Water treatment device and water treatment method

Abstract

Provided is a water treatment device and a water treatment method that can inhibit a decrease in water recovery of a reverse osmosis membrane device and perform flushing. A water treatment device (1) includes: a reverse osmosis membrane treatment device (10) that performs reverse osmosis membrane treatment on treated water and obtains permeated water and concentrated water; a discharge line (22) that discharges flushing drain water from a primary side of a reverse osmosis membrane; a recovery line (24) that sends the flushing drain water to a front stage of the reverse osmosis membrane treatment device (10); and a switching unit that switches a discharge destination of the flushing drain water through the discharge line (22) and the recovery line (24) at a specific timing during a flushing operation in which flushing water is supplied to the primary side of the reverse osmosis membrane at a specific flow rate and discharged from the primary side of the reverse osmosis membrane to clean the reverse osmosis membrane.

Description

Technical Field

[0001] This invention relates to a water treatment apparatus and a water treatment method equipped with a reverse osmosis membrane device. Background Technology

[0002] One method for restoring the clogging of reverse osmosis membranes used in reverse osmosis membrane systems is flushing. Flushing involves discharging water supplied to the primary side of the reverse osmosis membrane at a specific flow rate as flushing water from the primary side outlet pipe outside the system, thereby cleaning impurities and other debris adhering to the membrane surface on the primary side.

[0003] For example, Patent Document 1 describes a method for restoring the clogging of a reverse osmosis membrane by flushing it with water of low salt concentration, such as permeate water. However, in the method described in Patent Document 1, the flushing wastewater is discharged outside the system, thus reducing the water recovery rate of the reverse osmosis membrane device. Patent Document 1 does not specify the destination of the flushing wastewater.

[0004] Patent Document 2 describes a method where a branch pipe equipped with a valve is installed on the concentrate water piping of a reverse osmosis membrane unit, allowing switching between normal operation and flushing operation by opening and closing the valve. However, in the method of Patent Document 2, the flushing wastewater is also discharged outside the system, reducing the water recovery rate of the reverse osmosis membrane unit.

[0005] Patent document 3 describes a method that allows switching between normal operation and flushing operation at any time, with the flushing flow rate automatically adjusted according to a target value. In the method of patent document 3, the flushing wastewater is also discharged outside the system, reducing the water recovery rate of the reverse osmosis membrane unit.

[0006] Another approach is to improve water recovery by returning all flushing wastewater to the front end of the reverse osmosis membrane unit. However, in this method, particles and other contaminants in the flushing wastewater are returned to the front end of the reverse osmosis membrane unit, thus further concentrating these particles within the system and posing a risk of re-clogging the reverse osmosis membrane.

[0007] Existing technical documents Patent documents Patent Document 1: Japanese Patent Application Publication No. 2022-045877 Patent Document 2: Japanese Patent Application Publication No. 2019-177338 Patent Document 3: Japanese Patent Application Publication No. 2013-141621 Summary of the Invention

[0008] The technical problem that the invention aims to solve The purpose of this invention is to provide a water treatment apparatus and a water treatment method capable of flushing to suppress the decrease in water recovery rate of a reverse osmosis membrane device.

[0009] Technical solutions for solving technical problems This invention relates to a water treatment apparatus comprising: a reverse osmosis membrane treatment device, wherein a reverse osmosis membrane is used to treat water to obtain permeate and concentrate; a discharge line, wherein flushing wastewater is discharged from the primary side of the reverse osmosis membrane; a recovery line, wherein the flushing wastewater is sent from the primary side of the reverse osmosis membrane to the pre-stage of the reverse osmosis membrane treatment device; and a switching unit, wherein during flushing operation, the discharge destination of the flushing wastewater is switched at specific times via the discharge line and the recovery line, wherein during the flushing operation, flushing water is supplied to the primary side of the reverse osmosis membrane at a specific flow rate and discharged from the primary side of the reverse osmosis membrane to clean the reverse osmosis membrane.

[0010] Preferably, in the water treatment apparatus, the treated water or dilution water with a lower salt concentration than the treated water is used as the rinsing water.

[0011] Preferably, in the water treatment device, the switching unit switches the destination of the flushing drainage from the discharge pipeline to the recovery pipeline less than 5 minutes after the flushing operation begins.

[0012] Preferably, in the water treatment apparatus, the discharge pipeline is equipped with a turbidity measuring device. If the turbidity of the flushing wastewater measured by the turbidity measuring device reaches a certain value or below, the switching unit switches the discharge destination of the flushing wastewater from the discharge pipeline to the recovery pipeline.

[0013] Preferably, in the water treatment device, the discharge pipeline is connected to the raw water tank or reaction tank of the coagulation and sedimentation device, and the coagulation and sedimentation device removes fluoride by adding calcium agent to the fluoride-containing water to generate insoluble calcium salt.

[0014] Preferably, the water treatment apparatus further comprises: a turbidity removal membrane treatment device, wherein the turbidity removal membrane is used to treat the flushing wastewater discharged from the discharge pipeline; a return pipeline, wherein the filtered water treated by the turbidity removal membrane treatment device is returned to the pre-stage of the reverse osmosis membrane treatment device; and a liquid delivery pipeline, wherein the backwash wastewater of the turbidity removal membrane is delivered to the raw water tank or reaction tank of the coagulation and sedimentation device, wherein the coagulation and sedimentation device removes fluoride by adding a calcium agent to the fluoride-containing water to generate insoluble calcium salts.

[0015] This invention relates to a water treatment method, comprising: a reverse osmosis membrane treatment step, wherein a reverse osmosis membrane is used to treat water to obtain permeate and concentrate; a discharge step, wherein flushing wastewater is discharged from the primary side of the reverse osmosis membrane; and a recovery step, wherein the flushing wastewater is sent from the primary side of the reverse osmosis membrane to the pre-stage of the reverse osmosis membrane treatment step, wherein during flushing operation, the discharge step and the recovery step are switched at specific times, and during the flushing operation, flushing water is supplied to the primary side of the reverse osmosis membrane at a specific flow rate, and the flushing wastewater is discharged from the primary side of the reverse osmosis membrane to clean the reverse osmosis membrane.

[0016] Preferably, in the water treatment method, the treated water or dilution water with a lower salt concentration than the treated water is used as the rinsing water.

[0017] Preferably, in the water treatment method, the process switches from the discharge step to the recycling step less than 5 minutes after the flushing operation begins.

[0018] Preferably, in the water treatment method, if the turbidity of the flushing wastewater measured in the discharge step reaches a certain value or below, the process switches from the discharge step to the recycling step.

[0019] Preferably, in the water treatment method, the flushing wastewater discharged in the discharge process is sent to the raw water tank or reaction tank of the coagulation and sedimentation device, wherein the coagulation and sedimentation device adds calcium agent to the fluoride-containing water to generate insoluble calcium salt to remove fluoride.

[0020] Preferably, the water treatment method further includes a turbidity removal membrane treatment step, wherein the turbidity removal membrane is used to treat the flushing wastewater discharged in the discharge step, the filtered water treated by the turbidity removal membrane treatment step is returned to the pre-stage of the reverse osmosis membrane treatment step, and the backwash wastewater of the turbidity removal membrane is sent to the raw water tank or reaction tank of the coagulation and sedimentation device, wherein the coagulation and sedimentation device adds calcium agent to the fluoride-containing water to generate insoluble calcium salt to remove fluoride.

[0021] Invention Effects According to the present invention, a water treatment apparatus and a water treatment method are provided that can perform flushing to suppress the decrease in water recovery rate of a reverse osmosis membrane device. Attached Figure Description

[0022] Figure 1 This is a schematic structural diagram illustrating an example of a water treatment apparatus according to an embodiment of the present invention.

[0023] Figure 2 This is a schematic structural diagram illustrating another example of a water treatment apparatus according to an embodiment of the present invention.

[0024] Figure 3 This is a schematic structural diagram illustrating another example of a water treatment apparatus according to an embodiment of the present invention.

[0025] Figure 4 This is a schematic structural diagram illustrating another example of a water treatment apparatus according to an embodiment of the present invention.

[0026] Figure 5 This is a schematic structural diagram illustrating another example of a water treatment apparatus according to an embodiment of the present invention.

[0027] Figure 6 This is a schematic structural diagram illustrating an example of a coagulation and sedimentation apparatus for high-concentration flushing wastewater obtained using a water treatment device according to an embodiment of the present invention. Detailed Implementation

[0028] The following describes embodiments of the present invention. This embodiment is merely one example of implementing the present invention, and the present invention is not limited to this embodiment.

[0029] A schematic example of a water treatment apparatus according to an embodiment of the present invention is shown below. Figure 1 The structure will be explained.

[0030] Figure 1 The water treatment apparatus 1 shown includes: a reverse osmosis membrane treatment apparatus 10, wherein the water to be treated is treated by reverse osmosis membrane treatment to obtain permeate water and concentrate water; a discharge line 22, wherein flushing wastewater is discharged from the primary side of the reverse osmosis membrane; a recovery line 24, which branches off from the discharge line 22 and sends the flushing wastewater from the primary side of the reverse osmosis membrane to the pre-stage of the reverse osmosis membrane treatment apparatus 10; and valves 14 and 16 as switching units, which, during flushing operation, switch the discharge destination of the flushing wastewater at specific times through the discharge line 22 and the recovery line 24, wherein during the flushing operation, flushing water is supplied to the primary side of the reverse osmosis membrane at a specific flow rate and discharged from the primary side of the reverse osmosis membrane to clean the reverse osmosis membrane.

