treated is adjusted (pH adjustment step). The water to be treated, whose pH has been adjusted to the range of pH 7 to 9, is supplied by pump 21 through piping 25 to the nanofiltration device 11. In the nanofiltration device 11, NF permeate water and NF concentrated water are obtained from the water to be treated using a nanofiltration membrane (nanofiltration step). The NF permeate water is discharged through piping 27.

[0117] In the pH adjustment process, the pH of the water to be treated is adjusted to a range of pH 7 to 9. By adjusting the pH of the water to be treated to a range of pH 7 to 9, ammonia and silica permeate through the nanofiltration membrane, and most of the ammonia and silica are contained in the NF permeate. If the pH of the water to be treated is adjusted to a range of pH 8 to 9 in the pH adjustment process, the water to be treated with a pH adjusted to a range of pH 8 to 9 is supplied to the nanofiltration device 11, where the water to be treated is processed using a nanofiltration membrane to obtain NF permeate and NF concentrated water (nanofiltration process). The NF permeate is then sent through piping 27 to the ammonia treatment device 35, where the ammonia gas discharged in the nanofiltration process is treated to obtain treated water (ammonia treatment process). In the ammonia treatment process, ammonia gas is recovered from the NF permeate or the ammonia gas is decomposed.

[0118] The NF concentrated water obtained from the nanofiltration device 11 may be subjected to semipermeable membrane treatment using a semipermeable membrane. The NF concentrated water obtained from the nanofiltration device 11 is stored in the NF concentration tank 84 as needed, and then pumped from the NF concentration tank 84 through the piping 88 by the pump 18 to the first space 14 and the 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 module 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 tank as needed through the piping 92 and then discharged. At least a portion of the dilution water may be returned through piping 92 to the upstream side of the pump 21 in piping 25, which is the stage before the nanofiltration device 11 (return step).

[0119] 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).

[0120] 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).

[0121] 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 upstream stage of the nanofiltration device 11, through piping 106, 102, 96, and 92 (return step).

[0122] 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.

[0123] 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.

[0124] As described above, concentrated water (final-stage concentrated water) with reduced ammonia and silica content is recovered from the treated water containing ammonia and silica, thereby reducing the volume of the treated water. Furthermore, the NF permeate, concentrated water, and diluted water can be reused.

[0125] Alternatively, as described above, ammonia-concentrated water (final-stage concentrated water) with reduced silica content is recovered from the treated water containing ammonia and silica, thereby reducing the volume of the treated water.

[0126] The water treatment apparatus 7 shown in Figure 7 includes a pH adjustment device 13 as a pH adjustment means for adjusting the pH of the water to be treated to a range of 7 to 9, and a nanofiltration device 11 as a nanofiltration means for obtaining NF permeate water and NF concentrated water from the pH-adjusted water to be treated using a nanofiltration membrane. The water treatment device 7 uses semipermeable membrane modules connected in multiple stages, 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 device 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. For example, the semipermeable membrane treatment means may include 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 for concentration treatment. The water treatment device 7 may also include an ammonia treatment device 35 as an ammonia treatment means for treating ammonia gas discharged from the nanofiltration device 11.

[0127] In the water treatment device 7 of Figure 7, piping 31 is connected to the inlet of the pH adjustment device 13. The outlet of the pH adjustment device 13 and the inlet of the nanofiltration device 11 are connected by piping 25 via pump 21. The NF permeate outlet of the nanofiltration device 11 and the inlet of the ammonia treatment device 35 are connected by piping 27. Piping 37 is connected to the outlet of the ammonia treatment device 35. The NF concentrated water outlet of the nanofiltration device 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 outlets of each membrane module in the second-stage membrane module unit 100b and the first space inlets of each membrane module in 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.

[0128] 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.

[0129] In the water treatment apparatus 7, the water to be treated, containing ammonia and silica, is sent to the pH adjustment device 13 through the piping 31. In the pH adjustment device 13, the pH of the water to be treated is adjusted (pH adjustment step). The water to be treated, whose pH has been adjusted to the range of pH 7 to 9, is supplied to the nanofiltration device 11 through the piping 25 by the pump 21. In the nanofiltration device 11, NF permeate water and NF concentrated water are obtained from the water to be treated using a nanofiltration membrane (nanofiltration step). The NF permeate water is discharged through the piping 27.

