Water treatment apparatus and water treatment method

Abstract

To provide a water treatment apparatus and a water treatment method capable of suppressing a decrease in water recovery rate of a reverse osmosis membrane device and performing flushing.SOLUTION: A water treatment apparatus includes: a reverse osmosis membrane treatment device 10 that performs reverse osmosis membrane treatment on water to be treated to obtain permeate water and concentrate water; a discharge line 22 that discharges flushing wastewater from the primary side of the reverse osmosis membrane; a recovery line 24 that sends the flushing wastewater to a front stage of the reverse osmosis membrane treatment device 10; and switching means that switches a discharge destination of the flushing wastewater between the discharge line 22 and the recovery line 24 at predetermined timing during a flushing operation that supplies flushing water at a predetermined flow rate to the primary side of the reverse osmosis membrane, and discharges it from the primary side of the reverse osmosis membrane to clean the reverse osmosis membrane.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a water treatment device and a water treatment method including a reverse osmosis membrane device. [Background technology]

[0002] Flushing is a method for recovering blocked reverse osmosis membranes used in reverse osmosis membrane systems. In this method, water is supplied to the primary side of the reverse osmosis membrane at a predetermined flow rate, and then discharged as flushing wastewater from the primary side discharge pipe to the outside of the system, washing away impurities and other substances adhering to the primary side membrane surface.

[0003] For example, Patent Document 1 describes a method for recovering from blockage of a reverse osmosis membrane by flushing the membrane with water having a low salt concentration, such as reverse osmosis membrane permeate. However, in the method described in Patent Document 1, the flushing wastewater is discharged outside the system, which reduces the water recovery rate of the reverse osmosis membrane device. Patent Document 1 does not mention where to dispose of the flushing wastewater.

[0004] Patent Document 2 describes a reverse osmosis membrane device that has a branch pipe equipped with a valve in the concentrated water pipe, and switches between a normal operation process and a flushing operation process by opening and closing the valve. Even with the method in Patent Document 2, flushing wastewater is discharged outside the system, which reduces the water recovery rate of the reverse osmosis membrane device.

[0005] Patent Document 3 describes a method for switching between normal operation and flushing operation at any timing, and for automatically adjusting the flushing flow rate in the flushing operation to match a target value. Even with the method in Patent Document 3, flushing wastewater is discharged outside the system, which reduces the water recovery rate of the reverse osmosis membrane device.

[0006] Another method that can be considered is to return the entire flushing wastewater to the upstream stage of the reverse osmosis membrane device to increase the water recovery rate. However, this method involves returning the fine particles contained in the flushing wastewater to the upstream stage of the reverse osmosis membrane device, which runs the risk of further concentrating the fine particles within the system and causing the reverse osmosis membrane to clog again. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2022-045877 [Patent Document 2] Japanese Patent Application Publication No. 2019-177338 [Patent Document 3] Japanese Patent Application Laid-Open No. 2013-141621 Summary of the Invention [Problem to be solved by the invention]

[0008] An object of the present invention is to provide a water treatment device and a water treatment method that can perform flushing while suppressing a decrease in the water recovery rate of a reverse osmosis membrane device. [Means for solving the problem]

[0009] The present invention provides a water treatment device comprising: a reverse osmosis membrane treatment device that performs reverse osmosis membrane treatment on water to be treated using a reverse osmosis membrane to obtain permeate and concentrated water; a discharge line that discharges flushing wastewater from the primary side of the reverse osmosis membrane; a recovery line that transports the flushing wastewater from the primary side of the reverse osmosis membrane to an upstream stage of the reverse osmosis membrane treatment device; and a switching means that switches the discharge destination of the flushing wastewater between the discharge line and the recovery line at a predetermined timing during a flushing operation in which flushing water is supplied to the primary side of the reverse osmosis membrane at a predetermined flow rate and discharged from the primary side of the reverse osmosis membrane to clean the reverse osmosis membrane.

[0010] In the water treatment device, it is preferable that the water to be treated or diluted water having a lower salt concentration than the water to be treated is used as the flushing water.

[0011] In the water treatment device, it is preferable that the switching means switches the discharge destination of the flushing wastewater from the discharge line to the recovery line within 5 minutes after the start of the flushing operation.

[0012] In the water treatment device, a turbidity measuring device is provided in the discharge line, It is preferable that the switching means switches the discharge destination of the flushing wastewater from the discharge line to the recovery line when the turbidity of the flushing wastewater measured by the turbidity measuring device becomes equal to or lower than a predetermined value.

[0013] In the water treatment device, it is preferable that the discharge line is connected to a raw water tank or a reaction tank of a coagulation sedimentation device that adds a calcium agent to fluoride-containing water to form a sparingly soluble calcium salt to remove fluoride.

[0014] It is preferable that the water treatment device further comprises a turbidity removal membrane treatment device that treats flushing wastewater discharged from the discharge line using a turbidity removal membrane; a return line that returns filtrate treated by the turbidity removal membrane treatment device to a stage upstream of the reverse osmosis membrane treatment device; and a liquid delivery line that delivers backwash wastewater from the turbidity removal membrane to a raw water tank or a reaction tank of a coagulation sedimentation device that adds a calcium agent to fluoride-containing water to generate a sparingly soluble calcium salt to remove fluoride.

[0015] The present invention is a water treatment method comprising: a reverse osmosis membrane treatment step in which water to be treated is subjected to reverse osmosis membrane treatment using a reverse osmosis membrane to obtain permeate and concentrate; a discharge step in which flushing wastewater is discharged from the primary side of the reverse osmosis membrane; and a recovery step in which the flushing wastewater is sent from the primary side of the reverse osmosis membrane to a stage preceding the reverse osmosis membrane treatment step, wherein flushing water is supplied to the primary side of the reverse osmosis membrane at a predetermined flow rate and discharged from the primary side of the reverse osmosis membrane to clean the reverse osmosis membrane, and the discharge step and the recovery step are switched between at a predetermined timing during a flushing operation.

[0016] In the water treatment method, it is preferable that the water to be treated or diluted water having a lower salt concentration than the water to be treated is used as the flushing water.

[0017] In the water treatment method, it is preferable to switch from the discharge step to the recovery step within 5 minutes after the start of the flushing operation.

[0018] In the water treatment method, it is preferable to switch from the discharge step to the recovery step when the turbidity of the flushing wastewater measured in the discharge step becomes equal to or less than a predetermined value.

[0019] In the water treatment method, it is preferable that the flushing wastewater discharged in the discharging step is sent to a raw water tank or a reaction tank of a coagulation sedimentation apparatus in which a calcium agent is added to fluoride-containing water to form a sparingly soluble calcium salt to remove fluoride.

[0020] It is preferable that the water treatment method further comprises a turbidity removal membrane treatment step of treating the flushing wastewater discharged in the discharge step using a turbidity removal membrane, returning the filtrate treated in the turbidity removal membrane treatment step to a stage upstream of the reverse osmosis membrane treatment step, and sending the backwash wastewater from the turbidity removal membrane to a raw water tank or a reaction tank of a coagulation sedimentation apparatus in which a calcium agent is added to fluoride-containing water to form a sparingly soluble calcium salt to remove fluoride. [Effects of the Invention]

[0021] According to the present invention, it is possible to provide a water treatment device and a water treatment method that can perform flushing while suppressing a decrease in the water recovery rate of a reverse osmosis membrane device. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a schematic diagram illustrating an example of a water treatment device according to an embodiment of the present invention. [Figure 2] FIG. 10 is a schematic configuration diagram illustrating another example of a water treatment device according to an embodiment of the present invention. [Figure 3] FIG. 10 is a schematic configuration diagram illustrating another example of a water treatment device according to an embodiment of the present invention. [Figure 4] FIG. 10 is a schematic configuration diagram illustrating another example of a water treatment device according to an embodiment of the present invention. [Figure 5] FIG. 10 is a schematic configuration diagram illustrating another example of a water treatment device according to an embodiment of the present invention. [Figure 6] 1 is a schematic diagram showing an example of a coagulation-sedimentation device that uses high-concentration flushing wastewater obtained by a water treatment device according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0023] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following describes an embodiment of the present invention. The embodiment is an example of implementing the present invention, and the present invention is not limited to the embodiment.

[0024] An example of a water treatment apparatus according to an embodiment of the present invention is outlined in FIG. 1, and its configuration will be described.

[0025] The water treatment device 1 shown in Figure 1 includes a reverse osmosis membrane treatment device 10 that performs reverse osmosis membrane treatment on water to be treated using a reverse osmosis membrane to obtain permeate and concentrated water, a discharge line 22 that discharges flushing wastewater from the primary side of the reverse osmosis membrane, a recovery line 24 that branches off from the discharge line 22 and sends the flushing wastewater from the primary side of the reverse osmosis membrane to an upstream stage of the reverse osmosis membrane treatment device 10, and valves 14 and 16 as switching means that switch the discharge destination of the flushing wastewater between the discharge line 22 and the recovery line 24 at predetermined times during flushing operation in which flushing water is supplied to the primary side of the reverse osmosis membrane at a predetermined flow rate and discharged from the primary side of the reverse osmosis membrane to clean the reverse osmosis membrane.