[0031] exist Figure 1In the water treatment apparatus 1, a treated water pipeline 18 is connected to the inlet of the reverse osmosis membrane treatment unit 10 via a booster pump 12. The permeate outlet of the reverse osmosis membrane treatment unit 10 is connected to the permeate pipeline 20. A discharge pipeline 22 is connected to the concentrate / flushing drain outlet of the reverse osmosis membrane treatment unit 10 via a valve 14. A recovery pipeline 24 branches from the connection point of the discharge pipeline 22 with the concentrate / flushing drain outlet and the valve 14 via a valve 16. The valves 14 and 16 can also be combined into one three-way valve and installed at the branch point of the discharge pipeline 22 and the recovery pipeline 24. If necessary, a flow meter can be installed upstream of the booster pump 12 in the treated water pipeline 18, at least one of the discharge pipeline 22, the recovery pipeline 24, and the permeate pipeline 20 as a flow measurement unit to measure the flow rate in each pipeline. If necessary, a valve can also be installed upstream of the branch point of the recovery pipeline 24 in the discharge pipeline 22, and a flow meter can be installed between the valve and the branch point of the recovery pipeline 24.

[0032] The operation of the water treatment method and the water treatment apparatus 1 involved in this embodiment will be described.

[0033] The water to be treated is delivered to the primary side of the reverse osmosis membrane treatment unit 10 via the treated water pipeline 18 using a booster pump 12. In the reverse osmosis membrane treatment unit 10, the water to be treated is treated using a reverse osmosis membrane to obtain permeate and concentrate (reverse osmosis membrane treatment process).

[0034] The permeate obtained by reverse osmosis membrane treatment is discharged through permeate line 20, valve 14 is in the open state, valve 16 is in the closed state, and concentrated water is discharged through discharge line 22.

[0035] In the water treatment method and water treatment apparatus 1 of this embodiment, a normal operation process (reverse osmosis membrane treatment process) for obtaining permeate and concentrate by reverse osmosis membrane treatment is alternated with a rinsing process for cleaning the membrane surface of the primary side of the reverse osmosis membrane at specific intervals (e.g., periodic). The rinsing is a method of cleaning impurities and the like adhering to the membrane surface of the primary side by discharging rinsing water supplied to the primary side of the reverse osmosis membrane at a specific flow rate from the discharge line of the primary side.

[0036] After conducting research, the inventors discovered that the flushing wastewater contains a large number of particles that adhere to the primary side of the reverse osmosis membrane during the initial discharge period, typically between tens of seconds and several minutes. Therefore, it was found that by discharging the portion of the flushing wastewater with a high concentration of particles, it is possible to recover the remaining portion with a low concentration of particles, thereby suppressing reverse osmosis membrane clogging and preventing a decrease in water recovery rate.

[0037] For example, if flushing operation begins, the flushing water is delivered to the primary side of the reverse osmosis membrane treatment unit 10 via the treated water line 18 using the booster pump 12 at a lower pressure than in normal operation. Valve 14 is open, valve 16 is closed, and the flushing wastewater is discharged through the discharge line 22. In the initial discharge phase, for example, from tens of seconds to several minutes, a large amount of flushing wastewater containing particles attached to the primary side of the reverse osmosis membrane is discharged (hereinafter, sometimes referred to as "high-concentration flushing wastewater"). If most of the particles attached to the primary side of the reverse osmosis membrane are discharged, valve 14 is closed, valve 16 is open, and the discharge destination of the flushing wastewater is switched between the discharge line 22 and the recovery line 24. A flushing wastewater with a lower content of particles is discharged through the recovery line 24 (hereinafter, sometimes referred to as "low-concentration flushing wastewater"). This low-concentration flushing wastewater is then sent to the pre-treatment stage of the reverse osmosis membrane treatment unit 10. At this time, the low-concentration flushing wastewater can be sent, for example, to the treated water tank of the reverse osmosis membrane treatment device 10, or to the treated water pipeline 18.

[0038] By switching valves during flushing and changing the destination of the flushing drainage, the water recovery rate of the reverse osmosis membrane unit can be suppressed during flushing. Therefore, in water treatment where the reverse osmosis membrane is flushed at specific intervals, the decrease in water recovery rate can be suppressed, and the flushing drainage can be effectively utilized. In addition, it is particularly effective when the water being treated in the reverse osmosis membrane treatment unit 10 contains calcium and other substances that easily form calcium scale such as calcium carbonate and calcium fluoride.

[0039] The water treatment method and water treatment apparatus described in this embodiment enable the water recovery rate of the reverse osmosis membrane device to be, for example, 50% or more, preferably 60% or more.

[0040] By separating the high-concentration flushing wastewater at the initial stage of discharge, for example by supplying it to a wastewater treatment device such as a solid-liquid separation unit including a coagulation and sedimentation unit, the particles contained in the high-concentration flushing wastewater can be used as nuclei for the coagulation reaction, improving the coagulation properties and increasing the settling velocity in the coagulation and sedimentation process. Therefore, it is even more effective to supply the high-concentration flushing wastewater to the reaction tank of a coagulation and sedimentation unit.

[0041] In the initial stage of flushing drainage discharge, the high-concentration flushing drainage should preferably be delivered as evenly as possible to the raw water tank or reaction tank of the coagulation and sedimentation device. Therefore, a high-concentration flushing drainage storage tank can also be set up separately to store the high-concentration flushing drainage.

[0042] The discharge pipeline 22 is connected to the raw water tank or reaction tank of the coagulation and sedimentation device. The coagulation and sedimentation device removes fluoride by adding calcium to the fluoride-containing water to generate insoluble calcium salts. If high-concentration flushing wastewater is sent to the raw water tank or reaction tank, the formation of calcium salts can be promoted. This further reduces the fluoride concentration in the fluoride-containing water, improves the coagulation properties of the coagulation and sedimentation process, and enhances solid-liquid separation.

[0043] Furthermore, the latter part of the flushing wastewater (low-concentration flushing wastewater) contains a small amount of particles. Therefore, by returning it to the upstream stage of the reverse osmosis membrane treatment unit 10, such as the treated water tank of the reverse osmosis membrane treatment unit 10, water can be recovered again, thereby suppressing the risk of clogging of the reverse osmosis membrane treatment unit 10 and preventing a decrease in the water recovery rate. At this time, a low-concentration flushing wastewater storage tank can also be separately provided to store the low-concentration flushing wastewater. Alternatively, the low-concentration flushing wastewater can be removed with suspended solids using a turbidity removal membrane or the like, and then returned to the treated water tank of the reverse osmosis membrane treatment unit 10 for water recovery again.

[0044] At the initial discharge stage, for example, less than 5 minutes after the start of flushing operation, preferably within 10 seconds to less than 5 minutes, and more preferably within 30 seconds to 3 minutes, the destination of the flushing wastewater should be switched from the discharge line 22 to the recovery line 24. If the switch is made less than 5 minutes after the start of flushing operation, most of the particles adhering to the primary side of the reverse osmosis membrane will be discharged from the discharge line 22. The switching time from the discharge line 22 to the recovery line 24 from the start of flushing operation can be appropriately adjusted according to the ion concentration of the water being treated in the reverse osmosis membrane treatment unit 10, the interval of flushing operation, and the flow rate of the flushing water. In addition, by switching within 3 minutes after the start of flushing operation, the water recovery rate can be further improved. By switching within 30 seconds to 3 minutes after the start of flushing operation, the clogging of the reverse osmosis membrane and the reduction of the water recovery rate can be effectively suppressed.

[0045] For example, valves 14 and 16 can be configured as automatic valves, with timers installed on them. The timers activate, switching the drainage destination by opening valve 14 and closing valve 16 via the automatic valves. High-concentration flushing wastewater is discharged from discharge line 22, for example, to a coagulation and sedimentation unit. Alternatively, after a specific time measured by the timer, the automatic valves are switched, closing valve 14 and opening valve 16. Low-concentration flushing wastewater, as part of the flushing wastewater, is returned via recovery line 24 to, for example, the pre-treatment water tank of the reverse osmosis membrane treatment unit 10. For example, when the properties of the treated water from the reverse osmosis membrane treatment are stable, the timer can be used to switch the discharge destination of the flushing wastewater via discharge line 22 and recovery line 24.

[0046] There are no particular restrictions on the water that can be treated by reverse osmosis membranes, such as groundwater, river water, seawater, and wastewater discharged from various factories.

[0047] There are no particular limitations on the reverse osmosis membrane used in the reverse osmosis membrane treatment device 10; for example, polyamide-based or cellulose acetate-based reverse osmosis membranes can be used.

[0048] There are no particular restrictions on the water used for rinsing; for example, the treated water from the reverse osmosis membrane treatment unit 10 can be used. Alternatively, other rinsing water can be introduced from outside the system, such as dilution water with a lower salt concentration than the treated water, such as permeate from the reverse osmosis membrane treatment, concentrated water from the electro-regenerated deionization unit, treated water, or pure water. Furthermore, water whose pH has been adjusted using acids (e.g., acetic acid, hydrochloric acid, sulfuric acid, etc.) or bases (e.g., aqueous sodium hydroxide solution, etc.) can also be used as rinsing water.