[0130] In the pH adjustment process, the pH of the water to be treated is adjusted to a range of pH 7 to 9. By adjusting the pH of the water to be treated to a range of pH 7 to 9, ammonia and silica permeate through the nanofiltration membrane, and most of the ammonia and silica are contained in the NF permeate. If the pH of the water to be treated is adjusted to a range of pH 8 to 9 in the pH adjustment process, the water to be treated with a pH adjusted to a range of pH 8 to 9 is supplied to the nanofiltration device 11, where the water to be treated is processed using a nanofiltration membrane to obtain NF permeate and NF concentrated water (nanofiltration process). The NF permeate is then sent through piping 27 to the ammonia treatment device 35, where the ammonia gas discharged in the nanofiltration process is treated to obtain treated water (ammonia treatment process). In the ammonia treatment process, ammonia gas is recovered from the NF permeate or the ammonia gas is decomposed.

[0131] The NF concentrated water obtained from the nanofiltration device 11 may be subjected to semipermeable membrane treatment using a semipermeable membrane. The NF concentrated water obtained from the nanofiltration device 11 is stored in the NF concentration tank 84 as needed, and then pumped from the NF concentration tank 84 through the piping 108 by the pump 18 to the first space 14 of each membrane module of the first-stage membrane module unit 100a. The flow of water to the nanofiltration device 11 and the membrane module 10 may be performed using only the pump 21. Meanwhile, diluted water, which has been sent via the second space 16 of each membrane module of the fourth-stage membrane module unit 100d, the third-stage membrane module unit 100c, and the second space 16 of each membrane module of the second-stage membrane module unit 100b (described later), is sent through the piping 124 to the second space 16 of each membrane module of 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).

[0132] 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.

[0133] 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.

[0134] 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.

[0135] 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.

[0136] 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.

[0137] As described above, concentrated water (final-stage concentrated water) with reduced ammonia and silica content is recovered from the treated water containing ammonia and silica, thereby reducing the volume of the treated water. Furthermore, the NF permeate, concentrated water, and diluted water can be reused.

[0138] Alternatively, as described above, ammonia-concentrated water (final-stage concentrated water) with reduced silica content is recovered from the treated water containing ammonia and silica, thereby reducing the volume of the treated water.

[0139] 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.

[0140] 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.

[0141] 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.

[0142] 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.

[0143] 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.

[0144] 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.

[0145] 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.

[0146] 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.

[0147] The water to be treated can be any water containing ammonia and silica, and there are no particular restrictions. Examples of treated water include water containing divalent anions such as sulfate ions, ammonium ions, and silica, such as wastewater discharged from semiconductor factories and chemical plants. In particular, semiconductor factories use ammonia for wafer cleaning and sulfuric acid for scrubbing to treat the ammonia. Therefore, the wastewater contains ammonium ions and divalent anions such as sulfate ions. As an effective use of wastewater, the ammonia and sulfuric acid in the wastewater are recovered and reused.

[0148] The water to be treated 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) preferably contains, for example, 1,000 mg / L or more of ammonium ions, and preferably 2,000 to 100,000 mg / L. The water to be treated further preferably contains, for example, 1,000 mg / L or more of divalent anions such as sulfate ions, 5 mg / L or more of silica, and preferably 6,000 to 250,000 mg / L of divalent anions such as sulfate ions and 5 to 50 mg / L of silica.

[0149] 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 the water to be treated, and there are no particular restrictions.

[0150] 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.

[0151] 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 95-100%. 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 water being treated. 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.

[0152] 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 m 3 / 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)

[0153] 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.

[0154] 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.

[0155] 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.

[0156] The recovered material from the concentrated water consists of dissolved solid components (TDS) contained in the NF concentrated water, and examples of dissolved solid components include inorganic salts such as sodium sulfate, calcium sulfate, sodium chloride, and calcium chloride.

[0157] 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).

[0158] 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).

[0159] The temperature of the water to be treated may be adjusted before the nanofiltration process (nanofiltration device 11). An example of such a water treatment apparatus is shown in Figure 8.

[0160] The water treatment apparatus 8 in Figure 8 may, for example, in addition to the configuration of the water treatment apparatus 2 in Figure 2, further include a temperature control device 15 as a temperature control means for adjusting the temperature of the water to be treated, prior to the nanofiltration process (nanofiltration device 11).