[0026] In the water treatment device 1 of FIG. 1 , a water line 18 to be treated is connected to the inlet of the reverse osmosis membrane treatment device 10 via a pressure pump 12. A permeate line 20 is connected to the permeate outlet of the reverse osmosis membrane treatment device 10. A discharge line 22 is connected to the concentrate / flushing wastewater outlet of the reverse osmosis membrane treatment device 10 via a valve 14. A recovery line 24 branches off via a valve 16 from between the valve 14 and the connection point of the discharge line 22 with the concentrate / flushing wastewater outlet. The valves 14 and 16 may be combined into a single three-way valve and installed at the branch point of the discharge line 22 and the recovery line 24. If necessary, a flow meter may be installed upstream of the pressure pump 12 in the water line 18 to be treated, or in at least one of the discharge line 22, recovery line 24, and permeate line 20, as a flow rate measuring device for measuring the flow rate in each line. If necessary, a valve may be installed upstream of the branch point of the recovery line 24 in the discharge line 22, and a flow meter may be installed between the valve and the branch point of the recovery line 24.

[0027] The water treatment method and the operation of the water treatment device 1 according to this embodiment will be described.

[0028] The water to be treated is sent by a pressure pump 12 through a water to be treated line 18 to the primary side of a reverse osmosis membrane treatment device 10. In the reverse osmosis membrane treatment device 10, the water to be treated is subjected to reverse osmosis membrane treatment using a reverse osmosis membrane, and permeated water and concentrated water are obtained (reverse osmosis membrane treatment step).

[0029] The permeated water obtained by the reverse osmosis membrane treatment is discharged through a permeated water line 20, and the concentrated water is discharged through a discharge line 22 with the valve 14 open and the valve 16 closed.

[0030] In the water treatment method and water treatment device 1 according to this embodiment, a normal operation process (reverse osmosis membrane treatment process) in which permeate and concentrated water are obtained by reverse osmosis membrane treatment, and a flushing process in which the membrane surface on the primary side of the reverse osmosis membrane is washed at predetermined intervals (e.g., periodically) are alternately operated. Flushing is a method in which flushing water is supplied to the primary side of the reverse osmosis membrane at a predetermined flow rate and then discharged from the primary side discharge line to wash away impurities and the like adhering to the membrane surface on the primary side.

[0031] As a result of investigations by the present inventors, it was found that the flushing wastewater contains a large amount of fine particles that had adhered to the primary side of the reverse osmosis membrane during the initial discharge period, for example, from several tens of seconds to several minutes. Therefore, it was discovered that by discharging the portion of the flushing wastewater with a high concentration of fine particles from the system, it is possible to recover the remaining portion with a low concentration of fine particles, thereby suppressing clogging of the reverse osmosis membrane and reducing the reduction in water recovery rate.

[0032] For example, when flushing operation is initiated, the flushing water is pumped by the pressure pump 12 to the upstream side of the reverse osmosis membrane treatment device 10 through the treated water line 18 at a pressure lower than that used during normal operation. The flushing wastewater is discharged through the discharge line 22 with the valve 14 open and the valve 16 closed. During the initial stage of discharge, for example, from several tens of seconds to several minutes, the flushing wastewater (hereinafter sometimes referred to as "high-concentration flushing wastewater") contains many particles adhering to the upstream side of the reverse osmosis membrane. After most of the particles adhering to the upstream side of the reverse osmosis membrane have been discharged, the valve 14 is closed and the valve 16 is opened. The discharge destination of the flushing wastewater is switched between the discharge line 22 and the recovery line 24, and the flushing wastewater containing a small amount of particles (hereinafter sometimes referred to as "low-concentration flushing wastewater") is discharged through the recovery line 24. This low-concentration flushing wastewater is sent to the upstream stage of the reverse osmosis membrane treatment device 10. In this case, the low-concentration flushing wastewater may be sent to a water tank for storing water to be treated in the reverse osmosis membrane treatment device 10, or may be sent to the water line 18 for treatment, for example.

[0033] By switching the valve during flushing and changing the destination of the flushing wastewater in this way, flushing can be performed while suppressing a decrease in the water recovery rate of the reverse osmosis membrane device. Therefore, in water treatment in which the reverse osmosis membrane is flushed at predetermined intervals, a decrease in the water recovery rate can be suppressed and the flushing wastewater can be effectively utilized. This is also particularly effective when the water to be treated in the reverse osmosis membrane treatment device 10 contains calcium and other substances that are prone to calcium scale, such as calcium carbonate and calcium fluoride.

[0034] By using the water treatment method and water treatment device according to this embodiment, the water recovery rate of the reverse osmosis membrane device can be increased to, for example, 50% or more, preferably 60% or more.

[0035] By separating high-concentration flushing wastewater at the initial stage of discharge and sending it to a wastewater treatment device such as a solid-liquid separator including a coagulation sedimentation device, the fine particles contained in the high-concentration flushing wastewater can be used as nuclei for the coagulation reaction, thereby improving the coagulation properties and sedimentation rate in the coagulation sedimentation. Therefore, it is more effective to send the high-concentration flushing wastewater to a reaction tank of a coagulation sedimentation device, for example.

[0036] It is desirable that the high-concentration flushing wastewater at the initial stage of discharge be sent as uniformly as possible to the raw water tank or reaction tank of the coagulation sedimentation device, etc. Therefore, a high-concentration flushing wastewater storage tank for storing the high-concentration flushing wastewater may be provided separately, and the high-concentration flushing wastewater may be stored in the high-concentration flushing wastewater storage tank.

[0037] The discharge line 22 is connected to a raw water tank or a reaction tank of a coagulation sedimentation device that adds a calcium agent to fluoride-containing water to form sparingly soluble calcium salts to remove fluoride, and when the high-concentration flushing wastewater is sent to the raw water tank or the reaction tank, the reaction of forming calcium salts is promoted, thereby further reducing the fluoride concentration in the fluoride-containing water, improving the coagulation properties of the coagulation sedimentation, and improving solid-liquid separation properties.

[0038] Furthermore, because the amount of fine particles contained in the latter half of the flushing wastewater (low-concentration flushing wastewater) is small, the water can be recovered again by returning it to an upstream stage of the reverse osmosis membrane treatment device 10, for example, to the water tank to be treated of the reverse osmosis membrane treatment device 10, thereby suppressing the risk of clogging the reverse osmosis membrane treatment device 10 and preventing a decrease in the water recovery rate. In this case, a low-concentration flushing wastewater storage tank for storing the low-concentration flushing wastewater may be provided separately, and the low-concentration flushing wastewater may be stored in the low-concentration flushing wastewater storage tank. Furthermore, the low-concentration flushing wastewater may be subjected to turbidity removal using a turbidity removing membrane or the like before being returned to the water tank to be treated of the reverse osmosis membrane treatment device 10, for example, for water recovery.

[0039] The flushing wastewater discharge destination can be switched from the discharge line 22 to the recovery line 24 at the beginning of the discharge, for example, within 5 minutes of the start of the flushing operation, preferably within 10 seconds to 5 minutes of the start of the flushing operation, and more preferably within 30 seconds to 3 minutes of the start of the flushing operation. Switching within 5 minutes of the start of the flushing operation allows most of the fine particles adhering to the primary side of the reverse osmosis membrane to be discharged from the discharge line 22. The time from the start of the flushing operation to the recovery line 24 can be appropriately adjusted depending on the ion concentration of the water to be treated in the reverse osmosis membrane treatment device 10, the interval between flushing operations, the flow rate of the flushing water, and other factors. Furthermore, switching within 3 minutes of the start of the flushing operation can further increase the water recovery rate. Switching within 30 seconds to 3 minutes of the start of the flushing operation can effectively prevent clogging of the reverse osmosis membrane and a decrease in the water recovery rate.

[0040] For example, valves 14 and 16 may be automatic valves, and timers may be installed in valves 14 and 16. When the timer is activated, the automatic valve opens valve 14 and closes valve 16, switching the destination of the discharged water. The high-concentration flushing wastewater is discharged from discharge line 22 and sent to, for example, a coagulation sedimentation device. For example, after a predetermined time measured by the timer has elapsed, the automatic valve switches valve 14 to a closed state and valve 16 to an open state. Low-concentration flushing wastewater, which is a part of the flushing wastewater, is returned through recovery line 24 to, for example, a water tank upstream of the reverse osmosis membrane treatment device 10. For example, when the properties of the water to be treated in the reverse osmosis membrane treatment are stable, the destination of the flushing wastewater can be switched between discharge line 22 and recovery line 24 using a timer in this manner.

[0041] The water to be treated in the reverse osmosis membrane treatment is not particularly limited, and examples thereof include environmental water such as groundwater, river water, and seawater, and wastewater discharged from various factories.

[0042] The reverse osmosis membrane of the reverse osmosis membrane treatment device 10 is not particularly limited, but for example, a polyamide-based or cellulose acetate-based reverse osmosis membrane is used.

[0043] The water used as flushing water is not particularly limited, and may be, for example, water to be treated in the reverse osmosis membrane treatment device 10. Alternatively, other flushing water may be introduced from outside the system, or it may be dilute water with a lower salt concentration than the water to be treated, such as permeate from reverse osmosis membrane treatment, concentrated water or treated water from an electrodeionization device, or pure water. Furthermore, water whose pH has been adjusted with an acid (e.g., acetic acid, hydrochloric acid, sulfuric acid, etc.) or an alkali (e.g., sodium hydroxide aqueous solution, etc.) may be used as flushing water.