[0049] If the water to be treated by the reverse osmosis membrane treatment unit 10 or dilution water with a lower salt concentration is used as flushing water, the cleaning effect of the reverse osmosis membrane surface will be improved, and the risk of impurities being mixed in during the recycling and reuse of flushing wastewater, as well as the risk of poor coagulation caused by the mixing of substances into the forward coagulation and sedimentation device, etc., can be reduced.

[0050] The high-concentration flushing wastewater from the initial discharge stage of the flushing process can be sent from discharge pipeline 22 to a wastewater treatment device, such as a solid-liquid separation device (solid-liquid separation process) or an inorganic wastewater treatment device (inorganic wastewater treatment process), including a coagulation and sedimentation device (coagulation and sedimentation process) or a coagulation and pressurization flotation device (coagulation and pressurization flotation process). As for the coagulation and sedimentation device, any device that performs coagulation and sedimentation treatment is acceptable, without particular limitations. Examples include high-speed coagulation and sedimentation devices such as reaction tanks in coagulation and sedimentation devices that remove fluoride by adding calcium to fluoride-containing water to generate insoluble calcium salts. Among these, considering that the flushing wastewater contains calcium particles, it is particularly preferable to send the high-concentration flushing wastewater to a reaction tank in a coagulation and sedimentation device that removes fluoride by adding calcium to fluoride-containing water to generate insoluble calcium salts.

[0051] When high-concentration flushing wastewater is sent from discharge pipeline 22 to wastewater treatment devices such as coagulation and sedimentation units, the flushing process is operated at a lower pressure than normal operation, and no permeate water is discharged. At this time, water is not supplied to recovery pipeline 24. Furthermore, if a separate concentrate water pipeline is installed, it is also not supplied with water.

[0052] It may also include: a permeate tank for storing permeate water; and a flushing water supply line and pump as a flushing water supply unit, wherein the permeate water is delivered to the inlet of the reverse osmosis membrane; for example, a flushing mechanism for periodic flushing. Additionally, it may include a turbidity measuring device, wherein the turbidity of the flushing wastewater is measured, and if the turbidity of the flushing wastewater measured by the turbidity measuring device falls below a certain value, the discharge destination of the flushing wastewater is switched from the discharge line to the recovery line. An example of the above method is shown below. Figure 2 .

[0053] Figure 2 The water treatment apparatus 2 shown includes: a reverse osmosis membrane treatment apparatus 10, wherein reverse osmosis membrane is used to treat water to obtain permeate water and concentrated water; a discharge line 22, wherein flushing wastewater is discharged from the primary side of the reverse osmosis membrane; a recovery line 24, which branches off from the discharge line 22 and sends the flushing wastewater from the primary side of the reverse osmosis membrane to the pre-stage of the reverse osmosis membrane treatment apparatus 10; valves 14 and 16 as switching units, which, during flushing operation, switch the discharge destination of the flushing wastewater at specific times through the discharge line 22 and the recovery line 24, wherein flushing water is supplied to the primary side of the reverse osmosis membrane at a specific flow rate and discharged from the primary side of the reverse osmosis membrane to clean the reverse osmosis membrane; a turbidity measuring device 26 as a turbidity measuring unit, wherein the turbidity of the flushing wastewater is measured; and a permeate tank 28, wherein the permeate water is stored.

[0054] exist Figure 2In the water treatment device 2, the inlet of the reverse osmosis membrane treatment device 10 is connected to the treated water pipeline 18 via a booster pump 12. The permeate outlet of the reverse osmosis membrane treatment device 10 is connected to the inlet of the permeate tank 28 via a permeate pipeline 20. The concentrate / flushing drain outlet of the reverse osmosis membrane treatment device 10 is connected to a discharge pipeline 22 via a valve 14. A recovery pipeline 24 branches from the connection point of the discharge pipeline 22 with the concentrate / flushing drain outlet and the valve 14 via a valve 16. The valves 14 and 16 can also be combined into one three-way valve and installed at the branch point of the discharge pipeline 22 and the recovery pipeline 24. A turbidity measuring device 26 is installed between the concentrate / flushing drain outlet of the reverse osmosis membrane treatment device 10 and the branch point of the recovery pipeline 24 in the discharge pipeline 22. The outlet of the permeate tank 28 is connected to the booster pump 12 in the treated water pipeline 18 and the inlet of the reverse osmosis membrane treatment device 10 via a pump 30 and a flushing water supply pipeline 32. It should be noted that the turbidity measuring device 26 can be installed not only upstream of valve 14 in the discharge pipeline 22, but also downstream of valve 14 in the discharge pipeline 22, or upstream or downstream of valve 16 in the recovery pipeline 24. Multiple turbidity measuring devices 26 can also be installed at two or more of the aforementioned locations. If necessary, a flow meter can be installed upstream of the booster pump 12 in the treated water pipeline 18, in the discharge pipeline 22, in the recovery pipeline 24, in the permeable water pipeline 20, and in the flushing water supply pipeline 32 as a flow measurement unit to measure the flow rate in each pipeline. If necessary, a valve can be installed upstream of the branch point of the recovery pipeline 24 in the discharge pipeline 22, and a flow meter can be installed between this valve and the branch point of the recovery pipeline 24.

[0055] The water to be treated is delivered to the primary side of the reverse osmosis membrane treatment unit 10 via the treated water pipeline 18 using a booster pump 12. In the reverse osmosis membrane treatment unit 10, the water to be treated is treated using a reverse osmosis membrane to obtain permeate and concentrate (reverse osmosis membrane treatment process).

[0056] The permeate obtained by reverse osmosis membrane treatment is sent to the permeate tank 28 through permeate line 20 and stored. Valve 14 is in the open state, valve 16 is in the closed state, and the concentrated water is discharged through the discharge line 22.

[0057] In the water treatment unit 2, the primary side of the reverse osmosis membrane is flushed at specific intervals (e.g., periodically).

[0058] For example, if flushing operation begins, the permeate stored in the permeate tank 28 is used as flushing water. Pump 30 delivers the flushing water to the primary side of the reverse osmosis membrane treatment unit 10 via flushing water supply line 32 and treated water line 18. Valve 14 is open, and valve 16 is closed. The flushing wastewater is discharged through discharge line 22. The turbidity of the flushing wastewater is measured in discharge line 22 by turbidity measuring device 26 (turbidity measurement process). In the initial discharge phase, for example, from tens of seconds to several minutes, a large amount of high-concentration flushing wastewater containing particles attached to the primary side of the reverse osmosis membrane is discharged. When the turbidity of the flushing wastewater measured by turbidity measuring device 26 reaches a specific value or below, valve 14 is closed, valve 16 is open, and the discharge destination of the flushing wastewater is switched via discharge line 22 and recovery line 24. Low-concentration flushing wastewater with a low content of particles is discharged via recovery line 24. This low-concentration flushing wastewater is then sent to the pre-treatment stage of the reverse osmosis membrane treatment unit 10. At this time, the low-concentration flushing wastewater can be sent, for example, to the treated water tank of the reverse osmosis membrane treatment device 10, or to the upstream side of the booster pump 12 in the treated water pipeline 18.

[0059] Thus, by switching the valve based on the turbidity of the flushing wastewater measured by the turbidity measuring device 26 during flushing, the destination of the flushing wastewater is changed, thereby suppressing the decrease in water recovery rate of the reverse osmosis membrane unit during flushing. Therefore, in water treatment where the reverse osmosis membrane is flushed at specific intervals, the decrease in water recovery rate can be suppressed, and the flushing wastewater can be effectively utilized.

[0060] There are no particular restrictions on the specific value of turbidity. For example, when the turbidity is 1.0 or less, preferably 0.5 or less, the discharge destination of the flushing wastewater can be switched by the discharge line 22 and the recovery line 24, and the low-concentration flushing wastewater can be sent to the pre-stage of the reverse osmosis membrane treatment unit 10 through the recovery line 24. For example, when the properties of the water being treated by the reverse osmosis membrane vary greatly, the discharge destination of the flushing wastewater can be switched by the discharge line 22 and the recovery line 24 based on the turbidity of the flushing wastewater.

[0061] Alternatively, the discharge pipeline can be branched into 22 branches, including pipelines for discharging concentrated water and pipelines for discharging flushing wastewater. The high-concentration flushing wastewater can be transported to, for example, a solid-liquid separation device (preferably a coagulation sedimentation device or a coagulation pressurized flotation device) via the flushing wastewater discharge pipeline. An example of the above method is shown below. Figure 3 .

[0062] Figure 3The water treatment apparatus 3 shown includes: a reverse osmosis membrane treatment apparatus 10, wherein the water to be treated is treated by reverse osmosis membrane to obtain permeate water and concentrate water; a discharge line 22, wherein flushing wastewater is discharged from the primary side of the reverse osmosis membrane; a recovery line 24, which branches off from the discharge line 22 and sends the flushing wastewater from the primary side of the reverse osmosis membrane to the pre-stage of the reverse osmosis membrane treatment apparatus 10; a concentrate water line 36, which branches off from the discharge line 22 and discharges concentrate water; and valves 14 and 16 as switching units, wherein during flushing operation, the destination of the flushing wastewater is switched at a specific time via the discharge line 22 and the recovery line 24, wherein during the flushing operation, flushing water is supplied to the primary side of the reverse osmosis membrane at a specific flow rate and discharged from the primary side of the reverse osmosis membrane to clean the reverse osmosis membrane.