[0161] 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 temperature adjuster 15 may also be provided.

[0162] In the water treatment apparatus 8, the water to be treated, which contains ammonia, is sent through piping 31 to the pH adjustment device 13. In the pH adjustment device 13, the pH of the water to be treated is adjusted (pH adjustment step). The water to be treated, whose pH has been adjusted to the range of pH 7 to 9, is sent through piping 33 to the temperature adjustment device 15. In the temperature adjustment device 15, the temperature of the water to be treated 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 water to be treated may be adjusted after the temperature of the water to be treated (temperature adjustment step).

[0163] The treated water, whose pH and temperature have been adjusted, is supplied to the nanofiltration device 11 through piping 25 by pump 21. The nanofiltration process is then carried out in the same manner as in the water treatment device 2 shown in Figure 2. Water may be supplied to the nanofiltration device 11 and the membrane module 10 using only pump 21. The ammonia gas discharged in the nanofiltration process may be treated in the ammonia treatment device 35. The NF concentrated water obtained from the nanofiltration device 11 may be subjected to semipermeable membrane treatment using a semipermeable membrane.

[0164] As described above, concentrated water with reduced ammonia and silica content is recovered from the treated water containing ammonia and silica, thereby reducing the volume of the treated water. Furthermore, the NF permeate, concentrated water, and diluted water can be reused.

[0165] Alternatively, as described above, ammonia-concentrated water with reduced silica content is recovered from the treated water containing ammonia and silica, thereby reducing the volume of the treated water.

[0166] The pH adjustment device 13 includes, for example, means for adding a pH adjusting agent such as a pH adjusting agent addition pipe, 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 water to be treated to a range of pH 7 to 9, preferably a range of pH 8 to 9. pH adjustment may also be performed in piping, etc., without providing a pH adjustment tank.

[0167] Examples of pH adjusters include acids such as hydrochloric acid and sulfuric acid, and alkalis such as sodium hydroxide.

[0168] 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 water to be treated to a range of 20°C to 35°C, and more preferably 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 water to be treated is below 20°C, the silica precipitation concentration may decrease, and if it exceeds 35°C, the blocking performance of the nanofiltration membrane and semipermeable membrane may decrease.

[0169] 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 passing water through the semipermeable membrane module should be determined by the water quality of the water to be treated, the material of the semipermeable membrane module, etc. For example, it is preferable that the pH of the water to be treated be in the range of 7 to 9 and the water temperature be in the range of 20°C to 35°C.

[0170] 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.

[0171] 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.

[0172] The ammonia treatment device 35 can be any device that recovers ammonia gas from NF permeate or decomposes ammonia gas; there are no particular restrictions. Examples of ammonia treatment devices 35 include ammonia stripping devices.

[0173] An ammonia stripping treatment device is, for example, a distillation column with perforated plates or packing materials installed inside. Ammonia-containing water, which is the water to be treated, flows in from the top of the distillation column, and steam is blown in from the bottom. When the water to be treated and the steam come into contact, the free ammonia in the ammonia-containing water is pushed out into the steam. The expelled ammonia gas is sent through an ammonia gas piping to an ammonia gas decomposition treatment device, where it is decomposed. This ammonia gas decomposition treatment can be, for example, by decomposing it into harmless nitrogen through a catalytic reaction column packed with a catalyst, or by reacting it with sulfuric acid to produce ammonium sulfate, and it is also possible to recover and reuse the ammonia water.

[0174] This specification includes the embodiments described below. (1) A water treatment method for concentrating water to be treated that contains ammonia and silica, A pH adjustment step to adjust the pH of the water to be treated to a range of 7 to 9, A nanofiltration step is performed using a nanofiltration membrane to obtain NF permeate water and NF concentrated water from the treated water whose pH has been adjusted. Includes, The water to be treated contains 1000 mg / L or more of ammonium ions, 1000 mg / L or more of divalent anions, and 5 mg / L or more of silica, in a water treatment method.

[0175] (2) The water treatment method described in (1), In the pH adjustment step, the pH of the water to be treated is adjusted to a range of 8 to 9. A water treatment method further comprising an ammonia treatment step for treating ammonia gas discharged in the nanofiltration step.

[0176] (3) A water treatment method described in (1) or (2), A water treatment method further comprising a semipermeable membrane treatment step, which is performed after the nanofiltration step, to obtain concentrated water and diluted water from the NF concentrated water using a semipermeable membrane.