[0044] Using the water to be treated in the reverse osmosis membrane treatment device 10 or dilute water with a lower salt concentration as the flushing water not only improves the cleaning effect on the reverse osmosis membrane surface, but also reduces the risk of impurities being mixed in when the flushing wastewater is recovered and reused, and the risk of poor coagulation due to the mixing in of inhibitors into upstream coagulation and sedimentation devices, etc.

[0045] The high-concentration flushing wastewater discharged at the initial stage of the flushing process may be sent from the discharge line 22 to a wastewater treatment device (wastewater treatment process), such as a solid-liquid separation device (solid-liquid separation process) including a coagulation-sedimentation device (coagulation-sedimentation process) or a coagulation-pressure flotation device (coagulation-pressure flotation process), or an inorganic wastewater treatment device (inorganic wastewater treatment process). The coagulation-sedimentation device may be any device that performs coagulation-sedimentation treatment, and examples thereof include a high-speed coagulation-sedimentation device, such as a reaction tank of a coagulation-sedimentation device that adds a calcium agent to fluoride-containing water to generate a sparingly soluble calcium salt for fluoride removal. Among these, because the fine particles in the flushing wastewater contain calcium, it is particularly preferable that the high-concentration flushing wastewater be sent to a reaction tank of a coagulation-sedimentation device that adds a calcium agent to fluoride-containing water to generate a sparingly soluble calcium salt for fluoride removal.

[0046] When the high-concentration flushing wastewater is sent from the discharge line 22 to a wastewater treatment device such as a coagulation sedimentation device, the flushing process is operated at a lower pressure than the normal operation process, and permeate is not discharged. At this time, water is not passed through the recovery line 24. Furthermore, if a concentrated water line is provided separately, water is not passed through the concentrated water line either.

[0047] The system may include a permeate tank for storing permeate, a flushing water supply line and a pump as a flushing water supply means for sending the permeate to the inlet of the reverse osmosis membrane, and a flushing mechanism for periodically flushing the permeate. A turbidity measuring device may also be provided to measure the turbidity of the flushing wastewater, and when the turbidity of the flushing wastewater measured by the turbidity measuring device falls below a predetermined value, the flushing wastewater may be switched from the discharge line to the recovery line. An example of such a configuration is shown in Figure 2.

[0048] The water treatment device 2 shown in Figure 2 includes a reverse osmosis membrane treatment device 10 that performs reverse osmosis membrane treatment on water to be treated using a reverse osmosis membrane to obtain permeate and concentrated water, a discharge line 22 that discharges flushing wastewater from the primary side of the reverse osmosis membrane, a recovery line 24 that branches off from the discharge line 22 and sends the flushing wastewater from the primary side of the reverse osmosis membrane to an upstream stage of the reverse osmosis membrane treatment device 10, valves 14 and 16 as switching means for switching the discharge destination of the flushing wastewater between the discharge line 22 and the recovery line 24 at a predetermined timing during flushing operation in which flushing water is supplied to the primary side of the reverse osmosis membrane at a predetermined flow rate and discharged from the primary side of the reverse osmosis membrane to clean the reverse osmosis membrane, a turbidity measurement device 26 as turbidity measurement means for measuring the turbidity of the flushing wastewater, and a permeate tank 28 for storing permeate.

[0049] In the water treatment device 2 of FIG. 2 , a water line 18 to be treated is connected to the inlet of the reverse osmosis membrane treatment device 10 via a pressure pump 12. A permeate outlet of the reverse osmosis membrane treatment device 10 is connected to the inlet of a permeate tank 28 via a permeate line 20. A discharge line 22 is connected to the concentrated water / flushing wastewater outlet of the reverse osmosis membrane treatment device 10 via a valve 14. A recovery line 24 branches off via a valve 16 from between the connection point of the discharge line 22 with the concentrated water / flushing wastewater outlet and the valve 14. The valves 14 and 16 may be combined into a three-way valve and installed at the branch point of the discharge line 22 and the recovery line 24. A turbidity measuring device 26 is installed in the discharge line 22 between the concentrated water / flushing wastewater outlet of the reverse osmosis membrane treatment device 10 and the branch point of the recovery line 24. The outlet of the permeate tank 28 is connected to the water line 18 between the pressure pump 12 and the inlet of the reverse osmosis membrane treatment device 10 via a pump 30 and a flushing water supply line 32. The turbidity measuring device 26 may be installed not only upstream of the valve 14 in the discharge line 22 but also downstream of the valve 14 in the discharge line 22, or upstream or downstream of the valve 16 in the recovery line 24. A plurality of turbidity measuring devices 26 may be installed at two or more of the above-mentioned installation locations. If necessary, a flow meter may be installed as a flow rate measuring device to measure the flow rate in each line in at least one of the upstream side of the pressure pump 12 in the treated water line 18, the discharge line 22, the recovery line 24, the permeate line 20, and the flushing water supply line 32. If necessary, a valve may be installed upstream of the branch point of the recovery line 24 in the discharge line 22, and a flow meter may be installed between the valve and the branch point of the recovery line 24.

[0050] The water to be treated is sent by a pressure pump 12 through a water to be treated line 18 to the primary side of a reverse osmosis membrane treatment device 10. In the reverse osmosis membrane treatment device 10, the water to be treated is subjected to reverse osmosis membrane treatment using a reverse osmosis membrane, and permeated water and concentrated water are obtained (reverse osmosis membrane treatment step).

[0051] The permeated water obtained by the reverse osmosis membrane treatment is sent to and stored in the permeated water tank 28 through the permeated water line 20. The concentrated water is discharged through the discharge line 22 with the valve 14 open and the valve 16 closed.

[0052] In the water treatment device 2, flushing is performed to clean the primary side of the reverse osmosis membrane at predetermined intervals (for example, periodically).

[0053] For example, when the flushing operation is started, the permeate water stored in the permeate tank 28 is pumped as flushing water by the pump 30 through the flushing water supply line 32 and the treated water line 18 to the primary side of the reverse osmosis membrane treatment device 10. The flushing wastewater is discharged through the discharge line 22 with the valve 14 open and the valve 16 closed. The turbidity of the flushing wastewater is measured by the turbidity measuring device 26 in the discharge line 22 (turbidity measurement process). High-concentration flushing wastewater containing many particles adhering to the primary side of the reverse osmosis membrane is discharged during the initial discharge period, for example, from several tens of seconds to several minutes. When the turbidity of the flushing wastewater measured by the turbidity measuring device 26 falls below a predetermined value, the valve 14 is closed and the valve 16 is opened. The discharge destination of the flushing wastewater is switched between the discharge line 22 and the recovery line 24, and low-concentration flushing wastewater containing fewer particles is discharged through the recovery line 24. This low-concentration flushing wastewater is sent to the upstream stage of the reverse osmosis membrane treatment device 10. In this case, the low-concentration flushing wastewater may be sent, for example, to a treated water tank that stores the treated water of the reverse osmosis membrane treatment device 10, or may be sent upstream of the pressure pump 12 in the treated water line 18.

[0054] In this way, by switching the valve based on the turbidity of the flushing wastewater measured by the turbidity measuring device 26 during flushing and changing the destination of the flushing wastewater, it is possible to perform flushing while suppressing a decrease in the water recovery rate of the reverse osmosis membrane device. Therefore, in water treatment in which the reverse osmosis membrane is flushed at predetermined intervals, it is possible to suppress a decrease in the water recovery rate and make effective use of the flushing wastewater.

[0055] There are no particular restrictions on the predetermined turbidity value, but for example, when the turbidity is 1.0 or less, preferably 0.5 or less, the discharge destination of the flushing wastewater may be switched between the discharge line 22 and the recovery line 24, and the low-concentration flushing wastewater may be sent through the recovery line 24 to the upstream stage of the reverse osmosis membrane treatment device 10. For example, when there is a large variation in the properties of the water to be treated in the reverse osmosis membrane treatment, the discharge destination of the flushing wastewater may be switched between the discharge line 22 and the recovery line 24 based on the turbidity of the flushing wastewater.

[0056] The discharge line 22 may be branched into a line for discharging concentrated water and a line for discharging flushing wastewater, and the high-concentration flushing wastewater may be sent to, for example, a solid-liquid separator (preferably a coagulation sedimentation apparatus or a coagulation pressure flotation apparatus) through the line for discharging the flushing wastewater. An example of such a configuration is shown in FIG.

[0057] The water treatment device 3 shown in Figure 3 includes a reverse osmosis membrane treatment device 10 that performs reverse osmosis membrane treatment on water to be treated using a reverse osmosis membrane to obtain permeate and concentrated water, a discharge line 22 that discharges flushing wastewater from the primary side of the reverse osmosis membrane, a recovery line 24 that branches off from the discharge line 22 and sends the flushing wastewater from the primary side of the reverse osmosis membrane to an upstream stage of the reverse osmosis membrane treatment device 10, a concentrated water line 36 that branches off from the discharge line 22 and discharges concentrated water, and valves 14 and 16 as switching means that switch the discharge destination of the flushing wastewater between the discharge line 22 and the recovery line 24 at predetermined times during flushing operation in which flushing water is supplied to the primary side of the reverse osmosis membrane at a predetermined flow rate and discharged from the primary side of the reverse osmosis membrane to clean the reverse osmosis membrane.