[0063] exist Figure 3 In the water treatment device 3, a treated water pipeline 18 is connected to the inlet of the reverse osmosis membrane treatment device 10 via a booster pump 12. The permeate outlet of the reverse osmosis membrane treatment device 10 is connected to the permeate pipeline 20. A discharge pipeline 22 is connected to the concentrate / flushing drain outlet of the reverse osmosis membrane treatment device 10 via a valve 14. A recovery pipeline 24 branches from the connection point of the discharge pipeline 22 with the concentrate / flushing drain outlet and the valve 14 via a valve 16. A concentrate pipeline 36 branches from the branch point of the recovery pipeline 24 in the discharge pipeline 22 and the valve 14 via a valve 34. Valves 14 and 34 can also be combined into one three-way valve and installed at the branch point of the discharge pipeline 22 and the concentrate pipeline 36. If necessary, a flow meter can also be installed upstream of the booster pump 12 in the treated water pipeline 18, at least one of the discharge pipeline 22, the recovery pipeline 24, the concentrate pipeline 36, and the permeate pipeline 20 as a flow measurement unit to measure the flow rate in each pipeline. 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.

[0064] The water to be treated is delivered to the primary side of the reverse osmosis membrane treatment unit 10 via the treated water pipeline 18 using a booster pump 12. In the reverse osmosis membrane treatment unit 10, the water to be treated is treated using a reverse osmosis membrane to obtain permeate and concentrate (reverse osmosis membrane treatment process).

[0065] The permeate obtained through reverse osmosis membrane treatment is discharged through permeate line 20. Valve 34 is in the open state, and valves 14 and 16 are in the closed state. Concentrated water is discharged through discharge line 22 and concentrated water line 36.

[0066] In the water treatment unit 3, the primary side of the reverse osmosis membrane is flushed at specific intervals (e.g., periodically).

[0067] For example, if flushing operation begins, the pressurized pump 12 delivers flushing water to the primary side of the reverse osmosis membrane treatment unit 10 through the treated water line 18 at a lower pressure than the normal operating procedure. Valve 14 is open, and valves 16 and 34 are closed. The flushing wastewater is discharged through the discharge line 22. In the initial discharge phase, for example, from tens of seconds to several minutes, a large amount of high-concentration flushing wastewater containing particles and the like attached to the primary side of the reverse osmosis membrane is discharged. Once most of the particles and the like attached to the primary side of the reverse osmosis membrane have been discharged, valve 14 is closed, and valves 16 and 34 are open. The discharge destination of the flushing wastewater is switched between the discharge line 22 and the recovery line 24, and low-concentration flushing wastewater with a lower content of particles and the like is discharged through the recovery line 24. This low-concentration flushing wastewater is then sent to the pre-treatment stage of the reverse osmosis membrane treatment unit 10. At this time, the low-concentration flushing wastewater can be sent, for example, to the treated water tank of the reverse osmosis membrane treatment device 10, or to the upstream side of the booster pump 12 in the treated water pipeline 18.

[0068] By switching valves during flushing and changing the destination of the flushing wastewater, flushing can suppress the decrease in water recovery rate of the reverse osmosis membrane unit. Therefore, in water treatment where the reverse osmosis membrane is flushed at specific intervals, the decrease in water recovery rate can be suppressed, and the flushing wastewater can be utilized effectively. Furthermore, by installing pipelines for discharging concentrated water and flushing wastewater, liquids can be delivered to devices suitable for the properties of each liquid. For example, concentrated water can be delivered to a wastewater treatment device, high-concentration flushing wastewater can be delivered to a solid-liquid separation device, and low-concentration flushing wastewater can be delivered to the front end of the reverse osmosis membrane unit.

[0069] exist Figure 3 The method may also include: a water tank for storing permeate water; a supply line and pump as a flushing water supply unit, wherein the permeate water is delivered to the inlet of the reverse osmosis membrane, for example, a flushing mechanism for periodic flushing. An example of the above method is shown below. Figure 4 .

[0070] Figure 4The water treatment apparatus 4 shown includes: a reverse osmosis membrane treatment unit 10, wherein the water to be treated is treated using a reverse osmosis membrane to obtain permeate water and concentrate water; a discharge line 22, wherein flushing wastewater is discharged from the primary side of the reverse osmosis membrane; a recovery line 24, which branches off from the discharge line 22, and sends the flushing wastewater from the primary side of the reverse osmosis membrane to the pre-stage of the reverse osmosis membrane treatment unit 10; a concentrate water line 36, which branches off from the discharge line 22, and discharges concentrate water; valves 14 and 16 as switching units, wherein during flushing operation, the destination of the flushing wastewater is switched at specific times via the discharge line 22 and the recovery line 24, wherein flushing water is supplied to the primary side of the reverse osmosis membrane at a specific 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 the permeate water. The water treatment apparatus 4 may include a treated water tank 38 for storing the water to be treated from the reverse osmosis membrane treatment unit 10.

[0071] exist Figure 4 In the water treatment device 4, a treated water pipeline 40 is connected to the treated water inlet of the treated water tank 38. The treated water tank 38 is connected to the inlet of the reverse osmosis membrane treatment device 10 via a pressurization pump 12 and a treated water pipeline 18. The permeate outlet of the reverse osmosis membrane treatment device 10 is connected to the inlet of the permeate tank 28 via a permeate pipeline 20. A discharge pipeline 22 is connected to the concentrate / flushing drain outlet of the reverse osmosis membrane treatment device 10 via a valve 14. A recovery pipeline 24 branches from the connection point of the discharge pipeline 22 with the concentrate / flushing drain outlet and the valve 14 via a valve 16, and connects to the flushing drain inlet of the treated water tank 38. A concentrate pipeline 36 branches from the branch point of the recovery pipeline 24 in the discharge pipeline 22 with the valve 14 via a valve 34. Valves 14 and 34 can also be combined into one three-way valve and installed at the branch point of the discharge pipeline 22 and the concentrate pipeline 36. The outlet of the water tank 28 is connected to the booster pump 12 in the treated water pipeline 18 and the inlet of the reverse osmosis membrane treatment unit 10 via the flushing water supply pipeline 32 through the pump 30. If necessary, a flow meter can be installed as a flow measurement unit to measure the flow rate in each pipeline at at least one of the following: upstream of the booster pump 12 in the treated water pipeline 18, discharge pipeline 22, recovery pipeline 24, concentrate pipeline 36, permeate pipeline 20, flushing water supply pipeline 32, and treated water pipeline 40. If necessary, a valve can also be installed upstream of the branch point of the recovery pipeline 24 in the discharge pipeline 22, and a flow meter can be installed between the valve and the branch point of the recovery pipeline 24.

[0072] The water to be treated is stored in the water tank 38 as needed through the water treated pipeline 40. The water is then pumped from the water tank 38 to the primary side of the reverse osmosis membrane treatment unit 10 via the water treated pipeline 18 using the booster pump 12. In the reverse osmosis membrane treatment unit 10, the water to be treated is treated using a reverse osmosis membrane to obtain permeate and concentrate (reverse osmosis membrane treatment process).

[0073] The permeate obtained from reverse osmosis membrane treatment is sent to permeate tank 28 through permeate line 20 and stored. Valve 34 is open, and valves 14 and 16 are closed. Concentrated water is discharged through discharge line 22 and concentrated water line 36. When valve 16 is open and valves 14 and 34 are closed, concentrated water can also circulate in treated water tank 38 through discharge line 22 and recovery line 24. At this time, recovery line 24 also functions as a concentrated water circulation line. Recovery line 24 is connected to the upstream side of booster pump 12 in treated water line 18, and low-concentration flushing wastewater can also circulate in treated water line 18.

[0074] In the water treatment unit 4, the primary side of the reverse osmosis membrane is flushed at specific intervals (e.g., periodically).

[0075] For example, if flushing operation begins, the permeate stored in the permeate tank 28 is used as flushing water. Pump 30 delivers the flushing water to the primary side of the reverse osmosis membrane treatment unit 10 via flushing water supply line 32 and treated water line 18. Valve 14 is open, and valves 16 and 34 are closed. The flushing wastewater is discharged through discharge line 22. During the initial discharge phase, for example, tens of seconds to several minutes, a large amount of high-concentration flushing wastewater containing particles attached to the primary side of the reverse osmosis membrane is discharged. If most of the particles attached to the primary side of the reverse osmosis membrane are discharged, valve 14 is closed, and valves 16 and 34 are open. The destination of the flushing wastewater is switched via discharge line 22 and recovery line 24. Low-concentration flushing wastewater with a small amount of particles is sent to the pre-stage of the reverse osmosis membrane treatment unit 10, such as the treated water tank 38, via recovery line 24. Low-concentration flushing wastewater can also be sent upstream of the booster pump 12 in the treated water line 18.