[0177] (4) A water treatment method 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 method.

[0178] (5) A water treatment apparatus for concentrating water to be treated containing ammonia and silica, A pH adjustment means for adjusting the pH of the water to be treated to a range of 7 to 9, A nanofiltration means for obtaining NF permeate water and NF concentrated water from the treated water whose pH has been adjusted, using a nanofiltration membrane, Equipped with, The water treatment apparatus contains ammonium ions at a concentration of 1000 mg / L or more, divalent anions at a concentration of 1000 mg / L or more, and silica at a concentration of 5 mg / L or more.

[0179] (6)(5) A water treatment apparatus as described above, The pH adjusting means adjusts the pH of the water to be treated to a range of 8 to 9. A water treatment apparatus further comprising an ammonia treatment means for treating ammonia gas discharged by the nanofiltration means.

[0180] A water treatment apparatus as described in (7), (5), or (6), A water treatment apparatus further comprising a semipermeable membrane treatment means, located downstream of the nanofiltration means, for obtaining concentrated water and diluted water from the NF concentrated water using a semipermeable membrane.

[0181] A water treatment apparatus according to any one of (8), (5), to (7), 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. [Examples]

[0182] 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.

[0183] <Example 1> Water to be treated (treated water) with an ammonium ion concentration of 16,500 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 an effective membrane pressure of 1 MPa, 25°C, and pH 7). During this process, the pH of the water to be treated 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 by 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.

[0184] 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%.

[0185] [Table 1]

[0186] 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.

[0187] <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%.

[0188] [Table 2]

[0189] 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.

[0190] Thus, using the apparatus and method of the examples, it was possible to concentrate the water to be treated, which contains ammonia and silica, while reducing the silica concentration. [Explanation of Symbols]

[0191] 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, 37, 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, 35 Ammonia treatment equipment, 60a, 60b, 60c, 62a, 62b, 62c Dilution tank, 84 NF concentration tank, 86 Concentration tanks, 100, 100a, 100b, 100c, 100d membrane module units.

Claims

1. A water treatment method for concentrating water to be treated containing sulfate ions, ammonia, and silica, A pH adjustment step to adjust the pH of the water to be treated to a range of 7 to 9, A nanofiltration step is performed using a nanofiltration membrane to obtain NF permeate water and NF concentrated water from the treated water whose pH has been adjusted. Includes, The treated water contains ammonium ions at a concentration of 1000 mg / L or more, divalent anions at a concentration of 1000 mg / L or more, and silica at a concentration of 5 mg / L or more. The water treatment method is characterized in that the nanofiltration membrane has a silica rejection rate in the range of 0 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 method according to claim 1, In the pH adjustment step, the pH of the water to be treated is adjusted to a range of 8 to 9. A water treatment method characterized by further comprising an ammonia treatment step for treating ammonia gas discharged in the nanofiltration step.

3. A water treatment method according to claim 1 or 2, A water treatment method characterized by further comprising a semipermeable membrane treatment step, which is a step after the nanofiltration step, in which the NF concentrated water is treated with a semipermeable membrane to obtain concentrated water and diluted water.

4. A water treatment apparatus for concentrating water to be treated containing sulfate ions, ammonia, and silica, A pH adjustment means for adjusting the pH of the water to be treated to a range of 7 to 9, A nanofiltration means for obtaining NF permeate water and NF concentrated water from the treated water whose pH has been adjusted, using a nanofiltration membrane, Equipped with, The treated water contains ammonium ions at a concentration of 1000 mg / L or more, divalent anions at a concentration of 1000 mg / L or more, and silica at a concentration of 5 mg / L or more. 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 0 to 20%, and the ammonium ion rejection rate and sulfate ion rejection rate are in the range of 90% to 100%.

5. A water treatment apparatus according to claim 4, The pH adjusting means adjusts the pH of the water to be treated to a range of 8 to 9. A water treatment apparatus further comprising an ammonia treatment means for treating ammonia gas discharged by the nanofiltration means.

6. A water treatment apparatus according to claim 4 or 5, A water treatment apparatus characterized in that, after the nanofiltration means, it further comprises a semipermeable membrane treatment means that uses a semipermeable membrane to obtain concentrated water and diluted water from the NF concentrated water.

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