[0058] In the water treatment device 3 of FIG. 3 , a water line 18 to be treated is connected to the inlet of a reverse osmosis membrane treatment device 10 via a pressure pump 12. A permeate line 20 is connected to the permeate outlet of the reverse osmosis membrane treatment device 10. A discharge line 22 is connected to the concentrated water / flushing wastewater outlet of the reverse osmosis membrane treatment device 10 via a valve 14. A recovery line 24 branches off via a valve 16 from the discharge line 22 between the connection point of the discharge line 22 with the concentrated water / flushing wastewater outlet and the valve 14. A concentrated water line 36 branches off via a valve 34 from the discharge line 22 between the branch point of the recovery line 24 and the valve 14. The valves 14 and 34 may be combined into a three-way valve and installed at the branch point of the discharge line 22 and the concentrated water line 36. If necessary, a flow meter may be installed upstream of the pressure pump 12 in the water line 18 to measure the flow rate in at least one of the discharge line 22, the recovery line 24, the concentrated water line 36, and the permeate line 20. If necessary, a valve may be installed on the discharge line 22 upstream of the branch point of the recovery line 24, and a flow meter may be installed between the valve and the branch point of the recovery line 24.

[0059] The water to be treated is sent by a pressure pump 12 through a water to be treated line 18 to the primary side of a reverse osmosis membrane treatment device 10. In the reverse osmosis membrane treatment device 10, the water to be treated is subjected to reverse osmosis membrane treatment using a reverse osmosis membrane, and permeated water and concentrated water are obtained (reverse osmosis membrane treatment step).

[0060] The permeated water obtained by the reverse osmosis membrane treatment is discharged through the permeated water line 20. The concentrated water is discharged through the discharge line 22 and the concentrated water line 36 with the valve 34 open and the valves 14 and 16 closed.

[0061] In the water treatment device 3, flushing is performed to clean the primary side of the reverse osmosis membrane at predetermined intervals (for example, periodically).

[0062] For example, when flushing operation is initiated, the flushing water is pumped by the pressure pump 12 to the upstream side of the reverse osmosis membrane treatment device 10 through the treated water line 18 at a pressure lower than that used during normal operation. The flushing wastewater is discharged through the discharge line 22 with the valve 14 open and the valves 16 and 34 closed. High-concentration flushing wastewater containing many particles adhering to the upstream side of the reverse osmosis membrane is discharged during the initial discharge period, for example, from several tens of seconds to several minutes. After most of the particles adhering to the upstream side of the reverse osmosis membrane are discharged, the valves 14 and 34 are closed and the valve 16 is opened. The discharge destination of the flushing wastewater is switched between the discharge line 22 and the recovery line 24, and low-concentration flushing wastewater containing fewer particles is discharged through the recovery line 24. This low-concentration flushing wastewater is sent to an upstream stage of the reverse osmosis membrane treatment device 10. In this case, the low-concentration flushing wastewater may be sent, for example, to a treated water tank that stores the treated water of the reverse osmosis membrane treatment device 10, or may be sent upstream of the pressure pump 12 in the treated water line 18.

[0063] By switching the valve during flushing and changing the destination of the flushing wastewater in this way, flushing can be performed while suppressing a decrease in the water recovery rate of the reverse osmosis membrane device. Therefore, in water treatment in which the reverse osmosis membrane is flushed at predetermined intervals, a decrease in water recovery rate can be suppressed and the flushing wastewater can be effectively utilized. Furthermore, by providing a line for discharging concentrated water and a line for discharging flushing wastewater, the liquids can be sent to devices appropriate for the properties of each liquid, such as, for example, concentrated water to a wastewater treatment device, high-concentration flushing wastewater to a solid-liquid separation device, and low-concentration flushing wastewater to a stage upstream of the reverse osmosis membrane device.

[0064] The configuration shown in Figure 3 may also include a permeate tank for storing permeate, and a flushing water supply line and pump as flushing water supply means for sending the permeate to the inlet of the reverse osmosis membrane, and may also include a flushing mechanism for periodically flushing the permeate, for example. An example of such a configuration is shown in Figure 4.

[0065] 4 includes a reverse osmosis membrane treatment device 10 that performs reverse osmosis membrane treatment on water to be treated using a reverse osmosis membrane to obtain permeate and concentrate, a discharge line 22 that discharges flushing wastewater from the primary side of the reverse osmosis membrane, a recovery line 24 that branches off from the discharge line 22 and sends the flushing wastewater from the primary side of the reverse osmosis membrane to an upstream stage of the reverse osmosis membrane treatment device 10, a concentrated water line 36 that branches off from the discharge line 22 and discharges concentrate, and valves 14 and 16 as switching means for switching the discharge destination of the flushing wastewater between the discharge line 22 and the recovery line 24 at a predetermined timing during a flushing operation in which flushing water is supplied to the primary side of the reverse osmosis membrane at a predetermined flow rate and discharged from the primary side of the reverse osmosis membrane to clean the reverse osmosis membrane, and a permeate tank 28 for storing permeate. The water treatment device 4 may also include a treated water tank 38 that stores the water to be treated from the reverse osmosis membrane treatment device 10.

[0066] In the water treatment device 4 of Figure 4, a water line 40 is connected to the water inlet of the water tank 38. The water tank 38 and the inlet of the reverse osmosis membrane treatment device 10 are connected by a water line 18 via a pressure pump 12. The permeate outlet of the reverse osmosis membrane treatment device 10 and the inlet of the permeate tank 28 are connected by a permeate line 20. A discharge line 22 is connected to the concentrated water / flushing wastewater outlet of the reverse osmosis membrane treatment device 10 via a valve 14. A recovery line 24 branches off from the discharge line 22 between the connection point of the concentrated water / flushing wastewater outlet and the valve 14 via a valve 16, and is connected to the flushing wastewater inlet of the water tank 38. A concentrated water line 36 branches off from the discharge line 22 between the branch point of the recovery line 24 and the valve 14 via a valve 34. The valves 14 and 34 may be combined into a three-way valve and installed at the branch point of the discharge line 22 and the concentrated water line 36. The outlet of the permeate tank 28 is connected to the pressurizing pump 12 and the inlet of the reverse osmosis membrane treatment device 10 in the treated water line 18 via a pump 30 via a flushing water supply line 32. If necessary, a flow meter may be installed as a flow rate measuring device to measure the flow rate in at least one of the following lines: upstream of the pressurizing pump 12 in the treated water line 18, the discharge line 22, the recovery line 24, the concentrated water line 36, the permeate line 20, the flushing water supply line 32, and the treated water line 40. If necessary, a valve may be installed in the discharge line 22 upstream of the branch point of the recovery line 24, and a flow meter may be installed between the valve and the branch point of the recovery line 24.

[0067] The water to be treated is stored in a water tank 38 as needed through a water line 40, and is then pumped from the water tank 38 through a water line 18 by a pressure pump 12 to the primary side of the reverse osmosis membrane treatment device 10. In the reverse osmosis membrane treatment device 10, the water to be treated is subjected to reverse osmosis membrane treatment using a reverse osmosis membrane, and permeated water and concentrated water are obtained (reverse osmosis membrane treatment step).

[0068] The permeate obtained by the reverse osmosis membrane treatment is sent to the permeate tank 28 through the permeate line 20 and stored therein. The concentrated water is discharged through the discharge line 22 and the concentrated water line 36 with the valve 34 open and the valves 14 and 16 closed. The concentrated water may be circulated to the treated water tank 38 through the discharge line 22 and the recovery line 24 with the valve 16 open and the valves 14 and 34 closed. In this case, the recovery line 24 also functions as a concentrated water circulation line. The recovery line 24 may be connected to the treated water line 18 upstream of the pressure pump 12, and the low-concentration flushing wastewater may be circulated to the treated water line 18.

[0069] In the water treatment device 4, flushing is performed to clean the primary side of the reverse osmosis membrane at predetermined intervals (for example, periodically).

[0070] For example, when the flushing operation is initiated, the permeate water stored in the permeate tank 28 is pumped as flushing water by the pump 30 through the flushing water supply line 32 and the treated water line 18 to the primary side of the reverse osmosis membrane treatment device 10. The flushing wastewater is discharged through the discharge line 22 with the valve 14 open and the valves 16 and 34 closed. High-concentration flushing wastewater containing many particles adhering to the primary side of the reverse osmosis membrane is discharged during the initial discharge period, for example, several tens of seconds to several minutes. After most of the particles adhering to the primary side of the reverse osmosis membrane are discharged, the valves 14 and 34 are closed and the valve 16 is opened. The discharge destination of the flushing wastewater is switched between the discharge line 22 and the recovery line 24. The low-concentration flushing wastewater containing fewer particles is sent through the recovery line 24 to the upstream stage of the reverse osmosis membrane treatment device 10, for example, the treated water tank 38. The low-concentration flushing wastewater may be sent to the primary water line 18 upstream of the pressure pump 12.