[0076] By switching valves during flushing and changing the destination of the flushing wastewater, the reduction in water recovery rate of the reverse osmosis membrane unit can be suppressed during flushing. Therefore, in water treatment where the reverse osmosis membrane is flushed at specific intervals, the reduction in water recovery rate can be suppressed, and the flushing wastewater can be utilized effectively. In addition, by circulating the concentrated water in the treated water tank 38, the water recovery rate can be improved, for example.

[0077] High-concentration flushing wastewater can also be filtered using methods such as turbidity removal membranes. An example of the above method is shown below. Figure 5 .

[0078] Figure 5 The water treatment apparatus 5 shown includes: a reverse osmosis membrane treatment device 10, wherein the water to be treated is treated by reverse osmosis membrane treatment to obtain permeate water and concentrate water; a discharge line 22, wherein flushing wastewater is discharged from the primary side of the reverse osmosis membrane; a recovery line 24, wherein a branch line from the discharge line 22 is used to send the flushing wastewater from the primary side of the reverse osmosis membrane to the pre-stage of the reverse osmosis membrane treatment device 10; a concentrate water line 36, which branches from the discharge line 22 to discharge concentrate water; valves 14 and 16 as switching units, wherein during flushing operation, the destination of the flushing wastewater is switched at a specific time via the discharge line 22 and the recovery line 24, wherein flushing water is supplied to the primary side of the reverse osmosis membrane at a specific 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, wherein a turbidity removal membrane is used to treat the high-concentration flushing wastewater discharged from the discharge line 22.

[0079] exist Figure 5 In the water treatment device 5, the inlet of the reverse osmosis membrane treatment device 10 is connected to the treated water pipeline 18 via a booster pump 12. The permeate outlet of the reverse osmosis membrane treatment device 10 is connected to the permeate pipeline 20. The concentrate / flushing drain outlet of the reverse osmosis membrane treatment device 10 is connected to the inlet of the turbidity removal membrane treatment device 42 via a valve 14 and a discharge pipeline 22. The recovery pipeline 24 branches from the connection point of the discharge pipeline 22 with the concentrate / flushing drain outlet and the valve 14 via a valve 16. The concentrate pipeline 36 branches from the branch point of the recovery pipeline 24 in the discharge pipeline 22 with the valve 14 via a valve 34. Valves 14 and 34 can also be combined into one three-way valve and installed at the branch point of the discharge pipeline 22 and the concentrate pipeline 36. The filtered water outlet of the turbidity removal membrane treatment device 42 is connected to the filtered water pipeline 44, and the backwash drain outlet is connected to the backwash drain supply pipeline 46. If necessary, a flow meter can be installed upstream of the booster pump 12 in the treated water pipeline 18, in the discharge pipeline 22, in the recovery pipeline 24, in the concentrate water pipeline 36, and in the permeate water pipeline 20 as a flow measurement unit to measure the flow rate in each pipeline. If necessary, a valve can also be installed upstream of the branch point of the recovery pipeline 24 in the discharge pipeline 22, and a flow meter can be installed between the valve and the branch point of the recovery pipeline 24.

[0080] The water to be treated is delivered to the primary side of the reverse osmosis membrane treatment unit 10 via the treated water pipeline 18 using a booster pump 12. In the reverse osmosis membrane treatment unit 10, the water to be treated is treated using a reverse osmosis membrane to obtain permeate and concentrate (reverse osmosis membrane treatment process).

[0081] The permeate obtained through reverse osmosis membrane treatment is discharged through permeate line 20. Valve 34 is in the open state, and valves 14 and 16 are in the closed state. Concentrated water is discharged through discharge line 22 and concentrated water line 36.

[0082] In the water treatment unit 5, the primary side of the reverse osmosis membrane is flushed at specific intervals (e.g., periodically).

[0083] For example, if flushing operation begins, flushing water is delivered to the primary side of the reverse osmosis membrane treatment unit 10 via the treated water line 18 at a lower pressure than normal operating conditions using the booster pump 12. Valve 14 is open, and valves 16 and 34 are closed. The flushing wastewater is discharged through the discharge line 22. During the initial discharge phase, for example, from tens of seconds to several minutes, a large amount of high-concentration flushing wastewater containing particles and other contaminants attached to the primary side of the reverse osmosis membrane is discharged and passed to the turbidity removal membrane treatment unit 42. If most of the particles and other contaminants attached to the primary side of the reverse osmosis membrane are discharged, valve 14 is closed, and valves 16 and 34 are open. The discharge destination of the flushing wastewater is switched between the discharge line 22 and the recovery line 24, and low-concentration flushing wastewater with a lower content of particles and other contaminants is discharged through the recovery line 24. This low-concentration flushing wastewater is then sent to the pre-treatment stage of the reverse osmosis membrane treatment unit 10. At this time, the low-concentration flushing wastewater can be sent, for example, to the treated water tank of the reverse osmosis membrane treatment device 10, or to the upstream side of the booster pump 12 in the treated water pipeline 18.

[0084] High-concentration flushing wastewater is fed into the turbidity removal membrane treatment unit 42 for filtration using the turbidity removal membrane (turbidity removal membrane treatment step). The filtered water obtained through the turbidity removal membrane treatment is discharged through the filtered water line 44. The filtered water can be returned to the pre-stage of the reverse osmosis membrane treatment unit 10, such as the treated water tank of the reverse osmosis membrane treatment unit 10. At this time, the filtered water line 44 functions as a return line for returning the filtered water to the pre-stage of the reverse osmosis membrane treatment unit. The turbidity removal membrane can also be backwashed by sending backwash water from the secondary side of the turbidity removal membrane at specific intervals, for example, through the filtered water line 44. At this time, the backwash wastewater of the turbidity removal membrane can also be sent through the backwash wastewater delivery line 46 to, for example, a wastewater treatment unit, preferably a solid-liquid separation unit, more preferably a coagulation sedimentation unit or a coagulation pressurized flotation unit, and even more preferably a coagulation sedimentation unit, such as a reaction tank, wherein the coagulation sedimentation unit removes fluoride by adding a calcium agent to the fluoride-containing water to generate insoluble calcium salts. At this time, the backwash drainage supply line 46 functions as a backwash drainage supply line that supplies the backwash drainage of the turbidity removal membrane treatment device 42 to the reaction tank of the coagulation and sedimentation device, etc., which removes fluoride by adding calcium agent to fluoride-containing water to generate insoluble calcium salt.

[0085] By switching valves during flushing and changing the destination of the flushing wastewater, the reduction in water recovery rate of the reverse osmosis membrane unit can be suppressed during flushing. Therefore, in water treatment where the reverse osmosis membrane is flushed at specific intervals, the reduction in water recovery rate can be suppressed, and the flushing wastewater can be effectively utilized.

[0086] By passing high-concentration flushing wastewater through a turbidity removal membrane and performing backwashing, the solid components (SS) contained in the high-concentration flushing wastewater are concentrated. The backwash wastewater (i.e., concentrated SS water) is then sent to a coagulation sedimentation unit or a coagulation pressurized flotation unit, thereby improving the coagulation properties during coagulation sedimentation or coagulation pressurized flotation. In particular, sending the backwash wastewater concentrated with the solid components (SS) to the reaction tank of a coagulation sedimentation unit, where calcium is added to fluoride-containing water to generate insoluble calcium salts for fluoride removal, is more effective when using microparticles as nuclei for the coagulation reaction. Furthermore, in cases where the high-concentration flushing wastewater is acidic, it also helps reduce pH adjusters such as acids in the coagulation sedimentation. The filtered water from the turbidity removal membrane can be recycled again by returning it to the pre-treatment stage of the reverse osmosis membrane treatment unit 10, the treated water tank of the reverse osmosis membrane treatment unit 10, etc.

[0087] As an example of a wastewater treatment apparatus that utilizes the high-concentration flushing wastewater obtained by the water treatment apparatus according to this embodiment, a coagulation and precipitation apparatus for removing fluoride by adding a calcium agent to fluoride-containing water to generate insoluble calcium salts is shown below. Figure 6 .

[0088] Figure 6 The shown coagulation and sedimentation device 6 includes a reaction tank 50, an inorganic reaction tank 52, a coagulation tank 54, and a sedimentation tank 56.

[0089] exist Figure 6 In the coagulation and sedimentation device 6 shown, the fluoride-containing water inlet of reaction tank 50 is connected to fluoride-containing water pipeline 58. The outlet of reaction tank 50 is connected to the inlet of inorganic reaction tank 52 via pipeline 60. The outlet of inorganic reaction tank 52 is connected to the inlet of coagulation tank 54 via pipeline 62. The outlet of coagulation tank 54 is connected to the inlet of sedimentation tank 56 via pipeline 64. The treated water outlet of sedimentation tank 56 is connected to treated water pipeline 66, and the sludge outlet is connected to sludge pipeline 68. The flushing drainage inlet of reaction tank 50 is connected to flushing drainage addition pipeline 70, which is connected to discharge pipeline 22 or backwash drainage liquid delivery pipeline 46, and the calcium agent inlet is connected to calcium agent addition pipeline 72. The inorganic coagulant inlet of inorganic reaction tank 52 is connected to inorganic coagulant addition pipeline 74. The polymeric coagulant inlet of coagulation tank 54 is connected to polymeric coagulant addition pipeline 76.

[0090] The coagulation and sedimentation device 6 can be equipped with a fluoride-containing water tank as a raw water tank for storing fluoride-containing water. In this case, the fluoride-containing water tank and the fluoride-containing water inlet of the reaction tank 50 can be connected through a fluoride-containing water pipeline. In addition, the flushing drain inlet of the fluoride-containing water tank can also be connected to a flushing drain addition pipeline that is connected to the discharge pipeline 22 or the backwash drain liquid delivery pipeline 46.

[0091] After being stored in a fluoride-containing water tank as needed, fluoride-containing water is sent to a reaction tank 50 via fluoride-containing water pipeline 58. In reaction tank 50, high-concentration flushing wastewater from water treatment units 1-5 or backwash wastewater from the turbidity removal membrane treatment unit 42 is added to the fluoride-containing water via flushing wastewater addition pipeline 70. Calcium agent is then added via calcium agent addition pipeline 72. Through the reaction of fluoride and calcium agent, calcium fluoride, a sparingly soluble salt, is generated (calcium reaction process). Alternatively, high-concentration flushing wastewater from water treatment units 1-5 or backwash wastewater from the turbidity removal membrane treatment unit 42 can be added to the fluoride-containing water in the fluoride-containing water tank via flushing wastewater addition pipeline. The reaction solution is sent to an inorganic reaction tank 52 via pipeline 60. In inorganic reaction tank 52, inorganic coagulant is added to the reaction solution via inorganic coagulant addition pipeline 74 to carry out a coagulation reaction (coagulation reaction process). The reaction solution with added inorganic coagulant is sent to a coagulation tank 54 via pipeline 62. In coagulation tank 54, a polymeric coagulant is added to the reaction solution via polymeric coagulant addition pipeline 76 to carry out a polymeric coagulation reaction (polymeric coagulation reaction process). The reaction solution with added polymeric coagulant is then sent to sedimentation tank 56 via pipeline 64. In sedimentation tank 56, solid-liquid separation occurs through natural sedimentation (solid-liquid separation process). The resulting treated water is discharged through treated water pipeline 66, and the sludge is discharged through sludge pipeline 68 (the above constitutes the coagulation and sedimentation treatment process).

[0092] High-concentration flushing wastewater contains particles that act as nuclei, promoting calcium reactions and thus improving the quality of the treated water.

[0093] Fluorinated water is any water that contains fluoride, without any special restrictions. For example, it is wastewater discharged from semiconductor factories and other electronics industries, specifically etching wastewater, wafer cleaning wastewater, etc.

[0094] There is no particular limitation on the amount of fluoride contained in fluoride-containing water, for example, in the range of 0 mg / L to 5000 mg / L, preferably in the range of 50 mg / L to 2000 mg / L.

[0095] Calcium chloride, slaked lime (calcium hydroxide), and calcium carbonate can be used as calcium additives, with slaked lime being the preferred choice, especially considering the cost of the additives. Calcium additives can be used in powder form, as well as in aqueous solutions or slurries such as water.

[0096] The amount of calcium agent added to the reaction tank 50 is, for example, in the range of 1.1 to 1.2 times the stoichiometric equivalent of fluorine in terms of calcium stoichiometry.

[0097] Before adding fluoridated water and calcium agent to reaction tank 50, seed crystals can be pre-existing in reaction tank 50, or seed crystals can be supplied to reaction tank 50 simultaneously with the addition of fluoridated water and calcium agent. For stable treatment, it is preferable to pre-exist seed crystals in reaction tank 50 before adding the water to be treated and calcium agent to reaction tank 50. Here, particles or the like contained in high-concentration flushing drainage or backwash drainage of the turbidity removal membrane treatment device 42 also function as seed crystals.

[0098] The pH of the reaction solution in the reaction tank 50 is, for example, in the range of 4 to 11, preferably in the range of 4 to 9.

[0099] The amount of inorganic coagulant added to the inorganic reaction tank 52 is, for example, in the range of 50 mg / L to 1000 mg / L.

[0100] The pH of the reaction solution in the inorganic reaction tank 52 also depends on the type of coagulant used, for example, in the case of using polyaluminum chloride (PAC), it is in the range of 6 to 8.

[0101] As an inorganic coagulant, any inorganic coagulant suitable for inorganic coagulation treatment is acceptable; there are no particular restrictions. Examples of inorganic coagulants include: iron-based inorganic coagulants such as ferric chloride and polyferric sulfate; and aluminum-based inorganic coagulants such as aluminum sulfate and polyaluminum chloride (PAC). The type of inorganic coagulant used can be selected based on factors such as the properties of the fluoride-containing water being treated.

[0102] The amount of polymeric coagulant added to the coagulation tank 54 is, for example, in the range of 0.5 mg / L to 3 mg / L.

[0103] The pH of the reaction solution in the coagulation tank 54 is, for example, in the range of 5 to 8.

[0104] As a polymeric coagulant, any organic polymeric coagulant suitable for polymeric coagulation treatment is acceptable; there are no particular limitations. Examples of polymeric coagulants include nonionic, anionic, and cationic polymeric coagulants, among others. Examples include polyacrylamide, sodium polyacrylate, acrylamide-acrylate copolymer, sodium acrylamide propanesulfonate, chitosan, dimethylaminoethyl methacrylate, dimethylaminoethyl acrylate, and polyamidine. A single polymeric coagulant can be used, or two or more can be used in combination. The type of polymeric coagulant used can be selected based on factors such as the properties of the fluoride-containing water being treated.

[0105] pH adjusters can also be used in calcium reaction processes, coagulation reaction processes, and polymer coagulation reaction processes for pH adjustment. Examples of pH adjusters include acids such as hydrochloric acid and sulfuric acid; and alkalis such as sodium hydroxide aqueous solution.

[0106] There are no particular restrictions on the liquid temperature in the calcium reaction process, the coagulation reaction process, and the polymer coagulation reaction process; for example, it can be in the range of 15°C to 35°C. Separability varies due to viscosity and other factors, so it is preferable to maintain the liquid temperature as constant as possible.

[0107] Examples of sedimentation tanks 56 include pressurized flotation treatment and sedimentation separation. Sedimentation separation is not particularly limited, and examples include natural sedimentation treatment based on natural settling using sedimentation tanks and sludge blanket type sedimentation tanks.

[0108] There are no particular restrictions on the amount of fluoride in the resulting treated water; for example, it can be set to below 15 mg / L.

[0109] If high-concentration flushing wastewater is sent to reaction tank 50 or a fluoride-containing water tank for storing fluoride-containing water, the formation reaction of calcium salts is promoted. As a result, the fluoride concentration of the fluoride-containing water can be further reduced, the coagulation of the precipitate becomes better, and the solid-liquid separation in precipitation tank 56 is improved.

[0110] This specification includes the following implementation methods.

[0111] (1) A water treatment device comprising: A reverse osmosis membrane treatment device, wherein a reverse osmosis membrane is used to treat water to obtain permeate water and concentrated water; A discharge line is provided, through which flushing wastewater is discharged from the primary side of the reverse osmosis membrane; A recovery pipeline, wherein the flushing wastewater is delivered from the primary side of the reverse osmosis membrane to the pre-treatment stage of the reverse osmosis membrane treatment unit; and The switching unit, during flushing operation, switches the discharge destination of the flushing wastewater at a specific time through the discharge pipeline and the recovery pipeline. During the flushing operation, flushing water is supplied to the primary side of the reverse osmosis membrane at a specific flow rate and discharged from the primary side of the reverse osmosis membrane to clean the reverse osmosis membrane.

[0112] (2) The water treatment apparatus according to (1), wherein the treated water or dilution water with a lower salt concentration than the treated water is used as the rinsing water.

[0113] (3) The water treatment device according to (1) or (2), wherein the switching unit switches the discharge destination of the flushing drainage from the discharge pipeline to the recovery pipeline less than 5 minutes after the start of the flushing operation.

[0114] (4) The water treatment apparatus according to (1) or (2), wherein the discharge pipeline is equipped with a turbidity measuring device. If the turbidity of the flushing wastewater measured by the turbidity measuring device reaches a certain value or below, the switching unit switches the discharge destination of the flushing wastewater from the discharge pipeline to the recovery pipeline.

[0115] (5) The water treatment apparatus according to any one of claims (1) to (4), wherein the discharge pipeline is connected to the raw water tank or reaction tank of the coagulation and sedimentation device, and the coagulation and sedimentation device removes fluoride by adding calcium agent to fluoride-containing water to generate insoluble calcium salt.

[0116] (6) The water treatment apparatus according to any one of claims (1) to (5), wherein the water treatment apparatus further comprises: A turbidity removal membrane treatment device, wherein a turbidity removal membrane is used to treat flushing wastewater discharged from the discharge pipeline; A return pipeline, wherein the filtered water treated by the turbidity removal membrane treatment unit is returned to the pre-stage of the reverse osmosis membrane treatment unit; and The backwash drainage pipeline delivers the backwash drainage from the turbidity removal membrane to the raw water tank or reaction tank of the coagulation and sedimentation device, which removes fluoride by adding calcium to the fluoride-containing water to generate insoluble calcium salts.