[0071] By switching the valve during flushing and changing the destination of the flushing wastewater in this way, flushing can be performed while suppressing a decrease in the water recovery rate of the reverse osmosis membrane device. Therefore, in water treatment in which the reverse osmosis membrane is flushed at predetermined intervals, a decrease in the water recovery rate can be suppressed and the flushing wastewater can be effectively utilized. In addition, by circulating the concentrated water to the treated water tank 38, for example, the water recovery rate can be improved.

[0072] The high-concentration flushing wastewater may be filtered using a turbidity-removing membrane, etc. An example of such a configuration is shown in Figure 5.

[0073] The water treatment device 5 shown in Figure 5 includes a reverse osmosis membrane treatment device 10 that performs reverse osmosis membrane treatment on water to be treated using a reverse osmosis membrane to obtain permeate and concentrated water, a discharge line 22 that discharges flushing wastewater from the primary side of the reverse osmosis membrane, a recovery line 24 that branches off from the discharge line 22 and sends the flushing wastewater from the primary side of the reverse osmosis membrane to an upstream stage of the reverse osmosis membrane treatment device 10, a concentrated water line 36 that branches off from the discharge line 22 and discharges concentrated water, valves 14 and 16 as switching means for switching the discharge destination of the flushing wastewater between the discharge line 22 and the recovery line 24 at a predetermined timing during flushing operation in which flushing water is supplied to the primary side of the reverse osmosis membrane at a predetermined flow rate and discharged from the primary side of the reverse osmosis membrane to clean the reverse osmosis membrane, and a turbidity removal membrane treatment device 42 that treats the high-concentration flushing wastewater discharged from the discharge line 22 using a turbidity removal membrane.

[0074] In the water treatment device 5 of Figure 5, a water line 18 to be treated is connected to the inlet of the reverse osmosis membrane treatment device 10 via a pressure pump 12. A permeate line 20 is connected to the permeate outlet of the reverse osmosis membrane treatment device 10. A concentrated water / flushing wastewater outlet of the reverse osmosis membrane treatment device 10 is connected to the inlet of the turbidity removal membrane treatment device 42 by a discharge line 22 via a valve 14. A recovery line 24 branches off via a valve 16 from the discharge line 22 between the connection point of the discharge line 22 with the concentrated water / flushing wastewater outlet and the valve 14. A concentrated water line 36 branches off via a valve 34 from the discharge line 22 between the branch point of the recovery line 24 and the valve 14. The valves 14 and 34 may be combined into a three-way valve and installed at the branch point of the discharge line 22 and the concentrated water line 36. A filtrate line 44 is connected to the filtrate outlet of the turbidity removal membrane treatment device 42, and a backwash wastewater delivery line 46 is connected to the backwash wastewater outlet. If necessary, a flow meter may be installed as a flow rate measuring means to measure the flow rate in at least one of the treated water line 18 upstream of the pressure pump 12, the discharge line 22, the recovery line 24, the concentrated water line 36, and the permeate line 20. If necessary, a valve may be installed in the discharge line 22 upstream of the branch point of the recovery line 24, and a flow meter may be installed between the valve and the branch point of the recovery line 24.

[0075] The water to be treated is sent by a pressure pump 12 through a water to be treated line 18 to the primary side of a reverse osmosis membrane treatment device 10. In the reverse osmosis membrane treatment device 10, the water to be treated is subjected to reverse osmosis membrane treatment using a reverse osmosis membrane, and permeated water and concentrated water are obtained (reverse osmosis membrane treatment step).

[0076] The permeated water obtained by the reverse osmosis membrane treatment is discharged through the permeated water line 20. The concentrated water is discharged through the discharge line 22 and the concentrated water line 36 with the valve 34 open and the valves 14 and 16 closed.

[0077] In the water treatment device 5, flushing is performed to clean the primary side of the reverse osmosis membrane at predetermined intervals (for example, periodically).

[0078] For example, when flushing operation is initiated, the flushing water is pumped by the pressure pump 12 to the upstream side of the reverse osmosis membrane treatment device 10 through the treated water line 18 at a pressure lower than that used during normal operation. The flushing wastewater is discharged through the discharge line 22 with the valve 14 open and the valves 16 and 34 closed. During the initial stage of discharge, for example, from several tens of seconds to several minutes, high-concentration flushing wastewater containing many particles adhering to the upstream side of the reverse osmosis membrane is discharged and passed through the turbidity removal membrane treatment device 42. After most of the particles adhering to the upstream side of the reverse osmosis membrane are discharged, the valves 14 and 34 are closed and the valve 16 is opened. The discharge destination of the flushing wastewater is switched between the discharge line 22 and the recovery line 24, and low-concentration flushing wastewater containing fewer particles is discharged through the recovery line 24. This low-concentration flushing wastewater is sent to an upstream stage of the reverse osmosis membrane treatment device 10. In this case, the low-concentration flushing wastewater may be sent, for example, to a treated water tank that stores the treated water of the reverse osmosis membrane treatment device 10, or may be sent upstream of the pressure pump 12 in the treated water line 18.

[0079] The high-concentration flushing wastewater is passed through a turbidity removal membrane treatment device 42 and filtered through a turbidity removal membrane (turbidity removal membrane treatment step). The filtrate obtained by the turbidity removal membrane treatment is discharged through a filtrate line 44. The filtrate may be returned to an upstream stage of the reverse osmosis membrane treatment device 10, for example, to a water tank to be treated of the reverse osmosis membrane treatment device 10. In this case, the filtrate line 44 functions as a return line for returning the filtrate to an upstream stage of the reverse osmosis membrane treatment device. The turbidity removal membrane may be backwashed at predetermined intervals by, for example, sending backwash water from the secondary side of the turbidity removal membrane through the filtrate line 44. In this case, the backwash wastewater from the turbidity removal membrane may be sent through a backwash wastewater sending line 46 to, for example, a wastewater treatment device, preferably a solid-liquid separator, more preferably a coagulation sedimentation device or a coagulation pressure flotation device, or even more preferably, a reaction tank of a coagulation sedimentation device in which a calcium agent is added to fluoride-containing water to generate sparingly soluble calcium salts to remove fluoride. In this case, the backwash wastewater supply line 46 functions as a backwash wastewater supply line for supplying the backwash wastewater from the turbidity removal membrane treatment device 42 to a reaction tank or the like of a coagulation sedimentation device that adds a calcium agent to fluoride-containing water to generate sparingly soluble calcium salts to remove fluoride.

[0080] By switching the valve during flushing and changing the destination of the flushing wastewater in this way, flushing can be performed while suppressing a decrease in the water recovery rate of the reverse osmosis membrane device. Therefore, in water treatment in which the reverse osmosis membrane is flushed at predetermined intervals, a decrease in the water recovery rate can be suppressed and the flushing wastewater can be effectively utilized.

[0081] By passing high-concentration flushing wastewater through a turbidity removal membrane and backwashing it, the solids (SS components) contained in the high-concentration flushing wastewater are concentrated. The backwash wastewater (i.e., SS-concentrated water) is then sent to a coagulation sedimentation system or a coagulation flotation system, thereby improving the coagulation performance during coagulation sedimentation or coagulation flotation. It is particularly effective to send the backwash wastewater, which has concentrated the solids (SS components), to a reaction tank of a coagulation sedimentation system that adds a calcium agent to fluoride-containing water to generate sparingly soluble calcium salts to remove fluoride, thereby utilizing the fine particles as nuclei for the coagulation reaction. Furthermore, if the high-concentration flushing wastewater is acidic, this method can also contribute to reducing the use of pH adjusters such as acids in the coagulation sedimentation. The filtrate from the turbidity removal membrane may be recycled by returning it to the upstream stage of the reverse osmosis membrane treatment device 10, or to the water tank to be treated in the reverse osmosis membrane treatment device 10.

[0082] As an example of a wastewater treatment device that uses the high-concentration flushing wastewater obtained by the water treatment device of this embodiment, a coagulation sedimentation device is shown in FIG. 6. The coagulation sedimentation device adds a calcium agent to fluoride-containing water to generate sparingly soluble calcium salts to remove fluoride.

[0083] The coagulation settling device 6 shown in FIG. 6 includes a reaction tank 50, an inorganic reaction tank 52, a coagulation tank 54, and a settling tank 56.

[0084] In the coagulation settling apparatus 6 shown in FIG. 6 , a fluoride-containing water line 58 is connected to the fluoride-containing water inlet of the reaction tank 50. The outlet of the reaction tank 50 is connected to the inlet of the inorganic reaction tank 52 by a line 60. The outlet of the inorganic reaction tank 52 is connected to the inlet of the coagulation tank 54 by a line 62. The outlet of the coagulation tank 54 is connected to the inlet of the settling tank 56 by a line 64. A treated water line 66 is connected to the treated water outlet of the settling tank 56, and a sludge line 68 is connected to the sludge outlet. A flushing wastewater addition line 70 connected to the discharge line 22 or the backwash wastewater delivery line 46 is connected to the flushing wastewater inlet of the reaction tank 50, and a calcium agent addition line 72 is connected to the calcium agent inlet. An inorganic coagulant addition line 74 is connected to the inorganic coagulant inlet of the inorganic reaction tank 52. A polymer coagulant addition line 76 is connected to the polymer coagulant inlet of the coagulation tank 54.