[0117] (7) A water treatment method, comprising: The reverse osmosis membrane treatment process involves using a reverse osmosis membrane to treat the water to obtain permeate and concentrated water. The discharge process includes discharging flushing wastewater from the primary side of the reverse osmosis membrane; and The recovery process involves sending the flushing wastewater from the primary side of the reverse osmosis membrane to the pre-treatment stage of the reverse osmosis membrane process. During the flushing operation, the discharge process and the recovery process are switched at specific times. During the flushing operation, flushing water is supplied to the primary side of the reverse osmosis membrane at a specific flow rate and discharged from the primary side of the reverse osmosis membrane to clean the reverse osmosis membrane.

[0118] (8) The water treatment method according to (7), wherein the treated water or dilution water with a lower salt concentration than the treated water is used as the rinsing water.

[0119] (9) The water treatment method according to (7) or (8), wherein the process is switched from the discharge process to the recycling process less than 5 minutes after the start of the flushing operation.

[0120] (10) The water treatment method according to (7) or (8), wherein if the turbidity of the flushing wastewater measured in the discharge step reaches below a specific value, the process is switched from the discharge step to the recycling step.

[0121] (11) The water treatment method according to any one of (7) to (10), wherein the flushing wastewater discharged in the discharge step is sent to the raw water tank or reaction tank of the coagulation and sedimentation device, wherein the coagulation and sedimentation device removes fluoride by adding a calcium agent to the fluoride-containing water to generate an insoluble calcium salt.

[0122] (12) The water treatment method according to any one of (7) to (11), wherein the water treatment method further comprises: a turbidity removal membrane treatment step, wherein the flushing wastewater discharged in the discharge step is treated using a turbidity removal membrane. The filtered water treated by the turbidity removal membrane treatment process is returned to the pre-stage of the reverse osmosis membrane treatment process. The backwash water from the turbidity removal membrane is sent to the raw water tank or reaction tank of the coagulation and sedimentation device, which adds calcium to the fluoride-containing water to generate insoluble calcium salts to remove fluoride.

[0123] Example The present invention will be described in more detail below with examples and comparative examples, but the present invention is not limited to the following examples.

[0124] [Reverse osmosis membrane treatment and flushing] <Example 1> use Figure 4 The water treatment device 4 described herein undergoes a water flow test. In normal operation, a portion of the concentrated water is circulated through the recovery pipeline 24 to the treated water tank 38.

[0125] (Conditions for normal operation of the process) • Reverse osmosis membrane: Nitto Denko LFC3-LD-4040 • Water flow rate to be treated: 160L / h • Permeate flow rate of reverse osmosis membrane treatment unit 10: 140L / h • The concentrated water discharge flow rate of the reverse osmosis membrane treatment unit 10 is 20L / h • The concentrated water is circulated to the treated water tank 38 at a flow rate of 700 L / h. The water to be treated was adjusted by adding reagents (sodium bicarbonate and calcium chloride) to pure water. The water quality is shown in Table 1.

[0126] [Table 1]

[0127] Every 4 hours of water flow, the permeate water is used as flushing water, and a 10-minute flushing process is carried out at a flushing flow rate of 720L / h.

[0128] The total calcium concentration (mg / L) of the flushing wastewater was determined using calcium complexometric titration (JIS K 0101 Test Method for Industrial Water), and the turbidity was determined using a spectrophotometer (Hitachi, U-2900) using transmitted light turbidity (JIS K 0101 Test Method for Industrial Water). The water quality of the flushing wastewater is shown in Table 2.

[0129] [Table 2]

[0130] In Example 1, the flushing wastewater from the start of the rinsing process up to 5 minutes is discharged through the discharge line 22, and the flushing wastewater after 5 minutes (5 minutes) is returned to the treated water tank 38 as flushing recycled water through the recovery line 24. When the normal operation process to the rinsing process is considered as a cycle, the water recovery rate of Example 1, calculated by the following method, is 75.9%.

[0131] (Methods for calculating water recovery rate) In the "Normal Operation Process ~ Flushing Process" cycle, a loop is set up, and the flushing wastewater is returned to the treated water tank 38. The flushing wastewater from 5 minutes is recycled back to the treated water tank 38. Accordingly, the amount of treated water replenished is reduced, and therefore the water recovery rate is as shown below.

[0132] Recovery rate (%) = Permeate volume obtained in one cycle (L) / Treated water volume replenished in one cycle (L) = [(140L / h × 4h - 720L / h × (10 / 60)h) / (160L / h × 4h - 720L / h × (5 / 60)h)] × 100 = 75.9% In Example 1, the above cycle was repeated, and the reverse osmosis membrane did not show a significant tendency to clog and was able to operate stably. In addition, compared with the case where all the flushing water was discharged for 10 minutes (720L / h × 10min = 120L), the amount of flushing water for 5 minutes of the 10 minutes was recovered (60L), thus reducing the amount of flushing water in each cycle by 50%.

[0133] Following the same procedure as in Example 1, the flushing wastewater was completely disposed of through discharge line 22. The water recovery rate, determined by the following method, was 68.8%.

[0134] Recovery rate (%) = Permeate volume obtained in one cycle (L) / Treated water volume replenished in one cycle (L) = [(140L / h × 4h - 720L / h × (10 / 60)h) / (160L / h × 4h)] × 100 = 68.8% <Example 2> use Figure 4 The water treatment device 4 described herein underwent a water flow test. The normal operating conditions were the same as in Example 1. The water quality of the water to be treated is shown in Table 3.

[0135] [Table 3]

[0136] Every 4 hours of water flow, the permeate water is used as flushing water, and a 6-minute flushing process is carried out at a flushing flow rate of 720L / h.

[0137] Similar to Example 1, the total calcium concentration (mg / L) and turbidity of the flushing wastewater were measured. The water quality of the flushing wastewater is shown in Table 4.

[0138] [Table 4]

[0139] In Example 2, the flushing wastewater from the start of the rinsing process to less than 3 minutes is discharged through the discharge line 22, and the flushing wastewater after 3 minutes (3 minutes) is returned to the treated water tank 38 through the recovery line 24. When the normal operation process to the rinsing process is considered as a cycle, the water recovery rate of Example 2, calculated by the following method, is 80.8%.

[0140] (Methods for calculating water recovery rate) Recovery rate (%) = Permeate volume obtained in one cycle (L) / Treated water volume replenished in one cycle (L) = [(140L / h × 4h - 720L / h × (6 / 60)h) / (160L / h × 4h - 720L / h × (3 / 60)h)] × 100 = 80.8% In Example 2, the above cycle was repeated, and the reverse osmosis membrane did not show a significant tendency to clog, operating stably. Furthermore, compared to flushing and draining the water completely within 6 minutes, each cycle reduced the drainage volume by 50%, improving water recovery rate.

[0141] Following the same procedure as in Example 2, the flushing wastewater was completely disposed of through discharge line 22. The water recovery rate, determined by the following method, was 76.3%.

[0142] Recovery rate (%) = Permeate volume obtained in one cycle (L) / Treated water volume replenished in one cycle (L) = [(140L / h × 4h - 720L / h × (6 / 60)h) / (160L / h × 4h)] × 100 = 76.3% <Example 3> use Figure 4 The water treatment apparatus 4 described herein was subjected to a water flow test. The normal operating conditions were the same as in Example 1, and the same treated water as in Example 2 was used. Every hour of water flow, the permeate was used as flushing water, and a flushing process of 2 minutes was performed at a flushing flow rate of 720 L / h.

[0143] As in Example 1, the total calcium concentration (mg / L) and turbidity of the flushing wastewater were measured. The water quality of the flushing wastewater is shown in Table 5.

[0144] [Table 5]

[0145] In Example 3, the flushing wastewater from the start of the rinsing process to less than 30 seconds is discharged through the discharge line 22, and the flushing wastewater after 30 seconds (90 seconds) is returned to the treated water tank 38 through the recovery line 24. When the normal operation process to the rinsing process is considered as a cycle, the water recovery rate of Example 3, calculated by the following method, is 81.7%.

[0146] (Methods for calculating water recovery rate) Recovery rate (%) = Permeate volume obtained in one cycle (L) / Treated water volume replenished in one cycle (L) = [(140L / h × 1h - 720L / h × (2 / 60)h) / (160L / h × 1h - 720L / h × (1.5 / 60)h)] × 100 = 81.7% In Example 3, the reverse osmosis membrane did not show a significant tendency to clog and was able to operate stably. The flushing drainage volume was 720L / h × 2min = 24L, of which 18L was recovered in 1.5 minutes, thus reducing the volume by 18 / 24 = 75%.

[0147] Following the same procedure as in Example 3, the flushing wastewater was completely disposed of through discharge line 22. The water recovery rate, determined by the following method, was 72.5%.

[0148] Recovery rate (%) = Permeate volume obtained in one cycle (L) / Treated water volume replenished in one cycle (L) = [(140L / h × 1h - 720L / h × (2 / 60)h) / (160L / h × 1h)] × 100 = 72.5% <Example 4> use Figure 4The water treatment device 4 described herein was subjected to a water flow test. The normal operating conditions were the same as in Example 1, and the same treated water as in Example 2 was used. Every 30 minutes of water flow, the permeate was used as rinsing water, and a rinsing process of 2 minutes was performed at a rinsing flow rate of 720 L / h.

[0149] As in Example 1, the total calcium concentration (mg / L) and turbidity of the flushing wastewater were measured. The water quality of the flushing wastewater is shown in Table 6.