[0085] The coagulation settling device 6 may include a fluorine-containing water tank as a raw water tank for storing fluorine-containing water. In this case, the fluorine-containing water tank and the fluorine-containing water inlet of the reaction tank 50 may be connected by a fluorine-containing water line. Furthermore, a flushing wastewater inlet of the fluorine-containing water tank may be connected to the discharge line 22 or a flushing wastewater addition line connected to the backwash wastewater delivery line 46.

[0086] The fluorine-containing water is stored in a fluorine-containing water tank as needed, and then sent to the reaction tank 50 through a fluorine-containing water line 58. In the reaction tank 50, for example, high-concentration flushing wastewater from the water treatment devices 1 to 5 or backwash wastewater from the turbidity removal membrane treatment device 42 is added to the fluorine-containing water through a flushing wastewater addition line 70, and a calcium agent is further added through a calcium agent addition line 72, and a reaction between the fluorine and the calcium agent produces calcium fluoride salt, which is a sparingly soluble salt (calcium reaction step). In the fluorine-containing water tank, for example, high-concentration flushing wastewater from the water treatment devices 1 to 5 or backwash wastewater from the turbidity removal membrane treatment device 42 may be added through the flushing wastewater addition line. The reaction liquid is sent to the inorganic reaction tank 52 through a line 60. In the inorganic reaction tank 52, an inorganic coagulant is added to the reaction liquid through an inorganic coagulant addition line 74, and a coagulation reaction is carried out (coagulation reaction step). The reaction liquid to which the inorganic coagulant has been added is sent to the coagulation tank 54 through a line 62. In the coagulation tank 54, a polymer coagulant is added to the reaction liquid through a polymer coagulant addition line 76, and a polymer coagulation reaction occurs (polymer coagulation reaction process). The reaction liquid to which the polymer coagulant has been added is sent to the settling tank 56 through a line 64. In the settling tank 56, solid-liquid separation occurs by natural settling or the like (solid-liquid separation process). The resulting treated water is discharged through the treated water line 66, and the sludge is discharged through the sludge line 68 (the coagulation and sedimentation treatment process).

[0087] Fine particles contained in high-concentration flushing wastewater act as nuclei to promote calcium reactions, improving the quality of the treated water.

[0088] The fluorine-containing water is not particularly limited as long as it is water containing fluorine, and examples thereof include wastewater discharged from the electronics industry such as semiconductor factories, specifically etching wastewater and wafer washing wastewater.

[0089] The amount of fluorine contained in the fluoride-containing water is not particularly limited, but is, for example, in the range of 0 to 5000 mg / L, and preferably in the range of 50 to 2000 mg / L.

[0090] Examples of calcium agents that can be used include calcium chloride, slaked lime (calcium hydroxide), and calcium carbonate, with slaked lime being particularly preferred in terms of chemical costs. The calcium agent may be added in the form of a powder, an aqueous solution, or a slurry of water or the like.

[0091] The amount of calcium agent added to the reaction vessel 50 is, for example, in the range of 1.1 to 1.2 times the amount of fluorine in terms of the chemical equivalent of calcium.

[0092] Before the fluoride-containing water and the calcium agent are added to the reaction tank 50, seed crystals may be present in the reaction tank 50 in advance, or the fluoride-containing water and the calcium agent may be added to the reaction tank 50 and seed crystals may be supplied into the reaction tank 50 at the same time. For stable treatment, it is preferable that seed crystals be present in the reaction tank 50 in advance before the water to be treated and the calcium agent are added to the reaction tank 50. In this case, fine particles contained in the high-concentration flushing wastewater or the backwash wastewater of the turbidity removal membrane treatment device 42 also function as seed crystals.

[0093] The pH of the reaction solution in the reaction vessel 50 is, for example, in the range of 4 to 11, and preferably in the range of 4 to 9.

[0094] The amount of inorganic flocculant added in the inorganic reaction tank 52 is, for example, in the range of 50 to 1000 mg / L.

[0095] The pH of the reaction solution in the inorganic reaction tank 52 depends on the type of flocculant used, but is in the range of 6 to 8 when polyaluminum chloride (PAC) is used, for example.

[0096] The inorganic flocculant is not particularly limited as long as it can be used in inorganic flocculation treatment. Examples of inorganic flocculants include iron-based inorganic flocculants such as ferric chloride and polyferric sulfate, and aluminum-based inorganic flocculants such as aluminum sulfate and polyaluminum chloride (PAC). The type of inorganic flocculant to be used may be selected depending on, for example, the properties of the fluoride-containing water to be treated.

[0097] The amount of polymer flocculant added in the flocculation tank 54 is, for example, in the range of 0.5 to 3 mg / L.

[0098] The pH of the reaction liquid in the coagulation tank 54 is in the range of 5 to 8, for example.

[0099] The polymer flocculant is not particularly limited as long as it is an organic polymer flocculant that can be used in polymer flocculation treatment. Examples of polymer flocculants include, but are not limited to, nonionic polymer flocculants, anionic polymer flocculants, and cationic polymer flocculants. Examples include polyacrylamide, sodium polyacrylate, acrylamide-acrylate copolymer, sodium acrylamidopropanesulfonate, chitosan, dimethylaminoethyl methacrylate, dimethylaminoethyl acrylate, and polyamidine. The polymer flocculant may be used alone or in combination of two or more. The type of polymer flocculant to be used may be selected depending on, for example, the properties of the fluoride-containing water to be treated.

[0100] In the calcium reaction step, the aggregation reaction step, and the polymer aggregation reaction step, pH adjustment may be performed using a pH adjuster, such as an acid such as hydrochloric acid or sulfuric acid, or an alkali such as an aqueous sodium hydroxide solution.

[0101] The liquid temperature in the calcium reaction step, the aggregation reaction step, and the polymer aggregation reaction step is not particularly limited and is, for example, in the range of 15 to 35° C. Since the separability varies depending on the viscosity, etc., it is desirable to adjust the liquid temperature to be as constant as possible.

[0102] Examples of the sedimentation tank 56 include pressurized flotation treatment and sedimentation separation. The sedimentation separation is not particularly limited, but examples include natural sedimentation treatment using a sedimentation tank and a sludge blanket type sedimentation tank.

[0103] The amount of fluorine contained in the resulting treated water is not particularly limited, but can be, for example, 15 mg / L or less.

[0104] When the high-concentration flushing wastewater is sent to the reaction tank 50 or a fluoride-containing water tank for storing fluoride-containing water, the reaction for producing calcium salts is promoted. This allows the fluoride concentration of the fluoride-containing water to be further reduced, improving the coagulation properties of the coagulation-sedimentation and improving the solid-liquid separation properties in the settling tank 56.

[0105] The present specification includes the following embodiments. (1) a reverse osmosis membrane treatment device that performs reverse osmosis membrane treatment on water to be treated using a reverse osmosis membrane to obtain permeated water and concentrated water; a discharge line for discharging flushing wastewater from the primary side of the reverse osmosis membrane; a recovery line that sends the flushing wastewater from the primary side of the reverse osmosis membrane to a stage upstream of the reverse osmosis membrane treatment device; a switching means for switching the discharge destination of the flushing wastewater between the discharge line and the recovery line at a predetermined timing during a flushing operation in which flushing water is supplied to the primary side of the reverse osmosis membrane at a predetermined flow rate and discharged from the primary side of the reverse osmosis membrane to clean the reverse osmosis membrane; A water treatment device comprising:

[0106] (2) The water treatment device according to (1), The water treatment device uses the water to be treated or diluted water having a lower salt concentration than the water to be treated as the flushing water.

[0107] (3) The water treatment device according to (1) or (2), The switching means switches the discharge destination of the flushing wastewater from the discharge line to the recovery line within 5 minutes of starting the flushing operation.

[0108] (4) The water treatment device according to (1) or (2), A turbidity measuring device is provided in the discharge line; The switching means switches the discharge destination of the flushing wastewater from the discharge line to the recovery line when the turbidity of the flushing wastewater measured by the turbidity measuring device becomes equal to or lower than a predetermined value.

[0109] (5) A water treatment device according to any one of (1) to (4), The water treatment device, wherein the discharge line is connected to a raw water tank or a reaction tank of a coagulation sedimentation device that removes fluoride by adding a calcium agent to fluoride-containing water to form a sparingly soluble calcium salt.

[0110] (6) A water treatment device according to any one of (1) to (5), a turbidity removal membrane treatment device that treats the flushing wastewater discharged from the discharge line using a turbidity removal membrane; a return line for returning the filtered water treated by the turbidity removal membrane treatment device to a stage upstream of the reverse osmosis membrane treatment device; a backwash wastewater delivery line for delivering the backwash wastewater from the turbidity removal membrane to a raw water tank or a reaction tank of a coagulation sedimentation device that adds a calcium agent to fluoride-containing water to generate a hardly soluble calcium salt to remove fluoride; The water treatment device further comprises:

[0111] (7) a reverse osmosis membrane treatment step in which the water to be treated is treated using a reverse osmosis membrane to obtain permeated water and concentrated water; a discharge step of discharging flushing wastewater from the primary side of the reverse osmosis membrane; a recovery process in which the flushing wastewater is sent from the primary side of the reverse osmosis membrane to a stage preceding the reverse osmosis membrane treatment process; Including, A water treatment method in which flushing water is supplied to the primary side of the reverse osmosis membrane at a predetermined flow rate and discharged from the primary side of the reverse osmosis membrane to clean the reverse osmosis membrane, switching between the discharge process and the recovery process at a predetermined timing during a flushing operation.

[0112] (8) The water treatment method according to (7), The water treatment method, wherein the water to be treated or diluted water having a salt concentration lower than that of the water to be treated is used as the flushing water.

[0113] (9) The water treatment method according to (7) or (8), The water treatment method includes switching from the discharge step to the recovery step within 5 minutes of starting the flushing operation.

[0114] (10) The water treatment method according to (7) or (8), The water treatment method includes switching from the discharge step to the recovery step when the turbidity of the flushing wastewater measured in the discharge step becomes equal to or lower than a predetermined value.

[0115] (11) The water treatment method according to any one of (7) to (10), The flushing wastewater discharged in the discharge step is sent to a raw water tank or a reaction tank of a coagulation sedimentation apparatus in which a calcium agent is added to fluoride-containing water to form a sparingly soluble calcium salt and remove fluoride.

[0116] (12) The water treatment method according to any one of (7) to (11), The method further includes a turbidity removal membrane treatment step of treating the flushing wastewater discharged in the discharge step using a turbidity removal membrane, The filtrate treated in the turbidity removal membrane treatment step is returned to the upstream stage of the reverse osmosis membrane treatment step, The backwash wastewater from the turbidity removal membrane is sent to a raw water tank or a reaction tank of a coagulation sedimentation device in which a calcium agent is added to fluoride-containing water to form a sparingly soluble calcium salt, thereby removing fluoride. [Example]

[0117] EXAMPLES 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.

[0118] [Reverse osmosis membrane treatment and flushing] Example 1 A water flow test was carried out using the water treatment device 4 shown in Fig. 4. In the normal operation step, a portion of the concentrated water was circulated through the recovery line 24 to the water tank 38 for treatment.

[0119] (Normal operating conditions) Reverse osmosis membrane: Nitto Denko LFC3-LD-4040 ·Water flow rate to be treated: 160L / h Flow rate of permeated water from reverse osmosis membrane treatment device 10: 140 L / h Concentrated water discharge flow rate of reverse osmosis membrane treatment device 10: 20 L / h - Concentrated water circulation flow rate to treated water tank 38: 700 L / h

[0120] The water to be treated was prepared by adding reagents (sodium bicarbonate and calcium chloride) to pure water. The water quality is shown in Table 1.

[0121] [Table 1]

[0122] Every 4 hours of water flow, the permeated water was used as flushing water and a flushing step was carried out for 10 minutes at a flushing flow rate of 720 L / h.

[0123] The total calcium concentration (mg / L) of the flushing wastewater was measured by calcium chelate titration (JIS K 0101 Industrial Water Testing Method), and the turbidity was measured by transmitted light turbidity (JIS K 0101 Industrial Water Testing Method) using a spectrophotometer (Hitachi, U-2900). The water quality of the flushing wastewater is shown in Table 2.

[0124] [Table 2]

[0125] In Example 1, flushing wastewater from the start of the flushing process until less than 5 minutes was discharged through discharge line 22, and flushing wastewater from 5 minutes onwards (5 minutes' worth) was returned as flushing recovered water to treated water tank 38 through recovery line 24. When the normal operation process to the flushing process were considered as one cycle, the water recovery rate of Example 1 determined by the following method was 75.9%.

[0126] (Calculation method for water recovery rate) One cycle consists of the "normal operation process - flushing process", and the flushing wastewater is returned to the treated water tank 38. Five minutes' worth of flushing wastewater is recovered in the treated water tank 38. As a result, the amount of water to be treated that is replenished is reduced, and the water recovery rate is as follows: Recovery rate (%) = amount of permeated water obtained in one cycle (L) / amount of treated water replenished in one cycle (L) = [(140 L / h × 4 h - 720 L / h × (10 / 60) h) / (160 L / h × 4 h - 720 L / h × (5 / 60) h)] × 100 = 75.9%

[0127] In Example 1, the above cycle was repeated, and the reverse osmosis membrane operated stably without any significant clogging. Furthermore, compared to when the entire flushing wastewater for 10 minutes was discharged (720 L / h x 10 min = 120 L), only 5 minutes of the 10 minutes (60 L) was collected, resulting in a 50% reduction in the amount of flushing wastewater per cycle.

[0128] In the same manner as in Example 1, all of the flushing wastewater was discarded through the discharge line 22. The water recovery rate determined by the following method was 68.8%. Recovery rate (%) = amount of permeated water obtained in one cycle (L) / amount of treated water replenished in one cycle (L) = [(140 L / h × 4 h - 720 L / h × (10 / 60) h) / (160 L / h × 4 h)] × 100 = 68.8%

[0129] <Example 2> A water flow test was carried out using the water treatment device 4 shown in Figure 4. The conditions for the normal operation process were the same as in Example 1. Table 3 shows the quality of the water to be treated.

[0130] [Table 3]

[0131] Every 4 hours of water flow, the permeated water was used as flushing water, and a flushing step was carried out for 6 minutes at a flushing flow rate of 720 L / h.

[0132] The total calcium concentration (mg / L) and turbidity of the flushing wastewater were measured in the same manner as in Example 1. The water quality of the flushing wastewater is shown in Table 4.

[0133] [Table 4]

[0134] In Example 2, flushing wastewater from the start of the flushing process until less than 3 minutes was discharged through discharge line 22, and flushing wastewater from 3 minutes onwards (3 minutes' worth) was returned to treated water tank 38 through recovery line 24. When the normal operation process to the flushing process were considered as one cycle, the water recovery rate of Example 2 determined by the following method was 80.8%.

[0135] (Calculation method for water recovery rate) Recovery rate (%) = amount of permeated water obtained in one cycle (L) / amount of treated water replenished in one cycle (L) = [(140 L / h × 4 h - 720 L / h × (6 / 60) h) / (160 L / h × 4 h - 720 L / h × (3 / 60) h)] × 100 = 80.8%

[0136] In Example 2, the above cycle was repeated, and the reverse osmosis membrane operated stably without any significant clogging. Furthermore, compared to discharging all of the flushing wastewater for 6 minutes, the amount of wastewater discharged per cycle was reduced by 50%, improving the water recovery rate.

[0137] In the same manner as in Example 2, all of the flushing wastewater was discarded through the discharge line 22. The water recovery rate determined by the following method was 76.3%. Recovery rate (%) = amount of permeated water obtained in one cycle (L) / amount of treated water replenished in one cycle (L) = [(140 L / h × 4 h - 720 L / h × (6 / 60) h) / (160 L / h × 4 h)] × 100 = 76.3%

[0138] Example 3 A water flow test was carried out using the water treatment device 4 shown in Figure 4. The conditions for the normal operation process were the same as in Example 1, and the same water to be treated as in Example 2 was used. Every hour of water flow, the permeated water was used as flushing water, and a flushing process was carried out for 2 minutes at a flushing flow rate of 720 L / h.

[0139] The total calcium concentration (mg / L) and turbidity of the flushing wastewater were measured in the same manner as in Example 1. The water quality of the flushing wastewater is shown in Table 5.

[0140] [Table 5]

[0141] In Example 3, flushing wastewater from the start of the flushing process until less than 30 seconds was discharged through discharge line 22, and flushing wastewater from 30 seconds onwards (90 seconds worth) was returned to the treated water tank 38 through recovery line 24. When the normal operation process to the flushing process were considered as one cycle, the water recovery rate of Example 3 determined by the following method was 81.7%.

[0142] (Calculation method for water recovery rate) Recovery rate (%) = amount of permeated water obtained in one cycle (L) / amount of treated water replenished in one cycle (L) = [(140 L / h × 1 h - 720 L / h × (2 / 60) h) / (160 L / h × 1 h - 720 L / h × (1.5 / 60) h)] × 100 = 81.7%

[0143] In Example 3, the reverse osmosis membrane was able to operate stably without showing any significant tendency to clog. The flushing wastewater volume was 720 L / h × 2 min = 24 L, of which 1.5 minutes' worth (18 L) was recovered, resulting in a reduction of 18 / 24 = 75%.

[0144] In the same manner as in Example 3, the flushing wastewater was completely discarded through the discharge line 22. The water recovery rate determined by the following method was 72.5%. Recovery rate (%) = amount of permeated water obtained in one cycle (L) / amount of treated water replenished in one cycle (L) = [(140 L / h × 1 h - 720 L / h × (2 / 60) h) / (160 L / h × 1 h)] × 100 = 72.5%

[0145] Example 4 A water flow test was carried out using the water treatment device 4 shown in Figure 4. The conditions for the normal operation process were the same as in Example 1, and the same water to be treated as in Example 2 was used. Every 30 minutes of water flow, the permeated water was used as flushing water, and a flushing process was carried out for 2 minutes at a flushing flow rate of 720 L / h.

[0146] The total calcium concentration (mg / L) and turbidity of the flushing wastewater were measured in the same manner as in Example 1. The water quality of the flushing wastewater is shown in Table 6.