[0150] [Table 6]

[0151] In Example 4, the flushing wastewater from the start of the rinsing process to less than 10 seconds is discharged through the discharge line 22, and the flushing wastewater after 10 seconds (110 seconds) is returned to the treated water tank 38 through the recovery line 24. When the normal operation process to the rinsing process is considered as a cycle, the water recovery rate of Example 3, calculated by the following method, is 79.3%.

[0152] (Methods for calculating water recovery rate) Recovery rate (%) = Permeate volume obtained in one cycle (L) / Treated water volume replenished in one cycle (L) = [(140L / h × 0.5h - 720L / h × (2 / 60)h) / (160L / h × 0.5h - 720L / h × (110 / 60 / 60)h)] × 100 = 79.3% In Example 4, the reverse osmosis membrane did not show a significant tendency to clog and was able to operate stably. The flushing drainage volume was 720L / h × 2min = 24L, of which the volume recovered in 1 minute and 50 seconds (22L) was reduced, thus achieving a reduction of 22 / 24 = 91.7%.

[0153] Following the same procedure as in Example 4, the flushing wastewater was completely disposed of through discharge line 22. The water recovery rate, determined by the following method, was 57.5%.

[0154] Recovery rate (%) = Permeate volume obtained in one cycle (L) / Treated water volume replenished in one cycle (L) = [(140L / h × 0.5h - 720L / h × (2 / 60)h) / (160L / h × 0.5h)] × 100 = 57.5% [Coagulation and Sedimentation Treatment] <Example 1> The flushing wastewater discharged during the rinsing process of Storage Example 1, from the start of rinsing to less than 5 minutes, is allowed to flow into... Figure 6 The reaction tank 50 of the coagulation and sedimentation device 6 shown is subjected to coagulation and sedimentation treatment under the following conditions.

[0155] (Conditions for coagulation and sedimentation treatment) Fluoride-containing water: Wastewater from semiconductor factories • Flow rate of fluoride-containing water into reaction tank 50: 4L / h Fluoride concentration in fluoride-containing water: 30 mg-F / L • Calcium agent (hydrated lime) addition amount in reaction tank 50: 230 mg-Ca / L • Flushing drainage flow rate of reaction tank 50: 0.4L / h • Amount of inorganic coagulant (polyaluminum chloride (PAC)) added to inorganic reaction tank 52: 50 mg / L • The amount of polymeric coagulant (ORFLOCK ON-1H, manufactured by Organo Corporation) added to coagulation tank 54 is 1 mg / L. • Linear velocity (LV) of sedimentation tank 56: 1 m / h The fluoride concentration in the treated water was determined by atomic absorption spectrophotometry using an ion chromatograph (Thermo Fisher, Dionex Integrion), and the suspended solids (SS) concentration was determined by the glass fiber filter paper method (JIS K 0102 Industrial Wastewater Test Method). The results are shown in Table 7.

[0156] <Example 2> The flushing wastewater discharged during the rinsing process of Example 2, from the start of rinsing to less than 3 minutes, is stored and allowed to flow into... Figure 6 The reaction tank 50 of the coagulation and sedimentation apparatus 6 shown is otherwise identical to that in Example 1 for coagulation and sedimentation treatment. The fluoride concentration and SS concentration of the obtained treated water were measured. The results are shown in Table 7.

[0157] It is believed that in Examples 1 and 2, the particles contained in the flushing drainage become nuclei and promote calcium reactions, thereby reducing the fluoride concentration in the treated water. In addition, the cohesion becomes better and the solid-liquid separation is improved, and the SS concentration is also reduced.

[0158] <Comparative Example 1> The coagulation and sedimentation treatment did not use flushing drainage; otherwise, it was the same as in Examples 1 and 2, except that water from the semiconductor factory was circulated. The fluoride concentration and SS concentration of the obtained treated water were measured. The results are shown in Table 7.

[0159] In Comparative Example 1, the fluoride concentration and SS concentration of the treated water were worse compared to Examples 1 and 2.

[0160] [Table 7]

[0161] Therefore, in the embodiments, flushing can be performed to suppress the decrease in water recovery rate of the reverse osmosis membrane device.

[0162] Explanation of reference numerals in the attached figures 1, 2, 3, 4, 5 Water treatment unit; 6 Coagulation and sedimentation unit; 10 Reverse osmosis membrane treatment unit; 12 Booster pump; 14, 16, 34 Valves; 18, 40 Treated water pipeline; 20 Permeate water pipeline; 22 Discharge pipeline; 24 Recovery pipeline; 26 Turbidity measuring device; 28 Permeate tank; 30 Pump; 32 Flushing water supply pipeline; 36 Concentrated water pipeline; 38 Treated water tank; 42 Turbidity removal membrane treatment unit; 44 Filtered water pipeline; 46 Backwash drainage and liquid delivery pipeline; 50 Reaction tank; 52 Inorganic reaction tank; 54 Coagulation tank; 56 Sedimentation tank; 58 Fluoride-containing water pipeline; 60, 62, 64 Pipelines; 66 Treated water pipeline; 68 Sludge pipeline; 70 Flushing drainage addition pipeline; 72 Calcium agent addition pipeline; 74 Inorganic coagulant addition pipeline; 76 Polymer coagulant addition pipeline.

Claims

1. A water treatment device, characterized in that, have: A reverse osmosis membrane treatment device, wherein a reverse osmosis membrane is used to treat water to obtain permeate water and concentrated water; A discharge line is provided, through which flushing wastewater is discharged from the primary side of the reverse osmosis membrane; A recovery pipeline, wherein the flushing wastewater is delivered from the primary side of the reverse osmosis membrane to the pre-treatment stage of the reverse osmosis membrane treatment unit; and The switching unit, during flushing operation, switches the discharge destination of the flushing wastewater at a specific time through the discharge pipeline and the recovery pipeline. During the flushing operation, flushing water is supplied to the primary side of the reverse osmosis membrane at a specific flow rate and discharged from the primary side of the reverse osmosis membrane to clean the reverse osmosis membrane.

2. The water treatment apparatus according to claim 1, wherein, The treated water or diluted water with a lower salt concentration than the treated water is used as the rinsing water.

3. The water treatment apparatus according to claim 1 or 2, wherein, The switching unit switches the destination of the flushing drainage from the discharge pipeline to the recovery pipeline less than 5 minutes after the flushing operation begins.

4. The water treatment apparatus according to claim 1 or 2, wherein, The discharge pipeline is equipped with a turbidity measuring device. If the turbidity of the flushing wastewater measured by the turbidity measuring device reaches a certain value or below, the switching unit switches the discharge destination of the flushing wastewater from the discharge pipeline to the recovery pipeline.

5. The water treatment apparatus according to any one of claims 1 to 4, wherein, The discharge pipeline is connected to the raw water tank or reaction tank of the coagulation and sedimentation device, which adds calcium to the fluoride-containing water to generate insoluble calcium salts to remove fluoride.

6. The water treatment apparatus according to any one of claims 1 to 5, wherein, The water treatment device also includes: A turbidity removal membrane treatment device, wherein a turbidity removal membrane is used to treat flushing wastewater discharged from the discharge pipeline; A return pipeline, wherein the filtered water obtained from the turbidity removal membrane treatment unit is returned to the pre-stage of the reverse osmosis membrane treatment unit; and The backwash drainage pipeline delivers the backwash drainage from the turbidity removal membrane to the raw water tank or reaction tank of the coagulation and sedimentation device, which removes fluoride by adding calcium to the fluoride-containing water to generate insoluble calcium salts.

7. A water treatment method, characterized in that, include: The reverse osmosis membrane treatment process involves using a reverse osmosis membrane to treat the water to obtain permeate and concentrated water. The discharge process includes discharging flushing wastewater from the primary side of the reverse osmosis membrane; and The recovery process involves sending the flushing wastewater from the primary side of the reverse osmosis membrane to the pre-treatment stage of the reverse osmosis membrane process. During the flushing operation, the discharge process and the recovery process are switched at specific times. During the flushing operation, flushing water is supplied to the primary side of the reverse osmosis membrane at a specific 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, wherein, The treated water or diluted water with a lower salt concentration than the treated water is used as the rinsing water.

9. The water treatment method according to claim 7 or 8, wherein, The process switches from the discharge process to the recycling process less than 5 minutes after the flushing operation begins.

10. The water treatment method according to claim 7 or 8, wherein, If the turbidity of the flushing wastewater measured in the discharge process reaches a certain value or below, the process is switched from the discharge process to the recycling process.

11. The water treatment method according to any one of claims 7 to 10, wherein, The flushing wastewater discharged in the discharge process is sent to the raw water tank or reaction tank of the coagulation and sedimentation device, which adds calcium to the fluoride-containing water to generate insoluble calcium salts to remove fluoride.

12. The water treatment method according to any one of claims 7 to 11, wherein, The water treatment method further includes: The process includes a turbidity removal membrane treatment step, in which a turbidity removal membrane is used to treat the flushing wastewater discharged in the discharge step. The filtered water obtained from the turbidity removal membrane treatment process is returned to the pre-stage of the reverse osmosis membrane treatment process. The backwash water from the turbidity removal membrane is sent to the raw water tank or reaction tank of the coagulation and sedimentation device, which adds calcium to the fluoride-containing water to generate insoluble calcium salts to remove fluoride.

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