[0147] [Table 6]

[0148] In Example 4, flushing wastewater from the start of the flushing process until less than 10 seconds was discharged through discharge line 22, and flushing wastewater from 10 seconds onwards (110 seconds' worth) was returned to the treated water tank 38 through recovery line 24. When the normal operation process to the flushing process were considered as one cycle, the water recovery rate of Example 3 determined by the following method was 79.3%.

[0149] (Calculation method for water recovery rate) Recovery rate (%) = amount of permeated water obtained in one cycle (L) / amount of treated water replenished in one cycle (L) = [(140 L / h x 0.5 h - 720 L / h x (2 / 60) h) / (160 L / h x 0.5 h - 720 L / h x (110 / 60 / 60) h)] x 100 = 79.3%

[0150] In Example 4, the reverse osmosis membrane was able to operate stably without showing any significant tendency to clog. The flushing wastewater volume was 720 L / h x 2 min = 24 L, of which 22 L for 1 minute 50 seconds was recovered, resulting in a reduction of 22 / 24 = 91.7%.

[0151] In the same manner as in Example 4, all of the flushing wastewater was discarded through the discharge line 22. The water recovery rate determined by the following method was 57.5%. Recovery rate (%) = amount of permeated water obtained in one cycle (L) / amount of treated water replenished in one cycle (L) = [(140 L / h × 0.5 h - 720 L / h × (2 / 60) h) / (160 L / h × 0.5 h)] × 100 = 57.5%

[0152] [Coagulation and sedimentation treatment] Example 1 The flushing wastewater discharged in the flushing step of Example 1 for less than 5 minutes from the start of flushing was stored and flowed into the reaction tank 50 of the coagulation sedimentation device 6 shown in FIG. 6, where coagulation sedimentation treatment was carried out under the following conditions.

[0153] (Coagulation and sedimentation treatment conditions) Fluorine-containing water: semiconductor factory wastewater Flow rate of fluorine-containing water flowing into the reaction tank 50: 4 L / h Fluoride concentration in fluoridated water: 30mg-F / L Calcium agent (slaked lime) addition amount in reaction tank 50: 230 mg-Ca / L Flushing wastewater inflow rate to reaction tank 50: 0.4 L / h Amount of inorganic coagulant (polyaluminum chloride (PAC)) added in inorganic reaction tank 52: 50 mg / L Amount of polymer flocculant (Orflock ON-1H, manufactured by Organo Corporation) added in coagulation tank 54: 1 mg / L Linear velocity (LV) of settling tank 56: 1 m / h

[0154] The fluorine concentration of the resulting treated water was measured by atomic absorption spectrometry using an ion chromatograph (Dionex Integrion, manufactured by Thermo Fisher Scientific), and the SS concentration was measured by the glass fiber filter paper method (JIS K 0102 Industrial Wastewater Testing Method). The results are shown in Table 7.

[0155] <Example 2> The flushing wastewater discharged in the flushing step of Example 2 for less than 3 minutes from the start of flushing was pooled and allowed to flow into the reaction tank 50 of the coagulation-sedimentation device 6 shown in FIG. 6, and coagulation-sedimentation treatment was otherwise carried out in the same manner as in Example 1. The fluorine concentration and SS concentration of the resulting treated water were measured. The results are shown in Table 7.

[0156] In Examples 1 and 2, it is believed that the fine particles contained in the flushing wastewater acted as nuclei to promote the calcium reaction, thereby reducing the fluorine concentration in the treated water and improving the coagulation properties, thereby improving the solid-liquid separation properties and reducing the SS concentration.

[0157] <Comparative Example 1> The coagulation and sedimentation treatment was carried out in the same manner as in Examples 1 and 2, except that flushing wastewater was not used, and only semiconductor factory wastewater was passed through. The fluorine concentration and SS concentration of the resulting treated water were measured. The results are shown in Table 7.

[0158] In Comparative Example 1, the fluorine concentration and SS concentration of the treated water were worse than those in Examples 1 and 2.

[0159] [Table 7]

[0160] In this way, in the example, flushing could be performed while suppressing a decrease in the water recovery rate of the reverse osmosis membrane device. [Explanation of symbols]

[0161] 1, 2, 3, 4, 5 water treatment device, 6 coagulation sedimentation device, 10 reverse osmosis membrane treatment device, 12 pressure pump, 14, 16, 34 valve, 18, 40 treated water line, 20 permeate line, 22 discharge line, 24 recovery line, 26 turbidity measuring device, 28 permeate tank, 30 pump, 32 flushing water supply line, 36 concentrated water line, 38 treated water tank, 42 ​​turbidity removal membrane treatment device, 44 filtrate line, 46 backwash wastewater delivery line, 50 reaction tank, 52 inorganic reaction tank, 54 coagulation tank, 56 settling tank, 58 fluoride-containing water line, 60, 62, 64 line, 66 treated water line, 68 sludge line, 70 flushing wastewater addition line, 72 calcium agent addition line, 74 inorganic coagulant addition line, 76 polymer coagulant addition line.

Claims

1. a reverse osmosis membrane treatment device that performs reverse osmosis membrane treatment on the water to be treated using a reverse osmosis membrane to obtain permeated water and concentrated water; a discharge line for discharging flushing wastewater from the primary side of the reverse osmosis membrane; a recovery line that sends the flushing wastewater from the primary side of the reverse osmosis membrane to a stage upstream of the reverse osmosis membrane treatment device; a switching means for switching the discharge destination of the flushing wastewater between the discharge line and the recovery line at a predetermined timing during a flushing operation in which flushing water is supplied to the primary side of the reverse osmosis membrane at a predetermined flow rate and discharged from the primary side of the reverse osmosis membrane to clean the reverse osmosis membrane; A water treatment device comprising:

2. The water treatment device according to claim 1, 1. A water treatment device, comprising: a water treatment apparatus using, as the flushing water, the water to be treated or dilute water having a lower salt concentration than the water to be treated.

3. The water treatment device according to claim 1, The water treatment device is characterized in that the switching means switches the discharge destination of the flushing wastewater from the discharge line to the recovery line within five minutes of starting the flushing operation.

4. The water treatment device according to claim 1, A turbidity measuring device is provided in the discharge line; The water treatment device is characterized in that the switching means switches the discharge destination of the flushing wastewater from the discharge line to the recovery line when the turbidity of the flushing wastewater measured by the turbidity measuring device becomes equal to or lower than a predetermined value.

5. The water treatment device according to claim 1, 1. A water treatment device comprising: a water treatment system in which the discharge line is connected to a raw water tank or a reaction tank of a coagulation sedimentation device that removes fluoride by adding a calcium agent to fluoride-containing water to form a sparingly soluble calcium salt.

6. The water treatment device according to claim 1, a turbidity removal membrane treatment device that treats the flushing wastewater discharged from the discharge line using a turbidity removal membrane; a return line for returning the filtered water treated by the turbidity removal membrane treatment device to a stage upstream of the reverse osmosis membrane treatment device; a backwash wastewater delivery line for delivering the backwash wastewater from the turbidity removal membrane to a raw water tank or a reaction tank of a coagulation sedimentation device that adds a calcium agent to fluoride-containing water to generate a hardly soluble calcium salt to remove fluoride; The water treatment device further comprises:

7. a reverse osmosis membrane treatment step in which the water to be treated is treated using a reverse osmosis membrane to obtain permeated water and concentrated water; a discharge step of discharging flushing wastewater from the primary side of the reverse osmosis membrane; a recovery process in which the flushing wastewater is sent from the primary side of the reverse osmosis membrane to a stage preceding the reverse osmosis membrane treatment process; Including, A water treatment method characterized by switching between the discharge process and the recovery process at a predetermined timing during a flushing operation in which flushing water is supplied to the primary side of the reverse osmosis membrane at a predetermined flow rate and discharged from the primary side of the reverse osmosis membrane to clean the reverse osmosis membrane.

8. The water treatment method according to claim 7, A water treatment method characterized in that the water to be treated or diluted water having a lower salt concentration than the water to be treated is used as the flushing water.

9. The water treatment method according to claim 7, A water treatment method characterized in that the discharge step is switched to the recovery step within 5 minutes of starting the flushing operation.

10. The water treatment method according to claim 7, A water treatment method characterized in that when the turbidity of the flushing wastewater measured in the discharge step falls below a predetermined value, the discharge step is switched to the recovery step.

11. The water treatment method according to claim 7, The method for water treatment comprises sending the flushing wastewater discharged in the discharge step to a raw water tank or a reaction tank of a coagulation sedimentation apparatus in which a calcium agent is added to fluoride-containing water to form a sparingly soluble calcium salt to remove fluoride.

12. The water treatment method according to claim 7, The method further includes a turbidity removal membrane treatment step of treating the flushing wastewater discharged in the discharge step using a turbidity removal membrane, The filtrate treated in the turbidity removal membrane treatment step is returned to the upstream stage of the reverse osmosis membrane treatment step, The backwash wastewater from the turbidity removal membrane is sent to a raw water tank or a reaction tank of a coagulation sedimentation device for removing fluorine by adding a calcium agent to fluoride-containing water to form a sparingly soluble calcium salt.

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